V. Deepa

Inertia‐gravity waves associated with the tropical easterly jet over the Indian subcontinent during the South West Monsoon Period

Using the MST radar located at Gadanki (13.5°N, 79.2°E) winds were measured every four hours in the troposphere and lower stratosphere during a 72-hour period from 23 to 26 September 1997 when the tropical tropospheric easterly jet (TEJ) was present south of Gadanki with its core at a height of ∼16 km. Analysis of the radar data shows the presence of ∼56 hour oscillations (close to local inertial period of ∼51 hours) in the wind components with significant amplitudes. Examination of the corresponding horizontal wind vector shows clockwise rotation with altitude (upward energy propagation) in an altitude region (17.7–20.8 km) above the TEJ and anticlockwise rotation (downward energy propagation) in another altitude region (8.3–10.5 km) below. This indicates the generation of Inertia Gravity Waves (IGW) in the TEJ and their propagation both upwards and downwards from the source region. The inferred vertical and horizontal wavelengths of the IGW are ∼0.7 and ∼75 km respectively in the stratosphere and ∼1 and ∼143 km respectively in the troposphere.

Nonmigrating diurnal tides in the troposphere and lower stratosphere over Gadanki (13.5°N, 79.2°E)

A study of diurnal tidal oscillations in horizontal winds using Indian mesosphere-stratosphere-troposphere radar located at Gadanki (13.5°N, 79.2°E) shows that during autumnal equinox season diurnal amplitudes of 1-2 m s -1 of horizontal winds prevail in the troposphere. The vertical structure of amplitudes and phases indicate a vertical wavelength of ∼3 km in the lower troposphere and ∼6 km in the upper troposphere. A comparison of these amplitudes and vertical wavelengths with results from theoretical tidal models suggests that these oscillations in the lower troposphere are manifestation of nonmigrating diurnal tidal oscillations excited by eddy heat flux in the planetary boundary layer and those in the upper troposphere excited by latent heat release in deep convective clouds. However, nonmigrating diurnal tidal modes generated by solar radiation absorption by water vapor and clouds in the troposphere cannot be ruled out.