operated by los alamos national security, llc for the u.s. department of energy’s nnsa

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. Friedel1 ; S.K. Morley1 ; E. Spanswick1,2; T. E. Cayton1; E. Noveroske1 [email protected] (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. Co

nclu

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s 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)

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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.

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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.

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Los Alamos energetic electron data from the GPS constellation

4 RE circular, 50o inclination

ns08 07/1983 02/1984 BDD-I

ns10 10/1984-11/1992 BDD-I

ns18 01/1990- 12/1995 BDD-II

ns24 11/1991–11/2000 BDD-II

ns28 05/1992- 09/1996 BDD-II

ns39 07/1993–10/2005 BDD-II

ns33 04/1996–01/2007 BDD-II

ns41 12/2000 – today BDD-IIR

ns54 02/2001 – today CXD







ns55 10/2007 - today CXD


ns48 03/2008 – today BDD-IIR

100/200 keV – 10 MeV electrons

5/9 MeV – 60 MeV protons

L-v

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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 time0.1 in L

BDDBDDBlock II,IIABlock II,IIA

BDD Block IIRBDD Block IIRCXD Block IIRCXD 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

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