本文对定义北半球平流层春季最后增温事件(Stratospheric Final Warming,SFW)爆发日期的三种不同方法进行了比较分析.三种方法分别为:1)基于平流层极夜急流核心纬度带(60°—75°N)逐日纬向平均纬向风最后一次由西风转为东风的时间,简称为逐日风场反转法;2)将月平均纬向风场数据线性插值成逐日数据,然后基于插值后的逐日纬向平均纬向风由西风转为东风的时间,简称为月均风场插值法;3)90°N与60°N之间纬向平均温度经向梯度最后一次由负转正的日期,简称为温度梯度反转法.结果表明,由逐日风场反转法和月均风场插值法得到的SFW爆发日期基本一致,但是当平流层冬末和春初发生爆发性增温时,两种方法确定的SFW爆发日期易出现较大偏差;温度梯度反转法确定的SFW爆发日期早于逐日风场反转法确定的SFW爆发日期,在30 hPa等压面层,两种方法定义的平均日期相差16 d.由于逐日风场反转法在实际使用时更为常见,因此,以该方法为参考,对温度梯度反转法进行修订,结果表明,如果将温度梯度反转法中的阈值由0 K提高为3 K,以上利用温度和风场确定的SFW爆发日期则基本一致.
Abstract
This paper compares three methods in defining the onset of the boreal spring stratospheric final warming(SFW)events,which are based on the final reversal of daily circumpolar zonal wind direction(referred to as UD0),the reversal of zonal wind direction linearly interpolated from the monthly data(referred to as UM0),and the reversal of the meridional gradient of zonal-mean temperature between the North Pole and 60°N(referred to as TG0),respectively.The SFW onset date identified by the UM0 method is basically consistent with that by the UD0 method.However,in the presence of major stratospheric sudden warming events in late winter and early spring,considerable discrepencies are discovered between the results of the two methods.The SFW onset date identified by TG0 tends to be earlier than that by UD0.At 30 hPa,The mean date of SFW by the TG0 method is～16 days earlier than that by the UD0 method.As the UD0 method is more common in practical use,the TG0 method is revised with this method as a reference.The research results show that if the threshold of the TG0 method is lifted from 0 K to 3 K,the SFW onset date in this method has excellent agreement with that by the UD0 method.
关键词
平流层最后增温事件/爆发日期/逐日风场反转/月均风场插值/温度梯度反转
Key words
stratospheric final warming event/onset date/daily zonal wind reversal/monthly zonal wind interpolation/meridional temperature gradient reversal
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