Scott Thaller

Van Allen Probes EFW meetingUniversity of Minnesota

June 10-12, 2014

Electric field data quality “checklist”• The electric field data are spin fit • The VscXB field is subtracted• The field in the co-rotating frame is calculated and subtracted. • The antenna length correction is applied, but small ~1.• Data during eclipse times are removed• Data during charging intervals (Vsc < 0) are removed.• Data during spacecraft maneuvers and probe bias current

sweeps are removed • The wave forms have been inspected for the storms to check

for wake effect; wake effect intervals identified and removed• Probe bias currents for the interval are good.

(𝑉𝑠𝑐×𝐵

) 𝑦+𝐸

𝑐𝑜𝑟𝑜𝑡𝑦

𝐸𝑦 (𝑠𝑝𝑖𝑛 𝑓𝑖𝑡 ) (𝑚𝑔𝑠𝑒 )(𝑚𝑉 /𝑚)

The Ey data for the fit is fromNear Perigee: R < 2.0 REQuiet times: -10 <Dst <10From Sep 27, 2012 to Sep 1, 2013

Fit between measured and calculated Ey (mgse)

Ey (m

gse)

(mV/

m)

Ey (m

gse)

(mV/

m)

Corot. frame

Note the good agreement between the calculated (VscXB)y + Ecorot.y and the actual measured Ey (mgse) field near perigee .

Some residual is present, but we can still resolve some real E field, for example, there is some wave activity that appears to be present in this example.

RBSP A June 16, 2013 11:00 -22:30 UT

From Mozer 1973 The Ionospheric Dynamo is due to the atmospheric tides, and the induced ionospheric motion due to collision with the neutral atmosphere

𝐸𝑚≈𝐸 𝐼 √1/𝐿3

𝐸𝑚≈1.5 (𝑚𝑉 /𝑚 ) √ 11.53

≈0.82𝑚𝑉 /𝑚

𝐸𝑚≈2.0𝑚𝑉 /𝑚√ 133 ≈ 0.66𝑚𝑉 /𝑚

We may want to include the ionospheric dynamo E field in the EFW calibrations in the future.

At low L there is an electric field ~0.5-0.8 mV/m due to atmospheric tides. This is comparable to the residual field at low L and so may need to be added to the calibration.

Van Allen Probe A, June 10, 2013

Out bound

In bound

Note the asymmetries between the in and out bound portions of the orbit. In bound electric fields do not appear to penetrate to as low L shells as during out bound passes. But densities seem to erode more significantly to lower L on the in-bound parts of the orbit.Note the residual E field at low L, <2 RE.

May 15 –July 24 , 2013

Van Allen Probe A

Dens

ity (c

m-3

)O

ut b

ound

Ey-m

gse

(mV/

m)

Coro

tatin

g fra

me

Out

-bou

ndDe

nsity

(cm

-3)

In b

ound

Ey-m

gse

(mV/

m)

Coro

tatin

g fra

me

In-b

ound

Kp 7 to 9- Kp 6,6+,7-Kp 4,4+,5-Kp 5,5+,6-Kp 3,3+,4-Kp 2,2+,3-Kp 1,1+,2-Kp 0,0+,1-

Van Allen Probe A

Ey corot. frame

60-300 keV protons n flux

Plasma Density

A region of strong dawn-ward electric field is observed at low L (<3 RE) in the post midnight sector during the major storm on June 1, 2013. This region of dawn-ward field corresponds to the sharp decrease in ring current proton number flux and the sharp boundary of the plasmapause. Such dusk-ward electric field could be shielding

Ey Solar Wind

Dst

Δ𝐵𝐵𝑜

=2𝐸3𝐸𝑚

Ey – mgse

Ey – mgse (5 min ave.)

mV/

mm

V/m

mV/

m

Ring current energy change rate (J/s) 𝑑𝐸

𝑑𝑡 =32𝐸𝑚

𝐵𝑜

𝑑𝐷𝑠𝑡𝑑𝑡

𝐸𝑦=−𝑉 𝑥×𝐵𝑧

Dessler and Parker [1959]

E = energy of ring current particlesEm = energy of earth’s dipole above the surfaceBo = surface B field intensityΔB = disturbance field

Solar wind dusk-ward electric field (a), enhancements in magnetosphereic waves (b) and dusk-ward convection field (c) enhance during the same interval, as well as the rate of ring current energization (d).

(a)

(b)

(c)

(d)

(e)

Ey (m

gse)

(c

orot

ating

fram

e)

(mV/

m)

60-300 keV Protons

Dst

60-3

00 k

eV p

roto

nPr

essu

re

nPa

L sh

ell

L sh

ell

L sh

ell

Plas

ma

Dens

itycm

-3

Plasma density

Van Allen Probe AInboundMay 26 - June 6, 2013 Ey

The Ey (mgse) electric field in the co-rotating frame and corresponding plasmasphere erosion and ring current proton pressure increase. (the pressure shown here is a rough preliminary calculation)

Extras

Coverage, or number of points per RE – Kp binRBSP A Sep 27, 2012 – Apr. 15, 2014

Kp 7 to 9- Kp 6,6+,7-Kp 4,4+,5-Kp 5,5+,6-Kp 3,3+,4-Kp 2,2+,3-Kp 1,1+,2-Kp 0,0+,1-

Figure courtesy John Wygant

Spatial integration of E and Ey along RBSP A trajectory for June 1, 2013 02:00-08:30 UT

About 20 kV

25 kV

25 kV

Ey (mgse) (mV/m)

40 mV/m

4 km/s V spacecraft

∫𝐸⋅𝑉 𝑠𝑐𝑑𝑡

∫𝐸 𝑦⋅𝑉 𝑠𝑐𝑑𝑡