Morphological Characteristics of Precipitation Areas over the Tibetan Plateau Measured by TRMM PR

Abstract

The multidimensional morphological characteristics (including scale, horizontal shape and 3D morphology) of precipitation areas over the Tibetan Plateau in summer were studied using 15 years (1998–2012) of observational data from the precipitation radar onboard the Tropical Rainfall Measuring Mission satellite. As the scale of the precipitation area increased from 20 to 150 km, the near-surface rain rate (RR_av) of the precipitation area increased by up to 78% (from ∼1.12 to ∼2 mm h⁻¹). Linear precipitation areas had the lowest median RR_av (∼1 mm h⁻¹ over the eastern Tibetan Plateau), whereas square-shaped precipitation areas had the highest median RR_av (∼1.58 mm h⁻¹ over the eastern Tibetan Plateau). The 3D morphology was defined as the ratio of the average vertical scale to the average horizontal scale, where a large value corresponds to thin and tall, and a small value corresponds to plump and short. Thin-and-tall precipitation areas and plump-and-short precipitation areas had a greater median RR_av, whereas the precipitation areas with a moderate 3D morphology had the lowest median RR_av. The vertical structure of the precipitation-area reflectivity was sensitive to both size and 3D morphology, but was not sensitive to the horizontal shape. The relationship between RR_av and the morphological characteristics was most significant over the southern slopes of the Tanggula Mountains and the Tibetan Plateau east of 100°E. The morphological characteristics of precipitation areas are therefore closely related to the intensity of precipitation and could potentially be used to forecast precipitation and verify numerical models.

摘要

从宏观角度而言, 降水通常成片出现, 具有 “雨团” 特征; 从探测角度而言, “点” 是雷达播撒的像元, 而 “雨团” 是连续降水像元组成的集合. 基于 “点” 视角的研究通常利用像素或格点数据直接进行统计, 而 “雨团” 视角的研究则须先确定某一阈值进行识别, 再从 “团” 整体化的角度进一步运算. 这一办法虽增加了计算量, 但保留了每个独立 “雨团” 的特征, 为探讨降水规律提供了新思路. 本文利用热带测雨卫星测雨雷达 (TRMM PR) 十五年 (1998-2012) 的轨道级探测结果, 从 “雨团” 这一整体化视角出发, 识别、 定义并研究了夏季青藏高原雨团多维度的形态学特征 (包括尺度、 水平形状和空间形态). 当雨团尺度从 20 km 增长到 150 km 时, 雨团平均雨强随其尺度增加而增大, 增幅最多达到 78%; 细长雨团平均雨强最小, 近方形雨团平均雨强最大; 矮胖型和瘦高型雨团具有较大的平均雨强, 适中空间形态雨团平均雨强相对较小. 雨团回波垂直结构对尺度和空间形态敏感, 而对水平形状不敏感. 在传统的青藏高原降水大值区, 平均雨强与形态学参数的关系最为显著. 雨团形态与降水强度密切相关, 可望为预报降水和检验模式提供有用线索.