Near-tropopause bias in the Russian radiosonde-observed air temperature during the YOPP special observing periods in 2018

Abstract Taking advantage of a unique configuration of upper-atmospheric observing stations, we used enhanced radiosonde observations acquired during the Year of Polar Prediction (YOPP) at Ice Base Cape Baranova in 2018 to quantify the observational bias of a nearby station, i.e., GMO IM. E. K. Fedorova located 184 km to the southeast. Radiosonde observations from Fedorova are transmitted to the Global Telecommunications System and thus assimilated into numerical forecast products; however, those from Baranova are not, providing a situation favorable for quantifying observational bias. In comparison with the background field of the ERA5 reanalysis dataset, the Fedorova temperature profile exhibited cold bias in the lower stratosphere during the cold season in addition to a periodic warm/cold bias dipole in the upper troposphere and lower stratosphere. It is concluded that such bias is the product of both radiosonde sensor error and radar inaccuracies at Russian observational stations, given a similar result found at the Yuzhno-Sakhalinsk station.