A contrast in the precipitation characteristics across the Baiu front near Japan: TRMM and CMIP5 (Invited)

Baiu front is a stationary front with a massive precipitation, which sits at the boundary between an extratropical air mass and a subtropical air mass near Japan in early summer. It is well known that torrential rainfall is often observed in the latter part of the Baiu period, after the Baiu front migrates northward. In this study, we investigate characteristics of precipitation along the Baiu front using TRMM satellite data, and examine how precipitation is reproduced in the climate model data collected as the Coupled Model Intercomparison Project Phase 5 (CMIP5). To meet this end, we first define the Baiu front utilizing large-scale meteorological variables, in order to enable the definition of the Baiu front not only with observational data, but also with relatively coarse climate model data. Then, precipitation characteristics associated with the Baiu front, especially their contrasts across the front are studied in detail, utilizing the accumulated three dimensional precipitation data obtained from the TRMM Precipitation Radar (PR). Finally, reproducibilities of the Baiu front and associated precipitation in CMIP5 climate models are examined, in comparison with observed precipitation. The Baiu front in the western part of Japan was determined from the meridional distribution of the atmospheric stratification structure, depicted with vertical profiles of the equivalent potential temperature, associated with the subtropical jet. Utilizing TRMM PR precipitation data during June-July for 1998-2011, a clear contrast of precipitation characteristics is analyzed; in a manner that tall and vigorous convective rainfall is selectively observed in the southern side, while moderate stratiform rainfall dominates in the northern side. In CMIP5 models, on the other hand, a similar contrast across the Baiu front, but between the parameterized convective rain dominant in the southern side, and the large-scale condensation rain dominant in the northern side, is found associated with the diagnosed Baiu fronts. Although a direct comparison between the TRMM-observed rainfall characteristics and the CMIP5-simulated rainfall characteristics cannot be performed, the result indicates a potential in future projection of precipitation characteristics with climate models. (Acknowledgment) This study is supported by the Environment Research and Technology Development Fund (2A-1201) of the Ministry of the Environment, Japan, and the 7th RA of the Japan Aerospace Exploration Agency (JAXA) Precipitation Measuring Mission (PMM) science.