Assimilation experiments with CHAMP GPS radio occultation measurements

摘要: A one-dimensional bending-angle observation operator for assimilating GPS radio occultation (RO) measurements has been integrated into the ECMWF four-dimensional variational assimilation (4D-Var) system. We have performed forecast impact experiments with 60 days of CHAMP RO measurements, in addition to latest set conventional and satellite data that are assimilated operationally, including radiances from Atmospheric Infrared Sounder. It is demonstrated provide extremely good temperature information upper troposphere lower stratosphere. In southern hemisphere (SH), they produce a clear, statistically significant improvement r.m.s. fit radiosonde over day 1 5 range at 300, 200, 100 50 hPa. An improved radiosondes also evident hPa tropics. However, observations degrade 500 geopotential height (500Z) field SH. This appears be mainly caused by erroneous surface pressure increments Antarctica. As result, we modified tangent-linear adjoint routines, prior evaluation model-level pressures heights, order remove sensitivity model values pressure. improves SH 500Z scores, although small degradation still 2 range. A simple method estimating degrees freedom signal (DFS) large system noted applied estimate DFS during 12-hour window. The increase total 4D-Var ∼4%, per profile ∼34. Copyright © 2006 Royal Meteorological Society