Observing water vapor from satellites: a multi-parameter retrieval in the Arctic compared to MOSAiC in-situ measurements
Authors: Rückert Janna Elisabeth , Spreen Gunnar 
Published: December 2021

&lt;p&gt;Water vapor is a significant component of the hydrological cycle as well the Earth&amp;#8216;s atmosphere, being a crucial greenhouse gas. It contributes to the rapid warming of the Arctic, called Arctic amplification, by the water vapor feedback. However, obtaining a long-term dataset to monitor trends and variability of water vapor in the Arctic&lt;span lang=&quot;en-US&quot;&gt; - which is important to understand its role in Arctic amplification - &lt;/span&gt; is hampered by the sparseness of in-situ measurements and the challenges for satellite remote sensing retrievals. &lt;span lang=&quot;en-US&quot;&gt;M&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;onthly mean values of integrated water vapor (IWV) strongly differ (up to 30%) between different satellite products in the central Arctic &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;(&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;Crewell et al. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;(2021))&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;In the microwave domain, s&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;pace-borne radiometers allow water vapor retrieval over the open ocean &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;but&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; over sea ice the retrievals have higher uncertainties &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;and &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;are more challenging due to&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; high and variable sea-ice emissivity. &lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span lang=&quot;en-US&quot;&gt;H&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;ere we present a comparison of a satellite-based integrated water vapor retrieval to&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; in-situ measurements,&lt;/span&gt; &lt;span lang=&quot;en-US&quot;&gt;especially radiosondes,&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; taken during the MOSAiC campaign &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;(&lt;/span&gt;mosaic-expedition.org&lt;span lang=&quot;en-US&quot;&gt;)&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;The one-year MOSAiC ice drift expedition provides&lt;/span&gt; &lt;span lang=&quot;en-US&quot;&gt;a full year of IWV reference measurements in the central Arctic&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;The &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;satellite &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;retrieval is based &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;on microwave radiometer measurements from the AMSR-E/2 sensors at 6 different frequencies. Utilizing&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; an optimal estimation &lt;/span&gt;method allows to simultaneously retrieve integrated water vapor and six other geophysical parameters, including sea ice concentration and ice type (Scarlat et al., 2017, 2020). &lt;span lang=&quot;en-US&quot;&gt;Overall the satellite retrieval can reproduce the temporal water vapor variability. &lt;/span&gt; &lt;span lang=&quot;en-US&quot;&gt;We show how w&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;arm and moist air intrusions &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;are captured by the method. H&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;owever, significant biases are observed, which &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;we try to tackle by taking variable snow surface emissions into account.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span lang=&quot;en-US&quot;&gt;We aim for an &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;improved Arctic-wide &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;and longterm &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;water vapor dataset &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;that will&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; help to quantify how the&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; water vapor feedback contributes to Arctic amplification&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;&lt;em&gt;.&lt;/em&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;Crewell et al. (2021). A systematic assessment of water vapor products in the Arctic: from instantaneous measurements to monthly means, &lt;em&gt;Atmos. Meas. Tech.&lt;/em&gt;, 14, 4829&amp;#8211;4856, https://doi.org/10.5194/amt-14-4829-2021.&amp;#160;&lt;/p&gt;
&lt;p&gt;Scarlat et al. (2017). Experiences With an Optimal Estimation Algorithm for Surface and Atmospheric Parameter Retrieval From Passive Microwave Data in the Arctic. &lt;em&gt;IEEE J-STARS&lt;/em&gt;, 10, 3934&amp;#8211;3947. &amp;#160;https://doi.org/10.1109/jstars.2017.2739858&lt;/p&gt;
&lt;p&gt;&lt;span lang=&quot;en-US&quot;&gt;S&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;carlat et al. (2020). Sea Ice and Atmospheric Parameter Retrieval From Satellite Microwave Radiometers: Synergy of AMSR2 and SMOS Compared With the CIMR Candidate Mission. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;&lt;em&gt;J.&amp;#160;Geophys. Res. Oceans&lt;/em&gt;&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;, 125(3). https://doi.org/10.1029/2019JC015749&lt;/span&gt;&lt;/p&gt;