Pc5 micropulsation power at conjugate high‐latitude locations

Abstract

The micropulsation power, integrated over the Pc5 frequency range, has been calculated for the horizontal component of the geomagnetic field at two high‐latitude conjugate locations: Dumont D'Urville (corrected geomagnetic coordinates: 80.61°S, 235.76°E) and Mould Bay (corrected geomagnetic coordinates: 80.85°N, 272.65°E). Because of the different distances between the geographic and the geomagnetic poles in each hemisphere, the comparison between the Pc5 power observed at Dumont D'Urville and at Mould Bay shows the relative importance of geomagnetic and solar illumination effects in driving low‐frequency micropulsation activity. In particular, similarities observed at the two sites can be explained in terms of their common geomagnetic characteristics, while differences can be attributed to the different sunlight or solar zenith angle configurations. Results show that the local summer Pc5 power is statistically higher in the northern hemisphere than in the southern one. This hemispherical difference is smaller for the local equinoxes, and it is only very slight or absent for local winters. These findings are interpreted in terms of the proportionality between the Pc5 power and the ionospheric conductance, which is higher at Mould Bay owing to more permanent and direct sunlight conditions during local summers and equinoxes. Thus the different geographic coordinates affect the Pc5 power at the two considered sites so much so that their effect is visible regardless of the geomagnetic similarities. However, the influence of the geomagnetic activity on Pc5 power is found to be more significant than these geographical effects or than the seasonal effects. In fact, for Kp < 2 the difference in simultaneous observations at Mould Bay and at Dumont D'Urville is <∣10∣ nT2 with an occurrence >70%. The magnetic local time modulation of Pc5 power is similar in both hemispheres, since it is determined by the equivalent geomagnetic characteristics and regardless of possible geographical differences. In particular, the occurrence of higher Pc5 power observed at Mould Bay than at Dumont D'Urville is not localized in one specific magnetic local time sector. The present observations are compared with previous results regarding solar illumination effects on geomagnetic activity and on auroral brightness. Finally, no solar cycle effect is observed on either the Pc5 power level, on its hemispherical dependence, or on its daily modulation.