Multivariate analysis of Kelvin wave seasonal variability in ECMWF L91 analyses

Multivariate analysis of Kelvin wave seasonal variability in ECMWF L91 analyses
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ECMWF L91 分析中开尔文波季节变化的多变量分析

DOI：
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发表时间：
2018
期刊：
Atmospheric Chemistry and Physics
影响因子：
6.3
通讯作者：
N. Žagar
N. Žagar
中科院分区：
地球科学1区
文献类型：
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作者：
M. Blaauw;N. Žagar

文献摘要

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抽象。本文提出了线性开尔文波（KW）的多元分析方法 以2007-2013年期间运行的91级ECMWF分析为代表， 重点关注季节性变化。所应用的方法同时过滤 连续层结中的KW风和温度扰动 地球上的大气层三维空间滤波 对流层上部和平流层下部的KW结构是 基于Hough谐波，使用几十个线性化浅水 方程系统的球形地球上的等效深度范围从10公里到 几米。结果提供了全球KW能量谱。它显示出明显的季节性周期与KW活动 主要是在纬向波数1-2，其中高达50%以上的能量是观察到在冬至季节 与北方春季和秋季相比。在对流层上部和平流层下部的KW的季节变化被检查， 与背景风和稳定性的关系。 光谱带通滤波用于将可变性分解为三个周期范围： 季节性、季节内和月内变异组成部分。 结果表明，在对流层上部，随位置的变化，存在一个具有强偶极子结构的缓慢的季节性KW分量 这取决于整个季节中占主导地位的对流外流的位置。其最大强度出现在 在北半球夏季，东半球东风最强的时候。另外两个组成部分 代表垂直传播的千瓦，并观察到全年的季节性变化大部分 发现在波振幅依赖于背景东风和静态稳定性的季节性。
Abstract. This paper presents a multivariate analysis of the linear Kelvin waves (KWs) represented by the operational 91-level ECMWF analyses in the 2007–2013 period, with a focus on seasonal variability. The applied method simultaneously filters KW wind and temperature perturbations in the continuously stratified atmosphere on the spherical Earth. The spatial filtering of the three-dimensional KW structure in the upper troposphere and lower stratosphere is based on the Hough harmonics using several tens of linearized shallow-water equation systems on the spherical Earth with equivalent depths ranging from 10 km to a few metres. Results provide the global KW energy spectrum. It shows a clear seasonal cycle with the KW activity predominantly in zonal wavenumbers 1–2, where up to 50 % more energy is observed during the solstice seasons in comparison with boreal spring and autumn. Seasonal variability in KWs in the upper troposphere and lower stratosphere is examined in relation to the background wind and stability. A spectral bandpass filtering is used to decompose variability into three period ranges: seasonal, intra-seasonal and intra-monthly variability components. Results reveal a slow seasonal KW component with a robust dipole structure in the upper troposphere with its position determined by the location of the dominant convective outflow throughout the seasons. Its maximal strength occurs during boreal summer when easterlies in the eastern hemisphere are strongest. The two other components represent vertically propagating KWs and are observed throughout the year with seasonal variability mostly found in the wave amplitudes being dependent on the seasonality of the background easterly winds and static stability.