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ALADIN QUASI-OPERATIONAL BULLETIN N° 1E. Legrand (SCEM/Prévi/COMPAS) for"The ALADIN team"June 1, 1994 Since yesterday ALADIN has reached its quasi-operational status. As you surely did, we have also noticed the development of a numerical instability over Poland at 36 hours. Reasons for this abnormal behaviour are under investigation. It is extremely unlikely that the known phenomenon of orographic resonance with semi-Lagrangian time-stepping could be here at work. Let us however explain what happened in the last weeks before pre-operational implementation and why we could not detect beforehand this worrying behaviour. The next paragraph will however be a very technical one and can be jumped over without lost of any important general information. In order to be able to increase the horizontal resolution by a factor 1.3 we decided on 26/04 to use the semi-Lagrangian time-stepping developed by starting from the (yet under test) semi-Lagrangian version of ARPEGE. While the semi-Lagrangian algorithm in itself did not create too many problems (and they were solved rather quickly) it indirectly brought in our path two very serious difficulties.
In short, ALADIN is still quasi-operational, we are aware of some weaknesses and need further input from you for detecting any abnormal behaviour. In that sense, many BULLETINS like this one will be necessary and we would like to get from you as soon as possible the name of a contact point to which they could be sent directly. Finishing on a positive note, let us recall that the whole ARPEGE + ALADIN schedule will soon be pushed earlier by about one hour. This is currently supposed to happen on June the 13th. At that stage the window of RETIM ALADIN reception should roughly become 4 to 5 UTC. |