A new monthly climatology of global radiation for the arctic and comparisons with NCEP-NCAR reanalysis and ISCCP-C2 fields

Measurements from the Russian "North Pole" series of drifting stations, the United States drifting stations "T-3" and "Arlis II," land stations, and, where necessary, over the northern North Atlantic and coastal Greenland, empirically derived values from earlier Russian studies are used to compile a new gridded monthly climatology of global (downwelling shortwave) radiation for the region north of 65° N. Spatio-temporal patterns of fluxes and effective cloud transmittance are examined and comparisons are made with fields from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis and those derived from the International Satellite Cloud Climatology Project (ISCCP) C2 (monthly) cloud product. All months examined (March-October) show peak fluxes over the Greenland ice sheet. March, September, and October feature a strong zonal component. Other months exhibit an asymmetric pattern related to cloud fraction and optical depth, manifested by an Atlantic side flux minimum. For June, the month of maximum insolation, fluxes increase from less than 200 W m^-2 in the Norwegian and Barents seas to more than 300 W m^-2 over the Pacific side of central Arctic Ocean extending into the Beaufort Sea. June fluxes of more than 340 W m^-2 are found over the Greenland ice sheet. Effective cloud transmittance, taken as the ratio of the observed flux to the modeled clear sky flux, is examined for April-September. Values for the Atlantic sector range from 0.50-0.60, contrasting with the central Arctic Ocean where values peak in April at 0.75-0.80, falling to 0.60-0.65 during late summer and early autumn. A relative Beaufort Sea maximum is well expressed during June. The NCEP-NCAR and ISCCP products capture 50%-60% of the observed spatial variance in global radiation during most months. However, the NCEP-NCAR fluxes are consistently high, with Arctic Ocean errors in excess of 60 W m^-2 during summer, reflecting problems in modeled cloud cover. ISCCP fluxes compare better in terms of magnitude.