MODIS true color images: 16 August and 28 August 2011

Heavy rainfall associated with Hurricane Irene included 20.40 inches at Virginia beach, Virginia and 20.00 inches at Jacksonville, North Carolina (HPC summary). Winds gusted as high as 115 mph at Cedar Island, North Carolina. The effects of the heavy rain and strong winds can be seen in a before/after comparison of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above). On the “before” image (16 August 2011), there was a large smoke plume seen from a fire that was burning in the Great Dismal Swamp area in far southeastern Virginia; on the “after” image (28 August 2011), water turbidity was significantly enhanced due to suspended sediment across the Outer Banks region of North Carolina — and a narrow filament of sediment was being actually being entrained into the flow of the Gulf Stream.

AWIPS images of the corresponding MODIS 0.65 µm visible channel data and the MODIS Sea Surface Temperature (SST) product (below) showed that the enhanced turbidity features seen on the MODIS true color image generally exhibited slightly cooler SST values (in the middle to upper 70s F, blue color enhancement) compares to the waters located closer to the Gulf Stream (SST values in the lower 80s F, darker red color enhancement).

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature image

Farther to the north, another before/after MODIS true color image comparison revealed additional areas of sediment being carried off the coast of the Northeast US (below). Also note that there was a great deal of sediment in the Hudson River (perhaps better seen in this 20 August / 29 August comparison).

MODIS true color images: 26 August and 29 August 2011

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MODIS Total Precipitable Water product

The National Weather Service forecast office in Salt Lake City, Utah referred to the MODIS Total Precipitable Water (TPW) product (above) in their afternoon forecast discussion on 27 August 2011:

FXUS65 KSLC 272201
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
355 PM MDT SAT AUG 27 2011

.SYNOPSIS...HIGH PRESSURE NEAR THE FOUR CORNERS WILL DRIFT WEST AND
WEAKEN ON SUNDAY. A VERY MOIST AIRMASS WILL REMAIN IN PLACE SUNDAY
BRINGING SCATTERED THUNDERSTORMS TO UTAH. WESTERLY FLOW WITH A
GRADUAL DRYING TREND IS THEN EXPECTED ON MONDAY AND TUESDAY.

.DISCUSSION...UPPER LEVEL AREA OF HIGH PRESSURE REMAINS CENTERED
NEAR THE FOUR CORNERS AREA THIS AFTERNOON...KEEPING A VERY MOIST
AIRMASS IN PLACE ACROSS UTAH. GPS-MET SENSOR CONTINUES TO SHOW THAT
COLUMN PRECIPITABLE WATER IS HOVERING AROUND 1.20 INCHES IN SALT
LAKE CITY.  AFTERNOON MODIS IMAGERY INDICATES THAT PRECIPITABLE
WATER VALUES ARE GENERALLY 1.0 TO 1.25 INCHES STATEWIDE.

The MODIS TPW values were in general agreement with those seen on the GOES sounder TPW product (below), but with finer spatial resolution (4-km MODIS, vs 10-km GOES) the various TPW gradients appear smoother on the MODIS image.

GOES sounder Total Precipitable Water product

The Blended TPW product (below) displayed complete coverage (even in cloudy areas), but lacked the finer scale definition of the MODIS or GOES products due to the use of only Global Positioning System derived TPW data over inland areas.

Blended Total Precipitable Water product

The Percent of Normal TPW product (below) indicated that the TPW values present across the region were generally 150-200% above normal for the date.

Percent of Normal TPW product

Their forecast discussion went on to state:

AIRMASS QUICKLY DESTABILIZED IN THE EARLY AFTERNOON WITH SCATTERED
CONVECTION FORMING IN THE SOUTH AND EAST AND MORE ISOLATED COVERAGE
IN THE NORTHWEST.

The MODIS 0.65 µm visible channel image (below) showed the areas where organized convection had already developed across Utah and the surrounding states.

MODIS 0.65 µm visible chanel image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS. In addition, the VISIT training lesson “MODIS Products in AWIPS” is available to help users understand these products and their applications to weather analysis and forecasting.

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GOES-13 Visible (0.63 µm) images (click image to play animation)

Category two Hurricane Irene (shown in the rocking animation above) is over the South Atlantic Bight after moving through the Bahamas on August 25th. The projected path is over coastal North Carolina and then towards New England. What factors will control future changes in strength?

Morphed Microwave imagery (click image to play animation)

Morphed microwave imagery, above (and available from the CIMSS Tropical Cyclones site) shows a slow erosion in the inner eyewall during the first 12 hours of August 26, which suggests a possibly temporary decrease in organization to the storm. (Morphed microwave imagery from the 24th and 25th of August show how the eyewall structure changed as the hurricane moved through the Bahamas).

GOES Water Vapor (6.5 µm) image

Water vapor imagery (above) shows dry air west of Irene and ahead of Irene. Recall, however, that GOES Water Vapor signals are showing the temperature at the top of the water vapor. Over the hurricane, where water vapor is associated with deep convective clouds, cold temperatures (white and green in the enhancement) are indicated. The yellow enhancement surrounding Irene indicates warm water vapor that is therefore low in the atmosphere, but it does not quantify how much moisture is present. That is, there could be abundant moisture very low in the atmosphere. Total Precipitable Water (TPW) Percent of Normal maps, however, blended from GPS and GOES Sounder data over land, and from Microwave imagery over water, show relatively dry air over the southeastern part of the United States. MIMIC TPW also shows dry air west of Florida over the Gulf of Mexico. If that dry air can be entrained into the circulation of Irene, significant strengthening would not be expected. (Note also that the MIMIC TPW shows a very rich moisture source just off the coast of the northeast United States. As Irene moves northward, that moisture-rich air should fuel heavy rains).

GOES-13 Visible (0.63 µm), IR (10.7 µm) and auto-detected Overshooting Tops (click image to play animation)

Thunderstorms in the outer rainbands are still producing overshooting tops, a sign of the intensity of the storm, as shown above. Overshooting Tops and Thermal Couplets can also be viewed here. Detections from 1215 UTC on August 26th show overshoots (and thermal couplets) near the eye.

Aqua MODIS False Color RGB Image

The Aqua satellite overflew Irene before sunrise on August 26th. The above false color image, using water vapor, infrared and short-wave infrared data from the MODIS instrument onboard Aqua as red, green and blue input, shows that dry air had suppressed convection north of the center of the storm at that time. Since then, as shown in the visible imagery at the top of this blog entry, convection has eliminated this dryer region. (Aqua MODIS image courtesy of Dave Santek at SSEC).

MODIS 11.0 µm and POES AVHRR 10.8 µm IR images

AWIPS images of 1-km resolution MODIS 11.0 µm and POES AVHRR 10.8 µm IR data (above) displayed cloud top IR brightness temperatures as cold as -85ºC (darker violet color enhancement) at 09:45 UTC within some of the spiral bands of Irene.

NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image

A NOAA-19 false-color Red/Green/Blue (RGB) image (above; courtesy of Dave Santek, SSEC) showed a well-defined spiral band structure to the storm.

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GOES-13 0.63 µm visible channel images (click image to play animation)

AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed an interesting swirl of smoke aloft which moved eastward across the Upper Midwest region during the late afternoon hours on 25 August 2011.

The curved shape of the smoke feature was due to the cyclonic circulation associated with a transient potential vorticity (PV) anomaly, which was lowering the dynamic tropopause (taken to be the pressure level of the PV1.5 surface) as it moved eastward. A comparison of 1-km resolution MODIS 0.65 µm visible channel, 1-km resolution MODIS 6.7 µm water vapor channel, and 10-km resolution GOES-13 Total Column Ozone product images (below) showed that the PV anomaly was lowering the tropopause to about the 375 hPa pressure level. Upward vertical motion ahead of the PV anomaly was producing a “moist signal” on the MODIS water vapor image (but no clouds were yet seen on the corresponding MODIS visible image). In addition, GOES sounder Total Column Ozone levels were slightly elevated in the vicinity of this PV anomaly (as high as 340 Dobson Units, green color enhancement), compared to the background ozone levels of 100-110 Dobson Units.

MODIS visible and water vapor images + GOES-13 sounder Total Column Ozone product

It is interesting to note that the smoke feature did not exhibit any signal on the 1-km resolution MODIS 3.7 µm shortwave IR or 11.0 µm IR window images (below) — such thin smoke layers are effectively transparent to the warmer thermal radiation reaching the satellite from below. On the other hand, the hot signatures of cities and urban areas (showing up as darker black pixels) were quite obvious on the IR images.

MODIS 0.63 µm visible, MODIS 3.7 µm shortwave IR, and MODIS 11.0 µm IR window channel images

However, the smoke feature did exhibit a well-defined signature on the MODIS 1.4 µm near-IR “cirrus detection channel” image (below) — this channel is sensitive to any airborne particles that are efficient scatters of light (such as ice crystals, smoke, dust, volcanic ash, etc).

MODIS 0.65 µm visible channel and MODIS 1.4 µm "cirrus detection channel" images

As the smoke aloft began to approach Madison (station identifier KMSN on the satellite images) the feature was captured by the west-facing camera on top of the Atmospheric, Oceanic, and Space Sciences building on the University of Wisconsin campus (below; click image to play QuickTime animation). The airborne smoke layer contributed to a colorful yellow/orange sunset.

AOSS building west-facing rooftop camera images (click to play QuickTime animation)

NOAA ARL HYSPLIT model backward trajectories (below) showed that air parcels arriving over Madison (around the time that the leading edge of the smoke aloft moved overhead) had likely originated over Idaho and Wyoming, where several large wildfires had been burning during the previous days. Other fires burning across southeastern Montana may have also contributed to this smoke.

NOAA ARL HYSPLIT model backward trajectories arriving over Madison, Wisconsin

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