DATE2022-06-22 13:18:32
TITLEVariability of Mediterranean Sea Winter Surface Heat Loss Over the Past 70 Years
AUTHORSSimon Josey (1) ,Katrin Schroeder (2)
  1. 1) National Oceanography Centre, Southampton, (Uk) ,2) Consiglio Nazionale Delle Ricerche, Istituto Di Scienze Marine, Venice (Italy)
ABSTRACTVariability of Mediterranean Sea winter surface heat loss over the past 70 years is discussed using the ERA5 and 20CRv3 reanalyses. The focus is on the North-west Mediterranean and Aegean Seas which are the sites of strongest winter variability. In the North-west Mediterranean, the winter heat loss has weakened by 16 Wm-2 between the two halves of the period spanned by ERA5 (from -154 Wm-2 in 1951-1985 to -138 Wm-2 in 1986-2020) primarily because of reductions in the latent and sensible heat fluxes. In contrast, the Aegean Sea winter heat loss has remained unchanged with a value of -172 Wm-2 in both halves; similar results in each region are obtained with 20CRV3. The contrasting behaviour of the North-west Mediterranean and Aegean is shown to be primarily due to variations in the time evolution of the sea-air humidity and temperature gradients in each region. These gradients have weakened over the past 70 years in the North-west Mediterranean, due to more rapid warming of the near surface atmosphere than the sea surface. The corresponding sea-air temperature gradient in the Aegean has remained near-constant. The different time evolution of these quantities potentially reflects the combined effects of global heating and regional changes in atmospheric circulation (the hypothesis being that circulation changes offset the near surface atmospheric heating in the Aegean Sea but not in the North-west Mediterranean). The shift in the relative strength of the heat loss in the North-west Mediterranean and Aegean Seas has potentially significant consequences for dense water formation at these two sites, the wider Mediterranean Sea circulation and outflow to the Atlantic.