ULF Energy Transport Induced

by Magnetospheric Boundary Oscillations

Bill Lotko and Jeff Proehl Thayer School of EngineeringDartmouth College

Boundary oscillations induce internal MHD waves

Internal wave power is absorbed

Characterize:

Wave distribution

Energy transport

One-fluid, linear MHD

Cold plasma = 0 slow mode

Density

Dipole magnetic field

Boundaries L = 5, 10 and r = 2 RE

Radial boundary oscillation n = 1, m = 3, f = 6 mHz

Numerical solution, dissipation

Boundary-constrained, magnetic flux coordinates

Approach

mp E

3 6

0 L L R L rn(r,L)=n

v = 0

=

v

v

=

v = 0

Mode Structure v

v

b

b

b

1000

100

10

1

km/s

100

10

1

.1

nT

224

84

100

15

2

224

84

.5

.1

3

PHASE QUADRATURE

• Parallel – compare v and b

• Azimuthal – compare v and v

DIPOLE “LENS”

• Compressional signal

• Inner magnetosphere

• m 6

LARGE EQUATORIAL FLOWS

• v, 100 km/s at L = 7.5

Validation

100

50

0

GOES 7 – CANOPUS Mar 1990

% C

om

pA

zim

uth

, d

eg

90

-90

0 || B

φ

r

r

P +P

P +P +P

0 2 4 6

LFLR - LGOES

Ziesolleck et al. ’96

100 nT

b

b

2 nT

FLR

MP

Wave Energy Flux

9 W/m2

535 W/m2 36 W/m2

W/m2

1000

100

10

1

Compressional dipole lensEvanescent decay is counteracted by magnetic focusing at low m Outer magnetospheric, dayside Pc 5 waves can drive plasmaspheric cavity modes

Collective energy transportMode distribution + relative phases power flow and group propagation

Wave intensity energy pathways

Conclusions

Theory Program