A reexamination of long‐duration radial IMF events

Pi, Gilbert; Shue, J.‐H.; Chao, J. K.; Němeček, Zdenek; Šafránková, Jana; Lin, Chia Hsien

doi:10.1002/2014ja019993

Cited by 32 publications

(39 citation statements)

References 31 publications

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“…Median (1.20 nPa) and its quartiles (0.88 and 1.74 nPa) are also smaller than those for northward IMF conditions. The P SW distribution, which is more skewed toward lower values for the radial IMF, is in good agreement with the solar wind observations published in previous studies [ Suvorova et al ., ; Pi et al ., ]. This result implies that P SW distribution should be taken into account in this study.…”

Section: Observationsmentioning

confidence: 97%

“…Details of the selection criteria for radial IMF event are described in Pi et al . []. Under these criteria, 188 radial IMF events were identified from the data set for this study.…”

Section: Data Set and Event Identificationmentioning

confidence: 99%

“…To ignore small-scale disturbances in the IMF data, the time intervals that satisfy 0.8 ≤ |B X |/B < 0.9 within 15 min (three consecutive data points) were also included as parts of the radial IMF event. Details of the selection criteria for radial IMF event are described in Pi et al [2014]. Under these criteria, 188 radial IMF events were identified from the data set for this study.…”

Section: Data Set and Event Identificationmentioning

confidence: 99%

“…Previous studies found that P SW under radial IMF intervals is smaller than that under nonradial IMF intervals [i.e., Merka et al ., ; Suvorova et al ., ; Pi et al ., ; Huang et al ., ]. Since the reduction of P SW also controls the expansion of the magnetopause for radial IMF, it is unclear whether the expanded magnetopause during radial IMF conditions is solely related to the IMF orientation [ Suvorova et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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Global expansion of the dayside magnetopause for long‐duration radial IMF events: Statistical study on GOES observations

et al. 2016

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For decades, unusual locations of the magnetopause under radial interplanetary magnetic field (IMF) have been reported in many studies using in situ satellite observations. These studies have shown that the magnetopause is expanded either over all magnetic local times (MLTs) on the dayside (global expansion) or just near the noon (bullet‐like expansion) during radial IMF conditions. With limited observations near the magnetopause, the type of the magnetopause expansion is still undetermined. In this study, 19 years of dayside geosynchronous magnetic field data obtained from Geostationary Operational Environmental Satellites (GOES) are statistically processed to infer the shape of the dayside magnetopause under radial IMF conditions. The MLT distributions of geosynchronous magnetic fields for radial IMF are compared with those for northward IMF with the correction of solar wind dynamic pressure distributions between two different IMF conditions. After removal of the solar wind dynamic pressure effect, we have found that the geosynchronous magnetic field for radial IMF is smaller than that for northward IMF over almost all MLTs on the dayside regardless of magnetic latitudes and seasons. The difference between geosynchronous magnetic fields for the northward and radial IMFs supports the suggestion that the dayside magnetopause is globally expanded during the radial IMF conditions.

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Section: Observationsmentioning

confidence: 97%

“…Details of the selection criteria for radial IMF event are described in Pi et al . []. Under these criteria, 188 radial IMF events were identified from the data set for this study.…”

Section: Data Set and Event Identificationmentioning

confidence: 99%

Section: Data Set and Event Identificationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Global expansion of the dayside magnetopause for long‐duration radial IMF events: Statistical study on GOES observations

et al. 2016

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“…The radial IMF events are often found in the trailing region of high‐speed streams [ Neugebauer et al ., ; Jones et al ., ; Watari et al ., ]. On average, typical values of all solar wind parameters for the radial IMF are lower and quieter than those for other IMF orientations [ Neugebauer et al ., ; Watari et al ., ; Pi et al ., ]. The solar wind speed, the strength of the IMF, ion density, and ion temperature are reduced by 7%, 18%, 22%, and 36%, respectively [ Pi et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Evolution of the magnetic field structure outside the magnetopause under radial IMF conditions

Shue

Grygorov

et al. 2017

JGR Space Physics

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We use the Time History of Events and Macroscale Interactions during Substorms data to investigate the magnetic field structure just outside the magnetopause and its time evolution for radial interplanetary magnetic field (IMF) events. When the magnetic field drapes around the magnetopause in the magnetosheath region, an asymmetric magnetic field orientation in different hemispheres is expected. Our two‐case study reveals some conflicts with the predicted draped field configuration in the Southern Hemisphere. The magnetosheath Bz component had a different sign depending on the upstream IMF Bx component's polarity at the beginning of the radial IMF intervals. With time, the observed Bz became northward in both cases with increasing positive values through the events. The increasing value of the Bz component may be explained by two possible mechanisms: by a change of the upstream IMF and by a reconnection between magnetosheath and magnetospheric field lines. Our study shows that both mechanisms contributed to the observed changes. Thus, there was a correlation between the change of the upstream IMF conditions and an increase in the magnetosheath northward magnetic field component. The observed formation of the boundary layer near the magnetopause proves that the reconnection process was ongoing at least for a part of the time. We suggest two possible reconnection scenarios: one near subsolar point and another tailward of the one cusp due to lobe reconnection. The asymmetry of reconnection locations causes rearrangement of the magnetic field structure near the magnetopause and turns the observed magnetosheath Bz component even further into positive values.

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Kelvin‐Helmholtz wave at the subsolar magnetopause boundary layer under radial IMF

et al. 2016

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We present the first observation of the Kelvin‐Helmholtz (KH) rolled‐up vortex at the dayside magnetopause layers under a radial interplanetary magnetic field (IMF). The study uses measurements of four Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes aligned along the YGSE axis about 10 RE upstream of the Earth and located in different regions of the near‐Earth environment. THEMIS C and A serve as monitors of the quiet solar wind and fluctuating magnetosheath conditions, respectively, and THEMIS D and E observe the magnetopause and low‐latitude boundary layer (LLBL) crossings. The analysis shows the following: (1) a radial IMF changes to the southward pointing magnetosheath magnetic field; (2) dayside reconnection forms the thin but dense LLBL; (3) a large velocity shear at the LLBL inner edge excites a train of KH waves; and (4) in spite of a short path from the subsolar point (≈5 RE), one of the KH waves exhibits all features of a fully developed rolled‐up vortex.

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A reexamination of long‐duration radial IMF events

Cited by 32 publications

References 31 publications

Global expansion of the dayside magnetopause for long‐duration radial IMF events: Statistical study on GOES observations

Global expansion of the dayside magnetopause for long‐duration radial IMF events: Statistical study on GOES observations

Evolution of the magnetic field structure outside the magnetopause under radial IMF conditions

Kelvin‐Helmholtz wave at the subsolar magnetopause boundary layer under radial IMF

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