Alaskan Aurora

Early this morning, 5 November 2018, an aurora was visible over the state of Alaska. The aurora was large in areal extent and produced green hues over the Anchorage, AK night sky. A photo of the aurora can be seen, via the following link. Polar-orbiting satellite products observed the phenomenon; imagery is seen before (4 November 2018) and during the event (5 November 2018). Images courtesy of CIRA POLAR Slider.

VIIRS GeoColor @ 2327 UTC, 4 November 2018 (Before the Event)

GeoColor imagery combines 5 spectral channels, where three channels; the aerosol (~0.47um), visible (~0.64um) and vegetation (~0.87um) channels are used during the daytime to contrast between the ocean (i.e. blue, aqua colors), land (i.e. brown colors), overlying cloud cover (i.e. white smooth, thin, or clumpy textures) and snow (i.e. white colors resembling dendritic formations, especially over high, complex terrain).

Day/Night Band (DNB) @ 1349 UTC, 5 November 2018 (During the Event)

DNB product utilizes a sun/moon reflectance model that illuminates atmospheric features and in this case, senses emitted (i.e. auroras, city lights) and reflected light sources (i.e. clouds, snow) during the nighttime. Spatial resolution is at 750-meters and DNB imagery is taken during the new moon phase of the lunar cycle (i.e. moon below the horizon, no available moonlight). In this particular moon phase, without available moonlight, atmospheric features in the imagery are sensed via satellite from ‘atmospheric nightglow‘.

In this particular case, in the DNB imagery, the aurora produces an elongated, horizontal, white streak that dominates the scene. However, if one looks closely, the aurora was so bright (i.e. appearing to assist the atmospheric nightglow phenomenon in sensing features), it reflected light off the snowy surface, that the satellite sensed. Hint for readers: over Alaska, look to the north and to the south of the aurora, to find areas of snow. Ambient cloud cover is also noticed in the imagery.

Day/Night Band (DNB) @ 1349 UTC, 5 November 2018 – ‘Zoomed In’ (During the Event)

If the snow is not visually apparent to readers in the last image, refer to the following ‘zoomed in’ DNB imagery; where the domain is just south of the aurora. ‘Zoomed in’ DNB imagery highlights snow via dendritic formations (also seen in the VIIRS GeoColor, above) along the Alaskan coast. Notice, the emitted city lights from Kenai, AK and Nikiski, AK as well.

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