Gravity Waves Characteristics in Lower Stratosphere during Tropical Cyclones over the North Indian Ocean

Gravity wave studies associated with tropical cyclones over the north Indian Ocean have been made using COSMIC GPS radio occultation measurements. Gravity wave sources are generally located well below the tropopause or at lower altitudes where the intensity of tropical cyclones is high. The vertical profile of gravity wave energy from 18 to 25 km shows that an upward propagation of energy enhances the potential energy in the lower stratosphere (LS). The lower stratosphere experiences an enhancement in relative humidity and thus can be due to stratosphere-troposphere exchange processes as observed from AURA-MLS data caused by deep convection associated with tropical cyclones (TC). Intense convection associated with TC is characterized by low OLR value of nearly 120 W/m2. The study shows that an increase in potential energy in LS over the storm path before the TC which can be an indicator of the impending cyclone track. A prediction of the cyclone path can be done by estimating the energy enhancement in LS. The evolution of gravity wave activities along the latitudes and longitudes shows signatures of propagation of gravity waves along horizontal and vertical directions. This study shows that intense TC is a driving force for the transportation for water vapor from upper troposphere to lower stratosphere. The power spectral density of gravity waves shows that the vertical wavelength of 2.5 km carries most of the energy during Tropical cyclones. The spatial evolution of gravity waves has been studied in terms of potential energy, power spectral density and specific humidity in the lower stratosphere.