on the cause of solar differential rotation
DESCRIPTION
On the Cause of Solar Differential Rotation. 太陽差動自轉的成因. Ling-Hsiao Lyu Institute of Space Science, National Central University 呂凌霄 中央大學太空科學研究所. 11-years Solar Cycle Based on Sunspot Number. 22-years Solar Cycle Based on Leading Sunspot Magnetic Polarity. - PowerPoint PPT PresentationTRANSCRIPT
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On the Cause of Solar Differential Rotation
Ling-Hsiao LyuInstitute of Space Science, National Central Universit
y呂凌霄
中央大學太空科學研究所
太陽差動自轉的成因
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11-years Solar Cycle Based on Sunspot Number
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22-years Solar Cycle Based on Leading Sunspot Magnetic Polarity
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Solar Differential Rotation --> Solar Dynamo (-effects, -effects)
-->22-years Magnetic Solar Cycle
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Differential rotation is the major cause of solar cycle!
What is the cause of solar differential rotation?
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Differential Rotation in Solar InteriorSoHO/MDI Observation
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Solar Interior Structures
convection zone: r=1~0.86Rs(old model) r=1~0.7Rs(new model)
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Sound Speed Distribution in Solar Interior Abnormal plasma sound speed(c2=T/ distribution in the solar interior (MDI observation)c2)>0c2)<0
T : plasma temperature: average mass
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(A)
(B)
solar tachocline
region
(A) Differential Rotation
(B) Abnormal Plasma Temperature Distribution
MDI Observations(Kosovichev et al., 1997)
Cause Result(A) Turbulence Heating (B)
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Averge Mass Distribution in Standard Solar Model
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(C)
solar tachocline
region(C) Average Mass Distribution
in Standard Solar Model
Cause ResultUnder estimate mixing lengthUnder estimate Over estimate c2=T/ (B) Abnormal Plasma Temperature Distribution
(B)
(C)
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Sound Speed Distribution in Solar Interior Abnormal plasma sound speed(c2=T/ distribution in the solar interior (MDI observation)c2)>0c2)<0
T : plasma temperature: average mass
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Our ExplanationWe assume that a normal state means a hydrodynamic equilibrium state.
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Our Explanation on Abnormal c2 Distribution
Abnormal plasma sound speed(c2=T/ distribution in the solar interior (MDI observation)c2)>0c2)<0
Plasma TemperatureT1 > T2 > T3
Average Mass:
1 > 2 > 3
1 3
2
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Evidence onSmaller mixing length in the low latitude regionLarge mixing length in the high latitude region
Average mass
1>2>3
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Upper-half tachocline: (in solar convection zone) Poleward temperature gradient easterly windLower-half tachocline: (in solar radiative zone) Equatorward temperature gradient westerly wind
Zonal flow can lead to horizontal force balance in a rotational star or planet with latitudinal temperature gradient
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Easterly wind in the upper-half solar tachocline region (in solar convection zone).
WARM
WARM
COOL
Horizontal force balance:Poleward temperature gradient easterly wind
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Westerly wind in the lower-half solar tachocline region (in solar radiative zone)
HOT
WARM
WARM
Horizontal force balance:Equatorward temperature gradient westerly wind
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westerly wind easterly wind~60 degrees
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Initial formation of solar filaments’ magnetic field
BBO H observation of solar filaments 05/11/1998
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Zonal Flow in Rotational System --> Rossby wave
Stable Unstable
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Laboratory simulation of general circulation (1)
HOT
COOL
Holton (1992): This is not a Rossby wave, because is uniform in this case.
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Laboratory simulation of general circulation (2)
COOL
WARMe.g., Solar convection zone
Holton (1992): This is not a Rossby wave, because is uniform in this case.
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Formation of Rossby wave and Alfven waves in the coronal hole and boundary of coron
al hole region
B in lower latitude region can stabilize Rossby wave instability
B
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Rossby wave: H observation of solar filaments (02/22/1998)
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Rossby wave: MDI observation of solar magnetic field (02/22/1998)
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Rossby wave: Yohkoh SXT observati
on 07/05/1998
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Nonlinear Evolution of Rossby Wave Lead to Formation of Elephant-trunk Coronal Hol
e
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MDI Observation of Solar Differential RotationRed: faster, Blue: slower
Generation of large amplitude, nearly circularly polarized Alfven waves in the coronal hole region
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Ulysses observation of solar wind speed(1991-1998)
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It is believed that …observed large-amplitudeAlfven waves are responsible for solar wind acceleration in the polar coronal hole
Q: What is the energy source of these large-amplitude Alfven waves?
A: Rossby wave!
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Rossby wave on the Sun can result in plane polarized Alfven wave in the solar wind
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Theoretical Solutions of Steady State Nonlinear Alfven Waves and Rotational Structur
e in Ion-Electron Two-Fluid Plasma
(Lyu and Kan, 1989)(Lyu, 1991)
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Observation of Plane Polarized Alfven Waves in the Solar Wind
--- Evidence of Rossby wave on the Sun
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(1988)
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Mavromichalaki et al., 1988
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BBO H observation 05/11/1998
Our Model: Plasma in solar convection zone has
Higher Temperature in the Polar RegionEasterly Wind ==> Differential Rotation
Conclusion
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Discussion:Cause of Maunder Minimum and variations in solar activities:
Gravitational disturbances and/or tidal effects>> reduce density gradient (in the tachocline region)>> reduce diamagnetic current >> reduce temperature gradient>> reduce differential rotation>> reduce solar activities>> reduce sunspots number
Observations: (~ 90 years Gleissberg cycle) (tidal effect)Sunspots number decreases with increasing solar diameter.(Jupiter:11.86 yr.) (Saturn: 29.5 yr. ) (Uranus: 84 yr.)