Mesoscale variability in marine winds at mid-latitude
Mesoscale variability in marine winds at mid-latitude
复制标题
中纬度海洋风的中尺度变化
DOI：
--
复制
发表时间：
1984
期刊：
影响因子：
--
通讯作者：
J. G. Wilson
中科院分区：
文献类型：
--
作者：
J. Overland;J. G. Wilson
国家海洋和大气管理局WP-3D飞机在1980年11月和12月的风暴转移和反应试验期间收集了大约350公里的低空(50米和90米)侧风和沿平均风轨迹的风数据。观测到的海洋风场的中尺度变化由三种大气状态的速度相关张量来表征：云街、开放和封闭的蜂窝状对流以及前锋暖空气平流。在旧大陆空气流经较温暖的海洋，产生云街的情况下，垂直于平均风向的近海风场的中尺度变化的主要尺度是27公里。在这种情况下，动量转移的标准偏差是天气尺度(330公里)平均值的13%，它是用假定阻力系数不变的整体空气动力学方法从飞行轨迹的2公里子集计算出来的。开放蜂窝对流的中尺度变化优势尺度为62公里，闭合蜂窝对流的优势尺度为90公里。对于包含这两种单体类型的345公里飞行轨迹，中尺度动量输送(尺度大于2公里；恒定阻力系数)的标准偏差是天气尺度平均值的26%。暖空气平流个例没有可测量的中尺度变率。对于每个区域，可以用来估计中尺度变率的水平速度相关张量的模式与具有速度分量和天气状况相关系数的观测速度相关张量进行了拟合。这种一般模式与将中尺度风场解释为与云型相关的相干结构的集合是一致的，其中，与二维湍流的连续解释不同，在每种天气形势下，风场的空间变异性与物理确定的主导长度尺度(即单体或卷)有关。为了准确描述海面的区域风和通量，风速和温度数据应在主要的中尺度长度尺度上用适当的时间平均或空间平均进行平均，例如可以通过散射法获得，或者应明确说明对中尺度可变性的估计。结果还表明，海洋混合层的垂直通量增强发生在大气边界层结构的长度尺度上。
Wind data were collected by the National Oceanic and Atmospheric Administration WP-3D aircraft on low-level (50 and 90 m) crosswind and along-mean-wind tracks of approximately 350 km during the Storm Transfer and Response Experiment in November and December 1980. Observed mesoscale variations in the marine wind fields are characterized by the velocity correlation tensor for three atmospheric regimes: cloud streets, open and closed cellular convection, and prefrontal warm air advection. The dominant scale of mesoscale variation in the offshore wind field normal to the mean wind direction in the case of old continental air flowing over a warmer ocean, producing cloud streets, was 27 km. For this case, the standard deviation in momentum transfer, which was calculated from 2-km subsets of the flight track by the bulk aerodynamic method assuming a constant drag coefficient, was 13% of the synoptic scale (330km) mean. The dominant scale of mesoscale variation for open cellular convection was 62km, and the dominant scale for closed cellular convection was 90 km. The standard deviation of mesoscale momentum transfer (scales greater than 2 km; constant drag coefficient) for a 345-km flight track containing both cell types was 26% of the synoptic scale mean. The warm air advection case had no measurable mesoscale variability. For each regime a model of the horizontal velocity correlation tensor, which can be used to estimate a mesoscale variability, is fitted to the observed velocity correlation tensor with velocity component and weather regime dependent coefficients. This general model is consistent with an interpretation of the mesoscale wind field as an ensemble of coherent structures, associated with cloud type, in which the spatial variability of the wind field in each weather regime is associated with physically determined dominant length scales (i.e., cells or rolls), as contrasted with a continuum interpretation of two-dimensional turbulence. To accurately describe regional winds and fluxes at the sea surface, wind speed and temperature data should be averaged over the dominant mesoscale length scale with either a suitable time average or a spatial average, such as can be obtained by scatterometry, or an estimate of the mesoscale variability should be explicitly stated. It is also suggested that enhanced vertical flux in the oceanic mixed layer occurs at length scales of atmospheric boundary layer structures.