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26<h3 style="line-height: 100%;">3.8 Coupled model runs</h3>
27
28<p style="line-height: 100%;">Starting from version 3.4
29PALM allows coupled atmosphere-ocean model runs. By analogy with the
30modular structure of PALM, <span style="font-weight: bold;">mrun</span>
31starts the coupled model as two concurrent executables, the atmosphere
32version and&nbsp;the ocean version of PALM.</p>
33
34<p style="line-height: 100%;">Currently, the coupler
35is at an experimental stage using a simple MPI2 intercommunicator that
36matches the atmosphere and ocean processors one-to-one. This approach
37has&nbsp;limited flexibility and performance, because it requires
38identical horizontal numerical grids and it uses the same number of
39atmosphere and ocean processors, which does not necessarily guarrantee
40a good load balancing.</p>
41
42<p style="line-height: 100%;">The coupler establishes a
43one-way interaction between the
44atmosphere and the ocean. The atmosphere sends its bottom surface
45fluxes
46(temperature, humidity, momentum) to the ocean. The ocean sends its top
47surface temperature to the atmosphere. The atmosphere assumes
48saturation of humidity and zero wind speed at its bottom surface. For
49calculations with <a href="chapter_4.1.html#humidity">humidity</a>
50= .T. the atmospheric evaporation leads to a salinity flux in the ocean
51(see e.g. Steinhorn 1991, JPO 21, p. 1681).</p>
52
53<p style="line-height: 100%;">The full MPI-2
54standard must be available in order to use the coupling, and it must be
55activated by adding the preprocessor directive <tt><font style="font-size: 10pt;" size="2">-D__mpi2</font></tt>
56to <tt><font style="font-size: 10pt;" size="2">cpp_options</font></tt>
57in the .mrun.config configuration file. (Note: MPI-2 is
58not available for the IBM-Regatta systems.) To start a
59coupled&nbsp;model run,
60this must be requested with the <b>mrun</b> option <tt><font style="font-size: 10pt;" size="2">-Y</font>.</tt>
61This tells <span style="font-weight: bold;">mrun</span>
62to start two PALM executables. Coupled runs are only possible in
63parallel mode, which means that the <b>mrun</b> option <tt><font style="font-size: 10pt;" size="2">-K parallel</font></tt>
64must also be set.&nbsp;The <b>mrun</b> call
65for coupled runs has to include the following coupling-related options:
66</p>
67
68<ul>
69
70  <p style="line-height: 100%;"><tt><font style="font-size: 10pt;" size="2">mrun </font></tt><font style="font-size: 10pt;" size="2">...</font><tt><font style="font-size: 10pt;" size="2"> -K parallel -r
71&ldquo;d3# d3o# </font></tt><font style="font-size: 10pt;" size="2">...</font><tt><font style="font-size: 10pt;" size="2">&rdquo;</font></tt><tt><font style="font-size: 10pt;" size="2"> </font></tt><tt><font style="font-size: 10pt;" size="2">-X </font></tt><font style="font-size: 10pt;" size="2">...</font><tt><font style="font-size: 10pt;" size="2"> -Y</font></tt><tt>.</tt></p>
72
73</ul>
74
75<p style="line-height: 100%;">The <tt><font style="font-size: 10pt;" size="2">-X </font></tt><font style="font-size: 10pt;" size="2">...</font><tt><font style="font-size: 10pt;" size="2">&nbsp;</font></tt>option
76here specifies the total number of processors assigned to the coupled
77model. Currently, half of them are assigned to each of the two coupled
78executables. Therefore it is advisable to specify an even number
79with&nbsp;<tt><font style="font-size: 10pt;" size="2">-X </font></tt><font style="font-size: 10pt;" size="2">...</font><tt>
80</tt>. Otherwise, in case of an odd total number of processors,
81one processor remains idle.</p>
82
83<p style="line-height: 100%;">Each coupled executable has
84its own, unique set of I/O filenames; <a href="chapter_3.4.html#coupled">chapter 3.4</a> gives
85information on file name conventions of coupled runs. The configuration
86file .mrun.config has to be extended for coupled runs. It is
87recommended to duplicate existing file connection identifiers such as
88"d3#", "pr#" etc. using the coupled ocean filenames accordingly. For
89example,&nbsp;the example of the previous chapters could be
90duplicated as follows:</p>
91
92<pre style="line-height: 100%;"><a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2">PARIN</font></a><font style="font-size: 10pt;" size="2"> in:job:npe d3# ~/palm/current_version/JOBS/$fname/INPUT _p3d</font><br><font style="font-size: 10pt;" size="2">PARIN in:job:npe d3f ~/palm/current_version/JOBS/$fname/INPUT _p3df</font><br><a href="chapter_3.4.html#BININ"><font style="font-size: 10pt;" size="2">BININ</font></a><font style="font-size: 10pt;" size="2"> in:loc d3f ~/palm/current_version/JOBS/$fname/OUTPUT _d3d</font><br><font style="font-size: 10pt;" size="2">#</font><br><a href="chapter_3.4.html#BINOUT"><font style="font-size: 10pt;" size="2">BINOUT</font></a><font style="font-size: 10pt;" size="2"> out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT _d3d<br>#</font><br><a href="chapter_3.4.html#RUN_CONTROL"><font style="font-size: 10pt;" size="2">RUN_CONTROL</font></a><font style="font-size: 10pt;" size="2"> out:loc:tr d3# ~/palm/current_version/JOBS/$fname/MONITORING _rc</font><br><a href="chapter_3.4.html#HEADER"><font style="font-size: 10pt;" size="2">HEADER</font></a><font style="font-size: 10pt;" size="2"> out:loc:tr d3# ~/palm/current_version/JOBS/$fname/MONITORING _header</font><br><a href="chapter_3.4.html#PLOT1D_PAR"><font style="font-size: 10pt;" size="2">PLOT1D_PAR</font></a><font style="font-size: 10pt;" size="2"> out:loc:tr pr# ~/palm/current_version/JOBS/$fname/OUTPUT _pr_par</font><br><a href="chapter_3.4.html#PLOT1D_DATA"><font style="font-size: 10pt;" size="2">PLOT1D_DATA</font></a><font style="font-size: 10pt;" size="2"> out:loc:tr pr# ~/palm/current_version/JOBS/$fname/OUTPUT _pr_in<br>#<br></font><font style="font-size: 10pt;" size="2">PARIN</font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">_O</span> in:job:npe d3<span style="font-weight: bold;">o</span># ~/palm/current_version/JOBS/$fname/INPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">p3d</font><br><font style="font-size: 10pt;" size="2">PARIN<span style="font-weight: bold;">_O</span> in:job:npe d3<span style="font-weight: bold;">o</span>f ~/palm/current_version/JOBS/$fname/INPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">p3df</font><br><font style="font-size: 10pt;" size="2">BININ</font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">_O</span> in:loc d3<span style="font-weight: bold;">o</span>f ~/palm/current_version/JOBS/$fname/OUTPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">d3d</font><br><font style="font-size: 10pt;" size="2">#</font><br><font style="font-size: 10pt;" size="2">BINOUT</font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">_O</span> out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">d3d</font><br><font style="font-size: 10pt;" size="2">#</font><br><font style="font-size: 10pt;" size="2">RUN_CONTROL<span style="font-weight: bold;">_O</span></font><font style="font-size: 10pt;" size="2"> out:loc:tr d3<span style="font-weight: bold;">o</span># ~/palm/current_version/JOBS/$fname/MONITORING <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">rc</font><br><font style="font-size: 10pt;" size="2">HEADER</font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">_O</span> out:loc:tr d3<span style="font-weight: bold;">o</span># ~/palm/current_version/JOBS/$fname/MONITORING <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">header</font><br><font style="font-size: 10pt;" size="2">PLOT1D_PAR<span style="font-weight: bold;">_O</span></font><font style="font-size: 10pt;" size="2"> out:loc:tr pr<span style="font-weight: bold;">o</span># ~/palm/current_version/JOBS/$fname/OUTPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">pr_par</font><br><font style="font-size: 10pt;" size="2">PLOT1D_DATA</font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">_O</span> out:loc:tr pr<span style="font-weight: bold;">o</span># ~/palm/current_version/JOBS/$fname/OUTPUT <span style="font-weight: bold;">_</span></font><font style="font-size: 10pt;" size="2"><span style="font-weight: bold;">o</span>_</font><font style="font-size: 10pt;" size="2">pr_in</font><br></pre>
93
94<p style="line-height: 100%;">The coupled ocean model
95filenames in the first column (e.g.<font style="font-size: 10pt;" size="2"><span style="font-family: mon;"> </span><a href="chapter_3.4.html#PARIN">PARIN_O</a></font>)&nbsp;must
96be specified as given in <a href="chapter_3.4.html#coupled">chapter
973.4</a>; the file connection identifiers (e.g.&nbsp; <font style="font-size: 10pt;" size="2">d3o#</font>)
98and the file name extension (e.g. &nbsp;<font style="font-size: 10pt;" size="2"><span style="font-weight: bold;"><span style="font-family: mon;"></span></span>_</font><font style="font-size: 10pt;" size="2">o_</font><font style="font-size: 10pt;" size="2">p3d</font>)
99may be changed at the user's discretion.</p>
100
101<p style="line-height: 100%;">The coupler requires the
102following parameters to be equal in both <a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2"><span style="font-family: mon;"></span>PARIN</font></a>
103and&nbsp;<a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2">PARIN_O</font></a>:
104<a href="chapter_4.1.html#dx">dx</a>, <a href="chapter_4.1.html#dy">dy</a>, <a href="chapter_4.1.html#nx">nx</a>, <a href="chapter_4.1.html#ny">ny</a>, <a href="chapter_4.2.html#dt_coupling">dt_coupling</a>, <a href="chapter_4.2.html#end_time">end_time</a>, <a href="chapter_4.2.html#restart_time">restart_time</a>,
105<a href="chapter_4.2.html#dt_restart">dt_restart</a>.
106In the coupled atmosphere executable,&nbsp;<a href="chapter_4.2.html#bc_pt_b">bc_pt_b</a> is
107internally set and does not need to be prescribed; in the coupled ocean
108executable, <a href="chapter_4.2.html#bc_uv_t">bc_uv_t</a>&nbsp;is
109internally set ('neumann') and does not need to be prescribed. The
110coupled ocean parameter file&nbsp;<a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2">PARIN_O</font></a>
111should include dummy REAL value assignments to both <a href="chapter_4.1.html#top_momentumflux_u">top_momentumflux_u</a>
112and&nbsp;<a href="chapter_4.1.html#top_momentumflux_v">top_momentumflux_v</a>
113(e.g.&nbsp;top_momentumflux_u = 0.0, top_momentumflux_v = 0.0) to
114enable the momentum flux coupling.</p>
115
116<p style="line-height: 100%;">The coupling interval <a href="chapter_4.2.html#dt_coupling">dt_coupling</a>
117must be explicity set. In order to ensure synchronous coupling
118throughout the simulation, <a href="chapter_4.2.html#dt_coupling">dt_coupling</a>
119should be chosen larger than
120<a href="chapter_4.2.html#dt_max">dt_max</a>.</p>
121
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124
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126
127<p style="line-height: 100%;"><i>Last
128change:&nbsp;</i> $Id: chapter_3.8.html 197 2008-09-16 15:29:03Z raasch $</p>
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