Continuous Space Weather Observation: 10.7cm Solar Flux Index (SFI) & Sunspot Number
The Solar Flux Index is a measurement of solar radio noise emitted at a frequency of 2800 MHz (10.7 cm wavelength), recorded thrice daily by the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, Canada.
Higher SFI values (typically > 100–120) produce stronger ionization in the Earth's ionosphere (F2 layer), significantly elevating the Maximum Usable Frequency (MUF) for HF radio propagation across bands from 20m through 10m and 6m.
The Sunspot Number indicates magnetic disturbance and activity on the solar photosphere. Generated from global solar observatory networks and standardized by the Solar Influences Data Analysis Center (SIDC) and NOAA SWPC.
Sunspot numbers trace the progression of the ~11-year solar cycle. High sunspot counts coincide with enhanced EUV emissions, promoting long-distance amateur radio DX and ionospheric ducting.
The Planetary K-index (Kp) is a quasi-logarithmic measure (0–9) of horizontal geomagnetic activity over a 3-hour interval. Values ≤ 2 indicate quiet geomagnetic conditions, while ≥ 5 indicate geomagnetic storm levels.
The A-index (Ap) provides an equivalent 24-hour linear index (0–400) derived from planetary K-values. Low, quiet K and A values indicate a stable geomagnetic field essential for clear HF radio propagation.