Statistical Characteristics of Raindrop Size Distribution during Rainy Seasons in Northwest China

Abstract

Raindrop size distribution (DSD) is of great significance for understanding the microphysical process of rainfall and the quantitative precipitation estimation (QPE). However, in the past, there was a lack of relevant research on Xinjiang in the arid region of northwest China. In this study, the rainy season data collected by the disdrometer in the Yining area of Xinjiang were used for more than two years, and the characteristics of DSDs for all samples, for two rain types (convective and stratiform), and for six different rain rates were studied. The results showed that nearly 70% of the total samples had a rainfall rate of less than 1 mm·h−1, the convective rain was neither continental nor maritime, and there was a clear boundary between convective rain and stratiform rain in terms of the scattergram of the standardized intercept parameter ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:msub> <a:mrow> <a:mi mathvariant="normal">log</a:mi> </a:mrow> <a:mrow> <a:mn>10</a:mn> </a:mrow> </a:msub> <a:msub> <a:mrow> <a:mi>N</a:mi> </a:mrow> <a:mrow> <a:mi>w</a:mi> </a:mrow> </a:msub> </a:math> ) versus the mass-weighted average diameter ( <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" id="M2"> <d:msub> <d:mrow> <d:mi>D</d:mi> </d:mrow> <d:mrow> <d:mi>m</d:mi> </d:mrow> </d:msub> </d:math> ). When the raindrop diameter was less than 0.7 mm, DSDs of the two rainfalls basically coincided, while when the raindrop diameter was greater than 0.7 mm, DSDs of convective rainfall were located above the stratiform rain. As the rainfall rate increased, <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" id="M3"> <f:msub> <f:mrow> <f:mi>D</f:mi> </f:mrow> <f:mrow> <f:mi>m</f:mi> </f:mrow> </f:msub> </f:math> increased, while <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" id="M4"> <h:msub> <h:mrow> <h:mi mathvariant="normal">log</h:mi> </h:mrow> <h:mrow> <h:mn>10</h:mn> </h:mrow> </h:msub> <h:msub> <h:mrow> <h:mi>N</h:mi> </h:mrow> <h:mrow> <h:mi>w</h:mi> </h:mrow> </h:msub> </h:math> first increased and then decreased. In addition, we deduced the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" id="M5"> <k:mi>Z</k:mi> <k:mo>−</k:mo> <k:mi>R</k:mi> </k:math> (radar reflectivity-rain rate) relationship and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" id="M6"> <m:mi>μ</m:mi> <m:mo>−</m:mo> <m:mi mathvariant="normal">Λ</m:mi> </m:math> relationship (shape parameter-slope parameter of the gamma DSDs) suitable for the Yining area. These conclusions are conducive to strengthening the understanding of rainfall microphysical processes in arid regions and improving the ability of QPE in arid regions.