Reconstruction Of The Turbulent Heat Flux Data And Its Application In The Air-sea Relationship Over The North Pacific

The turbulent heat flux is the main passageway for air–sea interactions.However,due to lack of long-term observations for the turbulent heat flux,it is difficult to investigate the mechanisms of decadal variabilities in the North Pacific,such as the Pacific Decadal Oscillation.We here reconstructed the long-term turbulent heat flux in the North Pacific for the period 1921-2014 based on observations in the International Comprehensive Ocean-Atmosphere Data Set–International Maritime Meteorological Archive.The reconstructed turbulent heat flux data were testified and applied in the study of air-sea relationship in the North Pacific.In the reconstruction of turbulent heat flux data,in order to reduce possible inhomogeneities from different types of observations,only the reports from ships were selected to construct the turbulent heat flux.The SST,air temperature,wind and humidity are required in the reconstruction of turbulent heat flux data.The biases of these variables were reduced before using.Compared with other variables,the relative humidity was scarce in the early decades,so the linear regression method was applied to supplement the relative humidity data.Subsequently,the turbulent heat flux at each observation was calculated using the COARE3.5 algorithm.The data at each 5×5° grid was interpolated by the MFT distribution.Even by above steps,the turbulence heat flux data were missing in some regions and some time periods,so the DINEOF was employed to make up for the missing part.At this point,we can get the observation based reconstructed turbulent heat flux data over the north Pacific during 1921-2014.In the evaluation of the reconstructed turbulent heat flux products,we find that the reconstructed data are in good agreement with the short-time series available data in terms of climatology,correlation coefficient and trends.In the climatology,the reconstructed turbulent heat flux is basically consistent with the several other data in the spatial distribution,with the important physical feature that the maximum value locating in the Kuroshio and extension area.The reconstructed turbulent heat fluxes are well correlated with other data,with the correlation coefficients over 0.4 in most of the North Pacific.Both the reconstructed turbulent heat flux and other data show similar pattern of the trends.The reconstructed turbulent heat flux data were then compared with the long time series turbulent heat flux—ERA-20 C and20CR.The reconstructed latent heat flux and ERA-20 C latent heat flux are well correlated in the North Pacific;while the reconstructed latent heat flux and 20 CR latent heat flux are well correlated in the east and west of the North Pacific,but less correlated in the central part of the North Pacific,which may be due to the inconsistency of relative humidity between the two data.The reconstructed sensible heat interconnection has a good correlation with the sensible heat flux of ERA-20 C and 20 CR.In addition,the reconstructed data can well reproduce the main characteristics of air-sea interaction in the North Pacific—the atmosphere driving the ocean in most parts of the North Pacific,while the ocean forcing atmosphere in the sub-polar fronts,especially in the Kuroshio and the extensions.Therefore,the reconstructed turbulent heat flux data are reasonable.In the process of air-sea relationship in the North Pacific,different characteristics on inter-annual and decadal scales are found.On the decadal time scale,different time windows(more than seven years)are used to low-pass filtering.The results show that on the decadal time scale,the air-sea relationship in the North Pacific is mainly manifested by the ocean forcing on the atmosphere.On the inter-annual scale,the relationship is slightly different from that on the decadal scale.The ocean forcing the atmosphere is the main process in the area near 40°N in the North Pacific—the area of the junction zone of the subtropical circulation and the subtropical circulation.The gradient of SST there is very large,and the anomaly of ocean activity will cause the anomaly of the atmosphere.In the lower latitudes,the atmospheric driving of the ocean is the main manifestation.In addition,different processes of air-sea relationship dominate in different time scales in the North Pacific in boreal winter.On the decadal scale,it shows that shows that the ocean drives the atmosphere in most parts of the North Pacific Ocean in boreal winter.On the inter-annual time scale,there are two main processes of air-sea interaction on the inter-annual time scale.The atmosphere forces the ocean in most parts of the North Pacific.And the ocean also has a feedback on the atmosphere.Besides the local air-sea interaction in the subtropical region,the tropical oceans also have an impact on the atmosphere in the North Pacific.ENSO can influence the subtropical atmosphere through Pacific-North American pattern(PNA)teleconnection.