| 52. |
Yamaji, M., and H. G. Takahashi, 2023: Seasonal differences of precipitation and microphysical characteristics over the Asian monsoon region using spaceborne dual-frequency precipitation radar. J. Atmos. Sci., doi: 10.1175/JAS-D-22-0198.1, in press. [Web page] [BibTeX] [EndNote]
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| 51. |
Terao, T., Kanae, S., Fujinami, H., Das, S., Dimri, A. P., Dutta, S., Fujita, K., Fukushima, A., Ha, K., Hirose, M., Hong, J., Kamimera, H., Kayastha, R. B., Kiguchi, M., Kikuchi, K., Kim, H. M., Kitoh, A., Kubota, H., Ma, W., Ma, Y., Mujumdar, M., Nodzu, M. I., Sato, T., Su, Z., Sugimoto, S., Takahashi, H. G., Takaya, Y., Wang, S., Yang, K., Yokoi, S., and Matsumoto, J., 2022: AsiaPEX: Challenges and Prospects in Asian Precipitation Research, Bulletin of the American Meteorological Society, doi: 10.1175/BAMS-D-20-0220.1. [Web page] [BibTeX] [EndNote]
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| 50. |
Sugimoto, S., Xue, Y., Sato, T., and Takahashi, H.G., 2022: Influence of convective processes on weather research and forecasting model precipitation biases over East Asia. Climate Dynamics, doi: 10.1007/s00382-022-06587-5. [Web page] [BibTeX] [EndNote]
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| 49. |
Takahashi, H. G., M. Kiguchi, and S. Sugimoto 2022: Floods and droughts in Asia, Europe, and America, Handbook of Air Quality and Climate Change, Springer Nature, in production.
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| 48. |
Gupta, A., and H. G. Takahashi, 2021: Long-term changes in spatially coherent extreme precipitation systems over Central India. Atmos. Sci. Lett., e1118, doi: 0.1002/asl.1118. [Web page] [BibTeX] [EndNote]
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| 47. |
Sugimoto, S., K. Ueno, H. Fujinami, T. Nasuno, T. Sato, and H. G. Takahashi, 2021: Cloud-Resolving-Model Simulations of Nocturnal Precipitation over the Himalayan Slopes and Foothills. Journal of Hydrometeorology, 22, 12, 3171-3188, doi: 10.1175/jhm-d-21-0103.1. [Web page] [BibTeX] [EndNote]
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| 46. |
Hoshi, R., and H. G. Takahashi, 2021: Role of Oceanic Memory Effects in the Barents Sea in the Seasonal Linkage Between the Winter and Summer Arctic Oscillation. J. Geophys. Res. Atmos., 126, 23, e2021JD034799, doi: 10.1029/2021JD034799. [Web page] [BibTeX] [EndNote]
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| 45. |
Takahashi, H.G. and Fujinami, H., 2021: Recent decadal enhancement of Meiyu–Baiu heavy rainfall over East Asia. Sci. Rep., 11, 13665, doi:10.1038/s41598-021-93006-0. [Web page] [BibTeX] [EndNote]
[プレスリリース]
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| 44. |
Manalo, J.A., Matsumoto, J., Takahashi, H.G., Villafuerte, M.Q., II, Olaguera, L.M.P., Ren, G. and Cinco, T.A., 2021: The Effect of Urbanization on Temperature Indices in the Philippines. Int. J. Climatol. Accepted Author Manuscript, doi:10.1002/joc.7276. [Web page] [BibTeX] [EndNote]
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| 43. |
Xue, Y., Yao, T., Boone, A. A., Diallo, I., Liu, Y., Zeng, X., Lau, W. K.-M., Sugimoto, S., Tang, Q., Pan, X., van Oevelen, P. J., Klocke, D., Koo, M.-S., Lin, Z., Takaya, Y., Sato, T., Ardilouze, C., Saha, S. K., Zhao, M., Liang, X.-Z., Vitart, F., Li, X., Zhao, P., Neelin, D., Guo, W., Yu, M., Qian, Y., Shen, S. S. P., Zhang, Y., Yang, K., Leung, R., Yang, J., Qiu, Y., Brunke, M. A., Chou, S. C., Ek, M., Fan, T., Guan, H., Lin, H., Liang, S., Materia, S., Nakamura, T., Qi, X., Senan, R., Shi, C., Wang, H., Wei, H., Xie, S., Xu, H., Zhang, H., Zhan, Y., Li, W., Shi, X., Nobre, P., Qin, Y., Dozier, J., Ferguson, C. R., Balsamo, G., Bao, Q., Feng, J., Hong, J., Hong, S., Huang, H., Ji, D., Ji, Z., Kang, S., Lin, Y., Liu, W., Muncaster, R., Pan, Y., Peano, D., de Rosnay, P., Takahashi, H. G., Tang, J., Wang, G., Wang, S., Wang, W., Zhou, X., and Zhu, Y.: Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction Project, Phase I (LS4P-I): Organization and Experimental design. Geosci. Model Dev., accepted.
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| 42. |
Takahashi, Hiroshi G., 2020: Long‐term trends in snowfall characteristics and extremes in Japan from 1961 to 2012. International Journal of Climatology, doi: 10.1002/joc.6960. [Web page] [BibTeX] [EndNote]
1961年から2012年までの日本における降雪特性と豪雪の長期トレンド
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| 41. |
Takahashi, Hiroshi G., and Takuya Yamazaki, 2020: Impact of sea surface temperature near Japan on the extra-tropical cyclone induced heavy snowfall in Tokyo by a regional atmospheric model, SOLA, doi:10.2151/sola.2020-035. [Web page] [BibTeX] [EndNote]
[プレスリリース]
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| 40. |
Takahashi, H. G., N. Kamizawa, T. Nasuno, Y. Yamada, C. Kodama, S. Sugimoto, and M. Satoh, 2020: Response of the Asian Summer Monsoon Precipitation to Global Warming in a High-Resolution Global Nonhydrostatic Model. J. Climate, doi: 10.1175/JCLI-D-19-0824.1. [Web Page] [BibTeX] [EndNote]
[プレスリリース]
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| 39. |
Rakesh T. Konduru and Hiroshi G. Takahashi, 2020: Effects of convection representation and model resolution on diurnal precipitation cycle over the Indian monsoon region - Towards a convection-permitting regional climate simulation. Journal of Geophysical Research: Atmospheres, 125, e2019JD032150, doi: 10.1029/2019JD032150. [Web page] [BibTeX] [EndNote]
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| 38. |
Yamaji, M., H. G. Takahashi, T. Kubota, R. Oki, A. Hamada, and Y. N. Takayabu, 2020: 4-year climatology of global drop size distribution and its seasonal variability observed by spaceborne Dual-frequency Precipitation Radar. J. Meteor. Soc. Japan, 98, 755-773, doi:10.2151/jmsj.2020-038. [Web page] [BibTeX] [EndNote]
Special Edition on Global Precipitation Measurement (GPM): 5th Anniversary,
https://jmsj.metsoc.jp/special_issues_editions/GPM.html
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| 37. |
Sugimoto, S., H. G. Takahashi, and H. Sekiyama, 2019: Modification of Near-Surface Temperature Over East Asia Associated With Local-Scale Paddy Irrigation. J. Geophys. Res. Atmos., 124, 2665-2676, doi:10.1029/2018JD029434.[Web page] [BibTeX] [EndNote]
This study used two regional climate model experiments to assess the impact of paddy irrigation in the Sichuan Basin, China, on the near‐surface temperature across East Asia: a control experiment (CTL run), which was used to calculate soil moisture using an unmodified land surface scheme and a sensitivity experiment (SEN run) that incorporated an increase in soil moisture over the basin at the beginning of the rice‐growing season. Although the near‐surface temperature in the Sichuan Basin was higher in the CTL run than in the observations, it improved in the SEN run because of a change in the Bowen ratio associated with the increase in soil moisture. In the SEN run, the modification of local‐scale land surface wetness in the basin causes the decrease in the near‐surface temperature over northeastern China and its increase over southern China relative to that in the CTL run because of a change in the cloud convection associated with precipitation, which, in turn, modifies the solar and net radiation at the surface and the partitioning into the sensible and latent heat fluxes. The greenhouse effect associated with an increase in precipitable water in the SEN run also influences near‐surface warming over southeastern China and the ocean north of southwestern Japan, where the impacts of radiation processes and surface heat fluxes on the near‐surface temperature are small. Consequently, these results suggest that local‐scale modifications to land surface wetness in the Sichuan Basin result in changes in the spatial distribution of near‐surface temperatures over a part of East Asia.
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| 36. |
Takahashi, H. G., and J. Polcher, 2019: Weakening of rainfall intensity on wet soils over the wet Asian monsoon region using a high-resolution regional climate model. Progress in Earth and Planetary Science, 6, 26, doi:10.1186/s40645-019-0272-3.[Web page] [BibTeX] [EndNote]
This study estimated the sensitivity of rainfall characteristics (rainfall amount, rainfall frequency, rainfall intensity, and rainfall extremes based on 30-min intervals) to land-surface conditions over Southeast Asia, which has a wet land surface during the rainy season. To obtain the regional difference in sensitivity and simulate basic cloud-precipitation systems, we used a high-resolution regional climate model. To extract the systematic signals of sensitivity and exclude random errors, a series of six sensitivity experiments, which were driven by a reanalysis dataset and the observed sea surface temperature (SST), were conducted over the Indochina Peninsula. In our experiments, soil moisture was prescribed at 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45 m
3 m
−3 over the whole domain and during the whole calculation period. More experiments would allow us to divide the responses into systematic signals and random noise. The slope of a meteorological variable as a function of the six prescribed soil moisture values was defined as the sensitivity. It was found that the sensitivity of rainfall frequency to soil moisture was positive overall, whereas the sensitivity of rainfall intensity was negative overall, although evapotranspiration (sensible heat flux) increased (decreased) in a manner similar to the increase in soil moisture over the whole domain. The sensitivity of rainfall amount to an increase in soil moisture was dependent on the location. This implies that the response of rainfall characteristics to soil moisture is not simple, suggesting that changes in rainfall characteristics are not solely determined by evapotranspiration. In addition, the sensitivity of rainfall characteristics displayed remarkable regional characteristics. The characteristics described above were noticeable over the inland flat plains. We also discussed the mechanism in the response of rainfall characteristics to soil moisture. The coupling of an increase in water vapor in the planetary boundary layer and a decrease of sensible heat flux can explain the response. The increase in water vapor in the planetary boundary layer was associated with a reduction of the development of deep convections and an increase of boundary layer clouds.
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| 35. |
Kamizawa, N., and H. G. Takahashi, 2018: Projected Trends in Interannual Variation in Summer Seasonal Precipitation and Its Extremes over the Tropical Asian Monsoon Regions in CMIP5. J. Climate, 31, 8421-8439, doi:10.1175/JCLI-D-17-0685.1. [Web page] [BibTeX] [EndNote]
Long-term changes in the interannual variation in summer seasonal [June–August (JJA)] precipitation over the tropical Asian summer monsoon (ASM) region were investigated using 22 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) of the representative concentration pathway 4.5 (RCP4.5) run. Objective evaluations were performed with statistical tests to determine if there was an agreement among the multiple models. A robust increasing trend in fluctuations in the interannual variation in JJA precipitation over the ASM region was found. Expansions in both the wet and dry extremes of JJA precipitation anomalies were identified from the beginning to end of the twenty-first century, which were indicative of an intensification in interannual variation. These results indicate that the frequency and/or intensity of floods and droughts will likely increase under global warming. The spatial distribution of the projected expansion of wet and dry extremes differed over the ASM region. The signals in the wet extreme appeared throughout the whole ASM region, whereas those in the dry extreme were strong, particularly over the area from the Bay of Bengal to the equatorial western North Pacific, corresponding with the monsoon trough where the mean JJA precipitation increased.
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| 34. |
Takahashi, H.G., Watanabe, S., Nakata, M., and Takemura, T. 2018: Response of the atmospheric hydrological cycle over the tropical Asian monsoon regions to anthropogenic aerosols and its seasonality. Progress in Earth and Planetary Science (PEPS), 5, 44, https://doi.org/10.1186/s40645-018-0197-2. [Web page] [BibTeX] [EndNote]
This study investigates the impact of anthropogenic aerosols on the atmospheric hydrological cycle over the tropical Asian monsoon region (South Asian, Southeast Asian, and western North Pacific monsoons), using a coupled atmosphere-ocean global climate model (CGCM), Model for Interdisciplinary Research on Climate-Earth System Models. Three-ensemble historical (HIST) and sensitivity (piAERO) experiments for the period 1985-2005 are conducted. The piAERO experiment is the same as HIST, but with anthropogenic aerosol emissions kept at preindustrial values. The results show that, as a whole, the Asian monsoon precipitation is reduced by the increase in aerosol loading during boreal summer and winter. This decrease in precipitation corresponds to a decrease in precipitable water due to the cooling in surface air temperature (SAT), mainly over adjacent oceans. The cooling is explained by the sum of the direct and indirect effects of aerosols. A modulation of the Walker circulation occurs, which can be explained by the east-west horizontal SAT gradient over the tropics due to the spatially heterogeneous increase in aerosols. Concurrent with the modulation of the Walker circulation, the anomalous descending motions over the tropical Asian monsoon region are consistent with the decrease in precipitation. In addition, the changes in local Hadley circulation (or a shift of the inter-tropical convergence zone) are unclear over the Asian monsoon region and thus cannot explain the decrease in precipitation. Moreover, the detailed spatial pattern of the response of the atmospheric hydrological cycle over the Asian monsoon region has distinct seasonality. Interestingly, signals are distinct in regions where tropical disturbance activity is vigorous during both boreal summer and winter. However, uncertainties regarding aerosol-cloud-precipitation interactions in current climate models and internal variability in the climate models may have affected the results.
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| 33. |
Takahashi, H.G., 2018: A Systematic Tropospheric Dry Bias in the Tropics in CMIP5 Models: Relationship between Water Vapor and Rainfall Characteristics. Journal of the Meteorological Society of Japan. Ser. II, 96, 4, 415-423, doi:10.2151/jmsj.2018-046. [Web page] [BibTeX] [EndNote]
本研究では、第５期大気海洋結合モデル相互比較計画（CMIP５）での鉛直積分した水蒸気量（可降水量）の絶対値について、可降水量と降水特性の関係に着目して調べた。本研究において、CMIP５モデルにおける全球平均の可降水量が、観測値に比べて、系統的に低いことを見出した。この乾燥バイアスは、熱帯の海洋上においてもっとも顕著である。この乾燥バイアスは、CMIP５の結合モデルの海面水温バイアスに部分的に起因する。しか しながら、乾燥バイアスは、大気モデル相互比較計画（AMIP）の実験でも見られることから、別の要因も寄与していることが示唆される。可降水量と降水特性の関係を調べると、観測よりも低い水蒸気量の時に降水が発生しており、この傾向は乾燥バイアスの強いモデルでより顕著である。これは、降水特性の再現性と乾燥バイアスが関連していることを示しているかもしれない。
This study investigated the absolute values of column-integrated water vapor (precipitable water; PW) in the climate models used in the Coupled Model Intercomparison Project Phase 5 (CMIP5), in terms of the relationships between PW and precipitation characteristics. We identified that global mean PW values are systematically much lower in CMIP5 models than in observations. This dry bias is most profound over the tropical ocean. The dry bias is partly due to biases in sea surface temperatures in the CMIP5-coupled climate models. However, the dry bias is also present in Atmospheric Model Intercomparison Project (AMIP) experiments, which implies the existence of other factors. The relationship between PW and rainfall characteristics shows that rainfall occurs when water vapor levels are lower than in observations, particularly in models with a relatively strong dry bias. This suggests that the reproducibility of rainfall characteristics may be associated with the dry bias.
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| 32. |
Takahashi, H.G., and J. Mae B. Dado, 2018: Relationship between Sea Surface Temperature and Rainfall in the Philippines during the Asian Summer Monsoon. J. Meteor. Soc. Japan. Ser. II, 96, 3, 283-290, doi:10.2151/jmsj.2018-031. [Web page] [BibTeX] [EndNote]
過去の研究によると夏季アジアモンスーン期におけるフィリピンの風上側の近傍の海面水温とフィリピン西部の降水量は、負の相関関係にある。本研究では、海面水温、降水量、大気循環場の日データを用いて、その関係を検討した。本研究では、局所的な海面水温の影響のみに注目し、遠隔影響は扱わない。アジアモンスーンの西風が比較的強いような限定された気象条件下では、より暖かい海面水温は、より多くの降水量をもたらす。この結果は、上記の限定された気象条件を選んだときにのみ得られる。その理由は、海面水温と降水量の見かけ上の負相関により、暖かい海面水温による降水量の増加への影響が隠されてしまっているからである。その見かけ上の負相関は、降水が少なく、海面水温が暖かいという組み合わせが弱いモンスーン西風による弱い冷却と一致し、降水が多く、海面水温が冷たいという組み合わせが強いモンスーン西風による強い冷却と一致することにより説 明できる。これらの組み合わせにより、冷たい海面水温と多量の降水という見かけ上の統計関係を成り立たせる。冷たい海面水温は、強い西風の結果であり、多量の降水の原因ではない。これはまた、モンスーン西風がこの地域の降水量変動の主要な要因であることを示唆している。本研究では、降水量に対して、近傍の海面水温による正の寄与を示したが、海面水温は降水量変動に対して主要な要因ではない。この結論は、本研究のような気候学的に降水量変動が海からの風により支配されている沿岸地域にも当てはまると思われる。
We offer a new perspective on a relationship between sea surface temperature (SST) over the windward region of the Philippines and rainfall in the western Philippines during the Asian summer monsoon season, which has been known as the negative correlation, using observational daily SST, rainfall, and atmospheric circulation datasets. This study focuses on the local SST effect rather than the remote effect. A warmer local SST results in greater rainfall over the western Philippines under similar monsoon westerlies conditions, particularly during moderate and relatively stronger monsoon regimes. This result is obtained after selecting only the moderate or relatively stronger monsoon days, because the positive effect of SST on rainfall is masked by the apparent negative correlation between SST and rainfall. The warmer SSTs being associated with less rainfall correspond to weaker cooling by weaker monsoon westerlies and the cooler SSTs being associated with more rainfall correspond to stronger cooling by stronger monsoon westerlies. The cooler SSTs are the result of stronger monsoon cooling and are not the cause of the greater rainfall, which is the apparent statistical relationship. This also implies that the monsoon westerly is the primary driver of the variation in rainfall in this region. We conclude that the local SST makes a positive contribution toward rainfall, although it does not primarily control rainfall. This conclusion can be applicable to coastal regions where, climatologically, rainfall is controlled by winds from the ocean.
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| 31. |
Dado, J.M.B., and H.G. Takahashi, 2017: Potential impact of sea surface temperature on rainfall over the western Philippines. Progress in Earth and Planetary Science (PEPS), 4, doi:10.1186/s40645-017-0137-6. [BibTeX] [EndNote]
The study used a 5 km-resolution regional climate model, the Advanced Research Weather Research and Forecasting Model, to quantify the potential impact of sea surface temperature (SST) west of the Philippines on summer monsoon rainfall on the northwestern coast of the country. A set of control simulations (CTL) driven by ERA-Interim reanalysis data and the monthly National Oceanic and Atmospheric Administration Optimum Interpolation SST dataset was performed for the months of June to August of 1982–2012. A second set of simulations driven by climatological SST values was performed for the same period. The difference between these two simulation sets is analyzed to determine the sensitivity of rainfall to interannual variations in local SST, not remote SST, via a regional climate model. The CTL simulations represented spatial and temporal variations in rainfall well, yielding realistic climatological rainfall values with high spatial correlations with observations. The interannual correlation of monthly rainfall over the northwestern region of the Philippines was also high when compared to observations. The results showed that positive SST anomalies west of the Philippines induced positive rainfall anomalies in the northwestern Philippines via an increase in latent heat flux from the sea surface, implying that summer monsoon rainfall in the northwestern Philippines is modulated by interannual variations in SST west of the Philippines. The impact of SST on latent heat flux and rainfall were 20–40%, greatly exceeding the 7% approximation from the Clausius–Clapeyron equation, which can be explained by the enhancement of low-level winds and a weak warming of surface air temperature over the ocean.
本研究は、水平解像度5kmの領域気候モデル（Advanced Research Weather Research and Forecasting Model）を用いて、フィリピン西部の降水量に対して、同地域近傍の風上側の海面水温（SST）が、どの程度影響を与えているかについて定量的に評価した研究である。一連の標準実験（CTL）として、ERA-interim再解析とOISST海面水温データを初期境界値として、1982年から2012年までの31年間の各年の6月から8月を対象にシミュレーションを行った。感度実験（CLIM）として、CTLと同様の実験を実施したが、SSTの年々変動の降水への影響を調べるために、CTLでの下部境界のSSTを31年間の気候平均値のSSTに差し替えてシミュレーションを行った。これらのCTLとCLIMの差から、SSTの感度を取り出せる。この研究では、フィリピン近傍のSSTの影響を研究対象としており、SSTの遠隔影響（エルニーニョ現象の影響などのテレコネクション）は研究対象範囲外である。アジアモンスーンの降水量に対するSSTの遠隔影響の研究は多いが、近傍のSSTの影響を調べた研究は少ない。CTL実験の結果を、降水量の観測データと比較したところ、フィリピンでの降水量の時空間変動をよく再現していた。また、フィリピン西部の降水量の年々変動についても、よく再現されていた。結果として、フィリピンの風上側のSSTの偏差は、フィリピン西部の降水量に対して、正の感度を示した。また、海面からの潜熱も正の感度を示した。この結果は、フィリピン西部の夏季降水量は、モンスーン西風による影響が大きいことは知られていたが、さらに近傍のSSTにも影響を受けていることを示唆している。SST上昇に対する潜熱の増加は、20%から40%であり、クラウジウス・クラペイロンの式の示す約7%を大きく上回っていた。この潜熱の増加は、二つの効果によって説明できる。一つはSST上昇に伴う下層風の強化であり、もう一つは、地上気温の上昇がSST上昇よりも小さいことによって水面と水面直上での水蒸気量差の増加する効果である。
[日本語要約]
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| 30. |
Sugimoto, S., and H.G. Takahashi, 2017: Seasonal Differences in Precipitation Sensitivity to Soil Moisture in Bangladesh and Surrounding Regions. J. Climate, 30, 921-938, doi:10.1175/jcli-d-15-0800.1. [abstract] [pdf] [BibTeX] [EndNote]
Precipitation sensitivity to soil moisture and its seasonal and diurnal changes are investigated in Bangladesh and surrounding regions using a regional climate model with a 5-km grid spacing. In the control experiment, soil moisture is calculated by a land surface scheme, and simulated accuracy of seasonal and diurnal variations in precipitation intensity and frequency is capable of assessing the soil moisture impact on precipitation. In sensitivity experiments with wetter land surfaces, daytime precipitation intensity decreases over the southern plains for both the premonsoon and mature monsoon seasons because of the weakening of surface heating and vertical mixing in the planetary boundary layer (PBL). Weakened vertical turbulent flux of moisture reduces condensation heating and upward motion in the mid- and upper troposphere, which suppresses development of convective precipitation. The simulated precipitation intensity response to soil moisture suggests that land surface wetness contributes to the seasonal contrast in observed precipitation intensity (i.e., stronger in the premonsoon than the mature monsoon seasons). Meanwhile, the precipitation frequency response to soil moisture varies with season and by region. Over the southern plains in the wet land surface experiments, daytime precipitation frequency decreases (increases) during the premonsoon (mature monsoon) season compared with the dry land surface experiments, as influenced by seasonal differences in relative humidity and the condensation process in the lower troposphere. Around the northern mountainous area, higher soil moisture increases precipitation frequency regardless of season because of additional water vapor supply from the ground and frequent orographic precipitation forced by the mountainous topography.
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| 29. |
Takahashi, H.G., 2016: Seasonal and diurnal variations in rainfall characteristics over the tropical Asian monsoon region using TRMM-PR data. SOLA (Scientific Online Letters on the Atmosphere), 12A, 22-26, doi:10.2151/sola.12A-005. (Accepted on Aug., 2016) [abstract] [pdf] [bibtex] [EndNote]
Seasonal and diurnal rainfall characteristics, including the rainfall amount (RA), rainfall frequency (RF), and rainfall intensity (RI), were investigated over the tropical Asian monsoon region using Tropical Rainfall Measuring Mission Precipitation Radar (TRMM-PR) data. The results showed that the number of hours of high RF varied seasonally over land, although the diurnal peaks were mostly unchanged. Over Indochina, precipitation ended in the evening in April and May when the RA was low, whereas precipitation lasted until early morning from July to September when the RA was high. The seasonal changes in RF likely contributed to the changes in RA over land. Additionally, RI had two seasonal peaks occurring at the beginning and end of the summer monsoon over land regions; thus, RI was strongest during the two transition seasons. In contrast, both RF and RI had a single seasonal peak over the ocean.
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| 28. |
Ono, M., and H.G. Takahashi, 2016: Seasonal transition of precipitation characteristics associated with land surface conditions in and around Bangladesh. J. Geophys. Res. Atmos., 121, 11,190-111,200, doi:10.1002/2016JD025218. [abstract] [pdf] [bibtex] [EndNote]
This study examined the seasonal transition of precipitation characteristics and its association with land surface conditions in and around Bangladesh, where land surface conditions are predominantly wet. Hourly rain rate data from the Global Satellite Mapping of Precipitation Microwave‐Infrared Combined Product and 10 day soil moisture data from the Advanced Microwave Scanning Radiometer Earth Observing System were used over the 7 years from 2003 to 2009. Area mean values of soil moisture, and precipitation amount, frequency, and intensity were calculated for each 10 day period. Results showed that higher precipitation amount and frequency were observed over the wet soil conditions, which indicates that soil moisture was influenced by previous precipitation events. However, the soil moisture could also control the precipitation characteristics. The seasonal and interannual variations in all regions suggested that precipitation amount and frequency increased in moist soil conditions, which is associated with an increase of water vapor supplied from the moist land surface. Over a flat plain (87°E–91°E, 23°N–25°N), a higher afternoon precipitation intensity was observed over drier land surfaces. This relationship was observed on seasonal and interannual variations. This suggests that the land surface conditions in this region can affect the afternoon precipitation intensity to some extent, although changes of atmospheric conditions can be a major factor particularly for the seasonal changes. However, this relationship was not observed in mountainous regions. This can be explained by other factors, such as thermally induced local circulations by the surrounding topography, being stronger than the impact of land surface conditions.
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| 27. |
Adachi S.A, F. Kimura, H.G Takahashi, M. Hara, X. Ma, and H. Tomita, 2016: Impact of high-resolution sea surface temperature and urban data on estimations of surface air temperature in a regional climate. J. Geophys. Res., 121, 10,486-410,504, doi:10.1002/2016JD024961. [Abstract] [pdf] [bibtex] [EndNote]
We investigated the impact of using high‐resolution sea surface temperature (SST) data and a sophisticated urban model on the simulation of surface air temperature (SAT) in the Nagoya metropolitan area using a regional climate model. The spatially detailed structure of SST, expressed in high‐resolution SST data, had relatively little impact on SAT. On the other hand, the difference in areal mean value of SST strongly affected SAT across a wide range of land surfaces. When a spatially inhomogeneous distribution was used for the urban fraction and anthropogenic heat, and appropriate physical properties for building materials were given according to the specific urban categories, we achieved significant improvements in both the diurnal range of SAT and its daily mean. Based on a comparison with an additional sensitivity experiment for building albedo, the sophistication of urban fraction and thermal parameters related to building materials had a comparable impact on SAT as presumable building albedo in the daytime, while they indicated a larger impact on the nighttime SAT. We conclude that (1) the areal mean SST is critical rather than its resolution for the climatological average of SAT over the land; (2) the simultaneous refinement of the urban fraction and building material parameters, as well as an appropriate building albedo setting, greatly improves the representation of SAT; and (3) the refinement of areal mean SST and the urban data have the same degree of importance for a better representation of the SAT.
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| 26. |
Sugimoto, S., and H.G. Takahashi, 2016: Effect of Spatial Resolution and Cumulus Parameterization on Simulated Precipitation over South Asia. SOLA (Scientific Online Letters on the Atmosphere), 12A, 7-12, doi:10.2151/sola.12A-002. [Abstract] [pdf] [bibtex] [EndNote]
This paper evaluates the ability of a regional-scale climate model to simulate precipitation over the South Asian tropical region. Experiments were conducted using three different spatial resolutions, with and without cumulus parameterization (CP), to assess the influence of horizontal mesh size and the CP on regional-scale precipitation. The experiments that used a finer mesh size but no CP improved the spatial distribution of monthly precipitation relative to that in the experiments based on a coarser spatial resolution. Meanwhile, the impact of horizontal mesh size was much less in the experiments that included the CP because an overestimation of precipitation caused by the CP strongly affected the simulation accuracy in these experiments. Regional differences in diurnal variations in precipitation intensity and frequency were captured reasonably well in the pre-monsoon season regardless of the spatial resolution, and both with and without the CP. In contrast, the diurnal characteristics of precipitation were difficult to simulate during the mature monsoon season. During both seasons, those experiments that incorporated the CP tended to predicted a continuous weak precipitation due to the excessive release of convective instability; accordingly, precipitation intensity was weaker, and precipitation frequency greater than in those experiments that did not use the CP.
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| 25. |
Tanaka, K., T. Chatchai, W. Decha, N. Tanaka, H.G. Takahashi, N. Yoshifuji, Y. Igarashi, T. Sato, and M. Suzuki, 2015: Earlier Leaf Flush Associated with Increased Teak Defoliation. Forest. Sci., 61, 1009-1020, doi:10.5849/forsci.15-004. (Published on Dec. 20, 2015) [Web page] [BibTeX] [EndNote]
The goal of this study conducted at the Mae Mo teak plantation in northern Thailand was to test the hypothesis that early teak (Tectona grandis L. f.) leaf flush results in higher levels of insect defoliation. Based on photographic evidence in both 2010 and 2012, increases in soil moisture in the root zone before the spring equinox resulted in early flushing and subsequent leaf growth and expansion. Early leaf development was observed from 2010 to 2012 in response to wind and distribution of daily rainfall during northerly surges. Adverse growing conditions of shorter day lengths and low soil moisture, in 2001, 2008, 2010, and 2012, were associated with defoliation. The insect that appears to be primarily responsible for defoliation is the teak defoliator, Hyblaea puera (Cramer 1777). In 2011, reduced ambient temperature and a lower vapor pressure deficit reduced evaporative demands during the leaf growing period, resulting in greater soil moisture retention. In 2011, these conditions induced relatively faster leaf expansion and, subsequently, limited the extent of defoliation. There is a strong probability that early leaf flush in response to an increase in premonsoon rainfall was a major factor contributing to teak leaf defoliation over a 12-year period.
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| 24. |
Takahashi, H.G., S.A. Adachi, T. Sato, M. Hara, X. Ma, and F. Kimura, 2015: An Oceanic Impact of the Kuroshio on Surface Air Temperature on the Pacific Coast of Japan in Summer: Regional H2O Greenhouse Gas Effect. J. Climate, 28, 7128-7144, doi:10.1175/jcli-d-14-00763.1. (Published on Sep., 2015) [Abstract] [pdf, open access!!] [bibtex] [EndNote]
This study used a 4-km resolution regional climate model to examine the sensitivity of surface air temperature on the Pacific coast of Japan to sea surface temperature (SST) south of the Pacific coast of Japan during summer. The authors performed a control simulation (CTL) driven by reanalysis and observational SST datasets. A series of sensitivity experiments using climatological values from the CTL SST datasets over a 31-yr period was conducted. The interannual variation in surface air temperature over the Pacific coast was well simulated in CTL. The interannual variation in SST over the Kuroshio region amplified the interannual variation in surface air temperature over the Pacific coast. It was found that 30% of the total variance of interannual variation in surface air temperature can be controlled by interannual variation in SST. The calculated surface air temperature on the Pacific coast increased by 0.4 K per 1-K SST warming in the Kuroshio region. Note that this sensitivity was considerably greater during nighttime than during daytime. Concurrent with the warming in surface air temperature, downward longwave radiation at the surface was also increased. In summer, the increase in latent heat flux was considerably larger than that in sensible heat flux over the ocean because of SST warming, according to the temperature dependence of the Bowen ratio. This implies that the primary factor for the increase in surface air temperature in summer is increased moisture in the lower troposphere, indicating that the regional warming was caused by an increase in H
2O greenhouse gas.
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| 23. |
Kodama, C., Y. Yamada, A. Noda, K. Kikuchi, Y. Kajikawa, T. Nasuno, T. Tomita, T. Yamaura, H.G. Takahashi, M. Hara, Y. Kawatani, M. Satoh, and M. Sugi, 2015: A 20-year climatology of a NICAM AMIP-type simulation. J. Meteor. Soc. Japan Ser. II, 93, 393-424, doi:10.2151/jmsj.2015-024. (Published on Aug., 2015) [Abstract] [pdf] [bibtex] [EndNote]
A 20-year integration by the nonhydrostatic icosahedral atmospheric model (NICAM) with a 14 km mesh was conducted for the first time to obtain a climatological mean and diurnal to interannual variability of a simulated atmosphere. Clouds were explicitly calculated using a cloud microphysics scheme without cumulus convection scheme. The simulation was performed under the atmospheric model intercomparison project-type conditions, except that sea surface temperature was nudged toward observed historical values using the slab ocean model. The results are analyzed with a focus on tropical disturbances, including tropical cyclones (TCs) and the Madden-Julian oscillation (MJO).
NICAM simulates many aspects of atmospheric climatological mean state and variability. The geographical distributions of precipitation, including interannual, seasonal, and diurnal variations, are well reproduced. Zonal mean basic states, clouds, and top-of-atmosphere radiation are qualitatively simulated, though some severe biases such as underestimated low clouds, shortwave reflection, warmer surface, and tropical upper troposphere exist.
TCs and MJO are the main focus of the simulation. In the simulation, TCs are detected with the objective thresholds of maximum wind speed due to the realistic intensity of simulated TCs. The seasonal march of TC genesis in each ocean basin is well simulated. The statistical property of the MJO and tropical waves is well reproduced in the space-time power spectra, consistent with previous NICAM studies. This implies that the stratospheric variability is also reproduced, as partially revealed in this study. Asian monsoon analysis shows that climatological western North Pacific monsoon onset occurs near the observed onset, and that the Baiu front is reproduced to some extent. Some significant model biases still exist, which indicates a need for further model improvements. The results indicate that a high-resolution global nonhydrostatic model has the potential to reveal multiscale phenomena in the climate system.
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| 22. |
Takahashi, H.G., H. Fujinami, T. Yasunari, J. Matsumoto, and S. Baimoung, 2015: Role of tropical cyclones along the monsoon trough in the 2011 Thai flood and interannual variability. J. Climate, 28, 1465-1476, doi:10.1175/jcli-d-14-00147.1. (Accepted on Nov. 6, 2014) [Web page] [pdf, open access!!] [bibtex] [EndNote]
The atmospheric circulation patterns that were responsible for the heavy flooding that occurred in Thailand in 2011 are examined. This paper also investigates the interannual variation in precipitation over Indochina over a 33-yr period from 1979–2011, focusing on the role of westward-propagating tropical cyclones (TCs) over the Asian monsoon region. Cyclonic anomalies and more westward-propagating TCs than expected from the climatology of the area were observed in 2011 along the monsoon trough from the northern Indian subcontinent, the Bay of Bengal, Indochina, and the western North Pacific, which contributed significantly to the 2011 Thai flood. The strength of monsoon westerlies was normal, which implies that the monsoon westerly was not responsible for the seasonal heavy rainfall in 2011. Similar results were also obtained from the 33-yr statistical analysis. The 5-month total precipitation over Indochina covaried interannually with that along the monsoon trough. In addition, above-normal precipitation over Indochina was observed when enhanced cyclonic circulation with more westward-propagating TCs along the monsoon trough was observed. Notably, the above-normal precipitation was not due to the enhanced monsoon westerly over Indochina. Therefore, the 2011 Thai flood was caused by the typical atmospheric circulation pattern for an above-normal precipitation year. It is noteworthy that the effect of sea surface temperature (SST) forcing over the western North Pacific and the Niño-3.4 region on total precipitation during the summer rainy season over Indochina was unclear over the 33-yr period.
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| 21. |
Yamaji, M., and Takahashi, H.G., 2014: Asymmetrical interannual variation in aerosol optical depth over the tropics in terms of aerosol-cloud interaction. SOLA (Scientific Online Letters on the Atmosphere), 10, 185-189, doi:10.2151/sola.2014-039. (Accepted on Oct. 27, 2014) [Web page] [pdf] [bibtex] [EndNote]
We statistically investigated an interannual co-variation among aerosol optical depth (AOD), cloud effective radius (CER), and precipitation, focusing on aerosol-cloud interaction over the tropics. A three-month composite analysis for AOD, CER, and precipitation for 2000-2012 based on El Niño-Southern Oscillation phases during September-October-November (SON) and December-January-February shows that an increase (decrease) in AOD in the El Niño (La Niña) years was associated with a decrease (increase) in precipitation, particularly in SON over the Maritime Continent. Additionally, CER decreased in the El Niño years over the same region, which implies that CER was associated with interannual variation in aerosol burden; these results were statistically significant. Interannual variation in AOD and CER in SON in the Maritime Continent was asymmetrical, which can be explained by stronger aerosol-cloud interactions under drier conditions. Specifically, large amounts of aerosols suppressed cloud and precipitation formation, which leads to decreases in wet deposition and increases in emission under warmer and drier surface conditions. This feedback results in asymmetrical variation. Furthermore, the asymmetrical interannual variation was confirmed statistically.
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| 20. |
Yamashima, R., J. Matsumoto, K. Takata, and H.G. Takahashi, 2014: Impact of historical land-use changes on the Indian summer monsoon onset. Int. J. Climatol., 35, 2419-2430, doi:10.1002/joc.4132. [Web page] [pdf] [BibTeX] [EndNote]
We investigate the impact of historical land‐use changes (HLUCs) from 1700 to 1850 on the onset of the Indian summer monsoon (ISM), focusing on the onsets of broad‐scale ISM circulation and the local rainy season and their relationships, by conducting three equilibrium experiments under 1700, 1850, and 1992 conditions. During that time period, land use changed from primarily forest to cropland in India, eastern China, and Europe. This study used an atmospheric general circulation model, Model for Interdisciplinary Research on Climate version 3.2, coupled with a land surface scheme, Minimal Advanced Treatments of Surface Interaction and Runoff. The results showed that HLUC decreased rainfall amounts by more than 2 mm day
−1 during the onset phase and delayed the onset date of the local rainy season by approximately four pentads over the Indian subcontinent. The onset date over southeastern China was also delayed by four pentads. The changes in precipitation and the onset of the local rainy season result from the change in the surface water budget induced by HLUC, as discussed in previous work. Although ISM circulation activity, defined by a large‐scale land–sea thermal contrast, was slightly decreased from late May to early June, its onset date did not change. Thus, in the onset phase, HLUC affected the local rainy season onset over the same region, although the ISM circulation was weakened only marginally, showing no change in its onset timing. Hence, unlike the broad‐scale ISM circulation onset, the beginning of the local rainy season is dominantly influenced by local surface conditions.
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| 19. |
Villafuerte II, M. Q., J. Matsumoto, I. Akasaka, H.G. Takahashi, H. Kubota, and T. A. Cinco, 2014: Long-term trends and variability of rainfall extremes in the Philippines. Atmos. Res., 137, 1-13, doi:https://doi.org/10.1016/j.atmosres.2013.09.021. [pdf] [BibTeX] [EndNote]
Owing to the increasing concerns about climate change due to the recent extreme rainfall events in the Philippines, long-term trends and variability in rainfall extremes in the country are investigated using 60-year (1951–2010) daily rainfall data from 35 meteorological stations. Rainfall extremes are described using seven extreme precipitation indices (EPI) that characterize daily rainfall in terms of intensity, accumulation, and duration on a seasonal perspective. The nonparametric Mann–Kendall test is employed in combination with the moving blocks bootstrapping technique to detect significant trends in EPI. The results suggest a tendency toward a drying condition for the dry season, January–March (JFM), as indicated by statistically significant decreasing trends in seasonal wet days total rainfall (PCPTOT) associated with increasing trends in maximum length of dry spell (LDS). In contrast, statistically significant increasing trends in maximum 5-day rainfall (RX5day) and decreasing trends in LDS denote a wetting condition during the July–September (JAS) season, particularly at stations located in the northwest and central Philippines. The trends obtained are further assessed by examining the longer time series of EPI at four meteorological stations (Aparri, Dagupan, Iloilo, and Masbate) that have rainfall data from 1911 to 2010. The longer historical data revealed that the trends obtained in the shorter period (1951–2010) could either be consistent with the continuous long-term trends, as observed in RX5day during JAS at Aparri and Masbate, or represent interdecadal variability as was observed at Dagupan and Iloilo. The long-term (1911–2010) southwestward extension of the western North Pacific subtropical high associated with a weakening of the 850-hPa westerly wind over the South China Sea partly provides a possible cause of the trends in EPI during JAS, whereas the weakening of the East Asian winter monsoon contributed somewhat to the trends obtained during JFM. Furthermore, interannual variations in EPI are found to be influenced greatly by the El Niño–Southern Oscillation (ENSO). Composite analyses suggest that El Niño (La Niña) events are associated with statistically significant drier (wetter) conditions over the Philippines, especially during the seasons close to ENSO mature stage.
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| 18. |
Takahashi, H.G., and Idenaga, T., 2013: Impact of SST on Precipitation and Snowfall on the Sea of Japan Side in the Winter Monsoon Season: Timescale Dependency. J. Meteor. Soc. Japan Ser. II, 91, 639-653, doi:10.2151/jmsj.2013-506. (Accepted on Jul. 9, 2013) [Web page] [pdf] [BibTeX] [EndNote]
We investigated the impact of the sea surface temperature (SST) over the Sea of Japan on precipitation and snowfall on the Sea of Japan side of Honshu, Japan, using precipitation and snowfall data from Automated Meteorological Data Acquisition System (AMeDAS) stations, records of sea level pressure from meteorological stations, wind fields from the Japanese 25-year reanalysis (JRA25) dataset, and multiple SST datasets. We examined the data on various timescales from daily to monthly because SST over the Sea of Japan also varies on timescales shorter than a month. The results showed that the impact of SST over the Sea of Japan on precipitation on the Sea of Japan side was strongly timescale-dependent. On the shorter intraseasonal timescales of several days to a few weeks, SST had a clear impact on precipitation, while the impact was indistinct when the 15-day and monthly averaged precipitation and SST values were used. On the other hand, cold surges over the Sea of Japan primarily accounted for the amount of precipitation on the Sea of Japan side. The timing and strength of cold surges controlled precipitation on all timescales. We clearly found the impact of cold surges on SST on 15-day mean values, compared with the pentad mean values. To understand detailed impacts of SST on precipitation, including air-sea interaction processes over the Sea of Japan, synoptic and shorter intraseasonal timescales should be examined in addition to seasonal or interannual timescales.
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| 17. |
Ma, X., H. Kawase, S. Adachi, M. Fujita, H.G. Takahashi, M. Hara, N. Ishizaki, T. Yoshikane, H. Hatsushika, Y. Wakazuki, and F. Kimura, 2013: Simulating river discharge in a snowy region of Japan using output from a regional climate model. Adv. Geosci., 35, 55-60, doi:10.5194/adgeo-35-55-2013. [Web page] [pdf] [BibTeX] [EndNote]
Snowfall amounts have fallen sharply along the eastern coast of the Sea of Japan since the mid-1980s. Toyama Prefecture, located approximately in the center of the Japan Sea region, includes high mountains of the northern Japanese Alps on three of its sides. The scarcity of meteorological observation points in mountainous areas limits the accuracy of hydrological analysis. With the development of computing technology, a dynamical downscaling method is widely applied into hydrological analysis. In this study, we numerically modeled river discharge using runoff data derived by a regional climate model (4.5-km spatial resolution) as input data to river networks (30-arcseconds resolution) for the Toyama Prefecture. The five main rivers in Toyama (the Oyabe, Sho, Jinzu, Joganji, and Kurobe rivers) were selected in this study. The river basins range in area from 368 to 2720 km
2. A numerical experiment using climate comparable to that at present was conducted for the 1980s and 1990s. The results showed that seasonal river discharge could be represented and that discharge was generally overestimated compared with measurements, except for Oyabe River discharge, which was always underestimated. The average correlation coefficient for 10-year average monthly mean discharge was 0.8, with correlation coefficients ranging from 0.56 to 0.88 for all five rivers, whereas the Nash-Sutcliffe efficiency coefficient indicated that the simulation accuracy was insufficient. From the water budget analysis, it was possible to speculate that the lack of accuracy of river discharge may be caused by insufficient accuracy of precipitation simulation.
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| 16. |
Takahashi, H.G., N. N. Ishizaki, H. Kawase, M. Hara, T. Yoshikane, X. Ma, and F. Kimura, 2013: Potential impact of sea surface temperature on winter precipitation over the Japan Sea side of Japan: A regional climate modeling study. J. Meteor. Soc. Japan Ser. II, 91, 471-488, doi:10.2151/jmsj.2013-404. (Accepted on Apr. 27, 2013). [Web page] [pdf] [BibTeX] [EndNote]
In this study, a regional climate model (WRF-ARW; the Advanced Research Weather Research and Forecasting model) having a resolution of 4.5 km was used to examine the sensitivity of precipitation on the Japan Sea side of Japan to the sea surface temperature (SST) in the Japan Sea during winter. We performed a control simulation (CTL) driven by reanalysis and observational SST datasets. Three sensitivity experiments in which SSTs over the entire domain were 1K, 2K, and − 1K different from the CTL SST were conducted to examine the sensitivity of precipitation to SST. The calculated precipitation on the Japan Sea side increased by 6-12% K
−1 of SST warming. Concurrent with the precipitation changes, latent heat flux over the Japan Sea increased by 11-14% K
−1 of SST warming. Because the changes in surface relative humidity were very small, the increase can be explained by the Clausius-Clapeyron equation. The deviation from the 7% increase in latent heat flux calculated from this equation can be quantitatively explained by the development of the planetary boundary layer over the Japan Sea, which was related to an increase in sensible heat flux due to the SST warming. This result also implies that the 1 K uncertainty in simulated and projected SST over the Japan Sea among multiple atmosphere-ocean global climate models corresponds to an approximately 10% uncertainty in precipitation on the Japan Sea side of Japan.
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| 15. |
Fujita, M., H.G. Takahashi, and M. Hara, 2013: Diurnal cycle of precipitation over the eastern Indian Ocean off Sumatra Island during different phases of Indian Ocean Dipole. Atmos. Sci. Lett., 14, 153-159, doi:10.1002/asl2.432. (Accepted on Apr. 1, 2013) [Web page] [pdf] [BibTeX] [EndNote]
Observed difference in diurnal cycle of precipitation over the eastern Indian Ocean between positive and negative Indian Ocean Dipole (IOD) phases was investigated using a regional model. During the negative IOD phase, prominent precipitation peak was over the land during evening in both observation and model, while precipitation often appeared over the ocean during early morning. In the positive IOD phase, precipitation peak was shifted to the northern area where sea surface temperature was warm. The amount of precipitation in the southern area during the negative phase was more than three times larger than that in the positive phase.
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| 14. |
Tanaka, K., H.-J. Kim, K. Saito, H.G. Takahashi, M. Watanabe, T. Yokohata, M. Kimoto, K. Takata, and T. Yasunari, 2012: How have both cultivation and warming influenced annual global isoprene and monoterpene emissions since the preindustrial era? Atmos. Chem. Phys., 12, 9703-9718, doi:10.5194/acp-12-9703-2012. [Web page] [pdf] [BibTeX] [EndNote]
To examine the influence of both crop cultivation and surface air temperatures (SATs) on annual global isoprene and monoterpene emissions, which can lead to the formation of secondary organic aerosols (SOAs), we simulated, on a monthly basis, the annual emissions of volatile organic compounds (VOCs) during the period 1854–2000. The model estimates were based on historical climate data such as SATs, and downward solar radiation (DSR) reproduced with an atmospheric-ocean circulation model, as well as a time series of the global distribution of cropland (to test the hypothesis that conversion of forests into croplands lowers emissions). The simulations demonstrated that global SAT, DSR, the combination of SAT and DSR, and the expansion of cropland all affected emissions. The effect of cropland expansion (i.e., forest conversion) on annual emissions during this period was larger for isoprene (~7% reduction on a global scale) than for monoterpenes (~2% reduction), mainly because of the reduction in broadleaf evergreen forests (BEFs) in Southeast Asia, which have the highest and most constant emissions of isoprene and where both temperature and radiation are high all year round. The reduction in the Amazon region and in parts of Africa, which are other primary sources of annual global isoprene emissions, but where the conversion of BEF to cropland has been much smaller than in Southeast Asia, was less remarkable, probably because the broadleaf deciduous forests and C4 grasslands in these areas have lower and seasonal emissions; hence, their conversion has less effect. On the other hand, the difference in the emission factors (ε) between cropland and the other vegetation types was much lower for monoterpenes than for isoprene, although the ε for cropland was generally the lowest for both compounds. Thus, the expansion of cropland also contributed to the reduction in monoterpene emissions to some degree, but had less effect. A ~5% increase in emissions due to rising SAT was more than offset by the decrease in isoprene emissions and a concurrent ~2% reduction caused by a decrease in DSR. Overall, annual global isoprene emissions in 2000 were lower than in 1854 by 13 TgCyr
−1, whereas annual global monoterpene emissions were higher by 2.3 TgCyr
−1.
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| 13. |
Takahashi, H.G., 2012: Orographic low-level clouds of Southeast Asia during the cold surges of the winter monsoon. Atmos. Res., 131, 22-33, doi:http://dx.doi.org/10.1016/j.atmosres.2012.07.005. (Accepted on Jul. 6, 2012) [Web page] [pdf] [BibTeX] [EndNote]
This study is an examination of low clouds over Southeast Asia during northern fall and winter using albedo values derived from visible images, cloud-top temperatures from infrared radiation images from the Multi-functional Transport Satellite 1 (MTSAT-1), and rainfall-top height (storm height) from precipitation radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellites. To understand the cloud and precipitation activities associated with the winter monsoon cold surges along the eastern coast of the Indochina Peninsula, atmospheric circulation data from the Japanese 25-year reanalysis (JRA-25) were used. The results showed that low clouds were frequently observed in December, January, and February. In October and November, rainfall activity was relatively high, whereas, in northern winter, it was low, although the winter monsoon northeasterly was strong in both cases. The cloud-top height and storm height decreased with the seasonal march from northern fall to winter. Also examined in this study were the temporal variations in cloud activity on shorter time scales than those of the seasonal march. Concurrent with the cold surges along the eastern coast of the Eurasia, clouds varied on synoptic and intraseasonal time scales. The timing of low-cloud formation corresponded to the beginning of the cold surges. However, the low clouds along the eastern coast of the Indochina Peninsula may remain during the weakening phase of the cold surges.
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| 12. |
Takahashi, H.G., 2011: Long-term changes in rainfall and tropical cyclone activity over South and Southeast Asia. Adv. Geosci., 30, 17-22, doi:10.5194/adgeo-30-17-2011. (Accepted on Apr. 26, 2011) [Web Page] [pdf] [BibTeX] [EndNote]
Long-term changes in rainfall and associated tropical cyclone (TC) activity in transition seasons between the wet and dry seasons in South and Southeast Asia, namely boreal spring and fall, were examined, using gridded rainfall, TC tracks, and reanalysis datasets, the focus of discussion being the long-term changes in coastal regions. It was found that long-term changes in rainfall during the transition seasons in South and Southeast Asia were closely associated with those in TC activity over the north Indian Ocean and South China Sea. Rainfall in May increased in the last 40 years over and around Myanmar, which indicates an earlier monsoon onset over the western Indochina Peninsula. Rainfall over and around northern Vietnam also increased in the last 40 years during October, which is known as the monsoon retreat period. These increases were associated with the long-term changes in TC activity. Furthermore, although linear trends have been previously suggested, monotonically increasing or decreasing trends in these long-term changes were not found over the last 60 years.
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| 11. |
Takahashi, H.G., Y. Fukutomi, and J. Matsumoto, 2011: The impact of long-lasting northerly surges of the East Asian winter monsoon on tropical cyclogenesis and its seasonal march. J. Meteor. Soc. Japan Ser. II, 89A, 181-200, doi:10.2151/jmsj.2011-A12. (Accepted on Nov. 12, 2010) Special issue on MAHASRI. [Web page] [pdf] [BibTeX] [EndNote]
The impact of northerly surges of the East Asian winter monsoon on tropical cyclogenesis over the eastern Indian Ocean and maritime continent was examined for the 6-month period of October to March from 1979/1980 to 2006/2007 based on case studies and lag-composite analysis. We focused on long-lasting northerly surge events at 6- to 30-day (sub-monthly or intraseasonal) time scales over the South China Sea. In addition, we examined seasonal differences in the impact of northerly surges over the South China Sea on tropical atmospheric circulation. The results show that northerly surges occur frequently in the period from October to March. Long-lasting northerly surges over the South China Sea intrude into tropical regions. Over the eastern Indian Ocean and maritime continent, the surges are associated with the appearance of tropical cyclones. However, the impact of these surges varies with the seasonal march. In October and November, tropical cyclones occur over the South China Sea during the northerly surge events, enhancing positive vorticity over the South China Sea. A cyclone pair symmetric with respect to the equator also appears over the eastern Indian Ocean in November and is responsible for the enhancement of the horizontal gradient of zonal wind by the northerly surge. In contrast, in December, January, and February, an asymmetric cyclone pair (the so-called Borneo vortex) develops around Borneo. The asymmetric cyclone pair around the maritime continent is associated with intensification of low-level wind along a channel between the islands of Borneo, Sumatra, and Java. In March, no clear tropical cyclone appears over the tropical regions in association with the northerly surge.
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| 10. |
Takahashi, H.G., 2010: Seasonal changes in diurnal rainfall cycle over and around the Indochina Peninsula observed by TRMM-PR. Adv. Geosci., 25, 23-28, doi:10.5194/adgeo-25-23-2010. (Accepted on Feb. 16, 2010) [Web page] [pdf] [BibTeX] [EndNote]
This study used TRMM-PR data to examine seasonal changes in rainfall characteristics over the Indochina Peninsula, with a focus on the diurnal rainfall cycle. No distinct seasonal changes in the phases of diurnal variations of rainfall were found, even though low-level wind fields changed largely with the seasonal march. Regions with an afternoon maximum received large amounts of rainfall during the pre-monsoon season, whereas regions with a nocturnal or morning rainfall maximum received little rainfall during the pre-monsoon season. This result suggests that the difference in diurnal rainfall variations may be associated with the regional differences in seasonal march of monsoon rainfall over and around the Indochina Peninsula, through the different mechanism between evening and morning rainfalls.
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| 9. |
Ma, X., T. Yoshikane, M. Hara, Y. Wakazuki, H. G. Takahashi, and F. Kimura, 2010: Hydrological response to future climate change in the Agano River basin, Japan. Hydrol. Res. Lett., 4, 25-29, doi:10.3178/hrl.4.25. (Accepted on Mar. 03, 2010) [Web page] [pdf] [BibTeX] [EndNote]
To evaluate the impact of climate change on snowfall in Japan, a hydrological simulation was made in the Agano River basin by using a regional climate model’s output. A hindcast experiment was carried out for the two decades from 1980 to 1999. The average correlation coefficient of 0.79 for the monthly mean discharge in the winter season showed that the interannual variation of the river discharge could be reproduced and that the method can be used for climate change study. The future hydrological response to global warming in the 2070s was investigated using a pseudo-global-warming method. In comparison to data from the 1990s, the monthly mean discharge for the 2070s was projected to increase by approximately 43% in January and 55% in February, but to decrease by approximately 38% in April and 32% in May. The flood peak in the hydrograph was moved forward by approximately one month, changing from April in the 1990s to March in the 2070s. Furthermore, the projection for the 10-year average snowfall amount was projected to be approximately 49.5% lower in the 2070s than in the 1990s.
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| 8. |
Takahashi, H.G., T. Yoshikane, M. Hara, K. Takata, and T. Yasunari, 2010: High-resolution modelling of the potential impact of land-surface conditions on regional climate over Indochina associated with the diurnal precipitation cycle. Int. J. Climatol., 30(13), 2004-2020, doi:10.1002/joc.2119. (Accepted on Jan. 05, 2010) [Web page] [pdf] [BibTeX] [EndNote]
This study examined the impact of changes in land surface conditions on regional climate over Indochina using a high‐resolution regional climate model. Anthropogenically induced land surface changes are going on in this part of tropical Southeast Asia. Because a previous study suggested that deforestation in this area affected September precipitation, we chose September as the study period. We performed a control simulation (CTL) driven by reanalysis data combined with current land use and predicted soil moisture data. The CTL reproduced the spatial distribution of total precipitation well. In addition, it also simulated a distinct diurnal cycle of precipitation that was previously reported in observational studies. Two sensitivity experiments, assuming wetter and drier land surface conditions over the Khorat Plateau (northeast Thailand) compared with the current land surface condition, were conducted and examined the impact of land surface changes on precipitation. The results indicated that drier land surface conditions increased precipitation over the disturbed region. A pronounced increase in precipitation was found only during nighttime, which coincided with the peak in the climatological diurnal precipitation cycle. Climatologically, the diurnal peak in precipitation occurs from evening to early morning over the Khorat Plateau. Drier conditions intensified the diurnal variation of precipitable water associated with the thermally induced local circulation responsible for a horizontal gradient of near‐surface temperature. The effects of land use and land cover changes in the tropics are shown to be strongly related to the diurnal precipitation cycle.
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Takahashi, H.G., H. Fujinami, T. Yasunari and J. Matsumoto, 2010: Diurnal rainfall pattern observed by TRMM-PR around the Indochina Peninsula. J. Geophys. Res., 115, D07109, doi:10.1029/2009JD012155. (Accepted on Nov. 10, 2009) [Web page] [pdf] [BibTeX] [EndNote] American Geophysical Union (AGU)
This study addressed the diurnal cycle of rainfall during the summer monsoon season (May to September) around the Indochina peninsula, with a focus on the diurnal cycle's relationship to terrain. The investigation used 10 year (1998–2007) Tropical Rainfall Measuring Mission Precipitation Radar (TRMM‐PR) observations. Results revealed that the diurnal variations in rainfall over the Indochina region had three distinct peaks. An early afternoon maximum of rainfall occurred along the mountain ranges and on coastal land. Evening rainfall was observed near the foot of mountain ranges, in a valley, and in a basin‐shaped plain; this rainfall weakened before the middle of the night. Heavy rainfall in the early morning was found around the coasts over the eastern Gulf of Thailand and the Bay of Bengal, as well as over the eastern Khorat Plateau. We found that nearly half of the total rainfall occurred in the early morning over these regions, which indicated that early morning rainfall significantly contributes to the climatological rainfall pattern. Note that the regions with early morning heavy rain did not correspond to windward faces of mountains but to the windward plain or to an offshore area apart from the mountain ranges in the windward direction. Additional examination of rainfall frequency and rainfall intensity showed that this early morning heavy rainfall was composed of frequent or long‐lasting rainfall events with a strong intensity.
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Oouchi, K., A. T. Noda, M. Satoh, B. Wang, S.-P. Xie, H.G. Takahashi, and T. Yasunari, 2009: Asian summer monsoon simulated by a global cloud-system-resolving model: Diurnal to intra-seasonal variability. Geophys. Res. Lett.,36, L11815, doi:10.1029/2009GL038271. [Web page] [pdf] [BibTeX] [EndNote]
Interaction of convection and circulation is key to the Asian summer monsoon, but difficult to represent in global models. Here we report results from simulations for the summer of 2004 by a global cloud‐system‐resolving model, NICAM. At both 14‐ and 7‐km horizontal resolution, NICAM simulates the observed monsoon circulation patterns, and the northward propagation of precipitation. The 7‐km run simulates summer‐mean precipitation maxima in narrow bands along the western Ghats, Himalayan foothills, the Arakan Yoma highlands, and the Annamite range. Precipitation 1) is modulated by orography, 2) is affected by synoptic‐scale systems, and 3) displays a pronounced diurnal cycle, especially over Indo‐China, with its strong/weak signal propagating westward/eastward in the wet/dry phase of the intraseasonal oscillation. This set of simulations captures these intraseasonal changes of the Indian monsoon with high fidelity from June to early July. NICAM exhibits a positive bias in precipitation over the Indian Ocean, common to atmospheric models with prescribed sea surface temperature. This calls for the inclusion of ocean‐atmosphere coupling process to improve monsoon simulation skills.
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Hara, M., T. Yoshikane, H.G. Takahashi, F. Kimura, A. Noda, and T. Tokioka, 2009: Assessment of the Diurnal Cycle of Precipitation over the Maritime Continent Simulated by 20-km Mesh GCM using TRMM PR Data. J. Meteor. Soc. Japan Ser. II, 87A, 413-424, doi:10.2151/jmsj.87A.413. [Web page] [pdf] [BibTeX] [EndNote]
This study investigates precipitation over the Maritime Continent, comparing the precipitation simulated by a 20 km-grid Meteorological Research Institute General Circulation Model (MRI-GCM) and the near-surface rain data of TRMM 2A25. The focus is particularly the diurnal cycle and its phase distribution of precipitation. The features of the simulated precipitation mostly agree well with observations made over islands and straits having horizontal scales smaller than 200 km. However, these are quite different around larger islands, such as Sumatra and Borneo, particularly in the phase of the diurnal cycle. The MRI-GCM indicates maximum precipitation in the early afternoon on these islands, while the observed precipitation has its maximum at night. In particular, over the inland areas of the larger islands, the simulated diurnal cycle has almost a reversed phase. The simulated precipitation is remarkably weaker than the observation around the western coast of Sumatra Island, where a large discrepancy is also found in the phase distribution along a line perpendicular to the coast. A higher-resolution simulation using a non-hydrostatic model without convective parameterizations substantially improves the phase distribution over Borneo Island. The non-hydrostatic model simulates well the migration of the precipitation zone and the daily maximum at night in the inland areas. In contrast, the GCM fails to simulate the diurnal cycle over islands whose horizontal scale is larger than 200 km, although the 20 km grid spacing is small enough to reproduce the major aspects of the local circulations. The cause for this seems to be the cumulus convective parameterization, which may not adequately represent the coupling of convection and local circulations.
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Takahashi, H.G., T. Yoshikane, M. Hara and T. Yasunari, 2009: High-resolution regional climate simulations of the long-term decrease in September rainfall over Indochina, Atmos. Sci. Lett., 10, 14-18, doi:10.1002/asl.203. [Web page] [pdf] [BibteX] [EndNote] Royal Meteorological Society
We address the long‐term decrease in September rainfall over the Indochina Peninsula. Distinct long‐term decreases in rainfall along the monsoon trough across the Indochina Peninsula have been observed. We performed long‐term simulations and discuss the effects of long‐term changes in both the local surface conditions and large‐scale circulation. Using a 30‐year simulation for September for the period from 1966 to 1995 with land‐use conditions fixed at present‐day values and neglecting the recorded deforestation, we successfully simulated the observed long‐term decrease in rainfall. We therefore conclude that the weakening tropical‐cyclone activity over the Indochina Peninsula region is probably responsible for the decrease in rainfall.
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Takahashi, H.G., and T. Yasunari, 2008: Decreasing trend in rainfall over Indochina during the late summer monsoon: Impact of tropical cyclones. J. Meteor. Soc. Japan, 86, 429-438, doi:10.2151/jmsj.86.429. [Web page] [pdf] [BibTeX] [EndNote]
We examined the decreasing trend in rainfall during the late summer monsoon season (September) in Thailand from 1951 to 2000 and associated changes in tropical cyclone (TC) activity. Thailand receives significant rainfall from May to October and experiences two rainy peaks in late May to early June and in September. A previous study reported a decreasing trend in September rainfall in Thailand and, based on a regional climate model, suggested that the trend was associated with local deforestation. However, the long-term trend may also be affected by changes in large-scale circulation. Thus, the purpose of this study was to investigate changes in large-scale circulation associated with the decreasing rainfall trend. Westward-propagating TCs from the South China Sea and the western North Pacific brought most of the rainfall over Thailand in September. TCs include tropical depressions, tropical storms, severe tropical storms, typhoons, and residual lows. 70% of the rainfall amount in September was estimated to be associated with TCs. The 50-year time-series of September rainfall over Thailand showed a significant decreasing trend. TC activity defined by 700-hPa relative vorticity, showed a weakening trend over the Indochina Peninsula. TC tracks also suggested the weakening of TC activity over this area. The long-term trend in rainfall during the late summer monsoon season was closely associated with changes in TC activity over the Indochina Peninsula; these changes were likely caused by changes in the major course of TCs. Concurrent with the changes in TC tracks, there was a change in the TC steering current around the Philippines archipelago and Taiwan. This led to the TC activity over the Indochina Peninsula being inactive, probably resulting in the long-term decrease in rainfall over Thailand.
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Takahashi, H.G., and T. Yasunari, 2006: A climatological monsoon break in rainfall over Indochina -A singularity in the seasonal march of the Asian summer monsoon-. J. Climate, 19, 1545-1556, doi:10.1175/JCLI3724.1. [Web page] [pdf] [BibTeX] [EndNote] American Meteorological Society
This study investigated the climatological pentad mean annual cycle of rainfall in Thailand and the associated atmospheric circulation fields. The data used included two different data of rainfall: rain gauge data for Thailand from the Thai Meteorological Department and satellite-derived rainfall data from the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP). Climatological mean pentad values of rainfall taken over 50 yr clearly show a distinct climatological monsoon break (CMB) occurring over Thailand in late June. The occurrence of the CMB coincides with a drastic change of large-scale monsoon circulation in the seasonal march. The CMB is a significant singularity in the seasonal march of the Southeast Asia monsoon, which divides the rainy season into the early monsoon and the later monsoon over the Indochina Peninsula. A quasi-stationary ridge dynamically induced by the north–south-oriented mountain range in Indochina is likely to cause the CMB. The formation of the strong ridge over the mountain ranges of Indochina is preceded by a sudden enhancement (northward expansion) of the upstream monsoon westerlies along a latitudinal band between 15° and 20°N in late June. The CMB also has an impact downstream. The orographically induced stationary Rossby waves enhance the cyclonic circulation to the lee of Indochina, and over the South China Sea. The enhancement of cyclonic circulation may be responsible for the summer monsoon rains peaking in late June over the South China Sea and the western North Pacific, and in the baiu front.
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Kumagai, T., T. Saitoh, Y. Sato, H. Takahashi, O.J. Manfroi, T. Morooka, K. Kuraji, M. Suzuki, T. Yasunari and H. Komatsu, 2005: Annual water balance and seasonality of evapotranspiration in a Bornean tropical rainforest. Agr. Forest. Meteorol., 128, 81-92, doi:http://dx.doi.org/10.1016/j.agrformet.2004.08.006. [pdf] [BibTeX] [EndNote]
This study presents the results of 2 years combined field measurements of water vapor exchange with the atmosphere and simplified model calculations at Lambir Hills National Park, Sarawak, Malaysia (4°12′N, 114°02′E). The study site was located in a lowland mixed dipterocarp forest, a major type of Bornean tropical rainforest, where there is no clear seasonality in environmental factors such as radiation, temperature, vapor pressure deficits and precipitation; instead, unpredictable dry spells often occur throughout the year. Modified [Priestley, C.H.B., Taylor, R.J. (1972). On the assessment of surface heat flux and evaporation using large-scale parameters, Mon. Weather Rev. 100, pp. 81–92] and equilibrium evaporation expressions enabled us to understand further the environmental control of water vapor exchanges with the atmosphere and to produce a complete gap-filled data set of the hydrologic fluxes within this environment. The equilibrium evaporation from a well-watered surface sufficiently reproduced the transpiration rate (
Tr); any discrepancies between the equilibrium and actual evaporation rates were caused by unpredictable intra-annual dry spells, which reduced transpiration. There were some discrepancies during the study period because of exceptional dry sequences, but in normal years the annual transpiration rate can be obtained from the equilibrium evaporation expression. The estimated annual
Tr (1193.1 mm) and evapotranspiration (1545.0 mm) rates were nearly identical to the highest values reported for some humid tropical forests. Although, there were exceptional dry sequences during the study period, the annual average fraction of available energy dissipated by
Tr at this site (0.69) was almost the same as the medium value between the dry and wet seasons in Amazonian tropical forests. This implies that the annual dynamics of the latent heat flux for this tropical rainforest are under more humid conditions than those of other tropical rainforests.
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