48-hour simulated IR satellite imagery from the CRAS model (9-11 Nov 1975)

Today marks the 35-year anniversary of the powerful Great Lakes storm that was responsible for the sinking of the SS Edmund Fitzgerald (on 10 November 1975). Since the first operational geostationary weather satellites (SMS-1 and SMS-2) were relatively new back in 1975, the CIMSS Regional Assimilation System (CRAS) model was utilized to generate synthetic IR satellite images to provide an idea of what the satellite imagery might have looked like for this intense storm (CRAS model surface winds). A 48-hour sequence of synthetic IR images (above) shows the evolution of the model-derived cloud features at 1-hour intervals.

As part of the CIMSS involvement in GOES-R Proving Ground activities, CRAS synthetic forecast satellite imagery (IR and Water Vapor channels, below) is currently being made available in an AWIPS format for interested NWS forecast offices to add to their local AWIPS workstations (via LDM subscription). For more information, see the CRAS Imagery in D-2D site. VISIT training is also available on the topic.

CRAS forecast IR imagery in AWIPS

CRAS forecast water vapor imagery in AWIPS

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GOES-13 0.63 µm "visible channel" image

A quick look at a 1-km resolution GOES-13 0.63 µm visible channel image (above) would suggest that it was a cloud-free day across Arkansas, Tennessee, and the surrounding region on 08 November 2010.

However, a comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm “visible channel” , the MODIS 11.0 µm “IR window” channel, and the 1.3 µm “cirrus detection” channel (below) revealed that there was a patch of thin cirrus clouds and contrails over much of Arkansas and Tennessee. As with the GOES-13 visible channel, there was no indication of any cloud features on the MODIS visible image. On the MODIS IR image, there was a signature of some sort of cloud features over that region, but the IR brightness temperatures were quite warm (mostly above 0º C), which would be much too warm for cirrus clouds. However, the MODIS cirrus detection channel did a very good job at highlighting the patch of very thin clouds. This is due to the fact that the near-IR 1.3 µm channel is very effective for detecting features that are good scatterers of light (such as ice crystals, volcanic ash, airborne dust, etc).

MODIS 0.65 µm "visible", 11.0 µm "IR window", and 1.3 µm "Cirrus detection" images

Rather surprising, however, was the fact that this patch of cirrus clouds and contrails existed within a region that appeared to be a fairly dry area (indicated by the lighter blue to yellow color enhancement) on the MODIS 6.7 µm “water vapor” image (below). The pronounced dryness of the middle to upper troposphere was quite evident of the Little Rock, Arkansas rawinsonde data.

MODIS 6.7 µm "water vapor channel" image

A false color Red/Green/Blue (RGB) POES AVHRR composite image (below) did show a subtle hint of some brighter cloud features against the green to brown background of the land surface, but again not to the extent of what was seen on the MODIS cirrus detection channel image.

POES AVHRR false color Red/Green/Blue (RGB) image

If we examine the 1-km resolution POES AVHRR Cloud Top Temperature (CTT) product (below), we do begin to see features that exhibited CTT values of -50º C and colder (yellow color enhancement), which is more representative of what you would expect for cirrus cloud features.

POES AVHRR Cloud Top Temperature product

In addition, the 1-km resolution POES AVHRR Cloud Top Height (CTH) product (below) showed features with CTH values of 10-11 km (cyan color enhancement), which are also more representative of the altitude where cirrus cloud features would usually  be located. These altitudes also matched the Cloud Top Temperature values around -50º C on the rawinsonde data from Little Rock, Arkansas and Nashville, Tennessee.

POES AVHRR Cloud Top Height product

Given that these cloud features were obviously quite thin, the 1-km resolution POES AVHRR Cloud Optical Depth product (below) showed correspondingly low values.

POES AVHRR Cloud Optical Depth product

Another way to distinguish ice clouds from water droplet clouds is examine the 1-km resolution POES AVHRR Cloud Particle Effective Radius product (below). Ice crystals are typically much larger (in this case, at least 30-40 micrometers in diameter) than water droplets (usually around 20 micrometers or less in diameter).

POES AVHRR Cloud Particle Effective Radius product

Because of the very thin nature of these cirrus and contrail features, the 1-km resolution POES AVHRR Cloud Tye product (below) did seem to struggle in assigning the correct type to the features — although many were correctly identified as Cirrus (orange color enhancement).

POES AVHRR Cloud Type product

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GOES-13 6.5 µm water vapor images + surface frontal and pressure analyses

A strong Northeast US coastal storm developed on 08 November 2010, which produced as much as 3.56 inches of rainfall in Maine, 2.5 inches of snow in Massachusetts and New York, and wind gusts to 63 mph in Maine (and 75 mph on top of Mt. Washington, New Hampshire). AWIPS images of 4-km resolution GOES-13 6.5 µm “water vapor channel” data (above) showed a classic example of a signature of an occluding cyclone, with a spiral of dry air (yellow to orange color enhancement) wrapping inward around the storm center.

A sequence of 1-km resolution MODIS 6.7 µm water vapor images (below) shows a bit more detail at various stages of the storm’s life cycle.

MODIS 6.7 µm water vapor images + surface frontal and pressure analyses

A sequence of 1-km resolution POES AVHRR 10.8 µm “IR window” images (below) showed an arc of cold clouds that wrapped inland ahead of the occluded frontal boundary.

POES AVHRR 10.8 µm IR images + surface frontal and pressure analyses

Additional 1-km resolution POES AVHRR derived products can be used to further characterize the clouds over a particular region. For example, the 22:32 UTC Cloud Top Temperature (CTT), Cloud Height, and Cloud Type products are shown below. The coldest CTT values associated with the well-defined inland cloud arc were -55º C, with a maximum cloud height value of 11 km. The Cloud Type product can be used to discriminate between water droplet clouds, supercooled water droplet clouds, opaque ice crystal clouds, cirrus clouds, or clouds that are likely overshooting the tropopause.

POES AVHRR Cloud Top Temperature product

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Type product

Note to NWS forecast offices: MODIS and POES AVHRR satellite images and products such as those seen above can be added to your local AWIPS workstations via Unidata LDM subscription.

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Storm track of Tomas (during the period 29 September - 05 November 2010)

Tropical Storm Tomas became the 19th named storm of the 2010 Atlantic tropical cyclone season on 29 September 2010 (NHC advisory archive). The path of Tomas from the CIMSS Tropical Cyclones site can be seen above, along with a plot of the Advanced Dvorak Technique (ADT) intensity estimate (below) which showed that there were a number of fluctuations in the intensity of Tomas: it initially intensified into a Category 1 and then a Category 2 hurricane as it crossed the Windward Islands of the Lesser Antilles on 30-31 August, but then was degraded to a Tropical Storm due to unfavorable deep layer wind shear on 01 November. Atmospheric steering currents then helped Tomas turn to the north, and the storm re-intensified into a Category 1 hurricane as it passed between Cuba and Hispaniola on 05 November.

Automated Dvorak Technique (ADT) plot for Tomas

Animations of GOES-13 0.63 µm visible channel imagery and GOES-13 10.7 µm IR channel imagery (below) revealed a number of convective bursts as Tomas intensified into a Category 1 hurricane on 30 August.

GOES-13 0.63 µm visible channel images

GOES-13 10.7 µm IR images

A comparison of a GOES-13 10.7 µm IR image with the corresponding SSMI/S 85 GHz microwave image around 22:45 UTC on 30 August (below) showed that Hurricane Tomas had a large closed eye and a well-defined spiral band extending northward as the storm passed to the west of the Windward Islands of St. Lucia and St. Vincent.

Hurricane Tomas GOES-13 10.7 µm IR + SSMI/S 85 GHz microwave images

On 05 November, AWIPS images of POES AVHRR 10.8 µm IR data (below) showed that Hurricane Tomas was exhibiting IR brightness temperatures as cold as -93º C (darker purple color enhancement) as the storm passed between Jamaica and Hispaniola.

POES AVHRR 10.8 µm IR images

Note the improvement in cloud top temperature structure that can be seen on the 1-km resolution POES AVHRR IR image, compared to the corresponding 4-km resolution GOES-13 IR image (below). On the POES AVHRR image, subtle storm top gravity waves can be seen emanating southward away from the region of coldest cloud tops, and the transverse banding structure along the western and southwestern edge of the storm are better resolved.

POES AVHRR 10.8 µm IR image + GOES-13 10.7 µm IR image

Note to NWS users: POES AVHRR images and products can be added to your local AWIPS workstations (via Unidata LDM subscription): for more details, see the AVHRR Imagery and Products in D-2D site.

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