a) Politecnico di Milano (1), Istituto Agrario di S. Michele all'Adige (1), Uni Modena (2), Uni Brescia (1)

Table 3-6. Atmospheric electricity measurements (see legend in Table 3-1).

3.2.3 Mesoscale Convective Systems in the Alpine Environment 

Given the good coverage of the Po Valley by PBL instruments and in particular of the Lago Maggiore area during the SOP, the conditions for initiation of mesoscale convective systems are best observed and documented there. However, developing and moving systems can be tracked by aircraft and the high-technology standard Doppler radars all over the Po Valley. Particularly good observations will be possible, when the systems move over the ground-based target area.

3.3 North-east Italian / Slovenian Mission Area

This area is well covered by the operational Doppler radars near Bologna, Teolo, at Noventa di Piave and Cervignano del Friuli and the non-Doppler at Istrana with significant overlap of the scanning ranges of the Doppler radars. Furthermore the region is well covered by surface station networks as well as by a number of remote-sensing boundary layer instruments. In Slovenia an additional weather radar station will be set up for the time of the SOP. An overview is presented in Fig. 3-6.

Due to the excellent "background coverage" by operational instrumentation, no additional ground-based instrumentation is installed in this mission area. Rather it is proposed for airborne missions given the occurrence of important precipitation events.

However, one mobile upper-air sounding station for inflow probing as well as for upstream-measurements for the gap-flow studies (Brenner pass) is currently planned at Verona.

Figure 3-6. Layout of the north-east Italian / Slovenian mission area. Surface stations: see inset legend; Radiosoundings at Udine, Ljubljana and Verona; radar stations at Monte Grande, Noventa di Piave; Istrana, Fossalon die Grado and in western Slovenia; #: permanently installed RASS (Ostiglia); @: permanently installed (Doppler) sodar (Ostiglia, Porto Tolle, Fusina).

3.4 Rhine Valley Target Area

3.4.1 Rationale

The Rhine Valley between the town of Chur and the Lake of Constance is selected as target area for the investigations of the unstationary aspects of Foehn in a large valley and the interaction with the pre-existing PBL. The main arguments are the following:

• maximum frequency of Foehn events during the fall season (slightly higher than the Reuss valley, cf. Fig. 3-7),
• "broad" valley with well defined side-walls, length ca. 75 km,
• 3 d effects by side valleys,
• well defined geometry.

Fig. 3-7 illustrates the mean occurrence of Foehn during fall at a sample of Foehn-prone climatological stations in Switzerland. The basis of these statistics is the number of observations with Foehn where observations are made three times daily at 07, 13 and 19 local time. In Fig. 3-8 the probability of the occurrence of a given number of Foehn observations at Vaduz during the SOP season (15 August to 15 November) is illustrated. These statistics are based on a 26 year (1971-1996) record with three observations daily. The probability to have more than at least 6 Foehn observations is higher than 80 % (60 % for at least 12 events). The probability curve does not attain 100 % since no Foehn event occurred in 1978. However, general Foehn flow over the Alps is more frequent than these numbers suggest, since during autumn cold air in the valley floor may hinder the touch down of the Foehn to the ground. From the same data record it can be deduced that short Foehn episodes are more frequent than long-lasting periods (Fig. 3-9).

Figure 3-7. Mean number of Foehn observations during the fall season (Sept., Oct., Nov.) at a selection of meteorological stations in Switzerland (long-term records). Observations are carried out daily at 07, 13 and 19 local time; Rhine Valley. (courtesy of S. Bader)

Figure 3-8. Probability of a given number of Foehn observations (07/13/19 local time) to occur at Vaduz during the SOP season (15 August to 15 November). (courtesy of M. Bolliger, MeteoSwiss).

Figure 3-9. Number of events with a given number of consecutive Foehn observations (07/13/19 local time) at Vaduz. (courtesy of M. Bolliger, MeteoSwiss).

The Rhine Valley is a multi-national target area (A/CH/D/FL) and less investigated than the Reuss Valley (Gotthard). The upstream topography may be more complex, although it seems, that the Lago Maggiore area is in many cases of SW to S flow favourably located upstream of the Rhine Valley as it is for the Reuss Valley.

3.4.2 Instrumentation

An outline of the Rhine Valley target area is given in Fig. 3-10. The summary of special equipment installed during the SOP is listed in Table 3-7. Furthermore aircraft will be deployed to study the flow structure, vertical fluxes and turbulence. Stemme and Merlin are the candidate aircraft.

Table 3-7. Extra instruments in the Rhine Valley target area (see legend in Table 3-1).

Figure 3-10. Tentative layout of the Rhine Valley target area.

3.5 Brenner pass Target Area

The Brenner pass is by far the deepest gap in the Alpine chain. This makes it the target area for the investigation of gap flow and shallow Foehn. The Wipptal which is on the Austrian side of the Brenner pass, will be equipped with different types of additional in-situ (meteorological surface stations, microbarographs, radiosoundings) and remote-sensing (UHF profiler, NCAR scanning Doppler lidar) instruments. Deployment of the Merlin and Fokker, the Electra and the P-3 are also advisable to probe the structure of the flow through the gap.

The list of special instruments deployed in the Brenner target area is given in Table 3-8. An overview map is displayed in Fig. 3-11.

Table 3-8. Extra instruments in the Brenner target area (see legend in Table 3-1).

Figure 3-11. Tentative layout of Brenner target area for gap flow studies.

3.6 Research Aircraft

Table 3-9 presents a summary of the research aircraft proposed for participation in MAP. Their availability is very likely. The anticipated use of the individual aircraft for the scientific projects presented in chapter 2 together with the prominent instrumentation is also summarized in Table 3-9. Some general characteristics are summarized in Table 3-10 and visualized as "endurance-ceiling scatterplot" in Figure 3-12.

Table 3-9. Proposed research aircraft

Table 3-10. General characteristics of the aircraft.

  ^*) endurance adapted to runway length in Innsbruck (IBK)

Figure 3-12. Ceiling versus endurance of the aircraft listed in Table 3-10 (approximate). FA: Falcon; E: Electra; ME: Merlin; FO: Fokker ARAT; S10: Stemme S10VC; PP: Pilatus Porter.

3.7 Special METEOSAT Support for the SOP

3.7.1 Novel Scanning Strategy

Geostationary satellite coverage of the MAP area will be ensured by two METEOSAT spacecraft. The normal half-hourly image dissemination will be provided by METEOSAT 7, which will be the operational satellite at the time of the SOP (positioned at 0° longitude). METEOSAT 6, the back-up satellite, will be situated at 10° W and carry out rapid scans of the MAP area on demand. The rapid scan image data will be rectified to 0° degrees. The main interest is in rapid scanning with six or eight scans per 30 minutes. The current preference is for six rapid scans, that is an image repetition time of about 5 min providing the full-disk lines between approximately 39°N and 56° N latitude. A typical image of the infrared channel is shown in Fig. 3-13 a and the corresponding sea-land mask in Fig. 3-13 b.

Figure 3-13. METEOSAT infrared sample image (upper panel) for the radpid scan strategy and
corresponding sea-land mask (lower panel)

The period of rapid scanning will be requested by the MAP mission selection team with a lead time around 24 hours. It will probably not be possible to operate METEOSAT 6 in a permanent imaging mode, since the equipment used for MAP processing will also be used to provide redundancy for the prime operational and the INDOEX missions. It is foreseen to start imaging by METEOSAT 6 approximately six hours before the time requested for rapid scan coverage, in order to allow a sufficient warm-up phase for the image rectification system to stabilise. Then rapid scanning lasts for a period of about six hours. This period may be extended if the rapid scanning mode is interrupted to acquire one or two nominal images to stabilize the rectification algorithm. Rapid scans can be requested for any time of the day. 

3.7.2 Scientific Needs for "Special" Satellite Observations

Scientific needs for a METEOSAT rapid scan strategy during MAP can be seen in several aspects, namely deep convection monitoring, satellite wind field extraction, rainfall estimation and mesoscale analysis. Observations conducted by means of rapid scan from GOES-8/9 over the U.S. Great Plains have already contributed to document mechanism of storm evolution. Rapid scans of the order of 5 min by METEOSAT will greatly improve the monitoring of deep convective cloud formation and evolution within the MAP area. High-frequency METEOSAT imagery over the MAP area can contribute to wind derivation tests for ingestion into forecast models. Infrared precipitation estimation methods will be tested against an unprecedented data set of rain gauge and radar measurements. High-frequency scanning strategies give the possibility of obtaining rainfall maps at time intervals approaching the radar frequency. Better statistics and calibration are considered achievable. High-resolution mesoscale models will benefit from the availability of cloudiness and cloud temperature maps at a few minutes interval. Last but not least the availability of frequent scans in the water vapour channel is important for the analysis of convergence/divergence in the upper air structures. PV streamer research and upper-tropospheric feature studies, in general, will benefit from such images.