Study of transport and photochemistry around the tropical tropopause using Chemistry Climate Models

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There exists significant sub-seasonal variability in temperature and other parameters around the tropical troomuse. This is due to equatorial waves, intra-seasonal oscillations (ISOs), and other disturbances that are generated by tropical organized convection. Therefore, appropriate representation of tropical convection and tropical disturbances is crucial even for the Chemistry Climate Models (CCMs) that simulate and project stratospheric ozone, since these waves significantly influence the stratosphere-troposphere transport processes and help determine the coldest temperatures, affecting the dehydration processes in the tropical tropopause region. In this study, the wave activity in temperature and zonal and meridional winds at 100hPa in the tropics is analyzed for four CCMs that produced high time frequency winds and temperatures (CCSRNIES, CMAM, MRI, and WACCM) and for five reanalysis data sets (ERA40, ERA-Interim, JRA25, NCEP/NCAR (NCEP1), and NCEP-DEO AMIP-II (NCEP2)), using a zo … More nal-wavenumber-frequency spectral analysis method with a equatorially symmetric-antisymmetric decomposition.Features commonly observed in all data sets are equatorial Kelvin waves and mixed RossbY gravity OMRG) waves. ISOs, at frequencies smaller than O. 05 cycle per day, are mostly not statistically significant with respect to the background spectra estimated here; however, largest power is found in these regions. The activity for equatorial Kelvin waves, MRG waves, and symmetric eastward-moving ISO is defined as the integration of power spectral density in the respective zonal-wavenumber-frequency region for each wave/disturbance. The statistical significance is considered only for Kelvin and MRG waves. The ISO activity here is the upper limit. Results indicate that five reanalysis data sets have very different wave activities. The Kelvin and MRG wave activities in ERAs are 2-3 times greater than those in NCEPs; those in JRA25 are close to the average. The ISO activity (the upper limit) is rather similar for the five reanalysis data sets. The wave activities in the four CCMs are generally within the range of those in the reanalysis data. WACCM shows the greatest Kelvin and MRG wave activities, which are comparable to those in ERAs. CCSRNIES shows the smallest Kelvin wave activity, and MRI shows the smallest MRG activity. The ISO activity (the upper limit) in the CCMs is greater than that in the five reanalysis data sets except for CCSRNIES.The above results indicate that the reanalysis data currently available do not give the actual wave activities due to their large discrepancy. Analysis of radiosonde data and GPS occultation temperature data is necessary to investigate the actual wave activities. Less