|Title||Forecasts and assimilation experiments of the Antarctic Ozone Hole 2008|
|Publication Type||Technical memorandum|
|Secondary Title||ECMWF Technical Memoranda|
|Authors||Flemming, J, Inness, A, Jones, L, Eskes, H, Huijnen, V, Kinnison, D, Schultz, MG, Stein, O, Cariolle, D, Brasseur, GP|
The 2008 Antarctic ozone hole was one of the largest and longest lasting events in recent years. Predictions of the ozone hole were made in near-real time and hindcast mode with the ECMWF's integrated forecast system. The forecasts were carried out either with or without assimilation of satellite observations from multiple instruments to provide more realistic initial conditions. Three different chemistry schemes were applied for the description of stratospheric ozone chemistry: (i) a linearization of the ozone chemistry, (ii) the stratospheric chemical mechanism of the MOZART-3 chemical transport model (CTM) and (iii) the relaxation to a climatology implemented in the CTM TM5. Without assimilation, the forecasts showed model-specific shortcomings in predicting start time, extent and duration of the ozone hole. The assimilation of satellite observations from the MLS, OMI, SBUV-2 and the SCIAMACHY led to a significant improvement of the forecasts when compared with total columns and vertical profiles from ozone sondes. The combined assimilation of observations from multiple instruments helped to overcome limitations of the ultraviolet (UV) sensors at low solar elevation over Antarctica. The assimilation of data from MLS was crucial to obtain a good agreement with the observed ozone profiles both in the polar stratosphere and troposphere. The ozone analyses by the three model configurations were very similar despite the different underlying chemistry schemes. Bigger differences developed in the initialised forecasts only at the chemically instigated start of the ozone hole. The predictions of the ozone hole closure, which is mainly driven by dynamical processes, benefited much longer from the initialization with analyses. On the third forecast day, the specifics of the chemistry schemes became apparent but the forecasts were still close to the respective analyses. The initialisation with ozone analyses was beneficial at least up to 15 days.