Changes between Version 50 and Version 51 of OMI_observation_modules

Timestamp:

Jun 18, 2024, 11:19:37 AM (3 months ago)

Author:

lnerger

Comment:

--

OMI_observation_modules

@@ -180 +180 @@
 - **non-isotropic localization**: Nonisotropic localization was introduced with PDAF V2.2: `cradius` and `sradius` can be declared as vectors of length `thisobs%ncoords` and each element can get a different value. In this case, the values define a non-isotropic localization according to the values specified in `cradius` and `sradius`. PDAF-OMI will use these values to compute a directional localization radius.
 - **2D+1D factorized non-isotropic localization**: With PDAF V2.2.1 a factorized 2D+1D localization can be specified (see [wiki:OMI_observation_modules#thisobsdisttype explanation of disttype]. If the non-isotropic localization is used one can specify different weight functions for the vertical and horizontal directions. This is achieved by declaring `loweight` as a vector of size 2. Now the first element specifies the weight function (according to the table above) for the horizontal direction and the second element specified the wieght function for the vertical direction. When 'locweight' is used as a scalar variable, it specified the weight function in the horizontal direction while the weight function in the vertical dircetion is a constant value of one.
+- A common choice is to use `locweight=2` or `locweight=4` in combination with `cradius=sradius`. Choosing `sradius>cradius` is possible, but `sradius<cradius` should be avoided (one would set the weights of distant observation to zero, but would still assimilate them). 
 
 == `localize_covar_OBSTYPE` ==
@@ -206 +207 @@
 - **non-isotropic localization**: Nonisotropic localization was introduced with PDAF V2.2: `cradius` and `sradius` can be declared as vectors of length `thisobs%ncoords` and each element can get a different value. In this case, the values define a non-isotropic localization according to the values specified in `cradius` and `sradius`. PDAF-OMI will use these values to compute a directional localization radius.
 - **2D+1D factorized non-isotropic localization**: With PDAF V2.2.1 a factorized 2D+1D localization can be specified (see [wiki:OMI_observation_modules#thisobsdisttype explanation of disttype]. If the non-isotropic localization is used one can specify different weight functions for the vertical and horizontal directions. This is achieved by declaring `loweight` as a vector of size 2. Now the first element specifies the weight function (according to the table above) for the horizontal direction and the second element specified the wieght function for the vertical direction. When 'locweight' is used as a scalar variable, it specified the weight function in the horizontal direction while the weight function in the vertical dircetion is a constant value of one.
-
+- A common choice for the localization is to use `locweight=2` or `locweight=4` in combination with `cradius=sradius`. Choosing `sradius>cradius` is possible, but `sradius<cradius` should be avoided (one would set the weights of distant observation to zero, but would still assimilate them). 
+- Particular for the LEnKF: When choosing `locweight=1` (exponential decrease) with a finite value of `cradius` if might be that the localized covariance matrices are no longer positive semidefinite. Mathematically consistent for `locweight=1` would be to set `cradius` so that the full model domain is covered. The width of the localization weight function is then defined by `sradius`. For `locweight>1` one should set `cradius=sradius`.
 
 == Additional routines for 3D-Var ==