Here is an email that APOD received describing it:
My name is Ichi Tanaka, a Support Astrnomer of Subuaru Telescope, Hawaii.
On the early morning of 22 March we, Subaru Telescope observers on
the summit of Mauna Kea, noticed that there is a huge halo of light
above the eastern horizon. It was slowly expanding to
over 45 degrees in 5 minutes or more.
The event was captured by the Subaru Catwalk Night Camera and also by
CHFT's NNW webcam. The animated gif movie of the Subaru webcam is
attached. I also contacted Kanoa Withington in CFHT, and they
made a quite nice movie of the event. The link is below.
We have absolutely no idea about the nature of this. It
appears that the event happened not on the Summit area, but
much farther away, according to the comparison of the two videos.
This means that the size of the light halo is quite large.
After some discussion, we decided to send this to APOD, in the hopes
that APOD readers can help us to understand the nature of this event.
It seems to me that this is an excellent case for opportunity "Citizen Science" in that I bet the alert readers of APOD and the Asterisk can indeed figure this out. Please have at it!