Transcript ganglu_sec_seminar

Sun-Earth Connection:
Energy and Momentum Transfer from
the Solar Wind to the Magnetosphere
and the Ionosphere
Gang Lu
HAO/NCAR
Solar and Magnetospheric Energy Budget
Solar irradiance: 1017 W (with 0.1% variability)
Solar wind kinetic power: 1013~1014 W
Magnetospheric power: 1011~1013 W





auroral precipitation: 109 ~ 1011 W
Joule heating rate: 1010 ~ 1012 W
ring current injection: 1010 ~ 1012 W
plasma sheet heating: ~ 1011 W
Plasmoid ejections: 1010~ 1011 W
 coupling efficiency: 1~10 %
 energy input to the magnetosphere: 1023~1024 ergs
 energy released by a typical CME: 1031 ergs
Chapman-Ferraro Magnetosphere
stream
Cusp
C-F
Current
Layer
Earth
stream
Cusp
Side View
Top View
[Kennel, 1995]
Earth’s Magnetosphere
[Hill and Dessler, 1991]
Axford-Hines “Closed Model”
12
6
18
0
Possible Sources of Viscosity

B
Collision
Possible Source of Viscosity

B
Collision

B
Diffusive Entry
Possible Source of Viscosity

B
Collision

B
Diffusive Entry

B
Kelvin-Helmholtz Instability
Dungey “Open Model”
x
Southward IMF
[Lyons and Williams, 1985]
Northward IMF
[Potemra et al., 1984]
[Heppener & Maynard, 1987]
Magnetospheric Current Systems
[Kivelson and Russell,1995]
Ionospheric Currents (neglecting neutral winds)
Horizontal Current:
JH



J   N e e(Vi   Ve  )
 

 P E  Hb  E
JP
JH
Field-aligned Current:
 

j||    ( P E   H b  E )
JP
-
+
-
+
-
+

   0  E


  0 B    V
+
+

B
-
R1
R1
R1 +
+
R1
+
+
+
-
R1
R1
R1 +
+
R1
-
++
p +
-
e
+
+
+
+
-
R1
R1
R1 +
+
R1
-
++
p +

E
-
-
e
+
+
+

E
+
-
+
+
++
p +
-
e
-
+
+
+
+
-
+
+
++
p +
-
e
-
+
+
+
+
Energy Flow
Poynting’s Theorem:
 
2  
2

0 E 
B
EB

 J  E 
0


t  2 0
2 
0
Electric energy is much smaller than magnetic energy since:
0E 2
B2 V 2

 1
2
2 0 c
2
For quasi-steady-state conditions, the Poynting’s theorem reduces to:

 
J  E  0, magnetic energy
 
EB
0
J  E  0, mechanical energy
 
 J  E
mechanical or thermal energy
magnetic energy

J

E

J

J
 
JE0

E
 
JE 0
 
JE0
 
JE0

E
 
JE 0
 
JE0
 
JE0

E
 
JE 0
 
JE 0
 
JE0
 
JE0

E
 
JE 0
 
JE 0
 
JE0
 
JE0

E
 
JE 0
 
JE 0
 
JE0
Neutral Wind Dynamo Effects
Ionospheric energy dissipation/generation:
  
 
'   
J  E  J   E  J   E  U  ( J  B)
Joule heating Mechanical power
'   
where E  E  U  B is the electric field in the neutral wind frame
Joule heating with
 ' neutral
 wind:
  2
J  E   P ( E  U  B)
 2

 
  P E   P U  B  2 P U  ( E  B )
2
Field-aligned current (FAC) with neutral wind:
 

1 z2
j||  
  ( P E   H b  E )dz

sin I z
1
z2
  
 
1

  [ P (U  B )   H b  (U  B )]dz

sin I z
1
In general, neutral winds tend to reduce total Joule heating and FAC
Neutral Wind Dynamo Effects
At high-latitude regions, neutral wind has the “flywheel”
effect when there is a rapid reduction in plasma convection,
For example, due to the south-to-north turning of the IMF
Neutral wind is the major dynamo forcing at mid- and lowlatitude regions where they are mostly shielded from the
high-latitude electric field due to the magnetospheric forcing
Total Power
Wind Cooling
Mechanical PowerConvection Heating
Height-Integrated Power
Height-Integrated Field-aligned Current
Ion Drift Driven
Neutral Wind Driven
(courtesy of Mewaldt and Zurbuchen)
Magnetic Cloud
11:02
08:24
Magnetic Cloud
05:00
Magnetic Cloud
Magnetic Cloud
SEP
11:02
08:24
05:00
Impact of SEP on Upper Atmosphere
7.2x1025
Total Energy (x1024 ergs)
3.6x1024
3.2x1024
2.5x1024
1.1x1024
Total Power
Wind Cooling
Mechanical Power
Convection Heating
Height-Integrated Power
Total Power
Mechanical Power
Sun-Earth Connection:
Energy and Momentum Transfer from the
Solar Wind to the Magnetosphere and
Ionosphere
Gang Lu
HAO Seminar, 30 April 2003