4-1.                        SOLAR FLUX , A INDEX , K INDEX

Propagation is tied to the number of sunspots on the surface of the sun, since the areas around sunspots emit large amounts of ionizing radiation - extreme ultraviolet radiation. Increased sunspots correlate closely with better worldwide radio propagation. When there are more sunspots, the sun emits radiation that charges particles in the earth's ionosphere. Radio waves bounce off of (refract from) these charged particles, and the denser these clouds of ions, the better the HF propagation. The sunspot numbers are calculated by counting the spots on the visible solar surface and also by measuring their area.

Listening to WWV or checking propagation web sites will give the latest solar-terrestrial indices. It includes the 10.7cm solar flux index, Boulder A index and the Boulder K index.  Solar Flux at 10.7cm is essentially a measurement of the thermal radiation of the sun, and contributes nothing to the ionization process. Solar flux is measured at several points on the earth, for example one is an observatory in Penticton, British Columbia using an antenna pointed toward the sun connected to a receiver tuned to 2.8 GHz, which is at a wavelength of 10.7 cm. The 12-month running average of 10.7cm solar flux correlates very well with the 12-month running average of the sunspot number – called the smoothed sunspot number and abbreviated SSN. The higher the smoothed SFI number, the better. Typical daily SFI values have ranged from 67 (Jan 1997) to 370 (Jan 1991).

Other solar activity of concern to HF operators are solar flares and coronal holes, which can emit energetic protons and X-rays and cause a significant increase in the solar wind speed.  Energetic protons can cause polar cap absorption events (PCAs).  X-rays can cause blackouts on the daylight side of the Earth due to increased absorption in the D region.  And a significant increase in solar wind speed can result in geomagnetic storms that generally depress MUFs.

The A Index is an averaged quantitative measure of geomagnetic activity derived from a series of physical measurements.

The Boulder A  index in WWV announcements is linear in nature and ranges from 0 to 400, and is the 24-hour A index derived from the eight 3-hour K indices recorded at Boulder, Colorado. The K index is logarithmic in nature and ranges from 0 to 9, and is the result of a 3-hourly magnetometer measurement comparing the current geomagnetic field orientation and intensity to what it would have been under geomagnetically quiet conditions.

Suffice it to say that the geomagnetic activity, solar storms, X-Rays, flares, etc., can have an adverse effect on propagation. The Planetary A index  relates to geomagnetic stability. Magnetometers around the world are used to generate a number called the Planetary K index. A one-point change in the K index is quite significant. K index readings below 3 generally mean good stable conditions, and above 3 can mean high absorption of radio waves. Each point change reflects a significant change in conditions. Generally the higher the latitude of the measuring station, the higher the K and A indices reported. This is because the effects of geomagnetic instability tend to concentrate toward the polar regions of the globe.

Oversimplification can be very misleading in the complex field of propagation, but in general for long distance HF, the rule of thumb is the higher the SFI and the lower the A and K indices, the better the conditions on the higher frequencies. The A index should be under 14, and the solar activity low to moderate. If the A-index drops under 7 for a few days in a row and the SFI is up, watch for some really exciting intercontinental conditions.

You can hear the SFI, A and K indices  on WWV or WWVH or by calling 303-497-3235. Geophysical alerts are broadcast from WWV at 18 minutes after the hour and from WWVH at 45 minutes after the hour. Both stations operate in the high frequency (HF) portion of the radio spectrum. WWV and WWVH radiate 10,000 W on 5, 10, and 15 MHz. The radiated power is lower on the other frequencies: WWV radiates 2500 W on 2.5 and 20 MHz while WWVH radiates 5000 W on 2.5 MHz and does not broadcast on 20 MHz. Each frequency is broadcast from a separate transmitter. Although each frequency carries the same information, multiple frequencies are used because the quality of HF reception depends on many factors such as location, time of year, time of day, the frequency being used, and atmospheric and ionospheric propagation conditions. The variety of frequencies makes it likely that at least one frequency will be usable at all times.

These values are also available on all DX Packet Clusters (SH/WWV). Also you can find them on numerous pages on the internet, a good one is from WN6K at URL:  http://www.wn6k.cts.com/

Note that the K index reported on WWV is only updated every 3 hours and the A and SFI values are usually updated once a day at 21 UTC. The A index reported at 21 UTC is calculated from the last eight K index readings in Boulder, so it contains data that is 24 hours old when it is first posted.

For graphs that update every 5 minutes see http://www.sec.noaa.gov/today.html these show short term events long before they show in the WWV report. Also watch the K index graph at NOAA; it often differs from the WWV report, because the web page shows the estimated Kp (planetary K index) rather than just the reading from one site (Boulder) that is reported on WWV.

Classification of K-indices is as follows:

K0 = Inactive               K5 = Minor storm

K1 = Very quiet     K6 = Major storm

K2 = Quiet                   K7 = Severe storm

K3 = Unsettled            K8 = Very severe storm

K4 = Active                 K9 = Extremely severe storm

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

A0 - A7 = quiet

A8 - A15 = unsettled

A16 - A29 = active

A30 - A49 = minor storm

A50 - A99 = major storm

A100 - A400 = severe storm

4-1.                        6 METERS SPORADIC E SEASONS

Studies over many years for sporadic E propagation have shown peak activity in the summer months with another smaller peak in the winter. Nearly 80% of the yearly totals of Es propagation take place from May through August, with maximums occurring in June or July with June being the more common. Some Es can take place in late April and early September.

A lower but significant occurrence takes place in the month of December. March usually exhibits a definite minimum of Es. However, Es can occur on any day of the year and these are termed off-peak openings.

18 more pages in Chapter 4.