The HandyMan's Guide to Solar/Geomagnetic Conditions
by Paul Harden, NA5N

Geomagnetic Indices and Conditions

Kp Index Ap Index Geomagnetic Field Conditions HF Noise Aurora
0 0 - 2 Very Quiet S1 - S2 None
1 3 - 5 Quiet S1 - S2 Very Low
2 6 - 9 Quiet S1 - S2 Very Low
3 12 - 18 Unsettled S2 - S3 Low
4 22 - 32 Active S3 - S4 Moderate
5 39 - 56 Minor Storm S4 - S6 High
6 67 - 94 Major Storm S6 - S9 Very High
7 111 - 154 SEVERE Storm S9+ Very High
8 179 - 236 SEVERE Storm BLACKOUT Extreme

Kp Index Planetary K-Index, averaged over the past three hours and tends to be a measure of current conditions.
Ap Index Planetary A-Index, 24-hour average and represents overall geomegnetic field conditions for the UTC day.
HF Noise Approximate "S-Meter" noise level below 10Mhz.
Aurora Approximate level of auroral activity.
"High" conditions usually extends to Latitude 45 degrees
"Very High" conditions usually extends to about Letitude 35 degrees

SOLAR WIND averages 350-450 km/sec and density less than 10 p/cm^3 greater than 500 km/sec or high density can trigger geomagnetic activity.
SHOCK WAVE from a solar flare or Coronal Mass Ejection (CME) arrives at the Earth about 55 hours after the solar event.


Flare Class Type of Flare HF Radio Effects Resulting Geomagnetic Storm
A Very Small None None
B Small None None
C Moderate * Low Absorptons * Active to Minor
M Large * High absorption * Minor to Major
X Extreme * Possible Blackout * Major to Severe

* Conditions cited if Earth is in the trajectory of the flare emissions.
Flare class is further rated from 1-9, ex. M1, M2, M3...M9
The larger the number the larger the flare within that class. An X7-X9 is considered a "Grand Daddy" flare. Only a few have occured over the past 30 years and cause total disruptions to communications, huge auroras, power grid failures, etc. Radio and X-Ray emissions from a flare effect the Earth for the duration of the solar event, usually 30 minutes or less. The Earth is 8 light-minutes from the Sun.

Sunspot/Active Region Classifications
Sunspot Class Description of the Active Region Potential for Flare Activity
Alpha Unorganized, unipolar magnetic fields Little threat, but watched for growth.
Beta Bipolar magnetic fields between sunspots C class flares and posssible large M class.
Delta Strong, compact bipolar fields between spots High potential for M or X class major flare, Major Flare Alert issued.

This was contributed by Paul Harden, NA5N
National Radio Astronomy Observatory
VLA/VLBA Radio Telescopes
Socorro, New Mexico
Email Paul at