Convection in PIDCAP part I: Evaluating LAM convection

Leopold Haimberger, Michael Hantel

One goal of BALTEX is to quantify the energy and water cycle over the Baltic region through LAMs. The convective components of these cycles cannot be explicitly modelled and thus are parameterized. In this two-part paper we consider the total convective heat flux c as key sub-gridscale quantity. We use it, in the present Part I, for a model intercomparison. We have four European LAMs (EM, BM, REMO and HIRLAM) at our disposal and run them, both in the prognostic and in the diagnostic mode, for a 9-day target period (Aug/Sep 1995) located within the convectively active part of PIDCAP. We find in the prognostic mode that the vertical profile of c is in most cases characterized by boundary layer convection. The flux is strongest at the surface (c ≈ - 100 W/m2) and becomes weaker at higher levels. In three deep convection experiments we select columns with a maximum number of lightning events, a maximum precipitation rate and a maximum c. These events are rare (order of 1 % of all columns) but show free atmosphere fluxes of up to c ≈ -300 W/m2. This result is supported by the net condensation rate CON which is complementary to c. The differences between the LAMs in terms of c and CON are small but significant. From the analysed gridscale fields of the LAMs we further derive, in the diagnostic mode, profiles of c, CON and other convective parameters and compare them with their forecast equivalents. The comparison is best for the HIRLAM model. This suggests that the physical package of HIRLAM, due to its hybrid convection scheme STRACO, may be a bit more realistic than those of EM, BM and REMO. Conclusion of Part I is that the total convective heat flux c is useful to make the model physics comparable across LAMs. In Part II, the problem how to diagnose c from observed gridscale data will be reviewed.

Department of Meteorology and Geophysics
Meteorology and Atmospheric Physics
No. of pages
Publication date
Peer reviewed
Austrian Fields of Science 2012
1030 Physics, Astronomy
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