Seasonal variations of global stratospheric gravity wave activity revealed by COSMIC RO data

Seasonal variations of gravity waves over the globe in the stratosphere are investigated using radio occultation data from the Constellation Observing System for Meteorology, Ionosphere and Climate mission from September 2006 to June 2016. The global distributions of 10-year averaged seasonal means of gravity waves indicate that potential energy is large over tropical and subtropical latitudes (30°S-30°N) in all seasons, as well as over middle and high latitudes in winter hemisphere. Gravity wave potential energy and the outgoing longwave radiation (OLR) which is a proxy for deep convection are negative correlated at equatorial latitudes. This suggests that convection is the primary source of gravity waves in the Tropics. At 50°N and 50°S, gravity waves are mainly generated by the diverse terrains of mountains, and either propagate upward or are filtered out under the effect of background zonal wind. Intense eastward wind, which mainly happens in winter hemisphere, makes great contributions to the upward propagation of gravity waves, while 0 m/s wind level, which is apparent in summer hemisphere, filters out most of the gravity waves. This can explain the seasonal variations of gravity waves at middle and high latitudes.