Influence of upper air conditions on the Patagonia icefields
Influence of upper air conditions on the Patagonia icefields
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DOI：
10.1016/j.gloplacha.2006.11.025
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发表时间：
2007-10-01
影响因子：
3.9
通讯作者：
Raymond, C. F.
中科院分区：
文献类型：
--
作者：
Rasmussen, L. A.;Conway, H.;Raymond, C. F.
NCEP-NCAR再分析中记录的高空条件被用来调查1960-1999年期间巴塔哥尼亚冰原上空降水和降雪的变化。显然，尽管总降雨量没有变化，但气候变暖导致降雪量减少。假设一个地点的降雨量与特定临界方向上的相对湿度和风的成分的乘积成正比，在冰场以西的海洋上空的一点，两者都是在850百帕(类似1400米)处；它是以雨还是雪的形式落下，假定取决于该地点高度的温度是高于还是低于零下2摄氏度。由于冰场上或附近的降水记录稀少，无法确定比例常数，因此调查仅限于检查这些高空变量的相对变化。40年来，无论是冬季还是夏季，850百帕的增温都接近于0.5摄氏度，其影响是：(1)从雪到雨的转变类似于降水量的5%，总降水量变化不大；(2)消融区的年融化增加了类似0.5mW.E。至少自1870年以来，冰原一直在减少质量，因此，这一40年的趋势只代表了自小冰期以来适应气候变化的长期趋势的加速。(C)2006爱思唯尔B.V.保留所有权利。
Upper-air conditions archived in the NCEP-NCAR Reanalysis have been used to investigate changes in precipitation and snowfall over the Patagonia icefields during 1960-99. Apparently, whereas total precipitation has not changed, warming has caused a decrease in the amount falling as snow. Precipitation at a site is taken to be proportional to the product of the relative humidity and the component of the wind in a particular critical direction, both at 850 hPa (similar to 1400 m) at a point over the ocean to the west of the icefields; whether it falls as rain or snow is assumed to depend on whether the temperature at the elevation of the site is above or below +2 degrees C. The critical direction is assumed to be 270 degrees, which is perpendicular to the north-south trending Andes and is also the prevailing wind direction in this zone of strong westerlies. Because of the scarcity of precipitation records on or near the icefields, the constant of proportionality cannot be determined, so the investigation is limited to examining relative changes in those upper air variables. Warming at 850 hPa has been similar to 0.5 degrees C over the 40 years, both winter and summer, with the effects that it has: (1) shifted from snow to rain similar to 5% of the precipitation, the total of which has changed little, and (2) increased annual melt in the ablation areas by similar to 0.5 m w.e. The icefields have been losing mass since at least 1870, so this 40-year trend represents only an acceleration of the longer-term trend of adjusting to climate change since the Little Ice Age. (C) 2006 Elsevier B.V. All rights reserved.