====== Solar Terrestrial Data ======

From time to time you might come across an image like this, like those published at [[http://www.n0nbh.com|n0nbh.com]].


[[https://www.hamqsl.com/solar.html|{{https://www.hamqsl.com/solar101vhf.php?muf=athns&.gif?|Click to add Solar-Terrestrial Data to your website!}}]]


This is solar-terrestrial data. Solar-terrestrial charts are used to evaluate radio propagation conditions.

**TL;DR** [[hf:solar-terrestrial-data#quick_interpretation_tips|Quick Interpretation Tips]]

Here is a bit longer guide on how to interpret them.

 



===== Date and Time =====

**Example:** ''04 Apr 2025 1800 GMT''

This is the timestamp of the data in UTC (GMT). Data is typically refreshed every few hours.

===== Solar Indicators (Top Left) =====

These affect the ionosphere, which in turn impacts radio wave propagation.

^ Label ^ Meaning ^ Notes ^
| **SFI** (Solar Flux Index) | 178 | Higher SFI (100–200+) means better HF propagation |
| **SN** (Sunspot Number) | 124 | More sunspots = more ionization = improved HF conditions. 100-250 is the approximate range during solar maximum - see below for more info. |
| **A / K Index** | A=26, K=5 | A (avg daily geomagnetic activity), K (3-hour disturbances); lower values are better (A<20, K<4) |
| **X-Ray** | C2.1 | Solar flare level: A < B < C < M < X (ascending severity) |
| **304A** | 143.3 @ SEM | Ultraviolet measurement, proxy for ionization |
| **Ptn Flx** (Proton Flux) | 928 | High values degrade propagation, especially near poles |
| **Elc Flx** (Electron Flux) | 15500 | Can impact satellites and VHF communications |
| **Aurora** | 6.7 @ 1.9 | Indicates auroral activity strength |
| **Aur Lat** | 60.7° | Estimated latitude of visible aurora |
| **Bz** | -6.1 | Southward magnetic field = higher chance of geomagnetic storm |
| **SW** (Solar Wind) | 479.1 km/s | Speeds > 500 km/s may cause disturbances |

===== VHF Conditions (Middle) =====

VHF propagation conditions, especially E-skip and meteor scatter.

^ Band ^ Status ^
| **Aurora** | Band Closed |
| **6m EsEU** (Europe) | Band Closed |
| **4m EsEU** | Band Closed |
| **2m EsEU** | Band Closed |
| **2m EsNA** (North America) | Band Closed |
| **EME Deg** (Moonbounce) | Fair |

===== HF Conditions (Top Right) =====

Propagation quality on HF bands.

^ Band ^ Day ^ Night ^
| 80m–40m | Poor | Poor |
| 30m–20m | Poor | Poor |
| 17m–15m | Fair | Fair |
| 12m–10m | Fair | Poor |

  * ''Fair'': Usable but not ideal
  * ''Poor'': Weak or unreliable propagation

===== Geophysical Environment =====

^ Item ^ Meaning ^
| **Geomag Field** | MIN STORM — mild geomagnetic disturbance ongoing |
| **Sig Noise Level** | S4–S6 — background band noise (S1 = low, S9+ = high) |
| **MUF GR Athens** | 20.27 MHz — Max usable frequency in that region |
| **Solar Flare Prob** | 66% — Chance of a solar flare causing disruptions |

===== MUF Map (Bottom Color Bar) =====

Visual indicator of Maximum Usable Frequency (MUF) across regions.

  * Blue: <6 MHz — poor
  * Yellow/Orange: 8–16 MHz — moderate
  * Red: >18 MHz — good

===== Quick Interpretation Tips =====

  * **HF Operators:**
    * Look for: SFI > 100, SN > 50, A < 15, K < 4
    * Avoid when X-ray is M-class or higher, flare probability > 50%
  * **VHF Es Activity:**
    * Watch for summer months, E-skip openings, and open band indicators
  * **Aurora:**
    * More active with Bz negative and solar wind > 500 km/s

----

''Adapted from data provided by [[http://www.n0nbh.com|n0nbh.com]].''


===== Sunspot Number (SN) Overview =====

The **Sunspot Number (SN)** is a primary indicator of solar activity and directly influences HF radio propagation. SN varies over the 11-year solar cycle.

==== Typical Range of Sunspot Numbers ====

^ Solar Cycle Phase ^ Approx. SN Range ^ Description ^
| **Solar Minimum** | 0–20 | Very quiet sun, little or no sunspots. Weak HF propagation. |
| **Rising Phase**  | 20–100 | Increasing sunspots, improving conditions. |
| **Solar Maximum** | 100–250+ | High activity, excellent HF propagation. Watch for radio blackouts due to solar flares. |
| **Declining Phase** | 20–100 | Gradual drop in activity, conditions slowly degrade. |

  * All-time peaks have occasionally exceeded **250**, though rarely.
  * During deep minima, SN can remain near **0 for extended periods**.

==== What Is a "Good" SN for Radio Operators? ====

  * ''SN > 50'' → HF band openings become more consistent.
  * ''SN > 100'' → Excellent upper HF band propagation (15m, 12m, 10m).
  * ''SN < 30'' → Poor or unreliable conditions on high HF bands.

----

SN values are monitored by observatories like NOAA and SIDC. Regular updates available at [[https://www.swpc.noaa.gov/|NOAA Space Weather Prediction Center]].