Variable transforms

Introduction

This section describes the various variable transforms (or conversions) available within UFO.

All variable transforms are performed using a unique filter (Observation Filters) called Variable Transforms, as shown in the example below:

window begin: 2018-04-14T21:00:00Z
window end: 2018-04-15T03:00:00Z

observations:
- obs space:
   name: test_relative_humidity1
   obsdatain:
      obsfile: Data/ioda/testinput_tier_1/sfc_obs_2018041500_metars_small.nc
   simulated variables: [specific_humidity, air_temperature, surface_pressure]
obs filters:
- filter: Variable Transforms
   Transform: ["RelativeHumidity"]
   Method: UKMO
   Formulation: Sonntag

The Variable Transforms filter has the following available yaml settings:

• Transform: name of the variable transform that need to be performed. (see Variable transforms).

• Method: [Optional] Method used during the variable transformation. This usually refers to the different Met Center. (See individual Variable transforms for possible choices and definitions)

• Formulation: [Optional] Name of a specific formulation used during the variable transformation. (See individual Variable transforms for possible choices and definitions)

• UseValidDataOnly: [Optional | default = true] Should the variable transform be applied only to valid data?

  Warning

  If UseValidDataOnly=true, the variable transform is not applied to observations that have a QCflag equal to either missing or bounds.

The new variable derived by the filter is then stored in the observation space within the DerivedObsValue group. Since variables in groups with the Derived prefix “overshadow” variables from corresponding groups without that prefix (see Derived Variables), these variables can normally be accessed as if they were in the ObsValue group.

Warning

Each variable transform requires a specific set of variables (as specified in the documentation). If any compulsory variable is missing, the code will raise an exception and stop.

Variable transforms

The variable transforms available are:

Humidity

• Relative Humidity
• Specific Humidity

Pressure

• Pressure from Height (using the ICAO atmosphere)
• Pressure from Height over a vertical profile

Wind

• Eastward (u) and northward (v) wind component
• Wind speed and direction

Formulations

The formuations available are:

• Heights to pressures (using the ICAO atmosphere)
• Saturated Vapor Pressure from T

Table listing all the symbol used

• Symbol glossary