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dossiers/science_et_
techniques/the_satellites_
meteorologiques?page_
id=2802 for details on the
analysis of satellite images.
F-GZCP - 1st June 2009
83
produced infrared signatures comparable or colder than those of the clusters
that crossed the planned route of flight AF447, on 1st June 2009 towards 2 h 00.
In the night of 31 May to 1st June 2009, above the ocean, the ITCZ was the seat
of notable but discontinuous stormy activity; several convective clusters (multicell)
are identifiable, separated by the zones of cumulus, stratocumulus and
altocumulus.
2.3 Analysis of the cluster located on the planned route
2.3.1 Evolution observed between 0 h 00 and 3 h 00
Between 0 h 30 and 3 h 00, infrared imagery shows a region of development of
storm clouds in the ITCZ, north of Fernando de Noronha. The cumulonimbus
rapidly formed an extended and organised cluster according to a line oriented
west-east. Without being exceptional, the west-east extension of this cluster,
which crossed the planned route of flight 447, was sufficiently large, of the
order of 400 km (see the satellite image animation over three hours available
on the digital addition to the preliminary report).
Towards 2 h 00, this cluster certainly included some of the powerful
cumulonimbus associated with of the strong vertical movement zones, but
analysis of the infrared images does not show, in itself, temperatures at
the tops of clouds significantly colder than that of the tropopause. Analysis
of infrared imagery does not make it possible to draw a conclusion on the
presence of extremely powerful vertical movements, associated with of the
"overshoot" phenomena.
2.3.2 Detailed analysis of the image taken at 2 h 07
On the infrared images presented hereafter, the temperatures of cloud tops
that are lower than - 40 °C are coloured. This first "threshold" of -40 °C makes
it possible to define the zones for which the clouds had high tops, whether
divergent cirrus associated with the cumulonimbus anvils or of their "towers"
when they were not masked or when they had temporarily crossed the
tropopause.
The convective cluster located on the planned route of flight AF447 is indicated
by an oval on Figure 8. bearing in mind the timing system for the Météosat
images, this observation occurred at 2 h 07, or around three minutes before
the last FMS position communicated by ACARS by flight AF447 at 2 h 10 and
around seven minutes before the last ACARS message. No Météosat 9 images
coincide with the time of this last message: the nearest Météosat infrared
observations occurred around 7 minutes before and after the last message from
flight AF447.
F-GZCP - 1st June 2009
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Figure 8: Météosat 9 image, infrared channel 10.8 μ, made on 1st June at 2 h 07, with, in
colour, the temperatures at the cloud tops colder than -40 °C. This thresholding allows a fi rst
characterisation of the convective clusters.
The analysis then continues by adapting colder and colder thresholds, to
characterise the zones that are smaller and smaller, where the tops of the
clouds are higher and higher. Figures 9, 10, 11 and 12 that follow were obtained
from thresholds of -50 C, -60 C, -70 C and -75 C respectively. The last position
information communicated by the airplane at 2 h 10 (point named "ACARS
2 h 10") is indicated on these satellite images(2).
(2)The pixels of the
satellite image
have a resolution
of 3 km and are
positioned with
precision of the
order of a km,
much lower than
that of the GPS.
F-GZCP - 1st June 2009
85
Figure 9: Infrared Météosat 9 image taken on 1st June around 2 h 07
"thresholded", with masking of the temperatures above -50 °C
Figure 10: infrared Météosat 9 image taken on 1st June around 2 h 07,
"thresholded", with masking of the temperatures above -60 °C
F-GZCP - 1st June 2009
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Figure 11: infrared Météosat 9 image taken on 1st June at 2 h 07,
"thresholded", with masking of the temperatures above -70 °C
Figure 12: infrared Météosat 9 image taken on 1st June at 2 h 07,
"thresholded", with masking of the temperatures above -75 °C
F-GZCP - 1st June 2009
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It is notable that at 2 h 07 the coldest temperatures are of the order of -75 °C
to -80 °C, while the tropopause was located between FL500 and FL520, with a
temperature close to - 80 °C : some of the cumulonimbus in the cluster reached
the altitude of the tropopause and their stage of maturity, but imagery does
　
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