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|            NOAA Space Weather Scale for Geomagnetic Storms               |
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|     Category     |                           |          |                |
-------------------|                           | Physical | Avg. Frequency |
|Scale | Descriptor|          Effect           | Measure  |(cycle=11 years)| 
|------|-----------|---------------------------|----------|----------------|
|                                              |          |   number of    |
|                                              | Planetary|  storm events  |
|             Geomagnetic Storms               |  K Index |  (number of    |
|                                              |   (Kp)   |  storm days)   |
|------|-----------|---------------------------|----------|----------------|
| G5   |  Extreme  | HF (high frequency) radio |  Kp = 9  |   4 per cycle  |
|      |           | propagation may be        |          | (4 days/cycle) |
|      |           | impossible in many areas  |          |                |
|      |           | for one to two days,      |          |                |
|      |           | satellite navigation may  |          |                |
|      |           | be degraded for days.     |          |                |
|------|-----------|---------------------------|----------|----------------|
| G4   |  Severe   | HF radio propagation      |  Kp = 8  |  100 per cycle |
|      |           | sporadic, satellite       |          | (60 days/cycle)|
|      |           | navigation degraded for   |          |                |
|      |           | hours.                    |          |                |
|------|-----------|---------------------------|----------|----------------|
| G3   |  Strong   | HF radio may be inter-    |  Kp = 7  |  200 per cycle |
|      |           | mittent, intermittent     |          |(130 days/cycle)|
|      |           | satellite navigation.     |          |                |
|------|-----------|---------------------------|----------|----------------|
| G2   | Moderate  | HF radio propagation can  |  Kp = 6  |  600 per cycle |
|      |           | fade at higher latitudes. |          |(360 days/cycle)|
|      |           | latitudes.                |          |                |
|------|-----------|---------------------------|----------|----------------|
| G1   |   Minor   | Minor impact on HF radio  |  Kp = 5  | 1700 per cycle |
|      |           | propagation at higher     |          |(900 days/cycle)|
|      |           | latitudes.                |          |                |
|------|-----------|---------------------------|----------|----------------|

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|         NOAA Space Weather Scale for Solar Radiation Storms              |
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|     Category     |                           |          |                |
-------------------|                           | Physical | Avg. Frequency |
|Scale | Descriptor|          Effect           | Measure  |(cycle=11 years)| 
|------|-----------|---------------------------|----------|----------------|
|                                              |          |   number of    |
|                                              |Flux level|  storm events  |
|           Solar Radiation Storms             | >= 10 MeV|  (number of    |
|                                              |  (ions)* |  storm days)   |
|------|-----------|---------------------------|----------|----------------|
| S5   |  Extreme  | Complete blackout of HF   |   10^5   |   Fewer than   |
|      |           | communications possible   |          |  1 per cycle   |
|      |           | through the polar regions,|          |                |
|      |           | and position errors make  |          |                |
|      |           | satellite navigation      |          |                |
|      |           | extremely difficult.      |          |                |
|------|-----------|---------------------------|----------|----------------|
| S4   |  Severe   | Blackout of HF communi-   |   10^4   |  3 per cycle   |
|      |           | cations through the polar |          |                |
|      |           | regions and increased     |          |                |
|      |           | navigation errors over    |          |                |
|      |           | several days are likely.  |          |                |
|------|-----------|---------------------------|----------|----------------|
| S3   |  Strong   | Degraded HF radio propa-  |   10^3   |  10 per cycle  |
|      |           | gation through the polar  |          |                |
|      |           | regions and navigation    |          |                |
|      |           | position errors likely.   |          |                |
|------|-----------|---------------------------|----------|----------------|
| S2   | Moderate  | Small effects on HF radio |   10^2   |  25 per cycle  |
|      |           | through the polar regions |          |                |
|      |           | and navigation at polar   |          |                |
|      |           | caps possibly affected.   |          |                |
|------|-----------|---------------------------|----------|----------------|
| S1   |   Minor   | Minor impact on HF radio  |   10^1   |  50 per cycle  |
|      |           | in the polar regions.     |          |                |
|------|-----------|---------------------------|----------|----------------|
*Flux levels are 5 minute averages. Flux in particles x s-1 x ster-1 x cm-2. 
Based on this measure, but other physical measures are also considered.

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|             NOAA Space Weather Scale for Radio Blackouts                 |
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|     Category     |                           |          |                |
-------------------|                           | Physical | Avg. Frequency |
|Scale | Descriptor|          Effect           | Measure  |(cycle=11 years)| 
|------|-----------|---------------------------|----------|----------------|
|                                              |          |   number of    |
|                                              |GEOS X-ray|    events      |
|               Radio Blackouts                | by class |  (number of    |
|                                              | and flux*|  storm days)   |
|------|-----------|---------------------------|----------|----------------|
| R5   |  Extreme  | Complete HF radio blackout|   X20    |   Fewer than   |
|      |           | on the entire sunlit side | (2x10^-3)|  1 per cycle   |
|      |           | of the Earth lasting for  |          |                |
|      |           | several hours. Increased  |          |                |
|      |           | satellite navigation      |          |                |
|      |           | position errors on the    |          |                |
|      |           | sunlit side of the Earth. |          |                |
|------|-----------|---------------------------|----------|----------------|
| R4   |  Severe   | HF radio communication    |   X10    |  8 per cycle   |
|      |           | blackout on most of the   |  (10^-3) | (8 days/cycle) |
|      |           | sunlit side of Earth for  |          |                |
|      |           | one to two hours. Minor   |          |                |
|      |           | disruptions of satellite  |          |                |
|      |           | navigation possible on    |          |                |
|      |           | sunlit side of the Earth. |          |                |
|------|-----------|---------------------------|----------|----------------|
| R3   |  Strong   | Wide area blackout of HF  |    X1    | 175 per cycle  |
|      |           | radio communication, loss |  (10^-4) |(140 days/cycle)|
|      |           | of radio contact for about|          |                |
|      |           | an hour on sunlit side of |          |                |
|      |           | the Earth.                |          |                |
|------|-----------|---------------------------|----------|----------------|
| R2   | Moderate  | Limited blackout of HF    |    M5    | 350 per cycle  |
|      |           | radio communication on    | (5x10^-5)|(300 days/cycle)|
|      |           | sunlit side, loss of radio|          |                |
|      |           | contact for tens of       |          |                |
|      |           | minutes.                  |          |                |
|------|-----------|---------------------------|----------|----------------|
| R1   |   Minor   | Weak or minor degradation |    M1    | 2000 per cycle |
|      |           | of HF radio communication |  (10^-5) |(950 days/cycle)|
|      |           | on sunlit side, occasional|          |                |
|      |           | loss of radio contact.    |          |                |
|------|-----------|---------------------------|----------|----------------|
*Flux, measured in the 0.1-0.8 nm range, in W x m-2. 
Based on this measure, but other physical measures are also considered.