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Harrison, R. G., Nicoll, K., Takahashi, Y. and Yair, Y. (2015) Focus on high energy particles and atmospheric processes. Environmental Research Letters, 10 (10). 100201. ISSN 1748­9326 doi: https://doi.org/10.1088/1748­9326/10/10/100201 Available at http://centaur.reading.ac.uk/44815/ 

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Focus on high energy particles and atmospheric processes

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Environ. Res. Lett. 10 (2015) 100201 doi:10.1088/1748-9326/10/10/100201

EDITORIAL

Focus on high energy particles and atmospheric processes

RGilesHarrison1, KeriNicoll1, Yukihiro Takahashi2 andYoavYair3

1 Department ofMeteorology, University of Reading, UK2 HokkaidoUniversity, Japan3 Interdisciplinary Center,Herzliya, Israel

E-mail: k.a.nicoll@reading.ac.uk

Keywords: spaceweather, solar-terrestrial interactions, ionisation

AbstractThe letters published in the ‘Focus issue on high energy particles and atmospheric processes’ serve tobroaden the discussion about the influence of high energy particles on the atmosphere beyond theirpossible effects on clouds and climate. These letters link climate andmeteorological processes withatmospheric electricity, atmospheric chemistry, high energy physics and aerosol science from thesmallestmolecular cluster ions through to liquid droplets. Progress in such a disparate and complextopic is very likely to benefit from continued interdisciplinary interactions between traditionallydistinct science areas.

1. Introduction

High energy particles are constantly entering the atmo-sphere, from the Sun or from outside the solar system.They continually generate ionisation, but the subse-quent effects in the atmosphere, and especially the lowertroposphere, have long been a source of speculation,with physical mechanisms which can link the energeticparticles with atmospheric chemistry and physics stillunder active investigation. One reason for this may bethat the physical science communities concerned withstudying ionising radiation (particle and cosmic rayphysics), and the atmospheric effects of the ionisation(aerosol science, cloud physics and atmospheric electri-city) have become distinct. This follows from the 1950sinvention of the neutron monitor, moving away fromthe use of ionisation in particle physics. These topicswere originally more closely related, for example in thework of CTRWilson, winner of the 1927 Nobel Prize inphysics for the visualisation of cosmic ray ions throughcondensation of water droplets, who was inspired bystudying meteorological processes and atmosphericelectricity (Harrison2011).

Recent work investigating high energy particleeffects on the lower atmosphere has mostly con-centrated on evaluating possible effects on clouds,because of the sensitivity of climate to small changes inclouds and the ionisation known to be generated at

cloud heights. Through this potential route and oth-ers, the solar modulation of high energy particles isincreasingly recognised as presenting a range of possi-ble solar indirect effects on climate. A central motiva-tion in proposing this focus issue—encouraged by theunique position of Environmental Research Letters(ERL) in the physics community—was to strengthenthe interdisciplinary links between atmospheric sci-ence and energetic particle physics. Such a need wasimplied by the 2013 IPCC report on the physical sci-ence basis for Climate Change, which, despite addres-sing possible climate effects of cosmic rays,nevertheless did not even list the long-established con-jugate science areas of lightning, atmospheric elec-tricity, ions or ionisation in its index. As well as thecloud effects, this ERL focus issue considers the radia-tive effects of ions in clear air, perturbations in theatmospheric circulation and triggering of lightning.

2. Statistical studies

The generic study of high energy particle effects on theatmosphere requires a combination of modelling anddata analysis approaches, and a comprehensive reviewofthe many possible processes is given by Mironova et al(2015). (These are summarised in table 1.) The morespecific questionofwhether there is an appreciable effecton climate due to cosmic rays has often been considered

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by comparing surface neutron monitor data with aclimate ormeteorological parameter. Such comparisonsare necessarily statistical, using a variety of measuredatmospheric parameters with good long term globalcoverage,which are amenable to investigation.

2.1. RegressionmethodsBenestad (2013) considered whether persistentresponses to cosmic rays existed in global temperature,surface pressure and rainfall using multiple regressionanalysis. Whilst weak patterns in eastern Europe andthe Norwegian sea were identified in temperature andsurface pressure anomalies, these were not statisticallysignificant. Sloan and Wolfendale (2013) surveyed arange of climate-related data sources on differenttimescales, and constrained solar influences to havecontributed less than 10% of the twentieth centurywarming.

2.2. Superposed epochmethodsAveraging around many similar triggering events,which is known as a superposed epoch or compositingstudy, provides one method of reducing the effect ofnoise in the system being studied. A study of surfaceparameters using this approach was made by Lakenand Calogovic (2013), by using the daily span oftemperature (the diurnal temperature range, DTR) toprovide an indirect measurement of cloud changes.This quantity, averaged overmany sites, was examinedfor any response to common transient reductions(Forbush Decreases), or increases (Ground LevelEnhancements) in cosmic ray ionisation. Allowing forthe reduced sample sizes associated with the largerevents, no robust change in DTR was found reachingthe 5% significance level. Hence if there is an effect, itis too small to be detectable inDTRdata.

2.3. Large eventsRather than averaging together multiple small effects,another approach to studying particle effects is to

isolate a single but substantial event. The solar activityof early September 1859, and the flare observedvisually by the astronomer Richard Carrington, pro-vides a stimulus for such work. Calisto et al (2013)combined three-dimensional modelling of atmo-spheric chemistry with an ionisation model. Forscenarios likely to represent the Carrington flare, forwhich only scarce and indirect energy information isavailable (Aplin and Harrison 2014), Calisto et al(2013)’s modelling found increases of NOx in thepolar regions and up to a 20%decrease of stratosphericozone. Resulting radiative changes also led to changesin the zonal winds.

3.Mechanistic cloud and clear air studies

Effects on clouds can be considered using directmeasurements of specific cloud properties, as physicalroutes between the parameters have been proposedand are being evaluated. Carslaw et al (2002) distin-guished between two proposed routes by whichcosmic rays might affect clouds, (1) an ion-aerosolclear air mechanism and (2) an ion-aerosol near cloudmechanism. Since that review, the first mechanism,which concerns the generation of enhanced ultrafineaerosol concentrations able to affect the population ofcloud condensation nuclei and ultimately cloud dro-plet properties, has received the most attention, andexperimental work at CERN has identified circum-stances in which the particle formation can occur(Kirkby et al 2011).

3.1. Ion-induced particle effectsGrowth of ions to form particles sufficiently large tosustain droplet condensation at lower tropospherewater vapour concentrations, which are orders ofmagnitude less than those generated in aWilson cloudchamber, typically takes many hours. The growth issensitive to the amount and composition of trace gasconcentrations present and the loss of the trace gas topre-existing particles or droplets. The process has tobe comprehensively modelled to quantitatively evalu-ate the subsequent change in cloud, for comparisonwith other sources of variability. Yu and Luo (2014)used a detailed global atmospheric chemistry model tostudy the sensitivity of cloud condensation nuclei(CCN) generation to temperature. For the solarmaximum to minimum change in cosmic ray ionproduction assumed (and this quantity itself variesbetweenmodels andmeasurements), theCCNgenera-tion rate was shown to be enhanced by up to one orderof magnitude under a 0.2 °C temperature change.Direct evidence exists for particle formation in thestratosphere. Mironova and Usoskin (2014) showedgrowth of aerosol particles occurring at 10 to 25 km,following increased ionisation associated with solarenergetic particle events and ground levelenhancements.

Table 1. Summary of atmospheric processes associatedwith highenergy particles (afterMironova et al 2015).

Location Effect of high energy particles

MESOSPHERE Chemical effects (e.g. OHproduction) ofelectron and solar proton precipitation

NOproduction and subsequent downward

propagation to deplete stratospheric ozone

STRATOSPHERE Ozone depletion leading to cooling of polar

vortex interior

Aerosol enhancement

Chemical effects (e.g. nitric acid production)TROPOSPHERE Infra-red absorption of cluster ions

Changes in local lightning rates

Changes in global atmospheric electric circuit

Cloud effects

(Established effects are given in roman type, and suggested effects in

italics.)

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Environ. Res. Lett. 10 (2015) 100201 RGHarrison et al

3.2. Layer cloud global circuitmechanismVertical current flow occurs throughout the atmo-sphere in fair weather regions through the globalatmospheric electric circuit—a conceptual legacy ofCTR Wilson—and cosmic ray ionisation. This pro-vides a coupling mechanism between electrically-induced changes, for example from ionisationchanges, and low level layer clouds. The ion current’spassage through the cloud-clear air boundary, whichalso represents a change in electrical conductivity,leads to local charge separation in the droplet forma-tion and evaporation region, in proportion to thecurrent.

Voiculescu et al (2013) found a positive relation-ship betweenmid-latitude cloud cover and the inter-planetary electric field, which they considered couldbe occurring through the global circuit mechanism.A further suggestion of a global circuit effect wasmade by Lam et al (2013), as part of the atmosphericresponse to the By component of the InterplanetaryMagnetic Field. Lam et al (2013) showed differencesin the surface pressure patterns between large andsmall circumstances of By. A defining characteristicof the global circuit is its single maximum diurnalvariation, known as the Carnegie curve (Harri-son 2013). Harrison and Ambaum (2013) reportedan averaged diurnal variation in cloud base proper-ties similar to that of the Carnegie curve, in separateseries of data obtained during the polar night in thenorthern and summer hemisphere. Harrison et al(2015) have shown a sensitivity of cloud droplet dis-tributions to charging of small droplets, such as thattypical of layer cloud electrification induced by theglobal circuit.

3.3. Clear air ion absorptionThe two previous ion related mechanisms of ion-facilitated particle formation or clouddroplet chargingfrom ion transport represent complicated interactionsbetween atmospheric ionisation, current flow andclear or cloudy air. A much simpler direct effect ofcluster ions exists in principle through their absorp-tion of infra-red radiation. Using a narrow bandradiometer centred on an infra-red wavelength of9.15μm, Aplin and Lockwood (2013) showed atransient change in radiative absorption followingtriggering events sensed by a cosmic ray telescope,likely to be associated with the ionisation from cosmicray air showers. In principle, this direct effect can beincluded straightforwardly in climate models whenthe necessary cross-sections have been measured inthe laboratory, although three dimensional radiativetransfer modelling will be necessary to fully evaluatetheir contribution to the atmospheric radiation bal-ance (Aplin and Lockwood 2015).

4. Lightning and transient electrical effects

CTR Wilson recognised that the strong electric fieldsof thunderclouds could accelerate electrons and evenlead to upward propagating discharges (Wilson 1925a,Wilson 1925b). In this sense thunderclouds representan internal source of high energy particles within theatmosphere. Low light detectors have subsequentlydemonstrated a wide range of faint discharges orTransient Luminous Events associated with activethunderclouds (e.g. Füllekrug et al 2013a). The use oftwo or three dimensional lightning mapping arraysprovides a new tool in unravelling these complicatedphenomena. Füllekrug et al (2013b) show that electronacceleration from a positive lightning discharge canprecondition the above-thundercloud region as aplasma, facilitating formation of a relativistic electronbeam in a subsequent discharge. The thermal andrelativistic electrons were simultaneously detected byradiofrequency methods. Further remote detectionpossibilities require a detailed understanding of theelectron acceleration. An analysis of the electronacceleration at the tip of a lightning streamer is givenby Chanrion et al (2014), who, through Monte-Carlomodelling, show a decrease in peak electric fieldcoincides with the streamer velocity. Electrons are alsolost from the streamer tip, which in turnmay influencesubsequent streamer development.

Beyond their internally generated energetic parti-cles, thunderclouds may also be influenced by externalsources of particles. Statistical studies of particle effectson lightning rates are given by Scott et al (2014) andOwens et al (2014). Studies such as these require numer-ous well-defined particle source events, to allow com-parison of averaged lightning rates during these eventswith lightning rates without such events. Scott et al(2014) used lightning data from the UK Met Office’sradio detection system, and identified times of increasein low energy Solar Energetic Particles when the solarwind speed exceeded a threshold. These fast solar windstreams were associated with a substantial increase inlightning, and also thunder, as recorded manually froma range of UK sites. Owens et al (2014) interrogated thesame lightning and thunderday data differently, categor-ising it by polarity of the Heliospheric Magnetic Field.The opposite polarities showed a 40 to 60%difference inlightning. Clearly, the meteorological conditions for athunderstorm to develop are a pre-requisite for theseeffects to occur, but these studies strongly statisticallysupport a solar effect on terrestrial lightning.

5. Conclusions

Whilst the interest in cloud effects through thenucleation route is a major motivation for studyingthe role of high energy particles in the atmosphere, thisfocus issue illustrates that the topic is more diverse,

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Environ. Res. Lett. 10 (2015) 100201 RGHarrison et al

and there are strong avenues of related work inlightning, global circuit response and atmosphericchemistry. A combination of atmospheric responsesto high energy particles therefore seems likely, some ofwhich are summarised in figure 1. One particularconsideration for the statistical cloud studies andothers is whether the tropospheric ionisation is wellrepresented for low clouds by the neutron monitorcount rates recorded at the surface, which is domi-nated by production in the stratosphere. Local effectsof natural radioactivity and atmospheric variabilityprovide a complicating factor.

The origin of the lightning effects is particularlyintriguing, and Rycroft (2014) has suggested enhancedcurrent flow in the global circuit might lead toincreased lightning. It is possible that the solar windinfluence on lightning, however, combined with con-ventional meteorological modelling could ultimatelyprovide a new factor in forecasting hazardousweather.

References

AplinKL and LockwoodM2013Cosmic raymodulation of infra-red radiation in the atmosphere Environ. Res. Lett. 8 015026

AplinKL and LockwoodM2015 Further considerations of cosmicraymodulation of infra-red radiation in the atmosphereAstropart. Phys. 68 52–60

AplinKL andHarrisonRG2014Atmospheric electricfields duringtheCarringtonflareAstron. Geophys. 55 32–5

Benestad RE 2013Are there persistent physical atmosphericresponses to galactic cosmic rays? Environ. Res. Lett. 8 035049

CalistoM,Usoskin I andRoza E 2013 Influence of aCarrington-likeevent on the atmospheric chemistry, temperature anddynamics: revised Environ. Res. Lett. 8 045010

ChanrionO, Bonaventura Z, ÇinarD, BourdonA andNeubert T2014Runaway electrons from a ‘beam-bulk’model ofstreamer: application to TGFsEnviron. Res. Lett. 9 055003

FüllekrugM et al 2013bElectron acceleration above thundercloudsEnviron. Res. Lett. 8 035027

FüllekrugM et al 2013a Energetic charged particles abovethunderclouds Surv. Geophys. 34 1–41

HarrisonRG2011The cloud chamber andCTRWilson’s legacy toatmospheric scienceWeather 66 276–9

HarrisonRG2013TheCarnegie curve Surv. Geophys. 34 209–32HarrisonRG,Nicoll KA andAmbaumMHP2015On the

microphysical effects of observed cloud edge chargingQ. J. R.Meteorol. Soc. doi:10.1002/qj.2554

HarrisonRGandAmbaumMHP2013Electrical signature in polarnight cloud base variations Environ. Res. Lett. 8 015027

Kirkby J et al 2011Role of sulphuric acid, ammonia andgalactic cosmicrays in atmospheric aerosol nucleationNature476 429–33

LakenBA andCalogovic J 2013Does the diurnal temperature rangerespond to changes in the cosmic rayflux?Environ. Res. Lett. 8045018

LamMM,ChishamGand FreemanMP2013The interplanetarymagneticfield influencesmid-latitude surface atmosphericpressureEnviron. Res. Lett. 8 045001

Mironova I A andUsoskin IG 2014 Possible effect of strong solarenergetic particle events on polar stratospheric aerosol: asummary of observational resultsEnviron. Res. Lett. 9 015002

Figure 1.High energy particle effects in the conceptual framework of the global atmospheric electric circuit. Lightning is suggested tobe affected by energetic particles, whichmay in turn influence the currentflowing in the global circuit, asmay changes in theinterplanetary electric andmagneticfields or the solar wind. Influences on the atmosphere’s radiation exchange via changes in theterrestrial longwave (infra-red) radiation and short wave (visible) radiation, can occur through the formation of cloud condensationnuclei, droplet charging effects in layer clouds or the direct absorption of longwave radiation by cluster ions.

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Mironova IA,AplinKL,ArnoldF,BazilevskayaGA,HarrisonRG,KrivolutskyAA,NicollKA,RozanovEV,TurunenEand IlyaG2015UsoskinEnergetic particle influence on theEarth’satmosphere Space Sci. Rev.doi:10.1007/s11214-015-0185-4

OwensM J, Scott C J, LockwoodM, Barnard L,HarrisonRG,Nicoll K,Watt C andBennett A J 2014Modulation ofUKlightning by heliosphericmagneticfield polarityEnviron. Res.Lett. 9 115009

RycroftM J 2014Thunder and lightning—what determines whereandwhen thunderstorms occur?Environ. Res. Lett. 9 121001

Scott C J, HarrisonRG,OwensM J, LockwoodMandBarnard L2014 Evidence for solarwindmodulation of lightningEnviron. Res. Lett. 9 055004

SloanT andWolfendale AW2013Cosmic rays, solar activity andthe climate Environ. Res. Lett. 8 045022

VoiculescuM,Usoskin I andCondurache-Bota S 2013Cloudsblownby the solar windEnviron. Res. Lett. 8 045032

WilsonCTR1925a The acceleration ofβ-particles in strong electricfields such as those of thundercloudsProc. Camb. Philos. Soc.22 534–8

WilsonCTR1925bThe electricfield of a thundercloud and some ofits effects Proc. R. Soc. Lond.A 37 32D–7D

Yu F and LuoG 2014 Effect of solar variations on particleformation and cloud condensation nuclei Environ. Res.Lett. 9 045004

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