Mesoscale disturbances in the tropical stratosphere excited by convection: Observations and effects on the stratospheric momentum budget

Abstract The importance of the momentum flux of topographically generated mesoscale gravity waves to the extratropical middle atmosphere circulation has been well established for over a decade. Estimates of the zonal forcing due to tropical mesoscale gravity waves, however, are hampered by lack of data on their primarily convective sources. The advent of aircraft measurements over tropical convective systems now makes such estimates possible without the use of ad hoc assumptions about amplitudes and phase speeds. Aircraft measurements from NASA's 1980 Panama and 1987 STEP/Australia Missions show that convectively generated disturbances observed just above the tropopause have horizontal scales comparable to those of the underlying anvils (about 50–100 km) with peak-to-peak isentropic surface variations of about 300–400 m. Satellite imagery of tropical anvil evolution indicates a typical lifetime of about five hours. Assuming that each convective system's impact on the stratosphere can be modeled as a time-...