Model output associated with extreme convection 

Ensemble Control Forecast (ex-HRES) tends to over-forecast extreme convection, especially in the maritime tropics.  Forecast rapid vertical motion can result in spurious quasi-circular waves (sometimes rings) in convective precipitation fields. These gravity waves gradually spread outwards.  They can even move well upwind, giving a false impression of an eastward-moving trough.  The source of these false features should be identified and the effects discarded from forecasts.  Changes to the IFS moist physics in 2019 have reduced but not entirely removed this effect. 

Fig 9.6.6-1: An example of a forecast precipitation chart showing a very active convective area in the mid-Indian Ocean. The surrounding ring of forecast precipitation is associated with a spurious gravity wave (ripple effect) moving outward from the initial convective cell.  These rings of precipitation are incorrect and should be ignored.


Fig9.6.6-2: Ensemble control (Ex-HRES) forecast of precipitation associated with gravity waves propagating outward across central Africa from a pulse of very strong convection formed over the Gulf of Guinea (just to the southwest of the charts).  Model precipitation rate are shown for one such feature at T+120, T+132, T+144, data time 00Z 3 Sept 2018. The apparent trough is propagating anomalously against the flow and the precipitation is not correct.


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