3.1. localization¶

The localization class determines how spatial and temporal localization is performed, a crucial aspect of how an LETKF operates. This include localization for horizontal, vertical, temporal, and state variable components.

Warning

The localization configuration is perhaps the least finished part of UMD-LETKF. Things here will likely change quite a bit as localization methods are added for other domains, and/or a way to generically and flexibly specify localization is added.

Parameters

The following parameters are available regardless of which localization class is selected. Additional parameters, described in subsequent sections here, will be required depending on which localization class is selected.

class:

type: string, required

The name of the localization class to use.

Currently, UMD-LETKF has two built-in classes that can be used, additional localization classes can be implemented by the user. The following options are available:

loc_novrt - A generic class that has no localization in the vertical, only in the horizontal.
loc_ocean - Localization specific to the ocean.

Note

All localization radii defined below are given as a standard deviation of a Gaussian. (Even though they are implemented as a compact Gaspari-Cohn function)

3.1.1. loc_novrt¶

The loc_novrt localization class implements a basic horizontal-only localization. The bare minimum needed to have a working LETKF. No vertical localization is performed.

Parameters

hzloc:

type: hzloc, required

Horizontal localization specification used for all observation types.

Example

localization:
  class: loc_novrt
  hzloc:
    type: linearinterp_lat
    value:
    - {lat: 0.0,  radius: 500.0e3}
    - {lat: 90.0, radius:  50.0e3}

3.1.2. loc_ocean¶

The loc_ocean localization class implements a localization strategy specific to the ocean. Namely, satellite and insitu observations can be given a different horizontal localization radius (given the abundance of satellite observations compared to insitu, satellite observations should be given a smaller horizontal localization radius). Also, vertical localization of the satellite observations to just the ocean mixed layer, can be enabled

Parameters

save_diag:	type: logical, default: true If true, diagnostic information specific to the ocean localization will be saved. See loc_ocean Diagnostics for more information on the fields that are saved.
diag_file:	type: string, default: diag.loc_ocean.nc The file to which ocean localization diagnostics are saved, if `save_diag` is set to true. See loc_ocean Diagnostics for more information
hzloc_prof:	type: hzloc, `required` The horizontal localization specification for insitu profiles. Insitu profiles are determined to be the observations and platform types that are NOT included in the following `sat_obs` or `sat_plats` parameters.
hzloc_sat:	type: hzloc, `required` The horizontal localization specification for satellite observations. Satellite observations are determined to be the observations and platform types that are included in the following `sat_obs` or `sat_plats` parameters. For each observation, if its type matches one listed in `sat_obs`, or its platform type matches one listed in `sat_plats`, it is considered a satellite observation (it does not have to match both).
tloc_prof:	type: float, default: -1.0 Temporal localization for insitu profiles (in hours). If < 0, temporal localization is disabled.
tloc_sat:	type: float, default: -1.0 Temporal localization for satellite observations (in hours). If < 0, temporal localization is disabled.
vtloc_surf:	type: vtloc, default: type=none The vertical localization specification for satellite observations. Insitu profiles do not have any vertical localization.
sat_obs:	type: array of strings, optional An array of observation names that are to be treated as satellite observation for localization purposes. See Observation and Platform Names.
sat_plats:	type: array of strings, optional An array of platform names that are to be treated as satellite observations for localization purposed. See Observation and Platform Names

vtloc Parameters

Specification of the vertical localization.

type:

type: string, default: none

The type of vertical localization to use for the ocean. Currently two options are available:

none - vertical localization is off, observations impact the entire vertical column.
bkg_t - surface observations are localized to the surface mixed layer, as calculated from a change in background temperature criteria.

bkg_t_delta:

type: float, required

The change in background temperature (Celsius) from the surface to some depth, used for calculating the depth of the ocean mixed layer.

bkg_t_var:

type: string

The name of the background temperature variable used for calculating the mixed layer depth. This state variable name must be one of those given in state.statedef.

Example

localization:
  class: loc_ocean
  save_diag: true
  hzloc_prof:
    type: linearinterp_lat
    value:
    - {lat: 0.0,  radius: 720.0e3}
    - {lat: 90.0, radius: 200.0e3}
  hzloc_sat:
    type: linearinterp_lat
    value:
    - {lat: 0.0,  radius: 500.0e3}
    - {lat: 90.0, radius: 50.0e3}
  sat_plats:
   - ocn_sat
  vtloc_surf:
    type: bkg_t
    bkg_t_delta: 0.2
    bkg_t_var: ocn_t

3.1.3. Common Types¶

hzloc Parameters

This parameter type is used to specify the characteristics of the horizontal localization.

type:

type: string, required

The type of horizontal localization to use. Currently, the only valid option is linearinterp_lat. This type gives a horizontal localization radius that changes with latitude. Several latitudes are specified, along with the desired radius, and linear interpolation is used to calculate the radius for any valid latitude.

value:

type: array of lat/radius values

An array of lat / radius pairs. See the example below for clarification.

lat: absolute value of latitude in degrees
radius: horizontal localization radius, meters. Given as the standard deviation of a Gaussian.

Note that all latitude values are positive. Currently, different values cannot be given for southern/northern hemisphere. If 0.0 and 90.0 are not included in the list of latitudes, they are implicitly added using the radius of the nearest given latitude.

Example

Note that in this example a latitudes between 0.0 degrees and 5.0 degrees have a localization radius of 500 km, all latitudes above 50.0 degrees have a radius of 100 km. In between they are appropriately linearly interpolated.

hzloc:
  type: linearinterp_lat
  value:
    - {lat:  5.0, radius: 500.0e3}
    - {lat: 10.0, radius: 300.0e3}
    - {lat: 50.0, radius: 100.0e3}