Technical

Geomagnetic Indices and Conditions

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 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 Geomagnetic Indices and Conditions

Kp IndexAp IndexGEOMAGNETIC FIELD CONDITIONSHF NOISEAURORA
00-2Very QuietS1-S2None
13-5QuietS1-S2Very Low
26-9QuietS1-S2Very Low
312-18UnsettledS2-S3Low
422-32ActiveS3-S4Moderate
539-56MINOR StormS4-S6High
667-94MAJOR StormS6-S9Very High
7111-154SEVERE StormS9+Very High
8179-236SEVERE StormBlackoutExtreme
9300-400EXTREMELY SEVEREBlackoutExtreme

Solar Flare Classifications

FLARE CLASSTYPE OF FLAREHF RADIO EFFECTSRESULTING GEOMAGNETIC STORM
AVery SmallNoneNone
BSmallNoneNone
CModerate*Low Absorption*Active to Minor
MLarge*High Absorption*Minor to Major
XExtreme*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 CLASSDESCRIPTION OF THE ACTIVE REGIONPOTENTIAL FOR FLARE ACTIVITY
AlphaUnorganized, unipolar magnetic fieldsLittle threat but watched for growth
BetaBipolar magnetic fields between sun spotsC class flares and possible large M class
DeltaStrong, compact bipolar fields between spotsHigh 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.

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