The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (2011). The flare had a two-ribbon structure and was associated with a flux rope eruption and a halo coronal mass ejection (CME) as reported in the CACTus catalogue. Following the discovery of the second sunquake and the spatial association of both sources with the locations of the feet of the erupting flux rope (Zharkov et al 2011) we present here a more detailed analysis of the observed photospheric changes in and around the seismic sources. These sunquakes are quite unusual, taking place early in the impulsive stage of the flare, with the seismic sources showing little hard X-ray (HXR) emission, and strongest X-ray emission sources located in the flare ribbons. We present a directional time-distance diagram computed for the second source, which clearly shows a ridge corresponding to the travelling acoustic wave packet and find that the quake at the second source happened about 45 seconds to one minute earlier than the first source. Using acoustic holography we report different frequency responses of the two sources. We find strong downflows at both seismic locations and a supersonic horizontal motion at the second site of acoustic wave excitation.
Authors: Zharkov S.I., Green L.M., Matthews S.A. and Zharkova V.V.
Publication Status: Solar Physics, in press
Last Modified: 2012-08-30 10:09
The latitudinal distributions of sunspot areas and magnetic fields and their correlation with the background solar magnetic field in the cycle 23
The quasi 3D latitudinal distributions (butterfly diagrams) of sunspot areas and magnetic fields obtained within the whole mu-hemispheres in longitudes from the Solar Feature Catalogues for 9 years (1996-2005) of the cycle 23 are correlated with those of the low-resolution solar magnetic fields (SMF) obtained from Wilcox Solar Observatory. During the whole period of observations the sunspot areas reveal a strong positive correlation with SMF appearing at zero timelag and repeating at the 2-2.5 year time lags after or before the cycle start. The high positive correlation coefficients are also distributed into the four zones reflecting the sunspot migration directions: the two pre-polar zones above pm 45circ with the positive correlation increasing towards the poles (the sunspot migration towards the poles) and the two pre-equatorial zones from - 40circ to +40circ (the 'royal zone') with the positive correlation increasing toward the equator as seen in the butterfly diagrams. This correlation suggests a modulating effect of the symmetric component of SMF on the magnitude of magnetic field in flux tubes emerging as sunspots. The symmetric SMF componentshave the same signs in each hemisphere and they are changed to opposite over the period 2-2.5 year. Then, if the signs of the symmetric SMF coincides with the leading polarity signs in a one hemispehere and opposite in the other one, the flux tube emergence (and sunspot appearance) is supported by SMF in the first one and suppressed in the other. While in 2.5 years when the SMF sign is changed to the opposite, the flux emergence is supported in the other hemisphere but suppressed in the first one.
Authors: Zharkov, S.I., Gavryuseva, E.V. and Zharkova, V.V.
Publication Status: JASR, in press
Last Modified: 2007-04-12 16:33
Statistical Properties of Sunspots in 1996-2004. 1. Detection, North-South Asymmetry and Area Distribution
The first statistical results in sunspot distributions in 1996-2004 obtained from the Solar Feature Catalogues (SFC) are presented. A novel robust technique is developed for automated identification of sunspots on SOHO/MDI white light (WL) full disk solar images. The technique applies image standardisation procedures for elimination of the limb darkening and non-circular image shape, uses edge-detection methods to find the sunspot candidates and their edges and the morphological operations to smooth the features and fill in the gaps. The detected sunspots are verified with the SOHO/MDI magnetograms by strong magnetic fields being present in sunspots. A number of physical and geometrical parameters of the detected sunspot features are extracted and stored in the relational SFC database including umbra/penumbra masks in the form of run-length data encoding of sunspot bounding rectangle. The detection results are verified by comparison with the manual daily detection results in Meudon and Locarno Observatories in 2002 and by correlation (about 96%) with the 4 year sunspot areas produced manually at NOAA. Using the SFC data, sunspot area distributions are presented in different phases of the solar cycle and hemispheres that reveals a periodicity of the North-South asymmetry with a period of about 7-8 years. The number of sunspots increases exponentially with the area decrease with the index slightly increasing from -1.15 (1997) to -1.34 (2001).
Authors: Zharkov, S.I., Zharkova, V.V. and Ipson, S.S.
Publication Status: Solar Physics Topical Issue, 2005, in press
Last Modified: 2005-05-29 11:29