The circulation near the tropical tropopause and lower stratosphere affects climate in several ways. Temperatures and circulation at the tropopause control the concentration of stratospheric water vapor, affecting global surface temperature. Another example is the quasi-biennial oscillation in lower stratospheric zonal mean zonal winds, which modulates teleconnections to the Northern Hemisphere, affecting the occurrence of severe winter weather. Tropical gravity waves have roles in both of these processes, lowering cold point temperatures and providing much of the force that drives the quasi-biennial oscillation. In the tropics, gravity waves have the widest range of scales and periods, from kilometers to global scales and from minutes to several days. To observe and model these waves requires not only global coverage and fine spatial resolution but also high vertical resolution, since wave driving of the circulation tends to occur when and where the waves refract to short vertical wavelengths. Cold-point temperature variability (with associated water vapor changes) is also dominated by shorter vertical scale waves. The focus of this talk will be on understanding the sources and effects of tropical gravity waves at scales of hundreds to thousands of km. These remain poorly resolved and under-represented in global climate models and reanalysis datasets, and they remain a significant challenge for observations. Tropical gravity waves are generally forced by tropical convection, a parameterized process itself in models used for climate prediction and weather forecasting. Our approach uses high-resolution observations of precipitation to describe the sources of tropical waves in idealized global simulations, and we combine these with observations of tropical waves derived from analysis of satellite limb-sounding temperature measurements in the upper troposphere and lower stratosphere. Our results permit evaluation of the representation of tropical gravity waves in reanalyses. We also examine relationships of interannual and intraseasonal variability in tropical gravity waves and precipitation.
*email: alexand@nwra.com
*Preference: Invited