This icon computes the relative humidity from temperature, specific humidity and logarithm of surface pressure (lnsp) GRIB data. Lnsp is only required if the input data is specified on (hybrid) model levels. The computations are based on a mixed-phase Tetens formula used by IFS for diagnostic purposes (see here on p116 for details from the latest model cycle (CY45R1, at the time of the writing of this documentation).
From Macro/Python the icon can be called as relhum().
The Relative Humidity Editor
Data
Specifies the temperature and specific humidity GRIB data required for the application. If the input is on (hybrid) model levels it must contain the lnsp field as well.