Latitudinal variations of the convective source and propagation condition of inertio-gravity waves in the tropics
Latitudinal variations of the convective source and propagation condition of inertio-gravity waves in the tropics
复制标题
DOI：
10.1175/jas3891.1
复制
发表时间：
2007-05
影响因子：
3.1
通讯作者：
H. Chun;J. Goh;In‐Sun Song;L. Ricciardulli
中科院分区：
文献类型：
--
作者：
H. Chun;J. Goh;In‐Sun Song;L. Ricciardulli
分别使用高分辨率全球云图像（GCI）和 1 年（1985 年 3 月至 1986 年 2 月）每 6 小时 NCEP-NCAR 再分析数据检查热带地区（30°S–30°N）对流源和惯性重力波（IGW）垂直传播条件的纬度变化。对流源是通过使用 GCI 数据的亮温计算深对流加热 (DCH) 速率来估计的。发现 DCH 的纬度变化全年都很显着。年均DCH最大值与最小值之比为3.2，6-8月(JJA)和12-2月(DJF)平均值要大得多。谱分析表明，DCH的主周期为1天，纬向波长约为1600 km，相速谱为高斯型，峰值位于零相速处。在纬向波数和频域中，IGW 的垂直传播条件由两个因素决定：(i) 纬度，它决定科里奥利参数；(ii) 波传播目标高度范围内的基本状态风结构。研究发现，基态风对150~30 hPa之间平流层低层的波传播条件有显着影响，因此大部分源频谱被滤除。这不仅在存在强负切变的纬度高于15°的地区很突出，而且在赤道附近也很突出，那里与准两年期振荡（QBO）西风相相关的强正切变滤掉了对流源的大部分低频分量。地面频率和纬度之间没有简单的关系；低纬度地区并不总是有利于在平流层观测低频IGW。热带地区的基态风具有季节性、年际和年际变化，不仅对平流层波浪传播条件起着重要作用，而且对对流层对流源的产生也起着重要作用。
Latitudinal variations of the convective source and vertical propagation condition of inertio-gravity waves (IGWs) in the tropical region (30°S–30°N) are examined using high-resolution Global Cloud Imagery (GCI) and 6-hourly NCEP–NCAR reanalysis data, respectively, for 1 yr (March 1985–February 1986). The convective source is estimated by calculating the deep convective heating (DCH) rate using the brightness temperature of the GCI data. The latitudinal variation of DCH is found to be significant throughout the year. The ratio of the maximum to minimum values of DCH in the annual mean is 3.2 and it is much larger in the June–August (JJA) and December–February (DJF) means. Spectral analyses show that DCH has a dominant period of 1 day, a zonal wavelength of about 1600 km, and a Gaussian-type phase-speed spectrum with a peak at the zero phase speed. The vertical propagation condition of IGWs is determined, in the zonal wavenumber and frequency domain, by two factors: (i) latitude, which determines the Coriolis parameter, and (ii) the basic-state wind structure in the target height range of wave propagation. It was found that the basic-state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hPa, and accordingly a large portion of the source spectrum is filtered out. This is prominent not only in the latitudes higher than 15° where strong negative shear exists, but also near the equator where strong positive shear associated with the westerly phase of the quasi-biennial oscillation (QBO) filters out large portions of the lowfrequency components of the convective source. There is no simple relationship between the ground-based frequency and latitude; lower latitudes are not always favorable for low-frequency IGWs to be observed in the stratosphere. The basic-state wind in the Tropics, which has seasonal, annual, and interannual variations, plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere.