Meteosat-9 IR images

An Air France Airbus A330-200 — Flight #447 en route from Rio de Janeiro, Brazil to Paris, France — crashed in the tropical Atlantic Ocean on 01 June 2009 (surface analysis). Shortly after the last radio contact about 350 miles (565 km) northeast of Natal, Brazil (station identifier SBNT), the aircraft likely traversed an area of intense deep convection which had formed within a broad band of high total precipitable water along the Intertropical Convergence Zone (ITCZ). This convection could be seen on EUMETSAT Meteosat-9 10.8 µm IR images (above) in the region between 2º N to 4º N latitude and 25º W to 35º W longitude.  Some of the individual convective clusters appeared to be developing very quickly — this leads to speculation that turbulence in the vicinity of these rapidly-developing storms may have played a role in the accident.

A closer look at the ITCZ convection is shown using Meteosat-9 IR imagery with a magnification factor of 2 (below; also available as a QuickTime animation). There were a number of times when the minimum cloud top IR brightness temperature was -80º C or colder (light purple color enhancement), with the coldest cloud top temperature of -82º C occurring at 00:15 UTC. While this is certainly a cold cloud top temperature value, it cannot be considered “extreme” by any means: cloud top temperatures in tropical weather systems have been known reach -90º C or colder on occasion.

Air France Flight 447 last radioed their position at the  “INTOL” waypoint  at 01:33 UTC, and according to their flight plan they were then supposed to proceed to the “SALPU” and the “ORARO” waypoints along Airway UN873. At the INTOL waypoint, they communicated that they expected to reach the “TASIL” waypoint around 02:20 UTC (these waypoints are labeled on the IR images below). During  the 02:10-02:14 UTC timeframe, a series of automated ACARS fault messages was transmitted by the aircraft when it was approximately 54 miles from reaching the TASIL waypoint (the aircraft had possibly just cleared the northern fringes of the band of ITCZ convection around that time).

Meteosat-9 IR images (magnified by a factor of 2)

The brightness temperature difference values between the Meteosat-9 water vapor and IR window channels (6.2 µm – 10.8 µm) were calculated in an effort to try and highlight the most vigorous areas of convective development (below). The assumption is that when intense convection overshoots the tropopause into the warmer stratosphere, the water vapor that is pushed above the cloud top emits radiation at a warmer temperature than the actual cloud top below. Many pixels in the band of ITCZ convection exhibited WV-IR brightness temperature difference values in the 3-5º C range (darker red color enhancement). Of particular interest is the comparatively small cluster of convection that developed very rapidly around 02:00 UTC, near 1.75º N latitude and 31.7º West longitude (north of waypoint “SALPU”) — this cluster of convection exhibited WV-IR brightness temperature difference values as high as 4º C at 02:15 UTC. Could this rapidly-developing convective cell have generated severe turbulence that affected Air France flight 447 as it was passing nearby, en route to waypoint “TASIL”?

Meteosat-9 Water Vapor – IR brightness temperature difference

A comparison of the 3-km resolution Meteosat-9 10.8 µm IR and the 4-km resolution GOES-10 10.7 µm IR images (below; magnified to an effective resolution of 1 km) shows that the cloud top IR brightness temperatures  generally appeared to be about 3-6º C warmer on the GOES-10 imagery — the coldest GOES-10 IR brightness temperature was -77º C at 01:15 UTC. The coarser 4-km GOES-10 IR pixel resolution tended to “smooth out” the small-scale temperature structure of the cold cloud tops; therefore, a finer cloud top temperature structure was apparent on the 3-km resolution Meteosat-9 IR imagery.

Meteosat-9 and GOES-10 IR images

The 00:00 UTC rawinsonde report from Fernando de Noronha, Brazil (below) indicated that the tropical tropopause level was probably located near the 100 hPa pressure level (at a height of 16,649 meters, or 54,623 feet), where the minimum temperature was -77.7º C. The presence of cloud top IR brightness temperatures colder than -80º C on the Meteosat-9 imagery suggests that many of the strongest updrafts were likely penetrating the tropopause — and such overshooting thunderstorm updrafts have been known to initiate strong gravity waves aloft that have generated moderate to severe turbulence.

Fernando de Noronha rawinsonde report

Meteosat-9 6.25 µm “water vapor channel” images (below) showed none of the typical water vapor signatures associated with turbulence in the immediate region of the ITCZ convection — however, it did indicate the presence of a southwestward-propagating wave (located between 7-8º N latitude and 35-40º W longitude) that appeared to be responsible for initiating the formation of a patch of high clouds near 8º N 38º W. The water vapor imagery depicted a region of drier mid-tropospheric air immediately to the north of the ITCZ convection, suggesting synoptic-scale subsidence aloft in that area. Also note that within this region of drier air to the north of the ITCZ there was an interesting pattern of subtle impulses which were propagating westward.

Meteosat-9 water vapor images

Meteosat-9 water vapor winds from the CIMSS Tropical Cyclones site valid at 00:00, 03:00, and 06:00 UTC (below) showed that the upper tropospheric winds were weakly divergent over area of the ITCZ convection (150-300 hPa divergence plot), with only a minimal amount (5-10 knots) of deep layer wind shear in that particular region. The water vapor imagery also depicted  a “dry/moist gradient” signature associated with a subtropical jet stream which was moving over the northwestern coast of Africa — while the deep layer wind shear was increasing between the ITCZ convection and the subtropical jet (to a maximum value exceeding 60 knots), it is questionable whether the aircraft made it far enough to the northeast to be affected in any way by this increasing wind shear.

Meteosat-9 water vapor winds

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See also:

Air France Flight 447: A detailed meteorological analysis

NOVA: Crash of Flight 447

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GOES-12 10.7 µm IR images

The first tropical depression of the 2009 season formed off the US East Coast on 28 May 2009. An AWIPS animation of GOES-12 10.7 µm “IR window” images (above) revealed several bursts of convection as the canopy of cold cloud tops slowly increased in areal coverage.

One of the convective bursts occurred around 15:00 UTC , and a comparison of the 1-km resolution MODIS 11.0 µm IR window and the 4-km resolution GOES-12 10.7 µm IR window images around that time (below) depicted cloud top brightness temperatures several degrees colder on the MODIS image (-72º C, vs -68º C on the GOES-12 IR image).

MODIS 11.0 µm and GOES-12 10.7 µm IR images

Products from the CIMSS Tropical Cyclones site (below) showed that the coldest SSM/I microwave brightness temperatures (red colors) were found in the southeastern quadrant of the cold IR cloud shield. In addition, it could be seen that the tropical depression was situated over the warmer waters of the Gulf Stream (SST values greater than 24º C, green colors), which was likely aiding in the intensification process. The deep layer wind shear was also light, which was another factor that favored further intensification.

GOES-12 IR + DMSP Microwave + Sea Surface Temperature

The Blended Total Precipitable Water product (below) showed that TPW values were as high as 50-57 mm (2.0 to 2.2 inches, red colors) in the vicinity of the tropical depression. The POES AMSU Rainfall Rate product depicted rainfall intensities as great as 29 mm per hour (1.14 inch per hour) around 13:30 UTC.

Blended Total Precipitable Water + GOES-12 IR images

===== 29 MAY UPDATE =====

On the following day (29 May 2009), GOES-12 visible images from the CIMSS Tropical Cyclones site (below) indicated that the low-level circulation  had become separated from the cluster of deep convection which was located in the southeast  quadrant of the tropical depression — this was due to increasing amounts of deep layer wind shear across the region.

GOES-12 visible images

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MODIS 11.0 µm IR + GOES-12 10.7 µm IR images

AWIPS images of the 1-km resolution MODIS 11.0 µm  and the 4-km resolution GOES-12 10.7 µm “IR window” channels (above) showed a cluster of very cold cloud top temperatures (-88º C on MODIS, and -82º C on GOES, violet colors) associated with deep convection over the northwestern Gulf of Mexico on 28 May 2009. Also of interest is the appearance of  both transverse banding and an orthogonal gravity wave structure in the northwestern portion of the anvil edge (near the Mexico border).

A comparison of the MODIS 0.6 µm “visible channel”, 1.3 µm “cirrus detection channel”, 6.7 µm “water vapor channel”, and the 11.0 µm “IR window channel” (below) showed that the various satellite  channels differed in their  ability to detect the true western and northwestern extent of the cirrus anvil edge.

MODIS visible, cirrus detection, water vapor, and IR window channel images

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GOES-12 10.7 µm IR images

A west-to-east oriented stationary front was draped across the Upper Midwest and Great Lakes states on 19 May 2009. AWIPS images of the GOES-12 10.7 µm IR window channel (above) showed that there was a general lack of cloudiness in the vicinity of the frontal boundary, which allowed the thermal contrast on either side of the front to be seen (with the warmer air and darker gray land surfaces located south of the front). However, the IR imagery also seemed to indicate that the far eastern portion of the front was beginning to  sag southward, as seen by the of  surge colder IR brightness temperatures (lighter gray shades) along the northeastern Wisconsin shoreline of Lake Michigan.

A closer view of the northern portion of Lake Michigan using GOES-12 visible channel images (below) showed that there was a patch of lake stratus propagating quickly southwestward along the western shoreline of the lake, presumably along and just behind the leading edge of the advancing frontal boundary. Air temperatures at buoy 45002 dropped to 39º F as northeasterly winds increased behind the front.

GOES-12 visible images

AWIPS images of the MODIS 250-meter resolution “true color” image and the corresponding 1-km resolution MODIS 11.0 µm IR window image (below) revealed both the leading edge of the colder air (the transition from warmer red and yellow colors to the colder green colors) inland across the northeastern counties of Wisconsin, as well as a wave/undular bore signature on the waters of Lake Michigan.

MODIS true color image + MODIS 11.0 µm IR image

Consecutive image of the MODIS Land Surface Temperature (LST) product (below) also showed the southward progression of the colder air. In addition, note the appearance of the slightly warmer (lighter green color enhancement) southwest-to-northeast oriented tornado damage swath located farther inland — this damage swath was from the  07 June 2007 tornado event.

MODIS Land Surface Temperature (LST) images

Consecutive  250-meter resolution MODIS true color images (below) indicated that the wave/undular bore signature over the waters of Lake Michigan continued to propagate southward during this time, marking the leading edge of the advancing lake-enhanced cold frontal segment.

250-meter resolution MODIS true color images

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