GOES-14 0.63 µm visible channel images (click image to play animation)

McIDAS images of GOES-14 1-minute interval Super Rapid Scan Operations for GOES-R (SRSOR) 1-km resolution 0.63 µm visible channel images (above; click image to play animation) showed overshooting tops and cloud-top gravity waves associated with a large convective burst located just to the southwest of the center of Tropical Storm Isaac on 23 August 2012.

The corresponding 4-km resolution GOES-14 10.7 µm IR channel images (below) revealed the fluctuation of cold cloud top IR brightness temperatures in the -80 to -90º C range (light to dark purple color enhancement). The white tropical cyclone symbol denotes the 12:00 UTC position of the center of Tropical Storm Isaac according to the National Hurricane Center.

GOES-14 10.7 µm IR channel images (click image to play animation)

===== 24 August Update =====

GOES-14 0.63 µm visible channel images (click image to play animation)

A GOES-14 visible image animation from early morning on August 24th (above; click image to play animation), about 24 hours after the animation at top, continues to show active convection, although the storm itself remains poorly organized with an elongated center of circulation as seen on OSCAT scatterometer surface winds (below). The presence of increasingly organized curved convective banding is obvious, however.

GOES-13 10.7 µm IR channel images + OSCAT scatterometer surface winds

GOES-14 0.63 µm visible channel images and 10.7 µm images, 1200-1259 UTC 24 August 2012 (click image to play animation)

The animation above shows an hour of 1-minute visible (0.63 µm) and Infrared (10.7 µm) imagery starting at 1200 UTC on 24 Friday. The cold cloud tops of the active convection, and the episodic overshooting tops, are evident. Note that the slight flicker that is apparent in the 10.7 µm imagery may be due to the timing of space looks that the ‘cold end’ that is used in the IR calibration. An animation for the one hour starting 1800 UTC is below. Significant changes in the structure of the storm are apparent.

GOES-14 0.63 µm visible channel images and 10.7 µm images, 1800-1859 UTC 24 August 2012 (click image to play animation)

For more information on Isaac, refer to the CIMSS Tropical Cyclones site and the National Hurricane Center. One-minute imagery for the storm can be viewed in real time here.

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GOES-14 SRSOR 0.62 µm and 10.7 µm Imagery (click image to play animation)

GOES-14 is in SRSOR operations today and was well-positioned to monitor the flooding rains that occurred in Las Vegas (which received a daily record 1.65 inches of rainfall). The animation above shows cold cloud tops northeast of Las Vegas, with more convection moving in from the southwest. Click here for a large (85 M) animated gif file of one-minute imagery from 1415 UTC through 1859 UTC).

The Blended Total Precipitable Water product (TPW) for this afternoon shows a local maximum in TPW over the southwestern United States. A MIMIC TPW animation suggests that the moisture has originated from a surge up the Gulf of California. During the previous night-time hours, MODIS TPW values of 50-60 mm were seen across far southeastern California, far southwestern Arizona, and in the Las Vegas area as well.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (above) showed the convective cluster in southern California at 20:29 UTC (which was seen early on the GOES-14 image animation). Cloud top IR brightness temperatures were as cold as -69º C (dark red color enhancement), and a number of cloud-to-ground lightning strikes (mostly of negative polarity) were detected within a 15-minute period as this thunderstorm was growing in size and intensity.

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GOES-14 3.9 µm shortwave IR (left) and 0.63 µm visible (right) images (click image to play animation)

McIDAS images of GOES-14 1-minute interval Super Rapid Scan Operations for GOES-R (SRSOR) 4-km resolution 3.9 µm shortwave IR channel data and 1-km resolution 0.63 µm visible channel data (above; click image to play animation) showed a number of significant wildfires burning across parts of northern California on 21 August 2012. The largest and most intense fires exhibited pronounced “hot spots” (black to yellow to red color enhancement) on the shortwave IR imagery, with optically-thick smoke plumes on the corresponding visible imagery.

The GOES-14 satellite has been brought out of on-orbit storage to be tested in SRSOR mode through the end of October 2012, allowing it to provide images at 1-minute intervals for an extended period of time over special regions of interest (similar to the future GOES-R satellite, which will be capable of producing imagery at 30-second intervals over special sectors of interest).

During the previous night-time hours, a comparison of AWIPS images of 1-km resolution MODIS 3.7 µm data with the corresponding 4-km resolution GOES-15 3.9 µm shortwave IR data (below) demonstrated the value of improved spatial resolution for identifying the location of smaller fires, as well as more accurately assessing the location and shape of the more intense portions of larger actively burning fires.

MODIS 3.7 µm vs GOES-15 3.9 µm shortwave IR images

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Toggle between GOES-East Brightness Temperature difference (10.7µm and 3.9 µm) and Aqua MODIS Brightness Temperature difference (11 µm and 3.7 µm) (click image to play animation)

Toggle between GOES-East Brightness Temperature difference (10.7 µm and 3.9 µm) and Suomi/NPP VIIRS Brightness Temperature difference (10.8 µm and 3.74 µm) (click image to play animation)

Water clouds, such as those that develop when fog and low stratus form, have different emissivity properties at short IR wavelengths (around 3.9 µm) compared to longer IR wavelengths (around 11 µm). At shorter IR wavelengths, water cloud do not emit as blackbodies, meaning less radiation is emitted than is theoretically possible. Emissions at longer IR wavelengths are far closer to the theoretical maximum. The perceived temperature, then (computed based on the assumption that emissions are as blackbodies), based on the detected radiation at shorter IR wavelengths are cooler than the perceived temperature based on radiation detected at longer IR wavelenghts. This brightness temperature difference (BTD) field can be used to highlight regions of low clouds, as shown in the imagery above. Calm conditions over the central Appalachians have allowed fog formation especially in river valleys. The 1-km resolution of MODIS imagery (from Aqua) and VIIRS imagery (from Suomi/NPP) shows far higher detail than is available from GOES imagery.

A fog and low stratus detection scheme based solely on BTD fields, however, has shortcomings. For example, in the imagery above, no signal is available underneath the cirrus canopy that stretches from Georgia and South Carolina northeastward into southern New England. In addition, VIIRS, MODIS and GOES show fog/low stratus over western Ohio, but this plot of visibilities shows no serious obstructions to visibility in western Ohio where the BTD signal is strong (and significant visibility obstructions underneath the cirrus canopy in eastern Pennsylvania and Maryland where the BTD is weak). How can this satellite-based signal be improved?

MODIS 3.7 µm vs GOES-15 3.9 µm shortwave IR images

Model data — in this case, from the Rapid Refresh — can be used in a fused product to add information in regions where satellite data cannot be used, and to refine the satellite data elsewhere. IFR Probabilities — an algorithm developed for use with GOES-R ABI data, but applicable to both MODIS and GOES-East data — using MODIS data, above, show very high probabilities over the river valleys of Appalachia where both satellite and model predictors agree that fog or low stratus is likely. Lower, but still significant, probabilities that are based solely on model data, are present underneath the cirrus canopy in southeastern Pennsylvania southwestward to Georgia (because the satellite data cannot be used here, a somewhat lower probability occurs). And, significantly, the stratus deck over western Ohio, which is not associated with IFR conditions, is de-emphasized in the IFR probability field, because the model data shows IFR conditions are unlikely even though the satellite signal — caused by elevated stratus — is strong. Model data adds to and refines the satellite-only BTD field. A plot similar to the MODIS IFR probability, but using GOES Imager data, is here.

Finally, note in the toggle between the VIIRS BTD product and the GOES BTD product, above, that a signal in the GOES Imagery along the eastern shore of Lake Huron is not replicated in the data from Suomi/NPP. The one-pixel co-registration offset between the 3.9 and 10.7 channels, first noted here, persists.

(This blog post is an expanded version of one first posted here.)

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