Validation of MERRA reanalysis upper-level winds over low latitudes with independent rocket sounding data

Abstract

An evaluation of upper stratosphere lower mesosphere (USLM) horizontal winds from MERRA reanalysis is performed using rocket sounding observations that span more than 5 years (November 2002–November 2007) over Thumba (8.5°N, 77°E). With Rocket sonde profiles as reference, bias and root mean square deviation (RMSD) are computed between 10hPa and 0.1hPa (∼30–65km) on annual and seasonal time scales. The present results reveal that observations and reanalysis correlate reasonably well in zonal winds below 60km. The detailed comparison showed increasing RMSDs with height reaching largest value at 0.1hPa. RMSD noted in the zonal winds are larger than in the meridional winds. Positive biases are noted in the zonal winds around 50km with large values during seasonal transition period that led to 30% overestimation of the stratospheric semiannual amplitude. The meridional winds are not well reproduced in the reanalysis. Possible reasons for the differences between MERRA and rocket soundings are discussed. The present study is the first attempt to validate MERRA reanalysis data with observations in the USLM region. Over all good agreement in the zonal winds between MERRA reanalysis data and RH-200 is very encouraging and vouches for using the MERRA reanalysis zonal winds belowProd. Type: FTP 0.1hPa, but with caution around 1hPa.