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The 3-D Sun and Heliosphere at Solar Maximum

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The 3-D Sun and Heliosphere at Solar Maximum Meeting report uous fast wind was again evident although over a more limited latitude range. Despite the effects of interaction modifying the speeds, the The 3-D Sun and three types of solar wind stream can be easily distinguished using composition measurements. Bob Forsyth (IC, standing in for André Balogh) described magnetic field measure- heliosphere at ments. Although more variable than at mini- mum, the radial component of the heliospheric magnetic field remains on average independent of latitude at solar maximum. The heliospheric solar maximum current sheet separating the two polarities of the magnetic field, confined to the equatorial regions at solar minimum, was observed at the Bob Forsyth and Andy Breen report from the RAS G Discussion Meeting highest southern latitudes, but the solar maxi- Downloaded from https://academic.oup.com/astrogeo/article/43/3/3.32/192290 by guest on 29 September 2021 at the Geological Society on 11 January 2002. Presentations came from mum field reversal was definitely over when both the solar and heliospheric communities, on the 3-D structure and Ulysses reached the northern hemisphere. Silvia Dalla (IC) reported on solar energetic dynamics of the solar corona and heliosphere and their inter-relation particles (SEPs) at high latitudes. High-energy during the present maximum in the solar activity cycle. SEPs easily propagate to high latitudes at solar maximum with flux profiles remarkably simi- he first speakers compared the structure comparison to the south hole. lar to those observed by spacecraft in the eclip- of the solar corona seen by instruments Louise Harra (MSSL) reviewed 10 years of tic. However, lower energy SEPs do not appear Ton the SOHO spacecraft between solar X-ray corona observations by Yohkoh. Two to propagate to high latitudes as efficiently. minimum and maximum. At solar minimum, key topics were the physics of solar flares, Trevor Sanderson (ESTEC) discussed the bright dense streamers are confined to near the discussing reconnection models, and precur- influence of the Sun’s magnetic field on ener- solar equator while coronal holes show up as sors for coronal mass ejections (CMEs), for getic particles in the heliosphere, suggesting dark regions around the poles. At solar maxi- example, coronal dimming, the disappearance that the ease of access of SEPs to high latitudes mum, streamers appear at any latitude and of transequatorial loops, or the appearance of was related to the high tilt and/or warp of the coronal holes tend to be smaller and spread sigmoidal (S-shaped) structures in the corona. heliospheric current sheet at solar maximum. over all latitudes. It is generally accepted that Gareth Lawrence (Goddard) summarized Discussing near-relativistic electrons (0.4– fast solar wind originates from coronal holes observations of CMEs with the SOHO/LASCO 0.8c), George Simnett (Birmingham) presented and slow solar wind from around streamers. coronagraph, emphasizing the dependence of evidence that they were accelerated by CME- Shadia Habbal (Aberystwyth) used the CME occurrence rates and properties on the driven shocks at about 1 RS above the photo- SOHO/UVCS instrument to explore the transi- solar cycle. At solar maximum, most CMEs sphere, based on comparisons of timing between tion between the fast and slow solar wind in still originate in the equatorial regions but Type III radio bursts, CME launch times and the the inner corona beyond 1.5 RS, finding that there are more high-latitude events reflecting electron ejection into interplanetary space. the transition occurs within ±15–20° of the both the increase in complexity of the coronal In the final talk, Geraint Jones (IC) described streamer axes at all phases of the solar cycle, field and the loss of polar coronal holes. how comets could provide valuable information that the fast wind at solar maximum is not as Andy Breen (Aberystwyth) discussed the on conditions in the heliosphere throughout the fast as at minimum, and that the fast wind is interplanetary scintillation (IPS) technique for solar cycle. Tail structure and/or disconnections not necessarily associated with identifiable probing the solar wind in the inner heliosphere can indicate the location of the heliospheric coronal holes. This leads to the suggestion that between 30 and 70 RS at all heliolatitudes, a current sheet or slow/fast solar wind stream some magnetic field lines open to the helio- region not open to other measurement tech- boundaries. Comet C/2000 WMI (LINEAR) sphere may originate among the low-lying niques. IPS is a powerful tool for establishing was being observed at high southern heliolati- closed magnetic field structures in the corona. the evolution of the large-scale solar wind tudes to complement the Ulysses observations. Mihalis Mathioudakis (Belfast) reported on structures in this region and thus placing high- There were also posters, presented by Carl observations made with the SOHO/CDS er resolution in-situ measurements in context. Foley (MSSL) on radial temperature in large- instrument to determine the variation of elec- scale coronal structures, Lucie Green (MSSL) tron density in the inner corona as a function Ulysses on helicity evolution in an active region, Adam of radial distance and latitude, finding a lower During its second solar orbit, Ulysses revisited Mercer (Birmingham) following the dynamics electron density near the pole, in general agree- the polar regions of the heliosphere in Novem- of a twisted loop eruption out to 6.5 RS, Adam ment with observations made by Ulysses much ber 2000 and October 2001, this time under Rees (IC) on magnetic clouds observed by further out in the heliosphere. solar maximum conditions. In the first of four Ulysses and David Tsiklauri (Warwick) on the Sami Solanki (Lindau) used Ulysses data on talks on Ulysses results, Ruedi von Steiger (ISSI, interaction of nonlinear MHD waves with the charge state ratios of oxygen ions in the Bern) summarized the solar wind measure- solar wind plasma structures. solar wind to infer the freezing-in temperature, ments. Unlike solar minimum, when the polar The organizers would like to thank all the representative of the electron temperature in regions were dominated by continuous fast participants for their part in making the meet- the coronal source regions of the wind. At solar wind from the polar coronal holes, ing the great success it clearly was based on the solar minimum, the north polar coronal hole Ulysses encountered a chaotic mixture of slow, many positive comments from those present. G was found to be 20% cooler than the south, fast and transient (due to CMEs) streams in the possibly related to a larger coronal hole area south polar regions at solar maximum. In the Bob Forsyth (Imperial College) and Andy Breen and lower magnetic flux density at that time in north, as solar activity began to decline, contin- (Aberystwyth). 3.32 June 2002 Vol 43.
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