A comparative assessment of Kalpana-1 and MISR cloud tracked winds over the Indian Ocean region

Abstract

In this study, an attempt has been made to advance the error characteristic of atmospheric motion vectors (AMVs) derived from the infrared and water vapour channels of Kalpana-1 very high resolution radiometer by comparing against stereo motion vectors (SMVs) retrieved by tracking clouds from the multi-angle imaging spectro-radiometer (MISR) for a period of 9 months. Two different versions of the MISR SMVs with horizontal resolutions 70.4 and 17.6 km, respectively, are used for the inter-comparison. It is found that the Kalpana-1 AMV has stronger westerlies and southerlies than the MISR SMV at all latitudes and levels in majority of times. The performances of Kalpana-1 AMVs against MISR SMVs are assessed by doing a similar analysis where Meteosat-7 AMVs (infrared and water vapour AMVs) are also evaluated against the MISR SMVs for the same region. It is found that results of both AMVs (Kalpana-1 and Meteosat-7) with both sets of MISR SMVs are comparable with few exceptions. The zonal wind components of the MISR SMVs showed smaller mean wind difference and root mean square difference (RMSD) compared to the meridional wind components. The SMVs are typically assigned to higher altitudes than AMVs. Analysis related to the height discrepancies between MISR SMVs and AMVs shows that in the multi-layer cloud AMVs are tracked in upper level cloud targets, while SMVs are skewed more towards lower level. The accuracy is better for the low level where collocations are highly dense and gradually decreases towards the higher levels. Because of improvement in the MISR SMV retrieval algorithm, the errors in the meridional component of SMVs have improved in the recently released version with horizontal resolution of 17.6 km.