Jongchul Chae

Magnetic helicity may be transported to the solar corona through the solar surface either via the passage of helical magnetic field lines from below or via the shuffling of footpoints of preexisting coronal field lines. In this Letter, we show how to observationally determine the rate of magnetic helicity transport via photospheric footpoint shuffling from a time series of line-of-sight magnetograms. Our approach is not confined to the previously known shear motions, such as differential rotatio

We have determined nonthermal velocities in the quiet Sun at temperatures between 104 K and 2 ] 106 K by measuring the widths of a number of EUV and far-ultraviolet (FUV) lines taken with SUMER on board the SOHO spacecraft. The broadenings owing to the SUMER instrument and the nite opacity in each line have been carefully examined. The nonthermal velocity at temperatures below 2 ] 104 K is smaller than 10 km s~1. The velocity increases with temperature, reaches a peak value of 30 km s~1 around 3

We have studied the evolution of the photospheric magnetic field in active region NOAA 8668 for 3 days while the formation of a reverse S-shaped filament proceeded. From a set of full-disk line-of-sight magnetograms taken by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO), we have found a large canceling magnetic feature that was closely associated with the formation of the filament. The positive flux of the magnetic feature was initially 1.5 × 1021 Mx a

We analyzed simultaneous EUV data from the Transition Region and Coronal Explorer and Hα data from Big Bear Solar Observatory. In the active region studied, we found several EUV jets that repeatedly occurred where pre-existing magnetic flux was "canceled" by newly emerging flux of opposite polarity. The jets look like Yohkoh soft X-ray jets, but are smaller and shorter lived than X-ray jets. They have a typical size of 4000-10,000 km, a transverse velocity of 50-100 km s-1, and a lifetime of 2-4

The existence of prevailing redshifts in the UV lines formed in the solar transition region raises an important question concerning its physical origin and its role in the mass and energy balance of the outer solar atmosphere. A series of UV spectral lines observed by SUMER has been analyzed to obtain the spatial average of Doppler shifts in the quiet Sun as a function of temperature. The UV lines used for the analysis cover temperatures ranging from 104 to 106 K. The wavelength calibration has

From a comparison of the Solar and Heliospheric Observatory SUMER spectral data and a time series of Big Bear Solar Observatory magnetograms, we present observational clues to the physical origin of transition region explosive events. First, explosive events rarely occur in the interior of strong magnetic flux concentrations but rather are preferentially found in regions with weak and mixed polarity fluxes that display magnetic neutral lines. Second, the majority of explosive events happen durin

There has been some controversy as to whether the magnetic fields of vertical threads seen in quiescent prominences are predominantly vertical or horizontal. We report finding special patterns of flow in a quiescent prominence observed by the Solar Optical Telescope aboard Hinode. This prominence is a small hedgerow prominence composed of many vertical threads. To one side of it, we found a pattern of persistent horizontal flows of Hα-emitting plasma. These flows originated from a region in the

Our previous study has shown that the formation of a reverse S-shaped filament in NOAA active region 8668 was closely associated with a large canceling magnetic feature. In the present paper we investigate the response of the upper atmosphere at the region of this canceling magnetic feature. The UV and EUV data taken by the Transition Region and Coronal Explorer (TRACE) reveal that a series of jets and small eruptions took place there during the formation of the prominence. Plasma in each jet or

A solar prominence has either dextral or sinistral chirality depending on its axial field direction. We determine the magnetic helicity sign of filaments using high-resolution observations performed by Transition Region And Coronal Explorer. At EUV wavelengths, filaments sometimes appear as mixtures of bright threads and dark threads. This characteristic has enabled us to discern overlying threads and underlying ones and to determine the sign of magnetic helicity based on the assumption that the

A time sequence of high-quality images currently produced by high-resolution observations either from the ground or in space may be utilized to determine the transverse flow field on the plane of the sky with the help of optical flow techniques. We have examined the performance of three different methods—a well-known technique called local correlation tracking (LCT), a recently developed technique called the differential affine velocity estimator (DAVE), and a new technique called the nonlinear

Using high-resolution vector magnetograms of NOAA Active Region 10043, observed on 2002 July 26 with the Advanced Stokes Polarimeter and low-order adaptive optics system, we studied the magnetic field topology and line-of-sight velocities in two flux cancellation sites. We found that the magnetic field is near horizontal at the place where two opposite polarities cancel each other. In addition, we observed significant downflows of about 1 km s-1 near the polarity reversal line, where the field i

The existence and behavior of vertical fine structures of plasma—threads and knots—are a significant observational clue to understanding the magnetic structure and dynamics of quiescent prominences on the quiet Sun. Based on the equation of motion in ideal MHD, we reason that the non-hydrostatic support of plasma against gravity in general requires either the motion of plasma with a high value of downward acceleration (dynamical support) or the role of horizontal magnetic fields (magnetic suppor