Comparative Analysis of Surface Heat Fluxes in the East Asian Marginal Seas and Its Acquired Combination Data
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Eight different data sets are examined in order to gain insight into the surface heat flux traits of the East Asian marginal seas. In the case of solar radiation of the East Sea (Japan Sea), Coordinated Ocean-ice Reference Experiments ver. 2 (CORE2) and the Objectively Analyzed Air-Sea Fluxes (OAFlux) are similar to the observed data at meteorological stations. A combination is sought by averaging these as well as the Climate Forecast System Reanalysis (CFSR) and the National Centers for Environmental Prediction (NCEP)-1 data to acquire more accurate surface heat flux for the East Asian marginal seas. According to the Combination Data, the annual averages of net heat flux of the East Sea, Yellow Sea, and East China Sea are -61.84, -22.42, and -97.54Wm-2, respectively. The Kuroshio area to the south of Japan and the southern East Sea were found to have the largest upward annual mean net heat flux during winter, at -460- -300 and at -370- -300Wm-2, respectively. The long-term fluctuation (1984-2004) of the net heat flux shows a trend of increasing transport of heat from the ocean into the atmosphere throughout the study area.Keywords:
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Abstract. Estimations from meteorological stations indicate that the surface sensible heat flux over the Tibetan Plateau (TP) has been decreasing continuously since 1980s, and modeling studies suggest that such changes are likely linked to the weakening of the East Asian Monsoon through exciting Rossby wave trains. However, the spatial and temporal variations in the surface sensible and latent heat fluxes over the entire TP remain unknown. This study aims to characterize the monthly surface sensible and latent heat fluxes at 0.5° over the TP from 1984 to 2007 by synthesizing multiple data sources including ground measurements, reanalysis products, and remote sensing products. The root mean square errors (RMSEs) from cross-validation are 11.1 W m−2 and 17.8 W m−2 for the monthly fused sensible and latent heat fluxes, respectively. The fused sensible and latent heat flux anomalies are consistent with those estimated from meteorological stations, and the uncertainties of the fused data are also discussed. The annual sensible heat flux over the TP is shown to be decreasing by −1.1 W m−2 deacade−1 with dominant decreasing in summer (−3.9 W m−2 deacade−1), while the latent heat flux shows a decrease (increase) in spring (autumn) but at a magnitude less than that of the sensible heat flux. Such decreased tendency of the fused sensible and latent heat flux over the TP is consistent to the weakened East Asian Monsoon as well as the solar dimming. The associations among sensible and latent heat fluxes and the related surface anomalies such as mean temperature, temperature range, snow cover, and Normalized Difference Vegetation Index (NDVI) in addition to atmospheric anomalies such as cloud cover and water vapor show seasonal dependence, suggest that the land–biosphere–atmosphere interactions over the TP could display nonuniform feedbacks to the climate changes. It would be interesting to disentangle the drivers and responses of the surface sensible and latent heat flux anomalies over the TP in future research from evidences of modeling results.
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Sensible heat flux is an important index for reflecting exchange intensity at surface-atmosphere interface.With the fast development of Eddy Covariance(EC) technique,the local sensible heat flux measurement becomes easier and more reliable.To study regional or global exchanges,the pixel-size flux measurement becomes an important and key step for up-scaling.Large Aperture Scintillometer(LAS) is the best instrument for measuring pixel-size sensible heat flux.To evaluate its accuracy and uncertainty,in this paper,the sensible heat fluxes over cropland measured by LAS and EC methods were compared,especially the reasons for errors and uncertainties were analyzed.It shows that: ①No matter in daytime or nighttime,the changing trends of the sensible heat flexes by two methods are the same.The relationship between them is very good,especially during strong exchange periods.②There are still differences between two sensible heat fluxes.The mean abstract difference is less than 50 W/m2.Generally,when daytime flux is weak(about less than 70 W/m2),the flux measured by LAS(H LAS) is larger than that by EC(HEC),and when flux is strong,HLAS is smaller than HEC.③Due to the heterogeneous surface,the LAS footprint will be affected by the wind speed and wind direction.Advection may induce the uncertainty for LAS sensible heat flux.In addition,based on all the variables and parameters for LAS equations,the possible sources of the uncertainty,including the uncertainty of EC method and its effect on Bowen ratio,the inaccuracy and changeable parameters(e.g.zero plane displacement and surface roughness etc.) were analyzed.
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Different methods of measurement of momentum and sensible heat flux densifies are presented and compared above a gras covered fallow. The aerodynamic (AD) and eddy covariance (EC) methods are presented and compared for both momentum and sensible heat measurements. In addition, the temperature fluctuation (TF) method is compared to the HEC method for the sensible heat flux measurement. The AD and EC methods are in good agreement for the momentum flux measurements. For the sensible heat flux, the AD method is very sensible to temperature errors. So it is unusable during night and gives biased estimations during the day. The TF method gives only estimations of the sensible heat flux. It is in good agreement with the EC method during the day but diverges completely during night, being unable to disceming positive from negative fluxes. From the three methods, the EC method is the sole that allows to measure continuously both momentum and sensible heat flux but it requires a loud data treatment. We present in this paper the algorithm used for this treatment.
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Large Aperture Scintillometers (LAS), Bowen ratio and eddy covariance measurements and other observed data were employed to study sensible heat flux over homogeneous bare soil surface from March 20th to April 20th, 2002, at XiaoTangshan area, Beijing. The diurnal variation of sensible heat flux from LAS is analyzed in this paper, and the relation between sensible heat flux and weather conditions is discussed. Moreover, the related coefficient between LAS based surface sensible heat fluxes and the influencing factors such as soil weight moisture content in various depths, soil surface temperature and wind speed were analyzed. The analysis could help us to improve the accurate of LAS based surface sensible heat flux. Further, the comparisons of the scintillometer flux measurements with the measurements of Bowen ratio and eddy correlation methods were done in order to make more research on scaling-up of surface sensible heat flux from point to region.This investigation showed that LAS measurements were ideal for long-term monitoring over spatial scales relevant to atmospheric models and remote sensing observations. The conclusion was to be obtained that (1) diurnal variation characteristic of sensible heat flux was similar to that of air temperature under different weather conditions, having a peak value. Generally the peak values were different for different weather conditions. The sensible heat flux in fine day was about twice than that in cloud shadow; (2) the relation between soil weight moisture content and LAS based surface sensible heat flux was negative, soil weight moisture content in 10cm had the largest impact on LAS based surface sensible heat flux and the correlation coefficients were over -0.87; (3) the relation between soil surface temperature and LAS based surface sensible heat flux was positive, and the correlation coefficients were over 0.9;(4) the impact of wind speed on LAS based surface sensible heat flux was small and the correlation coefficients were below 0.5; (5) The sensible heat flux obtained using the eddy correlation, Bowen ratio and scintillometer methods showed good agreement, and the correlation coefficients were normally over 0.8.
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