Ocean-atmosphere Interaction In The Climate Process--Small Scale Air-sea Flux And Large Scale Tropical Ocean-atmosphere Interaction

Climate variability receives wide attention from the scientific community and the administrative organizations. Now it becomes one of the key research foci within the scope of climate science. Ocean and atmosphere, being the most important two components of the climate system, interact on different spatial and temporal scales. In general, this interaction can be classified into two classes, namely the small-scale interaction and large-scale one. For the small-scale case, the interaction strongly influences the air-sea flux processes. For the large-scale case, the interaction determines the low frequency variability of the climate system, of which the tropical inter-annual variability associated with ENSO is the most representative. The present work focuses on these two aspects.In the first case, the present work tries to provide one solution for the difficulties in determination of the air-sea flux in the coupled climate models, which is realized through explicitly description of the small-scale air-sea interaction process. The coupled atmosphere-ocean-ice-land model has now been one of the most important tools for climate simulation and assessment. However, it still suffers from some defects. The most significant one is the so-called climate drift. When the components of a coupled climate system model are joined together and freed from the constraints of fixed surface boundary conditions, the statistical state of the simulated climate diverges from the initial condition (and generally from the observed climate). Attention has been focused on two major sources of climate drift: lack of equilibrium in the initial condition of the component models (primarily the ocean) and incompatibilities in the fluxes across component interfaces. In the present generation of the coupled climate model systems, the air-sea flux is usually parameterized with the aid of the bulk formula and the transfer coefficient is a unified constant regardless of the real sea state, which is over-simplified and deserves questionable. However, many field experiments have revealed that the air-sea flux is strongly dependent on the sea state. Therefore the ocean surface wave, being a small-scale air-sea interaction process, may play a role in the climate system through its accumulative effects of the flux modulation. Thus Hasselmann (1991) conceived the establishment of the coupled atmosphere-wave-ocean model. This idea is hereby tackled in the present paper. As a first step, one AGCM (LMD) is coupled with one ocean surface wave model (WAM cycle 4) to test its feasibility. It is demonstrated that the coupled model, which takes explicit consideration of the sea state on the flux computation, is capable to give better climate simulation. In addition, the present paper also discovers an interesting fact that the oceanic mechanical forcing through the variation of the sea surface roughness state can influence the atmospheric general circulation in a significant way. Comparing the coupled model results with those from the AGCM alone reveals that the atmospheric response differs in the tropics and mid-to-high latitude region. In the tropical region, the atmosphere shows a baroclinic response while it shows an equivalent barotropic response pattern in the mid-to-high latitude region. This kind of atmospheric response resembles closely that from the SST forcing in the so-called AMIP experiments. Its importance for the climate system deserves further investigation.In the second case, the focus is given on the tropical large-scale ocean-atmosphere interaction associated with ENSO, which is considered as one of the most mechanisms of the global inter-annual climate variability. Progress on ENSO knowledge represents one of the milestone works for oceanography in last century. However, some basic aspects are still open to exploration. The present paper tries to illustrate the basic oceanic and atmospheric variability during the Pacific EL Ni?o/La Ni?a and Indian dipole cases based on the observation and re-analysis data. The atmospheric circulation is d...