RAS "G/MIST" discussion meeting
March 9 2001

Geological Society Lecture Theatre, Burlington House, Piccadilly, London

[Report published in Astronomy & Geophysics 42, 3.35-3.36 (2001)]

A. Programme B. Report

Living with an Active Star: Solar cycle changes, eruptive events and terrestrial consequences

Organisers: Dr Andy Breen (Aberystwyth) and Dr Mike Hapgood (Rutherford-Appleton Laboratory)


Ground and space-based observations have shown that the Sun is far from 
being a stable, unchanging object. Rather, we live within the outer atmosphere
of a variable star. Taking place just after solar maximum, this meeting draws 
together the results of recent research into the Sun-Earth energy flow and 
the terrestrial consequences of solar variability.

Other comments: Recent discoveries from space- and ground-based
instruments, from sophisticated computer modelling and from painstaking
analysis of long-period datasets have led to new insights into the physics
of the magnetically coupled Sun-Earth system. These, in turn, have led to
a new appreciation of the effects of solar activity on the Earth and
on man-made systems. This meeting, taking place just after the peak in the
11-year solar activity cycle, draws together the results of recent studies
of the active Sun, both on short time-scales (solar flares, coronal mass
ejections and their effects on geospace) and over longer periods (11-year
and longer solar variations and their terrestrial consequences) in a
series of invited and contributed talks and posters. The speakers include
many of the leading figures in the field, of solar-terrestrial physics as
well as Ph.D. students and younger researchers, presenting results that 
trace the effects of solar activity from their origins on the Sun, through
interplanetary space and their interactions with the Earth and man-made
The highlights of the meeting include reviews of the most recent
investigations into the link between solar flares and coronal mass
ejections (Fletcher, Harrison), the propagation of these events
though interplanetary space (Schwenn) and their interaction with the
magnetic field and upper atmosphere of the Earth (Cargill, Lanchester,
Aylward and Millward), as well as the effects of solar activity on
man-made systems (Thompson, Wrenn) and climate (Lockwood). The
results are placed in their historical context by the talk by Henry
The last talk of the meeting is by Mike Lockwood and reviews the most
recent developments in the very important investigation of the effects of
long-period solar changes on climate and the implications for interpreting
climate change. This talk is therefore of interest to a wide

09:30 Registration, coffee and poster viewing Morning Session Chair: Dr M. Hapgood (Rutherford-Appleton Laboratory) 09:55 Andy Breen (University of Wales, Aberystwyth): Introduction and announcements. 10:00 Lyndsey Fletcher (Glasgow University): "Solar flares and their relationship to coronal mass ejections" 11:10 Bob Bentley (Mullard Space Science Laboratory, University College London): "Signatures used for CME prediction" 10:20 Robert von Fay-Siebenburgen (Sheffield University): "Nanoscale eruptive events" 10:30 Richard Harrison (Space Science Division, Rutherford-Appleton Laboratory): "Coronal dimming and coronal mass ejection onsets" 10:40 Rainer Schwenn (Max-Planck Institut für Aeronomie, Katlenburg-Lindau, Germany): "Coronal mass ejection initiation, development and interplanetary propagation" 11:10 Alexi Glover (Mullard Space Science Laboratory, University College London): "Sigmoidal Solar Features and their Implications for coronal mass ejection prediction" 11:20 Henry Rishbeth (Southampton University): "The centenary of solar-terrestrial physics?" 11:40 Mark Lester (University of Leicester) : "On the Impact in the Ionosphere of Solar Variability: SuperDARN observations" 12:00 Peter Cargill (Imperial College of Science, Technology and Medicine, London): "Solar wind - magnetosphere coupling associated with Interplanetary CMEs: Lessons from global modelling" 12:30 LUNCH AND POSTER VIEWING Afternoon Session Chair: Dr W.P. Wilkinson (University of Brighton) 13:20 Betty Lanchester (Southampton University): "Magnetosphere-Ionosphere coupling under disturbed conditions: interpreting auroral signatures from above and below" 13:50 R. Balthazor (Sheffield University): "Magnetosphere-Ionosphere-Thermosphere coupling: understanding the building blocks in thermospheric reservoir heating" 14:00 Alan Aylward & George Millward (University College London): "Stirring up the thermosphere: ionosphere thermosphere coupling" 14:30 Nigel Fox (National Physical Laboratory): "Quantifying solar irradiance variability" 14:40 Alan Thomson (British Geological Survey): "Geomagnetic Induced Currents in Power Grids of Northern Europe: Terrestrial Consequences of Magnetic Storms in 2000" 14:50 Gordon Wrenn (T.S. Space Systems): "Relativistic Electrons, 1989-2000: a changing threat to spacecraft in the magnetosphere" 15:00 Mike Lockwood (Rutherford-Appleton Laboratory): "Long term variations in the coronal magnetic field and its implications for mankind's environment and systems" 15:30 Tea At Savile Row followed by the A&G (Ordinary) Meeting
9:30 Registration: No charge. Coffee will be provided in the Lower library of the Geological Society A simple lunch will be available for purchase in the Lower Library of the Geological Society 15:30 Tea will be provided in the Scientific Societies Lecture Theatre, Savile Row for those attending the A&G (Ordinary) Meeting at 16.00 A Drinks Party will be held in the Coffee Room of the Scientific Society's Lecture Theatre 18.00 to 19.00 cost just £1.00 per head.
Posters: "Solar energetic particles and radiation levels experienced by commercial flights" (provisional title) Bob Bentley (Mullard Space Science Laboratory, University College London) "Sigmoidal Solar Features and their Implications for coronal mass ejection prediction" Alex Glover (Mullard Space Science Laboratory, University College London) "Interplanetary propagation of coronal mass ejections: case studies" (provisional title) Alison Canals (University of Wales, Aberystwyth) "How to avoid effects of space weather on satellites - a Tsunami initiative" Norma B. Crosby, Andrew J. Coates (University College London), Richard B. Horne and Mervyn P. Freeman (British Antarctic Survey, Cambridge) "Scintillation intensity signatures of coronal mass ejections" (provisional title) Richard Fallows (University of Wales, Aberystwyth) "Trajectories of prominence eruptions and their association with the coronal activities" K. Hori and L. Culhane (Mullard Space Science Laboratory, University College London) "The European Science Foundation's Scientific Network SPECIAL, Space Processes and Electrical Changes Influencing Atmospheric Layers" Michael Rycroft (ISU Strasbourg) "Upgrading EISCAT - proposals for improving the effectiveness of EISCAT as a solar-terrestrial observatory" G. Wannberg (EISCAT Scientific Association, Kiruna) and Andy Breen (University of Wales, Aberystwyth)

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RAS G/MIST discussion meeting, 9 March 2001
Living with an Active Star: Solar cycle changes, eruptive events and terrestrial consequences

Meeting Report

by Andy Breen (University of Wales, Aberystwyth)

Published in Astronomy & Geophysics 42, 3.35-3.36 (2001)

The RAS discussion meeting on "Solar activity and terrestrial consequences", organised by Andy Breen (Aberystwyth) and Mike Hapgood (Rutherford-Appleton Laboratory) was held at Burlington House on 9th March 2001.

Flares and mass ejections

Mike Hapgood chaired the morning session, which opened with a review of solar flares and their relationship to coronal mass ejections (CMEs) by Lyndsay Fletcher (Glasgow). The phenomena both appear to have their origin in restructuring of the coronal magnetic field, but their relationship is far from clear. Furthermore, the flare volume is much smaller than that of the CME, CMEs and flares can originate at very different latitudes, there is no clear relationship in time between flares and CMEs and the standard 2-dimensional model of flares suggests spatial and timing relationships which are not seen in data. It is therefore not useful to think of a flare causing a CME or vice versa, but rather both types of event are consequences of changes in the configuration of the magnetic field in the corona. The magnetic field configuration also determines the relationship between the two phenomena - a flare that involves flux transfer rather than large-scale field opening may not be associated with a CME.

Staying with eruptive events in the solar atmosphere, but moving from large to small scales, Robertus Erdelyi (Sheffield), compared the results of 2D MHD simulations of micro-scale reconnection with measurements from instruments on the SOHO and TRACE spacecraft and observations in hydrogen alpha from Tenerife and La Palma. The results confirmed that micro-scale or even nano-scale flaring resulting from small-scale magnetic reconnection could be an important source of mass flux and momentum for the solar wind, and that these processes are important in the evolution of the corona.

Richard Harrison (Rutherford-Appleton Laboratory) then discussed the relationship between coronal dimming and coronal mass ejections, reporting results from a long-running SOHO multi-instrument campaign observing extreme ultra-violet signatures of CME onsets. Some 15 such events have been identified in this way, and detailed analyses of 7 of these were presented. All showed clear dimming of coronal emission lines, which served to identify the source region of the eruption and to estimate the amount of mass removed from the low corona. These mass estimates were very similar to the mass of material ejected through the outer corona as a CME. An intriguing fact is that in many cases the low coronal dimming appears to start before the CME onset.

Coronal mass ejections also formed the subject of the talk given by Rainer Schwenn (Max-Planck Institut für Aeronomie), who discussed their initiation, development and interplanetary propagation. Mass ejections, though notoriously variable in mass, velocity and morphology, are readily recognisable in coronagraph measurements. Importantly, a CME is an ejection of mass through the corona not an ejection of coronal mass.

When considering the terrestrial consequences of CMEs, it is important to recognise that small, unspectacular events can be highly geoeffective. The important point is the rotation of the magnetic field in the CME - a southward turn in the z-component of the interplanetary field is needed for a geoeffective event. The topology and orientation of filaments are the same before and after the eruption and in any ejected interplanetary magnetic cloud, suggesting that the likely geoeffectiveness of a CME can be estimated by considering the polarity of the region of origin.

One of the outstanding problems in understanding interplanetary CMEs is how the 3-part structure of CMEs in the corona (leading edge, void and core) evolves into the 2-part structure (shock and ejecta) seen in interplanetary space. In-situ observations have shown remnants of cold prominence material in the ejecta and hot material near the shock, but no evidence of a shock has been seen in coronal observations of even the fastest CMEs. It appears likely that the shock develops and starts to slow at distances somewhere between 30 and 60 R.

The next talk, given by Bob Bentley (Mullard Space Science Laboratory, UCL), concerned signatures used for CME prediction. To do this it is necessary to predict both the CME onset and the likely Bz of the event. A continued programme of observation, giving continuous coverage with good cadence in many wavelengths is required to reconcile the predictions of different models of CME initiation and development. Prediction of geoeffective CMEs is still some way off, but this should improve as new instruments become available.

Sun-Earth connections

Henry Rishbeth (Southampton), provided an historical context for discussions of the Sun-Earth system by presenting a review of the beginnings of solar-terrestrial physics The subject may be said to originate in 1900, with letters published by Lodge and Fitzgerald, suggesting that electron streams from the Sun were the cause of magnetic storms and aurora. Fitzgerald also speculated that the Earth has a "magnetic tail". Marconi's transatlantic radio transmission in 1901 was followed by Lodge's suggestion of an "ionosphere" produced by solar radiation. From this fascinating discussion of the beginnings of our field, the meeting came up to date with a talk by Mark Lester (Leicester) on the impact on the ionosphere of solar variability, as seen in SuperDARN observations. The Super Dual Auroral Radar Network (SuperDARN) can be used to monitor the high-latitude ionospheric convection pattern on a routine basis. These data can be used to understand the coupling between the solar wind, magnetosphere and ionosphere and as inputs for models of this coupled system. The propagation characteristics on the radar beams can also be used to investigate the effects of large solar events on the ionosphere, e.g. the black-out of all northern hemisphere SuperDARN radars caused by the Bastille Day storm in July 2000.

The last talk of the morning session was given by Peter Cargill (Imperial College), who reviewed the status of large-scale modelling of CMEs in the solar wind and their interaction with the magnetosphere. He showed that existing MHD models already do a quite reasonable job in the interplanetary medium, but that more physics needs to be included, particularly in the ring current and the interface with the ionosphere, thermosphere and lower layers of the neutral atmosphere. He further suggested that the ultimate aim of the modelling community should be a coupled solar corona to neutral earth atmosphere model, which could be achievable by the UK community in about 10 years.

Interpreting the aurora

The afternoon session, chaired by William Wilkinson (Brighton), was opened with a talk by Betty Lanchester (Southampton), on interpreting the aurora from above and below. Detectors on spacecraft now provide superb views of the aurora from space in wavelengths that separate the emissions resulting from electron and ion precipitation. The unique signature of proton precipitation is the Doppler-shifted emission from hydrogen atoms, formed by charge exchange with atmospheric molecules. Observations made with the Southampton/UCL imaging spectrograph on Svalbard have provided higher spectral resolution of the hydrogen Balmer beta line than any previous measurements. These measurements, combined with Lyman-alpha data from the IMAGE satellite and particle data from polar orbiting satellites, make it possible to establish the source and energy of the precipitating protons and their relation to the electron population.

Next, Richard Balthazor (Sheffield) discussed recent work on thermospheric heating and showed that factors such as fine-scale Joule heating, transonic effects of viscosity as neutrals approach Mach 1 and shock heating if they exceed this speed, as well as plasma wave heating can be important. Coupled ionosphere-thermosphere model results showed that high-speed ion flows could drive neutrals to supersonic velocities, producing around 1000 K of thermospheric heating at F-region altitudes.

Modelling the upper atmosphere

The theme of ionosphere-thermosphere coupling continued in the next talk, given by Alan Aylward. One framework that is being increasingly used to interpret observations of the "receiving end" of the solar-terrestrial system are 3-dimensional numerical models, represented in the UK by CTIP (the Coupled Thermosphere Ionosphere Plasmasphere). This model is already capable of accurately simulating long-term variability such as solar-cycle or seasonal effects, and in most circumstances the large-scale thermospheric and ionospheric consequences of geomagnetic activity. The development is now more towards understanding the coupling to regions above and below. The model has been extended to include the middle atmosphere. If the ultimate goal is to model solar-terrestrial interactions from the surface of the Sun to the surface of the Earth, this type of model will be the crucial "anchor" at the terrestrial end, though there is still a lot to be done to couple it to models of the lower stratosphere and troposphere and to models of the magnetosphere.

Nigel Fox (National Physical Laboratory), then spoke concerning measurement of the total radiative output of the Sun, the currently accepted record of which is based on an amalgamation of measurements from different space-based radiometers. An accuracy of around 0.1% is claimed for the individual instruments but the results may differ by as much as 0.5%, which is much greater than the variation over a solar cycle. A solar variability mission under development at the National Physical Laboratory uses new technologies to reduce uncertainties in irradiance by a factor of nearly 100. This improvement would aid climate modelling and aid studies of the physical processes occurring within the Sun.

Magnetic storms

The meeting then moved on to consider the effects of solar variability on technological systems, with a talk given by Alan Thompson (British Geological Survey). Magnetic disturbances can have severe consequences for power transmission systems, and the talk reviewed the impact of two magnetic storms in 2000 on power grids in Scotland and Finland. An example of monitoring equipment installed in the Scottish grid was discussed, and animations of the changes in measured induced current and the estimated geoelectric current were shown for northern Europe during the storms of 6th April and 15th July. The rapid time variations and spatial complexity of the disturbances were very apparent in these results.

Gordon Wrenn (T.S. Space Systems) presented results of a study of the effects on spacecraft of electrons accelerated to relativistic velocities by solar activity. "Phantom commands" occurring in spacecraft systems are often caused by changes in the space environment, with electrons in the MeV energy range penetrating the spacecraft skin. Results presented showed a remarkable degree of correlation between phantom commands and GOES observations of electrons with energies of more than 2 MeV. There is a clear association between high energy electrons and persistent coronal holes as well as with solar proton events and CMEs. This rare demonstration of environmental cause with engineering effect clearly establishes and important new aspect of "space weather".

Space climate change

The final talk of the meeting was given by Mike Lockwood (Rutherford-Appleton Laboratory) and concerned the recent discovery of long term variations in the coronal magnetic field the implications of this variation for mankind's environment and systems. The aa geomagnetic index provides a continuous record back to 1868, while sunspot number records and the number of nights when aurora were seen in southern Finland cover an even longer period, and all of these measures of magnetic activity have increased by a factor of about 2 over the last 100 years. Calculated values of aa derived from solar wind velocities over the whole period that interplanetary measurements are available showed a very high order of agreement with the actual aa index, with a correlation coefficient of 95-97%. There is a similarly high order of agreement between coronal source fluxes calculated from solar wind measurements and aa. This good agreement is maintained out of the ecliptic when source fluxes estimated from aa and determined from Ulysses measurements of the polar solar wind are compared, showing that aa provides a reliable long-term measure of the coronal source flux. The increase in aa seen over the last 100 years thus indicates that the coronal source flux has doubled since 1900, producing a decrease in cosmic ray flux, seen both in direct cosmic ray measurements and Beryllium 10 levels in ice cores. The ice core record shows that the coronal source flux was about 25% of its present value during the 17th century "little ice age", when sunspot numbers were very low, suggesting a link between coronal flux and climate.

Recent studies suggest that the proportion of flux emerging in the corona which contributes to the solar wind is governed by the relative areas of faculae and sunspots on the Sun. The faculae/sunspot area ratio also governs solar irradiance, and models of solar total irradiance all show a small increase over the 20th century. If this change in solar irradiance is used as an input to the Hadley centre climate model then an amplifying factor for solar effects of 2.5 is required to match the observed climate record. Increased shielding of the Earth from cosmic rays by the enhanced coronal flux, resulting in fewer ionisation nuclei in the atmosphere and a lower rate of cloud formation could provide this factor. It is important to note that including the solar-driven component of climate change increases the importance of the anthropogenic component over the second half of the century.

The meeting closed with thanks to the speakers and poster viewing.

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