Publications by Karen Aplin

Electricity in the Atmosphere: Ions in the Atmosphere

in Encyclopedia of Atmospheric Sciences: Second Edition, (2014) 9-13

KL Aplin, RG Harrison

© 2015 Elsevier Ltd. All rights reserved. Earth's atmosphere, like all planetary atmospheres, is constantly ionized by cosmic rays. Close to the surface, natural radioactivity is the dominant source of ionization. This article describes the generation and physical characteristics of atmospheric cluster-ions, including their size, composition, transport, and electrical properties, and gives an overview of relevant measurement technologies. The role of cluster-ions in weather and climate through modulating atmospheric particle formation and a range of other electrical effects is summarized. Nomenclature and categorization of atmospheric cluster-ions, and the properties of ions in the indoor environment are also briefly discussed.

Modelling of an asteroid photoelectron sheath and implications for a sample return mission


KL Aplin, AJ Macfaden, NE Bowles

Brief Communication: Earthquake-cloud coupling through the global atmospheric electric circuit


RG Harrison, KL Aplin, MJ Rycroft

Triboelectric charging of volcanic ash from the 2011 Grímsvötn eruption

Physical Review Letters 111 (2013)

IMP Houghton, KL Aplin, KA Nicoll

The plume from the 2011 eruption of Grímsvötn was highly electrically charged, as shown by the considerable lightning activity measured by the United Kingdom Met Office's low-frequency lightning detection network. Previous measurements of volcanic plumes have shown that ash particles are electrically charged up to hundreds of kilometers away from the vent, which indicates that the ash continues to charge in the plume [R. G. Harrison, K. A. Nicoll, Z. Ulanowski, and T. A. Mather, Environ. Res. Lett. 5, 024004 (2010)1748-932610.1088/1748-9326/5/2/024004; H. Hatakeyama J. Meteorol. Soc. Jpn. 27, 372 (1949)JMSJAU0026-1165]. In this Letter, we study triboelectric charging of different size fractions of a sample of volcanic ash experimentally. Consistently with previous work, we find that the particle size distribution is a determining factor in the charging. Specifically, our laboratory experiments demonstrate that the normalized span of the particle size distribution plays an important role in the magnitude of charging generated. The influence of the normalized span on plume charging suggests that all ash plumes are likely to be charged, with implications for remote sensing and plume lifetime through scavenging effects. © 2013 American Physical Society.

Cosmic ray modulation of infra-red radiation in the atmosphere

Environmental Research Letters IOP Publishing 8 (2013) 015026-015026

KL Aplin, M Lockwood

Lord Kelvin's atmospheric electricity measurements


KL Aplin, RG Harrison

Whether weather affects music

Eos 93 (2012) 347-348

KL Aplin, PD Williams

Smoke emissions from industrial western Scotland in 1859 inferred from Lord Kelvin's atmospheric electricity measurements

Atmospheric Environment 50 (2012) 373-376

KL Aplin

Lord Kelvin (William Thomson) made careful, calibrated measurements of the atmospheric Potential Gradient (PG) at three sites on the east side of Arran in 1859. The PG was always anomalously high in easterly and north-easterly winds. Positive space charge from sea spray may have contributed to the high PG at two coastal sites, but measurements made on Goatfell, inland and 100-175m above sea level are unlikely to have been affected by spray. Instead, pollution from the Scottish mainland seems the more likely cause of the high PG at Goatfell, which varied from 300 to 1000Vm -1 on 10th-11th October 1859, corresponding to smoke levels from 0.2 to 0.8mgm -3. Gaussian plume calculations, based on the atmospheric conditions described by Lord Kelvin, and constrained by early Glaswegian pollution measurements, indicate a substantial source region located on the Scottish mainland, 20-40km from Arran, emitting between 10-10 4kgs -1. © 2012 Elsevier Ltd.

Laboratory analogues of Martian electrostatic discharges

Planetary and Space Science (2012)

KL Aplin, T Goodman, KL Herpoldt, CJ Davis

Recent advances in global electric circuit coupling between the space environment and the troposphere

Journal of Atmospheric and Solar-Terrestrial Physics (2012)

MJ Rycroft, KA Nicoll, KL Aplin, R Giles Harrison

Atmospheric ionisation in Snowdonia

Journal of Physics: Conference Series 301 (2011)

KL Aplin, JH Williams

Atmospheric ionisation from natural radioactivity and cosmic rays has been measured at several sites in Snowdonia from 2005-present. The motivation for this project was a combination of public engagement with science, and research into the effects of ionisation on climate. A four-component atmospheric radiometer instrument is co-located with the ionisation detectors and the data is remotely logged and displayed on the Web. Atmospheric ionisation from natural radioactivity varies with local geology, and the cosmic ray ionisation component is modulated by solar activity and altitude. Variations due to all these effects have been identified and are described.

Measuring Martian lightning

Journal of Physics: Conference Series 301 (2011)

KL Aplin, CJ Davis, WJ Bradford, KL Herpoldt

Lightning is expected to occur on Mars within dust devils and dust storms, which are likely to discharge in the low pressure carbon dioxide environment. Despite this, radio emissions from Martian lightning have not yet been conclusively observed by remote sensing, nor have there been any in situ measurements of Martian atmospheric electricity. We report laboratory experiments to simulate Martian electrical discharges and measure the radio emissions from them, to facilitate searches of Martian lightning from spacecraft data. Voltage transients were observed in a tank in which Martian analogue simulant was allowed to become triboelectrically charged, and then fall to a sensing electrode. A plausible explanation for our results is that electrical discharges have taken place, caused by charge separation on differently sized particles as predicted by theory. Unlike in previous reports, we have been able to detect discharges without adding glass microballoons to the Martian analogue dust to facilitate the charging, although the addition of glass microballoons did enhance the transient rate.

Meteorological phenomena in Western classical orchestral music

Weather 66 (2011) 300-306

KL Aplin, PD Williams

Asteroid electrostatic instrumentation and modelling

Journal of Physics: Conference Series 301 (2011)

KL Aplin, NE Bowles, E Urbak, D Keane, EC Sawyer

Asteroid surface material is expected to become photoelectrically charged, and is likely to be transported through electrostatic levitation. Understanding any movement of the surface material is relevant to proposed space missions to return samples to Earth for detailed isotopic analysis. Motivated by preparations for the Marco Polo sample return mission, we present electrostatic modelling for a real asteroid, Itokawa, for which detailed shape information is available, and verify that charging effects are likely to be significant at the terminator and at the edges of shadow regions for the Marco Polo baseline asteroid, 1999JU3. We also describe the Asteroid Charge Experiment electric field instrumentation intended for Marco Polo. Finally, we find that the differing asteroid and spacecraft potentials on landing could perturb sample collection for the short landing time of 20min that is currently planned.

Use of coated silicon field emitters as neutralisers for fundamental physics space missions

Advances in Space Research (2011)

KL Aplin, BJ Kent, CM Collingwood, L Wang, R Stevens, SE Huq, A Malik

Compact cosmic ray detector for unattended atmospheric ionization monitoring.

Rev Sci Instrum 81 (2010) 124501-

KL Aplin, RG Harrison

Two vertical cosmic ray telescopes for atmospheric cosmic ray ionization event detection are compared. Counter A, designed for low power remote use, was deployed in the Welsh mountains; its event rate increased with altitude as expected from atmospheric cosmic ray absorption. Independently, Counter B's event rate was found to vary with incoming particle acceptance angle. Simultaneous co-located comparison of both telescopes exposed to atmospheric ionization showed a linear relationship between their event rates.

Tsunamis and geophysical warnings

Astronomy and Geophysics 51 (2010)

J Hunt, G Kopec, K Aplin

Meeting report Julian Hunt, Grant Kopec and Karen Aplin report on new techniques and practical approaches before, during and after devastating events such as tsunamis. © 2010 Royal Astronomical Society.

Results from the CERN pilot CLOUD experiment

Atmospheric Chemistry and Physics 10 (2010) 1635-1647

J Duplissy, MB Enghoff, KL Aplin, F Arnold, H Aufmhoff, M Avngaard, U Baltensperger, T Bondo, R Bingham, K Carslaw, J Curtius, A David, B Fastrup, S Gagné, F Hahn, RG Harrison, B Kellett, J Kirkby, M Kulmala, L Laakso, A Laaksonen, E Lillestol, M Lockwood, J Mäkelä, V Makhmutov, ND Marsh, T Nieminen, A Onnela, E Pedersen, JO P Pedersen, J Polny, U Reichl, JH Seinfeld, M Sipilä, Y Stozhkov, F Stratmann, H Svensmark, J Svensmark, R Veenhof, B Verheggen, Y Viisanen, PE Wagner, G Wehrle, E Weingartner, H Wex, M Wilhelmsson, PM Winkler

During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm−3s−1, and growth rates between 2 and 37 nm h−1. The corresponding H2O concentrations were typically around 106 cm−3 or less. The experimentally-measured formation rates and \htwosofour concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 °C).

Atmospheric electricity coupling between earthquake regions and the ionosphere

Journal of Atmospheric and Solar-Terrestrial Physics 72 (2010) 376-381

RG Harrison, KL Aplin, MJ Rycroft

We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF "tweeks", the amplitude and phase of very low frequency radio waves in the Earth-ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density. © 2009 Elsevier Ltd.

European Venus Explorer: An in-situ mission to Venus using a balloon platform

Advances in Space Research 44 (2009) 106-115

E Chassefière, O Korablev, T Imamura, KH Baines, CF Wilson, DV Titov, KL Aplin, T Balint, JE Blamont, CG Cochrane, C Ferencz, F Ferri, M Gerasimov, JJ Leitner, J Lopez-Moreno, B Marty, M Martynov, SV Pogrebenko, A Rodin, JA Whiteway, LV Zasova

Planetary balloons have a long history already. A small super-pressure balloon was flown in the atmosphere of Venus in the eighties by the Russian-French VEGA mission. For this mission, CNES developed and fully tested a 9 m diameter super-pressure balloon, but finally replaced it by a smaller one due to mass constraints (when it was decided to send Vega to Halley's Comet). Furthermore, several kinds of balloons have been proposed for planetary exploration [Blamont, J., in: Maran, S.P. (Ed.), The Astronomy and Astrophysics Encyclopedia. Cambridge University Press, p. 494, 1991]. A Mars balloon has been studied for the Mars-94 Russian-French mission, which was finally cancelled. Mars and Venus balloons have also been studied and ground tested at JPL, and a low atmosphere Venus balloon is presently under development at JAXA (the Japanese Space Agency). Balloons have been identified as a key element in an ongoing Flagship class mission study at NASA, with an assumed launch date between 2020 and 2025. Recently, it was proposed by a group of scientists, under European leadership, to use a balloon to characterize - by in-situ measurements - the evolution, composition and dynamics of the Venus atmosphere. This balloon is part of a mission called EVE (European Venus Explorer), which has been proposed in response to the ESA AO for the first slice of the Cosmic Vision program by a wide international consortium including Europe, Russia, Japan and USA. The EVE architecture consists of one balloon platform floating at an altitude of 50-60 km, one short lived probe provided by Russia, and an orbiter with a polar orbit to relay data from the balloon and probe, and to perform remote sensing science observations. The balloon type preferred for scientific goals is one, which would oscillate in altitude through the cloud deck. To achieve this flight profile, the balloon envelope would contain a phase change fluid. While this proposal was not selected for the first slice of Cosmic Vision missions, it was ranked first among the remaining concepts within the field of solar system science. © 2009 COSPAR.