Space Weather Lab — Propagation

Propagation — how your signal actually gets there

Propagation is the combination of physics (electromagnetics), the atmosphere (ionosphere + troposphere), and geometry. This page focuses on a practical operator model: what mode is likely, what changes it, and what it means for your station.

Today’s quick context (the two knobs you’ll check most)

F10.7 solar flux (baseline MUF support)

166

as of 2026-02-05T22:00:00

What does this mean to me?

Higher F10.7 tends to raise MUF (better odds for 15m/10m). Lower F10.7 means you’ll lean more on 20m/40m and nighttime low bands.

Kp (geomagnetic stability)

2

as of 2026-02-06T08:59:00

What does this mean to me?

When Kp rises, polar HF often degrades first. Expect more fades/flutter and more day-to-day variability.

Ionospheric layers (conceptual)

This is an original diagram (not a copied image) showing the ham-relevant roles of each region.

Which signals refract from which layer?

You’ll often hear "the layer reflects radio". More precisely: the ionosphere refracts HF when the electron density gradient is strong enough. Which region dominates depends on frequency, solar illumination, season, and latitude.

D region: mostly absorption (especially daylight). This sets your lower usable frequency (LUF).
E region: can support shorter-hop HF and is the home of Sporadic E (Es), which can open 10m/6m dramatically.
F region / F2: the main "DX engine" for HF skywave, especially 20m/15m/10m when solar support is strong.
VHF/UHF: usually line-of-sight; long distance is via tropospheric ducting, meteor scatter, aurora, Es (6m), or satellites.

What conditions affect the layers?

Solar illumination (day/night): D-region absorption is strongest by day; low bands improve after sunset.
Solar cycle baseline: higher EUV generally increases F-region density (higher MUF).
Geomagnetic storms: can deplete/redistribute ionization, increase absorption, and make propagation unstable (especially high latitude).
Season and latitude: change the ionosphere’s chemistry and sunlight geometry; affects typical MUF/LUF patterns.
Atmospheric waves: tides and gravity waves modulate density; can help explain rapid swings in conditions.

What does this mean to me?

Propagation is not random. If you track local time + season + F10.7 + Kp, you can usually predict which bands are worth your time.

Live absorption + aurora context (SWPC products)

D-RAP global HF absorption map — D‑RAP: when the dayside is bright red, expect higher LUF and weaker HF.

Aurora forecast - northern hemisphere — Aurora oval expansion correlates with higher Kp/G scale; can enable auroral VHF paths but destabilize polar HF.

Practical operating playbook (what this means to me)

This is a deliberately simplified “first-order” cheat sheet. Real-world propagation depends on path geometry, season, latitude, and current conditions — but this table helps you pick a band and a plan fast.

Band	Most Likely Modes	Typical “Engine”	Best Time	Operator Notes
80m	NVIS, regional, occasional DX	F region at high angles; D absorption sets the floor	Night	Best for local/regional nets; quieter after sunset; watch local noise.
40m	Regional + DX	F region	Late afternoon → night	Workhorse band when higher bands are weak; can support long-haul at night.
20m	DX, contesting, reliable day paths	F2 region (main HF refraction)	Day → early evening	First place to check for HF DX. When conditions are “meh,” 20m often still works.
15m	DX, strong daytime openings	F2 region (needs higher MUF)	Midday	Likes higher F10.7 and quiet geomagnetics; great when it’s open.
10m	DX, short skip, sometimes “wide open”	F2 region (high MUF) + sometimes Es	Midday (F2) / seasonal (Es)	When it opens it’s spectacular; when it’s closed it’s silent. Check beacons and FT8 activity.
6m	Sporadic E, meteor scatter, tropo, (rare) F2	E region (Es) + troposphere	Late spring/summer (Es)	Space weather is secondary most days; learn Es seasonality and watch cluster/beacons.
2m/70cm	Line-of-sight, tropo, aurora, satellites	Troposphere / magnetosphere interactions	Weather-driven / storms	Tropo follows weather patterns; aurora needs geomagnetic disturbance and has a distinctive “buzz.”

HF by band (rule-of-thumb)

80m/40m: strongest at night; great for regional + DX when noise permits.
20m: the most reliable DX workhorse; first place to check.
15m/10m: best when F10.7 is higher and geomagnetics are quiet; check around local noon.
When Kp is high: avoid polar routes first; try non-polar headings and lower bands at night.

VHF/UHF modes

2m/70cm: mostly line-of-sight; look for tropo enhancements (weather-driven).
6m: seasonal Sporadic E can create huge openings; space weather is secondary.
Aurora: during storms, you may get auroral scatter (distinctive distorted audio/tones).
Satellites: watch for scintillation/fades during disturbed conditions.

FCC + authoritative references (high-level)

I’m not reproducing FCC text verbatim here (copyright/licensing varies by source formatting), but you should treat the FCC rules and official handbooks as the canonical source for definitions and compliance.

FCC ECFR (47 CFR Part 97): ecfr.gov/.../part-97
NOAA SWPC (space weather products): swpc.noaa.gov/products-and-data
ITU-R P.533 (HF prediction reference, technical): itu.int/rec/R-REC-P.533

If you want, I can add a dedicated “Propagation Sources” section mirroring Sources page style.

SWPC forecast text (for planning)

:Product: 3-Day Forecast
:Issued: 2026 Feb 06 0030 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
A. NOAA Geomagnetic Activity Observation and Forecast

The greatest observed 3 hr Kp over the past 24 hours was 5 (NOAA Scale
G1).
The greatest expected 3 hr Kp for Feb 06-Feb 08 2026 is 4.67 (NOAA Scale
G1).

NOAA Kp index breakdown Feb 06-Feb 08 2026

             Feb 06       Feb 07       Feb 08
00-03UT       4.67 (G1)    4.00         4.67 (G1)
03-06UT       4.00         2.67         3.67     
06-09UT       3.33         1.67         3.33     
09-12UT       2.67         1.67         3.33     
12-15UT       2.67         2.33         2.00     
15-18UT       3.00         2.67         3.33     
18-21UT       3.33         3.33         3.33     
21-00UT       3.67         4.00         3.67     

Rationale: G1 (Minor) geomagnetic storms are likely on 06 and 08 Feb due
to the anticipated arrival of two CMEs glancing impacts near Earth.

B. NOAA Solar Radiation Activity Observation and Forecast

Solar radiation, as observed by NOAA GOES-18 over the past 24 hours, was
below S-scale storm level thresholds.

Solar Radiation Storm Forecast for Feb 06-Feb 08 2026

              Feb 06  Feb 07  Feb 08
S1 or greater   25%     25%     25%

Rationale: There is a chance for a S1 (Minor) solar radiation storms on
06-08 Feb due to the magnetic complexity and dynamic of the active
regions on the visible disk.

C. NOAA Radio Blackout Activity and Forecast

Radio blackouts reaching the R1 levels were observed over the past 24
hours. The largest was at Feb 05 2026 0436 UTC.

Radio Blackout Forecast for Feb 06-Feb 08 2026

              Feb 06        Feb 07        Feb 08
R1-R2           80%           80%           80%
R3 or greater   35%           35%           35%

Rationale: R1-R2 (Minor-Moderate) radio blackouts are expected, with a
chance for R3 (Strong) or greater levels on 06-08 Feb due to the
magnetic complexity and dynamic of the active regions on the visible
disk.

:Product: 27-day Space Weather Outlook Table 27DO.txt
:Issued: 2026 Feb 02 0938 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC contact on the Web
# https://www.swpc.noaa.gov/content/subscription-services
#
#      27-day Space Weather Outlook Table
#                Issued 2026-02-02
#
#   UTC      Radio Flux   Planetary   Largest
#  Date       10.7 cm      A Index    Kp Index
Feb 02     160           5          2
Feb 03     155           5          2
Feb 04     155           5          2
Feb 05     145           5          2
Feb 06     120           8          3
Feb 07     125           8          3
Feb 08     130           8          3
Feb 09     135          10          3
Feb 10     140           8          3
Feb 11     135           8          3
Feb 12     140           5          2
Feb 13     145          20          5
Feb 14     145          15          4
Feb 15     155          15          4
Feb 16     160          15          4
Feb 17     170          15          4
Feb 18     180          15          4
Feb 19     175          15          4
Feb 20     170          15          4
Feb 21     160          15          4
Feb 22     150           8          3
Feb 23     140           8          3
Feb 24     135          20          4
Feb 25     130          20          4
Feb 26     130           8          3
Feb 27     140           5          2
Feb 28     160           5          2