Junfeng Qiu

Rapid Penumbral Decay following Three X-Class Solar Flares

We show strong evidence that penumbral segments decayed rapidly and permanently right after three X-class solar flares. Two of the three events occurred very recently in NOAA Active Region 10486, an X17 flare on 2003 October 28 and an X10 flare on 2003 October 29. The third X2.3 flare was observed in solar active region NOAA AR 9026 on 2000 June 6. The locus of penumbral decay is related to flare emission, albeit with distinct differences for each event. We present difference images highlighting the rapid changes between pre- and postflare states of the flaring active region, which show distinct decaying penumbral segments and neighboring umbral cores becoming darker. Because of the lack of spectroscopic data, we cannot exclude the possibility that the observed changes are due to changes in the temperature structure of the flaring atmosphere, or to a corresponding reduction in opacity for a section of both umbra and penumbra. However, we argue against this possibility because the observed intensity changes are permanent, not transient. We instead propose a possible explanation that magnetic fields change from a highly inclined to a more vertical configuration within approximately 1 hr after the flares; i.e., part of the penumbral magnetic field is converted into umbral fields.

SUNSPOT UNIT AREA: A NEW PARAMETER TO DESCRIBE LONG-TERM SOLAR VARIABILITY

In this Letter we introduce a new parameter, the sunspot unit area (SUA), which describes the daily average size of sunspots produced by the dynamo in a solar cycle. The monthly average of the SUA is studied to show its variation during the solar cycle and is compared with the two commonly used parameters, sunspot numbers and sunspot areas. Our results show that (1) the new SUA parameter waxes and wanes during sunspot cycles in the same way as the other two parameters, but with a relatively small magnitude of fluctuations, (2) the Waldmeier effect and the Gnevyshev-Ohl rule, which appear in the variations of both sunspot numbers and sunspot areas, are not shown in the variations of SUA during solar cycles, and (3) the most pronounced period of SUA variation is about 10.13 yr, which is statistically significant at any time of the considered time span.

Magnetic Topology in 1998 November 5 Two-Ribbon Flare as Inferred from Ground-based Observations and Linear Force-free Field Modeling

We analyzed the three-dimensional structure of the linear force-free magnetic —eld. A longitudinal magnetogram of Active Region NOAA 8375 has been used as the photospheric boundary condition. The 1998 November 5 2B/M8.4 two-ribbon —are can be explained in the framework of quadrupolar recon- nection theory: the interaction of two closed magnetic loops that have a small spatial angle. The energy derived from soft X-ray telescope (SXT)/Y ohkoh data (3¨6 ) 1030 ergs) is 1 order of magnitude higher than the lower limit of —are energy predicted by Melroses model. The latter estimation was made using the linear force-free extrapolation. It was suggested that, taking into account the nonlinear character of the observed magnetic —eld, we can increase the lower limit of the magnetic energy stored in the studied magnetic con—guration. The revealed magnetic con—guration allows us to understand the observed loca- tion and evolution of the —are ribbons and the additional energy released during the gradual phase of the —are, as well. Besides, reconnection of closed magnetic loops can logically explain the connection between a two-ribbon —are and a giant X-ray post—are arch, which usually is observed after the —are onset. We emphasize that unlike the Kopp and Pneuman con—guration, the model discussed here does not necessarily require destabilization and opening of the magnetic —eld. Subject headings: Sun: —aresSun: magnetic —elds

Does High-Latitude Solar Activity Lead Low-Latitude Solar Activity in Time Phase?

Using data from the Carte Synoptique solar filaments archive, we investigate whether there is a time lag between high-latitude solar activity and low-latitude solar activity. The cross-correlation analysis of the number of high-latitude filaments per Carrington rotation (NHF) and that of low-latitude filaments per Carrington rotation (NLF) shows, although inconclusively, that NLF possibly lags behind NHF. The periodic characteristics of both NHF and NLF clearly indicate that the activity of high-latitude filaments is evidently leading the activity of low-latitude filaments. Thus, the present study suggests that high-latitude solar activity leads low-latitude solar activity in time phase.