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

Abstract

Abstract. In November 2008 and in March and April 2009the Indian MST radar (53 MHz) at Gadanki was operated during the daytime in a special experiment, with 600 m altitude resolution, for understanding the characteristics of lowlatitude mesospheric echoes (LLME). The data of three days when the echoes were strongest have been analysed in terms of spectral widths and radar volume reflectivities. Spectral widths of LLME show some decrease with altitude, with median values of 4-6 m s −1 at 69-72 km and of 2-4 m s −1 at 73-78 km. This corresponds to 20-200 mW kg −1 turbulent energy dissipation rates. It has been shown that stronger echoes have broader spectra consistent with a turbulent scattering mechanism. For the first time, the volume reflectivities for the strong LLME for Gadanki have also been calculated. They are in the range of 10 −17 -10 −15 m −1 , so LLME at Gadanki are somewhat stronger than those reported so far from Jicamarca, Peru (Lehmacher et al., 2009).

On the seasonal variations of reflectivity and turbulence characteristics of low‐latitude mesospheric echoes over Gadanki

“…[] and Belova et al . []. Figure shows the GSM cosmic noise along with the MST radar observed noise at 53 MHz (after properly scaling up) over Gadanki on different days and in different months as a function of sidereal time.…”

“…To account for the noise variation, the Global Sky Model (GSM) [de Oliveira-Costa et al, 2008] has been used to calculate the galactic noise contribution to T noise at 53 MHz over Gadanki. The contribution of galactic cosmic noise has been calculated as a function of time for all the days of observations following Kirkwood et al [2010] and Belova et al [2012]. Figure 2 shows the GSM cosmic noise along with the MST radar observed noise at 53 MHz (after properly scaling up) over Gadanki on different days and in different months as a function of sidereal time.…”

“…Thus, the system efficiency of 0.5 used here has uncertainty due to lack of calibration of receive path. The uncertainty in the volume reflectivity is estimated to be about a factor of 2 [ Belova et al ., ], which implies that the actual reflectivities could be two times the estimated values.…”

On the governing dynamics of the VHF radar echoes from the mesosphere and collision‐dominated lower E region over Gadanki (13.5°N, 79.2°E)

“…Turbulence is generated either by convective or dynamical instability depending on the background temperature and wind fields. Radar observations have also revealed that the low‐latitude mesospheric echoes could be linked with turbulent layer and/or spatially confined patchy regions [e.g., Royrvik , ; Sheth et al ., ; Lehmacher et al ., ; Chandra et al ., ; Belova et al ., ]. The descending layer‐type morphology of the echoing regions, which indicate the potential role of tidal/gravity wave dynamics on the echoing morphology, however, have not been paid attention so far.…”