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This icon returns a GRIB field of one of the following :

  • potential temperature
  • equivalent potential temperature
  • saturated equivalent potential temperature

Inputs are temperature, logarithm of surface pressure (lnsp)  (only if the input data is specified in model levels) and specific humidity (only if calculating equivalent potential temperature). See Holton, 3rd Ed, Appendix D, eq. D-9, for details on the scientific background

The generated fields can be simply visualised or saved as GRIB files.

From Macro/Python the icon can be called via the following set of functions: pott_m() , eqpott_m(), seqpott_m(), pott_p() , eqpott_p() and seqpott_p() (see description below).

The Potential Temperature Editor

The Potential Temperature editor belongs to a type of editors known as family editors which allows related sets of input specifications to be grouped in the same icon editor. The main computation type can be set via the Application parameter which offers these options:

  • Potential Temperature - To derive a potential temperature field from temperature data (and lnsp if using model levels)
  • Equivalent Potential Temperature - To derive an equivalent potential temperature field from temperature and humidity data (and lnsp if using model levels)
  • Saturated Equivalent Potential Temperature - To derive a saturated equivalent potential temperature field from temperature data (and lnsp if using model levels)

There is an additional top level option called Level Type to select the level type:

  • Model Levels - Derives the output using model levels. Requires an lnsp field additional to the temperature (and specific humidity) input data.
  • Pressure Levels - Derives the output using pressure levels. Requires only the temperature (and specific humidity) input data.

To operate with this icon first you need to select which type of potential temperature field you want to create (parameter Application) then set the type of level of your input (parameter Level Type ). The available parameters will then change in the editor according to your selection.


Script functions

In order to use this icon from Macro/Python you ned to use a different function for each top level parameter combination. For model levels the corresponding set of functions are as follows:

pott_m() , eqpott_m(), seqpott_m()

while for pressure levels the names are similar but take a different suffix:

pott_p() , eqpott_p() and seqpott_p()


Lnsp

Specifies the lnsp field as a GRIB icon. Only available/required when Level Type is set to Model Levels.

Temperature

Specifies the temperature field as a GRIB icon on either model or pressure levels.

Humidity

Specifies the specific humidity field as a GRIB icon on either model or pressure levels. Only available/required when Application is set to Equivalent Potential Temperature.


2 Comments

  1. yerni srinivas nekkali

    The pressure variable is not present in ERA5 hourly pressure level data. Only, the temperature is there. How can I calculate the potential temperature from the era5 data set? please suggest me.

  2. Sandor Kertesz

    For pressure level data the pressure is encoded in the grib message itself. So you just need to use the temperature parameter. E.g. a Python example:

    import metview as mv

# read pressure level temperature data
t = mv.read("my_t.grib")

# compute potential temperature
pt = mv.pott_p(temperature=t)

    See this gallery example (Python).