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Geomagnetic activity in September 1999
Mean Ap18.9No. 181 of 1138
G1+ days12
G3+ days1
Max Ap5022 Sep 1999
Daily Ap
Daily max Kp
| Date | Max Kp | Ap | Level |
|---|---|---|---|
| 12 Sep 1999 | 6o | 31 | G2 |
| 13 Sep 1999 | 6o | 46 | G2 |
| 14 Sep 1999 | 5- | 21 | G1 |
| 15 Sep 1999 | 6- | 27 | G2 |
| 16 Sep 1999 | 6o | 31 | G2 |
| 22 Sep 1999 | 8o | 50 | G4 |
| 23 Sep 1999 | 6+ | 28 | G2 |
| 26 Sep 1999 | 5+ | 20 | G1 |
| 27 Sep 1999 | 6- | 43 | G2 |
| 28 Sep 1999 | 5- | 27 | G1 |
| 29 Sep 1999 | 5- | 25 | G1 |
| 30 Sep 1999 | 5+ | 26 | G1 |
Same month a year earlier
| Month | Mean Ap | G1+ | G3+ |
|---|---|---|---|
| September 1998 | 12.7 | 3 | 1 |
| September 1999 | 18.9 | 12 | 1 |
Dates and time slots are UTC. Kp is the 3-hourly planetary geomagnetic index (0–9); Ap is the daily average disturbance. G1–G5 follow the NOAA storm scale (Kp 5- and above counted as G1). Aurora visibility also depends on weather and location. The latest values are preliminary.
About this page
Mean Ap 18.9 in September 1999, No. 181 of 1138 months since 1932; 12 days reached G1 or higher.