Surface freshwater flux variability and recent freshening of the North Atlantic in the eastern subpolar gyre
Surface freshwater flux variability and recent freshening of the North Atlantic in the eastern subpolar gyre
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DOI：
10.1029/2004jc002521
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发表时间：
2005-05-14
影响因子：
3.6
通讯作者：
Marsh, R
中科院分区：
文献类型：
--
作者：
Josey, SA;Marsh, R
[1]利用大气模式再分析和观测数据，研究了1960年至今，淡水（降水蒸发（P-E））的海气通量的变化及其与北大西洋副极地环流东半部观测到的淡水化的联系。从国家环境预测中心/国家大气研究中心和ERA-40再分析中获得了类似的结果，每一个都显示了20世纪70年代中期环流区域的P-E（主要是由于降水增加）的主要增加，从大约0.10 m yr（-1）增加到0.27 m yr（-1）。这一增长得到了冰岛、法罗群岛和爱尔兰独立雨量计观测记录的支持。在以东环流为中心的一个盒子上进行积分，1975 - 1989年期间的大气-海洋淡水通量比1960 - 1974年的早期增加了4 × 10 ~（12）m ~ 3。这一增加大约是与大盐度异常等主要平流事件相关的淡水过剩的两倍。研究了P-E的增加与该地区大气变率的两种主要模式，即北大西洋涛动（NAO）和东大西洋模式（EAP）之间的联系。EAP被认为是增加的主要原因，与NAO只发挥了次要作用。通过与北纬60度水文测量结果的比较，还研究了表面淡水通量趋势对海面盐度的影响，该测量结果显示自20世纪70年代中期以来的淡水化。所观察到的淡水化可以在很大程度上解释为对海气淡水交换变化的直接反应。
[1] Variability in the air-sea flux of freshwater (precipitation-evaporation (P-E)) and its connection to the observed freshening of the eastern half of the North Atlantic subpolar gyre over the period 1960 to present is investigated using atmospheric model reanalyses and observational data. Similar results are obtained from both the National Centers for Environmental Prediction/National Center for Atmospheric Research and ERA-40 reanalyses, each of which shows a major increase in P-E ( primarily due to increased precipitation) in the gyre region in the mid-1970s, from about 0.10 m yr(-1) to 0.27 m yr(-1). This increase is supported by independent rain gauge observations recorded in Iceland, the Faeroes, and Ireland. When integrated over a box centered on the eastern gyre, the atmosphere to ocean freshwater flux in the period 1975 - 1989 is 4 X 10(12) m(3) greater than that in the earlier period 1960 - 1974. This increase is about twice as large as the freshwater excess associated with major advective events such as the Great Salinity Anomaly. The link between the increase in P-E and the two major modes of atmospheric variability in the region, the North Atlantic Oscillation (NAO) and the East Atlantic Pattern (EAP), is investigated. The EAP is found to be the dominant cause of the increase, with the NAO only playing a minor role. The impact of the surface freshwater flux trend on sea surface salinity is also examined through comparison with hydrographic measurements at 60 degrees N, which show freshening since the mid-1970s. The observed freshening can be largely explained as a direct response to changes in the air-sea freshwater exchange.