Observations of 2–4 day inertia-gravity waves from the equatorial troposphere to the F region during the sudden stratospheric warming event of 2009

Abstract

We have observed strong 2–4 day wave activity in the F region peak critical frequency (foF2) at 7.5°N obtained from GPS radio occultation measurements of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites and the horizontal component of geomagnetic field variations over Tirunelveli (8.7°N, 77.8°E, 1.75°N dip angle) during the sudden stratospheric warming (SSW) event of 2009. A similar wave is observed strongly in the meridional winds observed by the MF radar at Tirunelveli. The meridional winds at 9°N and the equator obtained from ERA-Interim, which is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts, shows clearly the 2–4 day wave, propagating eastward with zonal wave number 6 over the central and eastern Pacific, both before and during the SSW event, and over the Indian sector during the SSW event only. The potential vorticity (PV) intrusion at 200 hPa to lower latitudes is near the central Pacific before the onset of the SSW event. However, during the SSW event, the PV intrusion is observed more strongly near the Indian sector in addition to the weaker intrusion near the central Pacific. It clearly indicates the Rossby wave propagation to equatorial latitudes in the form of PV intrusion, and it selectively enhances the periodicities generated owing to equatorial convective heating. These waves could propagate to upper heights and cause variations in the mesosphere-thermosphere-ionosphere system.