曲线拟合背景场在提取大气重力波参数中的缺陷

利用一次东亚副热带高空急流演变过程的高分辨率数值模拟结果,采用Morlet小波分析和Fourier功率谱分析方法,以3阶和4阶曲线拟合为例,研究了提取大气重力波参数时常用的曲线拟合背景场获取方法的缺陷.结果表明:虽然4阶拟合对原始风廓线的拟合程度高于3阶拟合,但基于4阶拟合背景场得到风速扰动垂直廓线后,所提取的重力波参数和实际情况的差异大于3阶曲线拟合方法的结果.因此,不能将背景场对原始风廓线的拟合程度作为判断重力波参数提取准确率的依据.曲线拟合方法在大多数情况下会使扰动场中包含背景场信号,且所包含的背景场信号强度差异很大,同时还会引入虚假波信号.所以在提取大气重力波参数时,采用曲线拟合方法获取背景场存在缺陷,需要设计更合理的背景场获取方法.

Deficiency of the curve fitting method for the background fields in atmospheric gravity wave parameters estimation

Based on the numerical simulation results for the case of subtropical upper level jet over east Asia, this paper took the 3th-order or 4th-order curve fitting for example to analyze the deficiency of the curve fitting method for background fields widely used in atmospheric gravity wave parameters (AGWPs) estimation with Morlet wavelet transform and Fourier power spectrum techniques. The results showed the deficiency of estimated AGWPs from the wind perturbation profile obtained from the background field with 4th-order curve fitting method was greater than that with 3th-order one, though the 4th-order background field is more realistic than 3th-order background field in simulating the original wind profile. Thus, the degree of fitting original wind profile by background fields cannot become the basis for judging accuracy in gravity wave parameters estimation, which will make the background field signal with different intensity which include the perturbation fields in most cases. And, the false signal would also be introduced. Therefore, it is necessary to develop a suitable method to obtain the background fields of the wind and temperature profiles in AGWPs estimation.