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Quiet Sun and Active Region Studies by Nobeyama Radioheliograph

Quiet Sun and Active Region Studies by Nobeyama Radioheliograph. Kiyoto SHIBASAKI Nobeyama Solar Radio Observatory NAO/NINS. Characteristics of NoRH for QS and AR studies. Full disk imaging capability Uniform data set for one solar cycle Polarization measurement at 17 GHz

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Quiet Sun and Active Region Studies by Nobeyama Radioheliograph

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  1. Quiet Sun and Active Region Studies by Nobeyama Radioheliograph Kiyoto SHIBASAKI Nobeyama Solar Radio Observatory NAO/NINS NBYM04@Kiyosato

  2. Characteristics of NoRH for QS and AR studies • Full disk imaging capability • Uniform data set for one solar cycle • Polarization measurement at 17 GHz • High temporal resolution and long (8hrs) continuous data (spectral analysis of oscillations) • Limited angular resolution • Ambiguity of weak (~several hundreds K) features

  3. Research subjects • QS • Polar brightening • Coronal hole brightening • AR • Magnetic field • Gyro-resonance, B||(polarization degree), B⊥(polarization reversal) • Sunspot • Umbral oscillation (thermometer) • Weak activities • Xbp / transient brightenings • Small and frequent brightening above δsunspots

  4. Published papers • QS • Coronal hole (Gopalswamy, 99, Krissinel et al, 00, Yoshiike et al., 00) • Polar region (Shibasaki, 98, Nindos et al, 99) • Large structure (Chertok, 01) • Global solar activity (Gelfreikh et al., 02, Gelfreikh et al., 02) • Limb brightening (Selhorst et al., 03, Selhorst et al, 04) • AR • S-component (Shibasaki et al., 94) • Polarization reversal (Ryabov et al., 99) • Umbral oscillation (Gelfreikh et al., 99, Shibasaki, 01) • AR evolution (Lara et al., 98, Kundu et al., 01) • Current sheet (Uralov et al., 00) • AR magnetic field (Zhang et al., 02) • Sunspot atmosphere (Yu et al., 02) • Weak Activities • X-bp (Kundu et al. 94, Gopalswamy et al., 96, Maksimov et al., 01) • Transient brightening (White et al., 94) • Small bursts above delta spot (Shibasaki, 96) • X-ray jets (Kundu et al., 97, Kundu et al., 99)

  5. Emission mechanisms • Thermal f-f emission • Tb = T (τ≫１） • Tb = Tτ∝EM/√T （τ≪１） • Thermal gyro-resonance emission • Tb = Tτ∝NTS　（τ≪１） 　N:density, T: temperature, S: harmonic number at 17 GHz: S = 3, B = 2000 Gauss, purely polarized

  6. Quiet Sun and solar cycle • Large structures • Limb brightening: studies of fine structure in the chromosphere • Polar brightening: studies of atmosphere in the polar region (anti-correlation with sunspot number) limb brightening + polar coronal hole • Coronal hole brightening/dimming: studies of lower atmosphere in the coronal hole

  7. Radio Synoptic Chart Heliographic Latitude Carrington Longitude

  8. Radio Butterfly Diagram

  9. Active regions • Diffuse component: • f-f emission from hot and dense plasma (Estimation of Emission measure) • magnetic field strength from circular polarization degree • Compact component • Magnetic field structure of sunspots (multi-wavelength) • Sunspot oscillation: 3-minutes oscillation/ upward traveling sound wave / temperature measurement / solar cycle dependence

  10. Gyro-resonance emission • Sunspot associated emission • At 17 GHz, 2nd harmonics: 3000 Gauss 3rd harmonics: 2000 Gauss • Thin iso-Gauss layer ~ (Vth/C) * LB • High degree of circular polarization (100 %) • Umbral oscillation • 3 min. oscillation of gyroresonance emission • Absorption of 5 min. oscillation • Mechanism: upward propagating sound wave generated at temperature minimum plateau region (lower cutoff frequency) • Diagnostic tool of sunspot temperature • Solar cycle variation of sunspot temperature

  11. Umbral Oscillation

  12. 17GHz Sound wave Gyroresonance layer (2000 Gauss) Temperature minimum umbra penumbra F = (g/4π)√(γμ/RT) 6 mHz ~ 4,000 K g: gravity, γ=5/3, μ=1.5, R:gas constant, T:temperature

  13. Solar Cycle Variation (1992～1994)+11 Year

  14. Relation to solar cycle phase • Activity cycle phase（θ）and frequency • F-3 (θ) = 5.58×（1 + 0.07 ×θ） ＝5.58 + 0.39×θ θ = (year – 1996.) / 11.　 　　　　0 ≦θ≦ 1、5.58 ≦F-3 ≦5.97 • Activity cycle and sunspot temperature • T3(θ) = (12/F-3)2 = 4.62 ×(1 – 0.14×θ) = 4.62 – 0.65 ×θ 4.62 ≧T3 ≧ 3.97（Sunspot cooling toward minimum: 650 K）

  15. Sunspot seismology • Windowed Fourier spectral analysis shows: • Frequency modulation of hours: appearance ofg-mode oscillation through the flux tube ? • High spectral resolution reveals spectral fine structures • Frequency difference in different location in umbra: sunspots consist of many elements (spaghetti model)

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