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documentation update for the coupling
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5        <TITLE>PALM chapter 3.8</TITLE>
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21<H3 STYLE="line-height: 100%">3.8 Coupled model runs</H3>
22<P STYLE="line-height: 100%">Starting from version 3.4 PALM allows
23coupled atmosphere-ocean model runs. By analogy with the modular
24structure of PALM, <B>mrun</B> starts the coupled model as two
25concurrent executables, the atmosphere version and&nbsp;the ocean
26version of PALM.</P>
27<P STYLE="line-height: 100%">Currently, the coupler is at an
28experimental stage using either a MPI2 (more flexible) or a MPI1
29intercommunicator that matches the atmosphere and ocean processors
30one-to-one. This approach has&nbsp;limited flexibility and
31performance, because it requires identical horizontal numerical grids
32and it uses the same number of atmosphere and ocean processors, which
33does not necessarily guarrantee a good load balancing.</P>
34<P STYLE="line-height: 100%">The coupler establishes a one-way
35interaction between the atmosphere and the ocean. The atmosphere
36sends its bottom surface fluxes (temperature, humidity, momentum) to
37the ocean. The ocean sends its top surface temperature to the
38atmosphere. The atmosphere assumes saturation of humidity and zero
39wind speed at its bottom surface. For calculations with <A HREF="chapter_4.1.html#humidity">humidity</A>
40= .T. the atmospheric evaporation leads to a salinity flux in the
41ocean (see e.g. Steinhorn 1991, JPO 21, p. 1681).</P>
42<P STYLE="line-height: 100%">If the full MPI-2 standard is available,
43it can be activated by adding the preprocessor directive <TT><FONT SIZE=2>-D__mpi2</FONT></TT>
44to <TT><FONT SIZE=2>cpp_options</FONT></TT> in the .mrun.config
45configuration file. Otherwise, PALM will use a coupling via MPI1. To
46start a coupled&nbsp;model run, this must be requested with the <B>mrun</B>
47option <TT><FONT SIZE=2>-Y “#1 #2”</FONT></TT><TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>,
48where </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#1</FONT></FONT></TT><TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>
49is the number of processors for the atmospheric and </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#2</FONT></FONT></TT><TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>
50the number of processors for the oceanic version of PALM (Please note
51that currently only one-to-one topologies are supported and </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#1</FONT></FONT></TT><TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>
52must be equal to </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#2</FONT></FONT></TT><TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>).
53</FONT></FONT></TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>Thi</FONT></FONT>s
54tells <B>mrun</B> to start two PALM executables. Coupled runs are
55only possible in parallel mode, which means that the <B>mrun</B>
56option <TT><FONT SIZE=2>-K parallel</FONT></TT> must also be set.&nbsp;The
57<B>mrun</B> call for coupled runs has to include the following
58coupling-related options:
59</P>
60<UL>
61        <P STYLE="line-height: 100%"><TT><FONT SIZE=2>mrun </FONT></TT><FONT SIZE=2>...</FONT><TT>
62        </TT><TT><FONT SIZE=2>-K parallel -r “d3# d3o# </FONT></TT><FONT SIZE=2>...</FONT><TT>”
63        </TT><TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT> </TT><TT><FONT SIZE=2>-Y
64        “#1 #2”</FONT></TT><TT>.</TT></P>
65</UL>
66<P STYLE="line-height: 100%">The <TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT>&nbsp;</TT>option
67here specifies the total number of processors assigned to the coupled
68model. Currently, half of them are assigned to each of the two
69coupled executables. Therefore it is advisable to specify an even
70number with&nbsp;<TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT>
71</TT>. Otherwise, in case of an odd total number of processors, one
72processor remains idle.</P>
73<P STYLE="line-height: 100%">Each coupled executable has its own,
74unique set of I/O filenames; <A HREF="chapter_3.4.html#coupled">chapter
753.4</A> gives information on file name conventions of coupled runs.
76The configuration file .mrun.config has to be extended for coupled
77runs. It is recommended to duplicate existing file connection
78identifiers such as &quot;d3#&quot;, &quot;pr#&quot; etc. using the
79coupled ocean filenames accordingly. For example,&nbsp;the example of
80the previous chapters could be duplicated as follows:</P>
81<PRE STYLE="line-height: 100%"><A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN</FONT></A> <FONT SIZE=2>in:job:npe d3# ~/palm/current_version/JOBS/$fname/INPUT _p3d</FONT>
82<FONT SIZE=2>PARIN in:job:npe d3f ~/palm/current_version/JOBS/$fname/INPUT _p3df</FONT>
83<A HREF="chapter_3.4.html#BININ"><FONT SIZE=2>BININ</FONT></A> <FONT SIZE=2>in:loc d3f ~/palm/current_version/JOBS/$fname/OUTPUT _d3d</FONT>
84<FONT SIZE=2>#</FONT>
85<A HREF="chapter_3.4.html#BINOUT"><FONT SIZE=2>BINOUT</FONT></A> <FONT SIZE=2>out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT _d3d</FONT>
86<FONT SIZE=2>#</FONT>
87<A HREF="chapter_3.4.html#RUN_CONTROL"><FONT SIZE=2>RUN_CONTROL</FONT></A> <FONT SIZE=2>out:loc:tr d3# ~/palm/current_version/JOBS/$fname/MONITORING _rc</FONT>
88<A HREF="chapter_3.4.html#HEADER"><FONT SIZE=2>HEADER</FONT></A> <FONT SIZE=2>out:loc:tr d3# ~/palm/current_version/JOBS/$fname/MONITORING _header</FONT>
89<A HREF="chapter_3.4.html#PLOT1D_PAR"><FONT SIZE=2>PLOT1D_PAR</FONT></A> <FONT SIZE=2>out:loc:tr pr# ~/palm/current_version/JOBS/$fname/OUTPUT _pr_par</FONT>
90<A HREF="chapter_3.4.html#PLOT1D_DATA"><FONT SIZE=2>PLOT1D_DATA</FONT></A> <FONT SIZE=2>out:loc:tr pr# ~/palm/current_version/JOBS/$fname/OUTPUT _pr_in</FONT>
91<FONT SIZE=2>#</FONT>
92<FONT SIZE=2>PARIN</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> in:job:npe d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/INPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_p3d</FONT>
93<FONT SIZE=2>PARIN</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> in:job:npe d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2>f ~/palm/current_version/JOBS/$fname/INPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_p3df</FONT>
94<FONT SIZE=2>BININ</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> in:loc d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2>f ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_d3d</FONT>
95<FONT SIZE=2>#</FONT>
96<FONT SIZE=2>BINOUT</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_d3d</FONT>
97<FONT SIZE=2>#</FONT>
98<FONT SIZE=2>RUN_CONTROL</FONT><FONT SIZE=2><B>_O</B></FONT> <FONT SIZE=2>out:loc:tr d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/MONITORING </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_rc</FONT>
99<FONT SIZE=2>HEADER</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc:tr d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/MONITORING </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_header</FONT>
100<FONT SIZE=2>PLOT1D_PAR</FONT><FONT SIZE=2><B>_O</B></FONT> <FONT SIZE=2>out:loc:tr pr</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_pr_par</FONT>
101<FONT SIZE=2>PLOT1D_DATA</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc:tr pr</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_pr_in</FONT></PRE><P STYLE="line-height: 100%">
102The coupled ocean model filenames in the first column (e.g.
103<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>)&nbsp;must
104be specified as given in <A HREF="chapter_3.4.html#coupled">chapter
1053.4</A>; the file connection identifiers (e.g.&nbsp; <FONT SIZE=2>d3o#</FONT>)
106and the file name extension (e.g. &nbsp;<FONT SIZE=2>_o_p3d</FONT>)
107may be changed at the user's discretion.</P>
108<P STYLE="line-height: 100%">The coupler requires the following
109parameters to be equal in both <A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN</FONT></A>
110and&nbsp;<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>:
111<A HREF="chapter_4.1.html#dx">dx</A>, <A HREF="chapter_4.1.html#dy">dy</A>,
112<A HREF="chapter_4.1.html#nx">nx</A>, <A HREF="chapter_4.1.html#ny">ny</A>,
113<A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>, <A HREF="chapter_4.2.html#end_time">end_time</A>,
114<A HREF="chapter_4.2.html#restart_time">restart_time</A>, <A HREF="chapter_4.2.html#dt_restart">dt_restart</A>.
115In the coupled atmosphere executable,&nbsp;<A HREF="chapter_4.2.html#bc_pt_b">bc_pt_b</A>
116is internally set and does not need to be prescribed; in the coupled
117ocean executable, <A HREF="chapter_4.2.html#bc_uv_t">bc_uv_t</A>&nbsp;is
118internally set ('neumann') and does not need to be prescribed. The
119coupled ocean parameter file&nbsp;<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>
120should include dummy REAL value assignments to both
121<A HREF="chapter_4.1.html#top_momentumflux_u">top_momentumflux_u</A>
122and&nbsp;<A HREF="chapter_4.1.html#top_momentumflux_v">top_momentumflux_v</A>
123(e.g.&nbsp;top_momentumflux_u = 0.0, top_momentumflux_v = 0.0) to
124enable the momentum flux coupling.</P>
125<P STYLE="line-height: 100%">The coupling interval <A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>
126must be explicity set. In order to ensure synchronous coupling
127throughout the simulation, <A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>
128should be chosen larger than <A HREF="chapter_4.2.html#dt_max">dt_max</A>.</P>
129<P STYLE="line-height: 100%">It's also possible to perform precursor
130runs (one atmospheric and one oceanic) followed by a coupled restart
131run. In order to achieve this, the parameter <A HREF="chapter_4.1.html#coupling_start_time">coupling_time_start</A>
132must be set according to the <A HREF="../misc/precursor_run_control.pdf">documentation.</A></P>
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135<P STYLE="line-height: 100%"><I>Last change:&nbsp;</I> $Id:
136chapter_3.8.html 197 2008-09-16 15:29:03Z raasch $</P>
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