K. N. Uma

On the Vertical Distribution of Mean Vertical Velocities in the Convective Regions during the Wet and Dry Spells of the Monsoon over Gadanki

AbstractThe Indian Mesosphere–Stratosphere–Troposphere (MST) radar observations of vertical distribution of mean vertical velocities w in convective regions during the wet and dry spells of the Indian summer monsoon over a tropical station at Gadanki, India (13.5°N, 79.2°E) are discussed. The composite w profile during the wet spell consistently shows a single peak at ~13 km whereas during the dry spell it shows two peaks, one at 5 km and another at 11–13 km. The characteristics of this altitudinal distribution in w are discussed in terms of background wind and thermal structure during both spells of the monsoon. Background w obtained from NCEP–NCAR reanalysis shows subsidence throughout the depth of the troposphere during the dry spell of the monsoon over Gadanki. Analysis of background wind and thermal structure clearly reveal that wind shear and temperature inversion in the midtroposphere are different in the dry spell compared to that of the wet spell, which may be the possible reason for the observed...

First observational study during a solar eclipse event on variations in the horizontal winds simultaneously in the troposphere-stratosphere-mesosphere-lower-thermosphere region over the equatorial station Thumba (8.5°N, 77°E)

The longest annular solar eclipse of the millennium occurred on 15 January, 2010, and was visible over the equatorial station Thumba (8.5°N, 77°E) around noon time. A host of experiments were carried out to study the variations due to the solar eclipse event on various geophysical parameters, from the Earth’s surface to ionospheric heights. The present study focuses on the variation in the horizontal winds in the height regions of 0–65 km and 80–100 km, using GPS-sondes, rocket-sondes and meteor wind radar. The observations were made during, and after, the maximum obscuration on the day of the eclipse, as well as at the same time on a control day. The observations showed a strengthening/weakening of winds along with directional changes both in zonal and meridional winds in the selected height domains. A drastic change from easterly to westerly is observed at 98 km during, and after, the maximum phase, but, for the meridional wind, the reversal is observed only after the maximum phase. Variations due to the eclipse were also observed around the tropopause and stratopause in both wind components. However, the observed changes in winds around the tropopause and stratopause could not be attributed unambiguously to the eclipse as day-to-day wind variability is not available in these height regions. The significance of the present study lies in reporting the variations in the horizontal wind components from the ground to the 100-km height region (with a gap around 65–80 km), and the characteristics of the atmospheric waves generated due to the mid-day annular solar eclipse.

VHF radar studies of the migrating and nonmigrating diurnal and semidiurnal tides over a tropical and an equatorial station

VHF radar measurements of winds are utilized to study the diurnal and semi-diurnal tides over Gadanki and Kotatabang. The tidal amplitudes exhibit maxima in UTLS region during June-September over Gadanki and during March and September over Kotatabang. The vertical wavelength is 3–5 km (Gadanki) and 25–30 km (Kotatabang), which reveal the existence of nonmigrating and migrating tides, respectively. Brightness temperature shows that over Gadanki(deep) and Kotatabang(shallow) convective clouds. Release of latent heat due to deep-clouds is found to be the main source mechanism for nonmigrating tides. The present study brings out the differences in tides over equatorial and low latitude.