Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

Abstract

Abstract. Sources and propagation characteristics of highfrequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5 • N, 79.2 • E) and Hyderabad (17.5 • N, 78.5 • E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of groundbased (MST radar, radiosondes, MF radar) and rocket-and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50-100 km and 150-300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (∼ 9 m s −1 km −1 ) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10-12 km altitude) and are thus identified to be the source for generating the observed highphase-speed, high-frequency gravity waves.

Climatology of Horizontal Winds in the Lower and Middle Atmosphere over an Equatorial Station - Thiruvananthapuram

“…The features seen in the observed zonal winds are reproduced in the model winds shown in Figure 4 b, except the presence of TEJ and descending easterlies in the mesosphere during March-May. There are reports about the climatological monthly mean structure of zonal and meridional winds obtained over Gadanki region using a variety of instruments 32 , which agree well with our present observations over Thiruvananthapuram.…”

“…The zonal wind observations in the 70-80 km height range over the Indian region provided by rocketsonde HRDI/UARS, and MST radar during 1977-2010 showed a decreasing trend of 2 m/s/year changing from strong eastward winds to weak westward winds in recent years 31 . Pramitha et al 32 also reported climatological monthly mean contours of temperature, zonal wind and meridional wind obtained over Gadanki region combining a variety of instruments.…”

Tuning of a convective gravity wave source scheme based on HIRDLS observations

“…However, there are also indications from radiosonde and ground-based measurements (e.g. Leena et al, 2012;Pramitha et al, 2015) and modeling (e.g. Preusse et al, 2014) that in the regions of deep convection GWs are excited around tropopause altitude.…”

Gravity-wave effects on tracer gases and stratospheric aerosol concentrations during the 2013 ChArMEx campaign

“…Previous studies have shown that GROGRAT is an efficient tool to identify GW sources (Guest et al, 2000(Guest et al, , 2002Pramitha et al, 2015) and to simulate GW-background interactions such as GW effects, wave filtering, space and time variability of GW activity and characteristics (Wei and Zhang, 2015). For example, GROGRAT simulations help to interpret global GW observed morphology derived from satellite observations .…”