A Diagnostic Study of Formation and Structures of the Meiyu Front System over East Asia

Abstract

The concept of a dew-point front was introduced, and its existence was identified near the periphery of the west Pacific subtropical anticyclone by using the daily 1 � � 1 � data of the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The dew-point front was a transitional belt between the moist southwest monsoon flow and the dry adiabatic sinking flow, marked by a large horizontal moisture gradient in the mid-lower troposphere. The dew-point front and the Meiyu front, to its north side, formed the Meiyu front system (MYFS). The Meiyu front was the north branch of the MYFS, and extended northward in the mid-lower troposphere. The dew-point front was the south branch of the MYFS, located between 500 hPa and 700 hPa. Along the dew-point front (Meiyu), westerly (easterly) and easterly (westerly) winds prevailed in the lower (upper) and upper (lower) troposphere respectively. Strong ascending motion in the passsageway between the two fronts was surrounded by subsidence. Further, a frontogenesis function was used to diagnose the frontogenesis of the MYFS. The analysis indicated that the convergence and deformation of the horizontal wind were important factors responsible for both the formation and development of the Meiyu front and the dew-point front.