AWIPS satellite images + surface analysis

A cold frontal boundary was moving southward across the Pacific Ocean and approaching the Hawaiian Islands on 29 September – 30 September 2008, as seen on a comparison of AWIPS visible, IR, and water vapor satellite imagery and corresponding surface analysis (above). According to the boundary layer Meteorological Assimilation Data Ingest System (MADIS) atmospheric motion vectors (below), the front was moving southward at a speed of around 15-20 knots — IR cloud top temperatures were warmer than 0º C along the frontal cloud band north of Hawaii, suggesting rather shallow cloud features.

AWIPS image of GOES-11 10.7 µm IR channel and MADIS winds

A closer view using GOES-11 visible imagery (below) revealed that a series of mesoscale vorticies had developed along the frontal boundary. Another interesting feature was the persistent volcanic plume downwind of the big island of Hawaii (streaming toward the southwest), due to ongoing activity at the Kilauea volcano since Spring 2008 (see the April 2008 CIMSS satellite blog entry). Also note the long, thin line of cumulus clouds below the volcanic plume, a result of lee-side convergence.

GOES-11 visible images

A comparison of GOES-11 and GOES-13 visible images (below) shows that the volcanic plume was even more apparent with the larger viewing angle and more favorable “forward scattering” geometry from the GOES-13 satellite (positioned at 105º W longitude, vs. 135º W longitude for GOES-11).

GOES-11 and GOES-13 visible images

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GOES-12 IR image + QuikSCAT WindSat wind vectors

An image of the GOES-12 10.7 µm IR channel (with an overlay of QuikSCAT WindSat wind vectors) from the CIMSS Tropical Cyclones site (above) revealed that wind speeds were near 50 knots within a curved band of deep convection located just to the east of the center of Subtropical Storm Laura on 29 September 2008.

Animations of the GOES-12 10.7 µm IR channel and visible channel images (below) showed the curved band of deep convection developing further and wrapping around the northern and then the western quadrants of the storm during the hours that followed; small-scale swirls were also seen on the visible imagery, rotating around the low-level center of Laura.

GOES-12 10.7 µm IR images

GOES-12 visible images

Laura was eventually classified as a Tropical Storm on the following day (30 September).

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GOES-12 6.5 µm water vapor images

GOES-12 6.5 micrometer “water vapor channel” imagery (above) revealed a pronounced warming/drying signature (darker orange colors) as Hurricane Kyle was beginning the transition to an extratropical system on 28 September 2008. GOES-12 water vapor brightness temperatures were as warm as 268º K (-5.15º C) at 16:45 and 17:02 UTC — and the rapid trend of warming/drying suggested that strong subsidence was occurring in that region.

A comparison of the 4-km resolution GOES-12 and the 1-km resolution MODIS water vapor channel data (below) yielded similar brightness temperature values within the core of the warm/dry region (-5.1º C on MODIS, -7.5º C on GOES-12).

GOES-12 6.5 µm and MODIS 6.7 µm water vapor images

Curiously, the GOES-12 sounder total column ozone product (animation) did not exhibit a high ozone feature co-located with the warm/dry pocket seen on the water vapor imagery (below) — if this dry air were due to a stratospheric intrusion or a tropopause fold, ozone values would normally increase to the 350-400 Dobson Unit range (green to red colors).

AWIPS images of GOES-12 water vapor and total column ozone

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GOES-12 sounder and GOES-12 imager water vapor channels

A fairly large cyclone developed and intensified off the southeast coast of the US on 24–25 September 2008. An animation of GOES-12 sounder and GOES-12 imager water vapor channel data (above) displayed an impressive structure associated with the system, with a well-defined dry slot wrapping around the southern and eastern quadrants of the storm. While not officially acquiring tropical (warm core) characteristics, the storm produced winds gusting as high as 55 mph and waves as high as 19 feet along parts of the Virginia and North Carolina coasts.

A sequence of AWIPS images of the 1-km resolution MODIS water vapor channel (below) showed better details of the storm structure during the period of intensification.

AWIPS images of the MODIS water vapor channel

GOES-12 visible images from 24 September and 25 September (below) revealed some impressive convection forming around the core of the storm.

GOES-12 visible images (24 September)

GOES-12 visible images (25 September)

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