Strong subsidence signal on water vapor imagery

February 22nd, 2012 |
GOES-15 6.5 µm water vapor channel images (click image to play animation)

GOES-15 6.5 µm water vapor channel images (click image to play animation)

AWIPS images of GOES-15 6.5 µm water vapor channel data (above; click image to play animation) displayed a signal of strong subsidence around the eastern periphery of a middle-tropospheric ridge of high pressure located over the eastern North Pacific Ocean on 22 February 2012. Note the rapid warming of water vapor brightness temperatures just off the coast of California, reaching abnormally high values of 14º C (darker orange color enhancement) by 21:00 UTC. This rapid middle-tropospheric drying created the appearance of a very strong moisture gradient on the water vapor imagery, being adjacent to the clouds and higher levels of moisture associated with the polar jet stream that was moving southeastward across the Pacific Northwest region of the US.

The magnitude of the dry air within the middle to upper troposphere was very apparent on rawinsonde data from Oakland, California (below).

Oakland, California rawinsonde reports

Oakland, California rawinsonde reports

Low cloud over snow cover in the Mid-Atlantic region, and blowing dust in New Mexico and Texas

February 20th, 2012 |
MODIS 0.65 µm visible image + MODIS Red/Green/Blue (RGB) false color image

MODIS 0.65 µm visible image + MODIS Red/Green/Blue (RGB) false color image

A comparison of AWIPS images of  MODIS 0.65 µm visible channel data with the corresponding MODIS false-color Red/Green/Blue (RGB) image (above) showed a large swath of snow on the ground on 20 February 2012, in the wake of a winter storm that moved across the Mid-Atlantic region the previous day.  The snow cover appears as shades of red on the false-color image, in contrast to the patches of supercooled water droplet clouds that persisted over the western half of the snow swath.

Farther to the west, strong winds (gusting to 60-70 mph) behind a cold front were causing an outbreak of blowing dust across parts of far eastern New Mexico and the Texas Panhandle. A comparison of a MODIS 0.65 µm visible channel image with the corresponding 1.3 µm “cirrus detection channel” image (below) demonstrated how the near-IR cirrus channel can be used to better identify the areal extent of the blowing dust (which might not be apparent on the visible channel imagery). The cirrus detection channel is sensitive to particles that are good scatterers of light, such as ice crystals, dust, volcanic ash, and smoke/haze.

MODIS 0.65 µm visible channel + MODIS 1.3 µm "cirrus detection channel" images

MODIS 0.65 µm visible channel + MODIS 1.3 µm "cirrus detection channel" images

A comparison of the MODIS 0.65 µm visible channel image with the corresponding MODIS 11-12 µm IR difference product (below) demonstrates how 11-12 µm difference values of 1-2 degrees C (yellow color enhancement) highlighted areas where the dust concentration was highest. Airborne dust particles have different emissivities at the 11 µm and 12 µm wavelengths, which allows such an IR difference product to be used to locate and track blowing dust. Recall that the older series of GOES satellites (GOES-8 through GOES-11) had a 12.0 µm IR channel that allowed the creation of a similar IR difference product — but on the latest satellites (GOES-13 through GOES-15) the 12.0 µm IR channel was replaced with a 13.3 µm channel.

MODIS 0.65 µm visible channel image + MODIS 11-12 µm IR difference image

MODIS 0.65 µm visible channel image + MODIS 11-12 µm IR difference image

A closer view of the blowing dust cloud can be seen using 250-meter resolution MODIS true-color RGB images from the SSEC MODIS Today site (below). Some of the primary source regions of the blowing dust (located in New Mexico) can be seen on the earlier Terra image at 17:56 UTC.

Terra and Aqua MODIS true color Red/Green/Blue (RGB) images

Terra and Aqua MODIS true color Red/Green/Blue (RGB) images

In the southeastern Texas Panhandle, a multiple-vehicle accident occurred along Highway 287 around 20:00 UTC (3:00 pm local time), causing a closure of that section of highway between Memphis and Childress (station identifier KCDS). McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (below; click image to play animation) showed that an optically thick band of blowing dust was moving through the region between Memphis and Childress around the time of the accident.

GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

Hole punch clouds and aircraft distrails over Georgia and South Carolina

February 17th, 2012 |
GOES-13 0.63 µm visible channel images

GOES-13 0.63 µm visible channel images

McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above) showed that there were a number of “hole punch clouds” and long “aircraft dissipation trails” (or “distrails”) drifting east-northeastward over eastern Georgia and the northern half of South Carolina on 17 February 2012. These features occur when aircraft ascend or descend through a cloud layer composed of supercooled water droplets — particles from the jet engine exhaust act as ice nuclei that initiate glaciation. The resulting relatively large ice crystals then begin to fall out of the supercooled water droplet cloud layer, causing the hole punch or aircraft dissipation trail to appear.

A closer view using a 250-meter resolution Terra MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; viewed using Google Earth) shows more structural details of some of the hole punch and distrail features at 15:47 UTC (10:47 am local time). The aircraft likely penetrated the supercooled water droplet cloud over Georgia, after which the hole punch and distrail signatures grew as the cloud drifted east-northeastwrad over South Carolina.

MODIS true color Red/Green/Blue (RGB) image (viewed using Google Earth)

MODIS true color Red/Green/Blue (RGB) image (viewed using Google Earth)

A comparison of 250-meter resolution Terra MODIS true-color and false-color Red/Green/Blue (RGB) images (below) helps to verify that the hole punch and distrail features were indeed composed of ice crystals (which appear as cyan on the false-color image, in contrast to the brighter white supercooled water droplet cloud features).

MODIS true-color and false-color Red/Green/Blue (RGB) images

MODIS true-color and false-color Red/Green/Blue (RGB) images

Fog and low clouds over the Ohio River Valley region

February 17th, 2012 |
GOES-13 fog/stratus product (click image to play animation)

GOES-13 fog/stratus product (click image to play animation)

AWIPS images of the GOES-13 fog/stratus product (above; click image to play animation) did not do a particularly good job of depicting a well-defined signal of the fog/stratus that was in place across parts of the Ohio River Valley region on 17 February 2012. Note that a number of stations were reporting night-time fog and/or freezing fog in parts of far eastern Missouri, southern Illinois and Indiana, and western Kentucky.

4-km resolution GOES-13 and 1-km resolution MODIS fog/stratus product

4-km resolution GOES-13 and 1-km resolution MODIS fog/stratus product

Even with the improved 1-km resolution of the MODIS fog/stratus product, no good signal was displayed at 03:40 UTC  (above) or at 07:52 UTC (below) over the areas that were reporting fog/freezing fog.

4-km resolution GOES-13 and 1-km resolution MODIS fog/stratus product

4-km resolution GOES-13 and 1-km resolution MODIS fog/stratus product

As part of CIMSS participation in GOES-R Proving Ground activities, new satellite products are being developed and tested — and one such product is an Instrument Flight Rules (IFR) Probability product (below; click image to play animation). This IFR Probability product blends satellite data and model fields to display regions where the cloud ceiling is likely to be between 500 and 1000 feet. The IFR Probability product did a much better job at highlighting the relatively large area where IFR cloud ceiling conditions were present at a number of reporting stations (some of which were experiencing cloud ceilings of 100 to 200 feet, along with freezing fog limiting the visibility to 0.3 miles at times) — for example: Effingham IL (K1H2) / Mount Vernon IL (KMVN) / Harrisburg IL (KHSB) / Lawrenceville IL (KLWV) / Bloomington IN (KBMG) / Cape Girardeau MO (KGCI) / Pahducah KY (KPAH).

GOES-13 IFR Probability product (click image to play animation)

GOES-13 IFR Probability product (click image to play animation)

GOES-13 0.63 µm visible channel images (below; click image to play animation) showed the areas of fog/stratus burning off quickly after sunrise — and the fog/stratus appeared to be relatively shallow in nature. The fact that the fog/stratus did not appear to be very thick may have been a factor that limited detection by the traditional GOES-13 (10.7-3.9 µm) and MODIS (11-3.7 µm) fog/stratus products.

GOES-13 0.63 µm visible channel image (click image to play animation)

GOES-13 0.63 µm visible channel image (click image to play animation)