Magnetospheric sawtooth events during the solar cycle 23

Cai, X.; Clauer, C. R.

doi:10.1002/2013ja018819

Cited by 21 publications

(30 citation statements)

References 49 publications

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“…Figure shows the time series of spatially averaged velocity magnitude for the two regions, with the blue line indicating a calculation of the solar wind driving,

E_{MP} = v_{x}^{4 / 3} B_{t}^{2 / 3} \overset{8 / 3}{\sin} ((/, θ) 2)

, where B t is the magnitude of the component of the IMF transverse to the magnetopause and θ is the IMF clock angle (

θ = \arctan (B_{y} / B_{z})

). The units of this function are discussed in Cai and Clauer [], where the authors empirically determined that a normalization factor of 100 makes the unit Wb/s. As discussed in section 1, this product characterizes the dayside merging rate and has been shown to correlate well with measures of magnetospheric activity [ Newell et al , ].…”

Section: Data Presentationmentioning

confidence: 99%

Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

et al. 2015

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Convection observations from the Southern Hemisphere Super Dual Auroral Radar Network are presented and examined for their relationship to solar wind and interplanetary magnetic field (IMF) conditions, restricted to periods of steady IMF. Analysis is concentrated on two specific regions, the central polar cap and the dayside throat region. An example time series is discussed in detail with specific examples of apparent direct control of the convection velocity by the solar wind driver. Closer examination, however, shows that there is variability in the flows that cannot be explained by the driving. Scatterplots and histograms of observations from all periods in the year 2013 that met the selection criteria are given and their dependence on solar wind driving is examined. It is found that on average the flow velocity depends on the square root of the rate of flux entry to the polar cap. It is also found that there is a large level of variability that is not strongly related to the solar wind driving.

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“…Figure shows the time series of spatially averaged velocity magnitude for the two regions, with the blue line indicating a calculation of the solar wind driving,

E_{MP} = v_{x}^{4 / 3} B_{t}^{2 / 3} \overset{8 / 3}{\sin} ((/, θ) 2)

, where B t is the magnitude of the component of the IMF transverse to the magnetopause and θ is the IMF clock angle (

θ = \arctan (B_{y} / B_{z})

Section: Data Presentationmentioning

confidence: 99%

Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

et al. 2015

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“…[], dΦ/d t “represents the rate magnetic flux is opened at the magnetopause.” If one wishes to express this as a real physical quantity in units of Wb/s, d Φ /d t in equation must be multiplied by a normalizing factor α . By comparing d Φ /d t with open magnetic flux in the polar cap, Cai and Clauer [] estimated this factor to be α = 10 4 km 2/3 s 1/3 nT 1/3 during periods of disturbed magnetospheric conditions associated with so‐called “magnetospheric sawtooth events.” Note that d Φ /d t × α would give magnetic flux transfer rate in units of mWb/s, which is easily converted to Wb/s. The reliability of this estimated normalization factor is not clear, especially when considering the entire range of possible solar wind and magnetospheric conditions, and thus, it is not applied in this paper.…”

Section: Resultsmentioning

confidence: 87%

GPS TEC variations in the polar cap ionosphere: Solar wind and IMF dependence

2016

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This statistical study examines the solar wind dependence of total electron content (TEC) variations arising from mesoscale (tens to hundreds of kilometers) structuring of the polar cap ionosphere. Six years of TEC measurements were collected from five high‐data rate Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN), from which high‐resolution magnetic local time‐latitude maps of TEC variation occurrence rate and amplitude were created. Ionosonde radars were used to identify TEC variations arising from ionization of the E and F region ionospheres. Statistical TEC maps were examined as a function of solar wind and interplanetary magnetic field (IMF) measurements. Statistical results showed that occurrence rate of TEC variations was highest in localized dayside regions, with exact local time and latitude of peak occurrence depending primarily on the dayside coupling rate of the solar wind and magnetosphere, as well as IMF orientation and magnitude in the Y‐Z plane. Occurrence of TEC variations throughout the polar cap increased with solar wind‐magnetosphere coupling rate and IMF magnitude. The solar wind dependence of occurrence rate largely reflected the location and rate of dayside magnetic reconnection and subsequent particle precipitation and polar cap convection. Amplitudes of TEC variations were largest around noon and increased throughout the polar cap with increased solar wind‐magnetosphere coupling rate. These statistical results improve upon the existing observational picture of the polar ionosphere and will potentially facilitate development of models and techniques for mitigating impacts of the polar ionosphere on navigation signals and communication links.

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“…The numbers in parentheses after each of the listed parameter ranges are the MS indices shown in . Bolded‐black entries are the ones that match the corresponding MS indices in associated with the out‐of‐sample STEs found in the extended STE list by Cai and Clauer []. The bolded entries thus validate the MS specifications given in .…”

Section: Discussionmentioning

confidence: 99%

“…If the loading process happens too quickly, the system can rapidly become fully unstable and subsequently release too much energy to remain marginally stable. Thus, the association of STEs with only a small range of eroded dayside magnetopause magnetic flux (10 6 –10 6.5 Wb) as found by Cai and Clauer [] may actually be related to the notion that both the loading and unloading processes for STEs are limited.…”

Section: Discussionmentioning

confidence: 99%

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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Magnetospheric sawtooth events during the solar cycle 23

Cited by 21 publications

References 49 publications

Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

GPS TEC variations in the polar cap ionosphere: Solar wind and IMF dependence

Magnetospheric state of sawtooth events

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