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Just what do the Sunspot and Geomagnetic and Solar Indices numbers mean?

While increasing SFI may be good for HF propagation, it also tends to correspond with high Ap and K indices, which cause D-Layer absorption and noisy band condition. Solar flux is measured in solar flux units (SFUs). It is the amount of radio noise or flux emitted at a frequency of 2800 MHz (10.7 cm, hence is it also called the 10.7 cm flux index).

While increasing SFI may be good for HF propagation, it also tends to correspond with high Ap and K indices, which cause D-Layer absorption and noisy band condition. Solar flux is measured in solar flux units (SFUs). It is the amount of radio noise or flux emitted at a frequency of 2800 MHz (10.7 cm, hence is it also called the 10.7 cm flux index).

Just what is the Planetary A index?
It is a measure of how disturbed the Earth's magnetic field is. It varies in
value from 0 to about 400, in linear steps. It is computed from the actual
deviations (non-quiet-time deviations) measured at a number of geomagnetic
observatories (mostly mid-latitude ones) around the world. A value of 30
represents minor storm conditions. Values of 50 represent major storm
conditions and values greater than 100 represent severe storm conditions. It
is derived from the planetary K indices (Kp). The A index is a planetary
daily value, while the Kp index is a planetary measurement derived every 3
hours. The Kp index is a semi-logarithmic index that varies from 0 to 9,
where a 5 represents minor storm conditions, a 6 represents major storm
conditions, and a value of 7 or greater represents severe storm conditions.

The K-index is a code that is related to the maximum fluctuations of horizontal components observed on a magnetometer relative to a quiet day, during a three-hour interval. The conversion table from maximum fluctuation (nT) to K-index, varies from observatory to observatory in such a way that the historical rate of occurrence of certain levels of K are about the same at all observatories. In practice this means that observatories at higher geomagnetic latitude require higher levels of fluctuation for a given K-index. The maximum positive and negative deviations during the 3-hour period are added together to determine the total maximum fluctuation. These maximum deviations may occur anytime during the 3-hour period.

The higher the K-index, the more unstable propagation becomes, the effect is stronger at high latitudes, but weaker near low latitudes.
When storm level is reached, propagation strongly degrades, possibly fade out at high latitudes.
Classification of K-indices are as follows:

K1=Very quiet
K5=Minor storm
K6=Major storm
K7=Severe storm
K8=Very severe storm
K9=Extremely severe storm

As with the K-index, the higher the A-index, the more unstable propagation becomes.
Classification of A-indices are as follows:

A0 - A7 = quiet
A8 - A15 = unsettled
A16 - A29 = active
A30 - A49 = minor storm
A50 - A99 = major storm
A100 - A400 = severe storm

The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in space weather and to some degree weather and climate on Earth. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun. Powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows, the solar cycle:

For the current Auroral Activity click the links below:, and

Weak Solar Activity Puzzles Scientists:

The above link is from Voice of America
To read more please click the link above.

At almost regular intervals, our sun displays phenomena benignly called sunspots.  Actually, they are violent storms.  

Space scientists closely observe this activity, because it may have adverse effects on communications, navigation and even power grids.  But the diminishing intensity of the last two solar cycles leaves them puzzled.

When gigantic electromagnetic storms occur on the sun, we see them eight minutes later, which is how long it takes the light to reach Earth.

It takes the first charged particles ejected by the storms 20 to 30 minutes to arrive. They are dangerous to humans, so if the storm is intense, astronauts aboard the International Space Station are advised to move into specially protected areas.

After a day or two comes the biggest part of the storm, the coronal mass ejection.

“That is billions of tons of solar material that’s blown away from the sun," said Alex Young of NASA's Heliophysics Science Division. "It’s traveling millions of kilometers an hour, but that is relatively slow.”

What are radio blackouts?

Radio blackouts are caused by bursts of X-ray and Extreme Ultra Violet radiation which are emitted during solar flares and affect the sunlit side of the Earth. Radio blackouts primarily affect High Frequency (HF) (3-30 MHz) communication, although fading and diminished reception may spill over to Very High Frequency (VHF) (30-300 MHz) and higher frequencies. These effects occur on the sunlit side of the Earth and are most intense at locations where the Sun is directly overhead. These blackouts are a consequence of enhanced electron densities caused by solar flare emissions. These emissions ionize the sunlit side of Earth, which increases the amount of energy lost as radio waves pass through the upper atmosphere. Radio blackouts are the most common space weather events to affect Earth. Minor events occur about 2000 times each solar cycle. Radio blackouts are by far the fastest space weather event to impact our planet. The electromagnetic emission produced during flares travels at the speed of light taking just over 8 minutes to travel from the Sun to Earth. Radio blackouts can last from several minutes to several hours depending on the duration of the solar flare. How severe a radio blackout is depends on the strength of the solar flare.

Highest Affected Frequency (HAF) during a solar flare

The Highest Affected Frequency (HAF) during an X-ray radio blackout during local noon is based on the current X-ray flux value between the 1-8 Ångström. The Highest Affected Frequency (HAF) can be derived by a formula. Below you will find a table where you can see what the Highest Affected Frequency (HAF) is during a specific X-ray flux.


GOES X-ray class & flux

Highest Affected Frequency

M1.0 (10-5)

15 MHz

M5.0 (5×10-5)

20 MHz

X1.0 (10-4)

25 MHz

X5.0 (5×10-4)

30 MHz



NOAA uses a five-level system called the R-scale, to indicate the severity of a X-ray related radio blackout. This scale ranges from R1 for a minor radio blackout event to R5 for a extreme radio blackout event, with R1 being the lowest level and R5 being the highest level. Every R-level has a certain X-ray brightness associated with it. This ranges from R1 for a X-ray flux of M1 to R5 for a X-ray flux of X20. On Twitter we provide alerts as soon as a certain radio blackout threshold has been reached. Because each blackout level represents a certain GOES X-ray brightness, you can associate these alerts directly with a solar flare that is occurring at that moment. We can define the following radio blackout classes:



GOES X-ray threshold by class & flux

Average frequency



M1 (10-5)

2000 per cycle (950 days per cycle)



M5 (5×10-5)

350 per cycle (300 days per cycle)



X1 (10-4)

175 per cycle (140 days per cycle)



X10 (10-3)

8 per cycle (8 days per cycle)



X20 (2×10-3)

Less than 1 per cycle


The image below shows the effects of an X1 (R3-strong) solar flare on the sunlit side of the Earth. We can see that the Highest Affected Frequency (HAF) is about 25 MHz there where the Sun is directly overhead. Radio frequencies lower than the HAF suffer an even greater loss. Image: NOAA SWPC - D Region Absorption Product.


Polar Cap Absorption Events

Radio blackouts also occur at Arctic latitudes during space radiation storms. These are known as Polar Cap Absorption Events and can last for days. These events are indicated by the S-scale which is used for space radiation storms. Polar Cap Absorption Events are not to be confused with radio blackouts that are caused by bursts of X-ray and Extreme Ultra Violet radiation which are emitted during solar flares. Polar Cap Absorption Events are caused by protons that enter Earth's atmosphere above the polar regions during space radiation storms.

Frequently Asked Questions about Aurora and Answers


Member Information

We wish to thank all of you that have made donations and contributions to Barc.


KD7TSN Brian and KF7DGW Patti

NQ7L James

KF7SW Rob,  


KE7EYN, Lee (KE7GGP Austin,  KE7INP Aubrey, and KE7HEK Jackie)


KF7SN Geary


KF7RK Bob (Equipment Contribution)

KD7CCK Rick (Equipment Contribution)





How Can You Join?

To join Barc all we need you to do is send us a letter or an email asking to join our club. And when you do send us a letter you may also send us a donation. 
Suggest gift: $25.00
Your membership goes to solely to support the 147.000Mhz. repeater. 



Mail your comments or donations to: 

BARC P.O. Box 236, Joliet, Mt. 59041-0236

Our Email: or Mel


The Pig and the Ham in Ham Radio!

The Moble Ham Radio Operator.



Legal disclaimer:

Note: The information contained in this site is for general use on Amateur Radio matters of interest only. While we here at BARC have made every attempt to ensure that the information contained in this site has been obtained from reliable sources. We are not responsible for any errors or omissions, or for the results obtained from the use of this information. All information in this Site is provided "as is", with no guarantee of completeness, accuracy, timeliness or of the results obtained from the use of this information, and without warranty of any kind, express or implied, including, but not limited to warranties of particular purpose. Anyone who may use any information from this website and the information is not correct does so at their own peril. Certain links in this Site connect to other Web Sites maintained by third parties over whom Beartooth Amateur Radio Club and or NQ7L has no control and makes no representations as to the accuracy or any other aspect of information contained in other Web Sites.  BARC operates this website as a free service to all Radio Amateurs and prospective Radio Amateurs.

The Beartooth Amateur Radio Club, NQ7L, KC7AX or any member will not be held responsible or libel in any way or manner for this information on this web site, which may also include bad or dead links.

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Beartooth Amateur Radio Club website is solely owned, created and managed by James NQ7L.

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