MODIS 11.0 µm IR Window channel brightness temperature

Pavlof Volcano (located at about 55.5 N, 162 W) in the Aleutian Islands had been experiencing a series of small eruptions that were captured by the constellation of polar-orbiting satellites that pass over the region. For example, a MODIS 11.0 µm IR Window channel image from 08:07 UTC on 16 May (above) showed a dark (warm) pixel over the volcano. That 0º C pixel was surrounded by values closer to -15º C.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images

A comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 3.74 µm shortwave IR images at 12:12 UTC on 16 May 2013 (above) showed the bright glow of the volcano on the DNB, centered over a warm thermal anomaly of 47.5º C (orange color enhancement) on the shortwave IR. These were both signatures of hot lava flows from the summit and down along the northwest flank of Pavlof.

Volcanic plume characteristics derived from Aqua MODIS at 13:50 UTC

The high spectral resolution of MODIS — 36 different channels in the visible and infrared — on board the Terra and Aqua satellites allows for creation of products that quantitatively describe the volcanic ash cloud, beyond just locating the hot spot of the volcano itself. False color imagery, shown above (top left panel, derived from the brightness temperature differences indicated in the figure) from Aqua MODIS at 13:50 UTC, nicely outlines the volcanic ash plume in shades of red. The other three figure panels show the Ash Cloud Height (very important information for aviation concerns), the Ash Cloud Particle Size (which is related to how long it will take to settle out — small particles stay in the atmosphere for a longer time) and Ash Cloud Loading (what is the mass of volcanic ash in the column?).

A later 4-panel suite of products derived from MODIS data on Terra, at 21:31 UTC, is shown below. In addition to the high spectral resolution on MODIS, the polar orbiter satellites have good horizontal resolution over Alaska as well.

Volcanic plume characteristics derived from Terra MODIS at 21:31 UTC

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 3.74 µm shortwave IR channel images at 22:08 UTC (below) showed the hazy signature of the volcanic plume on the visible image, as well as a warm thermal anomaly exhibiting a brightness temperature of 40º C (yellow color enhancement) on the shortwave IR image. A Volcanic Ash Advisory had been issued for altitudes between the surface and 15,000 feet, as the volcanic plume drifted southeastward at 15 knots.

Suomi NPP VIIRS 0.64 µm visible channel and 3.74 µm shortwave IR channel images

GOES imaging of this eruption suffers because of limited channels (5) on the GOES Imager, and because of degraded spatial resolution at the high latitudes (as result of the very large satellite viewing angle). However, the hazy signature of the volcanic plume could still be seen drifting southeastward from Pavlof on GOES-15 0.63 µm visible channel images (below; click image to play animation). The location of the Pavlof volcano is denoted by the “P” on the images. Also of interest in the animation is the motion of sea ice in the Bering Sea north of the Aleutians, which could be seen once a break in the clouds moved over that area.

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

An outbreak of tornadoes across the Dallas/Ft. Worth area in north Texas on 15 May 2013 produced up to 16 tornadoes (NWS summary) which were responsible for 6 fatalities. Hail as large as 4.0 inches in diameter and a wind gust as high as 80 mph also accompanied these severe thunderstorms (SPC storm reports). A McIDAS image comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation)  showed the rapid development of convection across the north Texas region, with the storms exhibiting a number of overshooting tops. The locations of Granbury (G) and Cleburne (C) were noted on the images, where EF-4 and EF-3 tornado damage occurred.

A similar comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 10.7 µm IR channel images (below; click image to play animation) showed the cold cloud top IR brightness temperatures associated with these storms, which were as cold as -63 C (darker red color enhancement) in the vicinity of Granbury and Cleburne around the time of the tornadoes.

GOES-15 (left) and GOES-13 (right) 10.7 µm IR channel images (click image to play animation)

GOES-13 sounder Lifted Index derived product images (click image to play animation)

These storms developed along an axis of instability and moisture that was located to the east of a dryline that was bulging eastward across north Texas — the GOES-13 sounder Lifted Index (LI) derived product images (above; click image to play animation) revealed LI values as low as -12.4 C (dark purple color enhancement) at 23:00 UTC, and the GOES-13 sounder Total Precipitable Water (TPW) derived product images (below; click image to play animation) showed that TPW values were as high as 46.7 mm or 1.84 inches (darker red color enhancement) at 22:00 UTC. METAR surface reports are plotted on the sounder images (Granbury is station identifier KGDJ, and Cleburne is station identifier KCPT).

GOES-13 sounder Total Precipitable Water derived product images (click image to play animation)

GOES-13 Sounder Derived Lifted Index (click image to play animation)

Strong convection in the late afternoon/early evening produced wind damage and heat bursts over southern Wisconsin late in the day on May 14, 2013 in a region where severe convection was not considered likely. GOES Sounder data did an excellent job of depicting the instability that developed in the late afternoon. The animation above shows strong destabilization starting shortly after 1800 UTC, and persisting as the convection moved through southern Wisconsin.

GOES-13 Sounder Derived Lifted Index

The instability associated with this convective event was very localized, and easily slipped in between the radiosonde stations. This is therefore another example of the benefit of the GOES Sounder DPI products: Not only do they provide hour-by-hour coverage, so that an evolving situation can be monitored, but they can show mesoscale features that are poorly sampled by conventional radiosonde data. The above image shows the 2346 UTC 14 May GOES Sounder DPI LI over the upper midwest; superimposed upon the image are the Lifted Indices computed from radiosondes and the LI computed from the GFS model. The strongest instability is not well sampled by the radiosonde network.

GOES-13 Sounder Derived CAPE

Convective Available Potential Energy (CAPE) can also be used to diagnose the potential for convection. In regions where CAPE values are large, convection can grow explosively. The AWIPS screen capture of CAPE computed from the sounder, above, shows values exceeding 4000 J/kg even after the convection has passed!

GOES-13 Visible (0.63 µm) Imagery (click image to play animation)

Visible imagery from GOES-13, above, shows the development of the convection as it moves into the area of diagnosed instability. The Microburst Windspeed Potential Index (MWPI) predicts maximum wind gusts that might occur given the thermal profiles associated with developing convection. Attributes that promote downbursts are steep mid-level lapse rates (to enhance convective instability) and abundant dry air (to enhance evaporative cooling). The two animations below (created using McIDAS-V and this bundle) show a maximum in MWPI (with values near 50 — the relationship between MWPI and convective gusts is here) developing over southwest WI as the convection develops. (Data are from the Rapid Refresh model run at 2200 UTC on Tuesday 14 May). The animation of model soundings over Madison (bottom) indicates strong destabilization and mid-level drying, two components that enhance the potential for microbursts. (McIDAS-V animations courtesy of Ken Pryor, NOAA/NESDIS)

Microbust Windspeed Potential Index (MWPI) from 2200 UTC 14 May-0100 UTC 15 May over Wisconsin. Data from Rapid Refresh Model

Rapid Refresh Model Soundings over Madison, WI from 2200 UTC 14 May-0100 UTC 15 May over Wisconsin

GOES Sounder DPI products are available here. YouTube videos of the convection, obtained from the cameras on the roof of SSEC, are available here (looking east) and here (looking north).

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

Each year, about every 6 months, the Earth-Sun-Satellite geometry is such that the GOES Imager can look right at the Sun. In the past, there were ‘keep-out zones’ in which the satellites did not image because it was known to be looking at the Sun during those times. The imagery above, from GOES-13, shows visible light in the night-time imagery. (Click here for a similar GOES-15 animation). Stray light values typically peak around 0500 UTC for GOES-East and around 0900 UTC for GOES-West.

In addition, imagery was not possible during the so-called ‘eclipse season’ because the satellites lacked sufficient batteries to power the instruments as they passed through Earth’s shadow. Now, an improved battery system on the current generation GOES-13/14/15 satellites allows for imaging to proceed while the satellite is in the Earth’s shadow.

This new scheduling, however, introduces issues. The GOES Imager is calibrated by periodic looks into deep space, regions from which only very small amounts of radiation (at 3.9, 6.5, 10.7 and 13.3 µm) are being emitted. These ‘space looks’ are on either side of the full-disk GOES Image. During the ‘eclipse season’, that space look can include part of the solar energy, meaning the very small amount of radiation that the satellite is designed to detect is actually potentially significant. Thus, the calibration of the image can be affected. NOAA NESDIS does operationally correct images with ‘stray light’, but this correction does not consider the impact of a corrupted space view. The GOES-13 stray light corrections were implemented in 2012, as discussed here on this blog.

In addition to the calibration images, solar radiation can also be scattered off clouds towards the imager. So, instead of detecting only emitted radiation at night, the GOES Imager is detecting emitted terrestrial radiation in addition to scattered/reflected solar radiation. This solar radiation contaminates the signal, and results in ‘too much’ radiance being detected, resulting in warmer-than-actual inferred blackbody/brightness temperatures.

GOES-13 imagery from infrared channels (click image to enlarge)

When Stray Light issues occur, the most noticeable effects are in the 3.9 µm channel (Above loop, bottom left) and in products that use the 3.9 µm channel, such as the brightness temperature difference (Above loop, top left). In other words, this calibration issue can affect derived products that use 3.9 µm data at night. The image below shows how the 3.9 µm imagery can change when Stray Light is an issue. Compare the 0415 UTC image, on the left, when Stray Light did not contaminate the space look, with the 0502 UTC image on the right, when Stray Light was an issue.

GOES-13 3.9 µm imagery

NESDIS is considering methods of mitigating the stray light issues that occasionally occur in the GOES Imager.

GOES-13 0.63 µm visible channel (top) and 3.9 µm shortwave IR channel (bottom) images (click to play animation)

McIDAS images of GOES-13 0.63 µm visible channel and 3.9 µm shortwave IR channel data (above; click image to play animation) showed the large smoke plumes and fire “hot spots” (dark black pixels on the shortwave IR imagery) associated with the Germann Road Fire in northwestern Wisconsin and the Green Valley Fire in Minnesota on 14 May 2013. The Germann Road Fire burned 8495 acres, making it the largest wildfire in northern Wisconsin in 33 years. In Minnesota, the Green Valley fire burned 7100 acres.

Items of interest to note on the GOES-13 imagery: (1) the presence of a well-defined lake breeze (lighter gray color enhancement on the IR images) which extended quite a distance inland from the colder waters of Lake Superior (which still exhibited Sea Surface Temperature values in the middle to upper 30s F); (2) the change in wind direction from southwesterly to westerly/northwesterly as a frontal boundary moved eastward across the region; (3) the apparent “flare-up” of the Germann Road Fire as the frontal boundary arrived around 00:45 UTC — the size of the cluster of black “hot spot” pixels increased on the shortwave IR image, concurrent with the rapid growth of an area of pyrocumulus clouds; (4) the eastward motion of the thin lake ice that remained on Mille Lacs in Minnesota (the large lake just south of the Green Valley smoke plume).

2 days after the fire, the burn scar was apparent on an Aqua MODIS false-color Red/Green/Blue (RGB) image (below), viewed using the SSEC Web Map Server. Note the “right turn”on the northern end of the burn scar, caused by a change from southwesterly winds to strong westerly winds in the wake of a frontal passage (which altered the direction of the fire’s progress).

Aqua MODIS false-color image showing wildfire location and burn scar

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

Strong northwesterly winds along the California coast interacted with the complex terrain and orientation of Monterey Bay to promote the formation of a cyclonic coastal eddy (known locally as an “Otter Eddy”) early in the day on 13 May 2013. McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the evolution of the eddy feature, which gradually dissipated by the early afternoon hours. “MRY” denotes the location of Monterey.

Farther to the north, an interesting type of “bow shock wave” formed downwind of Point Reyes (labelled “PR” on the images). Better detail of this feature could be seen in an AWIPS image of Suomi NPP VIIRS 0.64 µm visible channel data (below). At the time of this image, surface winds at the offshore buoy just to the north of Point Reyes were gusting to 33 knots (38 mph).

Suomi NPP VIIRS 0.64 µm visible channel image

Morphed Total Precipitable Water (click image to play animation)

The “cutoff low” system that had been slowly moving across the country for the past week spawned heavy rains which caused flooding in parts of the New York City (NYC) metropolitan area on the morning of 08 May 2013. The image above, of MIMIC Total Precipitable Water, showed a plume of moisture-rich air moving northwestward from the tropical Atlantic towards New York (in advance of the surface frontal system associated with the cutoff low). This region of enhanced precipitable water was seen on the previous day as well. The blended Total Precipitable Water Product (as described here) also showed a plume of higher-than-normal precipitable water air moving over New York City — values of 170+% of normal are over New York City, with a value exceeding 200% (in yellow) sits over the Atlantic Ocean.

GOES-13 6.5 µm water vapor imagery (click image to play animation)

High values of Total Precipitable Water were being been entrained by the circulation of the upper-level low, as shown in the animation of GOES-13 water vapor channel images above. The cyclonic circulation had drawn the moisture north and west into the NYC metropolitan region, and convection developing in the cyclonic flow was responsible for the heavy rainfall. A Suomi/NPP VIIRS 11.45 µm IR image, below, overlain with model-based 500-mb geopotential height fields, showed the strong convection and the cyclonic flow moving into New York. It is interesting to note that the southern tail end of the convection sat right over the Gulf Stream.

Suomi/NPP VIIRS 11.45 µm imagery

The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes. Discrete convective cells with cloud-top IR brightness temperatures colder than -60º C (darker red color enhancement) can be seen developing and moving northwestward over the NYC area on 4-km resolution GOES-13 10.7 µm IR channel images (below).

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

A closer view using 1-km resolution POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images at 10:09 UTC or 6:09 AM local time (below) revealed the texture and shadowing of overshooting tops on the visible image, with cloud-top IR brightness temperature values as cold as -67º C (dark red color enhancement).

POES AVHRR 0.64 µm visible channel and 10.8 µm IR channel images

GOES-13 0.63 µm visible channel imagery (below) showed the different bands of convection that developed offshore and moved inland across the NYC metropolitan area.

GOES-13 Visible Imagery (0.63 µm) (click image to play animation)

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

McIDAS images of 4-km resolution GOES-13 10.7 µm IR channel images (above; click image to play animation) showed the development of large thunderstorms that produced heavy rainfall (including 5.18 inches at San Sebastian) which led to flash flooding over parts of Puerto Rico (Local Storm Report) on 07 May 2013. Since their primary Doppler radar was out of service due to an upgrade to Dual-Polarization technology, the National Weather Service forecast office at San Juan had requested that the GOES-13 (GOES-East) satellite be placed into Rapid Scan Operations (RSO), which provided images as frequently as every 5-10 minutes (instead of the nominal 15-minute image interval). The coldest cloud top IR brightness temperature seen on the GOES-13 IR image sequence above was -69º C at 17:10 UTC.

Due to a full-disk scan at 18:00 UTC, there was a 30-minute gap between the 17:45 UTC and 18:15 UTC GOES-13 images. A timely overpass of the NOAA-19 polar-orbiting satellite at 18:03 UTC provided a 1-km resolution AVHRR 10.8 µm IR image during this 30-minute GOES-13 gap (below), which revealed that a new convective cell had rapidly developed over the northwestern portion of Puerto Rico (exhibiting a cloud-top IR brightness temperature as cold as -79º C).

NOAA-19 AVHRR 10.8 µm IR channel image

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below; click image to play animation) showed that an elongated plume of high TPW (50 to 60 mm or 2.0 to 2.4 inches, darker orange color enhancement) was rotating across the Puerto Rico region during this period, providing ample moisture to fuel the development of deep convection and heavy rainfall. Surface analyses suggest that the eastern portion of the TPW  plume was associated with the remnants of a cold frontal boundary, while an impulse over the Caribbean Sea was helping to transport higher TPW values from the south (TJSJ is the station identifier for San Juan, Puerto Rico).

MIMIC Total Precipitable Water product (click image to play animation)

Suomi NPP VIIRS 0.64 µm visible and 3.74 µm shortwave IR images

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and 3.74 µm shortwave IR channel data (above) showed 2 signatures of an ongoing low-level eruption of the Cleveland Volcano located on the Aleutian Island chain of Alaska: a “hot spot” of 45.5º C (red color enhancement) on the shortwave IR image, and a thin plume of gas, steam, and minor amounts of ash streaming eastward at 22:33 UTC on 04 May 2013. The Cleveland volcano began the eruption around 13:00 UTC earlier that day. The volcano is located on the western portion of Chuginadak Island (denoted by the cyan range ring centered on the island) — however, note that the mapping navigation is slightly off on the images (making the volcano hot spot and plume source appear as if they were located in the waters just west of the island).

Several hours later, a Suomi NPP VIIRS 0.7 µm Day/Night Band image at 12:18 UC on 05 May (below) showed the bright night-time glow of the erupting Cleveland volcano.

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Another feature of interest was the von Karman vortex street further to the east, as seen on 2 consecutive Suomi NPP VIIRS 0.64 µm visible channel images (below). Northwesterly flow within the marine boundary layer was being perturbed by the high terrain of the Aleutian Range on the tip of the Alaska Peninsula, with the resulting vortex street streaming southeastward downwind of the peninsula.

Suomi NPP VIIRS 0.64 µm visible channel images

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

A comparison of McIDAS images of 1-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation) showed the smoke plume from the Springs Fire near Camarillo, California on 02 May 2013. GOES-15 (positioned over the Equator at 135º West longitude) had a better viewing angle of the smoke plume, while GOES-13 (positioned at 75º West longitude) was in Rapid Scan Operations (RSO) mode and was therefore able to provide more frequent images.

AWIPS images of 4-km resolution GOES-15 3.9 µm shortwave IR data (below; click image to play animation) showed the development and rapid growth of the fire “hot spot” signature (dark black enhancment) after 14:01 UTC (7:01 AM local time). At Point Mugu (station identifier KNTD), the surface winds gusted to 27 knots from the southwest at 17 UTC, then shifted and gusted to 30 knots from the northwest at 19 UTC, and then shifted again and gusted to 30 knots from the southwest at 20 UTC. Surface visibility at this site was reported to be as low as 2 miles to the north and northeast of the station, with an overcast layer of smoke during most of the day. Not far inland at Sandberg (station identifier KSDB), winds gusted to 46 knots and the dew point temperature dropped to -19º F (making for a relative humidity of 2%!).

GOES-15 3.9 µm shortwave IR images (click image to play animation)

===== 03 May Update =====

AWIPS images of 1-km resolution Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band data at 09:41 UTC or 2:41 AM local time on 03 May (below) showed a very large fire “hot spot” (yellow to red to black color enhancement) on the shortwave IR image, and the Day/Night Band revealed the hazy signature of smoke aloft that had drifted offshore and south and southeastward along the southern California coast.

Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band images

During the following afternoon on 03 May, 250-meter resolution true-color and false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed the dense smoke plume continuing to drift offshore; the hottest active fire regions appeared as light red features on the false-color image.

MODIS true-color and false-color Red/Green/Blue (RGB) images