2018 Mini GEM, Washington DC

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Mini GEM 2018

The 2018 Mini GEM was held on December 9th, 2018 at the Hilton Alexandria Old Town in Alexandria, Virginia

Session 1 GEM challenge event

Scheduled presentations

Sarah Vines: Sarah talked about the location of the magnetopause given by the Shue model and the configuration of the X-line given by Trattner’s maximum shear angle model. Both models are based on solar wind input and the results are consistent with spacecraft measurements. Sarah also talked about the magnetopause motion, thickness, current density, shear angle, and the difference in plasma beta across the magnetopause. She identified the presence of cold ions and calculated the power spectra of the magnetosheath magnetic field.

Yuxi Chen: Yuxi compared properties of the magnetopause and the magnetosheath of MHD-EPIC, Hall MHD, and ideal MHD. These models provide similar magnetopause location and X-line extent, and reconnection jet speeds. But the Hall MHD model produces more structures/variability at the magnetopause than the MHD-EPIC.

Jeff Broll: Jeff discussed a way to identify LMN coordinates through performing MVAB and MDDB in an unsupervised manner.

Marcos Silveira: Marcos investigated whether the transients seen by MMS spacecraft during the magnetopause crossing are FTEs. He exemplified classic FTE signatures in aspects of magnetic field and particle properties and found that none of the seen transients fit into classic FTEs.

Open discussion

Yu Lin: Yu showed global hybrid simulations from ANGIE3D.

Naritoshi kitamura: Naritoshi presented the dependence of the statistical location of X-line on dipole tilt (seasons) and IMF Bx. He found that the X-line location can shift by a few Re in the north-south direction as seasons and IMF Bx change. The challenge event, however, has a smaller displacement from the equatorial plane than what the dependence suggests.

Discussion topics

- Quantitative metrics are needed to perform model/model and model/data comparisons and specific entropy could be used as a metric.

- Coordination is needed between modellers and observers to complete challenge event studies.

- For power spectra, it will be more useful to compute the spectral slope rather than comparing the spectra.

- The FTE presence and properties should be checked in the model.

Session 2: Dayside transients - local vs global effects on the magnetopause

Scheduled presentations

David Sibeck: David reviewed the impacts of hot flow anomaly (HFA). HFA produces pressure variations in the magnetosheath, traveling magnetopause waves, and traveling convection vortices in the ionosphere. In a fortuitous conjunction events, HFA causes a “bulge” of the magnetopause that is 10-20 Re long in the north-south direction, 2-4 Re in the east-west direction, and 1-9 Re in the sunward direction.

Martin Archer: Martin presented two major impacts of high speed jets. One is compressing the current sheet and triggering magnetic reconnection. One is creating indentation of the magnetopause. As magnetopause rebounds, a surface wave forms. He notes that the time scale of indentation/rebounding might be controlled by collective properties of HSJ or eigenvalues of the magnetopause surface waves. He presents one event where HSJ have a broad power spectrum in frequency while the magnetopause motion and ULF waves have a narrow spectrum.

Xochitl Blanco-Cano: Xochitl discussed how cavitons and spontaneous hot flow anomalies (SHFAs) can modify the bow shock, magnetosheath and possibly the magnetopause. Vlasiator simulations have shown that the arrival of SHFAs can cause shock weakening and the formation of magnetosheath cavities. More work is needed to understand if SHFAs can cause waves at the magnetopause similar to the ones produced by HFAs.

Open discussion

Katarina Nykyri: Katariina presented one event where HSJs likely drive a substorm. This implies that localized transients (though there might be many in quantity) can have global effect.

Discussion topics

- Does the transient size control the size of response?

- How do we differentiate between direct and seeding response.