How is the marine atmospheric boundary layer turbulence organized in the trades ?
Authors: Brilouet Pierre-Etienne , Lothon Marie , Bony Sandrine 
Published: March 2021

&lt;p&gt;Tradewind clouds can exhibit a wide diversity of mesoscale organizations, and the turbulence of marine atmospheric boundary layer (MABL) can exhibit coherent structures and mesoscale circulations. One of the objectives of the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field experiment was to better understand the tight interplay between the mesoscale organization of clouds, boundary-layer processes, and the large-scale environment.&lt;/p&gt;&lt;p&gt;During the experiment, that took place East of Barbados over the Western Tropical Atlantic Ocean in Jan-Feb 2020, the French ATR-42 research aircraft was devoted to the characterization of the cloud amount and of the subcoud layer structure. &lt;span&gt;During its 17 research flights, &lt;/span&gt;&lt;span&gt;it&lt;/span&gt; &lt;span&gt;sampled a &lt;/span&gt;&lt;span&gt;large diversity of large scale conditions and &lt;/span&gt;&lt;span&gt;cloud patterns&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;Multiple sensors onboard t&lt;span&gt;he aircraft measure&lt;/span&gt;&lt;span&gt;d&lt;/span&gt; &lt;span&gt;high-frequency &lt;/span&gt;&lt;span&gt;fluctuations of potential temperature, water vapour mixing ratio and wind , allowing &lt;/span&gt;&lt;span&gt;for &lt;/span&gt;&lt;span&gt;an extensive characterization &lt;/span&gt;&lt;span&gt; of&lt;/span&gt;&lt;span&gt; the turbulence &lt;/span&gt;&lt;span&gt;within&lt;/span&gt;&lt;span&gt; the subcloud layer. &lt;/span&gt; &lt;span&gt;A &lt;/span&gt;&lt;span&gt;quality-controled and calibrated turbulence data&lt;/span&gt;&lt;span&gt;set&lt;/span&gt;&lt;span&gt; was produced &lt;/span&gt;&lt;span&gt;on the basis of these measurements&lt;/span&gt;&lt;span&gt;, which is now &lt;/span&gt;&lt;span&gt; available on the EUREC4A AERIS data portal.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The &lt;/span&gt;&lt;span&gt;MABL &lt;/span&gt;&lt;span&gt;turbulent &lt;/span&gt;&lt;span&gt;structure i&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; studied &lt;/span&gt;&lt;span&gt;using this dataset, &lt;/span&gt;&lt;span&gt;through a spectral analysis &lt;/span&gt;&lt;span&gt;of the vertical velocity&lt;/span&gt;&lt;span&gt;. Vertical profiles of characteristic length scales reveal a non-isotropic structure with a stretching of the eddies along the mean wind. The organization strength of the turbulent field is also explored &lt;/span&gt;&lt;span&gt;by defining&lt;/span&gt;&lt;span&gt; a diagnostic based on the shape of the vertical velocity spectrum. &lt;/span&gt;&lt;span&gt;The &lt;/span&gt;&lt;span&gt;structure and the degree of organization of the &lt;/span&gt;&lt;span&gt;subcloud layer &lt;/span&gt;&lt;span&gt;are&lt;/span&gt;&lt;span&gt; characterized for &lt;/span&gt;&lt;span&gt; different type&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; of mesoscale &lt;/span&gt;&lt;span&gt;convective &lt;/span&gt;&lt;span&gt;pattern &lt;/span&gt;&lt;span&gt;and &lt;/span&gt;&lt;span&gt;as a function of&lt;/span&gt;&lt;span&gt; the large-scale environment, &lt;/span&gt;&lt;span&gt;including&lt;/span&gt; &lt;span&gt;near-&lt;/span&gt;&lt;span&gt;surface wind &lt;/span&gt;&lt;span&gt;and&lt;/span&gt; &lt;span&gt;lower-&lt;/span&gt;&lt;span&gt;tropospheric&lt;/span&gt;&lt;span&gt; stability conditions.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;