The Impacts of Atmospheric Ice Reduction in the Lower Troposphere on the Snow and Ice Processes over the Arctic

<p>&#160; &#160;Our research revealed a significant reduction of ice content in the lower troposphere with rapid Arctic warming, ranging 60&#176;N-80&#176;N and from ground to ~800hPa. As a result, the ice fraction has decreased in the low clouds; The rainfall events have increased since 1990s; Spring rainfall occurs earlier. These processes are important drivers for the arriving of &#8220;New Arctic". Under the high emission scenario, Arctic rainfall events will be more frequent due mainly to the local warming. Rainfall intensity will also increase, leading to a high probability of extreme rainfall events, and the rainfall extends to the center of Arctic Ocean and inland area of Greenland. The impacts of the above changes on the cryosphere are mainly reflected in the following aspects:</p> <ul> <li>Increased rainfall events will trigger and accelerate snow and ice melting by reducing albedo and releasing latent heat. Rainfall can reduce the snow albedo by 10% in a few hours. Compared with the gradual warming effect of rising temperature and downward longwave radiation, the impact of rainfall is much faster and more efficient;</li> <li>Earlier onset of rainfall events prolongs the melting period by nearly a month in the past 40 years, promoting the melting and shrinking of the cryosphere through positive feedback. The timing of rainfall onset is found to be an important predictor of the sea ice extent except for the well-known melting pond;</li> <li>Rainfall will likely invade inland area of Greenland more frequently with highly amplified jet streams driven by the decreased temperature contrast between the Arctic and the mid-latitude regions. Such events may serve as a harbinger of a more likely wet surface condition across the highest elevations of the ice sheet;</li> <li>With the warming of the climate, the decrease of ice fraction in the low clouds strengthens the shortwave radiation forcing, which slows down the Arctic warming rate in spring season to a certain extent.</li> </ul>