P.J. Moran

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.

Measurements of the solar wind over a wide range of heliocentric distances — a comparison of results from the first three Whole Sun Months

Abstract Co-ordinated observations of the Sun and inner heliosphere using a large number of space- and ground-based instruments were carried out in August–September 1996, August 1998 and August–September 1999 as the first, second and third Whole Sun Months. These observations provided unprecedented cover of the Sun and inner heliosphere at solar minimum (1996) and during the rising phase of the new solar cycle (1998, 1999). In this paper we review the observations made during the three Whole Sun Months and consider the changes in the large-scale structure of the heliosphere seen over the four years.

Eiscat measurements of interaction regions in the solar wind

Abstract EISCAT measurements of interplanetary scintillation (IPS) have shown that the solar wind is normally dominated by distinct fast and slow components of flow. A minority of observations show velocities intermediate between those of fast and slow streams. The properties of these events are consistent with observations of the compression region at the leading edge of a co-rotating interaction region (CIR) or, in a minority of cases, with the passage of a coronal mass ejection (CME) through the solar wind.

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.

Comparisons of interplanetary scintillation and optical measurements of solar wind acceleration with model results

Abstract Observations of the fast, high latitude solar wind show that acceleration of the fast wind is complete by 10 solar radii (R), while measurements from the LASCO instrument on SOHO show that most of the acceleration takes place inside 5 R. A series of observations were made in September 1997 using EISCAT and the C2 and C3 coronagraphs aboard SOHO to measure the solar wind velocity profile from 3 R out to beyond 30 R. The overlapping fields of view of the instruments allowed direct comparisons to be made between IPS and optical estimations of flow velocity. Together, these measurements provide strong constraints on any model seeking to provide an explanation of the acceleration of the fast solar wind. We present the results of a comparison between out observations and the most recent version of the Lindau-Warsaw solar wind acceleration model.

Interplanetary scintillation measurements of the solar wind above low-latitude coronal holes

Abstract Observations of interplanetary scintillation (IPS) made using the EISCAT facility provide accurate measurements of solar wind velocity between 15 and 120 solar radii. In this paper we present observations of the solar wind at low latitudes made between 1994 and 1997. Of 178 observations of the solar wind at low heliographic latitudes, 112 showed evidence of flow velocities significantly faster than the normal slow wind across a portion of the ray-path. In all cases, these enhanced flow speeds were clearly associated with coronal holes extending towards or across the heliographic equator. Fast flow from very close to the heliographic equator is clearly associated with equator-crossing coronal holes in all cases, suggesting that discrete streams of fast wind observed at low latitudes originate exclusively in coronal holes.

EISCAT measurements of the solar wind: Observations of interaction regions

Abstract EISCAT can make measurements of corotating interaction regions (CIRs) at distances of less than 30 solar radii to more than 120 solar radii from the Sun. These regions are characterised by velocities intermediate between those of undisturbed fast and slow flow and by increased levels of scintillation. The long baselines between the EISCAT sites make it possible to resolve two components of plasma velocity present in the IPS line of sight, while comparisons with white-light coronagraph measurements and IMP-8 velocity measurements allow regions of compressional interaction to be identified. In this paper we present results of a study of corotating interaction regions using EISCAT data taken between 1990 and 1996. We also discuss observations of transient events (Coronal Mass Ejections) in the solar wind.

The high-latitude solar wind in EISCAT interplanetary scintillation data, 1991–1999

Abstract Observations of interplanetary scintillation (IPS) have been used for more than 35 years to study the velocity and morphology of the solar wind. The long baselines available between the sites of the EISCAT facility allow high-resolution velocity measurements to be made with a high degree of accuracy. Measurements are available from every summer since 1989 and since 1991 a regular programme of observations has been carried out, allowing study of the large—scale structure of the solar wind during the declining phase of cycle 22 and the ascending phase of cycle 23.

Interplanetary scintillation measurements of high-speed flow in the low-latitude solar wind

Observations of interplanetary scintillation (IPS) made using the EISCAT facility provide accurate measurements of solar wind velocity between 15 and 120 solar radii (R). In this paper we present observations of the solar wind at low latitudes made between 1991 and 1998, with particular emphasis on flow from trans-equatorial coronal holes.

EISCAT measurements of the solar wind: Measurements of the fast and slow streams

Abstract EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130 solar radii (R). The results show that away from transients and interaction regions the solar wind consists of two distinct components - a fast stream with a velocity of ∼700–800 km/s and a slow stream at ∼300–400 km/s. Both the fast and slow streams finish their acceleration much closer to the Sun than expected, with the acceleration much closer to the Sun than expected, with the acceleration of the fast high latitude solar wind being effectively complete inside 10 R. The flow vector of the solar wind is normally purely radial to the Sun, although one set of observations suggests a small but significant deviation from radial flow.