Variation of geomagnetic index empirical distribution and burst statistics across successive solar cycles.
Variation of geomagnetic index empirical distribution and burst statistics across successive solar cycles.
复制标题
连续太阳周期中地磁指数经验分布和爆发统计的变化。
DOI：
10.1002/essoar.10508033.1
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Bergin A
中科院分区：
文献类型：
--
作者：
Bergin A
The overall level of solar activity, and space weather response at Earth, varies within and between successive solar cycles and can be characterized by the statistics of bursts, i.e., time series excursions above a threshold. We consider nonoverlapping 1‐year samples of the auroral electrojet index (AE) and the SuperMAG‐based ring current index (SMR), across the last four solar cycles. These indices, respectively, characterize high latitude and equatorial geomagnetic disturbances. We suggest that average burst duration τ̄ $\bar{\tau }$ and burst return period R̄ $\bar{R}$ form an activity parameter, τ̄/R̄ $\bar{\tau }/\bar{R}$ which characterizes the fraction of time the magnetosphere spends, on average, in an active state for a given burst threshold. If the burst threshold takes a fixed value, τ̄/R̄ $\bar{\tau }/\bar{R}$ forSMRtracks sunspot number, while τ̄/R̄ $\bar{\tau }/\bar{R}$ forAEpeaks in the solar cycle declining phase. Level crossing theory directly relates τ̄/R̄ $\bar{\tau }/\bar{R}$ to the observed index value cumulative distribution function (cdf). For burst thresholds at fixed quantiles, we find that the probability density functions ofτandReach collapse onto single empirical curves forAEat solar cycle minimum, maximum, and declining phase and for (−)SMRat solar maximum. Moreover, underlying empirical cdf tails of observed index values collapse onto common functional forms specific to each index and cycle phase when normalized to their first two moments. Together, these results offer operational support to quantifying space weather risk which requires understanding how return periods of events of a given size vary with solar cycle strength.
The overall level of solar activity, and space weather response at Earth, varies within and between successive solar cycles and can be characterized by the statistics of bursts, i.e., time series excursions above a threshold. We consider nonoverlapping 1‐year samples of the auroral electrojet index (AE) and the SuperMAG‐based ring current index (SMR), across the last four solar cycles. These indices, respectively, characterize high latitude and equatorial geomagnetic disturbances. We suggest that average burst duration τ̄ $\bar{\tau }$ and burst return period R̄ $\bar{R}$ form an activity parameter, τ̄/R̄ $\bar{\tau }/\bar{R}$ which characterizes the fraction of time the magnetosphere spends, on average, in an active state for a given burst threshold. If the burst threshold takes a fixed value, τ̄/R̄ $\bar{\tau }/\bar{R}$ forSMRtracks sunspot number, while τ̄/R̄ $\bar{\tau }/\bar{R}$ forAEpeaks in the solar cycle declining phase. Level crossing theory directly relates τ̄/R̄ $\bar{\tau }/\bar{R}$ to the observed index value cumulative distribution function (cdf). For burst thresholds at fixed quantiles, we find that the probability density functions ofτandReach collapse onto single empirical curves forAEat solar cycle minimum, maximum, and declining phase and for (−)SMRat solar maximum. Moreover, underlying empirical cdf tails of observed index values collapse onto common functional forms specific to each index and cycle phase when normalized to their first two moments. Together, these results offer operational support to quantifying space weather risk which requires understanding how return periods of events of a given size vary with solar cycle strength.