McIDAS-V images of CRAS model Precipitable Water pre-forecast spin-up

MODIS instruments (see here, as well) on board NASA’s Terra and Aqua satellites offer high resolution multi-banded views of the Earth’s atmosphere. Information from the channels can be used to derive total precipitable water in regions where clouds do not exist (as explained here). In the present case, MODIS TPW is compared to colocated TPW values in a CRAS model run that is centered on the direct broadcast MODIS ground station site at SSEC. Where the values differ, mixing ratios are adjusted so that the model value more closely matches the satellite-observed TPWs (Lapse rates are preserved in the adjustment). Satellite-observed TPWs are available only in clear fields of view; cloud initializations, however, are adding information where clouds are observed.

The case above (imagery produced using McIDAS-V) shows the 12-hour pre-forecast spin-up for the model with an initial time of 12:00 UTC on 25 August 2008. Six different MODIS orbits that were received at the SSEC direct broadcast ground station between 00:00 UTC and 12:00 UTC directly affect the initial model fields that are derived from GFS output. Note how the addition of MODIS data moistens the atmosphere in and around the remains of Tropical Storm Fay over the south central US, and also moistens the atmosphere over the Pacific Ocean west of California.

This method is used to introduce satellite information downloaded locally into a model run; more accurate initial fields are helpful in producing a more accurate forecast. In the present case, once the more accurate initial fields are generated, the model then steps forward in time (with GFS fields used to constrain the boundaries).

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GOES-12 and GOES-13 visible images (Animated GIF)

A comparison of GOES-12 and GOES-13 visible images centered near Rolla (station identifier KVIH) in southern Missouri (above) showed that widespread river valley fog was dissipating during the morning hours on 27 August 2008. Note the improvement in image-to-image navigation on the GOES-13 data (less “wobble” of the images), due to changes in the spacecraft design on the newer GOES-13 satellite.

A comparison of GOES-11 and GOES-13 water vapor channel images (below) demonstrates the improved detection of mesoscale mountain waves over far southwestern Alberta and northwestern Montana on that same day. The spatial resolution of the GOES-13 water vapor channel is 4 km, compared to 8 km on the older GOES-11 satellite.

GOES-11 and GOES-13 water vapor images (Animated GIF)

Mountain waves seen on water vapor imagery have long been recognized as an indicator of potential clear air turbulence. There was one pilot report (PIREP) of light to moderate turbulence at an altitude of 32,000 feet near Great Falls, Montana around 17:40 UTC (below).

AWIPS image of GOES water vapor image + PIREP

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GOES-12 IR + SSM/I microwave images (Animated GIF)

Hurricane Gustav rapidly intensified into a hurricane on 26 August 2008 (less than 24 hours after the first advisory was issued). As noted by the National Hurricane Center’s Gustav discussion number 6:

HURRICANE GUSTAV DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
1100 AM EDT TUE AUG 26 2008

AN AIR FORCE RECONNAISSANCE MISSION EARLY THIS MORNING FOUND PEAK FLIGHT-LEVEL WINDS OF 91 KT…AND AN SFMR SURFACE WIND OF 78 KT. THESE MEASUREMENTS SUPPORT AN INITIAL INTENSITY OF 80 KT.  A DROPSONDE RELEASED IN THE EYE OF GUSTAV DURING THE LAST AIRCRAFT PASS THROUGH THE CENTER JUST BEFORE 1200 UTC…FOUND A SURFACE PRESSURE OF 982 MB…BUT WITH 12 KT OF WIND AT THE SURFACE…SO THE MINIMUM PRESSURE HAS BEEN ESTIMATED SLIGHTLY LOWER.  THE AIRCRAFT AND EARLIER MICROWAVE SATELLITE IMAGERY INDICATE THE PRESENCE OF A VERY SMALL EYE…HOWEVER THE EYE HAS NOT YET BECOME APPARENT IN CONVENTIONAL SATELLITE IMAGERY.

A comparison of  imagery from the CIMSS Tropical Cyclones site (above) shows the shield of central dense overcast (cold cloud tops) on the GOES-12 IR image, with evidence of an eye structure showing up on the SSM/IS microwave image. 1-km resolution GOES-12 visible imagery (below) also did not display an eye with Hurricane Gustav during the morning hours.

GOES-12 visible images (Animated GIF)

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AWIPS images of MODIS and GOES shortwave IR channels (Animated GIF)

Lightning was the cause of a wildfire in southeastern Montana (about 45 miles east-southeast of Miles City) during the afternoon hours on 22 August 2008, which burned a total of about 2600 acres. AWIPS images of the MODIS 3.7 µm and GOES 3.9 µm shortwave IR channels (above) showed a significantly warmer “fire hot spot” on the MODIS 18:20 UTC image (51.0º C, orange pixels) compared to the 18:25 GOES image (36.5º C, dark black pixels). The fire hot spot on GOES imagery did not approach the temperatures seen on the MODIS image until about 20:15 UTC.

This wildfire could be viewed using GOES-11 (GOES-West), GOES-12 (GOES-East), and GOES-13 (undergoing a period of operational testing as “GOES-Central”) — you can see that there was a slight amount of image “wobble”  on the GOES-11 and GOES-12 shortwave IR and visible images, while the corresponding GOES-13 image navigation was very steady (below). Changes to the GOES-13 spacecraft have resulted in improved image navigation compared to the previous GOES satellites.

Also note that the smoke plume on the visible images was much more apparent on the GOES-12 and GOES-13 images — this is due to the fact that the forward scattering angle was more favorable from the viewing perspectives of GOES-12 (positioned at 35º W longitude) and GOES-13 (positioned at 105º W longitude) during the late afternoon hours, which helped to highlight the smoke plume as it drifted southeastward.

GOES-11 + GOES-12 + GOES-13 shortwave IR and visible images (Animated GIF)

A plot of the GOES-11, GOES-12, and GOES-13 3.9 µm shortwave IR brightness temperature values (below) showed a fair amount of variability between the maximum “fire hot spot” temperatures sensed by the different satellites. Although there was general agreement in the trend of increasing temperatures as the wildfire continued to burn, at times the measured IR temperatures differed by as much as 20º K (for example, at 19:45 UTC).  The different satellite viewing angle was a contributing factor to some of these differences — at times the fire was partially obscured by cloudiness that was moving through the region during that period.

GOES-11 / GOES-12 / GOES-13 3.9 µm IR brightness temperatures

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