<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 14 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hello All,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I’m running some simple ideal LES simulations of the neutral ABL forced with 10 m/s geostrophic wind. In validating vertical profiles the mean wind, velocity variance and momentum flux profiles agree well with other LES and experimental data. However, the velocity spectra begin to “roll-off” at unusually low wavenumbers, i.e. there is too much energy content at the highest wavenumbers (see the plots in the attached PDF). A comparison with Mirocha et al. (2010) indicates that this is not typical of WRF-LES.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>In an attempt to diagnose the problem I have tried increasing vertical resolution, 3 different SGS models (3D Smagorinsky, NBA-Stress, NBA-TKE) and simulations with and without a capping inversion, but the results are similar each time. This leads me to believe that the problem is related to one or more poorly selected options for numerics and as a result unphysical high frequency waves are generated in the domain.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Note that I am using the ‘em_les’ test case as the basis for my runs so I have 5<sup>th</sup> order RK3 in the horizontal and 3<sup>rd</sup> order RK3 in the vertical. I have set the acoustic timestep to be calculated automatically (i.e. namelist variable ‘time_step_sound=0’). It is worth noting that in purely convective simulations (no background wind) the velocity and temperature spectra look fine, so this is more evidence pointing to a problem with the advection scheme/numerics.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Has anyone else experienced this problem? Any comments or suggestions will be very helpful and most appreciated.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Anders<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><div style='mso-element:para-border-div;border:none;border-bottom:solid windowtext 1.5pt;padding:0in 0in 1.0pt 0in'><p class=MsoNormal style='border:none;padding:0in'><o:p> </o:p></p></div><p class=MsoNormal>Anders Nottrott<o:p></o:p></p><p class=MsoNormal><i>PhD Student, Mechanical and Environmental Engineering<o:p></o:p></i></p><p class=MsoNormal>University of California, San Diego<o:p></o:p></p><p class=MsoNormal>Department of Mechanical and Aerospace Engineering<o:p></o:p></p></div></body></html>