Abstract
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 20 m s−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.
Highlights
Wind plays a vital role in atmospheric energetics
Strong wind shears that are frequently observed beneath the Level Jet (LLJ) indicate that the winds increase very sharply below the core of the LLJ and reduce slowly above the jet core
One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds
Summary
Wind plays a vital role in atmospheric energetics. It transports heat, mass, moisture and pollutants from one place to another. Two such phenomena are the Low-Level Jet (LLJ) and Tropical Easterly Jet (TEJ) These two synoptic-scale jets are associated with the boreal summer (southwest) monsoon and located at 850 hPa and 150 hPa, respectively, over southern India (Joseph and Raman, 1966; Findlater, 1966, 1967; Mokashi, 1974; Desai et al, 1976). The WMO definition of the jet (wind speeds exceeds 30 m s−1), basically meant for the TEJ, may not be often valid for the LLJ In spite of this fact, a lowlevel (850 hPa) wind system having a strong wind and wind shear has been named as an LLJ. The LLJ observed over the Indian peninsula is an Afro-Asian cross-equatorial phenomenon. Joseph and Raman (1966) first examined the LLJ features over the peninsular India followed by Desai et al (1976), which confirms the existence of a westerly LLJ stream with strong vertical and Published by Copernicus Publications on behalf of the European Geosciences Union
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