Elevation-Dependent Trends in Precipitation Observed during NAME
Elevation-Dependent Trends in Precipitation Observed during NAME
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DOI：
10.1175/2008mwr2397.1
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发表时间：
2008-12
影响因子：
3.2
通讯作者：
A. Rowe;S. Rutledge;T. Lang;P. Ciesielski;S. Saleeby
中科院分区：
文献类型：
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作者：
A. Rowe;S. Rutledge;T. Lang;P. Ciesielski;S. Saleeby
利用2004年北美季风试验（NAME）增强观测期的雷达资料，研究了降水特征相对于当地地形的日变化趋势和垂直结构。由两个墨西哥气象局（SMN; Mexican Weather Service）的C波段多普勒雷达和NCAR的S波段偏振多普勒雷达（S-Pol）创建的反射率和降雨率的二维合成物被分为四个海拔组：水上，0-1000米（MSL），1000-2000米和大于2000米。使用这些复合材料的降水频率和平均降雨强度的分析揭示了一个强大的降水日趋势类似的NAME事件雨量计网络观察到的。西马德雷西方（SMO）的降水最频繁发生在下午，峰值频率在晚上移到低海拔地区。此外，低海拔地区的降水事件较少，但更大的强度（雨率）比那些在SMO。降水回波分为对流和层状成分，以便检查对流的垂直特性，使用从S-Pol的数据。反射率剖面和回波顶部高度的分析证实，在较低的地形对流更强烈，垂直发展比对流在SMO。根据科罗拉多州立大学NAME高空和地面网格分析估算的暖云深度，平均而言，在较低地形上的深度是SMO上的2倍。使用一个简化的随机模型下降的增长，它表明，这些差异在暖云深度可能解释所观察到的海拔依赖的降水强度的趋势。
Radar data from the 2004 North American Monsoon Experiment (NAME) enhanced observing period were used to investigate diurnal trends and vertical structure of precipitating features relative to local terrain. Two-dimensional composites of reflectivity and rain rate, created from the two Servicio Meteorologico Nacional (SMN; Mexican Weather Service) C-band Doppler radars and NCAR’s S-band polarimetric Doppler radar (S-Pol), were divided into four elevation groups: over water, 0–1000 m (MSL), 1000–2000 m, and greater than 2000 m. Analysis of precipitation frequency and average rainfall intensity using these composites reveals a strong diurnal trend in precipitation similar to that observed by the NAME Event Rain Gauge Network. Precipitation occurs most frequently during the afternoon over the Sierra Madre Occidental (SMO), with the peak frequency moving over the lower elevations by evening. Also, the precipitation events over the lower elevations are less frequent but of greater intensity (rain rate) than those over the SMO. Precipitation echoes were partitioned into convective and stratiform components to allow for examination of vertical characteristics of convection using data from S-Pol. Analyses of reflectivity profiles and echo-top heights confirm that convection over the lower terrain is more intense and vertically developed than convection over the SMO. Warm-cloud depths, estimated from the Colorado State University–NAME upper-air and surface gridded analyses are, on average, 2 times as deep over the lower terrain as compared with over the SMO. Using a simplified stochastic model for drop growth, it is shown that these differences in warm-cloud depths could possibly explain the observed elevation-dependent trends in precipitation intensity.