ToolComputedCited
Which towns sit under the oval at a given Kp?
Answer
| Country | Under the edge | Of |
|---|
Worked example
At Kp 2, SWPC's rule puts the average oval edge at 62 degrees geomagnetic. 0 of Glow's 0 indexed towns sit at or poleward of it.
At Kp 8, SWPC's rule puts the average oval edge at 50 degrees geomagnetic. 0 of Glow's 0 indexed towns sit at or poleward of it.
Each step of Kp moves the edge 2 degrees, about 220 km along the geomagnetic meridian, so the count grows fastest where towns are dense, such as Britain and the Upper Midwest.
The rule behind the list
SWPC's viewing tips give the equatorward edge of the auroral oval as about 66 degrees geomagnetic at Kp 0, moving about 2 degrees for each Kp step. Glow applies that rule to the IGRF-14 dipole latitude of each of its towns.
"It should be noted that the relationship between Kp and auroral latitude are approximate and represent averages." A town just poleward of the edge is not certain to see aurora overhead, and towns hundreds of kilometers equatorward can still see it low on the horizon.
Which towns are counted
The count covers Glow's indexed towns: GeoNames towns of 15,000 or more at 55 degrees geomagnetic and above, larger North American towns from 50 degrees, and southern towns at 45 degrees south and beyond. Near-duplicate suburbs are left out.
Questions
- Can I see the aurora at Kp 5 where I live?
- If your geomagnetic latitude is 56 degrees or more, SWPC's rule puts the average oval edge at or poleward of you. Check your value with the Kp tool.
- Why do the counts jump at some Kp values?
- Towns cluster in bands of latitude. When the edge crosses a dense band, such as central Britain, many towns join at once.
- Does the list include southern towns?
- Yes. The rule is symmetric, so southern towns count by the absolute value of their dipole latitude.