Space weather alert

Space weather impacts radio communication in a number of ways. Changes in ionospheric density and structure modify the transmission path and even block transmission of HF radio signals completely. In a typical sequence of space weather storms, the first impacts are felt during the solar flare itself. The solar x-rays from the sun penetrate to the bottom of the ionosphere (to around 80 km). There the x-ray photons ionize the atmosphere and create an enhancement of the D layer of the ionosphere. This enhanced D-layer acts both as a reflector of radio waves at some frequencies and an absorber of waves at other frequencies. The Radio Blackout associated with solar flares occurs on the dayside region of Earth and is most intense when the sun is directly overhead. The protons are guided by Earth's magnetic field such that they collide with the upper atmosphere near the north and south poles. The fast-moving protons have an affect similar to the x-ray photons and create an enhanced D-Layer thus blocking HF radio communication at high latitudes. During auroral displays, the precipitating electrons can enhance other layers of the ionosphere and have similar disrupting and blocking effects on radio communication. This occurs mostly on the night side of the polar regions of Earth where the aurora is most intense and most frequent.

Space weather alerts

X-ray flux levels

A solar flare is an explosion on the Sun. There are 3 categories:
  1. X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms.
  2. M-class flares are medium-sized; they can cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare.
  3. C-class flares are small with few noticeable consequences here on Earth.

Real time k-index

The K index showing the geomagnetic conditions, indicates HF noise primarily below 10 MHz.
(K=1; HF Noise= S1-S2), (K=3; HF Noise= S2-S3), (K=5; HF Noise= S4-S6), (K=7; HF Noise= S9+), (K=9; HF Noise= Black-out)

Auroral activity

When a solar wind blow reaches the Earth, it creates additional ionization in the areas around the magnetic poles. The radio propagation paths that cross the poles may be degraded because of increased absorption of the radio signal. The auroral activity index ranges from 0 to 100%.

North Pole Aurora South Pole Aurora


Sunspots are cooler areas on the solar surface. These active regions should be carefully watched for possible flare activity. A solar flare releases energy than can affect HF propagation:
  1. Ionizing radiation that arrives at earth immediatly;
  2. A supersonic shockwave riding along the solar wind;
  3. Dense particles behind the shockwave that arrives two to three days after the flare.
Good DX contacts are possible immediately following a solar flare until sundown due to improved reflectivity and the higher MUF opening higher bands. Night time conditions on 80-40 can be excellent. About two days after a solar flare, the shockwave arrives on earth triggering a geomagnetic storm.

Sunspots (Sunspot number)

Short historical graph of WWV numbers

The solar flux, indicating the level of ionization, affects HF propagation above 10 MHz. The solar flux does not affect 7 MHz and below, since the MUF seldom drops below 10 MHz. The higher the inonization the more reflective our ionosphere is to HF signals, and the higher the MUF. Sunspots are cooler areas on the solar surface. These active regions should be carefully watched for possible flare activity. A index, is derived by averaging the K-index. It ranges from 0-20 for quiet conditions, up to 400 for extreme conditions, representing the overall planetary geomagnetic conditions.

WWV Numbers

12 month ahead Cycle Prediction

Forecasts of the monthly mean sunspot number using the Standard Curve method (extension of the original method by M.Waldmeier). The method consists in the least-square fit and interpolation of a set of standard curves, each curve corresponding to the average shape of solar cycles of a narrow range of maximum value. The fit is done on the observed 13-month smoothed monthly sunspot number, using the last 24 available values. This is why the prediction actually starts 5 months before the last elapsed month and runs over 18 months (up to 12 months ahead). This method performs well in the middle of each cycle, but as all methods based purely on past solar activity, it becomes unreliable at the end of each cycle and during the minima.

CT1BOH - Josť Carlos Cardoso Nunes -