POLAR CORONAL JETS AT SOLAR MINIMUM

摘要

We present an analysis of six polar coronal jets observed by the Ultraviolet Coronagraph Spectrometer (UVCS) at solar minimum (1996). Four of the events were also recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) and/or the Large Angle Spectrometric Coronagraph (LASCO) C2 coronagraph. We compared the jets with others recorded in 1997. We modeled the observable properties of the jet from 1996 June 11, detected at 1.5 solar radius. It represents a type of polar jet in which H Ⅰ Lyα and O Ⅵ get brighter at the same time. The model reproduced the line properties with an electron density enhancement of a factor of 2 (with a resulting density of 4.8 x 10~6 cm~(-3)), an outflow velocity enhancement of a factor of 3 (yielding a velocity of 200 km s~(-1)), and an electron temperature decrease of a factor of 0.36 (with a resulting temperature of 5.3 x 10~5 K). We derived the jet's electron densities from the LASCO C2 white-light observations. They are a factor of 1.5 higher than in the interplume corona and comparable to those in plume regions within the C2 field of view. We developed a model for the origin of polar jets based on Wang's model for plumes. We envisioned that jets may be the result of short-lived bursts of base heating, while plumes may be the result of base-heating events that last longer than several hours. Models with the base heat flux near 3 x 10~5 ergs cm~(-2) s~(-1) come closest to matching the observations, though they are not entirely consistent.