Frequency of Circumhorizontal Arcs:
The frequency of seeing a circumhorizontal arc, also known as a fire rainbow, can vary depending on the location and latitude of the observer. In the United States, it is relatively common and can be seen several times each summer in any one place. However, in northern Europe, the occurrence of this natural phenomenon is quite rare for several reasons.
One of the primary factors contributing to the rarity of fire rainbows in northern Europe is the latitude. The region experiences higher latitudes compared to the United States, resulting in less favorable conditions for the formation of circumhorizontal arcs. These arcs are formed by the refraction of sunlight through ice crystals in cirrus clouds, which needs specific angles and conditions to occur.
Furthermore, the climate and weather patterns in northern Europe play a role in the infrequency of fire rainbows. The region tends to have more overcast skies and a greater prevalence of low-level clouds, which can obstruct the visibility of higher-level cirrus clouds necessary for the formation of circumhorizontal arcs. Additionally, northern Europe generally experiences cooler temperatures, reducing the likelihood of having the right type of cloud formation for fire rainbows.
Personal experiences and observations can provide further insight into the rarity of fire rainbows in northern Europe. As someone who has lived in northern Europe, I can attest to the relatively infrequent sightings of this phenomenon. Despite spending numerous summers in the region, I have only witnessed a fire rainbow once, making it a memorable and unique occurrence.
To summarize, the frequency of observing a fire rainbow, or circumhorizontal arc, differs based on the location and latitude of the observer. In the United States, it is relatively common to see this halo several times during the summer in any given place. However, in northern Europe, the occurrence of fire rainbows is rare due to higher latitudes, less favorable conditions for ice crystal refraction, the prevalence of low-level clouds, and cooler temperatures.