How many geomagnetic storm days were there in 1973?

94 UTC days reached Kp 5 (G1) or more in the GFZ record. 1 reached Kp 8 (G4).

What was the strongest geomagnetic storm of 1973?

The highest 3-hour Kp was 8+, first reached on April 1, 1973.

How far south could aurora reach in 1973?

At Kp 8+ SWPC's rule puts the average oval edge near 49.3 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 · 1973

Geomagnetic storms in 1973

Answer

In 1973 the GFZ Potsdam record has 94 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 1973 14th of 94 by storm days.

days at Kp 5 or more

GFZ Kp, 365 days

Storm days by month

April was the stormiest month with 15 storm days. Every month had at least one storm day. March, April, September and October together account for 44 of the 94, the equinox months SWPC links with larger storms.

Storm levels against the median year

By level, the year counts 94 at G1, 32 at G2, 12 at G3, 1 at G4, 0 at G5. The highest 3-hour value was Kp 8+, G4 Severe on NOAA's scale. The average day peaked at Kp 3.79, against 3.36 in the median year.

Days per NOAA G level, 1973 and the median of 94 complete years
Level	Kp	1973	Median year
G1 Minor	5	94	51.5
G2 Moderate	6	32	20
G3 Strong	7	12	6.5
G4 Severe	8	1	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 8+, SWPC's rule of thumb puts the average oval edge at 49.3 degrees geomagnetic. 1191 of Glow's 1218 towns sit at or poleward of that line, including 328 in United Kingdom, 246 in United States, 181 in Canada.

Highest days of 1973
Date (UTC)	Highest Kp
April 1, 1973	8+
April 14, 1973	8-
May 14, 1973	8-
September 9, 1973	8-
February 21, 1973	7+

G4 storm events

1 separate periods reached G4 (Kp 8) or more: April 1, 1973 (peak Kp 8+). For context, 1972 had 49 storm days and 1974 had 107 storm days.

April 1, 1973Kp 8+, 3 h at G4+

Questions

How many geomagnetic storm days were there in 1973?: 94 UTC days reached Kp 5 (G1) or more in the GFZ record. 1 reached Kp 8 (G4).
What was the strongest geomagnetic storm of 1973?: The highest 3-hour Kp was 8+, first reached on April 1, 1973.
How far south could aurora reach in 1973?: At Kp 8+ SWPC's rule puts the average oval edge near 49.3 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.