• 6.3.1.1 Introduction
• 6.3.1.2 OBCS configuration and compiling
• 6.3.1.3 Run-time parameters
  • 6.3.1.3.1 Enabling the package
  • 6.3.1.3.2 Package flags and parameters
  
  
• 6.3.1.4 Defining open boundary positions
• 6.3.1.5 Equations and key routines
  • 6.3.1.5.1 OBCS_READPARMS:
  • 6.3.1.5.2 OBCS_CALC:
  • 6.3.1.5.3 ORLANSKI
  • 6.3.1.5.4 OBCS_PRESCRIBE_READ
  • 6.3.1.5.5 OBCS_BALANCE
  • 6.3.1.5.6 OBCS_APPLY_*:
  • 6.3.1.5.7 OBCS_SPONGE
  • 6.3.1.5.8 OB's with nonlinear free surface
  
  
• 6.3.1.6 Flow chart
• 6.3.1.7 OBCS diagnostics
• 6.3.1.8 Reference experiments
• 6.3.1.9 References
• 6.3.1.10 Experiments and tutorials that use obcs

6.3.1 OBCS: Open boundary conditions for regional modeling

Authors: Alistair Adcroft, Patrick Heimbach, Samar Katiwala, Martin Losch

6.3.1.1 Introduction

6.3.1.2 OBCS configuration and compiling

As with all MITgcm packages, OBCS can be turned on or off at compile time

• using the packages.conf file by adding obcs to it,
• or using genmake2 adding -enable=obcs or -disable=obcs switches
• Required packages and CPP options:
  To alternatives are available for prescribing open boundary values, which differ in the way how OB's are treated in time: A simple time-management (e.g. constant in time, or cyclic with fixed fequency) is provided through S/R obcs_external_fields_load. More sophisticated ``real-time'' (i.e. calendar time) management is available through obcs_prescribe_read. The latter case requires packages cal and exf to be enabled.

Parts of the OBCS code can be enabled or disabled at compile time via CPP preprocessor flags. These options are set in OBCS_OPTIONS.h. Table 6.3.1.2 summarizes them.

6.3.1.3 Run-time parameters

Run-time parameters are set in files data.pkg, data.obcs, and data.exf if ``real-time'' prescription is requested (i.e. package exf enabled). These parameter files are read in S/R packages_readparms.F, obcs_readparms.F, and exf_readparms.F, respectively. Run-time parameters may be broken into 3 categories: (i) switching on/off the package at runtime, (ii) OBCS package flags and parameters, (iii) additional timing flags in data.exf, if selected.

6.3.1.3.1 Enabling the package

6.3.1.3.2 Package flags and parameters

6.3.1.4 Defining open boundary positions

There are four open boundaries (OBs), a Northern, Southern, Eastern, and Western. All OB locations are specified by their absolute meridional (Northern/Southern) or zonal (Eastern/Western) indices. Thus, for each zonal position a meridional index specifies the Northern/Southern OB position, and for each meridional position , a zonal index specifies the Eastern/Western OB position. For Northern/Southern OB this defines an -dimensional ``row'' array / , and an -dimenisonal ``column'' array / Positions determined in this way allows Northern/Southern OBs to be at variable (or ) positions, and Eastern/Western OBs at variable (or ) positions. Here, indices refer to tracer points on the C-grid. A zero (0) element in , means there is no corresponding OB in that column/row. For a Northern/Southern OB, the OB V point is to the South/North. For an Eastern/Western OB, the OB U point is to the West/East.

 For example
     OB_Jnorth(3)=34  means that:
          T( 3 ,34) is a an OB point
          U(3:4,34) is a an OB point
          V( 4 ,34) is a an OB point
 while
     OB_Jsouth(3)=1  means that:
          T( 3 ,1) is a an OB point
          U(3:4,1) is a an OB point
          V( 4 ,2) is a an OB point

For convenience, negative values for Jnorth/Ieast refer to points relative to the Northern/Eastern edges of the model eg. means that the point is a northern OB.

Add special comments for case #define NONLIN_FRSURF, see obcs_ini_fixed.F

6.3.1.5 Equations and key routines

6.3.1.5.1 OBCS_READPARMS:

6.3.1.5.2 OBCS_CALC:

• constant vertical profiles as specified in file data (tRef(Nr), sRef(Nr)) with zero velocities ,
• values determined via Orlanski radiation conditions (see below),
• prescribed time-constant or time-varying fields (see below).

6.3.1.5.3 ORLANSKI

6.3.1.5.4 OBCS_PRESCRIBE_READ

6.3.1.5.5 OBCS_BALANCE

6.3.1.5.6 OBCS_APPLY_*:

6.3.1.5.7 OBCS_SPONGE

6.3.1.5.8 OB's with nonlinear free surface

6.3.1.6 Flow chart

C     !CALLING SEQUENCE:
c ...

6.3.1.7 OBCS diagnostics

Diagnostics output is available via the diagnostics package (see Section 7.1). Available output fields are summarized in Table 6.3.1.7.

Table 6.4:  

6.3.1.8 Reference experiments

6.3.1.9 References

6.3.1.10 Experiments and tutorials that use obcs

• Ocean experiment in exp4 verification directory.

Copyright © 2006 Massachusetts Institute of Technology

Last update 2011-01-09