The Memphis Derecho of July 22 2003

July 31st, 2013 |
GOES-12 10.7 µm IR imagery (Click Image to play animation)

GOES-12 10.7 µm IR imagery (Click Image to play animation)

On the morning of July 22, 2003, a strong derecho moved through metropolitan Memphis, TN, with winds exceeding hurricane-force. The most significant impact of this storm was a loss of power caused in part by the many trees that were downed by the winds. The Storm Report for the day from the Storm Prediction Center shows a cluster of wind reports in and around Memphis and Shelby County. The National Weather Service office in Memphis produced a report on this event that includes radar imagery and a discussion of surface and upper-air observations. More information on this derecho is here. What do satellite data show for this event?

The animation of 10.7 µm imagery, above, shows the development of convection in southeast Kansas and northwest Arkansas that then moves eastward into the mid-South, hitting Memphis around 1200 UTC. Several overshooting tops are evident as the storms pass near Memphis, with the coldest brightness temperatures at 196K! Past derechosdiscussed on this blog (such as the one that hit the East Coast in 2012) were characterized by a channel of moisture and instability aligned with the storm motion, allowing the propagating thunderstorm complex access to a rich source of moisture and instability. This event in 2003 was no different. GOES-12 Sounder retrievals — during that year, 3×3 fields-of-view were used (versus single pixels now) — of Total Precipitable Water, Convective Available Potential Energy (CAPE) and Lifted Index (LI), show abundant moisture and instability aligned west-to-east across northern Arkansas. CAPE values exceeded 3000 J/kg, Total Precipitable Water was greater than 2 inches, and Lifted Indices were near -10.

GOES-10/GOES-12 Sounder-Derived Total Precipitable Water (3x3 Field of View) (Click Image to play animation)

GOES-10/GOES-12 Sounder-Derived Total Precipitable Water (3×3 Field of View) (Click Image to play animation)

GOES-10/GOES-12 Sounder-Derived Convective Available Potential Energy (CAPE) (3x3 Field of View) (Click Image to play animation)

GOES-10/GOES-12 Sounder-Derived Convective Available Potential Energy (CAPE) (3×3 Field of View) (Click Image to play animation)

GOES-10/GOES-12 Sounder-Derived Lifted Index (3x3 Field of View) (Click Image to play animation)

GOES-10/GOES-12 Sounder-Derived Lifted Index (3×3 Field of View) (Click Image to play animation)

GOES-12 Visible Imagery (Click Image to play animation)

GOES-12 Visible Imagery (Click Image to play animation)

Visible imagery, above, from GOES-12 shows the convection continuing to develop as it moves across the Mississippi River into Memphis. Several Overshooting tops are evident, as well as parallel cloud lines at the cirrus level that are usually associated with turbulence. GOES-10, as GOES-West, was also able to capture the convection as it moved through Memphis (below).

GOES-10 Visible Imagery (Click Image to play animation)

GOES-10 Visible Imagery (Click Image to play animation)

Farewell to GOES-10

November 30th, 2009 |


Shortly after midnight (EST) on December 1st, GOES-10 was decomissioned and boosted to a disposal orbit (approximately 300 km above the operational orbit). It was shut off because it lacks fuel for the required maneuvers to keep it on station.

GOES-K was launched 25 April 1997, with a life expectancy of five years. A solar array problem shortly after launch in May of 1997 was nearly fatal to the spacecraft; however, a yaw-flip maneuver (that is, flying the spacecraft upside-down) proved successful and GOES-10 has successfully served data nearly continuously since then. The first visible image from GOES is here. Early examples of Sounder and Imager are also available. For more examples of GOES-10 imagery, click here. GOES-10 served as GOES-West from 27 July 1998 (replacing GOES-9) until 21 July 2006 (when it was replaced by GOES-11). GOES-10 then moved from 135 West Longitude to 60 W Longitude, arriving on station in December 2006 to provide near-continuous data over South America (More information on GOES-10 is available here).

As a Geostationary satellite focused on South America, GOES-10 provided valuable information about the Air France Flight Crash over the Atlantic Ocean, volcanic eruptions over South America. In addition, as it moved from 135 W Longitude to 60 W Longitude, it was in Super Rapid-Scan Operation mode — that is, imagery was collected every minute over limited regions — to give insight into various meteorological phenomena. (For more links to GOES-10 imagery, click the GOES-10 category, or click here).

With the termination of GOES-10 operations, routine satellite observation of South America will fall to GOES-12, the operational GOES-East satellite. However, the operational demands on GOES-East preclude the high temporal observations that GOES-10 provided. For example, much of South America now has routine 15-minute coverage; GOES-East will provide only half-hourly coverage. This image loop shows the motion of a smoke plume — at 15-minute intervals — near the Tocantins River just south to the Amazon Delta. A similar loop from GOES-East is here. Reduced temporal resolution introduces greater error to both cloud-tracked features (derived winds) and fires detected.

Similar views from different vantage points can be important. Consider, for example, the twin views of northeast Brazil in the 4-micron band from GOES-10 and GOES-12.


Both platforms observe the fires in the Amazon River delta in the upper left part of the images. Note, however, that only GOES-East shows a very warm Lake behind Sobradinho Dam on the Sao Francisco River. Indeed, the 3.9-micron sensor has saturated on GOES-East (over the Equator at 75 W), but GOES-10 (over the Equator at 60 W) shows very little signature. This is an excellent example of Sun Glint in the 3.9 micron channel. Solar 3.9-micron radiation reflected from the lake is saturating the instrument on GOES-East. GOES-10, farther east, can look at the same region and not see the Sun Glint.

In contrast to GOES-East and GOES-West data, data from GOES-10 have been remapped before distribution since it arrived at 60 West back in late 2006. The remapping is necessary because the satellite inclination was large; indeed, it was more than 4 degrees on 25 November 2009.

Update: The Final Imager images from GOES-10: 0.65 microns; 3.9 microns; 6.8 microns; 10.7 microns; 12.0 microns; Infrared Channels in a loop.

Current plans are for GOES-13 to replace GOES-12 as GOES-East in April of 2010. Subsequently, GOES-12 will move to 60 W and resume GOES-10’s duties.

Mesocale Convective Complex in South America

November 19th, 2009 |
GOES-10 10.7 µm IR images

GOES-10 10.7 µm IR images

McIDAS images of the GOES-10 10.7 µm IR channel (above) showed very cold cloud top temperatures associated with a large Mesoscale Convective Complex (MCC) that developed over northern Argentina and moved across Uruguay and into far southern Brazil on 19 November 2009. The MCC exhibited unusually cold IR brightness temperature values, as low as -89º C (dark purple color enhancement) at 04:58 UTC. In addition, early in the animation you can see several “enhanced-v” signatures on the IR imagery — this satellite signature indicates that severe convective storms have a high potential for producing damaging winds, large hail, or tornadoes. There were media reports of a tornado and hail in parts of Uruguay, and according to the Metsul Blog this MCC produced very strong winds (gusting to 82 mph or 36.8 meters per second) and heavy rainfall (2.8 inches or 70 mm in 2 hours) as the storm moved into the Rio Grande do Sul region of southern Brazil.

GOES-10 (launched in 1997) is currently positioned in orbit at approximately 60 degrees West longitude in support of the Earth Observation Partnership of the Americas EOPA project or GEOSS Americas — however, due to end-of-life fuel conditions, GOES-10 will cease operations on 01 December 2009.

Air France Flight #447: did weather play a role in the accident?

June 1st, 2009 |
METEOSAT-9 IR images

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)

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

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

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

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 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

Meteosat-9 water vapor winds


See also:

Air France Flight 447: A detailed meteorological analysis

NOVA: Crash of Flight 447