Red auroras descend to Florida, marking first sighting since 2003 and 1989
A G4 – Severe geomagnetic storm on March 24, 2023, caused red auroras to appear over Florida and other low-latitude areas, marking the first such sighting in nearly 20 years. Numerous unusual phenomena were observed during this geomagnetic storm, including “aurora dunes” over Alberta, Canada.
On March 24, a G4 – Severe geomagnetic storm, the most intense in nearly six years, caused red auroras to descend as far south as Florida for the first time in almost two decades.
Bill Williams captured their stunning red glow on camera from the Chiefland Astro Village, overlooking the Suwannee River Basin and the Gulf of Mexico. Williams revealed that a 26-minute exposure intended for capturing the Winter Milky Way instead displayed an unusual red glow on the horizon.
According to Williams, the auroras at 29.4 degrees north latitude marked the farthest south they had been observed and were the first sightings in Florida since 2003 and 1989.
While most auroras are green, low-latitude sightings like those in Florida are predominantly red. The reason for this lies in the altitude of the oxygen atoms causing the auroras. Green auroras are generated by oxygen atoms approximately 150 km (93 miles) above Earth’s surface, whereas red auroras result from oxygen atoms between 150 km (93 miles) and 500 km (310 miles) above the surface.
A photo taken by Dean Cosgrove of Curtis, Nebraska (+40.6N), on the same night illustrates the altitude structure with red-on-green layers. From southern locations like Florida, the green auroras are obscured by the northern horizon, leaving the higher red auroras to dominate the display.
Other notable low-latitude red aurora sightings during the geomagnetic storm last week include New Mexico (+32.8N), North Carolina (+36.5N), Colorado (+40.4N), and California (+39.7N).
Numerous unusual phenomena were observed during this geomagnetic storm, including “aurora dunes” captured in a deep twilight photo by Alan Dyer of Gleichen, Alberta, at the onset of the storm.
The aurora dunes, horizontal green ripples to the left of Venus and the Moon, are a recently identified form of Northern Lights resembling ripples in desert sand.
Researchers first described the dunes in a paper published in 2020, identifying them as a “mesospheric bore” — a type of atmospheric gravity wave originating from Earth’s surface and becoming trapped in a thermal waveguide about 100 km (62 miles) high. When solar wind particles rain down on the bore, they illuminate its rippling structure.
For years, Arctic skywatchers have observed dunes without knowing their true nature. A breakthrough happened on October 7, 2018, when several groups took photos of dunes from distant locations in Finland. Triangulation showed the dunes to be approximately 100 km (62 miles) high with a pure, monochromatic wavelength of about 45 km (28 miles).
1 Red auroras over Florida (and elsewhere) – SpaceWeather – March 27, 2023
2 Aurora dunes seen during extreme storm – SpaceWeather – March 27, 2023
3 Citizen Scientists Discover a New Auroral Form: Dunes Provide Insight Into the Upper Atmosphere – AGU Advances – January 28, 2020 – https://doi.org/10.1029/2019AV000133 – OPEN ACCESS
Featured image credit: Bill Williams (via SpaceWeather)
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