Sensitivity of Wind Analyses to Barotropic Energetics during Summer¹

Abstract

The extended correction method of the University of Hawaii at Manoa (UHM), National Meteorological Center (NMC) Hough analysis, and subjective streamline analysis (SUB), were employed to provide grid-point winds by using the Data Systems Test (DST) data during the period from 30 August to 4 September 1975. These wind data were used for the computation of barotropic energetics over six limited regions in the Pacific and Indian Oceans.
No significant difference was encountered between UHM and NMC stream-function analyses. This is due to the fact that NMC analyzed data was used as a first guess in the UHM objective analyses. NMC velocity potential fields were extremely weak, while UHM analysis provided weak to moderate divergent winds with a major outflow center located over the summer monsoon region. This is attributed to an enhancement of the divergence fields by incorporating satellite observed outgoing longwave radiation data in the UHM analysis scheme. SUB analyses exhibited an extremely strong easterly jet over the equatorial Indian Ocean, and strong upper divergence over the Bay of Bengal. This is obviously due to no data smoothing and the introduction of climatological information in SUB over datasparse regions.
Over data-rich regions, the three analysis schemes show good resemblance in both sign and magnitude for energy exchanges between area-averaged zonal mean flows and disturbances. However, substantial differences between objective and subjective analyses were noted over data-sparse regions. For example, over the equatorial Indian Ocean, area-averaged zonal mean flow was barotropically unstable (stable) in UHM and NMC (SUB).