基于再分析数据的南大洋区域Ekman流时空分布规律研究

THE SPATIAL AND TEMPORAL DISTRIBUTION OF EKMAN CURRENT IN THE SOUTHERN OCEAN BASED ON REANALYSIS DATA

南大洋Ekman输运是全球大气-海洋耦合气候系统的重要组成部分,对该区域Ekman动力过程的研究极为重要。首先基于实测数据和文献资料,对GEKCO2(Geostrophic and Ekman Current Observatory 2)产品提供的Ekman流数据进行了评估,验证了数据的有效性;并结合CCMP(cross-calibrated multi-platform)、ERA5(the fifth generation European centre for medium-range weather forecasts atmospheric reanalysis)风场数据,采用经验正交函数分析法(empirical orthogonal function,EOF)等方法分析了2010—2018年南大洋Ekman流的时空变化规律。结果表明:(1)南大洋Ekman流速集中在9—11 cm/s,且具有很强的月际变化特征(7月最强,12月最弱);(2)南大洋40°S以北海域是Ekman流速随时间变化较大的区域;(3)南大洋Ekman流速的EOF分析显示:第一模态和风场存在较强的相关性,表现为流速在整体上同时增强或减弱;第二模态和南半球中高纬大气环流存在较强的相关性,表现为以50°S为界南北流速反向变化;(4)Ekman流左偏角度集中在60°—75°,其中概率密度最大值处所对应的角度为67.5°。通过矢量相关分析,得到30°—35°S海域的平均偏角存在月际变化。南大洋的Ekman动力过程对海洋环流和全球气候系统具有重大影响,本文对于进一步理解南大洋的Ekman过程具有一定的参考价值。

Ekman transport in the Southern Ocean is an important part of the global atmosphere ocean coupled climate system.It is very important to study the Ekman dynamic process in this region.The Ekman current data provided by GEKCO2 product was evaluated and its validity verified.In addition,combined with sea surface wind products(CCMP and ERA5),EOF analysis and other methods were used to analyze the spatial and temporal variation of Ekman current in the Southern Ocean from 2010 to 2018.Results show that first,the speed of Ekman current ranged 9—11 cm/s with a strong inter-monthly oscillation(the strongest in July and the weakest in December).Secondly,the speed of Ekman current varied greatly with time north of 40°S in the Southern Ocean.Thirdly,The EOF analysis of the speed of Ekman current indicates that the first mode had a strong correlation with the wind field,in which the speed increased or decreased at the same time on the whole.The second mode had a strong correlation with the middle and high latitude atmospheric circulation in the southern hemisphere,in which the speed from north to south was reversed with 50°S as the boundary.Fourthly,the left deviation angle of Ekman current was distributed in the range of 60°to 75°with the maximum probability density at 67.5°.Through the analysis of complex correlation,it was found that the average deviation angle in the area of 30—35°S varied monthly.This study provides a reference for further understanding of the Ekman process in the Southern Ocean.