Silt at the mouth of the Mississippi River

March 13th, 2018 |

CIMSS Natural True Color Imagery, 1515 – 1830 UTC on 13 March 2018 (Click to animate)

The CIMSS Natural True Color RGB, above, from 13 March 2018, shows the motion of alluvial sediment in the Gulf of Mexico in the outflow from various rivers. Muddy plumes from the Atchafalaya River in central Louisiana, the Mississippi River, and the Mobile River in Alabama are apparent. In particular, there is distinct northward motion during the 3 hours shown in this animation along the northern edge of the Mississippi River Delta.

A similar animation for 9 March 2018 is available here (courtesy Tim Schmit, NOAA and Mat Gunshor, CIMSS). Close monitoring of where the outflow from rivers is mixing with the Gulf of Mexico waters is a capability of GOES-16 Imagery when skies are clear.

Natural True Color is computed from GOES-16 Reflectance imagery using the “Blue” band (0.47 µm), the “Red” band (0.64 µm) and the “Veggie” band (0.86 µm), that latter being used to give information that in True Color Imagery from MODIS or Suomi NPP (for example) is supplied by a true “Green” band (0.55 µm).

The animation below shows True-Color imagery from MODIS for clear days between 30 January and 13 March 2018. The superior resolution of MODIS (on the Terra and Aqua spacecraft) and the presence of a 0.55 µm channel (in addition to 0.47 µm and 0.64 µm) allows for crisper imagery than from GOES-16; however, the ability to animate at small time scales over the Gulf of Mexico is a capability reserved for GOES-16 (and GOES-17, when it becomes operational). Terra and Aqua imagery are not useful if the overpass of the Polar Orbiters coincide with clouds; on days with variable cloud cover, GOES Imagery is more likely to provide useful information.

MODIS True Color Imagery for select dates between 30 January and 13 March 2018 (Click to animate)

Arabian Sea Ship Fire in the VIIRS Day Night Band

March 7th, 2018 |

VIIRS Day Night Band Visible (0.70 µm) Imagery from Suomi NPP (2056 UTC) and NOAA-20 (2146 UTC) on 6 March 2018 (Click to enlarge)

A large Maersk container vessel caught fire in the Indian Ocean on 6 March 2018 (news report 1, news report 2), killing 4 sailors and necessitating the evacuation of the ship (the MAERSK HONAM).

Suomi NPP and NOAA-20 (which trails Suomi NPP by half an orbit) both passed over the ship fire on 6 March. As a singular light source in the middle of the Indian Ocean, the ship fire was evident in the Day Night Band imagery, as shown above, at 10.5º N and 65.8º E). The ship drifted southward in the 50 minutes between VIIRS scans from the two satellites. (Similar signatures were apparent in the 1.61 µm, 2.25 µm and 4.05 µm imagery from VIIRS on the two satellites).

VIIRS Day Night Band Visible (0.70 µm) Imagery from Suomi NPP (2038 UTC) and NOAA-20 (2128 UTC) on 7 March 2018 (Click to enlarge)

One day later, on 7 March, above, Suomi NPP and then NOAA-20 (50 minutes later) again passed over the still-burning ship, then at 10.1º N and 65.6º E. A faint smoke plume is visible in the imagery from NOAA-20.

The zoomed-out image, below, might give you a better idea of how far away from the India and Africa this ship sits.

VIIRS Day Night Band Visible (0.70 µm) Imagery from NOAA-20 (2128 UTC) on 7 March 2018 (Click to enlarge)

(Hat tip to William Straka, CIMSS, for the imagery and also to Steve Miller, CIRA, for alerting us to this event)

Blowing Dust in Kansas

March 6th, 2018 |

GOES-16 Band 1 (“Blue Visible”) 0.47 µm Imagery, 1502 – 2132 UTC on 6 March 2018 along with surface METAR observation plots (Click to animate)

Strong northwesterly winds over the Great Plains to the west of a storm system over the mid-Mississippi River Valley have resulted in Red Flag Warnings over Oklahoma, and High Wind Warning and Dust Storm Warnings — including the closing of I-70 over Kansas. Visible Imagery in the “Blue Band”, above, shows little indication of the blowing dust (Click here for an animation without surface observations); dust is difficult to observe when sun angle are high. The higher-(spatial) resolution “Red Visible” animation, shown below, similarly struggles to identify with clarity where the dust is occurring.

The ‘Blue Band’ does detect plumes of smoke that develop over southern Kansas during this animation, plumes that originate over ‘hot spots’ in the 3.9 µm shortwave infrared imagery (not shown).

GOES-16 Band 2 (“Red Visible”) 0.64 µm Imagery, 1502 – 2132 UTC on 6 March 2018 along with surface METAR observation plots (Click to animate)

Infrared Imagery can be used to detect dust, both during the day and at night. This is because dust selectively absorbs energy. For example, energy at 10.3 µm that is emitted by the surface, and destined to be observed by the satellite, will be absorbed (and re-emitted from a higher, cooler level in the atmosphere) as it passes through the dust layer. Energy with a longer wavelength (12.3 µm), passes through dust mostly unaffected. Thus, a difference field between the two — the so-called Split Window Difference — will show negative values in regions where lofted dust is present in the atmosphere. An animation is shown below. As with imagery in this blog post, the colormap in the AWIPS display was changed to “Grid/Lowrange Enhanced”; dust regions are highlighted in yellow.  Dust is first detected in central Nebraska before it shows up in central and western Kansas. A closer view of the area where Interstate 70 was closed (between Goodland and Colby in northwestern Kansas) can be seen here.

GOES-16 Split Window Difference Field (10.3 µm – 12.3 µm) Imagery, 1502 – 2132 UTC on 6 March 2018 along with surface METAR observation plots (Click to animate)

The Cloud Phase Channel Difference field in AWIPS (Currently 10.3 µm – 8.5 µm, shortly to transition in AWIPS to 11.2 µm – 8.5 µm) can also detect dust (as was shown in this blog post), and that animation is shown below. Blowing Dust in this field is a bright green — and this Difference field (compared to the Split Window Difference) better identifies sources of plumes over western Kansas.

GOES-16 Cloud Phase Brightness Temperature Difference Field (10.3 µm – 8.5 µm) Imagery, 1502 – 2132 UTC on 6 March 2018 (Click to animate)

The Dust RGB, below, combines both the Split Window Differerence (the ‘Red Gun’) and the Cloud Phase Brightness Temperature Difference (the ‘Green Gun’), as well as the Clean Window (10.3 µm, ‘Blue Gun’, not shown). Dust in this RGB is typically bright pink, and its presence is notable over western Kansas.

GOES-16 Dust Red-Green-Blue (RGB) Composite Imagery, 1502 – 2132 UTC on 6 March 2018 (Click to animate)

Closer to sunset, at 2252 UTC on 6 March, the Dust Plume is readily apparent in the Band 1 and Band 2 imagery, shown below in a toggle with infrared channel differences and the Dust RGB.

GOES-16 Band 1 (“Blue Visible”) 0.47 µm Imagery, Band 2 (“Red Visible”) 0.64 µm Imagery, Split Window Difference (10.3 µm – 12.3 µm), Cloud Phase (10.3 µm – 8.5 µm) Brightness Temperature Difference and Dust RGB, all at 2252 UTC on 6 March 2018 (Click to enlarge)

Hat tip to Jeremy Martin, the SOO in the Goodland KS National Weather Service Office, for alerting us to this case!

Transitory Solar Reflectance in GOES-R Series Imagery

March 5th, 2018 |

GOES-16 Visible (0.64 µm) animation, 1637-1732 UTC on 5 March 2018 (Click to enlarge)

Animations of GOES-16 Visible, near-Infrared and shortwave Infrared over North America shortly before the Vernal Equinox, and shortly after the Autumnal Equinox, (that is, when the Sun is overhead in the Southern Hemisphere) show bright spots that propagate quickly from west to east (these features were first noted by Frank Alsheimer of the National Weather Service). The animation above shows the visible imagery (0.64 µm) over the Continental United States on 5 March 2018 (Click here for a slower animation speed). Brightening over regions between 30 and 40 N between 1637 UTC and 1732 UTC is apparent. The animation below of the shortwave infrared (3.9 µm) shows slight warming (Click here for a slower animation), as might be expected with reflected solar energy. The brightening is also apparent in the Band 4 “Cirrus”  (1.37 µm) — in fact, a closer look at southern Colorado reveals the bright signature of sunlight reflecting off solar panels at the Alamosa Solar Generating Facility (Google maps).

GOES-16 Shortwave Infrared (3.9 µm) animation, 1637-1732 UTC on 5 March 2018 (Click to enlarge)

The increased reflectance can cause the ABI Clear Sky Mask to mis-characterize clear regions as cloudy (See the animation below; click here for a slower animation). Thus, Cloud properties (Cloud-top Height, Temperature, Pressure, etc.) can be identified in clear regions.

GOES-16 Clear Sky Mask (White: Clouds ; Black : No Clouds) from 1637 UTC – 1732 UTC on 5 March 2018 (Click to enlarge)

The bright spots in the visible, and warms spots in the shortwave infrared, occur when the Earth’s surface, the GOES Satellite and the Sun are aligned on one line. If you were within the bright spot with a powerful telescope trained on the Sun, you would see the GOES Satellite transecting the solar disk. The location of these bright spots changes with season: they appear in the Northern Hemisphere shortly before the (Northern Hemisphere) vernal equinox and shortly after the (Northern Hemisphere) autumnal equinox. Similarly, they appear in the Southern Hemisphere shortly before the (Southern Hemisphere) vernal equinox and shortly after the (Southern Hemisphere) autumnal equinox. On the Equinox, the bright spots are centered on the Equator.

This animation (courtesy Daniel Lindsey, NOAA/CIRA and Steve Miller, CIRA) shows where the reflection disk moves during the days around the Northern Hemisphere Autumnal Equinox; a similar animation for the Northern Hemisphere vernal equinox would show a disk starting at the North Pole and moving southward with time.

The animation below (from this link that is used for calibration exercises), shows the difference in reflectance (Bands 1-6) or Brightness Temperature (Bands 7-16) between 1657 and 1652 UTC on 3 and 5 March 2018. Two things are apparent: The centroid of the largest difference in solar reflectance has moved southward in those two days, as expected; the effect of this solar backscatter is most obvious in the visible, near-infrared and shortwave infrared channels (that is, bands 1-7 on the ABI).  The effect is most pronounced in clear skies.

Time Difference in each of the 16 ABI Channels (1657 – 1652 UTC) on 3 and on 5 March 2018 (Click to enlarge)

This reflectance feature is also detectable in legacy GOES Imagery. However, the great improvements in detection and calibration in the GOES-R Series ABI (and AHI on Himawari-8 and Himawari-9) and the better temporal resolution with the GOES-R Series allows for better visualization of the effect.

The feature also shows up in “True Color” Imagery, shown below (from this site). Geocolor imagery (shown here), from CIRA, also shows the brightening.

CIMSS Natural True Color Animation ending 1757 UTC on 5 March 2018 (Click to enlarge)

Thanks to Daniel Lindsey and Tim Schmit, NOAA/ASPB, Steve Miller, CIRA and Mat Gunshor, CIMSS, for contributions to this blog post.