VERTICAL MOTION CHARACTERISTICS OF TROPICAL CYCLONES DETERMINED WITH AIRBORNE DOPPLER RADIAL VELOCITIES

Black ML.; Marks FD.; Burpee RW.

摘要

Vertical motions in seven Atlantic hurricanes are determined from data recorded by Doppler radars on research aircraft. The database consists of Doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers. The vertical motions are estimated throughout the depth of the troposphere from the Doppler velocities and bulk estimates of particle fallspeeds. Portions of the flight tracks are subjectively divided into eyewall, rainband, stratiform, and ''other'' regions. Characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions. Tn all of the regions, more than 70% of the vertical velocities range from -2 to 2 m s(-1). The broadest distribution of vertical motion is in the eyewall region where similar to 5% of the vertical motions are >5 m s(-1). Averaged over the entire dataset, the mean vertical velocity is upward at altitudes. Mean downward motion occurs only in the lower troposphere of the stratiform region. Significant vertical variations in the mean profiles of vertical velocity and reflectivity are discussed and related to microphysical processes. In the lower and middle troposphere, the characteristics of the Doppler-derived vertical motions are similar to those described in an earlier study using flight-level vertical velocities, even though the horizontal resolution of the Doppler data is similar to 750 m compared to similar to 125 m from the in situ flight-level measurements. The Doppler data are available at higher altitudes than those reached by turboprop aircraft and provide information oil vertical as well as horizontal variations. In a vertical plane along the radial flight tracks, Doppler up- and downdrafts are defined at each 300-m altitude interval as vertical Velocities whose absolute Values continuously exceed 1.5 m s(-1), with at least one speed having an absolute value greater than 3.0 m s(-1). The properties of the Doppler drafts are lognormally distributed. In each of the regions, updrafts outnumber downdrafts by at least a factor of 2 and updrafts are wider and stronger than downdrafts. Updrafts in the eyewall slope radially outward with height and are significantly correlated over larger radial and vertical extents than in the other three regions. If the downwind (tangential) slope with height of updrafts varies little among the regions, updrafts capable of transporting air with relatively large moist static energy from the boundary layer to the upper troposphere are primarily in the eyewall region. Downdrafts affect a smaller vertical and horizontal area than updrafts and have no apparent radial slope. The total upward or downward mass flux is defined as the flux produced by all of the upward or downward Doppler vertical velocities. The maximum upward mass flux in all but the ''other'' region is near 1-km altitude, an indication that boundary-layer convergence is efficient in producing upward motion. Above the sea surface, the downward mass flux decreases with altitude. At every altitude, the total net mass flux is upward, except for the lower troposphere in the stratiform region where it is downward. Doppler-derived up- and downdrafts are a subset of the vertical velocity field that occupy small fractions of the total area, yet they contribute a substantial fraction to the total mass flux, In the eyewall and rainband regions, for example, the Doppler updrafts cover less than 30% of the area but are responsible for >75% and >50% to the total upward mass flux, respectively. The Doppler downdrafts typically encompass less than 10% of the area yet provide similar to 50% of the total downward mass flux in the eyewall and similar to 20% of the total downward Aux in the rainband, stratiform, and ''other'' regions. [References: 44]

机译：多普勒雷达在研究飞机上记录的数据确定了七个大西洋飓风的垂直运动。该数据库由多普勒速度和反射率组成，这些多普勒速度和反射率来自垂直指向的雷达射线，这些射线沿着通过飓风中心的径向飞行分支收集。垂直运动是根据对流层深度的多普勒速度和粒子落速的总体估计来估计的。飞行轨迹的各个部分在主观上分为眼墙，雨带，层状和“其他”区域。垂直速度和雷达结构的特征被描述为整个数据集和四个区域中每个区域的高度函数。在所有区域中，垂直速度的70％以上在-2至2 m s（-1）之间。垂直运动的最广泛分布是在眼墙区域，其中> 5％m s（-1）的垂直运动占5％。在整个数据集中取平均值，平均垂直速度在海拔高度处向上。平均向下运动仅发生在层状区域的对流层下部。讨论了垂直速度和反射率平均轮廓中的显着垂直变化，并与微物理过程有关。在对流层中低层，尽管多普勒数据的水平分辨率与750 m相似，但多普勒数据的水平分辨率类似于750 m离原位飞行高度测量值125 m。在高于涡轮螺旋桨飞机所能到达的高度的情况下，可以获得多普勒数据，并且可以提供机油垂直和水平变化的信息。在沿径向飞行轨迹的垂直平面中，将多普勒上下气流定义为在每个300 m的高度间隔处，其垂直速度的绝对值连续超过1.5 ms（-1），并且至少一个速度的绝对值大于3.0毫秒（-1）。多普勒吃水的属性呈对数正态分布。在每个区域中，上升气流的数量要大于下降气流的2倍，并且上升气流的宽度和强度要大于下降气流的强度。与其他三个区域相比，眼墙的上升气流随高度径向向外倾斜，并且在更大的径向和垂直范围内显着相关。如果在各个区域之间随上升气流高度变化的顺风（切向）坡度变化很小，则能够将具有较大湿静能量的空气从边界层输送到对流层上层的上升气流主要位于眼墙区域。向下气流比向上气流影响的垂直和水平区域较小，并且没有明显的径向斜率。向上或向下的总质量通量定义为由所有向上或向下的多普勒垂直速度产生的通量。除“其他”区域外，所有区域中的最大向上质量通量都接近1公里的高度，这表明边界层会聚可有效产生向上运动。在海面以上，向下的质量通量随高度降低。在每个海拔高度处，总净质量通量都向上，除了在层状区域中对流层较低的地方，其对流层较低。多普勒衍生的上升和下降气流是垂直速度场的子集，占总面积的一小部分，但它们却对总质量通量贡献很大。例如，在眼墙和雨带区域，多普勒上升气流覆盖了小于面积的30％，但分别占向上总质量通量的> 75％和> 50％。多普勒下降气流通常只占不到10％的面积，但在雨带，层状和“其他”区域中，其提供的眼壁下降总通量的50％左右和下降辅助通量的20％左右。 [参考：44]

VERTICAL MOTION CHARACTERISTICS OF TROPICAL CYCLONES DETERMINED WITH AIRBORNE DOPPLER RADIAL VELOCITIES

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