A Feature Track Correction (FTC) Observation Operator applied to Aeolus-AMV Collocations

Ross N Hoffman,Katherine Lukens,Kevin Garrett,Kayo Ide

doi:10.5194/egusphere-egu21-8519

Abstract

&lt;p&gt;In this study we propose and test a feature track correction (FTC) observation operator for atmospheric motion vectors (AMVs). &amp;#160;The FTC has four degrees of freedom corresponding to wind speed multiplicative and additive corrections (&amp;#947; and &amp;#948;&lt;em&gt;&lt;strong&gt;V&lt;/strong&gt;&lt;/em&gt;), a vertical height assignment correction (&lt;em&gt;h&lt;/em&gt;), and an estimate of the depth of the layer that contributes to the AMV (&amp;#916;&lt;em&gt;z&lt;/em&gt;). &amp;#160;Since the effect of the FTC observation operator is to add a bias correction to a weighted average of the profile of background winds an alternate formulation is in terms of a profile of weights (&lt;em&gt;w&lt;sub&gt;k&lt;/sub&gt;&lt;/em&gt;) and &amp;#948;&lt;em&gt;&lt;strong&gt;V &lt;/strong&gt;&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;The FTC observation operator is tested in the context of a collocation study between AMVs projected onto the collocated Aeolus horizontal line-of-sight (HLOS) and the Aeolus HLOS wind profiles. &amp;#160;This is a prototype for an implementation in a variational data assimilation system and here the Aeolus profiles act as the background in the FTC observation operator. &amp;#160;Results were obtained for ten days of data using modest QC. &amp;#160;The overall OMB or collocation difference SD for a global solution applied to the independent sample is 5.49 m/s with negligible mean. &amp;#160;For comparison the corresponding simple (or pure) collocation SD is 7.85 m/s, and the null solution, which only interpolates the Aeolus profile to the reported height of the AMV and removes the overall bias, has an OMB SD of 7.23 m/s. These values correspond to reductions of variance of 51.0% and 42.3%, due to the FTC observation operator in comparison to the simple collocation and null solution, respectively.&lt;/p&gt;&lt;p&gt;These preliminary tests demonstrate the potential for the FTC observation operator for&amp;#160;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Improving AMV collocations (including triple collocation) with profile wind data.&lt;/li&gt; &lt;li&gt;Characterizing AMVs. For example, summary results for the HLOS winds show that AMVs compare best with wind profiles averaged over a 4.5 km layer centered 0.5 km above the reported AMV height.&lt;/li&gt; &lt;li&gt;Improving AMV observation usage within data assimilation (DA) systems. Lower estimated error and more realistic representation of AMVs with variational FTC (VarFTC) should result in greater information extracted. &amp;#160;The FTC observation operator accomplishes this by accounting for the effects of &lt;em&gt;h&lt;/em&gt; and &amp;#916;&lt;em&gt;z&lt;/em&gt;.&amp;#160;&lt;/li&gt; &lt;/ul&gt;

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