Dusty Cold Front moves south through the Southern Plains

November 11th, 2014
GOES-13 0.63 µm Visible imagery (click to play animation)

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

A strong cold front moved southward over the High Plains of the US on Monday 10 November, and the strong winds produced a dust cloud that was apparent in GOES-13 visible imagery, above. The leading edge of the dust cloud in the satellite imagery indicated precisely the leading edge of the cold front. The animation below shows hourly observations plotted on top of the GOES-13 visible imagery. The correspondence between the leading edge of the dust and the wind shift is obvious. Note that multiple stations report Haze (H) after the wind shift occurs.

GOES-13 0.63 µm Visible imagery and surface observations (click to play animation)

GOES-13 0.63 µm Visible imagery and surface observations (click to play animation)

GOES-15 viewed this event as well (Visible animation; Visible animation with observations). The dust in the atmosphere was far more apparent in the GOES-13 imagery, however. This case is an excellent demonstration of how dust effectively forward scatters visible light from the setting sun towards GOES-13 at 75º W, but does not so effectively back scatter towards GOES-15 at 135º W. The toggle below shows visible imagery from GOES-13 and GOES-15, both at 2200 UTC.

GOES-13 0.63 µm Visible imagery and GOES-15 0.62 µm Visible Imagery, both at 2200 UTC 10 November (click to enlarge)

GOES-13 0.63 µm Visible imagery and GOES-15 0.62 µm Visible Imagery, both at 2200 UTC 10 November (click to enlarge)

Both Aqua (MODIS) and Suomi NPP (VIIRS) viewed this haboob in mid-afternoon on 10 November. What can the multispectral views of this feature tell us? Both the Visible and Snow/Ice channels give similar views of the leading edge of the cold front (the biggest difference between the visible and snow/ice channel in this image is that water features are so much darker in the snow/ice channel because water strongly absorbs 2.1 µm radiation; differences in the clouds between the visible and the snow/ice (2.1 µm) channel arise from viewing water-based vs. ice-based clouds). The cirrus channel — 1.37 µm — does not see the surface but it does clearly reveal high clouds. The 3.9-µm image — shortwave infrared — shows very warm temperatures right at the leading edge of the cold front in eastern Colorado. This is a region where the dust is effectively reflecting solar radiation. The longwave infrared imagery (10.7 µm) shows a more uniform cold edge to the cloud. Finally, even the water vapor imagery shows a signal from this cold front (known as a lee-side frontal gravity wave). It is unusual for surface features to have a signal in water vapor imagery; when it does occur, the atmosphere is usually very dry, and that’s the case in this event. Note in the toggle here between GOES water vapor channel weighting functions (computed here) at Amarillo between 0000 UTC — before the cold front — and 1200 UTC — after the cold front — shows how the layer from which 6.5 µm radiation will be detected has dropped in altitude.

Aqua MODIS Visible, Snow/Ice, Cirrus, Shortwave IR, Water Vapor and Longwave IR Imagery at 1917 UTC, 10 November (click to enlarge)

Aqua MODIS Visible, Snow/Ice, Cirrus, Shortwave IR, Water Vapor and Longwave IR Imagery at 1917 UTC, 10 November (click to enlarge)

Suomi NPP viewed the cold front 10 minutes before Aqua, below, and also about 90 minutes later (Favorable orbital geometry allowed sequential orbits to view eastern Colorado). The shortwave IR (3.74 µm) show warmer signatures in some of the dust plumes compared to the longwave IR (11.35 µm), similar to Aqua, a difference that is likely due to solar radiation being reflected by the dust.

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 1907 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 1907 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 2049 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 2049 UTC, 10 November (click to enlarge)

Animations of 10.7 µm Brightness Temperature Data from GOES-13 showed the southward plunge of cold air overnight. The progress of this cold front could be monitored from space. Even the water vapor imagery continued to include a signature of the cold front.

GOES-13 Water Vapor (6.7 µm) Infrared Imagery (click to play animation)

GOES-13 Water Vapor (6.7 µm) Infrared Imagery (click to play animation)

The visible imagery at the top of this post ably captured the signature associated with blowing dust. Did the blowing dust continue through the night? Single-channel detection of dust at night is difficult. Historically, dust could be detected with brightness temperature differences between 10.7 µm and 12 µm channels on the GOES Imager, but that capability ended when the 13.3 µm channel replaced the 12 µm channel on the GOES Imager (the GOES-R ABI will contain a 12 µm channel). The VIIRS Day Night Band, below, from Suomi NPP at 0905 UTC on 11 November, does not show a distinct dust signature over south Texas. The leading edge of the front is obvious, however, as it is preceded by a Bore structure with parallel lines of clouds.

Suomi NPP VIIRS Day Night Band (.7 µm) Visible Imagery at 0905 UTC 11 November 2014 (click to enlarge)

Suomi NPP VIIRS Day Night Band (.7 µm) Visible Imagery at 0905 UTC 11 November 2014 (click to enlarge)

Airborne glacial silt from the Copper River Valley in Alaska

October 28th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of airborne glacial silt drifting southward out of the Copper River valley and over the adjacent waters of the Gulf of Alaska on 28 October 2014. The strong winds lofting the silt were very localized to the Copper River valley itself, with cold dense arctic air from further inland (air temperatures were 8 to 10º F at Gulkana, PAGV) accelerating through narrow mountain passes — note how winds at nearby Cordova (PACV) were generally calm during much of the period. As the western edge of the airborne silt reached Middleton Island (PAMD), the surface visibility dropped as low as 5 miles.

AWIPS II images of Suomi NPP VIIRS data provided a better view of the aerial coverage of the glacial silt: a comparison of VIIRS 0.64 µm visible channel and 1.61 µm near-IR “snow/ice channel” images (below) showed that the 1.61 µm image offered better contrast to help locate the edges of the feature. This 1.61 µm channel imagery will be available from the Advanced Baseline Imager (ABI) on GOES-R.

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR “snow/ice channel” images

Two consecutive VIIRS 1.61 µm images (below) revealed the changes in aerosol coverage between 21:43 UTC and 23:22 UTC.

Suomi NPP VIIRS 1.61 µm near-IR

Suomi NPP VIIRS 1.61 µm near-IR “snow/ice channel” images

The more dense portion of the airborne glacial silt particle feature exhibited a slightly warmer (darker gray) appearance on VIIRS 3.74 µm shortwave IR images, due to efficient reflection of incoming solar radiation.

Suomi NPP VIIRS 3.74 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images

A VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth site (below) offered a good view of the coverage of the glacial silt at 21:45 UTC.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

Re-suspended volcanic ash from the Novarupta volcano in Alaska

September 29th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of a plume of re-suspended volcanic ash originating from the region of the Novarupta volcano in Alaska, moving southeastward over the Shelikof Strait toward Kodiak Island on 29 September 2014. The 1912 eruption of Novarupta left a very deep deposit of volcanic ash, which often gets lofted by strong winds in the early Autumn months before snowfall covers the ash (another example occurred on 22 September 2013). Surface winds gusted as high as 30 knots at regional reporting stations, with numerical models estimating terrain-enhanced winds as high as 40-50 knots over the Novarupta ash field.

An AWIPS II image of POES AVHRR 0.86 µm visible channel data (below) showed the ash plume at 22:46 UTC; a pilot report at 22:45 UTC indicated that the top of the ash plume was between 4000 and 6000 feet above ground level.

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

A sequence of 3 Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) indicated that the re-suspended ash plume had been increasing in areal extent during that period.

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

A sequence of 4-panel products from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) shows False-color images, Ash/dust cloud height, Ash/dust particle effective radius, and Ash/dust loading (derived from either Terra/Aqua MODIS or Suomi NPP VIIRS data).

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

Hat tip to Mark Ruminski (NOAA/NESDIS) for alerting us to this event.

The King Fire in California

September 19th, 2014
Suomi NPP VIIRS true-color images

Suomi NPP VIIRS true-color images

The King Fire began burning in central California (between Sacramento and Lake Tahoe) during the evening hours on 13 September 2014. A sequence of daily (12-19 September) Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server site (above) showed that as the prevailing southwesterly wind pattern switched to easterly on 19 September, there was a major change in the transport of smoke from the King Fire. The final image in the series zooms out to show how much of central California had become over-run with thick smoke.

A comparison of AWIPS-II images of Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR image at 09:18 UTC or 2:18 AM local time (below) revealed the bright glow of the large fire complex, along with the large fire “hot spot” signature (black to yellow to red color enhancement).

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

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

Suomi NPP VIIRS 3.74 µm shortwave IR images during the overnight hours (just after 2 AM local time) on 17 and 18 September (below) showed the dramatic northeastward advance of the fire hot spot signature during that 24-hour period. Smoke from the fire was reducing the surface visibility to 3-4 miles as far to the northeast as Lovelock (KLOL) and Fallon (KNFL) in Nevada.

Suomi NPP VIIRS 3.74 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images