研究者詳細 - 藤波　初木

論文 - 藤波　初木

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Impact of Tropical Deforestation and Forest Degradation on Precipitation over Borneo Island 査読有り

Takahashi Atsuhiro, Kumagai Tomo'omi, Kanamori Hironari, Fujinami Hatsuki, Hiyama Tetsuya, Hara Masayuki

JOURNAL OF HYDROMETEOROLOGY 18 巻 ( 11 ) 頁： 2907 - 2922 2017年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）

Southeast Asian tropical rain forests in the Maritime Continent are among the most important biomes in terms of global and regional water cycling. How land use and land cover change (LULCC) relating to deforestation and forest degradation alter the local hydroclimate over the island of Borneo is examined using the Weather Research and Forecasting (WRF) Model with an appropriate land surface model for describing the influence of changes in the vegetation status on the atmosphere. The model was validated against precipitation data from Tropical Rainfall Measuring Mission (TRMM) satellite 3B42 measurements. A main novelty in this analysis is that the diurnal cycle of precipitation over the island, which is a dominant climatic characteristic of the Maritime Continent, was successfully reproduced. To clarify the impact of the LULCC on the precipitation regimes over the island, numerical experiments were performed with the model that demonstrated the following. Deforestation that generates high albedo areas, such as bare lands, would induce a reduction in precipitation because of reductions in evapotranspiration, convection, and horizontal atmospheric moisture inflow. On the other hand, a decrease in evapotranspiration efficiency without changing the surface albedo could increase precipitation due to an increase in convection and horizontal atmospheric moisture inflow in compensation for the decrease in evapotranspiration. In detail, on the Maritime Continent, through changes in the land surface heating process and land–sea breeze circulation, the LULCC would impact the amplitude of the diurnal precipitation cycle in each region as defined according to the distance from the coast, resulting in changes in the precipitation regimes over the island.

DOI： 10.1175/JHM-D-17-0008.1

Web of Science

Dominant Synoptic Disturbance in the Extreme Rainfall at Cherrapunji, Northeast India, Based on 104 Years of Rainfall Data (1902-2005) 査読有り

Murata Fumie, Terao Toru, Fujinami Hatsuki, Hayashi Taiichi, Asada Haruhisa, Matsumoto Jun, Syiemlieh Hiambok J.

JOURNAL OF CLIMATE 30 巻 ( 20 ) 頁： 8237 - 8251 2017年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）

The characteristics of active rainfall spells (ARSs) at Cherrapunji, northeast India, where extreme high rainfall is experienced, and their relationships with large-scale dynamics were studied using daily rainfall data from 1902 to 2005 and Japanese 55-Year Reanalysis from 1958 to 2005. Extreme high daily rainfalls occur in association with ARSs. The extremely large amounts of rainfall in the monsoon season are determined by the cumulative rainfall during ARSs. ARSs start when anomalous anticyclonic circulation (AAC) at 850 hPa propagates westward from the South China Sea and western North Pacific, and covers the northern Bay of Bengal. The AAC propagates farther westward and suppresses convection over central India during ARSs at Cherrapunji, and continues for 3 to 14 days. Consequently, a northward shift of the monsoon trough during the “break” in the Indian core region occurs. The westerly wind, which prevails in the northern portion of the AAC, transports moisture toward northeast India and enhances moisture convergence over northeast India with southerly moisture transport from the Bay of Bengal, and greatly intensifies the orographic rainfall. In the upper troposphere, the Tibetan high tends to extend southward with the onset of ARSs. A linear relationship can be seen between the length and total rainfall of an ARS. Longer ARSs tend to result in greater total rainfall. AACs with a greater zonal scale tend to produce longer and more intense ARSs. This study provides evidence for the effect of western North Pacific AACs on the Indian summer monsoon.

DOI： 10.1175/JCLI-D-16-0435.1

Web of Science

Contrasting Features of Monsoon Precipitation Around the Meghalaya Plateau Under Westerly and Easterly Regimes 査読有り

Fujinami Hatsuki, Sato Tomonori, Kanamori Hironari, Murata Fumie

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 122 巻 ( 18 ) 頁： 9591 - 9610 2017年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）

Precipitation features around the Meghalaya Plateau, northeast India, during summer are investigated using a 17 year (1998–2014) high-spatial-resolution Tropical Rainfall Measuring Mission precipitation radar data set. Precipitation around the plateau fell into two distinct regimes based on the low-level wind direction that fluctuates on intraseasonal time scales over Bangladesh, windward of the plateau: a westerly regime (WR) and an easterly regime (ER). Under the WR, strong low-level onshore southwesterlies across Bangladesh encounter the plateau, and localized strong low-level southerlies running parallel to the Arakan Mountains (i.e., the barrier jet) also blow toward the plateau, concentrating convective unstable air onto its southern slopes. The low-level wind fields and large-scale upper level divergent fields promote frequent and intense orographic rainfall along the southern slopes due to forced uplift, generating high precipitation. In contrast, under the ER, strong southeasterlies that blow along the Gangetic Plain without encountering the plateau and subsidence inhibit upward motion around the plateau, resulting in low precipitation. Diurnal variations in precipitation significantly affect the daily precipitation around the plateau under both regimes. High rainfall frequency persists over the southern slopes between 2100 and 1200 LT of the next day under the WR, whereas modest rainfall frequency occurs between 0000 and 0600 LT under the ER, with a daytime minimum and nocturnal maximum in both regimes. The atmospheric boundary layer processes over Bangladesh regulate the wind speed and vertical structure of the low-level wind toward the plateau, with deceleration during daytime and acceleration at night (i.e., nocturnal jet) that result in the nocturnal rainfall maximum.

DOI： 10.1002/2016JD026116

Web of Science

Sixteen-year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki 査読有り

Takeo, D., K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura and M. Yamamoto

Journal of Geophysical Research -Atmospheres 122 巻頁： 8770-8780 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We analyzed the horizontal phase velocity of gravity waves and medium-scale traveling ionospheric disturbances (MSTIDs) by using the three-dimensional fast Fourier transform method developed by Matsuda et al. (2014) for 557.7 nm (altitude: 90–100 km) and 630.0 nm (altitude: 200–300 km) airglow images obtained at Shigaraki MU Observatory (34.8°N, 136.1°E, dip angle: 49°) over ∼16 years from 16 March 1999 to 20 February 2015. The analysis of 557.7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region. In spring, summer, fall, and winter, the peak directions are northeastward, northeastward, northwestward, and southwestward, respectively. The difference in east-west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet. Comparison with tropospheric reanalysis data shows that the difference in north-south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to Shigaraki. The analysis of 630.0 nm airglow images shows that the propagation direction of MSTIDs is mainly southwestward with a minor northeastward component throughout the 16 years. A clear negative correlation is seen between the yearly power spectral density of MSTIDs and F10.7 solar flux. This negative correlation with solar activity may be explained by the linear growth rate of the Perkins instability and secondary wave generation of gravity waves in the thermosphere.

DOI： 10.0002/2017JA023919

Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan

Takeo D., Shiokawa K., Fujinami H., Otsuka Y., Matsuda T. S., Ejiri M. K., Nakamura T., Yamamoto M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 8 ) 頁： 8770 - 8780 2017年8月

Effects of the South Asian Monsoon Intraseasonal Modes on Genesis of Low Pressure Systems over Bangladesh 査読有り

Hatsuzuka Daisuke, Fujinami Hatsuki

JOURNAL OF CLIMATE 30 巻 ( 7 ) 頁： 2481 - 2499 2017年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）

The quasi-biweekly oscillation (QBW) is a dominant intraseasonal mode in summer rainfall over Bangladesh. Active phases of the QBW are often accompanied by low pressure systems (LPSs) such as vortex-type lows. This study investigated the effects of two intraseasonal modes, the QBW and the boreal summer intraseasonal oscillation (BSISO), on the genesis of LPSs over Bangladesh during 29 summer monsoon seasons. Daily lag composites of convection and low-level atmospheric circulation were constructed for active-phase cases with LPSs (LPS case) and without LPSs (non-LPS case) based on rainfall in the QBW over Bangladesh. In the QBW mode, a westward propagation of an anticyclonic anomaly from the western Pacific to the Bay of Bengal (BoB) is common in both cases. However, the anticyclonic center in the LPS case is located slightly to the east of that in the non-LPS case, which results in stronger cyclonic vorticity over and around Bangladesh. In contrast, the BSISO mode shows an opposite phase between the two cases: a cyclonic (anticyclonic) anomaly propagating northward from the equator to the BoB in the LPS case (non-LPS case). In the LPS case, the cyclonic anomaly in the BSISO mode enhances the westerly (easterly) flow over the BoB (Bangladesh) in the active phase, resulting in the enhancement of cyclonic vorticity over the northern BoB and Bangladesh, in cooperation with the QBW mode. These results suggest that both the QBW and BSISO modes have significant influence on the environmental conditions for LPS genesis over Bangladesh.

DOI： 10.1175/JCLI-D-16-0360.1

Web of Science

Interdecadal modulation of the interannual variability in precipitation and atmospheric circulation pattern over northern Eurasia 査読有り

Hiyama, T., H. Fujinami, H. Kanamori, T. Ishige, K. Oshima

Environmental Research Letters 11 巻頁： 065001 2016年6月

Trend and interannual variation in summer precipitation in eastern Siberia in recent decades 査読有り

Fujinami, H., T. Yasunari and T. Watanabe

International Journal of Climatology 36 巻頁： 355 - 368 2016年1月

Separating physical and biological controls on long-term evapotranspiration fluctuations in a tropical deciduous forest subjected to monsoonal rainfall 査読有り

Igarashi, Y., G. G. Katul, T. Kumagai, N.Yoshifuji, T. Sato, N. Tanaka, K. Tanaka, H. Fujinami, M. Suzuki, C. Tantasirin

Journal of Geophysical Research -Biogeosciences 120 巻頁： 1262-1278 2015年7月

Role of tropical cyclones along the monsoon trough in the 2011 Thai flood and interannual variability 査読有り

Takahashi, G. H., H. Fujinami, T. Yasunari, J. Matsumoto, S.Baimoung

Journal of Climate 28 巻頁： 1465-1476 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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.

Separating physical and biological controls on long-term evapotranspiration fluctuations in a tropical deciduous forest subjected to monsoonal rainfall

Igarashi, Y., G. G. Katul, T. Kumagai, N.Yoshifuji, T. Sato, N. Tanaka, K. Tanaka, H. Fujinami, M. Suzuki, C. Tantasirin

Journal of Geophysical Research -Biogeosciences- 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）

Evapotranspiration (ET), especially in the mainland of the Indochina Peninsula, can impact and is impacted by the Asian monsoonal (AM) system, thereby prompting interest in its long-term variability. To separate the physical and biological factors controlling ET variability in a tropical deciduous forest under the AM influence, 7 year eddy covariance and ancillary measurements were collected and analyzed. The 7 year mean rainfall (Pr) and ET along with their standard deviations were 1335 ± 256 and 977 ± 108 mm (about 73% of Pr), respectively, suggesting close coupling between these two hydrologic fluxes. However, other physical and biological drivers decouple seasonal and annual variations of ET from Pr. To explore them, a big-leaf model complemented by perturbation analysis was employed. The big-leaf model agreed well with the measured ET at daily to multiyear time scales, lending confidence in its ability to separate biological and physical controls on ET. Using this formulation, both first-order and second-order Taylor series expansions of the total ET derivatives were applied to the big-leaf model and compared with measured changes in ET (dET). Higher-order and joint terms in the second-order expansion were necessary for matching measured and analyzed dET. Vapor pressure deficit (D) was the primary external physical controlling driver of ET. Leaf area index (LAI) and bulk stomatal conductance (gs) were shown to be the main significant biological drivers of the transpiration component of ET. It can be surmised that rainfall variability controls long-term ET through physical (mainly D) and biological (mainly LAI and gs) factors in this ecosystem.

DOI： 10.1002/2014JG002767

Characteristics of low pressure systems associated with intraseasonal oscillation of rainfall over Bangladesh during boreal summer 査読有り

Hatsuzuka, D, T. Yasunari, H. Fujinami

Monthly Weather Review 2014年11月

Dynamics of distinct intraseasonal oscillation in summer monsoon rainfall over the Meghalaya-Bangladesh-western Myanmar region 査読有り

Fujinami, H., Tetsuzo Yasunari, Akihito Morimoto

Climate Dynamics 43 巻頁： 2147 - 2166 2014年

Advanced Asian summer monsoon onset in recent decades 査読有り

Kajikawa, Y., T. Yasunari, S. Yoshida and H. Fujinami

Geophysical Research Letters 39 巻 2012年

Seasonal and intra-seasonal modulation of tropical cyclogenesis environment over the Bay of Bengal during the extended summer monsoon 査読有り

Yanase, W., M. Satoh, H. Taniguchi and H. Fujinami

Journal of Climate 25 巻頁： 2914-2930 2012年

Characteristic intraseasonal oscillation of rainfall and its effect on interannual variability over Bangladesh during boreal summer 査読有り

Fujinami, H., D. Hatsuzuka, T. Yasunari, T. Hayashi, T. Terao, F. Murata, M. Kiguchi, Y. Yamane, J. Matsumoto, Md. N. Islam and A. Habib

International Journal of Climatology 31 巻頁： 1192-1204 2011年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Intraseasonal oscillation (ISO) of rainfall during the summer monsoon season (June–August) and its plausible effect on interannual variation (IAV) of total summer monsoon rainfall over Bangladesh are examined using daily rainfall data from 25 rain-gauge stations for 20 years (1981–2000). Submonthly scale (7–25 days) ISO is a dominant mode of summer rainfall fluctuation over Bangladesh. In the active (suppressed) ISO phases, a cyclonic (anticyclonic) circulation anomaly develops at the low-level troposphere from northeastern India to Bangladesh, and an anticyclonic (cyclonic) circulation anomaly appears over the Bay of Bengal, accompanied by the enhancement of westerly/southwesterly (easterly/southeasterly) moisture flux anomalies over Bangladesh. The IAV of total summer monsoon rainfall is significantly correlated with that of the rainfall variance, mainly in the submonthly scale, suggesting that the ISO activity controls the IAV of the total summer monsoon rainfall. Moreover, the spatial patterns of atmospheric circulation and convection associated with the ISO and the IAV are quite similar to each other around the monsoon trough, especially from northeastern India to Bangladesh. In wet monsoon years, more frequent strong submonthly scale ISOs and a larger number of rainy days related to the active ISO phase are evident compared with that of dry monsoon years. Climatologically, Bangladesh is one of the most predominant areas of submonthly scale ISO; however, 30–60-day ISO is not prominent. These characteristic features probably allow the submonthly scale ISO to modulate the total seasonal rainfall and the spatial patterns of circulation and convection over and near Bangladesh.

Diurnal rainfall pattern observed by Tropical Rainfall Measuring Mission Precipitation Radar (TRMM-PR) around the Indochina peninsula 査読有り

Takahashi, H. G., H. Fujinami, T. Yasunari, and J. Matsumoto

Journal of Geophysical Research 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

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.

DOI： 10.1029/2009JD012155

*The Effects of Midlatitude Waves over and around the Tibetan Plateau on Submonthly Variability of the East Asian Summer Monsoon 査読有り

Fujinami, H. and T. Yasunari

Monthly Weather Review 137 巻 ( 7 ) 頁： DOI: 10.1175/2009MWR2826.1 2009年7月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

梅雨(メイユ)期における中国長江・淮河流域のsubmonthly-scale(7～25日)の対流変動とそれに関係する循環場の変動をOLRとNCEP/NCAR再解析データを用いて解析した。長江・淮河流域で平均した対流偏差と上層の流線関数偏差には２つの異なる関係があることがわかった。一つはチベットの北～東側に沿って大きな相関が見られるパターン(NETパターンとする)、もう一つはチベットを横切って東西に高い相関が分布するパターンである(ATパターン)。NETパターンでは、対流偏差がチベット高原北東部～中国南部まで南下する。これは上～下層の偏西風波動が長江・淮河流域の北側で増幅することによる、梅雨(メイユ)前線の南下に対応している。ATパターンでは、対流活動偏差がチベット高原の西から長江・淮河流域まで東進する。これは、東進する上層の波束とそれに関係した高原からの対流活動が、高原の風下側で下層渦を励起することに関係している。アジアの亜熱帯ジェット気流に沿ったこれらの二つのパターンの循環場偏差は、ロスビー波として捉えられる。

Diurnal Variation of Water Vapor Mixing between the Atmospheric Boundary Layer and Free Atmosphere over Changwu, the Loess Plateau in China 査読有り

Atsuhiro Takahashi, Tetsuya Hiyama, Masanori Nishikawa, Hatsuki Fujinami, Atsushi Higuchi, Wei Li, Wenzhao Liu and Yoshihiro Fukushima

SOLA(Scientific Online Letters on Atmosphere) 4 巻頁： 33-36 2008年

Resolution dependency of the diurnal cycle of convective clouds over the Tibetan Plateau in a mesoscale model 査読有り

Sato, T., T. Yoshikane, M. Satoh, H. Miura, and H. Fujinami

Journal of Meteorological Society of Japan 84A 巻頁： 17-31 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

Sensitivity of precipitation diurnal cycle to the horizontal grid spacing was investigated using a mesoscale model without cumulus parameterization. Four numerical experiments with changing horizontal resolution are performed over one month with NCEP reanalysis boundary forcing. The studied range of grid spacing is from 3.5 km to 28 km which has been known as the intermediate scale to simulate mesoscale systems with/without cumulus parameterization. The target area is the Tibetan Plateau where pronounced diurnal cycle of convective systems is observed during the spring season.
Lower resolution runs (14 and 28 km grid) show delayed formation and delayed mature stage of the cumulus convection in comparison to satellite observations. On the other hand, higher resolution runs (3.5 and 7 km grid) reproduce the proper development of the clouds after local noon which is consistent with observations. The total hydrometeor content and rainfall rate increase with grid size. Such systematic relationship of resolution dependencies are confirmed even in the monthly mean diurnal cycle, although most of previous studies examined only short periods. These results suggest that finer resolution at less than 7 kilometer is necessary to simulate realistic phase of the precipitation diurnal cycle over the Tibetan Plateau.
The mechanism that is responsible for the resolution dependency is discussed. We suggest that the daytime convection which initially occurs due to unstable stratification over the Tibetan Plateau in spring tends to have a horizontal scale smaller than that is resolvable by the coarse resolution runs. The delayed cloud formation induces larger downward shortwave radiation, which increases surface fluxes and results in too strong rainfall in the coarser resolution runs.

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