Definitive Mapping in the Late Growth Phase

Definitive Mapping in the Late Growth Phase E. Spanswick, E. Donovan, J. McFadden, T.-S Hsu, C.-P Wang, S. Zaharia, L. Kepko, A. Lui, V. Angelopoulos

Precipitating Ions Why use ions?? • The large scale morphology of ion precipitation is believed to be a consequence of strong pitch angle scattering due to field line curvature. • The observed proton aurora is ubiquitous and extremely stable. • If the footprint of the proton aurora is purely a consequence of conditions in the magnetotail (i.e. location of sufficient stretching) then observations of the proton aurora can be used as an indicator of where these conditions map to in the ionosphere.

Dcurvature/DL Jeff Grant

Precipitating Ions Connecting in situ with ground-based measurements Start in the topside ionosphere… • We know which particles are precipitating (we can see the loss cone) • Where we know the mapping

Precipitating Ions Topside Ionosphere  Ground Predicting proton auroral luminosity from topside ionospheric ion data From 114 FAST passes near the Gillam MSP (with good proton auroral measurements), we have determined that… using FAST ESA measurements of down going ion energy flux we can derive the proton aurora luminosity at Gillam. integrated downward ion energy flux (erg cm-2 s-1) 486nm Intensity (R) = 65 X

Plasma Sheet Ion Fluxes Plasma Sheet  Ground Do the SAME calculation with THEMIS ESA. • **ASSUME strong pitch angle diffusion** • Find the size of the loss cone (FGM) • Find the total energy flux of ions in the loss cone (in the ESA energy range) • Since THEMIS doesn’t resolve the loss cone in the plasma sheet we assume that the distribution is isotropic within the 10degrees around field aligned.

Predicted Proton Auroral Luminosity The basis for a model free mapping • Given THEMIS-ESA and FGM data, we can estimate the proton auroral luminosity that would result from the particle population present at the satellite….. • this can be used as a model free mapping technique • How?? • If the luminosity @THEMIS is greater than the observed proton auroral brightness on the ground, we KNOW that the spacecraft maps inside the b2i. • If the luminosity @THEMIS is much lower than the observed proton auroral brightness on the ground, we KNOW that the spacecraft maps outside of the region of bright proton aurora.

Model Free Mapping Statistical location of the bright proton aurora Data used (days) Typically tailward of the of bright proton aurora 71.65 26.64 21.44 14.59 10.42 Typically inside the b2i 6.99

Model Free Mapping Statistical location of the bright proton aurora Data used (days) 2.81 Growth Phase Times* 1.13 0.82 0.60 0.34 0.32

Model Free Mapping Statistical location of the bright proton aurora Growth Phase Times* All data

The Transition Region Evolution from Late Growth Phase to Expansion Phase

1) The peak in proton auroral brightness almost always maps to inside 9 Re. 2) The ion IB almost always maps to outside 6 Re. 3) The onset arc almost certainly maps to inside 10 Re. From last presentation: How can we address the “almost” in result 3? Ask the question: “What is the probability that a 10-15 Rayleigh Hbeta aurora occurs on field lines threading the neutral sheet tailward of X (e.g., 8, 9, 10, etc.) Re in the late growth phase?” …. Answer is <10% (and 0 for tailward of 12 Re). 4) We now can identify the Kappa Boundary and location relative to the IB in the THEMIS in situ data for a few events… Thank you!

Model Free Mapping Event Specific -- 20090408 The peak in the proton aurora at Fort Smith prior to onset is on the order of 20R*. The proton aurora luminosity derived from THEMIS-D ESA is on the order of 3-4R prior to onset. **The onset arc (embedded in bright proton aurora) must be inside of THEMIS-D**

Definitive Mapping in the Late Growth Phase