Observations and numerical modelling of mountain waves over the Southern Alps of New Zealand
Observations and numerical modelling of mountain waves over the Southern Alps of New Zealand
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DOI：
10.1002/qj.49712656909
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发表时间：
2000-10-01
影响因子：
8.9
通讯作者：
Clark, TL
中科院分区：
文献类型：
--
作者：
Lane, TP;Reeder, MJ;Clark, TL
详细的个案研究山波观测新西兰南岛在南阿尔卑斯山实验。这项研究的目的是记录在该区域产生的波，探索高分辨率无线电探空仪数据可用于确定重力波参数的程度，在1996年10月20日的一幅可见光卫星图像上观测到有组织的波云，据认为，这些波云是由部分被困在南阿尔卑斯山上空的背风波本文利用探空资料，计算了部分俘获波的理论水平波长，并与卫星实测值进行了比较，两者符合较好。具体地说，该技术确定无线电探空仪探测的整个深度上的主导水平波长。这种方法使用坐标变换来考虑背景气流的垂直变化，从而考虑垂直波数的垂直变化以及无线电探空仪路径的变化。本文将此方法应用于一个探空观测中，以识别主导波型，并强调在分析山波时，一般不应将探空资料作为瞬时垂直剖面来处理，用一个高分辨率数值模式对观测到的山波进行了模拟，并用其结果检验了分析的一致性。数值模式产生的平流层下部动量通量的水平平均值为-0.02 N m（-2），尽管这个值可能被低估了至少四倍。
A detailed case study of mountain waves observed over the South Island of New Zealand during the Southern Alps Experiment is presented. The purpose of the study is to document the waves generated over this region, to explore the extent to which high-resolution radiosonde data can be used to determine gravity-wave parameters, and to estimate the vertical flux of horizontal momentum produced by flow over the Southern Alps.Organized wave clouds were observed in a visible satellite image on 20 October 1996 and are thought to have been produced by partially trapped lee waves. Using background how fields derived from a radiosonde sounding, the theoretical horizontal wavelength of the partially trapped mode is calculated and agrees well with that measured from the satellite image.A technique, called the horizontal projection method, is developed to analyse radiosonde soundings for mountain waves. Specifically, the technique determines the dominant horizontal wavelength over the entire depth of a radiosonde sounding. This method uses a coordinate transformation to take account of vertical changes in the background flow and, hence, vertical variations in the vertical wave number, as well as changes in the path of the radiosonde. This method is applied to a radiosonde sounding to identify the dominant wave mode, and emphasizes that radiosonde soundings should not, in general, be treated as instantaneous vertical profiles when analysing mountain waves.The mountain waves observed are simulated using a high-resolution numerical model and the results are used to check the consistency of the analysis. The numerical model produces a horizontally averaged value of momentum flux in the lower stratosphere of -0.02 N m(-2) although this value is probably underestimated by at least a factor of four.