GOES-12 Sounder Anomalies

November 25th, 2009 |

channel15loop

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.

Super Typhoon Nida (26W) in the West Pacific Ocean

November 25th, 2009 |
MTSAT-2 IR images

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

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

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

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

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

DMSP SSM/IS microwave image