Characterization of inertia gravity waves and associated dynamics in the lower stratosphere over the Indian Antarctic station, Bharati (69.4°S, 76.2°E) during austral summers

Abstract

Atmospheric gravity waves over the Polar Regions are found to have myriad effects on the dynamics and chemistry of the middle atmosphere. Data collected from high vertical resolution radiosonde measurements carried out in campaign mode from the Indian research base in Antarctica, Bharati (69.4°S, 76.2°E) during the austral summer seasons of 2014–2015, 2015–2016 and 2016–2017 were used to characterize inertia gravity waves (IGWs). Wavelet analysis technique is employed to identify and isolate individual IGW packets. IGWs in the lower stratosphere region are characterized in terms of their vertical and horizontal wavelengths, intrinsic frequencies, directions of propagation, momentum fluxes, energy densities and ground based phase speeds. The observed gravity waves have short vertical wavelengths (~ 2 km) and low intrinsic frequencies (1f–2f). Zonal and meridional components of momentum fluxes are found to have comparable magnitudes. From the direction of propagation estimates, it is observed that the IGWs have a marginal predisposition towards eastward propagation during austral summers. It is found that the lower stratospheric region over Bharati during summertime is dominated by IGWs from non-orographic sources. Evidences for generation of IGWs from an upper tropospheric jet streak observed over Bharati station are provided. The jet streak is found to be associated with the intrusion of low potential vorticity air from middle latitudes and the accompanied development of an anti-cyclonic circulation. The observations suggest that low potential vorticity intrusion happened as a result of breaking of poleward propagating Rossby wave. Spontaneous adjustment of the unstable jet could be responsible for the IGW generation. The significance of the present results lie in characterizing the summer time IGW over the Bharati station for the first time using wavelet based approach and identifying the possible source mechanism.