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Mechanism of Orographic Precipitation around the Meghalaya Plateau Associated with Intraseasonal Oscillation and the Diurnal Cycle

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Title: Mechanism of Orographic Precipitation around the Meghalaya Plateau Associated with Intraseasonal Oscillation and the Diurnal Cycle
Authors: Sato, Tomonori Browse this author →KAKEN DB
Keywords: Rainfall
Mesoscale processes
Mesoscale models
Diurnal effects
Intraseasonal variability
Issue Date: Jul-2013
Publisher: American Meteorological Society
Journal Title: Monthly Weather Review
Volume: 141
Issue: 7
Start Page: 2451
End Page: 2466
Publisher DOI: 10.1175/MWR-D-12-00321.1
Abstract: Mesoscale processes that cause tremendous amounts of precipitation around the Meghalaya Plateau, northeast India, were investigated using a regional atmospheric model, with a particular focus on the possible role of an intraseasonal oscillation (ISO) and the diurnal cycle. A numerical experiment was conducted using the Weather Research and Forecasting Model (WRF) to simulate a prominent submonthly-scale ISO event observed during June–July 2004. A WRF experiment successfully simulated the timing and magnitude of precipitation during the first active period and subsequent inactive period of the ISO, despite large biases in the second active period. The WRF experiment revealed that the magnitude of prevailing southwesterly winds in the lower troposphere differs significantly between active and inactive periods; strong southwesterly flow transports abundant moisture to the southern slope of the Meghalaya Plateau during the active period, which triggers forced lifting and brings orographic precipitation. However, low-level wind during the inactive period is too weak to overcome the vertical stratification barrier; hence, it is unable to reach the condensation level. The WRF experiment suggested that the diurnal cycle of precipitation is enhanced during the active period, exhibiting an evening to early morning maximum, as observed by the Tropical Rainfall Measuring Mission (TRMM). The experiment also indicated a prominent nocturnal low-level jet (LLJ) appearing at 900 hPa. The direction of the LLJ varies clockwise with time, which accelerates the preexisting southwesterly flow during 1800–0600 LT. The diurnal variation of the LLJ is responsible for the evening to early morning maximum of precipitation, thus contributing to the precipitation variability in the ISO.
Rights: © Copyright 2013 American Meteorological Society (AMS).
Type: article
URI: http://hdl.handle.net/2115/53972
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 佐藤 友徳

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