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

Park, J.‐S.; Shue, J.‐H.; Kim, Khan‐Hyuk; Pi, Gilbert; Němeček, Zdenek; Šafránková, Jana

doi:10.1002/2016ja022772

Cited by 25 publications

(22 citation statements)

References 45 publications

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“…Magnetopause expansion for nearly radial IMF was also demonstrated in a statistical study based on ≃6500 magnetopause crossings [ Dušík et al , ] or on magnetic fields obtained from Geostationary Operational Environmental Satellites (GOES) [ Park et al , ]. Their results showed a systematic increase of observed magnetopause distances for radial IMF conditions, from ≃0.3 R E at 90° to ≃1.7 R E at 0° or 180° cone angles with respect to empirical models.…”

Section: Introductionmentioning

confidence: 72%

A method to predict magnetopause expansion in radial IMF events by MHD simulations

et al. 2017

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This paper presents a method for taking into account changes of solar wind parameters in the foreshock using global MHD simulations. We simulate four events with very distant subsolar magnetopause crossings that occurred during quasi‐radial interplanetary magnetic field (IMF) intervals lasting from one to several hours. Using previous statistical results, we suggest that the density and velocity in the foreshock cavity decrease to ∼60% and ∼94% of the ambient solar wind values when the IMF cone angle falls below 50°. This diminishes the solar wind dynamic pressure to 53% and causes a corresponding magnetospheric expansion. We change the upstream solar wind parameters in a global MHD model to take these foreshock effects into account. We demonstrate that the modified model predicts magnetopause distances during radial IMF intervals close to those observed by THEMIS. The strong total pressure decrease in the data seems to be a local, rather than a global, phenomenon. Although the simulations with decreased solar wind pressure generally reproduce the observed total pressure in the magnetosheath well, the total pressure in the magnetosphere often agrees better with results for nonmodified boundary conditions. The last result reveals a limitation of our method: we changed the boundary conditions along the whole inflow boundary, although a more correct approach would be to vary parameters only in the foreshock. A model with the suggested global modification of the boundary conditions better predicts the location of part of the magnetopause behind the foreshock but may fail in predicting the rest of the magnetopause.

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Section: Introductionmentioning

confidence: 72%

A method to predict magnetopause expansion in radial IMF events by MHD simulations

et al. 2017

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“…The black lines show the position of the magnetopause (solid and dashed line) and bow shock (dotted) calculated from the models of Shue et al (), Liu et al (), and Chao et al (), respectively. According to previous studies (e.g., Jelínek et al, ; Park et al, ), the magnetopause models usually underestimate the standoff distance by about 2 R E during intervals of the radial IMF. Therefore, the lines showing bow shock and magnetopause locations were shifted by 2 R E sunward of the model positions to let the sketch close to the real situation.…”

Section: Event Overviewmentioning

confidence: 88%

Formation of the Dayside Magnetopause and Its Boundary Layers Under the Radial IMF

Němeček

Šafránková

et al. 2018

JGR Space Physics

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The global structure of magnetopause boundary layers under the radial interplanetary magnetic field (IMF) conditions is studied by a comparison of experimental and simulation results. In magnetohydrodynamic simulations, the hemispherical asymmetry of the reconnection locations was found. The draped field adjacent to the magnetopause points northward in the Northern Hemisphere, but it is oriented southward in the Southern Hemisphere at the beginning of the simulation for negative IMF B x . The magnetopause region affected by the positive IMF B z component enlarges over time, and the density profile exhibit a north-south asymmetry near the magnetopause. The experimental part of the study uses the Time History of Events and Macroscale Interactions during Substorm data. We analyze profiles of the plasma parameters and magnetic field as well as the ion pitch-angle distributions. The nonsimultaneous appearance of parallel and antiparallel aligned flows suggests two spatially separated sources of these flows. We have identified (1) the inner part of the low-latitude boundary layer (LLBL) on closed magnetic field lines; (2) the outer LLBL on open field lines; (3) the inner part of the magnetosheath boundary layer (MSBL) formed by dayside reconnection in the Southern Hemisphere; and (4) the outer MSBL resulting from lobe reconnection in the Northern Hemisphere.

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“…The thickness of the magnetosheath also decreases in response to the radial IMF conditions as a result of expanded magnetopause [ Jelínek et al ., ]. The previous results show that the magnetopause moves about 2 R E sunward in comparison with the model predictions, having a bullet‐like or globally expanded structure [ Slavin et al ., ; Dušík et al ., ; Jelínek et al ., ; Suvorova et al ., , Suvorova and Dmitriev , , , Park et al ., ]. The magnetopause also shows a local time asymmetry in its size and shape [ Huang 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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Global expansion of the dayside magnetopause for long‐duration radial IMF events: Statistical study on GOES observations

Cited by 25 publications

References 45 publications

A method to predict magnetopause expansion in radial IMF events by MHD simulations

A method to predict magnetopause expansion in radial IMF events by MHD simulations

Formation of the Dayside Magnetopause and Its Boundary Layers Under the Radial IMF

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

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