天气可预报性的时空分布

The temporal spatial distributions of weather predictability of different variables

中文关键词:  可预报性，位势高度，温度，纬向风速，经向风速

英文关键词:Predictability, Geopotential height, Temperature, Zonal wind, Meridional wind

中文摘要:

      为了能从非线性误差增长动力学的角度研究大气的可预报性问题，文章引入了可预报性研究的新方法——非线性局部Lyapunov指数。非线性局部Lyapunov指数及其相关统计量能够被用来定量地确定混沌系统可预报性的大小，真正地实现对可预报性的定量化研究。为了把非线性局部Lyapunov指数方法应用到实际的大气可预报性研究中，给出了一种利用大气的实际观测资料估计非线性局部Lyapunov指数的计算方法。在非线性局部Lyapunov指数方法的基础上，文中利用NCEP/NCAR再分析资料，对大气位势高度场、温度场、纬向风场、经向风场等要素场可预报性的时空分布进行了研究，结果表明：（1） 在500 hPa高度层上，对于不同的要素场，其可预报期限的大小以及时空分布规律都不一样；全球大部分地区位势高度场可预报期限最大，温度场和纬向风场次之，而经向风场的可预报期限最小。（2） 在500 hPa高度层上，位势高度场和温度场的纬向平均可预报期限基本上表现为一定的南北纬向带状分布，热带地区和南极地区的可预报期限最大，北极地区次之，南北半球中高纬度地区可预报期限相对较小。纬向风场可预报期限在热带地区最高，但是南北极地区可预报期限与邻近的中高纬度地区差别不大。经向风场可预报期限在南北两极地区最高，南北半球的中纬度和赤道附近地区可预报期限最小。（3） 在垂直方向上，纬向平均高度场、温度场以及纬向风场可预报期限基本上都是随高度升高而增加，高层的可预报期限明显大于低层；经向风场可预报期限随高度的变化比较复杂，不同的纬度有所不同。（4） 可预报性有明显的季节变化，不同要素场可预报期限高低值区的位置和强度随季节都有明显变化，对于全球大部分地区来说，冬季可预报性都大于夏季的。

英文摘要:

      To study the atmospheric predictability from the view of nonlinear error growth dynamics, a new approach using the Nonlinear Local Lyapunov Exponent (NLLE) is introduced by the authors recently. The NLLE and its derivatives can be used to quantify the predictability limit of chaotic dynamical systems. In order to apply the NLLE approach to the study of actual atmospheric predictability, a reasonable algorithm is provided to obtain the estimation of the NLLE and its derivatives by using the observational data. Based on the NLLE approach, the temporal-spatial distributions of weather predictability of different variables including geopotential height, temperature, zonal and meridional wind, are investigated by using the NCEP/NCAR reanalysis data, respectively. The results are summarized as follows: (1) At the 500 hPa level, the temporal-spatial distribution characteristics of the predictability limit are different for different variables. In general, the predictability limit of geopotential height is the largest in most regions, that of temperature and zonal wind the second, and that of meridional wind the smallest. (2) The predictability limits of geopotential height and temperature appear a zonal distribution with the relatively high value over the Antarctic, the tropics and the Arctic, and the relatively low value in the middle-high latitudes of northern and southern hemispheres. The predictability limit of zonal wind is the highest over the tropics, while that over the Antarctic, the Arctic and middle-high latitudes is the lowest. The predictability limit of meridional wind is the highest over the Antarctic and Arctic, while that over the tropics and middle-high latitudes is the lowest. (3) The predictability limits of geopotential height, temperature, and zonal wind are all found to increase with height. The predictability limit is below two weeks in the low troposphere, while the predictability limit is about one month in the low stratosphere. (4) For all variables, the predictability limit is found to vary with the seasons. For the most regions of the northern and southern hemispheres, the predictability limit in winter is higher than that in summer.