STRUCTURE AND SEASONALITY OF INTERANNUAL AND INTERDECADAL VARIABILITY OF THE GEOPOTENTIAL HEIGHT AND TEMPERATURE-FIELDS IN THE NORTHERN-HEMISPHERE TROPOSPHERE
STRUCTURE AND SEASONALITY OF INTERANNUAL AND INTERDECADAL VARIABILITY OF THE GEOPOTENTIAL HEIGHT AND TEMPERATURE-FIELDS IN THE NORTHERN-HEMISPHERE TROPOSPHERE
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DOI：
10.1175/1520-0442(1993)006
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发表时间：
1993-11-01
影响因子：
4.9
通讯作者：
LAU, KH
中科院分区：
文献类型：
--
作者：
WALLACE, JM;ZHANG, Y;LAU, KH
本文根据1946年以来北方半球热带外大气环流的NMC分析资料，研究了500-hPa高度场、海平面气压场和1000-500-hPa厚度场的年际和年代际变化的空间分型和季节特征。冬季季节平均500 hPa高度场的主导经验正交函数（θ）与太平洋/北美（PNA）遥相关型密切相关。其扩张的时间序列显示出一种趋势，从记录早期的主要负值（低于加拿大西部的正常高度）到20世纪80年代的主要正值。海平面气压的主导波在夏季和冬季是相似的，包含北大西洋涛动（NAO）的元素和极地和温度纬度之间的纬向对称的“跷跷板”。夏季和年平均500 hPa高度和厚度的主要季节变化特征在整个南半球几乎是同极性的。膨胀系数的时间序列与半球平均厚度的时间序列有很强的相关性。我们把这种模式称为“背景场”的表现形式，其对半球平均温度的线性依赖比其空间结构的细节更重要。这种背景场全年都有明显的存在，但在PNA型和其他区域遥相关型最弱的夏季表现得最为明显。它在厚度场中比在位势高度场中更明显的事实表明，它主要与热变率有关，而不是与动力变率有关。它的膨胀系数的时间序列是占主导地位的年代际时间尺度上的变化：它占一半的半球积分方差的厚度场与扰动周期超过5年。在1955年至1963年的NMC分析中，半球平均厚度和500百帕高度的大幅度和可能的虚假下降对与背景场有关的变化有很大的贡献，但是夏季和年平均厚度场的主导模态彼此之间以及与半球的主导模态之间仍然存在着很强的相关性，平均厚度，即使1963年之前的年份被排除在记录之外。地面气温资料表现出定性上类似的行为，从100年GCM模拟中得出的北半球830-515 hPa外热带厚度场也是如此，其中海表温度是根据气候平均年周期规定的。冬季PNA样型的长期趋势，加拿大西部的高度和温度上升，自20世纪70年代后期以来，它对半球平均冬季表面空气温度的大幅上升有很大的贡献，但它对半球平均高空温度或夏季表面空气温度的影响很小，这并没有上升到足以完全抵消20世纪50年代和60年代初的下降。
Spatial Patterns and seasonality of interannual and interdecadal variability in the 500-hPa geopotential height, sea level Pressure, and 1000-500-hPa thickness field are examined based on NMC analyses over the Northern Hemisphere extratropics from 1946 onward. The leading empirical orthogonal function (EOF) of wintertime seasonal mean 500-hPa height is closely related to the Pacific/North American (PNA) teleconnection pattern. The time series of its expansion exhibits a trend from predominantly negative values (below-normal heights over western Canada) in the early part of the record to predominantly positive values during the 1980s. The leading EOF of sea level pressure, which is similar in summer and winter, contains elements of the North Atlantic Oscillation (NAO) and a zonally symmetric ''seesaw'' between polar and temperature latitudes. Its expansion coefficient exhibits relatively little memory from season to season or from year to year.The leading EOFs of summertime and annual-mean 500-hPa height and thickness are of the same polarity throughout almost the entire hemisphere. The time series of their expansion coefficients are strongly correlated with the time series of hemispheric-mean thickness. We refer to such modes as manifestations of a ''background field'' whose linear dependence on hemispheric-mean temperature is more important than the details of its spatial structure. Such a background field is evidently present year-round, but it shows up most clearly during summer when the PNA pattern and other regional teleconnection patterns are weakest. The fact that it is more pronounced in the thickness field than in the geopotential height field suggests that it is primarily associated with thermal, rather than dynamical, variability. The time series of its expansion coefficient is dominated by variations on the interdecadal time scale: it accounts for half the hemispherically integrated variance of the thickness field associated with perturbations with periods longer than five years. The large and possibly spurious drop in hemispherically averaged thickness and 500-hPa height in the NMC analyses between 1955 and 1963 contributes substantially to the variance associated with the background field, but the leading modes of the summertime and annual-mean thickness fields remain strongly correlated with one another and with hemispheric-mean thickness even when the years prior to 1963 are excluded from the record. Surface air temperature data exhibit qualitatively similar behavior, as does the extratropical Northem Hemisphere 830-515-hPa thickness field derived from a 100-year GCM simulation in which sea surface temperature is prescribed in accordance with the climatological mean annual cycle.The long-term trend in the wintertime PNA-like pattern, with rising heights and temperatures over western Canada, has contributed substantially to the rather large rise in hemispheric-mean wintertime surface air temperature since the late 1970s but it has had little if any effect on the hemispheric mean temperature aloft, or on summertime surface air temperatures, which did not rise enough to completely offset the declines in the 1950s and early 1960s.