Observatory and Research on Extreme Phenomena over the Oceans (ORPHEO)
Quilfen, Yves; Chapron, Bertrand; Reul, Nicolas

Thanks to satellite-based observations, extreme weather events such as tropical cyclones or explosive mid-latitude storms and polar lows can be more commonly reported, directly analyzed (e.g. Quilfen et al., 2010, 2011, Reul et al., 2012, Hanafin et al., 2012) or indirectly characterized (Ardhuin et al., 2009, Collard et al, 2009; Delpey et al., 2010). These measurements are critical for short term forecasting, but also offer means to better question the role of extreme conditions for the state of ocean at local and global scales, and effects on ocean circulation and ocean heat transport. Energy inputs in the region of intense storm tracks are indeed thought to represent the main kinetic energy sources necessary to maintain the deep ocean stratified and to strengthens ocean stirring processes. As demonstrated by radiometers onboard the DMSP satellite series, WindSat, TRMM, AMSR-E and now SMOS, as well as by scatterometers onboard the ERS, ADEOS,QuikScat and METOP satellites, unprecedented synoptic observations of surface wind and atmospheric water content are now possible and are revealing the storm structures with impressive details. Satellite estimates donít necessarily provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors characteristics, but the combined use of sensors helps to build methods to retrieve geophysical content. For instance, while certainly limited by its relatively coarse across-track sampling, the altimeter dual frequency radar cross section measurements have been demonstrated to provide very valuable information. Altimeter signals can be processed using specialized algorithms to retrieve the surface wind speed and significant wave height, along with the rain rate in extreme weather events. Furthermore, the SMOS L-band radiometer has a large swath coverage to actually provide measurements the least affected by heavy precipitations. In this study, we then intend to further elaborate on these previous results to explore in depth these capabilities to observe and quantitatively characterize extreme events.