Diurnal variations of turbulence parameters over the tropical oceanic upper troposphere during SCSMEX

Abstract

Using the method of Thorpe analysis, the TKE (turbulence kinematic energy) dissipation rate (ɛ) and turbulence diffusivity (K) were derived from the RS (radiosounding) measurements in the tropical oceanic upper troposphere. The measurements were performed four times per day during two intense observation periods (May 5–25, and June 5–25) on the Kexue #1 scientific observation ship of SCSMEX (South China Sea Monsoon EXperiment) in 1998. There are three new features obtained from our analysis. First, the responses of ɛ and K to the onset of monsoon are negligible over the ocean at least for the data used here. Second, the temporal variations of ɛ and K are in a similar manner and exhibit strong diurnal variations. The diurnal variations achieve their maxima in the morning (08 LT) and early afternoon (14 LT), and achieve their minima in the evening (20 LT) and early morning hours (02 LT). The diurnal variations of turbulence parameters (ɛ and K) and their responses to the onset of monsoon are entirely different from those derived over land at similar latitudes. Finally, although the correlations between the variations of ɛ and MCSs (mesoscale convective systems), which were derived from TRMM (tropical rainfall measuring mission) satellite, are not very well in only few days, the diurnal variations of ɛ averaged over May and June are strongly correlated with the diurnal variations of MCSs with correlation factors of 0.79 and 0.94, respectively. This indicates that the turbulence and its diurnal variations over the tropic oceanic upper stratosphere region are highly related to the MCSs.