Current propagation conditions

How to interpret solar information figures:

Solar Flux: This flux number is measured from the amount of radiation on the 10.7cm band (2800MHz). It is closely related to the amount of ultraviolet radiation, which is needed to create an ionosphere. The lowest possible number for this solar flux is 63.75. Single hop propagation already starts at 70 in lower latitude areas. Worldwide long distance propagation (DX) may turn up already with a solar flux at 120. From experience, an average solar flux of 170 seems to be ideal for 10m-20m bands QRP DX with good possibilities during these conditions to reach every possible part of the globe with a simple dipole running as low as 5 Watts!

A and K index:
Geomagnetic activity indices, high indices (K:>5 or A:>20) means stormy conditions with an active geomagnetic field. The more active, the more unstable propagation with possible periods of total propagation fade-out. Especially around the higher latitudes and especially at the polar regions, where the geomagnetic field is weak, propagation may disappear completely. Extreme high indices may result in aurora propagation, with strongly degraded long distance propagation at all latitudes on HF. (Though Auroral DX is possible on VHF) Sporadic-E is strongest during low indices. Low indices result in relative good propagation, especially noticeable around the higher latitudes, when transpolar paths may open up. Maximum K-index is 9, and the A-index can exceed well over 100 during very severe storm conditions, with no maximum. The ARRL often reports the K-index from the Alaskian station where this index is known as the College K-index. Other stations reporting K-indices include Planetary and Boulder. In contrast, the A-indices are usually reported for the Planetary station only.

The higher the K-index, the more unstable propagation becomes, the effect is stronger at high latitudes, but weaker near low latitudes. When storm level is reached, propagation strongly degrades, possibly fade out at high latitudes.
Classification of K-indices are as follows:

• K0 =Inactive
• K 1= Very quiet
• K2 = Quiet
• K3 = Unsettled
• K4 = Active
• K5 = Minor storm
• K6 = Major storm
• K7 = Severe storm
• K8 = Very severe storm
• K9 = Extremely severe storm

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

• A0-7 = Quiet
• A8-15 = Unsettled
• A16-29 = Active
• A30-49 = Minor storm
• A50-99 = Major storm
• A100-400 = Severe storm

Background X-ray level: This may vary from B (very low), C (low to moderate), M (moderate to high) to X (high to extremely high), the higher the number after the letter, the stronger the X-ray radiation. So an X0.1 is stronger than an M9.9. High amounts of X-ray radiation causes intense ionization of the D-layer, resulting in strong absorption of HF-signals. Solar flares are commonly measured in the amount of X-ray radiation.

304A: Relative strength of total solar radiation at a wavelength of 304 Angstroms (30.4nm). Loosly correlates to the Solar Flux Index.

PTN Flux: Proton Flux measurement. The amount of proton activity in the solar wind. Primarily affects propagation in the E Layer.

ELC Flux: Electron Flux measurement. The amount of electron activity in the solar wind. Primarily affects propagation in the E Layer.

Aurora: N number reflects probabilty of aurora activity. Scale of 0 - 5 with 5 being high probability and 0 low.

(Credits: The notes above are from Edwin C. Jones, MD, PhD (AE4TM))

VHF Propagation forecast links:

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