Airborne lidar observations in the inflow region of a warm conveyor belt
Airborne lidar observations in the inflow region of a warm conveyor belt
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DOI：
10.1002/qj.827
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发表时间：
2011-07
影响因子：
8.9
通讯作者：
A. Schäfler;A. Dörnbrack;H. Wernli;C. Kiemle;S. Pfahl
中科院分区：
文献类型：
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作者：
A. Schäfler;A. Dörnbrack;H. Wernli;C. Kiemle;S. Pfahl
暖传送带（WCBs）是与温带气旋相关的关键气流结构。它们将来自气旋温暖区域的潮湿空气输送到靠近对流层顶的极向上位置，从而形成了细长的云带、强烈的潜热和地面降水。本研究利用基于轨迹的方法研究了不同运动中湿度和风的机载激光雷达观测的综合数据集，以确定与wcb的“幸运相遇”。2007年7月19日，中欧欧洲THORPEX区域运动（ETReC 2007）期间，一次飞越伊比利亚半岛的上游飞行与两个wbc相交：一个在上升开始3天后的对流层上层流出区，另一个在强上升之前的西班牙上空的边界层流入区。将激光雷达湿度测量值与欧洲中期天气预报中心（ECMWF）的分析场进行比较，发现在这个低对流层WCB流入区域（平均约为1 g kg - 1(14%)，峰值偏差高达7 g kg - 1），存在显著的正偏差，相当于对模拟湿度的高估。值得注意的是，这种巨大的偏置发生在一个潜在的动态高度相关的气团中，该气团随后将在WCB内被提升到对流层上层。拉格朗日水汽源诊断显示，这些大的水汽偏差发生在气团中，根据ECMWF的分析，这些气团从西地中海连贯地输送到西班牙，并在埃布罗河谷经历了强烈的水汽吸收。这表明，地面蒸散发、水平水汽平流和大气边界层水汽的湍流垂直输送的不准确可能导致ECMWF分析中西班牙夏季WCB流入区低对流层湿度的错误。版权所有©2011英国皇家气象学会
Warm conveyor belts (WCBs) are key flow structures associated with extratropical cyclones. They transport moist air from the cyclone's warm sector poleward and upward close to the tropopause level, leading to the formation of elongated cloud bands, intense latent heating and surface precipitation. In this study a comprehensive dataset of airborne lidar observations of moisture and wind from different campaigns has been investigated with a trajectory‐based approach to identify ‘lucky encounters’ with WCBs. On 19 July 2007, an upstream flight over the Iberian Peninsula during the European THORPEX Regional Campaign (ETReC 2007) in Central Europe intersected two WCBs: one in the upper tropospheric outflow region about 3 days after starting the ascent, and the other one in the boundary layer inflow region over Spain just prior to the strong ascent. Comparison of the lidar humidity measurements with analysis fields from the European Centre for Medium‐Range Weather Forecasts (ECMWF) reveals significant positive deviations, equivalent to an overestimation of the modelled humidity, in this low‐tropospheric WCB inflow region (of about 1 g kg−1 (14%) on average and with peak deviations up to 7 g kg−1). It is noteworthy that this substantial bias occurs in a potentially dynamically highly relevant air mass that will be subsequently lifted within a WCB to the upper troposphere. A Lagrangian moisture source diagnostic reveals that these large moisture deviations occur within air masses that, according to the ECMWF analyses, are coherently transported from the western Mediterranean towards Spain and experience intense moisture uptake over the Ebro valley. It is suggested that inaccuracies in surface evapotranspiration, horizontal moisture advection, and turbulent vertical transport of moisture in the atmospheric boundary layer potentially contribute to the erroneous low‐tropospheric humidity in the inflow region of this particular summertime WCB over Spain in the ECMWF analyses. Copyright © 2011 Royal Meteorological Society