First 405 GHz and 212 GHz solar flare observations were obtained during short campaigns while the new solar submillimeter-wave telescope (SST) was still undergoing adjustments at the CASLEO El Leoncito observatory in the Argentina Andes. We show here preliminary results for a large X1.1 class X-ray event occurred on 2000 March 22, which exhibited a small submm-w continuum response to the slow (minutes) bulk flare emission, and numerous subsecond spikes (100-300 ms), the brightest spikes reaching about 180 and 50 s.f.u. at 405 and 212 GHz, respectively.

Assuming LTE, we investigate the formation of the G band in the semiempirical flux-tube model of Briand & Solanki (1995). Preliminary results agree with observations of G-band bright-point contrast, even though the observed contrast depends sensitively on the amount of scattered light. It is the weakening of spectral lines in the flux tube that makes the bright-point contrast greater in the G band than in ordinary continuum. We also present LTE synthetic spectra for the full wavelength range from UV to IR. This serves to point out other promising pass bands for the observations of flux-tube structures.

Using the vector magnetic field data from the Huairou Solar Observing Station of Beijing Astronomical Observatory, we study their size-flux relations for various magnetic elements identified as pores and spots. More than 725 pores and spots which located near the central meridian are selected. The power-law relationships for the mature sunspots are derived, and, there are different power-law relationships for the different magnetic elements. We also find that there are not evident relations between size and flux of the pores and protosunspots. Such the results may be useful for understanding the physical conditions and dynamical processes of magnetic flux tubes in the solar plasma during the sunspot's formation. In addition, their characteristic size is also given.

We present results of the analysis of NOAA 8668, which was observed successively by space satellite (SOHO) and ground-based observatories (BBSO, Huairou). The combined observation offers us a good example of a region observed from low to high solar atmosphere. Several flares and a sigmoid filament were observed in the AR, and we observed the sigmoid filament from its birth to disintegration. The configuration of the magnetic field of the AR changed quickly as well as the loops. From EIT movies, we can even judge the sign of the sigmoid filament's magnetic helicity. The forming and heating of the loops were the result of magnetic reconnection, and the corona seemed heated when the loops became opened.

Authors have investigated the line-of-sight velocity difference in the radial direction of sunspot penumbrae simultaneously at two height levels, NiI 4857 and Hβ by the differential method. Power spectra of time series exhibit in the range under consideration three groups of periods: 30-40, 12-15, and 8-10 minutes. Particular emphasis has been placed on the low-frequency portion of the spectrum (0.5-2 mHz). In addition to the 12-minute oscillations as detected by Rimmele the line-of-sight velocity component that is caused by Evershed motion is responsible for oscillations with periods of 15-35 minutes, which occur concurrently at the two height levels.

We have extended our investigation of sunspot regions, with particular attention to the physics of the transition region between the chromosphere and the corona. In sunspot plumes, the most prominent features in the transition region intensity maps, we find downflows exceeding 25 km s−1. The observations show that the flow cannot be maintained by inflow from the corona and prompt a search for the origin of the flow and its possible relation to the origin of the sunspot plume. We find that the downflows in sunspot plumes are maintained by gas at transition region temperatures, streaming in flow channels from locations well outside the sunspot. Hence, the flow pattern in the transition region shows similarities to the inverse Evershed flow in the chromosphere. We present a working hypothesis that is based on the siphon flow mechanism.

The three-dimensional (3D) image of an Hα flare is reconstructed from its line-center and seriary off-center filtergrams. The reconstruction is based on the principle of the line formation theory that the contribution function (CF) of emergent specific line intensity describes the escape photon distribution from stellar atmospheric layers. Thus the reconstruction depends on the model atmosphere accepted which determines the CF. An Hα flare taking place on April 22, 1992 is utilized to illustrate the process.

During the MEDOC campaign #4 (October 1999), we observed an active region filament with the SUMER/SoHO spectrometer using the 584.33 Å HeI line. After a description of the HeI line profile in the filament, we present a Fourier analysis of SUMER long time observations. This analysis allows to detect oscillations in several ranges of periodicities: 6–20 min, 40–90 min. We discuss these periodicities in terms of Alfvén and magnetoacoustic waves obtained with a filament model developed by Joarder & Roberts (1993).

We have studied the temporal relationship between three selected prominence eruptions and their associated coronal mass ejections (CME). For these three events it is not possible to predict from the CME time history when the prominence would erupt. However, both are signatures of destabilisation of the global coronal magnetic field. The lack of a precise temporal relationship reflects the fact that several coronal stuctures are destabilised, and in general one will predominate in the CME structure. If this structure happens to be the same as that constraining the prominence, then the latter will erupt following the launch of the CME. If the prominence is constrained by a separate magnetic structure, then it may erupt before or after the main CME. Reconfiguration of the global coronal field probably drives a fast increase of the poloidal field in the prominence flux tube or introduces destabilising shear forces. Events on May 1, 1996, September 25-27, 1996, and May 31 1997 are discussed.

We present multi-instrument observations of AR 8048, made between June 3 and June 5 1997 as part of SoHO JOP033. This active region (AR) has a sigmoid-like global shape and undergoes transient brightenings through which the stored energy is released.

Using a magneto-hydrostatic model, we compute coronal magnetic field. The large-scale magnetic lines confirm the sigmoidal characteristics of the AR. The field lines most closely matching the hotter SoHO/CDS loops extend along the quasi-separatrix-Iayers (QSLs) of the coronal field. Transition region (TR) brightenings observed with SoHO/CDS can be associated with both QSL intersections with the photosphere, and places where separatrices corresponding to bald patches (BPs, sites where field lines are tangent to the photosphere) lie at the photospheric plane. There are suggestions that the element abundances measured in the TR may depend on the type of topological structure present. TR brightenings associated with QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values.

We study the reconnection and the chromospheric evaporation in flares using the numerical code including nonlinear anisotropic heat conduction effect (Yokoyama & Shibata 1998; 2001). The two-dimensional, nonlinear, timedependent, resistive, compressible MHD equations are solved. The evolution from the rise phase to (the early part of) the decay phase of a solar flare is qualitatively reproduced in this simulation. Based on the results, we obtained a relationship between the flare temperature and the coronal magnetic field strength. If we assume that the input of energy to a loop balances with the conduction cooling rate, the temperature at the loop apex is TA ≈ (2QL2/κ0)2/7 where Q is the volumetric heating rate, L is the half-length of the loop, and κ0 = 10−6 eGS is the Spitzer's thermal conductivity constant. In our simulations, the heating mechanism is magnetic reconnection so that the heating rate is described as Q = B2/(4π) · Vin/L · 1/sin θ, where B is the coronal magnetic field strength, Vin is the inflow velocity (≈ 0.1VA from our result and also from Petschek's theory), and θ is the angle between the slow-mode MHD shock and the loop and is approximately given by sin θ ≈ Vin/VA. By manipulating the equations, we find where ρ is the mass density of the corona. The simulation results show very good agreement with this scaling law.

We discuss intensity and velocity oscillations which were observed by SOHO in lines of C IV and Ne VIII formed in the EUV plume above a sunspot during a continuous time series of 4.3 hours. Applying a wavelet analysis, we find periods mainly around 3 mHz; the behavior in time is different for the different EUV lines and strongly intermittent, for the velocity oscillations in particular. Moreover, we discuss the observed oscillations within the frame of model calculations for the resonant transmission of magneto-atmospheric waves through realistic models of the sunspot atmosphere. The nonstationary behavior could hint at the appearance of blinkers in the umbral transition region.

In this paper, we show observed properties of tilt and twist of bipolar active regions magnetic fields, using magnetograph data at Huairou, Beijing Astronomical Observatory. We deduce that origin of the twist of magnetic fields is same as that of tilt of bipolar magnetic fields. In another word, they are primarily produced by Coriolis force acting on a rising flux tube through convection zone.

Supposing coronal magnetic fields are in a force-free state from the chromosphere to the height of two solar radii, we reconstruct 3D force-free magnetic fields by making use of a new numerical technique, in which the fields are represented by a boundary integral equation based on a specific Green's function. Vector magnetic fields observed on the photospheric surface can be taken as the boundary conditions of this equation. Magnetic fields in AR8270 on 14 July 1998 were employed as an example to exhibit the capability of this numerical technique.

In a few recent studies, 8 coronal mass ejections (CMEs) were identified to associate with a superactive region, AR 8100. They were all flare-CME events, It is found that the region is characterized by vigorous flux emergence and an imbalance of magnetic flux in two polarities. With the continuous flux emergence and its driven flux cancellation, the EUV dimming associated with flare activity increased in area. Whenever the dimming extended to an area of more than 50×50 square degrees on the solar surface, a flare in the region became CME-associated.

Using the observational Hα, radio and X-ray data, we measure the ascending movement of the filament in the active region, and derive the current intensity and the current distribution inside the filament. The comparison between the ascending filament and the position of the hard X-ray image shows that they are co-spacial. These results suggest that the physical process in the thermal and non-thermal phases of the flare could be explained respectively by the tearing instability occurred inside the filament and the revised Alfvén-Carlqvist current interruption theory. The theoretical calculations are basically consistent with the observations.

On 23 September 1998 there was a 3B/M7.1 flare event starting at 06:40 UT with more than 100 minute duration radio bursts of 1134 sfu peak flux at 2840 MHz and accompanying a CME. In this paper, the event is analyzed with the data observed by Beijing Astronomical Observatory (BAO), OSRA-Tremsdorf (AIP) and SSRT-ISTP. In particular, we compare the fine structures (FS) during the triggering phase revealed in different regimes and discuss their implications.

In this paper we describe the available methods for the non-constant-α force-free field reconstruction and study the associations between reconstructed 3-d coronal fields by a new technique and the 2B/X2 flare process from observations in AR 8100 on 4 November 1997.

We find an important piece of evidence for magnetic reconnection inflow in a flare on March 18, 1999. The flare occurred on the north-east limb, displaying a nice cusp-shaped soft X-ray loop and a plasmoid ejection typical for the long-duration-events. As the plasmoid is ejected, magnetic reconnection occurs at the disconnecting point. A clear ingoing pattern toward the magnetic X-point is seen. The velocity of this apparent motion is about 5 km sec−1, which is an upper limit on reconnection inflow speed. Based on this observation, we derive the reconnection rate as MA = 0.001 − 0.03, where MA is a Alfvén Mach number of the inflow.

We analyzed simultaneous data from Huairou Solar Observing Station (HSOS) and the Transition Region and Coronal Explorer (TRACE) of November 4, 1998 in the active region NOAA 8375. The magnetic fields in this region had the following properties: a main positive polarity line-of-sight field was surrounded by relatively weak negative polarity fields; many moving magnetic features emerged from the positive magnetic field, and cancelled (merged) with the opposite (the same) polarity fields. There was a filament on the neutral line between the main positive polarity field and its surrounding negative polarity fields. The filament was cut off at a magnetic cancellation site and separated into two segments. One segment erupted and disappeared; the other segment rose from one end, but another end was fixed at an interface of a pair of opposite magnetic polarities, finally the morphology of this segment appeared as an Hα surge. Comparing Hα filtergrams with EUV images, we noticed that the Hα surge was co-spatial with an EUV surge. The EUV surge was whiplike in shape, then sidewards moved. We suggest that the evolution of the EUV surge represent the process of EUV loop opening.