How many geomagnetic storm days were there in 2009?

3 UTC days reached Kp 5 (G1) or more in the GFZ record. 0 reached Kp 8 (G4).

What was the strongest geomagnetic storm of 2009?

The highest 3-hour Kp was 6-, first reached on July 22, 2009.

How far south could aurora reach in 2009?

At Kp 6- SWPC's rule puts the average oval edge near 54.7 degrees geomagnetic. Viewing reaches farther, since aurora can be seen from as far as about 1,000 km away.

Does Glow count 5- as a storm?

No. A level counts from the whole Kp value, so 5- (4.67) is below G1 and 8- is below G4. Other sites may round differently.

GFZ Potsdam Kp record · 2009

Geomagnetic storms in 2009

Answer

In 2009 the GFZ Potsdam record has 3 UTC days whose highest 3-hour Kp reached 5 or more, the G1 storm level, against a median of 51.5 for the 94 complete years since 1932. That ranks 2009 93rd of 94 by storm days.

days at Kp 5 or more

GFZ Kp, 365 days

Storm days by month

June was the stormiest month with 1 storm days. 9 of 12 months had none. March, April, September and October together account for 0 of the 3, the equinox months SWPC links with larger storms.

Storm levels against the median year

By level, the year counts 3 at G1, 0 at G2, 0 at G3, 0 at G4, 0 at G5. The highest 3-hour value was Kp 6-, G1 Minor on NOAA's scale. The average day peaked at Kp 1.77, against 3.36 in the median year.

Days per NOAA G level, 2009 and the median of 94 complete years
Level	Kp	2009	Median year
G1 Minor	5	3	51.5
G2 Moderate	6	0	20
G3 Strong	7	0	6.5
G4 Severe	8	0	2
G5 Extreme	9	0	0

A day counts at a level when its highest 3-hour Kp reached the whole value; 5- does not count as G1.

How far the oval reached

At the year's peak, Kp 6-, SWPC's rule of thumb puts the average oval edge at 54.7 degrees geomagnetic. 887 of Glow's 1218 towns sit at or poleward of that line, including 328 in United Kingdom, 111 in Canada, 97 in Sweden.

Highest days of 2009
Date (UTC)	Highest Kp
July 22, 2009	6-
August 30, 2009	6-
June 24, 2009	5
March 13, 2009	5-
February 14, 2009	4+

G4 storm events

No 3-hour Kp reached 8, so the year has no G4 storm event. For context, 2008 had 11 storm days and 2010 had 11 storm days.

Questions

How many geomagnetic storm days were there in 2009?: 3 UTC days reached Kp 5 (G1) or more in the GFZ record. 0 reached Kp 8 (G4).
What was the strongest geomagnetic storm of 2009?: The highest 3-hour Kp was 6-, first reached on July 22, 2009.
How far south could aurora reach in 2009?: At Kp 6- SWPC's rule puts the average oval edge near 54.7 degrees geomagnetic. Viewing reaches farther, since aurora can be seen from as far as about 1,000 km away.
Does Glow count 5- as a storm?: No. A level counts from the whole Kp value, so 5- (4.67) is below G1 and 8- is below G4. Other sites may round differently.

Sources and verification

GFZ Potsdam, Kp index datahttps://kp.gfz.de/en/data
Matzka et al. 2021, Geomagnetic Kp index, GFZ Data Serviceshttps://doi.org/10.5880/Kp.0001
NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora
NOAA Space Weather Scaleshttps://www.spaceweather.gov/noaa-scales-explanation

Quoted figures last checked against their sources on 2026-09-30; next review 2026-12-31. Computed figures come from SunCalc and the IGRF-14 dipole as described in the methodology. Every quote is listed in the sources ledger.