Seasonal variations of inertia gravity waves over Hyderabad (17.4 °N, 78.5 °E), a tropical station using radiosonde measurements

Abstract

Gravity waves play an important role not only in transferring the momentum and energy to the upper atmosphere but also significantly contribute in different global atmospheric phenomenon like Brewer-Dobson circulation along with planetary waves. Larger differences in the gravity wave model parameters with the real observations has recommended more observational studies for better predictions. In this paper, we have launched 80 GPS-radiosondes in different seasons (20 per each season) to parameterize the inertia gravity wave (IGW) characteristics over a tropical station Hyderabad (17.4° N, 78.5 °E). FFT analysis of zonal, meridional winds and temperature fluctuations shows the generation of IGW over this latitude irrespective of the presence of strong tides and Quasi Two Day Wave (QTDW). Monsoon and winter amplitudes are maximized in both tropospheric and stratospheric regions. Hodograph analysis is used to estimate the IGW parameters. No significant seasonal changes are observed in vertical and horizontal wavelengths and are ranged between 2 – 4 km and 100–1700 km respectively. Horizontal group velocities are found to be lesser in tropospheric region than stratospheric one, while the vertical group velocities showed the opposite nature in all the seasons. About 80–90% hodographs show the upward propagation of IGW in stratospheric region and the direction of horizontal wave propagation is not very clear. Vertical wavenumber spectra reveal the isotropic nature of the waves and agreed well with the universal spectrum of power law. The slopes reached canonical values (−3) in both the height regions for all the seasons. Kinetic energy variations in all the seasons show interesting facts about source regions in different seasons. Strong convection and wind shear along with tropical easterly jets are responsible for the generation of these waves in monsoon, whereas, sudden enhancement in meridional wind shear is the source mechanism during winter.