1. Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA U N C L A S S I F I E D A Detailed Look at Energetic Electron Dynamics in Response to Solar Wind Drivers at GPS Orbit R. H. W. Friedel 1 ; S.K. Morley 1 ; E. Spanswick 1,2 ; T. E. Cayton 1 ; E. Noveroske 1 friedel@lanl.gov (1- LANL, 2-U. Calgary) We present a case study of a very fast energetic electron dropout observed in the electron radiation belts between 1530 and 1730 UTC on 7 May 2007. The rapid loss occurred over the range L*>4 and across all observed energies above 230keV, over timescales of ~2hrs. The timescale for this event is incompatible with currently accepted loss mechanisms (magnetopause shadowing/outward diffusion or EMIC wave interaction). Initial ground-based precipitation measurements from riometers indicate a strong local time dependence (pre noon) that is statistically consistent with the occurrence location of high-latitude chorus. [A Rapid, global and prolonged electron radiation belt dropout observed with the Global Positioning System Constellation, S. K. Morley, R. H. W. Friedel, T.E Cayton and E. Noveroske, GRL submitted, December 2009] Acknowledgements: The authors thank Geoff Reeves (LANL) and Mike Henderson (LANL) for helpful discussions. Figures 1 and 2 were generated using the new SpacePy library in Python written by Steve Morley (under development at ISR-1, LANL). At and beyond geosynchronous orbit electron fluxes drop off slowly and roughly track the motion of the magnetopause - consistent with outward diffusion (Fig. 2, Panel 1). In the bottom three panels of Fig. 2 the edge of the sorted data marks the last closed drift shell for T89. Similarity between L and L* sorted data show that the Dst effect for this event is small/absent. Dropout was coincident with arrival of stream interface. Energies below ~410 keV recover strongly (plasmasheet source) while higher energies lack a recovery. Model plasmapause position indicates formation of a drainage plume, favoring EMIC loss mechanism yet this is unlikely as resonant energies would need to fall to ~230- 410 keV. Outward radial diffusion is further an unlikely candidate since transport timescales at L=4 are of the order of days. Riometer data however do indicate a significant absorption event in the 6-hour window bracketing the GPS loss even, in a MLT location consistent with statistical maps of high latitude chorus occurrence, indicating that precipitation by these waves could be a possibility. Conclusions  To our knowledge this is the fastest and most globally observed dropout reported to date (thanks to the unprecedented CXD data density).  Losses beyond geosynchronous are well correlated with magnetopause motion.  Inside GEO unrealistically large radial diffusion would be needed for losses to the magnetopause - riometer data shows possible precipitation loss by high latitude chorus.  However, current estimates of loss timescales dues to wave-particle interaction (hiss, chorus, EMIC or combination) are too low. FOR A DETAILED SURVEY OF THE LOSS RESPONSE OF THE ELECTRON RADIATION BELT IN RESPONSE TO HIGH-SPEED SOLAR WIND STREAMS, PLEASE SEE STEVE MORLEY’S POSTER (# SM11A-1571 ON MONDAY) Stream Interface Stream Interface from high-resolution OMNI data for period around 7 May 2007  Reversal in azimuthal flow velocity.  Extremely high proton density of ~60cm -3  Bz switches polarity across interface and reaches -15nT, remains variable afterwards  Dst reaches +34nT during density enhancement and then falls to -21nT (very small storm)  Kp 4-5, high convection Figure 1: Solar wind and planetary index data for the interval of 5 May to 10 May 2007. Panel 1 (top) shows KP, panel 2 Dst, panel 3 the plasma bulk speed, panel 4 the solar wind number density and panel 5 the interplanetary magnetic field z-component. Combined CXD Data L- and L*-sorted CXD data from 7 GPS Satellites for period around 7 May 2007 Figure 2: Panel 1 (top) shows (0.77-1.25 MeV) electrons sorted by T89 L; overplotted in red is the Shue et al. [1977] magnetopause standoff distance; overplotted in black is the Moldwin et al. [2002] plasmapause model. Lower three panels are 230-410 keV, 0.77-1.25 meV and 1.7-2.2 MeV energetic electrons sorted by L* (T89). Riometer absorption maps from 21 stations for period around 7 May 2007 Figure 3: Averaged riometer data surrounding the May 7th 2007 event. Each panel is a 6 hour average of data binned into 30 minute MLT and 5 degree latitude bins. Combined Riometer Data GPS Data Density Los Alamos energetic electron data from the GPS constellation 4 R E circular, 50 o inclination ns0807/1983 02/1984BDD-I ns1010/1984-11/1992BDD-I ns1801/1990- 12/1995BDD-II ns2411/1991–11/2000BDD-II ns2805/1992- 09/1996BDD-II ns3907/1993–10/2005BDD-II ns3304/1996–01/2007BDD-II ns4112/2000 – todayBDD-IIR ns5402/2001 – todayCXD ns5602/2003 – todayCXD ns6007/2004 – todayCXD ns5904/2004 – todayCXD ns6111/2004 – todayCXD ns5310/2005 – todayCXD ns5812/2006 – todayCXD ns5510/2007 - todayCXD ns5701/2008 – todayCXD ns4803/2008 – todayBDD-IIR 100/200 keV – 10 MeV electrons 5/9 MeV – 60 MeV protons L-value MLT One day – April 1, 2008 CXD instruments highly inter-calibrated – can be combined in L, time with NO adjustments. Yields unprecedented temporal and spatial coverage in region L = 4-10: 1hr in time 0.1 in L BDD Block II,IIA BDD Block IIR CXD Block IIR  21 Stations (10 Canadian, 7 Finnish, 4 Antarctic)  Increased absorption is pre noon during the time frame of the GPS dropout (middle left panel).  Riometers provide no information on the precipitating energy flux (it is an integrated effect above 30keV) but they identify the spatial extent of the precipitation region and also its lifetime.  Resolution 0.1 in L and 1hr in time  No adjustments in raw count data needed