Impact of Additional Assimilation of Dual-Polarimetric Parameters: Analysis and Forecasts in a Real Case
Authors: Zhuang Bing-Xue , Chung Kao-Shen , Tsai Chih-Chien 
Published: March 2022

&lt;p&gt;&lt;span&gt;&lt;span&gt;T&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;he purpose &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;of&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; this study is&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; to&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; investigat&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;e&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; the impact&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;of&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;assimilating &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;dual-&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;polarimetric parameters&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, i.e. differential reflectivity (Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DR&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;) and specific differential phase (K&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DP&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;), &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;in addition to&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;reflectivity (Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;H&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;) and radial wind (&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;V&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;r&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;)&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;in &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;a&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;severe&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; weather system.&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;A&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; squall line case forced by the synoptic southwesterly wind&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;i&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;s&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; selected to conduct the assimilation experiments. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Besides&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;,&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; different microphysics parameterization schemes, including GCE, MOR, WSM6 and WDM6&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, are examined in the experiments&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;The result&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;s&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;of the analysis field &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;show that assimilating additional&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DR&lt;/span&gt;&lt;/span&gt;&amp;#160;&lt;span&gt;&lt;span&gt;with&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; single moment scheme&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;s&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; (GCE and WSM6)&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; can &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;capture better &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;mean &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;raindrop size&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, yet it &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;deteriorate&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;s&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;the intensity of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;simulated&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;H&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; and K&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DP&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Differ from &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;GCE and WSM6&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;,&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; assimilating additional Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DR&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&amp;#160;with&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;double moment schemes&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; (MOR and WDM6) &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;would not&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;lead to&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; significant deterioration in&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; the&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; simulated Z&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;H&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; and K&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;DP&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;since&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;pr&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;ognostic hydrometeor variables &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;in double moment schemes &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;include both&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;mixing ratio &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;and&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; total number concentration&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;T&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;here will be more&amp;#160;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;flexibility&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; in&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;adjusting microphysical states&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; with two independent &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;prognostic hydrometeor variables&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;The results &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;of the short-term &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;quantitative precipitation &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;forecast&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; (QPF)&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; show that &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;assimilati&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;ng additional&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;dual-polarimetric parameters&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;with either single or double moment schemes&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;increases the&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; maximum of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;accumulated rainfall and &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the probability of heavy rainfall&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;In conclusion, &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;double moment schemes &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;can &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;make better use of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the extra information from &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;dual-&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;polarimetric parameters&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;;&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;further&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;more,&lt;/span&gt;&lt;/span&gt; &lt;span&gt;&lt;span&gt;assimilating additional dual-polarimetric parameters, even with single moment schemes, can &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;improve the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;performance of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;QPF, especially h&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;eavy rainfall events&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;