Centrifuging of hydrometeors and debris in tornadoes: Radar-reflectivity patterns and wind-measurement errors
Centrifuging of hydrometeors and debris in tornadoes: Radar-reflectivity patterns and wind-measurement errors
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DOI：
10.1175/mwr2934.1
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发表时间：
2005-06-01
影响因子：
3.2
通讯作者：
Wicker, LJ
中科院分区：
文献类型：
--
作者：
Dowell, DC;Alexander, CR;Wicker, LJ
对龙卷风的高分辨率多普勒雷达观测揭示了一个独特的龙卷风尺度特征，具有以下特性：龙卷风核心内的反射率最小值（之前被描述为“眼”），比龙卷风核心稍宽的高反射率管，以及这种高反射率管在地面附近逐渐变细。简单的一维和二维模型的结果演示了这些特性是如何发展的。模型中的重要过程包括由旋转气流产生的水凝物和/或碎片的离心喷射，以及由近地表流入和上升气流产生的某些物体的再循环，多普勒雷达对龙卷风中物体的运动而不是实际气流进行采样。由于物体以不同的速度和沿着不同的轨迹移动，误差被引入到基于雷达观测的龙卷风运动学分析中。在稳定的轴对称龙卷风中，物体相对于空气向外移动，并且在切向方向上比空气移动得更慢;此外，物体的垂直空气相对速度小于它在静止空气中的速度。空气运动和物体运动之间的差异对于具有更大特征下落速度的物体（即，更大、密度更大的物体），并且可以具有每秒数十米的量级。这些差异的估计为指定的对象和龙卷风的特点，可以从近似的一维model.Doppler On Wheels观测的30 May 1998年斯宾塞，南达科他州，龙卷风演示了如何明显的龙卷风结构可以改变时，雷达散射类型的变化。当斯宾塞龙卷风进入城镇，并开始放样碎片，发生变化的多普勒速度和反射率场是一致的平均散射体大小的增加。
High-resolution Doppler radar observations of tornadoes reveal a distinctive tornado-scale signature with the following properties: a reflectivity minimum aloft inside the tornado core (described previously as an "eye"), a high-reflectivity tube aloft that is slightly wider than the tornado core, and a tapering of this high-reflectivity tube near the ground. The results of simple one-dimensional and two-dimensional models demonstrate how these characteristics develop. Important processes in the models include centrifugal ejection of hydrometeors and/or debris by the rotating flow and recycling of some objects by the near-surface inflow and updraft.Doppler radars sample the motion of objects within the tornado rather than the actual airflow. Since objects move at different speeds and along different trajectories than the air, error is introduced into kinematic analyses of tornadoes based on radar observations. In a steady, axisymmetric tornado, objects move outward relative to the air and move more slowly than the air in the tangential direction; in addition, the vertical air-relative speed of an object is less than it is in still air. The differences between air motion and object motion are greater for objects with greater characteristic fall speeds (i.e., larger, denser objects) and can have magnitudes of tens of meters per second. Estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one-dimensional model.Doppler On Wheels observations of the 30 May 1998 Spencer, South Dakota, tornado demonstrate how the apparent tornado structure can change when the radar-scatterer type changes. When the Spencer tornado entered the town and started lofting debris, changes occurred in the Doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size.