Summer atmospheric conditions over the Japan/East Sea

Abstract

Abstract Atmospheric conditions over the Japan/East Sea (JES) during the 1999 warm season (May–August) were investigated using research vessel surface and sounding observations in conjunction with coastal station and moored buoy meteorological data. In the broad center of the sea, surface winds were weak and variable with a tendency to be northward in direction. Air temperatures were close to the sea-surface temperature but warmer on average. The lower atmospheric profiles were weakly unstable or stable with shallow inversions. The summer surface heat flux was dominated by radiation components. The large solar short-wave flux caused a large net gain of heat by the sea that was unchecked by the weaker, long-wave flux. Sensible and latent heat fluxes were both small due to modest air–sea temperature differences and weak winds. The surface wind stress was also weak. European Center for Medium-range Weather Forecasting (ECMWF) model surface fields compare favorably with our ship measurements in both summer of 1999 and the winter of 2000. The ECMWF model analysis followed the observed synoptic scale variations well but missed smaller scale variations. The ECMWF air temperature, dew point, pressure, wind speed, and wind direction were correlated with ship values at 0.8 or better. ECMWF forecasts and ship measurements of surface heat fluxes were well related. In the center of the JES, net fluxes in the winter and summer were correlated to 0.7–0.9, with winter the greater. ECMWF short-wave heat flux tended to exceed the ship-based values by 25–55 W/m2. ECMWF wind stress magnitude was best correlated with winter ship measurements, with correlations that reached 0.76–0.89, while wind stress components were more poorly correlated. In both seasons, ECMWF underestimated the wind stress by 15–25%. Monthly mean climatologies of the JES surface heat flux and wind stress were computed using the 1991–2001 ECMWF surface flux time series. The annual heat flux cycle varies from a maximum heating of +182 W/m2 in June to a maximum cooling of −322 W/m2 in December with the greatest loss at the SW edge of the sea. The annual-mean flux is −48 W/m2. The monthly mean wind stress in winter is nearly four times the mean summer value of 0.057 N/m2, with the winter stress towards the S–SE replaced by stress towards the N–NE in summer. The strongest stresses are over the North-central portion of the sea. Our ship/model comparisons suggest that the ECMWF heat flux is biased roughly 25–55 W/m2 high due to systematic model short-wave flux overestimation and that the ECMWF wind stress is biased roughly 15–25% low due to model under-estimation of wind stress.