Effects of Lower Magnetic Fields on the Thermosphere-Ionosphere

1/19
<strong>Effects</strong> <strong>of</strong> <strong>Lower</strong> <strong>Magnetic</strong> <strong>Fields</strong> on
the Thermosphere-Ionosphere
Erdal Yiğit 1 , and Aaron J. Ridley 1
1 University <strong>of</strong> Michigan, Ann Arbor, USA
email: erdal@umich.edu
Sunspot Workshop
Sunspot, New Mexico, USA, 19 - 22 September 2011
◭◭
◮◮
◭
◮
Back
Close

Contents
1 Introduction - Science Question 3
2/19
2 Introduction - Earth’s <strong>Magnetic</strong> Field 4
3 Model Description 6
4 Model Configurations 8
5 Model Simulations 10
6 Model Results 11
7 Electron Density Distributions 12
8 Temperature and Neutral Flows 14
9 Meridional Flow & Electron Density 15
10 Temperature Variations 16
11 Summary and Conclusion 17
◭◭
◮◮
◭
◮
Back
Close

Introduction - Science Question
This Study
How does
3/19
decreasing magnetic field impact
the thermosphere-ionosphere
system
◭◭
◮◮
◭
◮
Back
Close

Introduction - Earth’s <strong>Magnetic</strong> Field
• Tilted <strong>of</strong>fset dipole field
• Variable: magnitude and distribution
• Magnitude decreased in the last 150 years 10-15% and still decreasing...
• Geophysical (dynamics, chemistry) and biological impacts (pigeons,
bees).
4/19
◭◭
◮◮
◭
◮
Back
Close

Research Strategy & Outcome
This study
A General Circulation Model that simulates
the thermosphere-ionosphere self-consistently
+
<strong>Lower</strong> the magnetic field density
↓
Quantify the changes in the
thermosphere-ionosphere
5/19
◭◭
◮◮
◭
◮
Back
Close

Model description-I
Global Ionosphere Thermosphere Model (GITM)
• First principle nonhydrostatic general circulation model (GCM)
described in the work by Ridley et al. (2006)
• Vertical extent: 100-∼650 km
• Variable time step 2-4 s.
• Variable flexible grid resolution, e.g., 5 ◦ × 5 ◦ , 0.3125 ◦ × 2.5 ◦
(Yiğit and Ridley, 2011)
• GSWM, MSIS tidal forcing
• 2-way self-consistent thermosphere-ionosphere coupling
• Vertical momentum equation explicitly solved.
• Part <strong>of</strong> the Space Weather Modeling Framework (SWMF)
6/19
◭◭
◮◮
◭
◮
Back
Close

Model description-II
Global Ionosphere Thermosphere Model (GITM)
• Dynamics: ion drag, advection, tides, etc.
• Solar and Magnetospheric input:
- Joule heating
- Auroral heating
- High-latitude electric fields
- Interplanetary magnetic field (IMF)
- Solar F10.7 flux
- Solar wind speed
• Chemistry: Neutral densities <strong>of</strong> O, O 2 , N( 2 P ), N( 2 D), S( 2 P ), N 2 ,
and NO; and ion species O + ( 2 P ) ,O + 2 , N + ,O + ( 4 S), O + ( 2 D), N + 2 ,
and NO +
7/19
◭◭
◮◮
◭
◮
Back
Close

Model Configurations
Input
• Variable F10.7, hemispheric power, and IMF conditions from observations
• Empirical high-latitude electric fields (Weimer, 2005)
• Auroral particle precipitation (Fuller-Rowell and Evans, 1987)
• MSIS lower boundary fields
8/19
◭◭
◮◮
◭
◮
Back
Close

Model Configurations: Input
10
5
9/19
Bx (nT)
0
-5
-10
10
By GSM (nT)
5
0
-5
Bz GSM (nT)
-10
10
5
0
-5
-10
20
Figure 1: Heliospheric variations from
30 Aug - 1 Sept 2008.
Vx (km/s)
Density (/cc)
15
10
5
0
-350
-400
-450
-500
-550
Aug 30 Aug 31 Sep 01 Sep 02
Aug 30 to Sep 02, 2001 Universal Time
◭◭
◮◮
◭
◮
Back
Close

Model Simulations and Methodology
Period <strong>of</strong> simulations
• 30 August - 1 September 2008
• Analysis <strong>of</strong> 1 September 2008
10/19
Reducing the magnetic field
I. B 100%
II. B 95%
III. B 90%
IV. B 85%
V. B 80%
Then calculate the differences with respect to I.
◭◭
◮◮
◭
◮
Back
Close

Electron density distributions - 1200 UT
95% 90%
[e-] at 394.6 km Altitude 31-AUG-01 12:00:00.000
[e-] at 394.6 km Altitude 31-AUG-01 12:00:00.000
100.0 m/s
100.0 m/s
30
30
11/19
20
20
18
00
-7.35 3.97
10
0
-10
-20
-30
[e-]
18
00
-14.73 9.78
10
0
-10
-20
-30
[e-]
Figure 2: Polar distributions <strong>of</strong>
relative electron density changes
in percentage for decreasing magnetic
fields on 31 Aug 1200 UT.
Relative changes ion flows are
overplotted.
[e-] at 394.6 km Altitude 31-AUG-01 12:00:02.000
100.0 m/s
10
18
0
-10
-20
-30
00
85% 80%
-22.51 17.67
100.0 m/s
30
20
[e-]
[e-] at 394.6 km Altitude 31-AUG-01 12:00:00.000
18
00
-30.30 27.13
30
20
10
0
-10
-20
-30
[e-]
• v enhanced dramatically at
high-latitudes.
• n e increases around midnight
at midlatitudes, while everywhere
else n e decreases.
◭◭
◮◮
◭
◮
Back
Close

Electron density distributions - 0000 UT
95% 90%
[e-] at 394.6 km Altitude 01-SEP-01 00:00:00.000
100.0 m/s
30
[e-] at 394.6 km Altitude 01-SEP-01 00:00:00.000
100.0 m/s
30
12/19
20
20
18
00
-2.05 6.59
10
0
-10
-20
-30
[e-]
18
00
-4.42 13.33
10
0
-10
-20
-30
[e-]
Figure 3: Polar distribution <strong>of</strong>
relative electron density change
in percentage for decreasing magnetic
fields on 1 Sept 0000 UT.
Relative changes ion flows are
overplotted.
18
[e-] at 394.6 km Altitude 01-SEP-01 00:00:00.000
100.0 m/s
00
85% 80%
-7.08 23.44
30
20
10
0
-10
-20
-30
[e-]
[e-] at 394.6 km Altitude 01-SEP-01 00:00:00.000
100.0 m/s
18
00
-10.06 35.45
30
20
10
0
-10
-20
-30
[e-]
• v enhanced dramatically at
high-latitudes!
• n e increases around midnightdawn
at midlatitudes, while
everywhere else n e decreases.
◭◭
◮◮
◭
◮
Back
Close

Electron density distributions: Lat-lon
50.0 m/s
95% [e-] at 394.6 km Altitude at 01-SEP-01 00:00 UT
-5.33 6.59
6
4
2
0
-2
-4
-6
[e-]
Figure 4: Latitude-longitude distributions
<strong>of</strong> relative electron density
change in percentage for cases
95% and 80% magnetic fields. Relative
changes ion flows are overplotted.
13/19
80% [e-] at 394.6 km Altitude at 01-SEP-01 00:00 UT
50.0 m/s
-26.38 35.45
20
0
-20
[e-]
• Electron density increase around
midlatitudes and decrease at
high-latitudes
• Ion flows are faster at highlatitudes.
• Hemispheric differences.
◭◭
◮◮
◭
◮
Back
1
Close

Temperature and Neutral Flows
Temperature at 394.6 km Altitude at 01-SEP-01 00:00 UT
10.0 m/s
Temperature at 394.6 km Altitude at 01-SEP-01 00:00 UT
10.0 m/s
14/19
0.03 1.07
1.0
0.8
0.6
0.4
Temperature
0.2
0.0
0.10 2.36
2.0
1.5
1.0
Temperature
0.5
0.0
Temperature at 394.6 km Altitude at 01-SEP-01 00:00 UT
50.0 m/s
0.18 3.90
4
3
Temperature
2
1
0
Temperature at 394.6 km Altitude at 01-SEP-01 00:00 UT
1
Figure 5: Relative percentage difference in temperature.
Difference in neutral flows are overplotted.
100.0 m/s
0.26 5.71
5
4
Temperature
3
2
1
0
◭◭
◮◮
◭
◮
Back
Close

Meridional Flow & Electron Density
15/19
Figure 6: Merisional flow and electron density at a
high-latitude.
◭◭
◮◮
◭
◮
Back
Close

Temperature Variations
16/19
Figure 7: Universal
time variation <strong>of</strong>
neutral temperature at
68.75 ◦ , 2.5 ◦ E at 394
km on 31 August.
◭◭
◮◮
◭
◮
Back
Close

Summary and Conclusion
Ion flows
• With decreasing magnetic field, the ions become faster E × B/B 2
→ Variations in ion drag and Joule heating are expected!
→ Changes in dynamics and heat balance
• Variability (future work)
17/19
Electron density distributions
With decreasing B from 100 to 80%
• 6-35% increase in n e at midlatitudes at night
• Up to –35% change in n e at high-latitudes
◭◭
◮◮
◭
◮
Back
Close

Summary and Conclusion (cont’d)
Temperature and neutral flows
• Temperatures increase overall up to 5% (SH high-latitudes)
• Neutral flows are enhanced with decreasing B becoming more
equatorward during the night.
→ effects on chemistry
• Ion drag and Joule heating probably play a great role (future study).
18/19
Future Work
• Modeling the Sun-Earth connection.
• Impact <strong>of</strong> solar variability at various scales.
• Observational implications
• Ion drag and Joule heating.
◭◭
◮◮
◭
◮
Back
Close

References
Fuller-Rowell, T. J., and D. S. Evans (1987), Height-integrated Pederson and Hall conductivity patterns inferred from
TIROS-NOAA satellite data, J. Geophys. Res., 92, 7606–7618.
19/19
Ridley, A. J., Y. Deng, and G. Tóth (2006), The global ionosphere–thermosphere model, J. Atmos. Sol.-Terr. Phys., 68,
839–864.
Weimer, D. R. (2005), Improved ionospheric electrodynamic models and application to calculating Joule heating rates,
J. Geophys. Res., 110, A05306, doi:10.1029/2004JA010884.
Yiğit, E., and A. J. Ridley (2011), <strong>Effects</strong> <strong>of</strong> high-latitude thermosphere heating at various scale sizes simulated by a
nonhydrostatic global thermosphere-ionosphere model, J. Atmos. Sol.-Terr. Phys., 73, 592–600, doi:10.1016/j.jastp.
2010.12.003.
◭◭
◮◮
◭
◮
Back
Close