Representation of Waves in the Tropical Tropopause Layer in Analysis and Reanalysis Data

The tropical tropopause layer (TTL) is an important transition layer that controls water vapor entering the lower stratosphere from the upper troposphere through the freeze-drying process. Simulation studies on the water vapor transport and cirrus cloud formation use temperatures and winds from global analyses or reanalyses. It is well known that TTL temperatures in analyses and reanalyses have biases and are lacking in variability. To take account of temperature biases, model studies adjust reanalysis mean temperatures to match observed TTL temperatures. In addition to the mean TTL temperatures, temperature variability also has a significant impact on dehydration due to wave-induced extremely cold temperatures and changes in cloud particle properties. In this study, we introduce a cross-spectral analysis for winds and temperatures to identify various types of tropical waves including Rossby, Kelvin, mixed Rossby-gravity, and inertia-gravity waves for December 2012-February 2013 from radiosonde observations and GEOS-5 and ECMWF analysis. We further investigate the representation of TTL waves in MERRA and ERA-interim in a statistical sense to suggest a better method of wave parameterization for TTL dehydration simulations.