Sahara Aureole/Bishops Ring
Imaged by Mónika Landy-Gyebnár
The weather had been hot and dry with a warm air mass carried north from the Sahara. This was accompanied by fine desert dust. The lower troposphere was then cleansed by the arrival of a cold front and thunderstorms. The washed out dust was evident on cars and windows.
However, next day brought an the unusual sunrise at left followed by a milky sky rather than the intense blue expected after heavy rain. The presence of remaining dust was confirmed by this large aureole or Bishops Ring around the sun.
Somehow, fine Sahara dust had remained in the upper troposphere or had been transported across the tropopause to a greater height by the thunder cells.
Sunlight diffracted around the periphery of the dust particles has created the enlarged soft aureole - a Bishops Ring. These are usually associated with stratospheric volcanic dust and aerosol but they can be produced by lower level particulates.
Absent Aureole - Clean Air