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29<h3 style="line-height: 100%;">3.8 Coupled model runs</h3>
30
31<p style="line-height: 100%;">Starting from version 3.4
32PALM allows coupled atmosphere-ocean model runs. By analogy with the
33modular structure of PALM, <span style="font-weight: bold;">mrun</span>
34starts the coupled model as two concurrent executables, the atmosphere
35version and&nbsp;the ocean version of PALM.</p>
36
37<p style="line-height: 100%;">Currently, the coupler
38is at an experimental stage using a simple MPI2 intercommunicator that
39matches the atmosphere and ocean processors one-to-one. This approach
40has&nbsp;limited flexibility and performance, because it requires
41identical horizontal numerical grids and it uses the same number of
42atmosphere and ocean processors, which does not necessarily guarrantee
43a good load balancing.</p>
44
45<p style="line-height: 100%;">The coupler establishes a
46one-way interaction between the
47atmosphere and the ocean. The atmosphere sends its bottom surface
48fluxes
49(temperature, humidity, momentum) to the ocean. The ocean sends its top
50surface temperature to the atmosphere. The atmosphere assumes
51saturation of humidity and zero wind speed at its bottom surface. For
52calculations with <a href="chapter_4.1.html#humidity">humidity</a>
53= .T. the atmospheric evaporation leads to a salinity flux in the ocean
54(see e.g. Steinhorn 1991, JPO 21, p. 1681).</p>
55
56<p style="line-height: 100%;">The full MPI-2
57standard must be available in order to use the coupling, and it must be
58activated by adding the preprocessor directive <tt><font style="font-size: 10pt;" size="2">-D__mpi2</font></tt>
59to <tt><font style="font-size: 10pt;" size="2">cpp_options</font></tt>
60in the .mrun.config configuration file. (Note: MPI-2 is
61not available for the IBM-Regatta systems.) To start a
62coupled&nbsp;model run,
63this must be requested with the <b>mrun</b> option <tt><font style="font-size: 10pt;" size="2">-Y</font>.</tt>
64This tells <span style="font-weight: bold;">mrun</span>
65to start two PALM executables. Coupled runs are only possible in
66parallel mode, which means that the <b>mrun</b> option <tt><font style="font-size: 10pt;" size="2">-K parallel</font></tt>
67must also be set.&nbsp;The <b>mrun</b> call
68for coupled runs has to include the following coupling-related options:
69</p>
70
71<ul>
72
73  <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
74&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>
75
76</ul>
77
78<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
79here specifies the total number of processors assigned to the coupled
80model. Currently, half of them are assigned to each of the two coupled
81executables. Therefore it is advisable to specify an even number
82with&nbsp;<tt><font style="font-size: 10pt;" size="2">-X </font></tt><font style="font-size: 10pt;" size="2">...</font><tt>
83</tt>. Otherwise, in case of an odd total number of processors,
84one processor remains idle.</p>
85
86<p style="line-height: 100%;">Each coupled executable has
87its own, unique set of I/O filenames; <a href="chapter_3.4.html#coupled">chapter 3.4</a> gives
88information on file name conventions of coupled runs. The configuration
89file .mrun.config has to be extended for coupled runs. It is
90recommended to duplicate existing file connection identifiers such as
91"d3#", "pr#" etc. using the coupled ocean filenames accordingly. For
92example,&nbsp;the example of the previous chapters could be
93duplicated as follows:</p>
94
95<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>
96
97<p style="line-height: 100%;">The coupled ocean model
98filenames 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
99be specified as given in <a href="chapter_3.4.html#coupled">chapter
1003.4</a>; the file connection identifiers (e.g.&nbsp; <font style="font-size: 10pt;" size="2">d3o#</font>)
101and 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>)
102may be changed at the user's discretion.</p>
103
104<p style="line-height: 100%;">The coupler requires the
105following 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>
106and&nbsp;<a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2">PARIN_O</font></a>:
107<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>,
108<a href="chapter_4.2.html#dt_restart">dt_restart</a>.
109In the coupled atmosphere executable,&nbsp;<a href="chapter_4.2.html#bc_pt_b">bc_pt_b</a> is
110internally set and does not need to be prescribed; in the coupled ocean
111executable, <a href="chapter_4.2.html#bc_uv_t">bc_uv_t</a>&nbsp;is
112internally set ('neumann') and does not need to be prescribed. The
113coupled ocean parameter file&nbsp;<a href="chapter_3.4.html#PARIN"><font style="font-size: 10pt;" size="2">PARIN_O</font></a>
114should include dummy REAL value assignments to both <a href="chapter_4.1.html#top_momentumflux_u">top_momentumflux_u</a>
115and&nbsp;<a href="chapter_4.1.html#top_momentumflux_v">top_momentumflux_v</a>
116(e.g.&nbsp;top_momentumflux_u = 0.0, top_momentumflux_v = 0.0) to
117enable the momentum flux coupling.</p>
118
119<p style="line-height: 100%;">The coupling interval <a href="chapter_4.2.html#dt_coupling">dt_coupling</a>
120must be explicity set. In order to ensure synchronous coupling
121throughout the simulation, <a href="chapter_4.2.html#dt_coupling">dt_coupling</a>
122should be chosen larger than
123<a href="chapter_4.2.html#dt_max">dt_max</a>.</p>
124
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127
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129
130<p style="line-height: 100%;"><i>Last
131change:&nbsp;</i> $Id: chapter_3.8.html 115 2007-10-10 15:34:38Z letzel $</p>
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