Do Сyclones Steer Surface Turbulent Heat Fluxes in Mid Latitude Oceans?

Abstract:

Surface turbulent heat fluxes are responsible for variability of surface ocean heat budget on synoptic and interannual scales. This variability is driven by variations of near surface atmospheric characteristics controlled in midlatitudes by atmospheric cyclones. We focus on understanding the mechanisms of synoptic variability of surface turbulent fluxes and on the origins of extreme turbulent fluxes and their impact on the atmospheric dynamics. The main questions addressed in this study are (i) what are the large scale atmospheric conditions associated with extreme ocean surface fluxes and are they related to cyclones, (ii) what is the role of extreme surface fluxes in the variability of oceanic heat content, and (iii) which characteristics of atmospheric cyclones are sensitive to the surface ocean flux signals? To answer these questions, we derived characteristics of the extreme surface fluxes from their empirical probability distributions from the NCEP-CFSR reanalysis, 1979-onwards and analyse them together with cyclone characteristics over the midlatitudinal North Atlantic. Cyclone tracking has been performed using state of the art numerical tracking algorithm applied to the reanalysis SLP at 6-hourly resolution. We argue that the presence of the high pressure system following to the rare part of propagating cyclone is a critical condition for the formation of extreme surface ocean fluxes which are associated with the cyclone-anticyclone interaction zone rather than with cyclone per se. We also demonstrate that the fraction of oceanic heat loss due to extremes linked to the atmospheric circulation. Locally this fraction can be as large as 50%. We also show that over the Gulf Stream more than 60% of cyclogenesis were associated with extreme surface fluxes.