Rapid Scan Operations (RSO) imagery from 2 satellites

July 20th, 2009 |
GOES-11 and GOES-12 visible images

GOES-11 and GOES-12 visible images

The National Weather Service forecast office at Cheyenne WY requested that both the GOES-11 (GOES-West) and the GOES-12 (GOES-East) satellites be placed into Rapid Scan Operations (RSO) to monitor severe convection across their County Warning Area (CWA) on 20 July 2009:

SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE
NWS NCEP CENTRAL OPERATIONS CAMP SPRINGS MD
2114Z MON JUL 20 2009

GOES RSO INFO…

A GOES EAST RSO WILL BE IN EFFECT FROM 2226Z TILL 0426Z
AND GOES WEST RSO WILL BE IN EFFECT FROM 2203Z TILL
0403Z THIS EVENING AS REQUESTED BY WFO CYS /CHEYENNE/
WHO IS ON THE CUSP OF THE SATELLITE RSO COVERAGE AREAS
FOR SVR WX MONITORING SUPPORT.

While there were reports of hail up to 1.0 inch in diameter in the Cheyenne CWA, the thunderstorms that developed further to the east over western Nebraska and western Kansas were more severe (producing tornadoes in Kansas, and hail as large as 4.25 inches in diameter in both Kansas and Nebraska). A comparison of GOES-11 and GOES-12 visible images (above) shows the view of these storms from each satellite perspective. Note that some features were easier to see from the GOES-11 perspective, which allowed more of a view from the side (to reveal surface boundaries and flanking line development more clearly).

A comparison of GOES-11 and GOES-12 10.7 µm IR images (below) shows that the development of a distinct “enhanced-v” signature was apparent on imagery from both satellites from the 23:00 to 23:11 UTC period. The coldest IR brightness temperatures were -67º C (darker black color enhancement) from both GOES-11 and GOES-12.

GOES-11 amd GOES-12 10.7 µm IR images

GOES-11 amd GOES-12 10.7 µm IR images

These thunderstorms appeared to be propagating southward ahead of an advancing cold frontal boundary, and along a decaying stationary frontal boundary that was oriented northwest-to-southeast from western Nebraska into central Kansas. GOES sounder Derived Product Images (DPI) of Lifted Index (LI) and Total Precipitable Water (TPW) (below) indicated that there was an axis of instability (LI values of -4 to -6 º C) and moisture (TPW values of 20-30 mm, or 0.8 to 1.2 inches) along the stationary frontal boundary.

GOES sounder Lifted Index and Total Precipitable Water products

GOES sounder Lifted Index and Total Precipitable Water products

A few hours later, thunderstorms that developed ahead of the advancing cold front in Oklahoma and southern Kansas exhibited cloud top IR brightness temperatures as cold as -84º C (purple color enhancement) on AWIPS imagery of the MODIS 11.0 µm channel (below).

MODIS 11.0 µm IR image + SPC storm reports

MODIS 11.0 µm IR image + SPC storm reports

===== 21 JULY UPDATE =====

On the following day, MODIS 3.7 µm shortwave IR and MODIS Land Surface Temperature (LST) images (below) revealed a long swath of rain-cooled ground across far western Kansas. MODIS LST values were in the 75-85º F range (green colors) within the swath of rain-cooled ground, in contrast to LST values in excess of 110º F (darker orange colors) just to the west.

MODIS 3.7 µm shortwave IR + MODIS Land Surface Temperature product

MODIS 3.7 µm shortwave IR + MODIS Land Surface Temperature product

Interesting satellite signatures in the Arctic

July 16th, 2009 |
GOES-11 + GOES-12 water vapor imagery

GOES-11 + GOES-12 water vapor imagery

An intense upper-level low developed over the Canadian Arctic Archipelago on 14 July 2009, and subsequently migrated southwestward over the Northwest Territories, Yukon, and northeastern Alaska by 16 July 2009. AWIPS images of the GOES-11 + GOES-12 water vapor channel composite (above) showed a well-defined signature of the intensifying upper low during this period, with a large area of warmer/drier air (darker blue colors) within the circulation.

What was remarkable about this warm/dry signature on the water vapor imagery is the fact that such detail could be seen, in spite of the very large satellite viewing angle of the GOES satellites. Water vapor imagery is prone to the effect of “limb brightening” as the water vapor weighting function is shifted to higher, colder altitudes over the higher latitude regions — this tends to make water vapor imagery appear rather cold and “washed out” over the Arctic much of the time. However, in this case the dynamic tropopause (taken to be the pressure of the 1.5 Potential Vorticity Unit surface) was brought downward to the 850 hPa pressure level on 14 July (below) as the low intensified — and snow was even reported at Norman Wells (station identifier CYVQ) in the Northwest Territories on 16 July.

GOES water vapor imagery + GFS90 PV1.5 pressure

GOES water vapor imagery + GFS90 PV1.5 pressure

On the GOES water vapor imagery above there was a hint of some embedded vortex structure developing within the upper low circulation. These vorticies (which were likely small stratospheric intrusion vorticies) were much easier to identify on the 1-km resolution MODIS water vapor image than on the “8-km” resolution GOES-11 water vapor image (below) — this is partly due to the upward shift of the water vapor weighting function mentioned previously, and also due to the fact that the 8-km GOES-11 water vapor pixels were effectively about 30 km in size due to the very large satellite viewing angle.

GOES-11 + MODIS water vapor images

GOES-11 + MODIS water vapor images

Another interesting satellite signature was the appearance of a “thermal anomaly” over the Arctic Ocean north of Alaska on the GOES-11 10.7 µm IR window channel image at 09:00 UTC (below, bottom panels). At that particular time, there is a great deal of solar reflection off the water and ice surface, which appears very bright on the visible imagery (top panels), and very hot (dark black enhancement) on the 3.9 µm shortwave IR imagery (center panels). The intense solar reflection effectively causes the IR window channel brightness temperature to “roll over” from very warm to very cold values (black to white color enhancement). This IR window channel thermal anomaly does not appear if cloud cover masks the highly reflective nature of the water and ice in the Arctic Ocean.

GOES-11 visible, 3.9 µm IR, and 10.7 µm IR images

GOES-11 visible, 3.9 µm IR, and 10.7 µm IR images


GOES-11 visible images

GOES-11 visible images

Later in the day, GOES-11 visible imagery showed that the southern edge of the ice in the Arctic Ocean had receded a considerable distance from the northern coast of Alaska (above). The ice edge could be seen in greater detail using 1-km resolution MODIS true color imagery (below, courtesy of the GINA, University of Alaska Fairbanks SwathViewer).

MODIS true color image (courtesy of GINA, University of Alaska Fairbanks)

MODIS true color image (courtesy of GINA, University of Alaska Fairbanks)

Tropical Storm 07W (Molave): very cold cloud tops

July 16th, 2009 |
MTSAT-1R IR images

MTSAT-1R IR images

MTSAT-1R InfraRed (IR) images from the CIMSS Tropical Cyclones site (above) showed the rapid development of a cold Central Dense Overcast (CDO) as Tropical Storm 07W (Molave) intensified east of the Philippines in the West Pacific Ocean on 16 July 2009. It is interesting to note that the CDO was centered a considerable distance to the southwest of the low-level circulation of the tropical cyclone.

MTSAT-1R IR image

MTSAT-1R 10.3 µm IR image


4-km resolution MTSAT-1R 10.3 µm IR cloud top brightness temperatures (above) were a cold as -92.4º C (purple color enhancement) at 12:30 UTC. 1 hour and 15 minutes later, a 1-km resolution MODIS 11.0 µm IR image (below) indicated that cloud top IR brightness temperatures were still as cold as -92.1º C.

MODIS IR image

MODIS IR image

Volcanic plume over the Great Lakes region?

July 13th, 2009 |
GOES-11 and GOES-12 visible images

GOES-11 and GOES-12 visible images

A comparison of GOES-11 and GOES-12 visible channel images (above) revealed an aerosol plume aloft that was oriented northwest-to-southeast over the western Great Lakes region on 13 July 2009. This example shows the value of forward scattering to help in the identification these kinds of aerosol plumes — note how the plume is much brighter on the GOES-11 image than the GOES-12 image, due to the morning sun’s position in relation to GOES-11 (located at 135º West longitude) versus GOES-12 (located at 75º West longitude). Also note how the hazy aerosol plume tended to “disappear” on both the GOES-11 and the GOES-12 visible images as the sun angle increased during the morning hours.

Later in the day, this aerosol plume was easily seen on AWIPS images of the MODIS near-IR 1.3 µm “cirrus detection” channel (below). The so-called “cirrus detection” channel helps to identify features that are effective scatters of light — which includes cirrus ice crystals as well as airborne aerosols (such as dust, haze, volcanic ash, or volcanic sulfates).

MODIS near-IR cirrus detection images

MODIS near-IR “cirrus detection” images

This aerosol plume exhibited no obvious signal on any of the other conventional MODIS channels, such as the visible, IR window, and water vapor channels (below). So was this aerosol feature due to smoke aloft from fires in Canada or Alaska, or was it a high-altitude volcanic sulfate plume (likely from the Sarychev Peak eruptions earlier in the Summer)?

MODIS cirrus, visible, IR window, and water vapor channel images

MODIS cirrus, visible, IR window, and water vapor channel images

IASI SO2 image (courtesy of Université Libre de Bruxelles)

IASI SO2 image (courtesy of Université Libre de Bruxelles)

As it turns out, this plume was identified as an “SO2 alert” on the IASI SO2 product (above, courtesy of Université Libre de Bruxelles). This feature also exhibited SO2 concentrations of about 6-12 Dobson Units on the Aura OMI SO2 product (below, courtesy of NOAA/NESDIS).

OMI SO2 image (courtesy of NOAA/NESDIS)

OMI SO2 image (courtesy of NOAA/NESDIS)

NOAA ARL HYSPLIT backward trajectories (below) suggest that the aerosol plume had spent some time over the Arctic region during the previous week or so, where we had seen similar evidence of high-altitude aerosol plumes on the GOES-11 visible images in early July.

NOAA ARL backward trajectories

NOAA ARL backward trajectories