[GEM] THE GEM MESSENGER, Volume 28, Number 38

Newsletter Editor editor at igpp.ucla.edu
Mon Aug 13 19:28:06 PDT 2018


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     THE GEM MESSENGER
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Volume 28, Number 38
Aug.13,2018

Announcement submission website: http://aten.igpp.ucla.edu/gem/messenger_form/

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Table of Contents

1. GEM Interhemispheric Approaches to Understand M-I Coupling (IHMIC) Focus Group: 2018 Workshop Report

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1. GEM Interhemispheric Approaches to Understand M-I Coupling (IHMIC) Focus Group: 2018 Workshop Report
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From: Hyomin Kim, Robert Lysak, and Tomoko Matsuo (hmkim at njit.edu)

The GEM focus group, “Interhemispheric Approaches to Understand M-I Coupling (IHMIC)” addresses questions as to how to incorporate interhemispheric symmetry/asymmetry in geomagnetic fields and their effect on M-I coupling in observations and modeling/simulations. Studies have shown the interhemispheric differences which are manifested in various signatures: e.g., large-scale current systems, auroral forms, waves, ion upflow, outflow, particle precipitation, high-latitude convection and thermospheric winds. The focus group held two sessions on Friday, June 22nd at the GEM 2018 Workshop: one stand-alone session and one joint session with the “3D Ionospheric Electrodynamics and its impact on MIT coupling (IEMIT)” focus group.  

Session 1

The first session covered various types of interhemispheric differences: geomagnetic fields, current systems, auroras, radio emissions, etc. Michael Hartinger presented measurements from a recently completed chain of magnetometers on the East Antarctic Plateau, combined with magnetically conjugate stations on the west coast of Greenland. They used these measurements to make interhemispheric comparisons of current systems with different temporal and spatial scales. Multi-point ground magnetic perturbation observations show north-south hemisphere amplitude differences that vary with frequency. He suggested that more modeling and observations are needed to understand these differences. Kristian Snekvik presented interhemispheric differences in current systems and auroral signatures in association with the IMF By component. The flux asymmetrically added to the lobes results in a nonuniform induced By in the closed magnetosphere. The study discussed the mechanisms related to IMF By transported from open to closed field by tail reconnection and induced by asymmetric loading of the magnetospheric current systems. Observations of medium frequency (MF) radio emissions at multiple stations were discussed by James LaBelle. The emissions are emitted from the poleward expanding arc at substorm onsets. Therefore, this type of measurements can contribute to understanding hemispheric asymmetries by observing auroral radio emissions in the conjugate hemispheres. His group is now considering a new radio emission observation site in Canada conjugate to the existing station at South Pole. Using conjugate pairs of magnetometers (SYO in Antarctica and TJO in Iceland, and WSD in Antarctica and SNKQ in Canada), Robert McPherron performed a cross-correlation analysis to show that there are differences in Pi1 and Pi2 pulsation onset times and waveforms between hemispheres. The study found onsets occur later in sunlit hemisphere (difference is ~36 sec). Inter-hemispheric asymmetry in high-latitude FAC modes of variability associated with two categories of solar wind drivers: (1) high-speed streams and (2) transient flow related to coronal mass ejection are characterized by Yining Shi using empirical orthogonal function (EOF) analysis. Northern hemisphere shows stronger dayside By effect and more spatially defined EOFs. Northern hemisphere higher-order EOFs are more correlated with drivers and indices. An equinox event study (September 2017) shows stronger NH FACs for 75% of the time. Shin Ohtani presented a statistical comparison of the FAC and electron precipitation between the dark and sunlit hemispheres on the night side.  In the dark hemisphere, both the R1 and R2 currents are more intense, and electron precipitation is more energetic and intense, and estimated ionospheric conductance is higher than in the sunlit hemisphere. Apparently, the system configures itself in a self-consistent way in each hemisphere, and more energy is dumped into the dark ionosphere than into the sunlit ionosphere.  He discussed the result in terms of the interhemispheric asymmetry of the electron number density in the auroral acceleration region, and suggested that a local process affects a global structure of the M-I coupling. Tetsuo Motoba reported on "Asymmetric evolution of interhemispheric preonset aurora." He showed a preonset auroral arc event that was observed simultaneously at a geomagnetically conjugate Iceland-Syowa pair. Whereas the conjugate preonset auroral arc had some similarities, the temporal luminosity evolution was slightly different between both hemispheres. The associated Pi1 wave activity on the ground was also asymmetric. These results imply that the ionoshpere (auroral acceleration region) may play an active role in the evolution of the interhemispheric preonset aurora and related Pi1 pulsations.

SESSION 2

Although some speakers from the IEMIT FG did not necessarily discuss interhemispheric aspects, the joint session was arranged to promote studies of interhemispheric symmetries/asymmetries in MIT coupling processes. Robert Clauer presented initial results from the Antarctic 40- degree magnetic meridian that his group recently established. His study focuses primarily on comparison of magnetic field variations from the ground instruments, showing examples of agreements and disagreements between the conjugate locations in the context of the strong IMF By component. The results are also compared with the Weimer Ionosphere Model to show the detailed view of the inherhemispheric asymmetry in which asymmetries are more pronounced with larger By. Denny Oliveira investigated the effects of shock impact angle on ground geomagnetic field variations (dB/dt), generally associated with the generation of geomagnetic induced currents, in different latitude regions. In general, it is found that nearly frontal and high-speed shocks trigger large dB/dt enhancements. However, out of over 500 events, his study found at low latitudes 9 shocks which are associated with dB/dt > 100 nT/min. All shocks had high speed and struck the magnetosphere almost head-on, and all stations were located around noon local time. Since 100 nT/min has been recognized as a risk factor to power grid equipment, the study suggests space weather forecasters should take the shock impact angle when assessing risk prediction to human assets on the ground. Michelle Salzano statistically investigated substorm onset-associated Pi1B pulsations using ground search-coil magnetometers at conjugate ground stations. Using spectrograms of search-coil data, 154 events from South Pole and Iqaluit stations have been visually identified that are simultaneous at both stations; AL indices and SuperMAG fluxgate data have been analyzed to ensure correlation with substorm onset; a third pass of the data is currently being performed in the hopes of unearthing more events to fill in seasonal gaps; once this third pass concludes, onset time analysis will begin. Hyun-ju Connors presented satellite observations on May-15 2005 showing that thermospheric density and downward Poynting flux intensified near the cusp region shortly after a sudden enhancement of solar wind dynamic pressure. OpenGGCM-CTIM show that ionospheric Joule heating increased abruptly in the same region where the high density and Poynting flux are observed. Additionally, a pair of FACs are enhanced near the strong Joule heating region. Model experiments show that Psw enhancement is the primary source for the Joule heating and neutral density enhancements, but IMF By modulates the level of enhancement. The combined and coupled effect of Psw and IMF has a much more significant effect than the addition of the individual effects. Thus, the magnetosphere–ionosphere responds non-linearly to the coupling of different solar wind drivers. Doga Can Su Ozturk investigated the SI+ (positive sudden impulse associated with magnetospheric compression) and SI- (negative with decompression) processes and their effects on the geospace system using BATS-R-US global MHD code. The study showed that a two-step response existed in the magnetosphere and the ionosphere. The magnetospheric responses were in the form of vortex-like flows. Both in the decompression and compression cases, the initial response was related with the magnetopause boundary deformation and perturbed pre-existing flows. The second response was related with the magnetospheric flow vortices with opposite senses of rotation on the dawn and dusk sectors. These perturbed magnetospheric flows were associated with Field-Aligned Currents (FACs) during both stages and mapped to the ionosphere. Moreover, the ionospheric response due to these perturbation FACs preserved the two-step behavior, since the transient currents reversed directions between stages. The dawn-dusk asymmetry seen in the magnetospheric flows were also maintained. The GITM simulations driven with the high-resolution MHD model results showed that this behavior was further conveyed to the thermosphere, through ion-neutral coupling. Kevin Pham discussed the thermospheric impact on the magnetosphere in the one-way coupled system using various models including the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic simulation, the Ionosphere/Polar Wind Model (IPWM), The Thermospheric General Circulation Model (TIEGCM), and the ionospheric potential solver. One of his conclusions is that magnetosphere has a short memory in the standalone LFM and LFM coupled to ionosphere-thermosphere (CMIT). More specifically, the magnetospheric outputs of potential and field aligned currents do not remember differences in disruption. Precipitation passed to TIEGCM does not have any memory of the disruption even when the IMF Bz component is varied in the system. On the other hand, both F-region ionosphere and thermosphere remember the disruption 12+ hours later. This memory is carried into the one-way coupled polar wind model (IPWM). It is anticipated that when IPWM is two-way coupled into CMIT, the memory in outflow will impact magnetospheric memory. 


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