It's Snow Joke

  • Mars or Earth? Photo: NASA

    Rare Snow in Atacama Desert. Photo: MODIS Rapid Respose Team at NASA GSFC

    Atacama Desert from space. Photo: NASA World Wind

  • It's Snow Joke
    23.07.2011 13:53

    One of the driest corners of the earth received a surprising 80cm of snow earlier this month. The Atacama Desert receives an average of less than 50mm of rainfall every year and has often gone without any recordable rainfall in consecutive years. Indeed, some parts of the Atacama Desert have not received any rainfall for at least 400 years. An unusually active cold front swept across the region, bringing more snow than the Atacama had received in two decades. Roads were forced to close and emergency services had to rescue motorists trapped in their vehicles. 

    The Atacama Desert is situated close to the Pacific coastline in Chile and extends eastwards up into the foothills of the Andes mountains. The average daytime temperature in winter is 22C (72F) and during the night can reach as low as -2C (28F). In the summer the maximum temperature reaches around 32C (90F) with a night temperature only dipping as low as 16C (61F).

    It is, according to NASA, the driest desert in the world. This is a result of it being virtually cut off from sources of moist air by both the Andes to the east and the Chilean Coast Range immediately to the west. When air is forced to rise over these mountain barriers, it cools, condenses and precipitates on the peaks. It then descends into the Atacama Desert, devoid of all but a fraction of its original moisture.

    However, there is another important contributory factor which gives the Atacama its aridity. The Humboldt Current is a cold ocean current situated along the Pacific coast of Chile. Combined with a semi-permanent area of high pressure which extends eastwards from the Pacific, the cool sea temperature creates a stable coastal inversion layer – temperatures at sea level are much cooler than those a few hundred metres above. This has the effect of inhibiting deep cloud and precipitation development.

    By: Lindsay Dovey