Large hail in Argentina

February 8th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm, top) and “Clean” Infrared Window (10.3 µm, bottom) images, with hourly surface reports (metric units) for Córdoba, Argentina [click to play animated GIF — MP4 also available]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed the development of severe thunderstorms which produced very large hail in Córdoba, Argentina on 08 February 2018. Distinct above-anvil plumes were evident on the Visible imagery, with pulses of overshooting tops exhibiting Infrared brightness temperatures in the -70 to -80ºC range (black to white enhancement). The hail reportedly began around 1930 UTC or 4:30 PM local time.

The above-anvil plumes could also be seen in GOES-16 Near-Infrared “Snow/Ice” (1.61 µm) images (below).

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm) images, with hourly surface reports (metric units) for Córdoba, Argentina [click to play animated GIF — MP4 also available]

An Aqua MODIS True-color Red-Green-Blue (RGB) image viewed using RealEarth (below) showed the thunderstorm just west of Córdoba around 1850 UTC.

Aqua MODIS True-color RGB image [click to enlarge]

Aqua MODIS True-color RGB image [click to enlarge]

According to the Worldview site, the coldest Aqua MODIS cloud-top infrared brightness temperature at that time was -78ºC (below).

Aqua MODIS True-color and Infrared Window (11.0 µm) images [click to enlarge]

Aqua MODIS True-color and Infrared Window (11.0 µm) images [click to enlarge]

A time series plot of surface observations at Córdoba (below) showed the warm temperatures and high dew points prior to the arrival of the thunderstorms; there were a number of hail reports between 19 UTC and 02 UTC (4 PM to 11 PM local time).

Time series of surface observations at Córdoba, Argentina [click to enlarge]

Time series of surface observations at Córdoba, Argentina [click to enlarge]

Cloud glaciation caused by perturbations

February 8th, 2018 |

GOES-16 ABI Band 2 (0.64 µm) Visible Imagery, 1222 – 1712 UTC on 8 February 2018 (Click to animate)

The animation above shows visible imagery from GOES-16 (0.64 µm) over Pennsylvania on 8 February 2018.  Northwest flow over the ridges of the Appalachians is causing stable waves clouds that are parallel to the topography.  However, the animation shows point sources over Somerset and Cambria counties — in southwestern Pennsylvania — that are changing the character of the clouds and disrupting the linear cloud features.  The animation of the GOES-16 ABI 1.61 µm “Snow/Ice” channel, below, shows that the point sources are causing glaciation in the clouds.  Glaciated clouds contain ice, and ice strongly absorbs energy at 1.61 µm, so glaciated clouds appear dark.  The point sources, likely smokestacks, are perturbing the flow and likely introducing freezing nuclei into the supercooled clouds.  As a result, supercooled cloud liquid water droplets freeze.  The toggle between visible 0.64 µm and near-infrared 1.61 µm at 1312 UTC and at 1402 UTC suggests that different smokestacks are operating at different times of the day.  Note that later in the animations, mid-level clouds move in that obscure the view of the lowest clouds.

In addition to glaciated clouds, snow on the ground appears dark as well.  Snow on the ground in the Susquehanna River Valley, is very bright in the 0.64 µm imagery, and darker in the 1.61 µm.  The darkest regions over south central Pennsylvania and northern Maryland are likely regions where snowfall was followed by freezing rain:  the layer of ice on top of the snow will absorb 1.61 µm energy more readily than the snow itself.  This chart from the National Weather Service Eastern Region shows ice accumulations less than 0.10″ in that region.

GOES-16 ABI 1.61 µm Near-Infrared Imagery, 1222 – 1712 UTC on 8 February 2018 (Click to animate)

There is a GOES-16 Baseline Product that determines cloud-top phase.  The toggle below, showing imagery 1412 UTC on 8 February, suggests a change from supercooled (bright green) to mixed phase (dark green) to ice (red) in the region.  The 2-km native resolution of the Cloud Phase product (ATBD can be read here) vs. 1-km for 1.61 µm (and 0.5-km for 0.64 µm ) might account for some of the differences between what the 1.61 µm channel suggests over southwestern Pennsylvania and what the Cloud Phase product diagnoses.  (In addition, the GOES-16 Baseline Cloud Phase product has not yet reached Provisional Maturity Status).

GOES-16 Baseline Cloud Phase Product and GOES-16 Snow/Ice 1.61 µm Near-Infrared Imagery, 1412 UTC on 8 February 2018. (Click to enlarge)

So, glaciation of clouds can be induced as shown above by turbulence/freezing nuclei introduced by large smokestacks. The 1-minute animations below shows a region of supercooled clouds from 1515 UTC to 1715 UTC. Note the periodic appearance of hole-punch clouds. In this case, aircraft to/from Chicago O’Hare are likely penetrating the thin supercooled cloud layer, and the passage of the planes is causing glaciation. The clouds within the hole punch cloud are glaciated, and therefore dark in the 1.61 µm imagery: energy at that wavelength is absorbed, not reflected as happens in the visible wavelengths.

Ice in Lake Michigan is visible in the 0.64 µm, but not apparent in the 1.61 µm. Lake Ice and water both absorb 1.61 µm energy. Lake ice reflects 0.64 µm energy.

GOES-16 ABI Visible (0.64 µm) Imagery, 1515-1715 UTC on 8 February 2018 (Click to animate)

GOES-16 ABI Near-Infrared “Snow/Ice” (1.61 µm) Imagery, 1515-1715 UTC on 8 February 2018 (Click to animate)

Satellite signatures of SpaceX Falcon Heavy rocket launch

February 6th, 2018 |

GOES-16 "Red" Visible <em>(0.64 µm, top),</em> Near-Infrared "Snow/Ice" <em>(1.61 µm, middle)</em> and Shortwave Infrared <em>(3.9 µm, bottom)</em> images, with plots of surface reports [click to play animation]

GOES-16 “Red” Visible (0.64 µm, top), “Blue” Visible (0.47 µm, middle) and Near-Infrared “Snow/Ice” (1.61 µm, bottom) images, with plots of surface reports [click to play animation]

GOES-16 (GOES-East) “Red” Visible (0.64 µm), “Blue” Visible (0.47 µm) and Near-Infrared “Snow/Ice” (1.61 um) images (above) captured the signature of rocket plumes from the SpaceX Falcon Heavy launch at Kennedy Space Center, Florida on 06 February 2018. Bright areas of water droplet clouds were seen both at the surface near Launch Complex 39A and aloft just east of the Florida coast on the 20:47:28 UTC and 20:52:28 UTC images (the satellite was scanning those cloud features at 20:48:33 / 20:55:33 UTC or 3:48:33 / 3:55:33 PM Eastern Standard Time, respectively). The plume aloft looked like this from the surface. Due to significant lower-tropospheric wind shear, the near-surface launch pad plume drifted slowly toward the northwest, while the higher-altitude plume moved more quickly toward the northeast. Strong upper-tropospheric winds — 86 knots at 140 hPa or 14.4 km on the 12 UTC sounding — led to a 2 hour launch delay until speeds dropped to within safe flight criteria.

Looking farther to the east-northeast over the Atlantic Ocean, a pair of warm thermal anomalies — likely from the recently-separated twin Side Core booster engines (left) and the still-active single Center Core booster engine (right) — were seen on the corresponding 20:47:28 UTC GOES-16 Upper-level (6.2 µm), Mid-level (6.9 µm) and Low-level (7.3 µm) Water Vapor images (below). A similar warm signature in Water Vapor imagery was observed following a previous SpaceX rocket launch in March 2017.

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, middle) and Low-level (7.3 µm) images [click to play animation]

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, middle) and Low-level (7.3 µm, bottom) images [click to play animation]

While Shortwave Infrared (3.9 µm) imagery is useful for detection of thermal anomalies associated with wildfires or volcanic eruptions, in this case the warm signature (darker gray) was much less distinct compared to what was seen on the water vapor imagery (below).

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, middle) and Shortwave Infrared (3.9 µm, bottom) image [click to enlarge]

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, middle) and Shortwave Infrared (3.9 µm, bottom) image [click to enlarge]

Sensing the surface with water vapor imagery

February 6th, 2018 |

GOES-16 Low-level (7.3 µm) Water Vapor images [click to play animation]

GOES-16 Low-level (7.3 µm) Water Vapor images [click to play animation]

As a cold, dry arctic air mass moved across the western Great Lakes on 06 February 2018, portions of the land-water boundaries of Lake Superior, Lake Michigan and Lake Huron were very distinct on GOES-16 (GOES-East) Low-level (7.3 µm) Water Vapor images (above). The motion of low-altitude lake effect clouds were also apparent in the imagery.

Plots of weighting functions for the three GOES-16 ABI Water Vapor bands (7.3 µm, 6.9 µm and 6.2 µm) are shown below, calculated using rawinsonde data from Green Bay, Wisconsin and Gaylord, Michigan. With cold air and low values of Total Precipitable Water at these 2 sites (1.53 mm / 0.06 in and 1.88 mm / 0.07 in, respectively), the height of their weighting functions was shifted to significantly lower altitudes compared to what would be observed in a standard atmosphere. This enabled the contrasting thermal signature of the land/water boundaries to easily reach the satellite sensors, passing through what little moisture existed within the atmospheric column. While the peak of the violet 7.3 µm weighting function plots descended to the 879 hPa pressure level at both sites (which was approximately 1.2 km above the surface), a significant contribution could be seen originating from the surface itself.

Weighting function plots for the three GOES-16 Water Vapor bands, calculated using rawinsonde data from Green Bay, Wisconsin [click to enlarge]

Weighting function plots for the three GOES-16 Water Vapor bands, calculated using rawinsonde data from Green Bay, Wisconsin [click to enlarge]

Weighting function plots for the three GOES-16 Water Vapor bands, calculated using rawinsonde data from Gaylord, Michigan [click to enlarge]

Weighting function plots for the three GOES-16 Water Vapor bands, calculated using rawinsonde data from Gaylord, Michigan [click to enlarge]

Note that the peaks of the blue 6.9 µm weighting function plots were also anomalously low, reaching the 802 and 754 hPa pressure levels — however, in contrast to the 7.3 µm plots there was very little contribution from the actual surface, and the presence of secondary peaks at higher altitudes led to some absorption and subsequent re-emission of upwelling radiation by that layer of colder moisture aloft. As a result, only the faint outline of Lake Superior and its lake effect clouds were occasionally seen on Mid-level 6.9 µm Water Vapor imagery (below).

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]