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 |
| 9 | 300-400 | EXTREMELY SEVERE | Blackout | Extreme |
Kp – Planetary K-index, averaged over past 3 hours and tends to be a measure of current conditions
Ap – Planetary A-index, 24-hour average and represents overall geomagnetic field conditions for the UTC day
HF Noise – Approximate “S-meter” noise level <10 MHz
Aurora- Approximate level of auroral activity
* High conditions usually extends to: Latitude 45 deg.
* Very High conditions extends to about: Latitude 35 deg.
* Extreme conditions can extend to below: Latitude 35 deg.
Solar Wind-averages 350-450 km/sec and density <10 p/cm^3 >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.
Solar Flare Classifications
| FLARE CLASS | TYPE OF FLARE | HF RADIO EFFECTS | RESULTING GEOMAGNETIC STORM |
| A | Very Small | None | None |
| B | Small | None | None |
| C | Moderate | *Low Absorption | *Active to Minor |
| M | Large | *High Absorption | *Minor to Major |
| X | Extreme | *Possible Blackout | *Major to Severe |
(*) – Conditions cited if Earth is in trajectory of flare emissions
Flare class 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, causing total dispruption to communications, huge aurora’s, 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.
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 sun spots | C class flares and possible large M class |
| Delta | Strong, compact bipolar fields between spots | High potential for a M of X class major flare. Major Flare Alert issued |
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From an e-mail posting by Paul Harden, NA5N, to the Low Power Amateur Radio Discussion E-mail List 06 January 1999
© 1999 by Paul Harden, National Radio Astronomy Observatory, Socorro, New Mexico
“Above information may be freely used in other newsgroups, ham radio reflectors, non-profit journals, etc., without permission, providing credit is cited.”