Meteosat-7 10.8 µm IR images

EUMETSAT Meteosat-7 10.8 µm IR images from the CIMSS Tropical Cyclones site (above) showed the formation of a well-defined eye as Tropical Cyclone Giovanna (12S) intensified from a Category 3 to a Category 4 storm over the Indian Ocean late in the day on 12 February 2012.

Tropical Cyclone Giovanna maintained a Category 4 intensity as it approached the island nation of Madagascar on 13 February, with the diameter of the eye contracting somewhat on IR imagery as Giovanna was undergoing an eyewall replacement cycle (below).

Meteosat-7 10.8 µm IR images

A few hours prior to landfall, a timely overpass of the EUMETSAT Metop-A satellite allowed a nice view of the surface wind structure using ASCAT scatterometer winds (below).

Meteosat-7 10.8 µm IR images + MetOp-A ASCAT scatterometer surface winds

As the tropical cyclone approached the eastern coast of Madagascar, the erosion of the eastern semicircle of the inner eyewall of Giovanna could be seen in the MIMIC-TC product (below).

MIMIC-TC microwave product

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GOES-12 10.7 µm IR channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-12 10.7 µm IR channel data (above; click image to play animation) showed the development of a very large mesoscale convective system (MCS) over Argentina on 07 February 2012. A number of smaller, discrete thunderstorms initially began to develop around 14:45 UTC, which then eventually merged into a large MCS having large areas which exhibited cloud top IR brightness temperatures of -80 C and colder (purple color enhancement). Multiple “enhanced-v” storm top signatures could be seen at various times, which is a satellite signature of thunderstorms that are capable of producing either tornadoes, large hail, or damaging winds.

Much more detail in the cloud top IR brightness temperature structure can be seen in a 375-meter resolution Suomi NPP VIIRS 11.45 µm image at 18:21 UTC (below). The coldest VIIRS IR brightness temperatures sensed was -96 C (darker violet color enhancement) — much colder than the -77 C seen on the corresponding 18:15 UTC GOES-12 IR image. The black striping seen along the right side of the image is an artifact of the side-to-side scan strategy of the VIIRS instrument; software to remove these artifacts and create a smoother-looking image is under development.

Suomi NPP VIIRS 11.45 µm IR image

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EUMETSAT Meteosat-9 0.635 µm visible channel images (click image to play animation)

McIDAS images of EUMETSAT Metosat-9 0.635 µm visible channel images (above; click image to play animation) showed a very large outbreak of airborne Saharan dust streaming off the continent of Africa and moving west-southwestward out over the adjacent waters of the eastern Atlantic Ocean on 07 February 2012. In addition, a pair of long von Karman vortex streets can be seen moving southwestward from the Cape Verde islands.

While the viewing angle was more extreme, the Saharan dust could also be seen on GOES-13 0.63 µm visible channel images (below).

GOES-13 0.63 µm visible channel images + surface reports

The emergence of this Saharan dust over water can be seen to occur around 00:00 UTC on 06 February on the Meteosat-9 Saharan Air Layer tracking product (below).

EUMETSAT Meteosat-9 Saharan Air Layer tracking product

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

AWIPS images of the 4-km resolution GOES-13 10.7 µm – 3.9 µm “fog/stratus product” (above; click image to play animation) showed a large area of fog and/or stratus (yellow to orange color enhancement) that was increasing in areal coverage during the pre-dawn hours on 06 February 2012. Although the fog/stratus product is useful for locating the presence and temporal trends of such features, it does not offer any reliable indication of whether it is fog on the ground or stratus cloud aloft.

One product that attempts to give the forecaster some quantitative information is the GOES Low CLoud Base (LCB) prodcut (below; click image to play animation), which attempts to blend surface observations with satellite data to indicate whether the cloud base is above or below the threshold of 1000 feet.

GOES-13 Low Cloud Base product (click image o play animation)

With 1-km resolution data, the MODIS instrument aboard the polar-orbiting Terra and Aqua satellites offers a similar “fog/stratus product” (below) that provides better clarity, especially regarding the exact location of the edges of the fog and/or stratus.

MODIS fog/stratus product images

In this particular case, a number of locations beneath the western and southern edge of the fog/stratus feature were expereincing freezing fog (below) and visibilities of 1/4 mile or less, which was creating hazardous road conditions and prompting the issuance of Freezing Fog Advisories.

MODIS fog/stratus product with METAR surface reports

As part of CIMSS participation in GOES-R Proving Ground activities, products are being developed which can provide more quantitative information about such parameters as Fog Depth and the Probability of Marginal Visual Flight Rules (MVFR) or Instrument Flight Rules (IFR) conditions (below). In this case, across the southwestern part of Iowa (where widespread freezing fog was being reported), the fog depth was as high as 1400-1500 feet, with probabilities of MVFR and IFR conditions as high as 75-90% and 60-75%, respectively.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

Shortly after sunrise, it is interesting to note that a comparison of 1-km resolution POES AVHRR 0.63 µm visible channel, 3.74 µm “shortwave IR” channel, and 10.8 µm channel “IR window” channel images (below) revealed that part of the swath of fresh snow cover (as deep as 4-6 inches) across western Iowa could be seen through the translucent western edge of the fog/stratus deck that was beginning to burn off during the morning hours. The fog/stratus deck appears warmer (darker gray enhancement) om the 3.74 µm image, due to the sensitivity of that channel to the reflection of solar radiation off the tops of supercooled water droplet clouds.

Farther to the south, note the presence of narrow fingers of valley fog in the Ozark Mountains and surrounding regions in Oklahoma, Arkansas, and Missouri.

POES AVHRR 0.63 µm visible, 3.74 µm "shortwave IR", and 10.8 µm "IR window" images

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