Large-Scale Control on the Patagonian Climate
Large-Scale Control on the Patagonian Climate
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DOI：
10.1175/jcli-d-12-00001.1
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发表时间：
2013-01-01
影响因子：
4.9
通讯作者：
Rojas, M.
中科院分区：
文献类型：
--
作者：
Garreaud, R.;Lopez, P.;Rojas, M.
巴塔哥尼亚位于南美洲南部，是一个广阔而偏远的地区，拥有丰富的过去环境记录，但气象站数量很少。该地区的降水主要是由西风流中的扰动产生的，并受到南部安第斯山脉的强烈影响。迎风面的隆起导致太平洋沿岸和安第斯山脉西坡的高湿条件；相比之下，下坡沉降使东部平原干燥，导致干旱、高度蒸发的条件。作者利用长达 30 年的高分辨率数值模拟的结果，研究了巴塔哥尼亚当地气候（降水和近地表气温）年际变化对大规模环流异常的依赖性。低层纬向风的变化占天气和年际时间尺度降雨量变化的很大一部分。纬向风还通过改变季节性温度平流的强度来控制气温年循环的幅度。还研究了南美洲南部纬向流逐年变化的主要模式。中高纬度地区之间常年存在偶极子。分隔相反符号的风异常的节点会随着季节的变化而移动，导致南半球夏季在巴塔哥尼亚上空形成偶极子，在冬季形成单极子。再分析数据还表明，在过去四十年中，巴塔哥尼亚中北部的西风流量大部分减少，导致安第斯山脉西部出现干燥趋势，但该大陆南端却出现了适度的增加。
Patagonia, located in southern South America, is a vast and remote region holding a rich variety of past environmental records but a small number of meteorological stations. Precipitation over this region is mostly produced by disturbances embedded in the westerly flow and is strongly modified by the austral Andes. Uplift on the windward side leads to hyperhumid conditions along the Pacific coast and the western slope of the Andes; in contrast, downslope subsidence dries the eastern plains leading to arid, highly evaporative conditions.The authors investigate the dependence of Patagonia's local climate (precipitation and near-surface air temperature) year-to-year variability on large-scale circulation anomalies using results from a 30-yr-long high-resolution numerical simulation. Variations of the low-level zonal wind account for a large fraction of the rainfall variability at synoptic and interannual time scales. Zonal wind also controls the amplitude of the air temperature annual cycle by changing the intensity of the seasonally varying temperature advection.The main modes of year-to-year variability of the zonal flow over southern South America are also investigated. Year round there is a dipole between mid-and high latitudes. The node separating wind anomalies of opposite sign migrates through the seasons, leading to a dipole over Patagonia during austral summer and a monopole during winter. Reanalysis data also suggests that westerly flow has mostly decreased over north-central Patagonia during the last four decades, causing a drying trend to the west of the Andes, but a modest increase is exhibited over the southern tip of the continent.