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

Abstract

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 distribution 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 6X 10-4 m/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).

Multi-scale Features of Baiu, the Summer Monsoon over Japan and the East Asia

“…Therefore the winter monsoon season is the dry season, in general, over East Asia. An airmass transformation takes place, when the cold dry continental airmass flows over the warm sea surface (Ninomiya, 1968(Ninomiya, , 1976Ninomiya and Akiyama, 1976).…”

A Numerical Experiment of Airmass Transformation Processes Over Warmer Sea

“…In the AMTEX region during the cold air outbreaks, Ninomiya (1976) performed a momentum budget analysis and showed that the excess of the pressure gradient force over the Coriolis force, i.e., -* (u -ug) , and the frictional force are the major terms in the momentum balance in the northerly wind component, which is almost parallel to the lower wind direction. Furthermore, the budget analysis indicates that the pressure gradient force in the downstream direction decreases with height.…”

“…The first one is the difference of the role of the horizontal advection ; it has a decelerating effect in the numerical experiment, while it has an accelerating effect in the observational analysis (Ninomiya, 1976 andNitta andSo, 1980). The acceleration rate due to the pressure gradient force caused by the heat supply from the sea can be estimated as (gF*(0)(1+k)(2*um)-1), while the deceleration rate due to the surface friction is estimated as (CDu2m/h).…”

“…Although the observational studies on momentum balance in the mixed layer over the sea are very few (e. g., Ninomiya, 1976;Nitta and So, 1980), their budget analyses indicate that the frictional force determined as a residual and the pressure gradient force are the main factors in the momentum balance in the downstream direction.…”

An Energetics Analysis of Cyclonic Development in the Asian Winter Monsoon¹

“…Ninomiya (1976) studied the kinetic energy budget in the mixed layer over the Kuroshio. Kung (1977b) analyzed the large-scale energy transformation over the Kuroshio region.…”