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 <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
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

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.


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.

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