Ham Radio operators, shortwave radio enthusiasts often talk about propagation index numbers, the status of the solar cycle and geomagnetic conditions. Why? What do the numbers mean? On many ham radio frequencies, especially on HF, these factors determine whether worldwide contacts can be made with very little effort (low power and a modest antenna) or radio blackout conditions exist (no contacts possible). The following information, adapted from NOAA, can be helpful in these numbers.

The National Oceanic and Atmospheric Administration (NOAA) uses WWV and WWVH to broadcast geophysical alert messages that provide information about solar terrestrial conditions. Geophysical alerts are broadcast from WWV at 18 minutes after the hour and from WWVH at 45 minutes after the hour. The messages are less than 45 seconds in length and are routinely updated every 3 hours (typically at 0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100 UTC). Updates are more frequent when activity warrants.

The geophysical alerts provide information about the current and predicted solar terrestrial conditions found useful for long distance HF radio communications and other applications. The alerts use a standardized format and terminology that requires some explanation. The terms used in the announcements are defined below:

Solar flux is a measurement of the intensity of solar radio emissions with a wavelength of 10.7 cm (a frequency of about 2800 MHz. The daily solar flux measurement is recorded at 2000 UTC by the Dominion Radio Astrophysical Observatory of the Canadian National Research Council located at Penticton, B.C., Canada. The value broadcast is in solar flux units that range from a theoretical minimum of about 50 to numbers larger than 300. During the early part of the 11-year sunspot cycle, the flux numbers are low; but they rise and fall as the cycle proceeds. The numbers will remain high for extended periods around sunspot maximum.

The A and K indices are a measurement of the behavior of the magnetic field in and around the Earth. The K index uses a scale from 0 to 9 to measure the change in the horizontal component of the geomagnetic field. A new K index is determined and added to the broadcast every 3 hours based on magnetometer measurements made at the Table Mountain Observatory, north of Boulder, Colorado, or an alternate middle latitude observatory. The A index is a daily value on a scale from 0 to 400 to express the range of disturbance of the geomagnetic field. It is obtained by converting and averaging the eight, 3-hour K index values. An estimate of the A index is first announced at 2100 UTC, based on 7 measurements and 1 estimated value. At 0000 UTC, the announced A index consists entirely of known measurements, and the word “estimated” is dropped from the announcement.

Space Weather describes the conditions in space that affect earth and its technological systems. Space weather is a consequence of the behavior of the sun, the nature of Earth’s magnetic field and atmosphere, and our location in the solar system.

Space Weather storms observed and expected are characterized using the NOAA Space Weather scales. The abbreviated table below shows the levels of activity that are included in the announcements and the associated terminology. The descriptor used to identify observed or expected conditions is the maximum level reached or predicted. The NOAA Space Weather Scales are further described on the Space Environment Center web site.

NOAA Space Weather Scales Geomagnetic Storms Solar Radiation Storms Radio Blackouts Descriptor G5 S5 R5 Extreme G4 S4 R4 Severe G3 S3 R3 Strong G2 S2 R2 Moderate G1 S1 R1 Minor

Geomagnetic storm levels are determined by the estimated 3-hourly Planetary K-indices which are that are derived in real time from a network of western hemisphere ground-based magnetometers.

Geomagnetic Storm levels Planetary K indices Geomagnetic storm level K = 5 G1 K = 6 G2 K = 7 G3 K = 8 G4 K= 9 G5

Solar Radiation storms levels are determined by the proton flux measurements made by the primary GOES satellite.

Solar Radiation Storm levels Flux level of > 10 MeV particles Solar Radiation Storm level 10 S1 102 S2 103 S3 104 S4 105 S5

Radio Blackouts are determined by the x-ray level measured by the primary GOES satellite.

Radio Blackouts Peak x-ray level and flux Radio Blackout level M1 and (10-5) R1 M5 and (5 x 10-5) R2 X1 and (10-4) R3 X10 and (10-3) R4 X20 and (2 x 10-3) R5





Every geophysical alert consists of three parts as shown in tables 3.4 and 3.5. Table 3.4 describes the information contained in the geophysical alert. Table 3.5 provides example text from an actual message.

Section Table 3.4 - Information in Voice Message 1 The solar-terrestrial indices for the day: specifically the solar flux, the A index, and the K index. 2 Space Weather storms observed during the previous 24 hours. Includes all observed geomagnetic storms, solar radiation storms (proton events) and Radio blackouts (class M1 and greater flares). 3 Space Weather expected during the following 24 hours.

Section Table 3.5 - Example of Actual Geophysical Alert Message 1 Solar-terrestrial indices for 08 November follow.

Solar flux 173 and Mid-Latitude A-index 14

The Mid-latitude K-index at 1500 UTC on 08 November was 3. 2 Space Weather for the past 24 hours has been severe.

Solar radiation storm(s) reaching the S4 level is in progress.

Radio blackouts(s) reaching the R2 level occurred. Alternate

section 2 No Space Weather storms have been observed during the past 24 hours. 3 Space Weather for the next 24 hours is expected to be severe.

Solar radiation storms reaching the S4 level are expected to continue.

Radio blackouts reaching the R2 level are expected. Alternate

section 3 No Space Weather storms are expected during the next 24 hours.