Profiles of the H and K lines of CaII in disk flares

The profiles of the resonance lines of Caii have been studied in two large disk flares and in the surrounding plage. In the brightest portions of the flares no self-reversal in the central emission core was detected; self-reversed cores were present in the less bright portions of the flares. We find that as the intensity of the emission core increases the separation of the H₂ and K₂ peaks decreases monotonically, becoming unobservable at intensities near to 0.90 the local continuum. Possible reasons for the behavior of the H and K lines in flares are considered. It is suggested that the largest density enhancements in flares are found near the strongest magnetic field.     

Impulsive brightenings/velocity transients in quiescent solar prominences

In some quiescent prominences, areas are found where the H emission profiles are centrally reversed. By combining good spatial, spectral, and temporal resolution, the detailed behavior of these reversal regions has been investigated. Many of the regions show a growth and subsequent decay in the affected area, peak intensity, line width, and depth of the central reversal. Lifetimes of the time-varying reversal features range from 10 to more than 60 min, and they are found near the edges of the prominence fine structure. These events are similar to the impulsive events that the authors discussed in an earlier paper, and may share a common cause. The detailed behavior of the H line profiles is consistent with these reversal features being true self-reversal of the line, indicating unusually high column masses in these areas. Some models of condensation of coronal material to the prominence state predict temporary regions of high density, perhaps high enough to produce the observed reversal. This implies that reversal features are the result of on-going condensation of coronal material into already formed prominences, a result which impacts models of prominence formation and stability.Visiting Astronomer, National Solar Observatory (Sacramento Peak) of National Optical Astronomy Observatories, operated by Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

IV. Water resource modelling using remote sensing and object-oriented simulation

Remote sensing technology has matured significantly over the past decade. Operational satellites provide reliable, periodic coverage for all areas of the Earth. Data from these satellites are in a digital format that provides enhanced flexibility in hydrological modelling. Considerable advances in acquiring hydrological data from airborne and in situ sensors have also been achieved. Additionally, data from non-traditional remote sources such as weather radar from which spatial and temporal rainfall rates may be estimated are widely available. These new data acquisition capabilities have been paralleled by equal advancements in digital array processing and geographic information systems, which allow the effective extraction of both temporal and spatial information. This paper examines the use of object-oriented programming techniques to create dynamic hydrological models, and explores their potential to receive real and near real-time data from remote sensors as input to improve hydrological forecasting. In particular, the COE SSARR model is used to illustrate how an established hydrological model may be adapted to create a dynamic object model.     

Magnetic fields in flares and active prominences

We study the longitudinal magnetic field in a number of active limb prominences showing fields in excess of 30 G. The objects fall into three groups: surges, caps and active region prominences. There appears to be an upper limit of 150–200 G for the field strength in prominences.

A model of surges is presented in which a pre-surge axi-symmetric magnetic field is established by a line current in the corona. We observe particle acceleration in surges that indicates v×B≠0 in these objects during periods comparable to the Alfvén transit time.

The strong fields observed in caps seem to run between parts of active regions in accordance with Hale's law of sunspot group polarities.

     

Oscillations of a loop prominence preceding a limb flare

Observations of a limb flare and an associated loop prominence were obtained in H with the 512 channel magnetograph of the Kitt Peak National Observatory. Simultaneous radial and torsional oscillations with a period near 75 s, wavelength of 37 000 km, and amplitude of 1–2 km s^–1 were detected in the loop approximately 90 min before the onset of the flare. We interpret these coupled oscillations in terms of a kink instability of a current carrying flux tube. The magnitude of the steady-state component of current is estimated to be 6 × 10¹⁰ ampères.Visiting Astronomer, Kitt Peak National Observatory, operated by Aura, Inc., under contract with the National Science Foundation.Visiting Student, Kitt Peak National Observatory.     

Motions and magnetic fields in quiescent prominences

An observed relation between line-of-sight velocities and the longitudinal component of the magnetic field in quiescent prominences is discussed. Weak fields in quiescent prominences are associated with large velocities determined from Doppler shifts of resolved emission knots and Doppler line widths measured in Ca ii K line. It is suggested that the observed irregular motions in prominences are driven by photospheric horizontal convection coupled by the prominence magnetic field. An energy flux of 3 × 10⁵ ergs cm^–2 sec^–1 present in the form of Alfvén waves in quiescent prominences is consistent with the observations.     

The starting frequencies of type III bursts

During the period 1960 to 1966 the monthly averages of the starting frequencies of type III bursts declined with the level of solar activity and reached a minimum near the minimum of the solar cycle in 1964. The electron densities corresponding to the observed starting frequencies are close to those expected at the base of the K corona. It is shown that sufficient free-free absorption may occur in the corona above the appropriate plasma levels to account for the observed behavior of the starting frequencies of the bursts. The daily variation in the starting frequencies is attributed to structural variation of the inner corona. Quiescent prominences may be responsible for establishing periods of anomalously low-starting frequencies.