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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GOES-13 10.7 µm IR channel images (click image to play animation)

Automated detection of overshooting tops allows identification of regions of intense convective updrafts that penetrate into the stratosphere. Overshooting tops correlate well with regions of intense rainfall and with severe weather. In tropical systems, overshooting tops are most frequent during intensification. The loop above shows overshooting tops (identified as the yellow thunderstorm symbol) superimposed on GOES-13 10.7 µm IR channel imagery as Hurricane Irene moved over the southern Bahamas. This is during a time when the hurricane was slowly strengthening.

The automatic detection of overshooting tops is done using a GOES-R Proving Ground algorithm, developed in preparation for GOES-R that is scheduled to be launched in late 2015 or early 2016. Overshooting tops that are detected over the Continental United States using data from GOES-East (GOES-13) are available at this website. As Irene moves northward over the Atlantic south of Cape Hatteras and east of Georgia and South Carolina on August 25th through the 27th, overshooting tops, if they are present, will be indicated; their presence suggests a vigorous hurricane. This website shows overshooting tops (automatically detected using Meteosat data) over the tropical Atlantic west of Africa; there is a correlation between tropical wave intensification and OT frequency.

GOES-13 IR/WV Difference image

GOES-13 Overshooting Tops

Overshooting tops can also be detected by subtracting the GOES-13 10.7 µm and 6.5 µm imagery (that is, IR – Water Vapor brightness temperatures). Overshooting tops inject water vapor into the stratosphere where it is more readily detected and therefore produces a larger signal on the difference product. For example, this image, also above, left, (taken from the CIMSS Tropical Cyclones site) shows the WV/IR difference at 1945 UTC on 24 August. Compare it to this image (also above, right) that shows the auto-detected tops at 1932 UTC (None were detected at 1945 UTC). (Click for Visible imagery for 1932 UTC and 1945 UTC) Note that the difference field shows a very large region where overshooting tops are indicated to the west of the hurricane eye — this is more likely a cirrus shield than a region of many overshoots which are brief in nature — and a region to the northeast of the hurricane eye is in a region where an overshoot was detected at 1932 UTC. By 1945 UTC, the initial overshoot may be collapsing, but the high cirrus shield will still be present, and the difference field detects it.

Overshooting tops continue to be detected in Irene’s eyewall at 2115 UTC, 2125 UTC and 2132 UTC. The burst of overshoot production seems to end by 2140 UTC, however.

Some of the convective bursts that were producing the overshooting tops can be seen in an animation of GOES-13 0.63 µm visible channel images (below; click image to play animation; also available as a QuickTime movie). The GOES-13 satellite continued to be in Rapid Scan Operations mode, providing images as frequently as every 5-10 minutes. It is interesting to note the “trochoidal motion” (or wobble) of the eye of Hurricane Irene as it moved northwestward across the Bahamas during the day.

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

A sequence of 1-km resolutiion POES AVHRR 12.0 µm IR images (below) revealed a number of areas which exhibited cloud top IR brightness temperatures of -80ºC or colder (purple color enhancement) — the coldest seen was -87ºC at 12:30 UTC.

POES AVHRR 12.0 µm IR images

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

On 22 August 2011 Tropical Storm Irene intensified to become the first Atlantic basin hurricane of the 2011 season. McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed that while no eye was yet apparent, a number of discrete convective bursts could be seen during the day. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes.

An animation of GOES-13 10.7 µm IR images from the CIMSS Tropical Cyclones site (below) showed that large convective bursts continued into the night-time hours, as Hurricane Irene reached Category 2 intensity.

GOES-13 10.7 µm IR images

The presence of a central dense overcast meant that no eye was apparent on the GOES IR imagery — but a DMSP SSMIS 85 GHz microwave brightness temperature image (below) showed that an eye was indeed in the process of forming at 00:48 UTC on 23 August.

DMSP SSMIS 85 GHz microwave brightness temperature image

===== 23 August Update =====

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

On 23 August 2011, some hints of an eye began to appear early in day on GOES-13 0.63 µm visible channel images (above), but the view of an eye structure became obscured by a series of large convective bursts later in the day. As requested by the National Hurricane Center, the GOES-13 satellite remained in Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes.

In a comparison of AWIPS images of 1-km resolution POES AVHRR 0.65 µm visible and 10.8 µm IR data (below), the hints of an eye structure could be more easily seen on the visible image, while widespread “transverse banding” within the upper level cirrus outflow was very evident on the IR image.

POES AVHRR 0.65 µm visible and 10.8 µm IR images

Later, during the evening hours, the signature of an eye began to appear on GOES-13 10.7 µm IR images from the CIMSS Tropical Cylones site (below).

GOES-13 10.7 µm IR images

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GOES-13 10.7 µm IR images

TROPICAL STORM IRENE SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
700 PM AST SAT AUG 20 2011

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE TROPICAL WAVE EAST OF THE LESSER ANTILLES FOUND A SMALL LOW-LEVEL CIRCULATION CENTER JUST SOUTHWEST OF A LARGE CONVECTIVE BURST AND A MINIMUM PRESSURE OF ABOUT 1006 MB. THE PLANE ALSO MEASURED A MAXIMUM WIND OF 53 KT AT 1400 FT AND BELIEVABLE WINDS OF ABOUT 45 KT FROM THE SFMR. THUS ADVISORIES ARE BEING INITIATED ON TROPICAL STORM IRENE WITH AN INITIAL INTENSITY OF 45 KT.

GOES-13 10.7 µm IR images from the CIMSS Tropical Cyclones site (above) showed the large convective burst, along with the location and initial NHC forecast track of the center of Irene.

Within the large convective burst feature, GOES-13 IR / Water Vapor brightness temperature difference product images (below) displayed negative values (green to yellow to red color enhancement) indicative of intense overshooting tops — a signature that is favorable for continued intensification.

GOES-13 IR / Water Vapor brightness temperature difference images

===== 21 August Update =====

The GOES-13 satellite was placed into Rapid Scan Operations (RSO) beginning at 10:15 UTC on 21 August (providing images as frequently as every 5-10 minutes), to monitor Tropical Storm Irene as it approached Puerto Rico. McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation) showed the development of a well-defined cyclonic circulation, as well as a few low-level outflow boundaries propagating outward along the southwestern quadrant of the storm.

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

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