Wind Profile and Kinetic Energy Budget in the Mixed Laye of Polar Air-Mass Transformed over Kuroshio Region

[摘要] The characteristic features of the wind profile, the momentum and kinetic energy budget in the mixed layer of the polar air-mass transformed over the Kuroshio region are analyzed for the three periods of polar outbreak in AMTEX '74 and '75.While there is a strong geostrophic wind shear in the mixed layer, the wind distribu-tion in the mixed layer is characterized by the almost vertically uniform northerly winds. In the lower part of the mixed layer, the strong ageostrophic winds are directed toward the low pressure, while in the upper part of the mixed layer, the strong ageostrophic winds are directed toward the high pressure. These characteristic features indicate vertical (convective)mixing of momentum.The momentum budget calculations show that the magnitude of the frictional force in the lowest 50 mb is about 6×10-4m/sec2. The kinetic energy budget calculations show that the generation of K and the frictional loss of K approximately balance in the lower part of the mixed layer. In the upper part of the mixed layer, however, the balance is primarily between the “negative generation term” (i.e., ageostrophic winds are directed toward the high pressure) and the substantial decrease of K.The results of calculation also indicate that both the generation and the frictional loss of K are very large (∼5 watt/m2) in the anticyclonic branch of the polar outbreak (i.e., over the western AMTEX region) and relatively small (∼2 watt/m2) in the cyclonic branch of the outbreak (i.e., over the eastern AMTEX region).

[学科分类] 大气科学