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MODULE cov_cutoff

Contact: Jeff Anderson
Reviewers:  
Revision: $Revision: 1.5 $
Release Name: $Name: pre_iceland $
Change Date: $Date: 2005/06/08 17:07:18 $
Change history: see CVS log

OVERVIEW

Computes the weight with which an observation should impact a state variable that is separated by a given distance. The distance is in units determined by the location module being used.




OTHER MODULES USED

types_mod
utilities_mod



PUBLIC INTERFACE

use cov_factor_mod, only : comp_cov_factor

Optional namelist interface &cov_cutoff_nml may be read from file input.nml.




PUBLIC COMPONENTS


var = comp_cov_factor(z_in, c, localization_override)
real(r8)                              ::  comp_cov_factor 
real(r8), intent(in)                  ::  z_in 
real(r8), intent(in)                  ::  c 
real(r8), optional                    ::  localization_override 

Description

Returns a weighting factor for observation and state variable separated by distance z_in and with a half-width distance, c. Three options are provided and controlled by a namelist parameter. The optional argument localization_override controls the type of localization if it is present.

z_in     The distance between an observation and state variable.
c Factor that describes the localization function. Describes the half-width of the functions used here.
localization_override Controls localization type if present. Same values as for namelist control.
var Covariance value returned.



NAMELIST

We adhere to the F90 standard of starting a namelist with an ampersand '&' and terminating with a slash '/'.

namelist / cov_cutoff_nml /  select_localization
Contents Type Description
select_localization integer Selects the localization function.
1 = Gaspari-Cohn 5th order polynomial with halfwidth c.
2 = Boxcar with halfwidth c (goes to 0 for z_in > 2c).
3 = ramped boxcar. Has value 1 for z_in < c and then reduces linearly to 0 at z_in = 2c.



FILES




REFERENCES

Gaspari and Cohn QJRMS, 125, 723-757. (eqn. 4.10)

ERROR CODES and CONDITIONS

RoutineMessageComment
comp_cov_factor Illegal value of "select_localization" in cov_cutoff_mod namelist Only values 1 through 3 select a localization function.



KNOWN BUGS




FUTURE PLANS




PRIVATE COMPONENTS

Discussion