Large-Scale Aspects of Air-Mass Transformation over the East China Sea during AMTEX'74

Abstract

Large-scale aspects of the air-mass transformation over the East China Sea during AMTEX '74 (February 14-28, 1974) are studied based on the synoptic and heat energy budget analysis.
Both the synoptic and budget situations over the East China Sea vary according to the alternation of the subtropical air-mass and the polar air-mass.
The synoptic situations in the earlier period are characterized by the small air-sea temperature difference, the southerly wind and very weak thermal advection in the lower layer. The amount of the total heat energy supply from the sea is small (200ly/day) during this period. The moisture and heat supply from the sea primarily contributes to the local time change of moisture and temperature in the lower layer.
The synoptic situations for the latter period are characterized by the large air-sea temperature difference, the northerly wind, and strong cold advection in the lower troposphere below the inversion layer. The amount of the total heat energy supply from the sea is as large as 1200 ly/day. In spite of the strong cold advection, the temperature fall (∂T/∂t) is small, because the cold advection is primarily balanced by the diabatic heating due to the energy supply from the sea. The results of the budget calculations also indicate that the diabatic heating is mainly confined in the lower layer below the inversion.
The time variation of the vertical stability in the lower troposphere is also analysed in relation to the formation of the inversion layer. The results of analysis indicate that the differential thermal advection is the primal factor to control the vertical stability. It is also shown that the differential diabatic heating cancels some part of the differential advection during the period of cold air outbre