Where does Glow's Kp history come from?

The GFZ Potsdam file of Kp since 1932, checked 2026-09-30. Values after 2026-08-31 are nowcasts that GFZ may still revise.

What counts as a storm day?

A UTC day whose highest 3-hour Kp reached 5 or more, the G1 level on NOAA's scale. Glow counts whole values, so 5- (4.67) does not count.

What is a G4 storm event on Glow?

A run of 3-hour blocks at Kp 8 or more, joining blocks that start within 24 hours of each other. Events with a single G4 block are listed but not indexed.

Can Kp history tell me if aurora was seen in my town?

No. Kp is a planetary index. The storm reach tool turns it into how often the average oval edge reached your latitude.

GFZ Potsdam Kp record

Kp history since 1932

Answer

The GFZ Potsdam record holds every 3-hour Kp since 1932. Across 94 complete years the median year has 51.5 storm days at Kp 5 or more. 1951 had the most, 141, and 2009 the fewest, 3.

194

G4 storm events since 1932

GFZ Kp, 1932 to 2026-09-29

Storm days, year by year

Storm days rise and fall with the roughly 11-year solar cycle, which shows as waves in the strip above. 2026 has 38 storm days in the 272 days recorded so far. Each bar links to its year page with the month-by-month count, the highest days and how far SWPC's rule puts the oval edge at the year's peak.

By decade

Averaging complete years by decade smooths out the cycle. The table lists the mean storm days per year, the number of G4 events that started in each decade and the highest 3-hour Kp. A decade that holds more cycle peaks than another will score higher without any change in the Sun's long-term behaviour.

Complete years only; storm days are days at Kp 5 or more
Decade	Storm days a year	G4 events	Highest Kp
1930s	48	14	9
1940s	73	28	9
1950s	91	33	9
1960s	54	24	9
1970s	66	22	9
1980s	73	19	9
1990s	68	21	9-
2000s	44	21	9
2010s	27	3	8+
2020s	33	9	9

Every G4 storm event

Glow finds 194 G4 events, runs of Kp 8 or more, since 1932. 23 of them reached Kp 9, the top of the scale. The most recent began on January 19, 2026.

1930s

1940s

1950s

1960s

1970s

1980s

1990s

2000s

2010s

2020s

Questions

Where does Glow's Kp history come from?: The GFZ Potsdam file of Kp since 1932, checked 2026-09-30. Values after 2026-08-31 are nowcasts that GFZ may still revise.
What counts as a storm day?: A UTC day whose highest 3-hour Kp reached 5 or more, the G1 level on NOAA's scale. Glow counts whole values, so 5- (4.67) does not count.
What is a G4 storm event on Glow?: A run of 3-hour blocks at Kp 8 or more, joining blocks that start within 24 hours of each other. Events with a single G4 block are listed but not indexed.
Can Kp history tell me if aurora was seen in my town?: No. Kp is a planetary index. The storm reach tool turns it into how often the average oval edge reached your latitude.

Sources and verification

GFZ Potsdam, Kp indexhttps://kp.gfz.de/en/data
GFZ Kp file since 1932https://kp.gfz.de/app/files/Kp_ap_Ap_SN_F107_since_1932.txt
Matzka et al. 2021, Geomagnetic Kp indexhttps://doi.org/10.5880/Kp.0001

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.