generation of the transpolar potential ramon e. lopez dept. of physics ut arlington
TRANSCRIPT
![Page 1: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/1.jpg)
Generation of the transpolar potential
Ramon E. Lopez
Dept. of Physics
UT Arlington
![Page 2: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/2.jpg)
2
How does the solar wind drive convection?
Dungey [1961]ReconnectionMost of the potential -up to hundreds of kV
Axford and Hines (1961)Viscous interaction~20-30 kV
![Page 3: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/3.jpg)
Linear reconnection driving by the
solar wind
so
![Page 4: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/4.jpg)
Transpolar Potential Saturation (storm main phases)
See also Ober et al., (2003), Hairston et al. (2003)
![Page 5: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/5.jpg)
5
Linear regime - Geoeffective length
• The solar wind voltage across the 32 Re Y-extent of the dayside magnetopause is 204 KV for every mV/m in the solar wind
• So the actual projection of the solar wind voltage onto the X-line (which extends from terminator to terminator) must be less
• From previous figure we get TP = 46*VBz + 15Solar wind projection is 7.2 Re in Y-extent
• What does the LFM do?
![Page 6: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/6.jpg)
LFM MHD Simulation Potential
![Page 7: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/7.jpg)
Viscous Potential increases with Solar Wind speed
![Page 8: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/8.jpg)
The Potential has 2 parts (for now)Viscous Potential - Φv(V, n, Σp) We determine this for each parameter set ofruns, then subtract it from the total potential
Reconnection Potential - Φr(V, n, Σp, B)
The potential along the mergingline is the rate at which flux crosses the merging line.
![Page 9: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/9.jpg)
LFM MHD Simulation Potential
![Page 10: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/10.jpg)
10
The geoeffective
length is directly
confirmed by following
plasma flow streamlines
from the solar wind
See also Merkin et al. (2005)
![Page 11: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/11.jpg)
11
What controls the projection of the solar wind on the X-line?
• The flow is determined by the total forces acting in the magnetosheath.
• When B in the solar wind gets large, the nature of the force balance changes from a plasma pressure-dominated flow to a magnetic stress-dominated flow.
• I argue that this transition is what controls the transition to the saturation of the transpolar potential
![Page 12: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/12.jpg)
12
Y-extent of streamlines intersecting X-line shrinks for beta<1
![Page 13: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/13.jpg)
13
Geoeffective lengths give Reconnection Potential
![Page 14: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/14.jpg)
14
Density dependence• Higher density
needs higher Bz to transition to beta<1 in sheath, hence larger potentials in the saturation regime
n = 8/cc, Bz = -10 nT
n = 5/cc, Bz = -10 nT
![Page 15: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/15.jpg)
15
Conductivity dependence
• Higher ionospheric conductivity results in greater magnetopause erosion, a thicker magnetosheath, lower beta in the sheath, more diversion of the flow, hence smaller a saturation potential
Σ = 5 mho, Bz = -10 nT
Σ = 10 mho, Bz = -10 nT
![Page 16: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/16.jpg)
16
Velocity dependence• Higher solar wind
speed produces a larger pressure force in the magnetosheath
• This reduces the geoeffective length in the solar wind
400 km/s
33.9 kV
8.3 RE
600 km/s
48.7 kV
5.9 RE
800 km/s
101.3 kV
4.0 RE
Solar WindSpeed
ViscousPotential
GeoeffectiveLength
Sound Speed dependence as well!
![Page 17: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/17.jpg)
17
LFM shows expected behaviors
![Page 18: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/18.jpg)
18
How does this agree/differ with the
Siscoe-Hill model?
![Page 19: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/19.jpg)
19
What are these potentials?Φm given by solar wind electric field times the geoeffective length
Φs given by the value of the Region 1 current that weakens the dayside field by about 50%
Region 1 takes over from the Chapman-Ferraro current and exerts force balance with the solar wind
![Page 20: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/20.jpg)
The bow shock current
QuickTime™ and a decompressor
are needed to see this picture.
![Page 21: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/21.jpg)
Where does the current go?
![Page 22: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/22.jpg)
Look at the direction of the current in the volume at Z=0
Bz = -20 nTV = 400 km/sn = 5 Cs = 40 km/s
![Page 23: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/23.jpg)
The magnetic force can be the largest force in the
magnetosheath if beta<1
![Page 24: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/24.jpg)
Now we can understand the dependence on the geoeffective length
on beta and solar wind V
The larger the divergence of the flow, the smaller the geoeffective length.
Larger plasma pressure causes a greater divergence
When JxB takes over, a larger B causes a greater divergence
![Page 25: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/25.jpg)
What about closure of the
bow shock current
through the ionosphere?
![Page 26: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/26.jpg)
Thesecurrents
exist!
Lopez et al., 2008
JASTP
![Page 27: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/27.jpg)
Vx = 400km/s, Vz = -150 km/s, Bz = -15 nT
φnorth > φsouth with Σpconstant. This cannot be due to reconnection!
More current flows to the north!
€
σ p
JyDensity
![Page 28: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/28.jpg)
Driving via the Bow Shock GeneratorThe current in the bow shock is a generator
This dynamo current acts as a source for potential
Bz = -20 nT, V = 400 km/s, n = 5/ccCurrent streamlinesDensity color-coded
![Page 29: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/29.jpg)
Interhemispheric asymmetry and the Convection Reversal Boundary
location for large southward IMF
• Summer hemisphere has higher FAC, lower potential relative to winter hemisphere
• Convection reversal boundary in both hemispheres located in open field line region - not at the boundary between open and closed field lines
• This is necessary since the reconnection potential must be the same in both hemispheres
![Page 30: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/30.jpg)
Halloween storm observations are consistent
![Page 31: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/31.jpg)
31
Aug 10,2000
TextText
0 nT
0 nT
-13.5 nT nT
![Page 32: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/32.jpg)
32
Good northern hemisphere passClear convection pattern
![Page 33: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/33.jpg)
33
66.8˚66.5˚
Upward FAC
![Page 34: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/34.jpg)
Closed 2-cell convection in the polar cap driven by closure of bow shock current
DMSP F13 path
Polar cap
![Page 35: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/35.jpg)
Let’s not restrict ourselves to Bz<0Wilder et al. (2007, 2009) have shown saturation for northward IMF in SuperDarn observations
LFM saturates for large northward IMF
DMSP data do the same thing
![Page 36: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/36.jpg)
36
What about large By?
LFM exhibits saturation
![Page 37: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/37.jpg)
37
AIME and DMSP confirm it
VBy = 8 mV/mWell withinsaturation
![Page 38: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/38.jpg)
38
Sample DMSP Observations
VBy = 8.1 mV/m
ΦF13 = 99.2 kV
ΦF15 = 100.5 kV
F13
F15
![Page 39: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/39.jpg)
39
5 mho 20 mhoβ-dependent saturation onset
![Page 40: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/40.jpg)
Reconsider the Siscoe-Hill model
The value of the saturation potential is lower for east-west IMF (and lower still for northward IMF)
Therefore Region 1 currents are lower for a By-saturated potential compare to a Bz-saturated one
Neither force balance nor dayside Region 1 magnetic perturbation control the onset of saturation. However, the transition to a magnetically-dominated magnetosheath does.
![Page 41: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/41.jpg)
What about closure of the
bow shock current for large By?
![Page 42: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/42.jpg)
42
OMNI data:Bx = -5.5 nTBy = -13.2 nTBz = -2.1 nT
January 10, 1997CME-driven
storm
![Page 43: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/43.jpg)
43
Precipitating electrons - the upward current in the polar cap?
![Page 44: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/44.jpg)
44
Convection reversal coincident with the precipitation!
![Page 45: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/45.jpg)
45
![Page 46: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/46.jpg)
46
Lobe cell convection
• Birkeland Current driven by bow shock will drive convection
• All on open field lines
• Lobe cell convection may not be reconnection driven
![Page 47: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/47.jpg)
Bow shock dynamo and coupling to geospace
• The solar wind flow energy dissipated at the bow shock creates a dynamo (J•E<0). This in part powers dayside merging (Siebert and Siscoe, 2002).
• The bow shock current closes in part through the ionospheric load (J•E>0) where it can impose a potential in the polar cap and dissipate solar wind mechanical energy extracted at the shock
• This represents a means of driving ionospheric and magnetospheric convection without reconnection or viscous interaction at the magnetopause - it is a third fundamental mode of driving convection!
![Page 48: Generation of the transpolar potential Ramon E. Lopez Dept. of Physics UT Arlington](https://reader036.vdocuments.us/reader036/viewer/2022062315/56649cae5503460f94971bf0/html5/thumbnails/48.jpg)
Conclusions• The behavior of the reconnection part of the transpolar
potential can be understood in terms of basic physics (Faraday’s Law, MHD momentum equation)
• The divergence of the magnetosheath flow explains the magnitude of the linear potential, the transition to the saturated potential, and dependencies on solar wind
• The closure of the bow shock current in the ionospheric polar cap is distinct from both reconnection and the viscous interaction. It is a fundamental mechanism by which solar wind mechanical energy extracted at the shock is deposited in the geospace system.
• Thus there are three sources of ionsopheric potential: reconnection, viscous interaction, and bow shock current closure