Asian dust signatures at Barrow: observed and simulated. Incursions and impact of Asian dust over Northern Alaska

Atmospheric aerosols affect the Earth´s radiation budget both directly, through interactions with solar and terrestrial radiation, and indirectly, as cloud condensation and ice nuclei. Against the typically clean polar atmospheres, small increases in aerosol concentrations can perturb radiative fluxes significantly. During spring 2002, dust storms from the deserts of China and Mongolia were tracked over the Arctic, establishing that such remote regions are not immune to the dispersion of Asian dust. Increased aerosol optical depths and lidar measurements at Barrow, AK, in conjunction with trajectory analyses and dust transport provide corroborating evidence for transport of dust to the Arctic. The primary impact of the dust layer can be determined by examining its radiative properties relative to the underlying snow and intervening pristine background environment. Through a sequence of ground-based visibility measurements of the aerosols coupled with lidar measurements of the layer height, a realistic dust cloud was ported into Moderate Resolution Transmittance (MODTRANT™) code. A suite of MODTRAN calculations, constructed around this cloud description, provided spectrally integrated forcing terms at the surface, along with estimates of the local heating/cooling at altitude, with and without the dust cloud. This then led to a closure experiment where MODTRAN predictions of surface forcing are in remarkably good agreement with measurements for a set of solar-zenith angles and aerosol optical depths.