Low-level clouds in wintertime Arctic: Lead impacts and radiative forcing

Abstract:

Arctic low-level clouds, which are ubiquitous and often mixed-phase, exert a large influence on Arctic surface radiative fluxes and Arctic climate feedbacks yet are not well presented in numerical models. Here we first examine the effects of wintertime leads (elongated cracks or openings within the polar ice pack that are open water or thin, recently frozen ice) on low-level clouds over the Arctic basin, using 6-year cloud products from CloudSat and CALIPSO and lead product from AMSR-E. By controlling the large-scale meteorology and utilizing a k-means cluster analysis algorithm to group the low clouds, we find that, in the pan-Arctic winter, less low-level cloud is associated with greater large-scale lead flux (sensible heat flux per unit area over open leads multiplied by lead fractional area), while greater low-level cloud is associated with lower large-scale lead flux, which is just opposite to the present understanding. In addition, preliminary results suggest that less low-level cloud has a higher net longwave cooling at the surface, compared to the greater low-level cloud group (shown in the figure below). Motivated by this, we then use a synergistic measurement from the A-Train remote sensors to retrieve the radiative properties of the single-layer low-level clouds, especially those generated by wintertime leads, using a suite of algorithms. Case studies and characteristics of the Arctic low-level cloud properties, with a focus on longwave cloud radiative forcing at the surface and the longwave vertical cloud radiative heating, will be discussed. These results provide insights into evaluating GCM coarse simulations that parameterize boundary layer clouds when budgeting the Arctic radiative energy.