海气通量涡相关法计算中的时间尺度分析

基于黄海上连续14 d的浮标观测资料,采用多尺度分解法确定了海气通量涡相关法计算中的截断时间尺度,并分析了该截断时间尺度的特征及其对感热通量计算的影响。研究结果是:由多尺度分解法获得的湍通量截断时间尺度可将总通量中湍通量和中尺度通量分离开来,截断时间尺度随着湍流强度或水平风速的增加而增加,且感热通量的截断时间尺度大于动量通量的截断时间尺度;在弱湍流状态下(σw<0.3 m/s),动量通量和感热通量的截断时间尺度主要分布在100 s左右,湍通量和总通量之间差别较大;在湍流较强时(σw>0.3 m/s),动量通量和感热通量的截断时间尺度主要分布在800 s左右,湍通量和总通量之间差别较小;通过计算和分析不同截断时间尺度下感热通量的平均值和不确定性,可以看出截断时间尺度对感热通量的平均值的影响较小,但对感热通量的不确定性有很大的影响,这两种影响之间的差别会随着湍流强度的增加而减小。海气通量涡相关法计算中,正确的截断时间尺度的选取可以获得真实可靠的海气通量数据,也为进一步认识和了解上层海洋与大气之间的相互作用提供重要的科学依据。

Mean properties of mesoscale eddies in the Kuroshio recirculation region

Using a 19-year altimetric dataset, the mean properties and spatiotemporal variations of eddies in the Kuroshio recirculation region are examined. A total of 2 001 cyclonic tracks and 1 847 anticyclonic tracks were identifi ed using a geometry-based eddy detection method. The mean radius was 57 km for cyclonic eddies and was 61 km for anticyclonic eddies, respectively, and the mean lifetime was about 10 weeks for both type eddies. There were asymmetric spatial distributions for eddy generation and eddy termination, which were domain-dependent. Mean eddy generation rates were 2.0 per week for cyclonic eddies and were 1.9 per week for anticyclonic eddies. Both type eddies tended to deform during their lifetime and had different propagation characteristics, which mainly propagated westward and southwestward with velocities 4.0–9.9 cm/s, in the Kuroshio recirculation region. Further discussion illustrates that the eddy westward speed maybe infl uenced by the combined effect of vertical shear of horizontal currents and nonlinearity of eddy. To better understand the evolution of eddy tracks, a total of 134 long-lived tracks(lifetime ≥20 weeks) were examined. Comparison between short-span eddies(lifetime ≥4 weeks and <20 weeks) and long-lived eddies is also conducted and the result shows that the short-span and long-lived eddies have similar time evolution. Finally, eddy seasonal variations and interannual changes are discussed. Correlation analysis shows that eddy activity is sensitive to the wind stress curl and meridional gradient of sea surface temperature on interannual timescales. Besides, the strength and orientation of background fl ows also have impacts on the eddy genesis.

Wavelet Analysis and Nonparametric Test for Climate Change in Tarim River Basin of Xinjiang During 1959-2006

Using wavelet analysis,regression analysis and the Mann-Kendall test,this paper analyzed time-series(1959-2006) weather data from 23 meteorological stations in an attempt to characterize the climate change in the Tarim River Basin of Xinjiang Uygur Autonomous Region,China.Major findings are as follows:1) In the 48-year study period,average annual temperature,annual precipitation and average annual relative humidity all presented nonlinear trends.2) At the 16-year time scale,all three climate indices unanimously showed a rather flat before 1964 and a detectable pickup thereafter.At the 8-year time scale,an S-shaped nonlinear and uprising trend was revealed with slight fluctuations in the entire process for all three indices.Incidentally,they all showed similar pattern of a slight increase before 1980 and a noticeable up-swing afterwards.The 4-year time scale provided a highly fluctuating pattern of periodical oscillations and spiral increases.3) Average annual relative humidity presented a negative correlation with average annual temperature and a positive correlation with annual precipitation at each time scale,which revealed a close dynamic relationship among them at the confidence level of 0.001.4) The Mann-Kendall test at the 0.05 confidence level demonstrated that the climate warming trend,as represented by the rising average annual temperature,was remarkable,but the climate wetting trend,as indicated by the rising annual precipitation and average annual relative humidity,was not obvious.