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some fully developed cumulonimbus. The most active of these four clusters,
located the furthest East, had developed suddenly 3 h 30 previously.
Towards 2 h 10, the cluster resulting from of this merging was still in its
horizontal extension phase, probably spreading of the anvils cumulonimbus
that were already at maturity. Imagery suggests that the strongest
cumulonimbus that made it up completed their development, but the
presence of convective "towers" under their anvils was very probable, even
if the imagery does not make it possible to confirm this, in the absence of a
thermal signature of "overshoot" phenomena.
2.4 Observations by an aircraft equipped with the amdar system
Some airliners are equipped with AMDAR systems (Aircraft Meteorological
Data Relay) that allow them to make observations of wind, temperature
and, in certain cases, of turbulence, then to transmit them in real time to
meteorological centres, in the form of a coded AMDAR message. The message
only identifies the transmitting aircraft by a code that does not make it possible
to identify either the airline or the flight.
These messages are transmitted in more or less real time to the meteorological
services (97% of the messages are sent in 90 minutes). The wind and temperature
observations are used to feed the digital weather forecast models.
In cruise, the frequency of the measurements is of the order of 7 to 8 minutes.
The observations made all along the flight path relate directly to the conditions
at the flight level, but do not, unlike infrared imagery, make it possible to
appreciate the conditions outside of the flight path, nor the three dimensional
extension of the phenomena encountered.
During the night of 31 May to 1st June, an airplane equipped with the AMDAR
system followed a route apparently similar to that of flight AF447, passing in
the vicinity of the same storm clusters, around 30 minutes earlier, at flight level
FL325. This aircraft only transmitted the wind and temperature measurements.
Figure 17 below indicates the positions of this airplane until 2 h 06 UTC (the
position most to the north of the flight path in the middle of the image),
overlaid with the Météosat infrared 9 image taken towards 1 h 52 UTC, with a
threshold to identify the cluster and the cumulonimbus, using the same classes
of colour as for figure 8. The observation position that is most representative
of the cluster is that at 1 h 44, indicated by a square.
F-GZCP - 1st June 2009
92
Figure 17: fl ight path of an airplane equipped with the AMDAR system until 2 h 06 UTC
overlaid with the Météosat 9 infrared observation, with a threshold, at 1 h 52 UTC
A variation of the temperature and of the wind measured before and after
the passage of the cluster is observable. The differences in temperature are
the only significant elements, but can be explained by the airplane’s change
in flight level, from level FL330 to the south of the cluster to level FL350 after
crossing it.
These AMDAR observations do not provide anything notable for the analysis
undertaken based on the infrared imagery, which is much more representative
of the storm phenomena encountered on the flight path of flight AF 447.
On the other hand, the superimposition of the flight path of the airplane and of
the infrared Météosat 9 images shows that the aircraft crossed the convective
cluster in a zone where the top temperatures of the cumulonimbus were cold,
comparable to those observed a few minutes later.
F-GZCP - 1st June 2009
93
3. Conclusions on the analysis of the meteorological situation
From a climatology perspective, the general conditions and the position of the
Inter-tropical Convergence Zone over the Atlantic were normal for a month of
June. The clusters of cumulonimbus characteristic of this zone were indeed
present, with significant spatial heterogeneity and a life of a few hours.
The infrared images taken every 15 minutes by the Météosat 9 geostationary
satellite are the best source of information to appreciate the evolution of these
clusters, but they do not make it possible to directly observe the conditions
encountered at the flight level. Further, the two most representative images
were taken around 7 minutes before and after the last ACARS message from
flight AF 447.
Analysis of infrared imagery does not allow any conclusion as to the exceptional
character of the storm activity in the area where flight AF447 disappeared, but
it shows, on the planned flight route, the existence of a cluster of powerful
cumulonimbus, identifiable from 1 h 30 UTC. This cluster resulted from the
　
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