Tropical moisture being drawn into a “Rex block” cut-off low

October 13th, 2011 |
GOES-15 6.5 µm water vapor channel images (click image to play 3-day animation)

GOES-15 6.5 µm water vapor channel images (click image to play 3-day animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click image to play 3-day animation) showed a plume of tropical moisture being drawn into the circulation of a large cut-off low that was part of a “Rex block” that had formed over the far East Pacific Ocean during the 11 October – 13 October 2011 period.

An AWIPS image of 1-km resolution MODIS 6.7 µm water vapor channel data with an overlay of 1-hour MADIS atmospheric motion vectors or “satellite winds” (below) showed better detail of the moisture plume structure, and indicated that this moisture was being drawn into the circulation of the cut-off low at speeds as great as 50-60 knots.

MODIS 6.7 µm water vapor image + MADIS atmospheric motion vector winds

MODIS 6.7 µm water vapor image + MADIS atmospheric motion vector winds

AWIPS images of the MIMIC Total Precipitable Water product (below; click image to play animation) revealed that the plume of tropical moisture was likely composed of contributions from the remnants of Hurricane Jova (which had moved inland across western Mexico on 12 October) and Tropical Storm Irwin (which had been meandering across the Eastern Pacific Ocean for 8 days, reaching Category 1 hurricane intensity on 07 October).

MIMIC Total Precipitable Water product (click image to play animation)

MIMIC Total Precipitable Water product (click image to play animation)

 

The first 0ºF (-18ºC) temperature of the season in Alaska

October 12th, 2011 |
GOES-11 10.7 µm IR images

GOES-11 10.7 µm IR images

The first “official” 0ºF (-18ºC) temperature of the 2011/2012 winter season in Alaska was recorded at Anaktuvuk Pass on 12 October 2011. AWIPS images of “4-km resolution” GOES-11 10.7 µm IR data (above) indicated that portions of the Brooks Range in northern Alaska were beginning to exhibit IR brightness temperatures of -20ºC and colder (cyan to blue color enhancement), with Anuktuvuk Pass (station identifier PAKP) situated between a quasi-stationary deck of colder (darker blue) clouds to the east and another area of multi-layered clouds approaching from the west. Due to the very large viewing angle from the geostationary GOES-11 satellite positioned over the equator, the effective resolution of the IR pixels over northern Alaska was actually on the order of 10-15 km.

A more detailed view was available using a 1-km resolution POES AVHRR 12.0 µm IR image at 05:40 UTC (below), which did a better job of portraying the arc of colder (-20ºC to -28ºC, cyan to darker blue) high-elevation portions of the Brooks Range, as well as the boundaries of the cloud deck that was covering parts of northeastern Alaska. With calm winds and no clouds at Anaktuvuk Pass, strong radiational cooling allowed the temperature to get much colder than adjacent areas with a blanket of cloud cover.

POES AVHRR 12.0 µm IR image

POES AVHRR 12.0 µm IR image

The corresponding 05:40 UTC POES AVHRR Cloud Top Height product (below) showed that the northeastern Alaska cloud deck extended to heights of 3-4 km (darker violet color enhancement).

POES AVHRR Cloud Height product

POES AVHRR Cloud Height product

A MODIS Cloud Type product at 07:03 UTC (below) indicated that the cloud deck covering northeastern Alaska was primarily a “mixed phase” (supercooled water and ice, darker green color enhancement) feature.

MODIS Cloud Type product

MODIS Cloud Type product

Snow cover in southeastern Wyoming

October 10th, 2011 |
MODIS true color Red/Green/Blue (RGB) image

MODIS true color Red/Green/Blue (RGB) image

A significant rain and snow event occurred across parts of southeastern Wyoming and western Nebraska on 08 October 2011 (see NWS Cheyenne story) — snowfall amounts as high as 12.0 inches were reported near Cheyenne , Wyoming with 2.73 inches of rain reported farther to the northeast near Crawford in western Nebraska. Two days later (on 10 October 2011), a large patch of low-elevation snow cover could still be seen in far southeastern Wyoming  on a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image  from the SSEC MODIS Today site (above, viewed using Google Earth).

MODIS 0.65 µm visible channel image + MODIS 2.1 µm "snow/ice channel" image

MODIS 0.65 µm visible channel image + MODIS 2.1 µm "snow/ice channel" image

On a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and MODIS 2.1 µm “snow/ice channel” data (above), snow cover (along with clouds) appears bright on the visible image, but snow appears very dark on the snow/ice image (since snow is a very strong absorber at that particular wavelength).

Another method to discriminate between clouds and snow cover is to use different MODIS images to create a 3-channel RGB false color image — snow cover appears darker red on such a false color image (below), which used MODIS channels 01/07/07 as the Red/Green/Blue components.

 

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

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

In far southeastern Wyoming, the areas that still had significant snow cover exhibited much colder MODIS Land Surface Temperature (LST) values (below), with LSTs ranging from the middle 30s F (darker green color enhancement) over deeper snow cover to the upper 60s to low 70s (darker orange color enhancement) over adjacent areas of bare ground.

MODIS Land Surface Temperature product

MODIS Land Surface Temperature product

With the high October sun angle helping to produce warm temperatures (the daytime high at Cheyenne, Wyoming that day reached 59ºF or 15ºC) the patch of lower-elevation snow cover just to the north of Cheyenne began to melt during the day, as can be seen on an animation of GOES-15 0.63 µm visible channel images (below; click image to play animation).

 

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

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MODIS 11.0 µm IR image + topography

MODIS 11.0 µm IR image + topography

Another feature of interest on the satellite images was the formation of a  “cloud banner” or “cloud crest” just downwind of the ridge of higher terrain that ran northwest to southeast across the Wyoming/Colorado border region — this cold cloud feature could be seen on the 1-km resolution MODIS 11.0 µm IR image (above). The 4-km resolution MODIS Cloud Phase product (below) showed this to be an ice phase cloud feature (salmon color enhancement), with the 4-km resolution MODIS Cloud Top Temperature (CTT) product indicating CTT values as cold as -45ºC (darker blue color enhancement).

MODIS Cloud phase product + MODIS Cloud Top Tempeature product

MODIS Cloud phase product + MODIS Cloud Top Tempeature product

The 1-km resolution MODIS 6.7 µm water vapor channel image (below) revealed a signature of mountain waves farther downwind of the cloud banner feature. A few hours later (at 23:58 UTC), there was a pilot report of light turbulence in that region at an altitude of 37,000 feet.

MODIS 6.7 µm water vapor channel image

MODIS 6.7 µm water vapor channel image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

Large algae bloom in Lake Erie

October 9th, 2011 |
MODIS true color and false color images

MODIS true color and false color images

A previous blog post discussed the sediment features seen in southern Lake Michigan in early October of 2011. However, looking a bit farther to the east over Lake Erie several days later, a 09 October 2011 comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a notable contrast between the two lakes: large green colored features covered much of western Lake Erie, compared to the cyan colored sediment that was seen in southern Lake Michigan (as well as southern Lake Huron).

According to the NASA Earth Observatory site, this is one of the worst algae blooms in Lake Erie in decades, brought about in part due to large amounts of runoff into the lake following a period of above-normal precipitation. The thickest portions of the algae bloom appear brighter green in the false color images, similar to the way that dense vegetation does.

A comparison of the consecutive Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images (below, viewed using Google Earth) seemed to suggest a slight northward movement of the algae features during the 91 minutes between the two images.

Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images

Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images

An animation of GOES-15 0.63 µm visible channel images (below) confirmed the gradual northward movement to the algae bloom features over western Lake Erie during the day. Surface winds were generally light out of the south across the region, so most of this motion was likely driven by lake currents.

GOES-15 0.63 µm visible channel images

GOES-15 0.63 µm visible channel images