General characteristics of Gravity Wave Potential Energy Density at 54 &#186;N and 69 &#186;N
Authors: Strelnikova Irina , Baumgarten Gerd , Baumgarten Kathrin , Ern Manfred , Gerding Michael , Lübken Franz-Josef 
Published: March 2021

&lt;p&gt;&lt;span&gt;We present results of seven years of gravity waves (GW) observations between 2012 and 2018. The measurements were conducted by ground-based lidars in K&amp;#252;hlungsborn (54&amp;#176;N, 12&amp;#176;E) and at ALOMAR (69&amp;#176;N, 16&amp;#176;E). Our analysis technique includes different types of filtering which allow for selection of different ranges from the entire GW-spectrum. We studied &lt;/span&gt;&lt;span&gt;wave&lt;/span&gt;&lt;span&gt; properties as a function of altitude and location and summarized the results in monthly and seasonally mean profiles. &lt;/span&gt;&lt;span&gt;Complementary&lt;/span&gt;&lt;span&gt; data is taken from the satellite-based SABER instrument. Additionally, we consistently applied our analysis technique to the reanalyses data from MERRA-2 and ERA-5. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;A&lt;span&gt; seasonal cycle of &lt;/span&gt;&lt;span&gt;gravity wave potential energy density &lt;/span&gt;&lt;span&gt;(&lt;/span&gt;&lt;span&gt;GWPED&lt;/span&gt;&lt;span&gt;)&lt;/span&gt;&lt;span&gt; with maximum values in winter is present at both stations in nearly all lidar/SABER measurements and in reanalysis data. For SABER and for lidar the winter &lt;/span&gt;&lt;span&gt;to &lt;/span&gt;&lt;span&gt;summer ratios are a factor of &lt;/span&gt;&lt;span&gt;about&amp;#160;3&lt;/span&gt;&lt;span&gt;. The winter &lt;/span&gt;&lt;span&gt;to &lt;/span&gt;&lt;span&gt;summer ratios are nearly identical at both stations. &lt;/span&gt;&lt;span&gt;GWPED&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; from reanalysis are smaller compared to lidar. The difference increases with altitude in winter and reaches almost two orders of magnitude around 70&amp;#160;km.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;GWPEDs per volume&lt;/span&gt;&lt;span&gt; decrease&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; with height &lt;/span&gt;&lt;span&gt;differently for the winter and summer seasons,&lt;/span&gt;&lt;span&gt; irrespective of filtering method and location. &lt;/span&gt;&lt;span&gt;In summer for altitudes above roughly 5&lt;/span&gt;&lt;span&gt;0&lt;/span&gt;&lt;span&gt;&amp;#160;km, GWPED is nearly constant or even increases with height. &lt;/span&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;his feature is very pronounced at ALOMAR and to a lesser extent also &lt;/span&gt;&lt;span&gt;at&lt;/span&gt;&lt;span&gt; K&amp;#252;hlungsborn. This behavior is seen &lt;/span&gt;&lt;span&gt;by both, lidar and SABER&lt;/span&gt;&lt;span&gt;. The observed variation of GWPED with height can not be explained by conservation of wave action alone. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The &lt;/span&gt;&lt;span&gt;GWPED at K&lt;/span&gt;&lt;span&gt;&amp;#252;&lt;/span&gt;&lt;span&gt;hlungsborn is significantly larger compared to ALOMAR. This observation is opposite to simple scenarios which take into account the potential impact of background winds on GW filtering and Doppler shifts of vertical wavelengths and periods. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;W&lt;/span&gt;&lt;span&gt;e present results of &lt;/span&gt;&lt;span&gt;observations and&lt;/span&gt;&lt;span&gt; analyses &lt;/span&gt;&lt;span&gt;and suggest geophysical explanations of our findings.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;