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Understanding Large-Scale Dimming in Solar Emissions: Insights from Multifrequency Observations

This study examines a significant darkening event observed in extreme ultraviolet and radio emissions surrounding a solar eruptive event in July 2004. Using data from SOHO and other telescopes, the research explores possible causes of the observed dimming phenomenon and its implications for solar dynamics. The findings shed light on the complex interplay between various solar processes and highlight the importance of multi-frequency observations in solar physics research.

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Understanding Large-Scale Dimming in Solar Emissions: Insights from Multifrequency Observations

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  1. A large-scale darkening observed in EUV and radio emissions V. Grechnev, A. Uralov, I. Kuzmenko, I. Chertok et al.

  2. SOHO/EIT 304 Å Before, during, and after 2004 July 13

  3. SOHO/EIT 195 Å & LASCO/C2 • SOHO telescopes show an eruptive event:

  4. 00:16:50 00:48:08 00:07:52 00:19:42 00:13:37 00:21:36 TRACE 171 Å

  5. Big Bear H images Flare and eruptive filament

  6. Mauna Loa H images Original image Fixed-base difference

  7. 2004 July 13 event: • GOES M6.7 in AR 10646 (N15W49) • Very impulsive microwave burst • Flux 1200 sfu @ 17 GHz • Duration ~10 min • H flare not reported by patrol stations • but Big Bear images show it • Filament eruption and CME

  8. 304 Å Probable causes of large darkening in HeII 304 Å • Dimming due to density depletion? – Usually well observed in 195 Å • Occultation by absorbing material: • resonant absorption in cooler HeII (<50000 K)? • non-resonant absorption in H (<10000 K)?

  9. Evolution of 195 Å dimming

  10. 304 Å 195 Å Summary on 195 Å dimming • Density-depletion 195 Å dimming lives much longer • Configuration quite different •  Not a density-depletion dimming Min{Images} Images[0] Min{Images}/ Images[0]

  11. NoRH shows • Ejected material: • First bright on the disk • Then bright above the limb, and dark on the disk • Dark moving feature is not large • Ejecta is inhomogeneous

  12. EIT 304 Å observation Multi-frequency radio fluxes • NoRP & Ussuriysk 2.8 GHz • Solid: observed • Dotted: thermal emission of flare subtracted • Normalized to the quiet sun’s level • Absorption  • TFil < TQS 3.75 = 23,000 K

  13. AreaEIT304=0.067 , GHz Frequency dependence of radio absorption • Symbols: observed • Solid: calculated considering the ejecta and corona above it  Ejected mass  (6–9)·1015 g with depth = (20–200) Mm

  14. Epilogue-I • The phenomenon was due to occultation of the quiet sun rather than an active region • This unique event was revealed from EIT 304 Å data and independently from Ussuriysk 10.7 cm records • It was possible to detect it from total flux radio records thanks to shortness of the main burst

  15. Epilogue-II • Murphy’s Low works perfectly: • No SSRT 5.7 GHz data • No high-cadence CORONAS-F/SPIRIT 304 Å data …Which would be important… • Nevertheless, non-imaging multi-frequency total flux records allowed us to study the event

  16. We acknowledge • Shibasaki San and NSRO for the opportunity to work here under perfect conditions • Staff members of the NSRO for the hospitality

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