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 the same diagnostic formula as in IFS: the vapour pressure is derived with respect to water above 273.16 K, to ice below 250.16 K, and to a mixed phase in between. See the IFS documentation at http://www.ecmwf.int/research/ifsdocs/ for detailsa 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 script (Macro/Python) the icon can be called as relhum(). | 