GLOBAL SPECTRA OF ENERGY AND ENSTROPHY AND THEIR FLUXES DURING JULY 1979

Transient and stationary spectra of kinetic energy (KE), available pot ential energy (APE) and enstrophy (EN), and their spectral fluxes as a function of the two-dimensional wavenumber n were computed for July 1 979. Triangular truncation at zonal wavenumber 42 was used for computa tion. The slopes of various spectra in the wavenumber range 14 less-th an-or-equal-to n less-than-or-equal-to 25 were obtained by fitting a s traight line in log-log scale by the least square method. The transien t KE, APE and EN spectra in the lower (upper) troposphere had slopes - 2.21 (- 2.30), - 2.65 (- 2.64) and - 0.36 (- 0.46), respectively. The effect of stationary and divergent motion on the slope values was inv estigated. The possible correlation between the slope and percentage o f transient component in the combined energy and enstrophy was examine d to identify the transient motion of the atmosphere with the two-dime nsional homogeneous isotropic turbulence. The vertically averaged slop e of kinetic energy and enstrophy in the lower (upper) troposphere was close to the value at 700 (200) h Pa level. The spectral fluxes of ki netic energy and enstrophy in the wavenumber range 14 less-than-or-equ al-to n less-than-or-equal-to 25 satisfied, to a very rough approximat ion, the criteria of inertial subrange. The stationary fluxes were sma ll. The estimated stationary-transient component of flux was larger, c omparable and less than the corresponding transient flux of APE, KE an d EN. Representative levels for computation of energy and enstrophy sp ectra and their fluxes in the lower and upper troposphere were identif ied.