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should pose any problems in getting good wind measurements from this site.
Figure 11. Looking South-South-East from Site 5.
Figure 12. Looking West from Site 4.
Sensor Site #6
Site 6 is to the South-East of the East end of the runway, and is approximately 20
meters below the runway height. The tower is 15 meters tall. This is an unobstructed site.
Figure 13 is a view looking to the South-East of the site, and Figure 14 is a view looking
to the West.
Figure 13. Looking South-East from Site 6.
Figure 14. Looking West from Site 6.
Sensor Site #7
Site 7 is South of the runway, approximately 15 meters below the runway height.
The tower is 15 meters tall. This is an unobstructed site, with a small ditch to the East.
This ditch can be seen in both Figure 15, which looks to the South-East, and Figure 16,
which looks to the East.
Figure 15. Looking South-East from Site 7.
Figure 16. Looking East from Site 7.
Sensor Site #8
Site 8 is to the South of the mid-point of the runway, at an elevation of
approximately 15 meters below the runway height. The tower is 15 meters tall. The
terrain slopes down and then up going to the East, as can be seen in Figure 17, and is
relatively flat to the West. There are some agricultural hot-houses in close proximity to
the South-East, as can be seen in Figure 18. Neither of these features should pose any
problems in making good wind measurements.
Figure 17. Looking East from site 8.
Figure 18. Looking south-east from site 8
Sensor Site #9
Site 9 is located to the South of the runway, towards its West end. It is situated
approximately 16 meters below the runway height. The tower is 20 meters tall. This is an
unobstructed site with relatively flat ground surrounding it. Figure 19 is a view looking to
the South of the site, and Figure 20 looks to the West-North-West. The dirt mound that
can be seen in Figure 20 is due to some road work, and does not pose any problems with
the site.
Figure 19. Looking South from site 9.
Figure 20. Looking West-North-West from site 9.
Sensor Site #10
Site 10 is to the South-West of the West end of the runway. It is approximately 30
meters below the runway height. The tower is 25 meters tall. There is a new apartment
complex with three storey buildings just to the South of the site – as can be seen in Figure
21. The only potential problem would be with winds from the south, but as the sensor site
is slightly above the first floor of the buildings, and with height of the tower, there should
not be any significant degradation in the wind measurements. Furthermore, the prevailing
winds are from the Easterly directions. Figure 22 is a view looking to the West-North-
West of the site, showing the unobstructed terrain in that direction.
Figure 21. Looking South from site 10.
Figure 22. Looking West-North-West from site 10.
The Over-alerting Problem
One of the items that UCAR was asked to look at during the Tenerife site visit
was a persistent over-alerting with the LLWAS system. It was quite clear on inspection
that the problem was not of a meteorological nature, but rather, something to do with the
system hardware or software. Almos subsequently discovered a database error in the
Airport Configuration File (ACF). Almos then generated and loaded a new ACF that
should solve the problem.
Another problem that was observed during the visit was intermittency in some of
the sensor readings. Telvent personnel believed that the problem was due to a lack of
solar battery power at some of the sites, which in turn was due to a lack of maintenance at
the sites.
Discussions with Airport Meteorological and Air Traffic Staff
On 10 February, a meeting was held with airport meteorological staff and air
traffic controllers. One interesting wind shear condition was discussed: a persistent
summertime condition wherein pilots lose airspeed when descending through 1000 feet
on landings from the West. Air traffic controllers indicated that airspeed loses on the
order of 30 knots had been encountered. These are significant values, and have resulted in
go-around procedures on occasion.
Without further investigation, it is unclear what the specific mechanisms are that
could be generating this vertical shear of the horizontal wind phenomenon. Nevertheless,
a few potential causes can be postulated. From Figure 23, it is clear that the island of
Tenerife is dominated by the Pico de Teide, a 3718 meter volcanic peak. Vortices shed
off of this large terrain feature are one potential cause. It is well-known that verticallyaligned
vortices, known as a von Karman street, can be shed by oragraphic features such
as the Teide. However, there is also a secondary terrain feature which is located in close
　
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