Here you can find a laymans guide to the various geomagnetic conditions which affect radio propagation.
This article was originally written by Paul Harden, NA5N.
Solar wind with averages of 350-450 km/sec and density <10 p/cm^3 >500 km/sec or high density can trigger geomagnetic activity.
Shock waves from a solar flare or Coronal Mass Ejection (CME) arrives at the Earth about 55 hours after the solar event.
The table below outlines the various conditions that may be experienced.
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.
Geomagnetic Indices and Conditions
|Kp Index||Ap Index||GEOMAGNETIC FIELD CONDITIONS||HF NOISE||AURORA|
|6||67-94||MAJOR Storm||S6-S9||Very High|
|7||111-154||SEVERE Storm||S9+||Very High|
Solar Flare Classifications
|FLARE CLASS||TYPE OF FLARE||HF RADIO EFFECTS||RESULTING GEOMAGNETIC STORM|
|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.
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|
Extract trom 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.
The above information may be freely used in other newsgroups, ham radio reflectors, non-profit journals, etc., without permission, providing credit is cited.