Characteristics of the turbulence echo observed with the equatorial atmosphere radar (EAR) and simultaneous hourly radiosondes

We investigate characteristics of the turbulence echo at 3-9 km altitudes observed with the Equatorial Atmosphere Radar (EAR) at 100.32oE, 0.20oS, Kototabang, West Sumatera, Indonesia. Radiosondes were simultaneously launched every hour for 25 times from 6 UTC on 15 December 2005, which provides a unique opportunity to analyze the hourly variations of the atmospheric parameters. We refer to the relation on the radar reflectivity [[EQUATION]], where M, N2, ε and F are the refractive index gradient, Brunt-Väisälä frequency squared, the turbulence kinetic energy dissipation rate and the filling factor of turbulence in the radar range volume, respectively. The echo power is converted to the range normalized signal-to-noise ratio (So) with the oblique beam at 10o off the zenith. At 3-6 km altitudes, So was largely affected by passage of convective clouds during 9-23 UTC. At 6-9 km, the intense So appeared as several systematic layers with downward phase progression due to atmospheric gravity waves. M2/N2 considerably affects the time-height variations of So at all altitudes, and their two-dimensional cross-correlation value is 0.60 and 0.63 at the 3-5.5 km and 6-9 km altitude layers, respectively. We delineate the Richardson number (Ri) from the temperature and wind velocity with radiosondes with the 10 m interval. Then, we calculate the percentage occurrence of Ri within a 200 m height layer for Kelvin-Helmholtz instability (0<Ri<0.25) and convective instability (Ri<0), which are defined as Ri-KHI and Ri-CI, respectively. Ri-KHI increased at 6.6-7.4 km during 13-20 UTC, which coincides with the enhancement of the spectral width with the oblique beams ([[EQUATION]]. A peculiar event of the enhanced So associated with the large [[EQUATION]] is found at 6-8 km during 13-20 UTC. We investigate the relation between η with M2/N2 and [[EQUATION]], where [[EQUATION]]is calculated from [[EQUATION]] and N. We define F as the sum between Ri-KHI and Ri-CI. The time-height structure of the calculated η is remarkably consistent with the observed So. The maximum of η appears in between the individual peaks of M2/N2 and εo, and therefore, the height structure of η is explained only by combining the effects of both M2/N2 and εo.