GOES-11 6.7 µm water vapor images

Under normal conditions of westerly flow aloft, one might expect to see occasional standing waves to the east of the Sierra Nevada mountain range; however, due to the presence of a strong cut-off low over the southwestern US, the winds aloft over Nevada and California were from the northeast on 29 November 2009 — and AWIPS images of the 8-km resolution GOES-11 6.7 µm water vapor channel (above) showed a signature of mountain waves to the west of the crest of the Sierra Nevada. This type of lee wave signature on water vapor imagery indicates the potential for clear air turbulence in the proximity of the waves — however, there were no pilot reports of turbulence noted in the immediate area of the lee wave signature (possibly due to the time of day, when air traffic is generally at a minimum).

A pair of 1-km resolution MODIS 6.7 µm water vapor images at 06:20 and 10:38 UTC (below) showed the advantage of higher spatial resolution for detecting such mesoscale signatures.

MODIS 6.7 µm water vapor images

A comparison of the 8-km resolution GOES-11 6.7 µm water vapor, 4-km resolution GOES-14 6.5 µm water vapor, and 4-km resolution GOES-12 6.5 µm water vapor images (below) further demonstrated the effects of varying spatial resolution as well as varying satellite viewing angle in resolving the lee wave signatures to the west of the Sierra Nevada. GOES-14 (positioned at 105º West longitude) had the best viewing angle of the region, and its 4-km resolution water vapor channel did a better job of depicting both the areal coverage and the temporal duration of the lee wave structure — especially compared to GOES-11 (positioned at 135º West longitude) with its 8-km resolution water vapor channel. Using GOES-14 imagery, the onset of the lee wave structure was easier to see, and the duration of the lee wave event was also longer. In addition, even though the viewing angle from GOES-12 (positioned at 75º West longitude) was very large — about 65 degrees — the 4-km resolution water vapor channel still managed to show a fairly good signature of the lee waves.

GOES-11, GOES-14, and GOES-12 water vapor images

Note that the water vapor images also suggested the formation of a downwind “cloud banner” or “cloud crest” after about 06 UTC. The 4-km resolution MODIS Cloud Phase product (below) showed a growing ice phase cloud feature (salmon color enhancement) over central California between 06:20 and 10:38 UTC.

MODIS Cloud Phase product

However, the 4-km resolution MODIS Cloud Top Temperature product (below) only indicated cloud top temperature values as cold as -20 to -22º C (green color enhancement) within the glaciated cloud banner feature over central California.

MODIS Cloud Top Temperature product

Another view of the central California cloud banner feature using the 1-km resolution AVHRR Cloud Type product at 09:39 UTC (below) indicated that it was composed of cirrus clouds (yellow enhancement), with supercooled water droplet clouds (cyan color enhancement) immediately upwind over the Sierra Nevada.

AVHRR Cloud Type product

Furthermore, the corresponding 1-km resolution AVHRR Cloud Top Temperature product (below) indicated significantly colder cloud top temperature values of -60º to -70º C (blue to white colors) within the central California cloud banner feature.

AVHRR Cloud Top Temperature product

Finally, it is interesting to note that the GOES-11 10.7 µm IR image (below, upper left panel) showed absolutely no signature of the lee cloud banner — due to the thin nature of this glaciated cloud feature, a great deal of radiation from the warmer land surface below was “bleeding up” though the ice cloud and was masking its presence on IR imagery. The GOES-11 6.7 µm water vapor image, however, did show a better signature of the presence of the cloud banner feature (lower left panel).

GOES IR, GOES water vapor, AVHRR Cloud Top Temperature, and AVHRR Cloud Top Height

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Measurements from the GOES-12 Sounder instrument have shown increased noise over the past weeks. The noise in the signal does not occur with any persistence, but it can be very noticeable, as shown in the loop above of gif imagery taken from the UW CIMSS Derived Products Page. The images above are for Channel 15 (4.4 microns, a wavelength used to investigate the upper atmosphere), a channel on the GOES-12 sounder that has shown considerable noise since launch. Note the marked increase in noise, however, for the 2300 UTC image in the loop.

In addition, increased noise is also affecting channels 13 and 14 (4.57 and 4.53 microns, respectively) and channels 16-18 (4.13, 3.98 and 3.76 microns, respectively). Compare the noise in the images from 25 November at 1800 UTC (significant, noticeable noise in Channels 13-17) and at 1700 UTC (Noise noticeable only in the usually noisy Channel 15).

These noisy satellite observations do impact derived products such as Precipitable Water cloud mask: The 1800 UTC product that uses the noisy data from 1800 UTC shows the speckled result of noise over the southern Plains; the 1700 UTC observations that use the cleaner 1700 UTC data, do not contain such speckles.) The affected channels are used to determine the cloud mask. When there is amplified noise — especially if it results in very cold temperatures that are inferred to be high clouds — then a faulty cloud mask is a result. This is especially true at night when the Channel 18 brightness temperature is compared to the Channel Channel 8, and a cloud is inferred if there is a significant difference between the two. See, for example, this image from 01 UTC on 24 November. The speckling in the cloudtop pressure over Texas results from subtle noise signals in the 3.76-micron band (Channel 18). If these sounder data are being used to quantify the presence of clouds, the increasing noise in the shortwave infrared channels may be problematic.

GOES-14, located above the Equator near 105 W, is currently undergoing science testing. A comparison of Sounder band 15 from GOES-12 to the same band on GOES-14 shows the remarkably cleaner signal from GOES-14.

GOES-12 is scheduled to remain the operational GOES-EAST through March of 2010. It will be replaced by GOES-13.

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MTSAT-2 IR images

MTSAT-2 IR images from the CIMSS Tropical Cyclones site (above) revealed a well-defined eye associated with Super Typhoon Nida on 25 November 2009. Typhoon Nida underwent a period of very rapid intensification — increasing by 50 knots of speed in 12 hours — as seen on the CIMSS Automated Dvorak Technique plot (below). Low values of deep layer wind shear and warm sea surface temperatures were favorable factors aiding further intensification.

CIMSS Automated Dvorak Technique (ADT) intensity estimate plot

An AWIPS image of the MTSAT-2 IR channel with an overlay of ASCAT scatterometer winds (below) showed a core of strong winds (greater than 48 knots, red wind vectors) surrounding the eye of Nida; the maximum ASCAT wind speed at that time was only 62 knots in the northern quadrant (but ASCAT wind speeds in excess of 34 knots tend to be underestimated).

MTSAT-2 IR image + ASCAT scatterometer winds

A MODIS 11.0 µm IR image (below) depicted the very cold cloud tops within the eyewall region, with a minimum value of -87º C (black to gray color enhancement). However, there were some incredibly cold cloud tops of -97º C (violet color enhancement) in one of the outer bands in the northwest quadrant of Nida.

MODIS 11.0 µm IR image

An animation of the MIMIC morphed POES microwave images (below) showed a contracting eyewall as the typhoon was experiencing rapid intensification just southwest of the island of Guam.

MIMIC morphed microwave image animation

UPDATE: A microwave image from the DMSP SSM/IS instrument (below) revealed a concentric eyewall structure at 19:43 UTC. A couple of hours later, the 21:00 UTC advisory from the Joint Typhoon Warning Center listed the winds of Super Typhoon Nida at 160 knots with gusts to 195 knots!

DMSP SSM/IS microwave image

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From an email received on the morning of 23 November 2009: “Several hours ago, shortly past 7:00Z today, telemetry received from QuikSCAT indicates that the antenna rotation rate has dropped to zero and remains at zero. The motor remains powered. The system can be operated safely in this state for an indefinite period. The QuikSCAT operations team will be meeting later this morning, but in all likelihood this is probably the end of the nominal mission.”

The image above shows the last QuikSCAT data processed on the AWIPS system at the Cooperative Institute for Meteorological Satellite Studies (CIMSS). The scatterometer wind data show the flow around a developing cyclone located southeast of the southern tip of Greenland. The underlying GOES-12 IR and water vapor images also reveal a classic baroclinic leaf pattern southeast of the developing cyclone, which is a satellite signature of impending cyclogenesis.

With the loss of QuikSCAT, the only scatterometer winds available in AWIPS are those from ASCAT. For additional information, see the VISIT training modules QuikSCAT Winds and ASCAT Winds.

Addendum (24 November 2009): A loop of infrared imagery over the North Atlantic using imagery from every three hours after the image above nicely shows the evolution of cyclogenesis. The swirl at low levels diagnosed by QuikSCAT is evident as is the development of a comma shape to the higher clouds. Both are hallmarks of the developing storm.

The 1200 UTC analysis from 24 November shows a vigorous cyclone has developed over the North Atlantic from the region where the QuikSCAT near-surface winds showed a swirl on Monday.

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