GOES-13 0.63 µm visible images

McIDAS images of GOES-13 0.63 µm visible channel data (above) revealed the formation of a packet of wave clouds over the northern Gulf of Mexico, associated with an undular bore moving southward ahead of an advancing cold frontal boundary on 08 May 2010.

The clouds eventually cleared out enough to reveal portions of the oil slick (which remained off the coast of Louisiana following from the explosion and sinking of the Deepwater Horizon offshore oil rig) on 250-meter resolution Red/Green/Blue (RGB) MODIS true color and false color images sourced from the SSEC MODIS Today site (below). Since the oil slick feature was once again located within the sun glint portion of the MODIS image swath, it was very easy to detect on the true color (created using bands 1/4/3 as the R/G/B channels) and false color (created using bands 7/2/1 as the R/G/B channels) imagery.

It appears as though a thin filament of the oil slick has recently been drawn westward (away from the core area of the oil slick near the source), and has been entrained into the sediment outflow region of the Mississippi River. You can follow the changes in appearance of the oil slick on this comparison of MODIS true color image from 21, 25, and 29 April and 01, 04, and 08 May.

MODIS true color (bands 1/4/3) and false color (bands 7/2/1) images

The oil slick appears as a light gray feature on an AWIPS image of the MODIS 0.65 µm visible channel data, but shows up as a very warm (darker gray to black enhancement) area on the MODIS 3.7 µm “shortwave IR” image due to a high amount of sun glint reflection of solar radiation off the oil slick surface. However, note that the oil slick feature does not exhibit any sort of signature at all on the MODIS 11.0 µm “IR window” image (below).

MODIS 0.65 µm visible, 3.7 µm

===== 09 MAY UPDATE =====

MODIS true color (bands 1/4/3) and false color (bands 7/2/1) Red/Green/Blue (RGB) images

The oil slick was once again a very obvious feature in the 250-meter resolution MODIS true color and false color images on 09 May 2010 (above). In this case, note the appearance of the light pink colored pixel near the center of the oil slick on the false color image — the near-IR Band 7 used in that particular RGB image is also sensitive to hot surfaces (for example, due to a fire), which would make such a feature show up as a light pink feature. Indeed, an AWIPS image of the MODIS 3.7 µm shortwave IR channel data (below) confirmed the presence of a relatively hot pixel (43.5º C, orange color enhancement), which could have been due to a small spot fire that was set in an attempt to burn off some of the surface oil.

MODIS 0.65 µm visible and 3.7 µm shortwave IR images

===== 10 MAY UPDATE =====

MODIS true color (bands 1/4/3) and false color (bands 7/2/1) images

The oil slick was once again a prominent feature in the 250-meter resolution MODIS true color and false color images on 10 May 2010 (above). However, note that the appearance of the oil slick was a bit different than what was seen on the previous days when sun glint was helping to illuminate the feature: on this particular day, the “brighter” portion of the oil slick appeared to be surrounded by a very dark signature. It is not entirely clear what this “dark signature” was on the MODIS true color imagery — but one idea is that it could have been due to oil that was still sub-surface (and had not yet come to the surface where it could then help to reflect light back up toward the satellite in the sun glint region of the overpass swath).

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Meteosat-9 SEVIRI volcanic ash retrieval products

The Icelandic volcano Eyjafjallajökull (which started to become active again in late March 2010) continued to remain active into early May, with another significant plume being observed on 06 May 2010. EUMETSAT Meteosat-9 SEVIRI volcanic ash retrieval products (above) showed a plume streaming southeastward from Iceland, with the maximum ash cloud height reaching 17.27 km. These volcanic ash retrieval products provide a demonstration of the type of products that will be available with the ABI instrument on the GOES-R satellite — they are available in near-realtime on the CIMSS GOES-R Proving Ground site.

A Terra MODIS Red/Green/Blue (RGB) image (using bands 01/04/03) shows the brown ash plume curving southeastward and then southward over the eastern Atlantic Ocean (below).

Terra MODIS RGB image (using bands 01/04/03)

As a result of this most recent volcanic eruption, some airports in Scotland, Northern Ireland and the Irish Republic were closed on 06 May.

===== 07 MAY UPDATE =====

A Terra MODIS RGB image using bands 01/04/03 (below) showed a very long and narrow volcanic plume emanating from Eyjafjallajökull on 07 May.

Terra MODIS RGB image (using bands 01/04/03)

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MODIS 0.65 µm visible image + MODIS Sea Surface Temperature product + NAM surface winds

AWIPS images of the MODIS 0.65 µm visible channel data (above) revealed a few dark features within the otherwise bright sun glint region just off the coast of Florida and Georgia on 05 May 2010. The corresponding MODIS Sea Surface Temperature (SST) product indicated that SST values were also quite warm within these dark visible image features (SST values as high as 79ºF, darker red colors) — in fact, just as warm as those seen a bit farther to the east within the Gulf Stream. In contrast, to the north of the dark/warm features, the MODIS SST values were only around 69-70ºF (yellow to green colors).

This type of visible image “dark signature” over water illuminated by sun glint has been observed before — for example, over Lake Michigan — and is recognized as a signature of regions of very light or calm winds. The surface wind field from the NAM20 model (cyan wind barbs) did show a west-to-east oriented axis of calm winds just to the south of the dark/warm signature noted on the MODIS imagery. In this case, the MODIS imagery could have been used to identify the slight southward bias of the NAM20 model wind fields at that time.

MODIS 0.65 µm visible image + NAM surface winds + HPC surface frontal analysis

The Hydometeorological Prediction Center (HPC) surface frontal analysis for 15 UTC is overlaid on the MODIS visible image (above). Judging from the location of the dark features on the visible image, it would appear the the weak cold front had not yet advanced as far southeastward as the area of light/calm winds seen just after 16 UTC .

MODIS true color image (visualized using Google Earth)

A closer view using a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image — created using MODIS bands 1/4/3 as the R/G/B channels — acquired from the SSEC MODIS Today site (above, visualized using Google Earth) is annotated to point out the subtle yet potentially important clues as to the exact location of the leading edge of the cold frontal boundary at the time of the Terra satellite overpass (approximately 16:18 UTC). This example also suggests that frontal boundaries do not necessarily resemble the nice smoothly-drawn features we see on weather maps, but instead can be complex in their shape due to various interactions with terrain, coastlines, etc.

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MODIS true color and false color RGB images

A comparison of the 18:50 UTC 250-meter resolution Aqua MODIS true color Red/Green/Blue (RGB) image — created using MODIS bands 1/4/3 as the R/G/B channels — and the corresponding false color RGB image — created using MODIS bands 7/2/1 as the R/G/B channels — acquired on 04 May 2010 from the SSEC MODIS Today site (above) showed the oil slick from the Deepwater Horizon oil rig explosion and collapse in the northern Gulf of Mexico 14 days earlier. Due to prolonged wind and wave action, the shape and size of the oil slick signature appeared to have changed and spread out in terms of areal coverage (compared to that seen for several days following the accident).

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