European interests in GDC science: synergy,

science and lessons

I. Jonathan Rae

Mullard Space Science Lab, UCL

jonathan.rae@ucl.ac.uk

Scientific synergies with GDC

Global causes and consequences of solar wind-

magnetosphere-ionosphere-thermosphere

coupling

• Local reconnection creates global consequences

• Large-scale energy transfer via EM waves

• Field-aligned currents

Time dependence and localization

• Explosive energy release in substorms

• Auroral Acceleration

The interchange between the magnetosphere

and thermosphere through the ionosphere

• Storm-time dynamics

• Energetic particle precipitation

• Thermospheric driving

Rae e

t al. [

2009]

Rodger

et al. [

2013]

Fors

yth

et

al. [2017]

Co-PI: Graziella Branduardi-Raymont (MSSL)

• ESA/CAS with 2023 launch to study the global scale

dynamic response of the magnetosphere to solar wind

variability

• Soft X-ray Imager to image the solar wind driving

• In situ package for solar wind and IMF

• UV global auroral imager for magnetospheric dynamics

Solar wind Magnetosphere

Ionosphere Link Explorer (SMILE)

Local process with

global consequences:

Direct and Indirect

energy transfer

• THEMIS fluid scales

• Cluster ion scales

• MMS electron scales

• We need to understand energy

transfer with global context

Court

esy:

S.

Schw

art

z, c

ross-s

cale

team

Courtesy: DMSP/NOAA. Note that this data is not

coincident with the statistical Gjerloev & Hoffman

(2002) map

Large-scale field-aligned

currents: the substorm

example

• Understanding the coupling of the

magnetosphere to the ionosphere

remains an outstanding issue

• And one we are only beginning to

understand

McPherron et al., (1973)

Gjerloev & Hoffman (2002)Mu

rph

y e

t al. [

20

13

]

Single spacecraft FAC assumptions

• For a sufficiently large current sheet,

Ampère’s law can be simplified to

• Perturbation field is from FAC only

• Current is sheet-like and field

perturbation is in one component

• Spacecraft passes normally through

current sheet

• Current does not move, rotate or

change amplitude during crossing

−𝜕𝐵𝑌𝜕𝑥

= 𝜇0𝑗𝑧

Y

X

BY

Z

VSC,X

BY

jZ

Y

X

BYZ

VSC,X

BY

jZ

Lessons learned from Swarm: when are our assumptions

violated?

jZ

t

jZ

x

Pearson’s r = 1jZ,A

jZ,C

Fit gradient > 1

Cross-scale coupling provides driving

and feedback

FACs

Alternative FACs

3-7 s

Filter

27-60 s Filter >60 s Filter3-7 s; 22.5-52.5 km

17h10m 17h15m 17h20m 17h25m

-10

-5

0

5

10

FA

C D

en

sity

(mA

/m2)

Swarm-A (10 s shift)Swarm-C

17h10m 17h15m 17h20m 17h25m

0.0

0.2

0.4

0.6

0.8

1.0

Co

rr.

Co

eff

17h10m

67.9222.88

17h15m

80.1900.59

17h20m

70.9406.91

17h25m

52.8608.78

0.0

0.5

1.0

1.5

2.0

Lin

. F

itG

rad

ien

tUT

MLAT

MLT

27-60 s; 202.5-450.0 km

17h10m 17h15m 17h20m 17h25m

-1.0

-0.5

0.0

0.5

1.0

1.5

17h10m 17h15m 17h20m 17h25m

0.0

0.2

0.4

0.6

0.8

1.0

17h10m

67.9222.88

17h15m

80.1900.59

17h20m

70.9406.91

17h25m

52.8608.78

0.0

0.5

1.0

1.5

2.0

>60 s; >450.0 km

17h10m 17h15m 17h20m 17h25m

-0.4

-0.2

0.0

0.2

0.4

17h10m 17h15m 17h20m 17h25m

0.0

0.2

0.4

0.6

0.8

1.0

17h10m

67.9222.88

17h15m

80.1900.59

17h20m

70.9406.91

17h25m

52.8608.78

0.0

0.5

1.0

1.5

2.0

Fors

yth

et

al. [

20

14

]

The magnetospheric substorm: explosive

energy release into the ionosphere

Ra

e e

t a

l. [

20

09

]

Primary: Diagnosing substorm

auroral acceleration

• From ground measurements, we have

shown that substorm onset starts with

auroral and magnetic waves

– Same time, same place,same frequency,

same characteristics

• We know the particle characteristics of

wave-driven auroral acceleration

• Require observations of aurora with

simultaneous particle measurements of

the precipitating electrons (and ions)

that cause it

Hen

ders

on

et

al. [

20

09

]

Equatorward arc

Spatially periodic

Brightening (“beads”)

Beads grow and bend

plasma instability

Beads form vortex

Which breaks-up

Substorm physics from the ground and lessons

• One of the great

successes of the THEMIS

mission is the clear

ground-based component

that puts spacecraft into

context

• But also provides new

insight into

magnetospheric

processes!

Kalm

on

iet

al. N

atC

om

ms

[20

18

]

Distinguishing between drivers - Alfvén wave

driven aurora

2 RE geocentric

3 RE4 RE 5 RE

Energy flux in

~keV electron beams

Energy flux in Shear Alfvén

Waves

Shear Alfvén Waves become

dispersive as they approach

Earth, and may transfer energy to

electrons

GDC altitudes

Wave-driven acceleration

Cou

rtesy: A

nd

y K

ale

6000 km

5000 km

4000 km

3000 km

2000 km

Dense ionosphere

< 300 km

7000 km

2 RE geocentric

Auroral density cavity: 3-6,000 km

B

Quasi-static electric potentialstructures linked to density cavity

6000 km

5000 km

7000 km

2 RE geocentric

GDC altitudes

Distinguishing between

drivers – Quasi-static

potential driven aurora

Distinguishing between auroral drivers

• Quasi-static potential

drops

– mono-energetic

electron acceleration

• Shear Alfven Waves

– broadband electron

acceleration

Quasi-

static

Wave-

driven

Newell et al. [2009]

Energetic Particle Precipitation: where do

electrons go?

Ho

rne

[2

00

7],

Na

ture

Ph

ysic

sOutward

Substorm

Injection

Local

Acceleration

Precipitation

The importance of energetic particle (EPP)

precipitation on atmospheric chemistry

• Understanding a 60 year physics problem

• Understanding the natural variation in

global temperatures

• Understanding the role of EPP in the

destruction of ozone

• EISCAT 3D

Particle precipitation

Production of NOx and HOx

Change in dynamics

mesosphere & stratosphere

Destruction of mesospheric

and upper stratospheric O3

Implications for

Climate

In-situ EPP and HOx measurements

• NOAA POES measurements usually used to estimate particle precipitation

• ~835 km Sun synchronous orbit

• Numerous approximations required for scientifically useful data

• Close relationship between EPP and HOx

• Input into chemistry climate models reveal surface temperature redistribution

through EPP

Rod

ger

et

al. [

20

13

]

Clil

verd

et

al. [

20

14

]

Energetic Particle Precipitation and Polar

Surface temperatures

• Chemistry Climate models show that

when EPP are included, surface

temperature variations of -0.5 to +2 K,

relative to the no precipitation case.

• Experimentally verified during the

winter months when NOx and HOx

are long-lived

Sep

pä

läet

al. [

20

09

]R

ozan

ov

et

al. [

20

05

]

Secondary: Particles inside the loss cone

• All* currently flying instruments measure only a small fraction of

precipitation, and assume symmetry

• Able to only measure strong precipitation events

• Weak precipitation thought to be crucial

Loss Cone angle at

specific location

Typical Measurement

Examples: NOAA POES 0°

Cou

rtesy:

Cra

ig R

od

gerFull Measurement

Requirement

Feedback on magnetospheric

dynamics • Reconnection, energy loading and

electromagnetic wave penetration

and radiation belt morphology

• Don’t forget EISCAT 3D