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In January of 2016, the Ross Sea sector of the West Antarctica ice sheet experienced a 3-week-long melting episode. Here we quantify the association of the large-extent and long-lasting melting event with the enhancement of the downward longwave (LW) radiative fluxes at surface due to water vapor, cloud, and atmospheric dynamic feedbacks using the ERA-Interim data set. The abnormally long-lasting temporal surges of atmospheric moisture, warm air, and low-level clouds increase the downward LW radiative energy flux at the surface during the massive ice-melting period. The concurrent timing and spatial overlap between poleward wind anomalies and positive downward LW radiative surface energy flux anomalies over West Antarctica due to warmer air temperature and increases in atmospheric water vapor and cloud coverage provide direct evidence that warm and moist air advection from lower latitudes to West Antarctica causes the rapid long-lasting warming and vast ice mass loss in January of 2016.

Plain Language Summary The melting of the fringing ice shelves from below by warm ocean water is thought to be the leading factor responsible for the retreat of the West Antarctica ice sheet in the past several decades. The analysis presented here shows that atmospheric processes through the long-range transport of heat and moisture from lower latitudes to West Antarctica by the atmospheric circulation can lead to temporal surges of downward longwave radiative fluxes at the surface, substantially warming the surface. Atmospheric poleward heat transport plays a key role for individual ice sheet melting events in West Antarctica, such as the ice sheet melting episode over Ross Sea sector of the West Antarctica Ice Sheet in January 2016.