Observations of nonclassical frontal propagation and frontally forced gravity waves adjacent to steep topography
Observations of nonclassical frontal propagation and frontally forced gravity waves adjacent to steep topography
复制标题
邻近陡峭地形的非经典锋面传播和锋面强迫重力波的观测
DOI：
--
复制
发表时间：
2001
期刊：
影响因子：
--
通讯作者：
D. Levinson
中科院分区：
文献类型：
--
作者：
P. Neiman;F. Ralph;R. L. Weber;T. Uttal;L. Nance;D. Levinson
通过对科罗拉多锋岭沿线沿着的遥感和现场资料的综合分析，本研究描述了背风面北极锋与地形调制流之间的相互作用。这些相互作用导致了非经典的锋面行为和结构横跨东北部科罗拉多。浅北极锋最初向西南方向前进，朝向前山脉山麓，然后向东撤退。然后，第二股北极气流向西迁移到山麓。在其最初的西南推进过程中，锋面表现出类似障碍物的密度流特征。它最初的进步中断了强大的下坡西北气流与高振幅的山波下游的大陆分水岭，并通过时间减少的密度对比度在整个前由于昼夜加热的冷空气和弱冷平流的暖空气。北极气流的方向和深度也影响锋面传播。浅的，障碍状的前积极产生垂直传播和垂直捕获的重力波，因为它先进的下坡西北气流，导致对流层中部透镜状波云高处跟踪的前。由于锋面进入了一个地区，那里有强烈的下坡风和山波向下游延伸到高平原，科罗拉多东北部的波场包括锋面强迫重力波和真正的山强迫重力波。从每小时的观测计算的一系列的得分参数配置文件揭示了锋前和锋后波环境之间的鲜明对比。因此，分析共振波模式计算的基础上的Scorer参数配置文件显示，波支持在postfrontal制度显着不同的支持在前额环境。这一结果与风廓线观测结果一致，表明在浅锋通道后，垂直运动的幅度在平均海平面以上16公里处大幅下降。
Through the integrated analysis of remote sensing and in situ data taken along the Front Range of Colorado, this study describes the interactions that occurred between a leeside arctic front and topographically modulated flows. These interactions resulted in nonclassical frontal behavior and structure across northeastern Colorado. The shallow arctic front initially advanced southwestward toward the Front Range foothills, before retreating eastward. Then, a secondary surge of arctic air migrated westward into the foothills. During its initial southwestward advance, the front exhibited obstacle-like, density-current characteristics. Its initial advance was interrupted by strong downslope northwesterly flow associated with a high-amplitude mountain wave downstream of the Continental Divide, and by a temporal decrease in the density contrast across the front due to diurnal heating in the cold air and weak cold advection in the warm air. The direction and depth of flow within the arctic air also influenced the frontal propagation. The shallow, obstacle-like front actively generated both vertically propagating and vertically trapped gravity waves as it advanced into the downslope northwesterly flow, resulting in midtropospheric lenticular wave clouds aloft that tracked with the front. Because the front entered a region where strong downslope winds and mountain waves extended downstream over the high plains, the wave field in northeastern Colorado included both frontally forced and true mountain-forced gravity waves. A sequence of Scorer parameter profiles calculated from hourly observations reveals a sharp contrast between the prefrontal and postfrontal wave environments. Consequently, analytic resonant wave mode calculations based on the Scorer parameter profiles reveal that the waves supported in the postfrontal regime differed markedly from those supported in the prefrontal environment. This result is consistent with wind profiler observations that showed the amplitude of vertical motions decreasing substantially through 16 km above mean sea level (MSL) after the shallow frontal passage.