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of its characteristics. Its top temperatures cooled suddenly, which indicates
it was the seat of a very rapid vertical development, more than 3 h hours 30
before the arrival of flight AF447. Then, its overall activity was maintained
with some cumulonimbus developed up to the tropopause.
Figure 16: evolution of the top temperature of the cluster marked A on fi gure 15. The time on
the lower scale is defi ned in relation to 0 h 37
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2.3.4 Summary
Analysis of infrared Météosat 9 imagery indicates that the cluster that was
crossing the planned flight path of the airplane towards 2 h 10, had formed
1 h 30 previously by the merging of four pre-existing clusters that contained
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.
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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.
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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.
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Interim report on the accident on 1st June 2009 to the Airbu(33)
