Seasonal variation of vertical eddy diffusivity in the troposphere, lower stratosphere and mesosphere over a tropical station

Abstract

Abstract. Long-term VHF radar (53 MHz with 3 • beamwidth) observations at Gadanki (13.5 • N, 79.2 • E), India, during the period from September 1995 to August 1999 are used to study monthly, seasonal and annual medians of vertical eddy diffusivity, K in the troposphere, lower stratosphere and mesosphere. First, the spectral width contribution due to non-turbulent effects has been removed for further analysis and the monthly, seasonal medians of K are calculated. The monthly median of K in the troposphere shows maximum and minimum in June-July and November-December, respectively. In general, large values of K are seen up to 10 km and then decrease with height. Larger values of K are observed during monsoon and post-monsoon than in winter and summer. In general, the maximum and minimum values of the annual median of K (in logarithmic values) in the troposphere are found to be 0.25 and −1.3 m 2 s −1 respectively. In the mesosphere, the monthly median of K shows maximum and minimum during June-July and November-December, respectively, similar to the lower atmosphere. The value of K in the mesosphere becomes larger and it increases with height up to 75 km and again decreases above that height.The maximum values are seen during the summer, followed by equinoxes and a minimum during the winter. In general, the maximum and minimum values of K (in logarithmic values) are found to be 0.7 and 0.3 m 2 s −1 , respectively, in the mesosphere. A comparison of Doppler spectral parameters in different beam directions shows anisotropy in both signalto-noise ratio (SNR) and spectral widths in the mesosphere, whereas it shows isotropy in SNR and anisotropy in the spectral widths in troposphere and lower stratosphere.

Impacts of SABER CO2‐based eddy diffusion coefficients in the lower thermosphere on the ionosphere/thermosphere

“…Figure 2c shows that the AO and SAO in percent differences have been removed but there are still higher-frequency oscillations with magnitudes below 5%. This is consistent with past studies showing AO and SAO in eddy diffusion coefficients [Kirchhoff and Clemesha, 1983;Fukao et al, 1994;Lübken, 1997;Khattatov et al, 1997;Rao et al, 2001;Sasi and Vijayan, 2001]. Our estimated K zzC profiles exhibit AO and SAO.…”

Diurnal and seasonal variability of TKE dissipation rate in the ABL over a tropical station using UHF wind profiler

“…Various features of LAWP at Gadanki are given by Krishna Reddy et al (2001). Many researchers have examined the possibility of deducing the turbulence parameters like eddy dissipation rate (e) and eddy diffusivity (K h ) from the observed Doppler spectrum of the wind profiler (e.g., Gage and Balsley, 1978;Gossard, 1990;Gage, 1990;Narayana Rao et al, 2001;Satheesan and Krishna Murthy, 2002). One of the limitations of UHF radar for the studies on atmospheric turbulence is its sensitivity to the hydrometeors.…”

Spectral characteristics and scatter cross-section of low latitude mesospheric echoes measured by the Indian MST radar at Gadanki

“…The Indian MST radar at Gadanki (13.5 • N, 79.2 • E) detects echoes from mesospheric altitudes during noon hours (Rao et al, 2001). A climatological study by Kumar et al (2007) has revealed the main characteristics of LLME in terms of occurrence, strength, altitude and seasonal dependencies.…”