Abstract. Global Positioning System Zenith Total Delay (GPS ZTD) can provide information about the water vapour in atmosphere. Its assimilation into the analysis used to initialize a model can then improve the weather forecast, giving the right amount of moisture and reducing the model spinup. In the last year, an high density GPS network has been created on the Basilicata region (south of Italy) by the Italian Space Agency in the framework of a national project named MAGIC2. MAGIC2 is the Italian follow on of the EC project MAGIC has. Daily operational data assimilation experiments are performed since December 2003. The results show that the assimilation of GPS ZTD improves the forecast especially during the transition from winter to spring even if a no very high model resolution (9km) is used.

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In this work, observations of polar stratospheric clouds (PSC) carried out during one flight of the stratospheric research aircraft Geophysica deployed in the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign in September–October 1999 are presented. An analysis of data from the two lidars and a backscatter sonde on board the Geophysica aircraft is presented, coupled with temperature measurements. The observations are analyzed with the aid of a mesoscale model to provide air mass thermal histories and a microphysical box model to simulate PSC formation. The results obtained from this comparison are discussed in view of the theories for PSC formation processes.

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SUMMARYAn analysis is presented of the MM5 high-resolution operational weather forecasts performed during the Special Observing Period (SOP) of the Mesoscale Alpine Programme (MAP). The domain-averaged model biases of both surface pressure and 2 m temperature suggest MM5 shortcomings related to the surface temperature cycle. The root mean square errors (r.m.s.e.s) for temperature, wind and relative humidity at two different levels and for several forecast times support this nding. The model results show dif culties in forecasting the 2 m temperature during periods of fair weather; furthermore, a few dif culties are found in forecasting the minimum of the temperature for regions under strong marine in uence, such as Baleari station. The equitable threat score (ETS), for a few selected IOPs (Intensive Observing Periods) having precipitation over the Po Valley, is used together with the areal distribution of the r.m.s.e.s to evaluate the MM5 at high resolution over the Alpine region. The results show reasonable skill in this region when the model is used in the high-resolution mode. The ETS using only the stations over the mountains or the plains, suggests a better model skill in the mountain areas than in the valley; whereas the r.m.s.e.s show an MM5 tendency to produce larger errors on the eastern side of the Po Valley than on the western side.Finally, the analysis of the precipitation time series for IOP 2b, at a few selected stations, con rms the model tendency to underestimate the rainfall at stations located along the Po Valley and to shorten the period of the precipitation.