Greenland mass balance by 2100 using a coupled atmospheric (MAR) and ice sheet (PISM) models
Authors: Delhasse Alison , Beckmann Johanna , Fettweis Xavier 
Published: March 2021

&lt;p&gt;&lt;span&gt;The G&lt;/span&gt;&lt;span&gt;reenland ice sheet (GrIS)&lt;/span&gt;&lt;span&gt; is a key contributor to see level rise&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;By &lt;/span&gt;&lt;span&gt;melting&lt;/span&gt;&lt;span&gt; in surface, ice sheet is &lt;/span&gt;&lt;span&gt;thinning&lt;/span&gt;&lt;span&gt; and reach&lt;/span&gt;&lt;span&gt;es&lt;/span&gt;&lt;span&gt; higher temperature which &lt;/span&gt;&lt;span&gt;accelerate the&lt;/span&gt;&lt;span&gt; melting processes &lt;/span&gt;&lt;span&gt;coming from Global Warming&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;The main goal of our research is to improve the representation of &lt;/span&gt;&lt;span&gt;melt-elevation feedback, which is crucial to determine how and when GrIS &lt;/span&gt;&lt;span&gt;will melt and will&lt;/span&gt;&lt;span&gt;&amp;#160;involve in a near future, &lt;/span&gt;&lt;span&gt;by coupling two kind of numerical models.&lt;/span&gt; &lt;span&gt;The d&lt;/span&gt;&lt;span&gt;ifficulty&lt;/span&gt; &lt;span&gt;to&lt;/span&gt; &lt;span&gt;model &lt;/span&gt;&lt;span&gt;this feedback relies on the fact that ice-sheet models (&lt;/span&gt;&lt;span&gt;ISMs)&lt;/span&gt;&lt;span&gt; can &lt;/span&gt;&lt;span&gt;r&lt;/span&gt;&lt;span&gt;eproduce&lt;/span&gt;&lt;span&gt; the dynamic of the ice sheet and thus provide an evolution of the surface elevation, whereas (&lt;/span&gt;&lt;span&gt;regional) &lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;limate&lt;/span&gt;&lt;span&gt; models (&lt;/span&gt;&lt;span&gt;RCMs)&lt;/span&gt;&lt;span&gt; can &lt;/span&gt;&lt;span&gt;r&lt;/span&gt;&lt;span&gt;epresent&lt;/span&gt;&lt;span&gt; the &lt;/span&gt;&lt;span&gt;ice/snow and atmosphere interaction&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;trough&lt;/span&gt;&lt;span&gt; the s&lt;/span&gt;&lt;span&gt;urface mass balance (SMB)&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;A coupling between these models appears as a solution and &lt;/span&gt;&lt;span&gt;has &lt;/span&gt;&lt;span&gt;already be&lt;/span&gt;&lt;span&gt;en&lt;/span&gt;&lt;span&gt; accomplish&lt;/span&gt;&lt;span&gt;ed&lt;/span&gt;&lt;span&gt;. However, &lt;/span&gt;&lt;span&gt;ISMs&lt;/span&gt; responses &lt;span&gt;to &lt;/span&gt;&lt;span&gt;a same&lt;/span&gt;&lt;span&gt; forcing field &lt;/span&gt;&lt;span&gt;may be&lt;/span&gt;&lt;span&gt; quite different, &lt;/span&gt;&lt;span&gt;while SMB from different RCMs are relatively m&lt;/span&gt;&lt;span&gt;ore &lt;/span&gt;&lt;span&gt;similar&lt;/span&gt;&lt;span&gt; with the same forcing&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Coupling c&lt;/span&gt;&lt;span&gt;ould&lt;/span&gt;&lt;span&gt; therefore &lt;/span&gt;&lt;span&gt;be&lt;/span&gt;&lt;span&gt; dependent of which I&lt;/span&gt;&lt;span&gt;SMs&lt;/span&gt;&lt;span&gt; are used.&lt;/span&gt;&lt;span&gt; T&lt;/span&gt;&lt;span&gt;o avoid a coupling,&lt;/span&gt;&lt;span&gt; c&lt;/span&gt;&lt;span&gt;ostly&lt;/span&gt;&lt;span&gt; in computing time, &lt;/span&gt;&lt;span&gt;SMB &lt;/span&gt;&lt;span&gt;vertical &lt;/span&gt;&lt;span&gt;gradient a&lt;/span&gt;&lt;span&gt;s a&lt;/span&gt;&lt;span&gt; function of &lt;/span&gt;&lt;span&gt;local elevation &lt;/span&gt;&lt;span&gt;variations could be used by ISMs &lt;/span&gt;&lt;span&gt;to correct SMB&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;N&lt;/span&gt;&lt;span&gt;onetheless&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;these&lt;/span&gt;&lt;span&gt; SMB gradients are computed with a RCM using a fixed topography, which could introduce biases if &lt;/span&gt;&lt;span&gt;the surface&lt;/span&gt;&lt;span&gt; elevation vary significantly.&lt;/span&gt; &lt;span&gt;H&lt;/span&gt;&lt;span&gt;ere we decide to &lt;/span&gt;&lt;span&gt;full &lt;/span&gt;&lt;span&gt;couple the RCM MAR, &lt;/span&gt;&lt;span&gt;specifically developed for polar climate and forced at his lateral boundaries by CESM2 (a CMIP6 model, &lt;/span&gt;&lt;span&gt;scenario ssp585&lt;/span&gt;&lt;span&gt;),&lt;/span&gt;&lt;span&gt; with the I&lt;/span&gt;&lt;span&gt;SM&lt;/span&gt;&lt;span&gt; PISM. The coupling means that, each year, we exchange ice thickness f&lt;/span&gt;&lt;span&gt;rom&lt;/span&gt;&lt;span&gt; PISM to update&lt;/span&gt;&lt;span&gt; the&lt;/span&gt;&lt;span&gt; topography and ice mask of MAR, and SMB from MAR &lt;/span&gt;&lt;span&gt;to update forcing field&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; of PISM&lt;/span&gt;&lt;span&gt;. First of all the aim is &lt;/span&gt;&lt;span&gt;to analyze what became the GrIS in 2100 with this e&lt;/span&gt;&lt;span&gt;xtreme scenario&lt;/span&gt;&lt;span&gt;. Then we want &lt;/span&gt;&lt;span&gt;to d&lt;/span&gt;&lt;span&gt;efine&lt;/span&gt;&lt;span&gt; a &lt;/span&gt;&lt;span&gt;coupling time threshold to determine&lt;/span&gt;&lt;span&gt;&amp;#160;after how much years &lt;/span&gt;&lt;span&gt;an&lt;/span&gt;&lt;span&gt; update of &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; topography in MAR &lt;/span&gt;&lt;span&gt;is needed&lt;/span&gt;&lt;span&gt; by &lt;/span&gt;&lt;span&gt;varying&lt;/span&gt;&lt;span&gt; the time step &lt;/span&gt;&lt;span&gt;(from 1 to 5, 10, 20, 30 and 50 years)&lt;/span&gt;&lt;span&gt; of &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;coupling. &lt;/span&gt;&lt;span&gt;The &lt;/span&gt;&lt;span&gt;final &lt;/span&gt;&lt;span&gt;aim is to determine until when &lt;/span&gt;&lt;span&gt;the MAR based &lt;/span&gt;&lt;span&gt;SMB gradient&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; are valid &lt;/span&gt;&lt;span&gt;for a same topography in MAR. &lt;/span&gt;&lt;/p&gt;