A-index og K-index

A Index and K Index

The Earth's magnetic field is continuously monitored by a network of magnetometers. These readings are converted into the A and K index values.

The K index is computed once every three hours (eight times a day) and the values can range from 0 to 9, with 0 being inactive, and 9 representing an extreme severe storm condition. The values are quadi-logarithmic.

• K = 0 Inactive
• K = 1 Very quiet
• K = 2 Quiet
• K = 3 Unsettled
• K = 4 Active
• K = 5 Minor storm
• K = 6 Major storm
• K = 7 Severe storm
• K = 8 Very severe storm
• K = 9 Extremely severe storm

The A index is linear, and is computed from the eight previous K index values. It ranges from 0 (quiet) to 400 (severe storm).

• A = 0 - 7 Quiet
• A = 8 - 15 Unsettled
• A = 16 - 29 Active
• A = 30 - 49 Minor storm
• A = 50 - 99 Major storm
• A = 100 - 400 Severe storm

Generally, propagation conditions are best when the A index is 15 or lower, and the K index is 3 or lower.