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5        <TITLE>PALM chapter 3.8</TITLE>
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7        <META NAME="AUTHOR" CONTENT="Siegfried Raasch">
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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. If MPI-2 support is available, <B>mrun</B> starts the coupled model as two
24concurrent executables, the atmosphere version and&nbsp;the ocean
25version in analogy with the modular structure of PALM.</P>
26<P STYLE="line-height: 100%">Currently, the coupler is at an
27experimental stage using either a MPI2 (more flexible) or a MPI1
28intercommunicator that matches the atmosphere and ocean processors
29one-to-one. This approach has&nbsp;limited flexibility and
30performance, because it requires identical horizontal numerical grids
31and it uses the same number of atmosphere and ocean processors, which
32does not necessarily guarrantee a good load balancing.</P>
33<P STYLE="line-height: 100%">The coupler establishes a one-way
34interaction between the atmosphere and the ocean. The atmosphere
35sends its bottom surface fluxes (temperature, humidity, momentum) to
36the ocean. The ocean sends its top surface temperature to the
37atmosphere. The atmosphere assumes saturation of humidity and zero
38wind speed at its bottom surface. For calculations with <A HREF="chapter_4.1.html#humidity">humidity</A>
39= .T. the atmospheric evaporation leads to a salinity flux in the
40ocean (see e.g. Steinhorn 1991, JPO 21, p. 1681).</P>
41<P STYLE="line-height: 100%">If the full MPI-2 standard is available,
42it can be activated by adding the preprocessor directive <TT><FONT SIZE=2>-D__mpi2</FONT></TT>
43to <TT><FONT SIZE=2>cpp_options</FONT></TT> in the .mrun.config
44configuration file. Otherwise, PALM will use a coupling via MPI1. To
45start a coupled&nbsp;model run, this must be requested with the <B>mrun</B>
46option <TT><FONT SIZE=2>-Y “#1 #2”</FONT></TT>,
47where </TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#1</FONT></FONT></TT>
48is the number of processors for the atmospheric and </FONT></FONT></TT><FONT FACE="Andale Mono"><FONT SIZE=2>#2</FONT></FONT></TT>
49the number of processors for the oceanic version of PALM (Please note
50that currently only one-to-one topologies are supported and </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#1</FONT></FONT></TT>
51must be equal to </FONT></FONT></TT><TT><FONT FACE="Andale Mono"><FONT SIZE=2>#2</FONT></FONT></TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3>).
52</FONT></FONT></TT><FONT FACE="Times New Roman, serif"><FONT SIZE=3></FONT></FONT>This
53tells <B>mrun</B> to start two PALM executables. Coupled runs are
54only possible in parallel mode, which means that the <B>mrun</B>
55option <TT><FONT SIZE=2>-K parallel</FONT></TT> must also be set.&nbsp;The
56<B>mrun</B> call for coupled runs has to include the following
57coupling-related options:
60        <P STYLE="line-height: 100%"><TT><FONT SIZE=2>mrun </FONT></TT><FONT SIZE=2>...</FONT><TT>
61        </TT><TT><FONT SIZE=2>-K parallel -r “d3# d3o# </FONT></TT><FONT SIZE=2>...</FONT><TT>”
62        </TT><TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT> </TT><TT><FONT SIZE=2>-Y
63        “#1 #2”</FONT></TT><TT>.</TT></P>
65<P STYLE="line-height: 100%">The <TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT>&nbsp;</TT>option
66here specifies the total number of processors assigned to the coupled
67model. Currently, half of them are assigned to each of the two
68coupled executables. Therefore it is advisable to specify an even
69number with&nbsp;<TT><FONT SIZE=2>-X </FONT></TT><FONT SIZE=2>...</FONT><TT>
70</TT>. Otherwise, in case of an odd total number of processors, one
71processor remains idle.</P>
72<P STYLE="line-height: 100%">Each coupled executable has its own,
73unique set of I/O filenames; <A HREF="chapter_3.4.html#coupled">chapter
743.4</A> gives information on file name conventions of coupled runs.
75The configuration file .mrun.config has to be extended for coupled
76runs. It is recommended to duplicate existing file connection
77identifiers such as &quot;d3#&quot;, &quot;pr#&quot; etc. using the
78coupled ocean filenames accordingly. For example,&nbsp;the example of
79the previous chapters could be duplicated as follows:</P>
80<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/$fname/INPUT _p3d</FONT>
81<FONT SIZE=2>PARIN in:job:npe d3f ~/palm/current_version/JOBS/$fname/INPUT _p3df</FONT>
82<A HREF="chapter_3.4.html#BININ"><FONT SIZE=2>BININ</FONT></A> <FONT SIZE=2>in:loc d3f ~/palm/current_version/JOBS/$fname/OUTPUT _d3d</FONT>
84<A HREF="chapter_3.4.html#BINOUT"><FONT SIZE=2>BINOUT</FONT></A> <FONT SIZE=2>out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT _d3d</FONT>
86<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/$fname/MONITORING _rc</FONT>
87<A HREF="chapter_3.4.html#HEADER"><FONT SIZE=2>HEADER</FONT></A> <FONT SIZE=2>out:loc:tr d3# ~/palm/current_version/JOBS/$fname/MONITORING _header</FONT>
88<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/$fname/OUTPUT _pr_par</FONT>
89<A HREF="chapter_3.4.html#PLOT1D_DATA"><FONT SIZE=2>PLOT1D_DATA</FONT></A> <FONT SIZE=2>out:loc:tr pr# ~/palm/current_version/JOBS/$fname/OUTPUT _pr_in</FONT>
91<FONT SIZE=2>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/$fname/INPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_p3d</FONT>
92<FONT SIZE=2>PARIN</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> in:job:npe d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2>f ~/palm/current_version/JOBS/$fname/INPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_p3df</FONT>
93<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/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_d3d</FONT>
95<FONT SIZE=2>BINOUT</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc restart ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_d3d</FONT>
97<FONT SIZE=2>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/$fname/MONITORING </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_rc</FONT>
98<FONT SIZE=2>HEADER</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc:tr d3</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/MONITORING </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_header</FONT>
99<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/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_pr_par</FONT>
100<FONT SIZE=2>PLOT1D_DATA</FONT><FONT SIZE=2><B>_O</B></FONT><FONT SIZE=2> out:loc:tr pr</FONT><FONT SIZE=2><B>o</B></FONT><FONT SIZE=2># ~/palm/current_version/JOBS/$fname/OUTPUT </FONT><FONT SIZE=2><B>_o</B></FONT><FONT SIZE=2>_pr_in</FONT></PRE><P STYLE="line-height: 100%">
101The coupled ocean model filenames in the first column (e.g.
102<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>)&nbsp;must
103be specified as given in <A HREF="chapter_3.4.html#coupled">chapter
1043.4</A>; the file connection identifiers (e.g.&nbsp; <FONT SIZE=2>d3o#</FONT>)
105and the file name extension (e.g. &nbsp;<FONT SIZE=2>_o_p3d</FONT>)
106may be changed at the user's discretion.</P>
107<P STYLE="line-height: 100%">The coupler requires the following
108parameters to be equal in both <A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN</FONT></A>
109and&nbsp;<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>:
110<A HREF="chapter_4.1.html#dx">dx</A>, <A HREF="chapter_4.1.html#dy">dy</A>,
111<A HREF="chapter_4.1.html#nx">nx</A>, <A HREF="chapter_4.1.html#ny">ny</A>,
112<A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>, <A HREF="chapter_4.2.html#end_time">end_time</A>,
113<A HREF="chapter_4.2.html#restart_time">restart_time</A>, <A HREF="chapter_4.2.html#dt_restart">dt_restart</A>.
114In the coupled atmosphere executable,&nbsp;<A HREF="chapter_4.2.html#bc_pt_b">bc_pt_b</A>
115is internally set and does not need to be prescribed; in the coupled
116ocean executable, <A HREF="chapter_4.2.html#bc_uv_t">bc_uv_t</A>&nbsp;is
117internally set ('neumann') and does not need to be prescribed. The
118coupled ocean parameter file&nbsp;<A HREF="chapter_3.4.html#PARIN"><FONT SIZE=2>PARIN_O</FONT></A>
119should include dummy REAL value assignments to both
120<A HREF="chapter_4.1.html#top_momentumflux_u">top_momentumflux_u</A>
121and&nbsp;<A HREF="chapter_4.1.html#top_momentumflux_v">top_momentumflux_v</A>
122(e.g.&nbsp;top_momentumflux_u = 0.0, top_momentumflux_v = 0.0) to
123enable the momentum flux coupling.</P>
124<P STYLE="line-height: 100%">The coupling interval <A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>
125must be explicity set. In order to ensure synchronous coupling
126throughout the simulation, <A HREF="chapter_4.2.html#dt_coupling">dt_coupling</A>
127should be chosen larger than <A HREF="chapter_4.2.html#dt_max">dt_max</A>.</P>
128<P STYLE="line-height: 100%">It's also possible to perform precursor
129runs (one atmospheric and one oceanic) followed by a coupled restart
130run. In order to achieve this, the parameter <A HREF="chapter_4.1.html#coupling_start_time">coupling_time_start</A>
131must be set according to the <A HREF="../misc/precursor_run_control.pdf">documentation.</A></P>
133<P STYLE="line-height: 100%"><BR><FONT COLOR="#000080"><A HREF="chapter_3.7.html"><FONT COLOR="#000000"><IMG SRC="left.gif" NAME="Grafik1" ALIGN=BOTTOM WIDTH=32 HEIGHT=32 BORDER=1></FONT></A><A HREF="index.html"><FONT COLOR="#000080"><IMG SRC="up.gif" NAME="Grafik2" ALIGN=BOTTOM WIDTH=32 HEIGHT=32 BORDER=1></FONT></A><A HREF="chapter_3.9.html"><FONT COLOR="#000000"><IMG SRC="right.gif" NAME="Grafik3" ALIGN=BOTTOM WIDTH=32 HEIGHT=32 BORDER=1></FONT></A></FONT></P>
134<P STYLE="line-height: 100%"><I>Last change:&nbsp;</I> $Id:
135chapter_3.8.html 197 2008-09-16 15:29:03Z raasch $</P>
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