Comparison of atmospheric infrared sounder temperature and relative humidity profiles with NASA African Monsoon Multidisciplinary Analyses (NAMMA) dropsonde observations

Abstract

The 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA) field campaign was conducted to investigate the Saharan Air Layer (SAL) activity and its influence on Atlantic tropical cyclones. During the field campaign, 197 dropsonde soundings were collected from 13 research flights over the eastern Atlantic (10°N–22°N, 16°W–34°W) between 19 August and 12 September 2006 which provide a valuable data set to examine the uncertainty of the temperature and relative humidity profiles retrieved from the Atmospheric Infrared Sounder (AIRS) data in the SAL region. Comparing AIRS retrievals with the dropsonde observations indicates that AIRS profiles have a RMS difference of 1.35°C in temperature at the eight standard pressure levels and a RMS difference of 13.8% in relative humidity on seven standard pressure layers from 1000 hPa to 300 hPa. In particular, the RMS differences of temperature and relative humidity range from 0.79°C to 1.61°C and from 10.1% to 15.3%, respectively, from 1000 hPa to 300 hPa. Note that the uncertainty is estimated under sky conditions with active cloud activity because many NAMMA dropsondes were released in the cloud clusters or in the circulation of named tropical cyclones. This study suggests that in the SAL or the region with cloud activity the AIRS relative humidity/temperature has the RMS error within/approaching the design expectation for clear sky conditions.