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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NOAA-18 10.8 µm IR image

A McIDAS image of the NOAA-18 10.8 µm IR channel (above) showed a region of very cold surface temperatures (darker blue to violet color enhancement) over the interior of Alaska on 19 November 2009, especially in the vicinity of Chandalar Lake (station identifier PALR) and Anuktuvuk Pass (station identifier PAKP). In addition, note the appearance of the warm signature of large cracks or “leads” in the ice over the Arctic Ocean (orange to red color enhancement), to the north and northeast of Kuparuk (station identifier PAKU).

A closer view with an overlay of the surface air temperatures (below) revealed a number of narrow fingers of very cold air — this represented the drainage of the coldest air into mountain valleys along the southern portion of the Brooks Range. The coldest IR brightness temperature in that area was -44º F, which happened to match the coldest surface air temperature from first-order weather stations of -44º F at Bettles (located near the center of the image). Bettles reported record low daily minimum temperatures of -45º F on 17 November, -46º F on 18 November, -47º F on 19 November, and -46º F on 20 November (the high temperature was only -40º F on that day!) — the normal high/low temperatures for Bettles during this period are +3º F and -10º F. This stretch of record cold temperatures followed a record 2-day snowfall of 23.7 inches on 11-12 November (the greatest 2-day snowfall on record for Bettles during the month of November).

However, note that the IR image also suggested the presence of a deck of clouds to the east of the very cold valley signatures — and surface air temperatures were significantly warmer under this cloud deck.

NOAA-18 10.8 µm IR image (with surface air temperatures)

AWIPS images of the AVHRR Cloud Type, Cloud Top Temperature, and Cloud Top Height products (below) indicated that the patch of clouds to the east and southeast of Bettles (station identifier PABT) was composed of supercooled water droplets (cyan color enhancement), with cloud top temperatures in the -30 to -38º C range and cloud top heights in the 3-5 km range. Note that the cloud product algorithms showed values of cloud properties over the region surrounding Bettles (even though it was clear there) — the very cold surface temperatures of -40 C and colder tricked the algorithms into thinking that there were high cirrus clouds over that particular area.

AVHRR Cloud Type, Cloud Top Temperature, and Cloud Top Height products

GOES-11 10.7 µm IR images (below) gave some subtle indication that this cloud deck was moving slowly northward across the region to the east of Bettles (note that north is toward the upper right corner, due to the North America projection of these particular AWIPS images).

GOES-11 10.7 µm IR images

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