Weatherwatch: ​why does Antarctic ice melt in the depths of winter?

Recent research on the rate of Antarctic ice melt points to the effect of warm föhn winds

Scientists have long known that the amount of ice in the Antarctic is steadily decreasing. They were surprised, however, to discover recently that up to a quarter of the melting occurs in the depth of winter, when the average temperature is 15C below freezing. The melting is caused by a phenomenon called the föhn effect.

The föhn or foehn wind was first noted in the Alps, and occurs when a wind blowing over mountains descends on the far side. The increase in pressure at lower altitude causes the mass of air to warm up by about one degree per hundred metres. Such a wind blowing down from a high mountain range can easily rise above freezing. The Chinook wind in the Rocky Mountains is sometimes called “snow eater” for its capacity to strip snow from the slopes.