Vertical and lateral propagation characteristics of intraseasonal oscillation from the tropical lower troposphere to upper mesosphere

Using a mesosphere‐stratosphere‐troposphere (MST) radar and a Rayleigh lidar collocated at the Indian tropical station, Gadanki (13.5°N, 79.2°E), European Centre for Medium‐Range Weather Forecasts (ECMWF) Re‐Analysis data and the horizontal wind velocities measured by the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED Doppler Interferometer (TIDI) instrument onboard the TIMED satellite, the present study makes a report on the lateral and vertical propagation characteristics of an intraseasonal oscillation (ISO, 20–40 day period band), propagating from the lower troposphere to the upper mesosphere region during the winter (November, December, January, and February) months of the years 2004–2005. It is found that the ISO had its origin in the tropical lower troposphere and propagated laterally and vertically to the upper mesosphere through the subtropical latitudes by partial refraction and reflection processes about the subtropical westerly jet. Corresponding enhancements in the wavelet spectrum of outgoing long‐wave‐radiation (OLR, NOAA interpolated) indicate that convective forces in the lower troposphere are one of the main sources for the generation of the ISO. From the phase of the ISO in the horizontal winds, as observed by the MST radar, it is found that the ISO propagated upward from the lower troposphere up to near the tropopause, where it got sharply attenuated. From the ECMWF data, it is observed that the ISO was refracted to the subtropical latitudes, through the tropical tropopause, from where it got radiated upward into the stratosphere. The phase propagation of the filtered winds shows that the ISO arched back toward the tropical latitudes and propagated to the mesospheric region.