Patch of thin cirrus and contrails over Arkansas and Tennessee

November 8th, 2010 |
GOES-13 0.63 µm "visible channel" image

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

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

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

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

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

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

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

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

POES AVHRR Cloud Type product

Strong Northeast US coastal storm

November 8th, 2010 |
GOES-13 6.5 µm water vapor images + surface frontal and pressure analyses

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

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

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 Temperature product

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Type 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.