Thursday, 13 January 2005
Feasibility of a reanalysis using only surface data
Climate variability and global change studies are increasingly focused on understanding and predicting regional changes of daily weather statistics. Assessing the evidence for such variations over the last hundred years requires a daily tropospheric circulation dataset. The only available data for the early 20th century are error-ridden hand-drawn analyses of the mean sea level pressure field over the northern hemisphere. Modern data assimilation systems have the potential to improve upon these maps, but prior to 1948, there are few digitized upper-air sounding observations available for such a reanalysis. We investigate the possibility that the quantity of newly recovered surface pressure observations is sufficient to generate a useful reanalysis of at least the lower tropospheric circulation back to 1900. Surprisingly, we find that with an ensemble data assimilation system, one should be able to produce high-quality reanalyses of even the upper troposphere using only surface pressure observations. The errors of such upper-air circulation reanalyses would be comparable to the 2 day errors of current operational weather forecasts.