Andrew Robert Breen

Fast solar wind after the rapid acceleration

[1]xa0We have studied the radial dependence of the velocity of high-latitude fast solar wind in the heliocentric distance range of 0.13–0.9 AU. For this study a new tomographic analysis method which can evaluate uncertainties was developed to obtain velocity distribution maps on two reference spheres at 0.13 and 0.3 AU using interplanetary scintillation (IPS) observations. First of all, it is tested that this tomographic method has enough sensitivity and reliability to investigate the radial dependence of the wind velocity. The analysis was made for the IPS observations during 3 years, from 1995 to 1997, when solar activity was minimum. From this analysis, average velocities of 770–780 km s−1 were obtained at distances of 0.13–0.3 AU, which were 19 ± 17 km s−1 lower than those at 0.3–0.9 AU. The results from this work, taken together with measurements of SOHO/LASCO, EISCAT and MERLIN [Breen et al., 2002], Helios [Schwenn et al., 1978], and Ulysses [McComas et al., 2000], indicate that the fast wind is accelerated almost to its final flow velocity within 20 Rs and a small but not negligible acceleration exists beyond 30 Rs which tends to become smaller at farther heliocentric distances.

Large-scale structure of the fast solar wind

We present the results of a comprehensive study of the fast solar wind near solar minimum conditions using interplanetary scintillation (IPS) data taken with the EISCAT system in northern Scandinavia, and a recent extremely long baseline observation using both EISCAT and MERLIN systems. The results from IPS observations suggest that the fast wind inside 100 solar radii (R-circle dot) can be represented by a two-mode model in some cases but this distinction is much less clear by in situ distances beyond 1 astronomical unit (215 R-circle dot). Two distinct fast streams are seen in the extremely long baseline IPS observation; comparison of the IPS line of sight with a synoptic map of white light indicates the faster mode overlies the polar crown and the slower fast mode overlies an equatorial extension of the polar coronal hole.

Extremely long baseline interplanetary scintillation measurements of solar wind velocity

[1]xa0We present results of observations of interplanetary scintillation (IPS) made using the telescopes of the MERLIN and EISCAT networks in which the beam separation approached 2000 km, much larger than in any previous IPS experiments. Significant correlation between the scintillation patterns was observed at time lags of up to 8 s and fast and slow streams of solar wind were very clearly resolved. One observation showed clear evidence of two discrete modes of fast solar wind, which we interpret as originating in the crown of the northern polar coronal hole and in an equatorward extension of the polar hole. We suggest that experiments of this type will provide a new and important source of information on the temporal and spatial variation of small-scale turbulence in the solar wind. The improved velocity resolution available from extremely long baseline measurements also provides new information on the development of the large-scale velocity structure of the solar wind in interplanetary space.

Large-scale structure of the solar wind from interplanetary scintillation measurements during the rising phase of cycle 23

Multi-site measurements of interplanetary scintillation (IPS) can provide information on solar wind velocity at any heliolatitude or longitude and over a wide range of heliocentric distances, with the coverage limited only by the availability of suitable radio sources and the geometry of the observing system. The EISCAT facility has been used to make IPS measurements every summer from 1989 to the present day. In this paper we discuss results from solar minimum in 1996, through the rising phase of cycle 23 to the spring of 2000. We discuss the changes in the large-scale structure of the solar wind seen in the EISCAT IPS data and compare them with results from the Nagoya IPS system and with structures seen in coronal white-light intensity.

Slow and fast solar wind acceleration near solar maximum

Abstract 2-site measurements of interplanetary scintillation (IPS) provide measurements of solar wind speed in regions of the heliosphere which are otherwise inaccessible. We present results from co-ordinated observations made with the EISCAT and MERLIN facilities during 1999 and 2000, covering heliocentric distances from 7 to 80 solar radii (R) predominantly in the slow solar wind. The 1999 results are compared with optical measurements from LASCO covering 4–30 R. Most slow acceleration appears to take place between 5 and 10 R, but the slow wind continues to accelerate out to 25–35 R. Some of the observations included identifiable fast flow, and in these regions acceleration began lower down and was much more rapid, with 50% of cruising speed reached by 4–5 R and acceleration complete inside 10 R — results which are similar to those from solar minimum.

Combined STELab, EISCAT, ESR, and MERLIN IPS observations of the solar wind

The technique of interplanetary scintillation (IPS) can be used to probe interplanetary space between the Sun and Earth most-commonly in terms of speed and also by using the scintillation-level (g-level) as a proxy for density. We combine the large spatial-scale 3D tomographic techniques previously only applied to IPS data from the Solar Terrestrial Environment Laboratory (STELab) array, Nagoya University in Japan, and the previously operational Cambridge IPS system in England, with the finer-scale capabilities of the longer baselines between the systems of the Multi-Element Radio-Linked Interferometer Network (MERLIN) in the UK, and the European Incoherent SCATter (EISCAT) radar and the EISCAT Svalbard Radar (ESR) in northern Scandinavia. Using the UCSD 3D reconstruction technique, we present results of detailed measurements of speed in the solar wind and also those of solar wind flow-directions, constrained by the large-scale density tomography through the use of a kinematic model, as well as applying this tomographic technique for the first time to the MERLIN, EISCAT, and ESR IPS solar wind speed observations in terms of velocity.

The relationship between electron density and electron temperature under quiet conditions in the Auroral zone

A theoretical model accurately predicts the electron temperature in the daytime F-region given the observed values of electron density, ion temperature, the daily average value of 10.7-cm solar radiation and the MSIS-86 model of the neutral atmosphere. The model was originally developed using data from Malvern, St.Santin and Arecibo and has now been confirmed using data from EISCAT on geomagnetically quiet days. The quality of EISCAT data is good enough to allow the comparison of predicted and observed values of Te on an hourly basis, including estimates of cooling by heat conduction. The agreement is very good for all data from quiet conditions, with an overall correlation coefficient of 90%. The relationship can also be used to indicate the ratio of [N2] to [O] over the height range 250–340 km.

Theoretical model of electron temperature and electron density: Comparisons with IRI and MSIS

Abstract An earlier theoretical model (UW-87) accurately predicted the electron temperature in the daytime F-region but suggested N2 concentrations significantly greater than the predictions of MSIS-86. This discrepancy is resolved when the model is developed to include the effects of vibrationally excited nitrogen molecules and electronically excited oxygen ions on the F-region recombination rate. The revised model (UW-92) continues to predict electron temperatures close to the layer peak with great accuracy but it is now more closely consistent with MSIS. However, the electron temperatures predicted by this model, which are in close agreement with EISCAT observations, are significantly higher than the values predicted by the international Reference Ionosphere.