Cheng Fang

A semi-empirical model of sunspot umbra

Abstract Based on data obtained with the Kitt Peak Observatory Solar Tower, we have constructed a semi-empirical model of sunspot umbra. Non-LTE calculation was used. The main features are: (1) The temperature structure of the corona and the transition region is similar to the VAL3C quiet sun model. (2) The chromosphere structure is characterized by a temperature plateau; the temperature in the upper layers ishigher than those of the quiet sun and the penumbra; (3) The minimum temperature is 3130 K, about 300 K less than that of the penumbra model. (4) the temperature structure of the photosphere is similar to those in previous models, while the micro-turbulent velocity is somewhat less. We find there is no radiative balance in the whole atmosphere. The net radiative loss rate has a maximum in the middle chromosphere and it is negative in the temperature minimum region.

Application of the complete linearization method to the analysis of solar prominence emission spectrum

We analysed the emission spectra of solar prominences using the complete linearization method [5] and found simultaneously the optical depth at the line centre τ0, the doppler width of the line ΔλD and the damping width a. The results show 1) that the complete linearization method has a larger radius of convergence, 2) that we must consider the variation of the source function with depth, when determining τ0, and 3) that the calculated values of the damping constant for the Hα, Hβ of hydrogen and H and K lines of Calcium are all much greater than the theoretical values from doppler broadening and radiation damping, showing that other mechanisms besides these two also contribute to the broadening of prominence lines.

Simultaneous monochromatic and spectral observations of two large loop prominence groups

Abstract Using the solar tower telescope of Nanjing University, we observed the two large loop prominence groups of 1982 Dec. 20 and 1983 Feb. 9. Hα photographs and spectra around the Hα and H and K lines were obtained simultaneously. From these data, we derived a line of sight velocity distribution, which agrees perfectly with the distribution for matter falling freely without viscosity. From the widths of the Hα and the K lines, we found the loop material to have a uniform kinetic temperature and a turbulent velocity that increases with height. From the central intensities of the lines we derived a density of n(H) ≅ 1.3 − 2.6 × 1010 cm−3. A possible mechanism of the formation of loop prominence groups and their relation with flares are discussed.

Structure and photometry of the solar corona at the total eclipse of 1997 March 9

Abstract At the solar total eclipse of 1997 March 9, we made a series of photographic observations of the solar corona in Mohe City (Xilinji), Heilongjiang Province. On images taken with different exposures, there are many characteristic coronal structures including long and broad coronal streamers in both east and west equatorial regions, plumes containing over 20 polar rays as well as coronal holes in both south and north polar regions. Comprehensive results of measurements of the structures and brightness in the coronal images, and of the morphology and structures, and isophotometric contours and brightness profiles in both east and west equatorial regions and both south and north polar regions are presented.

CCD polarimetry of the solar corona at the 1997-03-09 solar eclipse☆☆☆

Abstract We give the treated results of our CCD polarimetric data of the solar corona obtained during the 1997-03-09 total eclipse, including the profiles of absolute brightness and degree of polarization along 12 directions (including the two equatorial and two polar directions) in the middle corona (1.6−3.2 R ⊙ )

A combined analysis of Hα, microwave and hard X-ray bursts of the flare of 1993-10-02☆

Abstract We present the results of multi-wave observations of the Class 1N/C6.5 flare of 1993-10-02. We compared monochromatic images of the flare, two-dimensional spectra around Hα, microwave bursts at 2840 MHz and hard X-ray burst data. We derived the intensity curves of different kernels in the Hα image, compared them with the time profiles of the microwave and hard X-ray bursts, gave the evolution of the brightness field of the chromosphere flare region, determined the magnetic field configuration from the magnetograms and hence proposed a possible interpretation of the generation and heating of the flare.

A study of the white light flare of 1974 September 10

Abstract We have made a detailed analysis of the spectral data of the white light flare of 1974 September 10. Using a non-LTE theory we have calculated a semi-empirical atmosphere model and its radiation loss. From the spectra we found (1) a Balmer jump amounting to 11% at the flare maximum, (2) strong and broad Balmer line emission, the width of the higher order terms reaching a minimum between main quantum number 8 and 9, and (3) the continuum emission peaking at about the same time as the microwave emission, a few minutes before the H α flare maximum. These features may be common to all white light flares. Analysis shows that the heating in the photosphere and lower chromosphere is probably produced by backwarming of the enhanced emission in the upper chromosphere, while the heating of the upper chromosphere is probably due to bombardment by high-energy electron beams.

The solar surge of 1982-12-30☆

Abstract We describe the morphology of the flare-accompanying solar surge of 1982-12-30 at S10W20 on the solar disk and give the time evolution of its velocity field. Observations of the spectrum show that there was rotating motion of 20–30 km/s during the ascent, which decreased in the course of time.

Analysis of high time resolution spectra of the 1991-10-24 white-light flare

Abstract This paper analyzes the spectrum of a Class 2N/X2.1 white-light flare obtained by the Nanjing University Solar Tower Multi-Wavelength Spectrograph on 1991-10-24 with a high time resolution (5s). A systematic comparison of the line profiles and continuum strength with the X-ray and radio burst data shows that the flare is a Type-I white-light flare with the following characteristics: 1) During the flare impulsive phase the central intensities of lines in different wavelengths, the continuum, the line half-widths, the red asymmetry of the wings and the hard X-ray burst at the high energy portion all reached maximum at the same time. 2) The Hα line had a half-width of 10 A when the continuum emission reached maximum, and showed strong line reversal at the center. Hβ and Hγ also showed line reversal. 3) The five lines observed all showed clear red asymmetry, which lasted some 1 min. Based on these results, we find electron-beam bombardment, combined with chromospheric evaporation and condensation can provide a good qualitative interpretation of the energy storage and release of this white-light flare.

Spectral analysis of the 1984 October 18 solar prominence

Abstract On the basis of [11], we calculated the various physical parameters of the solar prominence of 1984 October 18, using further the method of complete linearization and a semi-empirical model on the N-LTE theory. Our conclusions are: 1. When finding the doppler width of prominence lines δλD, the method of complete linearization is more accurate than the classical method. 2. Our semi-empirical model based on the N-LTE computer program of [9] gave a central temperature of the prominence of ∼ 5900 K, the temperature increasing from the centre outwards, a turbulence velocity of 5.5 ∼ 6.5 km/s, and a mean hydrogen density n H = 3.8 × 10 11 cm −3 . Calcium was found to be mainly as CaII and CaIII, with n (CaIII) ⪢ n (Call). 3. Our calculated distribution of the column density of hydrogen over energy levels showed that the lower energy levels are in N-LTE, the higher ones, in LTE.