SFI (70 = poor / 160 = good / 280 = fabulous) Solar Flux Index The SFI (62.5 to 300) is the amount of solar radio noise measured at 2800 MHz and is updated daily. The SFI gives us an idea of how well the ionospheric F-Layer can support radio communication on HF, and more especially on 20 meters through 10 meters. Numbers below 75 are quite poor, while those above 160 are very good.
SN (2 = poor / 90 = good / 220 = fabulous) Sunspot Number The SN (0 to 250) is a calculation that is roughly 10 X the number of sunspot groups facing us + the number of individual sunspots facing us, and is updated daily. The SN typically follows the SFI, and offers another indicator of F-Layer ionizati
A Plntry (4 = calm / 40 = minor storm / 80 = severe) A, planetary The Ap index is the daily average long-term stability of Earth’s magnetic field, the subscript ‘P’ meaning planetary, or averaged from several locations around the earth. The value ranges from 0 to 400, with anything over 100 indicating unfavorable conditions for radio propagation.
K Plntry (1 = calm / 5 = minor storm / 7 = severe) K, planetary The Kp index is the daily average short-term stability of Earth’s magnetic field, the subscript ‘P’ meaning planetary, or averaged from several locations around the earth. The value ranges from 0 to 9, with anything over 5 indicating unfavorable conditions for radio propagation.
X-Ray (A1.1 = good / C5.0 = moderate / X2.3 = severe) X-Rays X-ray emissions most heavily impact the ionospheric D-Layer, such that the stronger the radiation, the lower the ability of radio waves to propagate by skywave refraction. The intensity of X-ray radiation striking the atmosphere, ranging from A0.0 to X9.9, is defined by a class (A, B, C, M, and X), followed by a logarithmic quantity (0.0 to 9.9) that defines the intensity within the class.
304A (80 = poor / 150 = good / 240 = fabulous) 304 Angstroms The 304A (0 to unknown) is the relative strength of total solar radiation in the UV (ultraviolet) range, originating primarily from ionized Helium in the Sun’s photosphere, and often follows the SFI value.
Sig Noise Level (S0 = great / S4 = fair / S7 = horrible) The signal noise level is a logarithmic measurement (in 6 dB-increments, like you see on an S-meter) of the noise generated as a result of the solar wind, compared with the noise floor. The greater the disturbance in the solar wind, mostly due to interaction with Earth’s magnetic field, the higher the S-value