Abstract
Baroclinic instability in an inviscid fluid with parabolic potential temperature profiles is investigated. Unlike the classical Eady model, there is no short wave cutoff. In addition to the longwave disturbances, which are similar to the Eady waves, shortwave disturbances can also develop in the lower atmosphere, where the stratification is weaker. The growth rate of the short waves increases with increasing stratification aloft. The results show that shortwave disturbances can penetrate into the upper stable layer. The growth rate and disturbances of those waves may be associated with an effective Burger number, which is defined as(The equation is abbreviated)where h(superscript *)is the height of the maximum vertical heat flux(w(superscript ')θ(superscript '))and λ is the horizontal wavelength. Numerical simulations obtained from a nonlinear mesoscale model in Part Ⅱ also confirm that the short waves can develop into a surface front within a few days. Those short waves may correspond to the medium-scale disturbances observed over the AMTEX (Air Mass Transformation EXperiment) region.
Highlights
Baroclinic instability in an inviscid fluid with parabolic potential temperature profiles is investigated
One of the most important phenomena observed during the AMTEX (Air Mass Transformation EXperiment) was the occurrence of medium-scale distur bances over the East China Sea in winter (Nitta et al, 1973)
The longwave disturbances in the Mode I region are quite similar to the classical Eady problem, which has a larger growth rate and propagates faster than short waves in the Mode II region
Summary
One of the most important phenomena observed during the AMTEX (Air Mass Transformation EXperiment) was the occurrence of medium-scale distur bances over the East China Sea in winter (Nitta et al, 1973). The length scale of the medium-scale disturbances was 1000-2000 km in the east-west direction. The disturbances became active in a moist lower troposphere under conditions of a less stable thermal stratification, and are not associated with an upper. The conventional baroclinic instability and symmetric instability have been applied to study the medium-scale disturbances. Observations indicated that the stratification in the lower atmosphere was much less than in the upper atmosphere during the AMTEX. Blumen (1979) and Nakamura (1988) applied baroclinic instability to study the development of the mesoscale disturbances over the Atlantic Ocean
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