Richard R. Fisher

Physical Properties of Polar Coronal Rays and Holes as Observed with the Spartan 201-01 Coronagraph

Physical conditions and characteristics of polar coronal rays and polar coronal holes are derived from white-light coronal observations aboard the Spartan 201-01 spacecraft and the ground-based K-coronameter in Mauna Loa, Hawaii, on 1993 April 11-12. An array of polar rays extending from 1.16 to 5.0 R☉ was observed in both the north and south polar coronal hole regions. They appear as coherent structures at much higher altitudes than previously observed. Densities and scale height temperatures are estimated as a function of radial height for the holes and the rays. These profiles suggest that there is extended heating up to heights of 1.4-2.6 R☉.

Flow properties of the solar wind derived from a two-fluid model with constraints from white light and in situ interplanetary observations

We derive the flow properties of the solar wind in coronal holes using a two-fluid model constrained by density profiles inferred from simultaneous space-based SPARTAN 201–01 and ground-based Mauna Loa White Light coronagraph observations, and by in situ interplanetary measurements. Also used as a guide is the hydrostatic temperature profile derived from the density gradient. Density profiles are inferred between 1.16 and 5.5 Rs, for two different density structures observed along the line of sight in a polar coronal hole. The model computations that fit remarkably well the empirical constraints yield a supersonic flow at 2.3 Rs for the less dense ambient coronal hole, and at 3.4 Rs for the denser structures. The novel result that emerges from these fits is a proton temperature twice as large as the electron temperature in the inner corona, reaching a peak of 2 × 106 K at 2 Rs.

The COR1 inner coronagraph for STEREO-SECCHI

The Solar Terrestrial Relations Observatory (STEREO) is a pair of identical satellites that will orbit the Sun so as to drift ahead of and behind Earth respectively, to give a stereo view of the Sun. STEREO is currently scheduled for launch in November 2005. One of the instrument packages that will be flown on each of the STEREO spacecrafts is the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI), which consists of an extreme ultraviolet imager, two coronagraphs, and two side-viewing heliospheric imagers to observe solar coronal mass ejections all the way from the Sun to Earth. We report here on the inner coronagraph, labeled COR1. COR1 is a classic Lyot internally occulting refractive coronagraph, adapted for the first time to be used in space. The field of view is from 1.3 to 4 solar radii. A linear polarizer is used to suppress scattered light, and to extract the polarized brightness signal from the solar corona. The optical scattering performance of the coronagraph was first modeled using both the ASAP and APART numerical modeling codes, and then tested at the Vacuum Tunnel Facility at the National Center for Atmospheric Research in Boulder, Colorado. In this report, we will focus on the COR1 optical design, the predicted optical performance, and the observed performance in the lab. We will also discuss the mechanical and thermal design, and the cleanliness requirements needed to achieve the optical performance.

Large-scale coronal temperature and density distributions, 1984-1992

Abstract : In this Letter we characterize the temperature and the density structure of the corona utilizing spectrophotometric observations at different heights but it the same latitude during the descending phase of cyclic 21 through the ascending phase of cyclic 22. The data include ground-based intensity observations of the green (FE XIV Lambda 5303) and red (Fe x Lambda 6374) coronal forbidden lines, photospheric magnetographs from the National Solar Observatory, Kitt Peak, and synoptic maps of white-light K-coronal polarized brightness, pB. from the High Altitude Observatory. A determination of plasma temperature T can be estimated from the intensity ratio Fe x/Fe XIV (where T is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. Distributions of the electron temperature from the line ratio and the polarized brightness which yields electron density of the corona during the descending and the ascending phases of solar cycles 21 and 22 are presented. These data refer to structures of the corona which are relatively large scale, having a temporal coherence of at least two or more synoptic rotation periods, such as the streamer belt, the individual helmet streamers, and the larger coronal holes. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale structures in the solar magnetic fields: this organization tends to persist through most of the magnetic activity cycle.

Coronal density and temperature structure from coordinated observations associated with the total solar eclipse of 1988 March 18

This paper explores and compares diagnostics for temperature and density within large-scale structures of the inner corona based on cospatial and cotemporal spectrophotometric observations made at the time of the total solar eclipse of 1988 March 17/18. In the analysis a determination of plasma temperature T can be derived unambiguously from the intensity ratios Fe XIV/XUV or Fe XIV/Fe X since all the emission lines come from the ionized state of Fe and the ratios are only weakly dependent on density. These temperatures and the densities found in well-defined large-scale coronal structures are discussed. The emission-line temperature is found to be high (local maxima) in the coronal structures with enhanced white-light emission and associated with new cycle high-latitude magnetic fields separated from the old cycle polar field of opposite polarity. Also the average of the ratio of scale-height temperature/temperature over the entire range of position angle is roughly unity although the ratio is higher than unity (1.3-1.6) in the three most prominent streamers.

Coronal streamers and fine scale structures of the low latitude corona as detected with Spartan 201‐01 White Light Coronagraph

The solar corona was observed with an externally occulted White Light Coronagraph carried on the SPARTAN 201-01 spacecraft for a 47 hour period beginning on April 11, 1993. At this phase of the descending solar magnetic activity cycle there were well developed coronal helmet streamers located over both the east and west limbs of the sun. Of additional interest in the SPARTAN data are the finer scale streamer structures observed in the low latitude corona which are partially resolved by the SP201-01 instrument. The purpose of this investigation was to determine the physical and morphological characteristics of the streamers and the fine scale ray structures observed in the region between streamers. A comparison of these low latitude rays with the polar rays observed in the north and south polar holes during the same flight suggest that they have similar morphology and physical characteristics.

Solar Wind Consequences of a Coronal Hole Density Profile: Spartan 201-03 Coronagraph and Ulysses Observations from 1.15 R? to 4 AU

Spartan 201 is a small shuttle-launched and -retrieved satellite, whose mission is to study the origins of the solar wind. It carries on board two instruments, the Ultraviolet Coronal Spectrometer and the White-Light Coronagraph. The third mission of the Spartan 201 (1995 September 7-10) spacecraft was to provide a solar context for the in situ particles and fields measurements during the north polar passage of the Ulysses spacecraft. In this Letter, we characterize the physical conditions of the north polar coronal hole as derived from white-light coronal observations by the Spartan 201-03 White-Light Coronagraph, the ground-based K coronameter in Mauna Loa, Hawaii, and Ulysses observations of in situ particles and their velocity. For the first time, we are able to combine in situ and path-integrated measurements in a coronal hole, to yield a consistent electron density (N) profile from the Sun to the Earth and the outer heliosphere. By using the value of N measured by Ulysses (1.8-4 AU), we are able to determine the actual value of N and not just an upper limit in the polar coronal hole, near the Sun. The current N profile suggests that the acceleration of the fast solar wind in a coronal hole is complete by 10-15 R, much closer to the Sun than had been previously expected.

Solar Polar Sail mission: report of a study to put a scientific spacecraft in a circular polar orbit about the sun

The Solar Polar Sail Mission uses solar-sail propulsion to place a spacecraft in a circular orbit 0.48 Au from the Sun with an inclination of 90 degrees. The spacecrafts orbit around the Sun is in 3:1 resonance with Earth phased such that the Earth-Sun-spacecraft angle range from 30 degrees to 150 degrees. The polar view will further our understanding of: (1) the global structure and evolution of the corona, (2) the initiation, evolution, and propagation of coronal mass ejections; (3) the acceleration of the solar wind; (4) the interactions of rotation, magnetic fields, and convection within the Sun; (5) the acceleration and propagation of energetic particles; and (6) the rate of angular momentum loss by the Sun. Candidate imaging instruments are a coronagraph, an all-sky imager for following mass ejections and interaction regions from the Sun to 1 AU, and a disk imager. A lightweight package of fields and particle instruments is included. A mission using a 158 m square sail with an effective areal density of 6 g/m2 would cost approximately

Spartan 201 Coronal Spectroscopy during the Polar Passes of Ulysses

LR 250-300M for all mission phases, including the launch vehicle. This mission depends on the successful development and demonstration of solar-sail propulsion.

Temperature Structure of the High-Latitude Corona

Spartan 201 is a shuttle deployed spacecraft that is scheduled to perform ultraviolet spectroscopy and white light polarimetry of the extended solar corona during two 40 hour missions to occur in September 1994 and August 1995. The spectroscopy is done with an ultraviolet coronal spectrometer which measures the intensity and spectral line profile of HI Lyα up to heliocentric heights of 3.5 solar radii. It also measures the intensities of the OVI doublet at 1032 and 1037 Å and of Fe XII at 1242 Å. The HI Lyα line profile measurements are used to determine the random velocity distribution of coronal protons along the line-of-sight. The absolute HI Lyα intensities can be used together with electron densities from the white light coronagraph to estimate electron temperatures from hydrogen ionization balance calculations, and bulk outflow velocities from models of Doppler dimmed resonant scattering. Intensities of minor ion lines are used to determine coronal abundances and outflow velocities of O5+. Ultraviolet spectroscopy of extended coronal regions from the 11 April 1993 mission of Spartan 201 are discussed.