Universal Time Variations in Space Weather

Forecasting Occurrence and Intensity of Geomagnetic Activity With Pattern‐Matching Approaches

“…They also allow for timeof-day/time-of-year response pattern of the stations, thereby reducing uncertainties related to using just two stations. Lockwood et al (2019) showed aa H agrees well with am Mayaud, 1981), a similar index but with much greater suppression of longitudinal sampling effects achieved by using multiple stations in each hemisphere. The disadvantage of am for the present study, of course, is that the data sequence is much shorter as the greater data requirement means it can only be constructed back to 1959.…”

Universal Time Variations in the Magnetosphere and the Effect of CME Arrival Time: Analysis of the February 2022 Event that Led to the Loss of Starlink Satellites

“…If the variations of V N P and V SP were of the same amplitude and in antiphase then although there would be more power deposited in the northern polar cap (and/or stored in the northern tail lobe) for half the day, and then more in the southern hemisphere for the other half so that the sum of the two would be constant. However these motions are not of equal amplitude, nor are they exactly in antiphase and this leaves a net UT variation in power deposited or (stored in that tail) globally (Lockwood et al, 2021).…”

“…Another factor that we also investigate in the present paper is the effect on cycles of energy storage and dissipation of motions of the magnetic poles in any geocentric frame of reference, caused by Earth's rotation (Lockwood et al, 2021). These introduce Universal Time (UT) variations which are close to being in antiphase in the two hemispheres and which are larger in the southern hemisphere because the offset of the magnetic and rotational poles is greater.…”

“…We repeated our analysis for δt = 10min and δt = 30min and found only small changes to our results. Note that there is a potential improvement we could make to Equation 8in that the rate could be made a function of solar wind dynamic pressure p SW and the dipole tilt angle δ as there are observations that indicate that, together, they influence the rate of nightside reconnection by squeezing the tail (Schieldge & Siscoe, 1970;Caan et al, 1973;Kokubun et al, 1977;Karlsson et al, 2000;Finch et al, 2008;Hubert et al, 2009;Yue et al, 2010;Lockwood, 2013;Lockwood et al, 2021). This would not influence the voltage Φ N 1 as it would also raise SML from which it is computed; however, it would influence Φ N 2 .…”

“…In this section we add to the effects of this the UT variations caused by the diurnal rotation of Earth's eccentric magnetic field. The motions are computed using the eccentric dipole model of the geomagnetic field by Koochak and Fraser-Smith (2017), as discussed by Lockwood et al (2021).…”