The current status of transition-region models is reviewed in this report. To understand modeling problems, various flow features that influence the transition process are discussed first. Then an overview of the different approaches to transition-region modeling is given. This is followed by a detailed discussion of turbulence models and the specific modifications that are needed to predict flows undergoing laminar-turbulent transition. Methods for determining the usefulness of the models are presented, and an outlook for the future of transition-region modeling is suggested. Singer, Bart A. Unspecified Center...

The current status of transition-region models is reviewed in this report. To understand modeling problems, various flow features that influence the transition process are discussed first. Then an overview of the different approaches to transition-region modeling is given. This is followed by a detailled discussion of turbulence models and the specific modifications that are needed to predict flows undergoing laminar-turbulent transition. Methods for determining the usefulness of the models are presented, and an outlook for the future of transition-region modeling is suggested.

Solar Physics publishes up to two Topical Issues per year that focus on areas of especially vigorous and active research. The present Topical Issue contains papers of recent results on the solar corona, as well as on the transition region and low solar wind. The majority of these papers, which were all refereed in accordance with the standards of Solar Physics, were presented in August 1999 at a workshop held in Monterey, California. The authors were offered the opportunity to present relevant parts of their contributions on an accompanying CD ROM of this Topical Issue. The Sun's magnetic field is responsible for the spectacularly dynamic and intri cate phenomenon that we call the corona. The past decade has seen an enormous increase in our understanding of this part of the solar outer atmosphere, both as a result of observations and because of rapid advances in numerical studies. The Yohkoh satellite has observed the Sun now for over eight years, producing spectac ular sequences of images that convey the complexity of the corona. The imaging and spectroscopic instruments on SOHO have added information on the cooler part of the corona. And since April of 1998 TRACE has given us very high resolution images of the 1-2 MK corona, at cadences that allow detailed observations of field oscillations, loop evolution, mass ejecta, etc.

The solar transition region, which spans the temperature range from about 20,000 to 1,000,000 K, separates the chromosphere from the corona. All the energy that heats the corona and powers the solar wind must pass through this part of the solar atmosphere. This book summarizes recent ultraviolet and extreme ultraviolet observations of the transition region, the empirical models derived from them, and the physical models that try to explain both the observations and the empirical models. The observational focus is on quiet solar transition region observations made with Skylab and subsequent rocket and satellite experiments. The book also presents a unified discussion of the analysis of ultraviolet and extreme ultraviolet spectroscopic data, including the determination of the emission measure and density and temperature diagnostics. This will be useful to astrophysicists who are confronting high-resolution ultraviolet and extreme ultraviolet data from astrophysical plasmas for the first time.