<div dir="ltr"><div><div><div><div><div><div><div><div><div>Hi Carlos,<br></div>When I go back to refer to your email, I had other three questions: <br></div>1) You said in your previous email that "You just choose dx and dy depending on what is your final domain". To be more explicit. I guess what you mean is "dx" and "dy" should depends on input meteorological data, but I can choose parent_grid_ratio and number of nested domains to reach a desired resolution at the final domain? Am I correct? <br><br></div>2) Does dx and dy have to be EXACTLY consistent with input meteorological data? I am using some approximation expression to convert resolution in degree to resolution in km. But even for degree 0.25, I did not get integer value. So it seems that dx does NOT need to be exactly consistent with resolution in meteorological data. Then I have a interesting question. For example, my meteorological is of resolution 1 degree (corresponding resolution in km is 111 km), can I set dx=30000 (30km) in the namelist? <br><br></div>3) About time_step<br></div>It says in the user manual (chapter 5):<br> <a href="http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3.8/users_guide_chap5.htm#restart">http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3.8/users_guide_chap5.htm#restart</a><br><br></div>a) time_step is "time
step for integration seconds (recommended 6*dx in km for a typical case)" with maximum of 8*dx and minimum of 3*dx. <br></div><div>b) It also says at somewhere else in the user manual that "Make sure that the <span style="font-family:"courier new"">time_step</span>
is set to comply with the fine-grid domain (typically 6*DX)." <br></div><div><br></div>But in an example namelist in chapter 5, they are using the following parameters: (I am just copy a portion of it here)<br><p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new"">&domains</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>time_step<span> </span>= 180,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>max_dom<span>
</span><span> </span>= 1,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>e_we<span> </span>= 74,<span> </span>112,<span>
</span>94,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>e_sn<span> </span>= 61,<span> </span>97,<span>
</span>91,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>e_vert<span> </span>= 30,<span> </span>30,<span>
</span>30,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>p_top_requested<span> </span>= 5000,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>num_metgrid_levels<span> </span>= 27,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>num_metgrid_soil_levels<span> </span>= 4,</span></p>
<p class="gmail-MsoPlainText"><span style="font-size:10pt;font-family:"courier new""><span> </span>dx<span> </span>= 30000,
10000,<span> </span>3333.33,</span></p>
<span style="font-size:10pt;font-family:"courier new""><span> </span>dy<span> </span>= 30000,
10000,<span> </span>3333.33,<br><br><br></span></div><span style="font-size:10pt;font-family:"courier new"">Which obviously implies that the time_step in this example is calculated based on the most coarse grid instead of the finest grid. <br><br></span></div><span style="font-size:10pt;font-family:"courier new"">What is your opinion over this?<br><br><br></span></div><div class="gmail_extra"><br><div class="gmail_quote">2016-09-06 16:21 GMT-04:00 Carlos Ross <span dir="ltr"><<a href="mailto:cf.ross@gmail.com" target="_blank">cf.ross@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">for questions 1 and 2, yes. You just choose dx and dy depending on what is your final domain (I usually model 1 km, so the first one is 27km, so I have 27, 9, 3 and 1 km of resolution), and also depends on what is your input data (in my case, 0,25 degrees)<div><br></div><div>The next questions:</div><div>1) the input is from the geog folder, for geogrid. </div><div>2) you just choose 1 time step.</div><div>3) there is no constrain, the default is 27 I think, and then you can choose any other number of vertical levels and set the levels if you want. e_we must be the same in wps and input.</div><div>4) <font color="#000000" face="lucida grande, trebuchet ms, verdana, helvetica, arial, sans-serif">p_top should be less than the top level in your meteorological input. the default 5000 is 50 mb for example.</font></div><div><font color="#000000" face="lucida grande, trebuchet ms, verdana, helvetica, arial, sans-serif"><br></font></div><div><font color="#000000" face="lucida grande, trebuchet ms, verdana, helvetica, arial, sans-serif">You should try the domain wizard to set up your model, it's easier for choose the domains <a href="http://esrl.noaa.gov/gsd/wrfportal/DomainWizard.html" target="_blank">http://esrl.noaa.gov/<wbr>gsd/wrfportal/DomainWizard.<wbr>html</a></font></div><div><br></div><div><font color="#000000" face="lucida grande, trebuchet ms, verdana, helvetica, arial, sans-serif"><br></font><div><br></div></div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">2016-09-06 16:08 GMT-03:00 Zhixuan Cao <span dir="ltr"><<a href="mailto:hitcaozx@gmail.com" target="_blank">hitcaozx@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Thank you Carlos. Could you check the following statements so that I can confirm that I understand you correctly. <div>1) So if giving e_we, e_sn, dx and dy, the dimension of the computation domain can be determined, right? Choosing of dx and dy is up to me without additional constrain?</div><div>2) I should only give dx and dy for the first (coarse) domain, and not necessary to give that for other child domains because they can be inferred from parent_grid_ratio.</div><div><br></div><div>I have more other questions (sorry -):</div><div>1) How could I know what is the input resolution for each domain? More specifically, if I am using gfs data, I knew from the file name that the resolution can be 0.25 degree, 0.5 degree or 1 degree. What should be the corresponding grog_data_res for this case. </div><div><br></div><div>2) Is there any criteria to determine parent_time_step_ratio?</div><div>3) Is there any constrain on determine e_vert? By constrain, I mean, for example, e_we in namelist.input should be consistent with that in namelist.wps. If not, I can determine e_vert based on desired resolution in vertical direction?</div><div>4) How to determine the p_top_requested? </div><div><br></div><div>Thank you again.</div><span class="m_8346178699215189273HOEnZb"><font color="#888888"><div><br></div><div>Zhixuan Cao</div></font></span><div><div class="m_8346178699215189273h5"><div><div><br><div><blockquote type="cite"><div>On Sep 6, 2016, at 1:47 PM, Carlos Ross <<a href="mailto:cf.ross@gmail.com" target="_blank">cf.ross@gmail.com</a>> wrote:</div><br><div><div dir="ltr">Hi Zhixuan,<div>You're a bit confused.</div><div><br></div><div>e_we and e_sn are the domain dimensions. in X and Y.</div><div><span style="font-size:12.8px">geog_data_res is the resolution of the input data.</span><br></div><div><span style="font-size:12.8px">dx and dy are the resolution of the main domain.</span></div><div><span style="font-size:12.8px">parent_grid_ratio is the ratio starting from the main domain.</span><br></div><div><span style="font-size:12.8px"><br></span></div><div><span style="font-size:12.8px">As example:</span></div><div><span style="font-size:12.8px"><br></span></div><div><div><span style="font-size:12.8px"> parent_id = 1,1,2,</span></div><div><span style="font-size:12.8px"> parent_grid_ratio = 1,3,3, (resolution of each domain: 27km, 9km, 3km)</span></div><div><span style="font-size:12.8px"> i_parent_start = 1,20,15,</span></div><div><span style="font-size:12.8px"> j_parent_start = 1,35,15,</span></div><div><span style="font-size:12.8px"> e_we = 100,75,60 (domain dimensions: 100x100, 75x75, 60x60 everyone in grid points)</span></div><div><span style="font-size:12.8px"> e_sn = 100,75,60</span></div><div><span style="font-size:12.8px"> geog_data_res = '10m','5m','2m', (input resolution for each domain)</span></div><div><span style="font-size:12.8px"> dx = 27000, (first domain resolution)</span></div><div><span style="font-size:12.8px"> dy = 27000,</span></div></div><div><span style="font-size:12.8px"><br></span></div></div><div class="gmail_extra"><br><div class="gmail_quote">2016-09-03 17:57 GMT-03:00 Zhixuan Cao <span dir="ltr"><<a href="mailto:hitcaozx@gmail.com" target="_blank">hitcaozx@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi<br>
I feel confused on the exact meaning of some parameters in namelist.wps, following user manual can not solve my confusion. Could someone give me some advice on this?<br>
<br>
Here do these following parameters work together to determine the resolution of grids for nested domain simulation?<br>
parent_grid_ratio<br>
i_parent_start<br>
j_parent_start<br>
e_we<br>
e_sn<br>
geog_data_res<br>
<br>
1) If geog_data_res gives resolution of grid, then it seems that I do not need e_we and e_sn.<br>
2) For nested domain simulation, should geog_data_res be consistent with parent_grid_ratio? For example, if parent_grid_ratio = 1, 3 then geog_data_res has to be something like geog_data_res = 9m, 3m.<br>
3) In the tutorial, it says that ( e_we = n* parent_grid_ratio +1) and ( e_sn = n* parent_grid_ratio +1). I guess I can use different n for e_we and e_sn. Am I right? But is there any constrain on n besides that n has to be a positive integer?<br>
<br>
Thank you very much!<br>
<br>
Zhixuan Cao<br>
<br>
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