OSE with ARPEGE-SH during the YOPP-SH SOP

Within the Year of Polar Prediction- Southern Hemisphere (YOPP-SH) Special Observing Period (SOP) 15/11/2018-15/02/2019, additional observations (such as radiosonde) have been performed in Antarctica and used in real time by global operational numerical weather prediction (NWP) models. However, afterwards, it was difficult to see the impact of this effort in terms of forecast quality especially by comparing with previous same periods. An objective evaluation is necessary at least to provide a feed-back for the “observation’s providers” but also for the NWP community.

Therefore an Observing System Experiments (OSE) was performed with the YOPP-SH version of the global model ARPEGE: ARPEGE-SH and a 4Dvar assimilation. The purpose of this OSE was to remove all the YOPP extra radiosondes in order to retrieve the number of sounding data used during “normal” year (not YOPP).

Unfortunately all the extra radiosondes have been localized at the existing ones, so it was “only” an increase of the frequency not a real change in terms of spatial coverage.

The presentation will briefly describe the ARPEGE-SH configuration and then show some impact in the assimilation cycle with some focus on super-site and specific events. The impact on the forecast quality against observations and ECMWF analysis will be discussed.