Like in the previous three interim reports there is no change to be mentioned here with respect to the initial description within the contract. Since this is a joint interim and final report, the latter will however be copied just below.

«The following is the methodology which will be employed (slight variations may occur) :

This NWP specific method is born out of three facts. First, meteorologists do not have any controlled laboratory: the atmosphere is their only «truth» and it never passes twice through the same state at any place. Hence a model is not only a forecasting tool but also a proxy laboratory for experimentation of new ideas that otherwise cannot be put to any acid test. While this concept leads to a study of the models for understanding their behaviour nearly as much as that of the atmosphere in upstream research, in the case of research for NWP it introduces the above-mentioned complex hierarchy of testing procedures. Second, the need to only consider applications that can be run without ever diverging or failing and at a speed characterised by the rule of thumb «one minute of elapse time for one hour of simulation» introduces constraints that need to be taken into account at a quite early stage of the process, something unknown in many other scientific activities. Third, the atmospheric behaviour is chaotic and its modelling reflects this fact through very non-linear characteristics. The truth about the validity of any assumption or tuning choice is thus very delicate to capture and may require an enormous amount of computing power (until statistical significance is reached) but for the design of rather sophisticated multi-stage validation protocols that aim at avoiding non-linearly induced pitfalls.»

In fact, one can retrospectively say that all the progress registered thanks to the ALATNET effort closely followed the above-described method, as anticipated at the start of the network. More important probably, all young researchers were trained in awareness of this methodology and its tight constraints, a tuition that should hopefully help them all along their further scientific activity.