Engineering topics

Maltby, P.

Publications and source records attributed to Maltby, P..

3 records

NASA NTRS1991

Multiple flow velocities in the transition region

Observations with the High Resolution Telescope and Spectrograph (HRTS) of the C IV lines at 1550 A above sunspots reveal the coexistence of several distinct high velocity gas components within the instrument resolution element of 1 x 1 arcsec. A further investigation of the HRTS material demonstrates that such multiple gas velocities are not restricted to the temperature region around 100,000 K, where the C IV lines are formed, but that the gas flows with essentially unchanged speed through all temperature layers from 250,000 K to 10,000 K. Furthermore, the phenomenon is not restricted to sunspots, but occurs also in other solar regions, often most easily distinguished in active regions. The characteristics of the velocity fields are described. The mass fluxes are analyzed, and the requirements they place on the resolving power of future space instruments are discussed.

Brekke, P.↗

NASA NTRS1988

Gas flows in the transition region above sunspots

Strong downflows and moderate upflows in the transition region over a sunspot have been observed with the Spacelab 2 HRTS in 1985. The flows are found to be persistent, and it is suggested that they are common. Data show that the downflows are supersonic and that there is more than one characteristic flow speed in the downflows. Evidence is provided for constant downflows in the 30,000-230,000-K temperature range.

Kjeldseth-Moe, O.↗

NASA NTRS1986

A new sunspot umbral model and its variation with the solar cycle

Semiempirical model atmospheres are presented for the darkest parts of large sunspot umbrae, regions have called umbral cores. The approach is based on general-purpose computational procedures that are applicable to different types of stellar atmospheres. It is shown that recent umbral intensity measurements of the spectral energy distribution may be accounted for by an umbral core atmospheric model that varies with time during the solar cycle; the observed center-limb variation can be accounted for by the properties of the model. Three umbral core models are presented, corresponding to the early, middle, and late phases of the solar cycle. These three models also may be regarded as having the properties of dark, average, and bright umbral cores respectively. The effects of atomic, opacity, and abundance data uncertainties on the model calculations are briefly discussed. For comparison, a new reference model for the average quiet solar photosphere is given.

Maltby, P.↗