Nonlinear kinetic energy transfer in the upper troposphere during summer monsoon 1979

Abstract

Upper tropospheric (300-100 hPa) nonlinear kinetic energy (KE) converts to rotational and divergent motion and the conversion is computed in the wavenumber domain for July 1979 in the latitude belt 10°S-30°N. They are further partitioned into stationary and transient components. It is shown by comparing the rotational and divergent KE spectra for stationary and transient motions that the best nondivergent level is 300 hPa, and 200 hPa is the most representative level in the upper troposphere for monsoon studies. Wavenumbers 3 and 7 are identified as the most preferred transient waves from the rotational transient kinetic energy spectrum. It is concluded that in the planetary-scale dynamics of the monsoon region, wave-wave interaction plays a secondary role. The net gain of rotational kinetic energy is proportional to its value, and the proportionality constant is nearly the same for all wave categories. It is found that planetary and synoptic waves in the upper troposphere during the monsoon are maintained by energy transfer from divergent kinetic energy. KE in the monsoon region is transported by nonlinear wave-wave interaction. In particular, transient synoptic-scale eddies are also maintained by energy transfer from transient synopticscale divergent motion. It is further inferred from the energy balance that the stationary-transient wave-wave interaction is important for the maintenance of transient subsynoptic waves. It is noticed that kinetic energy conversion for transient subsynoptic waves is from the divergent to the rotational component at 200 hPa only and is opposite to that in the upper troposphere. The energy budget for transient waves 3 and 7 is investigated.