Bruce Ingleby, ECMWF
Impact of a large reduction in the number of Russian radiosonde reports
CoauthorsMark Rodwell, Lars Isaksen
Abstract: In January 2015, as a result of budget constraints, Russia cut its radiosonde program from two ascents per day to one. ECMWF performed impact studies (using data from 2013/2014) to look at the likely impact and made representations via WMO. In April 2015 the Russian decision was reversed and the radiosondes went back to two ascents per day. There are 111 radiosonde stations in Russia, some ceased their 00 UTC ascent and others ceased their 12 UTC ascent, the ECMWF trials mirrored this as closely as possible. The 48 hour forecast verification for the cooler months tested (December-February and April) showed 4-10% degradation in 500 hPa height fields over Russia and about 3% degradation in 850 hPa temperature - as measured by root-mean-squared differences from analyses. The signal is also present in winds and relative humidities. At longer lead-times, these degradations first advect east and then affect the entire Northern Hemisphere. These are moderately large forecast impacts. Over Russia radiosondes form the main information source for the lower/mid-troposphere - there are few reports from aircraft ascents/descents and no wind profilers. The uncertainty of surface emissivity (especially when there may be snow/ice on the ground) means that lower-tropospheric satellite sounding channels are not currently used over land. These results show that Russian radiosondes provide a very valuable contribution to the global observing system. Because of the large number of radiosonde stations involved it was possible to get a clear signal - it is much more difficult to assess the impact of a few radiosonde stations when smaller changes are contemplated.