Abstract: This paper presents the diurnal and seasonal variation of Turbulence Kinetic Energy (TKE) dissipation rate (e) in the Atmospheric Boundary-Layer (ABL) over a tropical station, Gadanki (13.51 N, 79.21 E) in India. Doppler spectral width measurements made by Lower Atmospheric Wind Profiler (LAWP) operating at 1357MHz are utilized to estimate e in the height region of 0.5–4.0 km on clear air days. Various non-turbulent spectral broadenings are calculated and separated out from the observed spectral width before estimating e. It is found that in the lower tropospheric height region e is in the range from 105.0 to 101.0m2 s3. e showed significant diurnal variation in the boundary-layer. The larger values of e, 10–2.7m2 s3, are noted to be associated with the Convective Boundary-Layer (CBL). The parameter e is also showing significant seasonal variation. In summer and monsoon seasons the boundary-layer depths are observed up to a height of 4.0km while the same are confined to below 2.0km in post-monsoon and winter seasons.

Abstract: Three-year high-resolution wind observations of the wind profiler have been utilized to characterize the diurnal and seasonal features of the monsoon Low-Level Jet (LLJ) over a tropical station, Gadanki (13.5 N, 79.2 E), with a focus on the diurnal variability of low-level winds. The Boreal summer monsoon winds show a conspicuously strong westerly LLJ with average wind speed exceeding 20ms−1. The L-band wind profiler measurements have shown an advantage of better height and time resolutions over the conventional radiosonde method for diurnal wind measurements. An interesting diurnal oscillation of LLJ core has been observed. It is varying in the height range of 1.8±0.6 km with the maximum and minimum intensity noticed during the early morning and afternoon hours, respectively. The jet core (wind maxima) height is observed to coincide with the inversion height. Strong wind shears are normally located beneath the LLJ core. The sole wind profiler observations are capable of identifying the monsoon phases, such as onset, break and active spells, etc. The mutual influence between the LLJ and the boundary layer has been discussed. One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds. The day-to-day change in the LLJ structure depends on the latitudinal position of the LLJ core.