Observation And Regional Model Study Of Ocean-to-Atmosphere Forcing Over The Kuroshio Extension In Spring And Its Mechanism

Latest high-resolution satellite microwave measurements are used to study the air-sea interactions over the Kuroshio and its Extension(KE)in spring season, especially over the oceanic fronts.Results indicate that surface wind speed over the KE is positively related to its underlying sea surface temperature(SST),in particular,the surface wind speed and SST are highly correlated when the oceanic fronts are well developed,and ocean hydrodynamic instabilities cause the KE to meander and result in large SST variations.This positive SST-wind correlation over the strong Kuroshio Current and its Extension is opposite to the negative one often observed in basin scale over the North Pacific.The latter correlation is usually considered to be indicative of atmosphere-to-ocean forcing while the former one is clearly indicative of ocean-to-atmosphere forcing.The microwave scatterometer SeaWinds was launched on the QuikBird satellite in June 1999.We refer to this instrument as QuikScat(or QSCAT)to distinguish it from the nearly identical SeaWinds scatterometer on Midori-â…¡(ADEOS-â…¡),launched December,2002.The primary mission of these SeaWinds scatterometers is to measure winds near the ocean surface.They are also useful for some land and sea ice applications.The SeaWinds instruments are the third in a series of NASA scatterometers that operate at Ku-band(i.e.,a frequency near 14 GHz).The first Ku-Band scatterometer was flown on SeaSat in 1978. Eighteen years later,NSCAT was launched on Japan's Midori-â… (ADEOS-â… ) spacecraft in August 1996.The Europeans also fly satellite scatterometers, which operate at C-band(approx.5 GHz),on their ERS spacecrafts.Since 2000,the New Generation Sea Surface Temperature(NGSST) Development Group(Leader:Hiroshi Kawamura)has been working on a new satellite-based SST product,which utilizes benefits of the modem satellite/in situ-based ocean observing systems and overcomes weaknesses of the present operational SST products(Literatures,Sample products).Real-time generation and distribution of the new SST products for open oceans has started.The demonstration operation of NGSST-O Ver.1.0 is carried out at the following WEB/FTP sites Satellite SST observations from infrared radiometers(AVHRR, MODIS)and a microwave radiometer(AMSR-E)are objectively merged to generate the SST product,which is quality-controlled,cloud-free,high-spatial resolution(0.05 degree-gilded),wide-covering(50 degree x 50 degree),and daily SST digital map.Using the satellite-derived SSTs,a first guess(mean SST weighted by the auto-correlations in an observational window)is calculated,and then the grid SSTs are produced through an optimum interpolation scheme with de-correlation scales of 200km in latitude/longitude directions and 5 days in time. In order to represent the small-scale and high-frequency SST variations,these processes have been tested and established.The analyzed area Of new SST (13-63N,116-166E)covers the whole areas of the Okhotk Sea,Bohai/Yellow Sea and East China Sea as well as the western North Pacific Ocean.Since the grid size is 0.05 degree,the pixel and line numbers of SST map are both 1000.A high-resolution regional atmospheric model is used to study the possible mechanism for surface wind adjustment to SST variations.As the regional model is forced by NCEP/NCAR reanalysis and observed SSTs the model well simulates the positive SST-Wind correlation,i.e.,high(weak)surface winds are found to be associated with warm(cold)SSTs.Further analysis demonstrates that the vertical mixing of momentum near the surface proposed by Wallace et al. (1990)is responsible for the atmospheric response to SST variations over the KE oceanic fronts.Namely an increase in SST reduces the static stability of the near-surface atmosphere,intensifying the vertical turbulence mixing and bringing faster moving air from aloft to the sea surface,and vice versa.