Tropical Depression #1

May 28th, 2009
GOES-12 10.7 µm IR images

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

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

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

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

GOES-12 visible images

Convection in the Gulf of Mexico

May 28th, 2009
MODIS 11.0 µm IR + GOES-12 10.7 µm IR images

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 IR, visible, cirrus, and water vapor channel images

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

A lake-enhanced cold frontal segment

May 19th, 2009
GOES-12 10.7 µm IR images

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

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

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

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

250-meter resolution MODIS true color images

GOES-11 Super Rapid Scan Operations (SRSO) images

May 13th, 2009
GOES-11 SRSO visible images

GOES-11 SRSO visible images

The GOES-11 satellite was once again placed into Super Rapid Scan Operations (SRSO) on 13 May 2009, providing images as frequently as every 1 minute during portions of the late afternoon and early evening hours. The GOES-11 visible channel imagery (above; also available as a QuickTime animation) shows the explosive development of severe convection along a dryline in Oklahoma, Kansas, and Missouri. According to the SPC Storm Reports, this line of storms produced several tornadoes, hail up to 2.75 inch in diameter, and wind gusts to 80 mph.

GOES-11 10.7 µm IR imagery (below; also available as a QuickTime animation) revealed that the cloud top temperatures quickly cooled to values of -60º to -70º C (red to black colors) as these thunderstorms developed and intensified.

GOES-11 10.7 µm IR images

GOES-11 10.7 µm IR images

The plot of the coldest GOES-11 IR brightness temperatures (below) for the initial (and largest)  storm that formed in eastern Kansas  shows that the minimum cloud top temperatures cooled to within a few degrees of the -64º C tropopause temperature (taken from the Topeka, Kansas rawinsonde report) after around 22:00 UTC. It is interesting to note that there was a slight cloud top temperature warming seen at 22:45 UTC — which is about 7 minutes prior to the first reported tornado from that particular storm. If this type of “pre-tornado cloud top temperature warming” signal is something that frequently occurs, then having access to satellite imagery at a high temporal resolution will be critical to utilizing any possible predictive value of such a signal.

Plot of GOES-11 10.7 µm IR brightness temperatures

Plot of GOES-11 10.7 µm IR brightness temperatures

A comparison of the 4-km resolution GOES-11 10.7 µm and the 1-km resolution NOAA-15 10.8 µm IR images (below) demonstrates the value of higher spatial resolution: a clear “enhanced-v” signature was seen on the NOAA-15 image, while no such signature was obvious on the GOES-11 image. Note that the minimum cloud top brightness temperature in the overshooting top region was 15º C colder on the NOAA-15 IR image. Also, due to the large satellite viewing angle from the GOES-11 satellite (the satellite zenith angle for Topeka, Kansas is 61 degrees), a significant parallax shift was apparent with this particular storm — the overshooting top region was displaced farther to the northeast of Emporia, Kansas (KEMP) on the GOES-11 IR image.

GOES-11 10.7 µm and NOAA-15 10.8 µm IR images

GOES-11 10.7 µm and NOAA-15 10.8 µm IR images