The Footprints of 16-Year Trends of Arctic Springtime Cloud and Radiation Properties on September Sea-Ice Retreat

The most prominent September sea-ice decline during the period of 2000-2015 occurs over the East Siberian Sea, the Laptev Sea, and the Kara Sea where we define our area of focus (AOF: 78°- 85°N, 60°-155°E). In this study, we investigate linear trends of springtime (March-June) cloud and radiation properties over the Arctic (defined as latitudes north of 70 °N in this study) using 16 years of NASA Clouds and the Earth’s Radiant Energy System (CERES) satellite observations. Spatial distributions show that the most visible increase of springtime cloud fraction (CF) are found through mid-March to mid-May. Similarly, cloud water path (CWP) increases along with CF over the Kara Sea and the Laptev Sea through March and April. Due to the positive feedback of clouds in the Arctic, the surface downward longwave (LW_down) flux significantly increases over a fan-shaped area from the central Arctic Ocean to the coasts of Russia in March through mid-April. As for the surface downward shortwave (SW_down) flux, the most discernable change begins in mid-April; a one-month lag behind that of the CF, CWP, and LW fluxes. The 16-year correlation patterns of CF, CWP, and LW fluxes exhibit nearly simultaneous signals as their correlations change from positive in spring (March, April, and May; MAM) to negative in early summer (mid-June) over the AOF, which is an important indicator of September sea-ice retreat. However, statistically significant positive correlations between the surface SW_down flux and September sea-ice concentration (SIC) are only found in April. The partial correlations are also calculated, indicating that the impacts of springtime net LW/SW fluxes on relationships between clouds and September sea-ice extent (SIE) vary with time, while clouds play critical roles in establishing connections between September SIE and radiative fluxes.