In my output from one of the convection case study examples (expid g4a4) I find values of relative humidity > 100%. This is the case even when I output the values on model levels. The values larger than 100% all occur in the upper troposphere. So one question is how is the relative humidity calculate (with respect to water or ice)?

thanks 

 

4 Comments

  1. Filip Vana

    This is absolutely normal. It indicates areas with supersaturation. You don't need to worry about those values as they could be found also in observed humidity profiles.

  2. Victoria Sinclair

    I see really large values of relative humidity - up to 150%. Is this normal? I agree values just above 100% are ok as they are supersaturated, but 150% RH seems a lot to me.  

  3. Filip Vana

    Yes, for very cool areas even 150% are still perfectly normal (although it shouldn't go much beyond this limit). You should be aware that for temperatures bellow -23 Celsius the saturation of water vapour is calculated with respect to ice.

  4. Filip Vana

    Here is a bit more on supersaturated relative humidity kindly provided by R. Forbes:

    Attached is a plot of the RH wrt ice as a function of temperature. Ice supersaturations in the IFS
    are allowed up to water saturation (T>-40degC) and up to the homogeneous nucleation limit T<-40degC.
    So values of 150% can be reached at temperature of -50degC or colder. These supersaturations are
    observed near the tropopause.
    The relevant reference is: Tompkins, A. M., Gierens, K. and Rädel, G. (2007),
    Ice supersaturation in the ECMWF integrated forecast system. Q.J.R. Meteorol. Soc., 133: 53–63.