The Generalized Equilibrium Feedback Assessment And Its Preliminary Application In Oceanic Feedback To Atmosphere

In the long-term climate change, the atmosphere variance usually is not determined only by a single ocean forcing, but depends on various ocean forcings. How to distill each ocean's contribution to atmosphere in observation is challenged. In the framework of Frankignoul's method (hereafter EFA), we develop the generalized equilibrium feedback assessment (GEFA) method to separate each ocean's influence to atmosphere. Using the unified approach GEFA, we present a comprehensive assessment of the atmospheric response to major ocean variability modes based on NCEP Reanalysis sea surface temperature (SST), 250hPa and 850hPa geopotential height monthly data. Furthermore, using GEFA combined with the singular value decomposition (SVD), we also detect the North Atlantic optimal feedback modes from SST field onto sea surface heat flux and 500hPa geopotential height respectively. The main conclusion is in the following:A new statistic method, the generalized equilibrium feedback assessment (GEFA), is developed to separate the regional SST forcing from each other. Its utility is confirmed by a simple thermal coupled model. And in its simple application of the observed air-sea boundary thermal feedback in North Atlantic, the results not only confirm the dominant negative local feedback of SST anomaly to heat flux, but also detect non-local feedback of gulf region SST anomaly to downstream heat flux in subpolar region.In comprehensive analysis of the observed atmospheric response to major ocean variability modes using GEFA, it is found that the classical response to ENSO consist of two parts, one responding to the tropical Pacific ENSO mode (TP1)and the other to the tropical Indian Ocean Monopole mode (IOM)(also named TI1). The Pacific ENSO mode generates a significant baroclinic Rossby wave response locally over the tropical Pacific as well as equivalent barotropic wave train responses remotely in the extratropics. The IOM mode forces a predominantly zonally symmetric response throughout the tropics as well as in the extratropics. In addition, the modest responses to other oceanic modes are also identified. The North Pacific SST horse-shoe mode appears to generate an equivalent barotropic warm SST-high response locally over the Aleutian Low and to influence the North Atlantic Oscillation (NAO) downstream, while the North Atlantic SST anomaly of tripole mode tends to force a local response on NAO.For the application of GEFA combined with SVD in the observed North Atlantic ocean-atmosphere system, it indicates that the optimal feedback mode of heat flux to SST is still dominated by local negative feedback, with an upper bound of about 40W m ?2 K?1 for basin scale anomalies. As to 500hPa geopotential height optimal response, it seems the North Atlantic Oscillation is very sensitive to the dipole pattern SST forcing, with an upper bound of about 70 mK ?1.In brief, GEFA is a useful statistical method in study of the ocean-atmospheric interaction. The results obtained by GEFA provide the bases for long-term climate prediction. These results also help to understand the mechanism of the oceanic feedback to atmosphere.