Polar Brightening and Solar Wind
K. Shibasaki (NSRO/NAOJ),
K. Fujiki, and M. Tokumaru(STEL/Nagoya‐U) ）2013/11/24

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Nobeyama Radioheliograph (NoRH)
http://solar.nro.nao.ac.jp/norh/• Specification– 84 elements of 80 cm dishes– EW: 490 m, NS: 220 m– full disk
– 17 GHz (I & V) and 34 GHz (I)– 10 /5 arcsec (17/34 GHz) res.
– 1 second cadence• 0.1 cadence during flares• Operation– 1992.6 ~– daily 8 hr (Local noon 03UT +/‐4h)– Full automatic operation– Images around local noon andevery 10 min. are on the WEB
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NoRH Array Configuration

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3Radio emission fromthe Quiet (non‐flaring) Sun•

Emission mechanisms– mainly thermal emission (thermal electrons)• free‐free emission
b• gyro‐resonance emission– simple mechanism (classical EM), electrons are in LTE state, continuum
emission: DEM measurements are not possible– small contribution from non‐thermal emission (small flares)

T   Te d

•Features– solar disk
– active regions– dark filaments / prominences– coronal holes– network and fine structures (high spatial resolution, ALMA?)

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Long‐term Global Solar Activity
Inferred from Microwave
Observation

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Synthesis of Radio Butterfly Diagram

Nobeyama
RadioheliographObservation Since
1992

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Daily Images(7000)

Carrington
Rotation Maps(260)

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Radio Butterfly
Diagram6

Radio Butterfly Diagram（1992.7‐2011.8）

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Correlation between radio brightness
and mag. field strength at polar region

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IPSmeeting@NagoyaU• ＋：Np、△：Sp• Corr. Coeff. =0.86• North：0.84• South：0.89• Radio brightness
at polar regions isa good indicatorof polar magnetic
field, eventhough physicalmechanisms arequite different.

8Why polar regions are bright in microwave
1.

Limb brightening effect– Due to unknown heating mechanisms of upper atmosphere
2. Coronal hole effect– Polar regions are covered by CHs. > enhanced limb brightening– During solar max. period > no CHs, dark filaments absorb / suppress
limb brightening
3. Magnetic activity effect– Good correlation between unipolar mag. field strength and polar
brightening (even in low CHs) suggests hotter chromosphereassociated with strong mag. field.
– Enhanced chromospheric heating is needed in open magnetic fieldregion (what mechanism? wave/flare?) proportional to B.

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9Long‐term Global Interplanetary
Activity Inferred from IPS
Observation

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Solar Wind Speed Measurement using
Interplanetary Scintillation by STEL/Nagoya U.

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Solar Wind Speed

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Solar Wind Velocity (STEL)

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Radio Brightness (Nobeyama)

Northern High Latitude Brightness
and Solar Wind Speed• N55~N80 averaged
radio brightness ( Tb –10,500K, solid) andsolar wind speed (km/s,dotted)

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Correlation between radio brightness andsolar wind speed at northern high latitude• Correlation Coeff. = 0.83
• Wind speed is nearly
constant (750 km/s) atTb ≥ 11,000 K

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Southern High Latitude Brightness
and Solar Wind Speed• S55~S80 averaged
radio brightness ( Tb –10,500K, solid) andsolar wind speed(km/s, dotted)

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Correlation between radio brightness andsolar wind speed at southern high latitude• Correlation Coeff. = 0.79
• Less clear relation (Tb –speed) compared to thenorthern hemisphere2013/11/24

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Why solar wind speed and radio brightnessshow so good correlation at high latitude• Both radio brightness and solar wind speed
depends on polar field– Radio brightness depends on lower atmosphere– Solar wind speed depends on higher atmosphere• During solar maximum period:
polar field is weak > closed magnetic field> suppress Tb and inefficient solar windacceleration
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19Summary• NoRH observed long‐term, global activities of the Sun– NoRH characteristics• full disk observation• robust calibration method (redundant array, good uv coverage forextended quiet Sun disk (position, brightness)• proper frequency selection of 17 GHz for polar activity obs.
• long and steady operation for 20 years• We need further observations to study the current
anomalous condition of global solar activity, not only
to understand solar activity itself but also its influence
to the interplanetary space and to the earth upper
atmosphere.
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