日本周辺域，特に日本海から太平洋にかけての地域は，冬季モンスーンに伴う多降水帯としてよく知られる．この領域では，いわゆる冬型気圧配置の変化が降水や雲分布の変化をもたらすが，降水システムの詳細，特に太平洋上のそれはよく知られていない．そこで，降水形態の特徴を明らかにすることを目的として，冬季降水の鉛直構造と海面の環境場の比較を行った．使用した主なデータは，Tropical Rainfall Measuring Mission (TRMM) (Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible and Infrared Scanner (VIRS)), CRL Airborne Multiparameter Precipitation Radar (CAMPR), Special Polarimetric Ice Detection and Explication Radar (SPIDER) である．解析対象領域は115°E-180°E，25°N-40°Nに設定した．
冬季日本周辺地域にみられる雲分布を，寒気の吹き出し時，および低気圧または前線の通過時に主観的に分類し，降水の鉛直構造をTRMM-PRを用いて比較した．寒気の吹き出しに伴う降水エコーは，高度2 kmに集中していた．降水頂はTRMM-VIRSから得られた雲頂高度の約60 %に及んでいた．この鉛直構造は，統計としては太平洋側と日本海側でよく類似していた．一方，低気圧および前線による降水は，高度3 km程度の降水頂を持つものを多く含んでいたが，6 km以上の高度を持つ降水も認められた．降水頂は雲頂高度の半分程度で，寒気の吹き出し時における鉛直構造との違いが認められた．これらの特徴は，CAMPRおよびSPIDERによる事例解析の結果でも支持された．さらに，TMIによる各チャンネルの輝度温度の分布は両者の放射特性の違いを明らかにし，これらの結果から，両者の降水システムの構造の把握が可能となった．
分類された降水形成時に対応する海面の環境場を比較した．寒気の吹き出し時には，海面からの顕熱・潜熱フラックスの合計は800 W m-2に達し，そのうち，顕熱フラックスは日本海側と太平洋側沿岸部でほぼ同じであった．一方，太平洋側は日本海側に比べ潜熱フラックスの寄与が大きくなった．これは，太平洋側の黒潮流により，海面と大気の比湿の差が日本海側に比べ高くなることが要因である．一方，低気圧または前線の通過時には，海面からの熱フラックスが殆どみられなかった．これは，暖湿気流の移流により，海面と大気の温度差・比湿の差が殆どなかったためである．また，QSCATの海上風から算出された収束を比較したところ，両者のパターンの収束の強さはほぼ同じであった．
以上の結果をまとめると，寒気の吹き出し時に伴う降水は，殆どが海面からの水蒸気供給と海上風の収束によって生じるが，潜熱の寄与が日本海側と太平洋側で異なっていた．一方，低気圧および前線周辺域の降水は，周辺領域からの吹き込みによる水蒸気供給によって生じることが示された．

Ocean around Japan is well known as the precipitation zone of the winter monsoon. In this region, the change of the surface pressure pattern causes large changes of precipitation and cloud distributions. However, vertical structures for each type of precipitation systems have not yet been well studied, especially over the Pacific Ocean. In order to clarify the characteristics of the winter precipitation, the vertical structures are compared with the environment of sea surface. In this thesis, Tropical Rainfall Measuring Mission (TRMM) (Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible and Infrared Scanner (VIRS)), CRL Airborne Multiparameter Precipitation Radar (CAMPR), and Special Polar metric Ice Detection and Explication Radar (SPIDER) data are mainly used. The analyzed area is 25-40N and 115-180E.
The cloud distributions around Japan in winter are classified into the cold outbreak pattern and the low and front pattern, and their vertical structures of precipitation are compared each other. The top height of precipitation echoes for the cold outbreaks pattern is about 2 km, which is about 60 % of the cloud top height. Its distribution over the Japan Sea is similar to that over the Pacific Ocean. On the other hand, the top height for the low and front pattern is around 3 km, which is about a half of the cloud top height. Some echoes reach about 6 km for the low and front patterns, while only a few echoes reach the 4 km for the cold outbreak pattern. These characteristics were supported by the results of case studies using CAMPR and SPIDER data. Moreover, the distribution of TMI brightness temperature for each frequency clarifies their difference in radiance property.
The heat fluxes and some related parameters of these two systems are compared. The cold outbreaks make the sum of sensible and latent heat fluxes possible to reach about 800 W m-2. The sensible heat flux over the Japan Sea is similar to that over the coastal region in the Pacific Ocean. The contribution of the latent heat flux over the Pacific Ocean is larger than that over the Japan Sea. This is because the specific humidity over the Pacific Ocean is larger than that over the Japan Sea due to the Kuroshio Current. On the contrary, on approaching the low and front, the sensible and the latent heat fluxes are very small. This is because the differences of temperature and specific humidity between the sea surface and the atmosphere are small. The convergence derived from QSCAT wind vector between the cold outbreak pattern and the low and front pattern are compared. The values of convergence is almost the same between the two patterns.
Over the Japan Sea and the Pacific Ocean, most of the moisture for the precipitation of the cold outbreaks is supplied from the sea surface, though the contributions of latent heat flux over the two regions are different. On the other hand, the precipitation around the low and front is caused by the moisture supply from the surrounding regions.