Are steady magnetospheric convection events prolonged substorms?

Walach, Maria-Theresia; Milan, S. E.

doi:10.1002/2014ja020631

Cited by 35 publications

(71 citation statements)

References 36 publications

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“…Walach and Milan [] also found a similar change in IMF B z (without time shift) just prior to the sawtooth injection time (by ~ 25 min). If the epoch (injection) times in Walach and Milan [] can be measured by the Dst times, then their Figure also shows an average AE (= AU − AL ) that peaks at ~ 800 nT at ~ 2 h before the epoch and decreases afterward, consistent with our results of AE conditions for Ψ during and Ψ after (see Table ).…”

Section: Discussionsupporting

confidence: 76%

“…We should note here that the elevated V sw (> 500 km s − 1 ) on average for Ψ after seems to be somewhat inconsistent with the result of Walach and Milan [], who found such elevated V sw condition to be related to the occurrences of sawteeth, instead. Although the histogram for V sw in Figure does show that l = 4 occurs about 30% of the times during sawtooth intervals, this condition is only the second most probable V sw condition during STE intervals.…”

Section: Discussionmentioning

confidence: 99%

“…Although the histogram for V sw in Figure does show that l = 4 occurs about 30% of the times during sawtooth intervals, this condition is only the second most probable V sw condition during STE intervals. Closer examination of the V sw panel for sawtooth events in Figure 3 of Walach and Milan [] reveals that the average V sw near sawtooth injection (epoch time) is ~ 510 km s −1 , but that a higher average V sw (~530 km s −1 ) is actually found at both ~ 1.5 h before and ~ 1 h after the epoch time. Thus, the average V sw for sawtooth events determined by Walach and Milan [] seems to be qualitatively consistent with the underlying V sw conditions associated with STE we found here (see Figure and Table ).…”

Section: Discussionmentioning

confidence: 99%

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Magnetospheric state of sawtooth events

2016

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Magnetospheric sawtooth events, first identified in the early 1990s, are named for their characteristic appearance of multiple quasiperiodic intervals of slow decrease followed by sharp increase of proton differential energy fluxes in the geosynchronous region. The successive proton flux oscillations have been interpreted as recurrences of stretching and dipolarization of the nightside geomagnetic field. Due to their often extended intervals with 2–10 cycles, sawteeth occurrences are sometimes referred to as a magnetospheric mode. While studies of sawtooth events over the past two decades have yielded a wealth of information about such events, the magnetospheric state conditions for the occurrence of sawtooth events and how sawtooth oscillations may depend on the magnetospheric state conditions remain unclear. In this study, we investigate the characteristic magnetospheric state conditions (specified by Psw interplanetary magnetic field (IMF) Btot, IMF Bz Vsw, AE, Kp and Dst, all time shifted with respect to one another) associated with the intervals before, during, and after sawteeth occurrences. Applying a previously developed statistical technique, we have determined the most probable magnetospheric states propitious for the development and occurrence of sawtooth events, respectively. The statistically determined sawtooth magnetospheric state has also been validated by using out‐of‐sample events, confirming the notion that sawtooth intervals might represent a particular global state of the magnetosphere. We propose that the “sawtooth state” of the magnetosphere may be a state of marginal stability in which a slight enhancement in the loading rate of an otherwise continuous loading process can send the magnetosphere into the marginally unstable regime, causing it to shed limited amount of energy quickly and return to the marginally stable regime with the loading process continuing. Sawtooth oscillations result as the magnetosphere switches between the marginally stable (loading) and unstable (unloading) phases.

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Section: Discussionsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Magnetospheric state of sawtooth events

2016

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“…2.4. In the case where dayside and nightside reconnection occur together, steady magnetospheric convection can ensue (e.g., Sergeev et al 1996;Walach and Milan 2015). In the substorm of Fig.…”

Section: Substormsmentioning

confidence: 99%

Overview of Solar Wind–Magnetosphere–Ionosphere–Atmosphere Coupling and the Generation of Magnetospheric Currents

Milan¹,

Clausen²,

Coxon³

et al. 2017

Earth's Magnetic Field

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We review the morphology and dynamics of the electrical current systems of the terrestrial magnetosphere and ionosphere. Observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) over the three years 2010 to 2012 are employed to illustrate the variability of the field-aligned currents that couple the magnetosphere and ionosphere, on timescales from minutes to years, in response to the impact of solar wind disturbances on the magnetosphere and changes in the level of solar illumination of the polar ionospheres. The variability is discussed within the context of the occurrence of magnetic reconnection between the solar wind and terrestrial magnetic fields at the magnetopause, the transport of magnetic flux within the magnetosphere, and the onset of magnetic reconnection in the magnetotail. The conditions under which the currents are expected to be weak, and hence minimally contaminate measurements of the internallyproduced magnetic field of the Earth, are briefly outlined.

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“…The reason why the steady state is mostly achieved during active intervals (except for northward IMF quiet-time conditions) still needs to be explained. Recently, Walach et and Milan (2015) showed that a large fraction of SMCs can be viewed as "driven expansion phases", i.e. where the IMF remains southwards for a prolonged time interval after substorm onset.…”

Section: Introductionmentioning

confidence: 99%

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

Hubert¹,

Gérard²,

Milan

et al. 2017

Ann. Geophys.

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Abstract. We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average ∼ 0.745 GWb, standard deviation ∼ 0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of ∼ 450 km s −1 . We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals.

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Are steady magnetospheric convection events prolonged substorms?

Cited by 35 publications

References 36 publications

Magnetospheric state of sawtooth events

Magnetospheric state of sawtooth events

Overview of Solar Wind–Magnetosphere–Ionosphere–Atmosphere Coupling and the Generation of Magnetospheric Currents

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

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