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First panel is the EFW spin fit (10.5 s) electric field in ~ dawn-dusk direction. This measurement is dominated by waves with amplitudes >32 mV/m ptp during.

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Presentation on theme: "First panel is the EFW spin fit (10.5 s) electric field in ~ dawn-dusk direction. This measurement is dominated by waves with amplitudes >32 mV/m ptp during."— Presentation transcript:

1 First panel is the EFW spin fit (10.5 s) electric field in ~ dawn-dusk direction. This measurement is dominated by waves with amplitudes >32 mV/m ptp during during every storm as indicated by SYM H (third panel). The second panel is the dawn-dusk electric field averaged over 10 minutes from both spacecraft (superposed). This is nomally the convection electric field- but it also includes contributions fromm injection events. Notice the convection electric field is directed preferentially in the positive dawn-dusk direction- the direction of sunward convection. Notice also the convection electric field is often peaks at ~4 mV/m which is very comparable to the magnitude of the "solar wind electric field" (Vx sw x Bz sw). The solar wind electric field and the measured RBSP electric fields are largest during the main phase of geomagnetic storms and smaller during the recovery phase. The bottom panel shows the solar wind flow pressure and Bmag. These typically are enhanced at the beginning of the storm and models indicate thesubsolar magnetopause can move within ~8-9 Re durng the intial phases of the storm when ULF are strong. This may lead to effective radial transport outward and loss of particles throug magnetopause shadowing. Towards the end of the storms, during periods of lower flow pressure, when the estimated position of the magnetopause is outward many storm have large wave electric fields. These are times when relativistic fluxes increase to and often above the pre-storm levels. includes only EFW above 3.2 Re

2 SYM-H Ey (10 min ave) – Convection- Efield Ey (10.5s ave) Waves/ Injection Events ECT REPT/MagEIS Electrons May- June 2013 Storms

3 C BA AFTER BEFORE

4 SYM-H Ey (10 min ave) – Convection- Efield Ey (10.5s ave) Waves/ Injection Events ECT REPT/MagEIS Electrons May- June 2013 Storms Solar Wind Pressure Summary Almost all intervals of radiation belt increase or decrease are associated with large amplitude electric fields associated with waves 1-5 minutes Waves at the beginning of storms are often associated with solar wind pressure increases that move the magnetopause close to the Earth. These periods are aasociated with decreases. Wave occuring after the pressure enhancements often are associated with electron increases

5 Before After Slides for Beomagnetic Storm of 5/25-5/

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7 A B AFTER BEFORE Time Lag between A and B

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15 Summary: Abrupt enhancements or relativistic electrons on temporal scales of 1-5 minutes occur during the main and recover phase of geomagnetic storms. We investigate these "prompt" changes during late May and early June of 2013 when the RBSP were "closely spaced" along their orbit with time lags between 20 minutes and 70 minutes. This allows a "before" and "after" snapshot of the relativistic particles and the electric and magnetic fields. In addition, it allows us to time motions of relativistic particle fronts and the driving magnetic and electric field changes. In addition, the apogee is on the night-side. Inbound passes pass directly through the outer belts nearl local midnight. Outbound passess encounter the belts between dusk and pre-midnight local time sectors We focus on two kinds of changes... rapid temporal changes in the outer boundary of the position of the outer boundary of the outer belt and the motion of "discrete fronts" over the two spacecraft. During these times the outer beltpasses over the two spacecraft over periods of 1-5 minutes when they are spatial separated by 0.4 to 1 Re typically in azimuth but also radially.

16 The outer belts and these prompt changes occur in concert with large amplitude fluctuations in the electric fields in the dawnward direction of +/- 10 mV/m over (but ranging up to 40 mV/m) time scale of 1-5 minutes. Some of the largest electric fields are "unipolar" and directed dawnward. They dominate the azimuthal electric field component and should be especially effective in driving particles Earthward consistent with injection events. Their azimuthal correlation distance is ~1 Re. For Ey ~ mV/m fields over Δy ~1 Re~ E Δy = kV. These vales are large compared to the steady-state large scale potential across the polar caps and flucutating over time scales comparable to drift periods of relativistic electrons. These fields are comparable or shorter than Alfen travel times along a field line and may never be completely communicated to the ionosphere in steady state. The relativistic fluxes enhancments near the outer boundary of the radiation belt and the leading edge of flux enhancements exterior are associated with slight (20 nT) magnetic cavities/ dcrements. These values are a fraction of the back ground B- fields of nT. The are also associated with southward dipping of the magnetic field and/or poloidal fluctuations on time scales of minutes

17 The motion of Relativistic Particle Boundaries/Fronts/Injections East/ West and Inward and Outward. Injection Events. Betatron Acceleration or Big Spikey Fields Are the so-called cavities really cavities or are they temporal effects. The role of the magnetic cavities.. The Role of Ring Current protons injection fronts in creating the Cavities. Why do the relativistic electrons enhancments coincide with the cavities... the cavities are strongly dominated by the back ground fields. Observation: The cavities move from one spacecraft to another in concert with relativistic fluxes. Observations; They are associated with signifcant parallel Poynting flux towards the nearest hemisphere.

18 The next two slides present Probe A and Probe B data over several orbits during which relativistic fluxes change between the two passes. Probe B leads Probe A by about 70 minutes. The Plot of Probe B has been shifted by 70 minutes so that time stationary spatial structures are vertically aligned. So for example: the perigees of the spacecraft, the inner belts, the slot region are all aligned vertically. Many structures near apogee and in the outer belts are not aligned. The relativistic electron fluxes appear to "move" or "grow" or "decrease". All of these temporally varying structures are associated with strong electric fields (10-20 mV/m) over time scales of 20s to 20 minutes. Some resemble ULF waves. Others are unipolar and look like injection events. You can see the temporal changes between the two spacecraft, by rapidly flipping back and forth between the next two "BEFORE" and "AFTER" slides to create the illusion of a "movie". Use the "advance to next slide" and" go back to previous slide" ekys on your computer

19 Summary A general pattern of relativistic evolution during a major storm is an initial decrease in MeV fluxes by several orders of magntiude during the early stages followed by increases in fluxes by several orders of magnitude during the peak and recover phases. Over the entire period of the storm, the net effect may be a net increase or decrease typically by an order of magntude for a moderate storm. This study studies the storms during Spring of 2013 when the RBSP spacecaft on inbound passes passed through the radiation belts near local midnight. This is the first such study of the role of electric fields in accelerating energetic particles near local midnight since CRRES storms were not observed near midnight. Here we establish from some of the first measurements of electric fields during storms near local midnight, that strong electric fields mV/m), either waves or implusive unipolar waves, or both are present during the intervals of flux decreases decreases and also during the increases. relativistic electron enhancements associated with injection events that result in increases in flux by several orders of magnitude that alter the spatial structure of the radiation belts (broaden) There are also increases the flux at the peak of the outer belts by factors of 2-8.

20 We have investigated most of the storms of Spring 2013 but focus on those storms for which the Van Allen Probes are "closely spaced" along their orbits, that is their time lag along theirnearly identical orbits is about one hour or less. At apogee this corresponds to about 1 Re in separation mostly along the azimuthal direction.

21 Slides for 6/07 to 6/08

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27 Close-up View of Relativistic Flux Increase In the next slide, we look at a close up of one of the relativistic electron flux changes. We include a slide showing the Probe positions at this time. The increase occurs at Probe A first followed by B several minutes later. This implies propagation of the flux enhancement towards dusk at roughly km/s There is a similar time delay in associated perturbations in the magnetic field. Most of the flux enhancement are almost simultaneous between the spacecraft with time delays of less than one to several minutes. We are still looking at them

28 A: 2.0 MeV B A 3.6 MeV B A B

29 The Storm of 5/25/2013 The next series of slides presents measurements from 5/25/2013. This is another storm when the spacecraft were separated by about a 1 Re near apogee. You can see the initial decrease in REPT relativistic fluxes during the main phase and then a subsequent increase towards the end. Overall, from before the storm to after, the storm resulted in an increase in fluxes by almost an order of magnitude. This increase lasted until the next storm. The incidence of strong electric fields at the times of the decrease and increases are shown in the lower panel.

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33 Geomagnetic Storm of 6/08

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37 Brought to you from the "Cinematography Division" Space Plasma Physics Group University of Minnesota. and " Okey Dokey Productions"

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42 file+ 2013_04_RBSP_ECT_LT.png EFW E-Fields and ECT (REPT, MagEIS Electron Fluxes during Geomagnetic Storms of April 2013

43 file : RBSP_ECT_LT_EFW_E_Field_month_gd.png ord pdf EFW E-Fields and Relativistic Electron Fluxes from ECT (MagEIS and REPT) During the Geomagnetic Storms of June, 2013

44 EFW E-Fields and ECT Energetic Electrons (REPT/MagEIS) for Geomagnetic Storms of April, 2013 E-Field (duskward) 10.5 sec resolution Ey mgse

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49 Close Encounters on the Storm of 6/01/2013 (20 minute time lag RBSP B leads.) Observation of Intrusion of relativistic plasma

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53 BEGIN of TIME LAG Dispalcement for 6/07/2013

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59 END of TIME LAG DISPLACEMENT

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62 Next Slide shows Probe B (blue) sees fluxes first then Probe A (red) Implies eastward motion of relativistic electron front- Drift direction of energetic electrons? Expansion of "plasma sheet"? Orbit Plot for 6/07/2013 3:00 UT Encounter with Relativistic Electron Front

63 Next Slide shows Probe B (blue) sees fluxes first then Probe A (red) Implies eastward motion of relativistic electron front- Drift direction of energetic electrons? Expansion of "plasma sheet"? Orbit Plot for 6/07/2013 3:00 UT Encounter with Relativistic Electron Front

64 file name : rbsp_A_B_REPT_timing_6_07_2013_3UT_0.25HR_vg.png/pdf Relativistic Electron Front 6/07/2013 "Propagation" from B to A 2-4 minute delay Outbound pass Probe A leads B by ~30 minutes. Azimuthal separation; A East of B Probe A is in region of weaker B field B is in stronger Azimuthal eastward/dusk transport of energetic particle front km Separation of spacecraft ~4,000 km at 3:00UT (TBR) Probe A leads outbound Probe B trails REPT MeV electron flux

65 file name : rbsp_A_B_REPT_timing_6_07_2013_3UT_0.25HR_vg.png/pdf Relativistic Electron Front 6/07/2013 "Propagation" from B to A 2-4 minute delay Probe A leads outbound Probe B trails A REPT MeV electron flux GOES 13

66 file name : rbsp_A_B_REPT_timing_6_07_2013_3UT_0.25HR_vg.png/pdf Relativistic Electron Front 6/07/2013 "Propagation" from B to A 2-4 minute delay Outbound pass Probe A leads B by ~30 minutes. Azimuthal separation; A East of B Probe A is in region of weaker B field B is in stronger Azimuthal eastward/dusk transport of energetic particle front km Separation of spacecraft ~4,000 km at 3:00UT (TBR) Probe A leads outbound Probe B trails REPT MeV electron flux

67 Postion of Probes (colored dots) during outer edge of discrete flux decrement at 4:00 UT on 6/07/2013. Probe A leads Probe B by about 30 minues or ~ 0.5 Re.

68 Probe A leading outbound..

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