GEM Dayside Kinetics Challenge

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Observations:

Solar Wind Conditions

Provided by: Rishi Mistry (Imperial College) and Heli Hietala (UCLA).
  1. Summary of the solar wind analysis:
     The interval of interest starts with IMF discontinuity S1 and ends with IMF discontinuity S2. The average solar wind conditions (GSM) from the solar wind analysis Excel file are:

    |B| (nT) Bx (nT) By (nT)Bz (nT)Vx (km/s)Vy (km/s) Vz (km/s)n (/cm3) Ti (eV)Te (eV)alpha fraction
    before S1 6.4 2.7 -2.5 -5.1 -360.1 5.0 -2.2 8.2 8.2 10.3 0.03-0.05
    S1-S2 6.2 0.1 -0.6 -5.7 -361.3 3.7 -11.1 8.3 7.4 10.3 0.05-0.08
    simulate 6 0 0 -6 -365 0 0 9.5 9 9 0

    Timing: Discontinuity S2 behaves consistently at all four spacecraft, and its expected arrival time at subsolar bow shock is around 2:45 UT (between 2:39 UT and 3:04 UT). This is consistent with the smooth rotation seen by MMS in the magnetosheath between 2:50 UT and 3:05 UT.

    Discontinuity S1, however, gives very different normal vectors at different spacecraft (it may have been non-planar), and hence wildly different arrival times: perhaps around 2:29 UT, but the spread is from 1:11 UT to 3:10 UT. In MMS magnetosheath data (about 2:15 UT ->) there is no clear evidence for a sharp rotation. The conclusion is that either

      a) S1 arrived earlier, and/or

      b) crossing the bow shock, S1 turned into such a smooth/weak change in the field direction that it is not clear in the MMS near-magnetopause data.


    Therefore it is possible that the IMF orientation during (some of) the MMS reconnection observations between 1:50 and 2:35 UT may have been a bit different from purely southward (see the above table), but that is uncertain and the effect is probably relatively small.
  2. Detailed analysis of the solar wind conditions (Excel file).
    Excel work sheets have solar wind conditions, bow shock arrival times for each solar wind monitor (ACE, Wind, ARTEMIS P1 and P2) and discontinuity normals.
  3. Density and composition:
    • ACE SWEPAM gives alpha to proton ratio of ~0.05 between S1 and S2, and ~0.03 before S1.
    • Wind SWE gives alpha number density of ~0.6/cc between S1 and S2, and ~0.4/cc before S1. These correspond to ratios of 0.08 and 0.05.
    • Wind 3DP (on-board moments) gives alpha number density of ~0.45/cc between S1 and S2, and ~0.25/cc before S1. These correspond to ratios of 0.06 and 0.03.
    • In summary: before S1 there was 3-5% of alphas, and between S1 and S2 there was 5-8% of alphas.
    • Simulation approach: Assume pure proton plasma and use n=9.5/cc instead of 8/cc because that better represents the mass density, which actually determines the ram pressure and the magnetopause location. If n_total = 8.3/cc and 5% is alpha particles, then the mass density is 8.3*(0.95 + 4*0.05) amu/cc = 9.54 amu/cc.
  4. Plots of solar wind conditions from ACE, Wind, and the two ARTEMIS spacecraft (GSE)

    Data plot of ACE solar wind Data plot of WIND

    Data plot from ARTEMIS P1 Data plot from ARTEMIS P2

Magnetospheric conditions

Modeling results

CCMC Contact: Lutz Rastaetter
Last modified: Mar. 10, 2017