Protons - Part TwoRemodelling the Models

Quick Recap

Three types of fluxes we regularly see inastronomy

Light

Neutrinoes

Particles

The last one is the most important to me

The Westmorland Gazettegoes New Scientist

Particles hitting the Earth

How Do Protons Interact?

• Ionisation – removal of an electron

• Charge exchange – as ionisation, but oneof the interactors gains the electron fromthe other

• Excitation – energetic and electronic

• Dissociation – The tearing apart of amolecule

The ICE Interactions

The DICE Interactions

The RIDE Interactions

What are the differencesbetween Electron and Proton

Interactions?

• Mass difference – proton closer to theaverage mass of atmospheric particlesthan e-

• Charge difference – one +ve, one –ve

• e- cannot undergo charge exchange andleave the flux tube during its journey – it isconfined

Do protons matter?

• They are less likely to lead to light beingproduced in the aurora than e-

• They carry less energy in

• They are usually represented by anadditional e- flux in general models

• But they do act differently than an e- flux –and some of the implications arediscussed in the following paper…

The Paper

Ionisation by Energetic Protons inThermosphere-IonosphereElectrodynamics GeneralCirculation Model

M. Galand

R. G. Roble

D. Lummerzhein

The paper’s points

1. Introduction – what is going on?

2. Parameterization – faster models

3. Use of this in a 1D atmospheric model –even faster models

4. Predictions from the 3D model – moreprecise computing

5. Discussion and summary – did it work?Was it all worth it? Where did it fail?

1.0 How to build an atmosphere

• Choose your favorate atmosphericparticles and decide on their densities

• Add in your favorate ions• Add in dynamics, e-fields and effects• Use a chemical balance model to mix the

two together, should anything happen…• Beat with 125,000 protons until a result

appears• It works for me…

But there’s more

• To expand, take account of the winds, thedifferent pressures and all other factorsthat alter the atmospheric and ionosphericcompositions over the surface of the Earth

• The first example gives you a 1D GlobalMean Model

• The Second example gives a GlobalCirculation Model, or GCM

This paper

The authors examine, using two models anda parameterisation of the precipitationcode, how the proton aurora affects theatmosphere. In particular, the productionof Nitric Oxide, which has been observedwith the Student Nitric Oxide Explorer –SNOE – satellite to be linked with theaurora.

2.0 Parameterizations

• Monte Carlos or Boltzmann?

• Monte Carlos more precise – takes up farmore computational time

• This paper compares the GCM transportmodel with a parameterization of thatmodel

But parameterise what?

• Proton interactions produce a Bragg peakof ionisation, a characteristic shape of howthe rate changes with depth

• The depth in the atmosphere the peakappears at is determined by the energy ofthe incoming protons

• The area under the peak is determined bythe flux of the protons

The Bragg Peak

Boltzmann Transport Equatiobns

• One way to model the Bragg curve is touse Boltzmann’s Equation to model thecoupled transport of a beam of Hydrogenatoms and Protons, this requires a numberof approximations

• They can be grouped together by sayingthis models the centre of a large beam ofhigh-flux protons below a certain altitude

Further simplifications

• In order to parameterise the transport equations,the rate of ionisation was stated as proportionalto energy loss

• Loss function determined as a power-law• Power laws for neutral species N2, O2 and O

added together, wieghted according to cross-sections, masses and energy loss factors takenfrom the larger model

• Average energy loss per electron-ion pairproduction event then worked out as a functionof total energy loss

Even more…

• Secondaries are putin by assuming alower energyrequirement forproduction of ionelectron pairs

Does it work?

• Depends on whetheror not you believe theoriginal model… here’sthe results comparedto that

• Note how energy andflux change the shapeof the curve

• KE = 1,5,15keV• Normalised to 1 erg s-1

Does it work?

• Ionisation is done in twostages – the first is fromthe method described forgeneral ionisation, thesecond is to usefragmentation ratios todetermine how many ionscome from dissociation,itself proportional toionisation here

• Breakdown of curve:

3.0 Application part 1

• 1-D in space Thermosphere-IonosphereGlobal Mean Model

• Just a latitudanally averaged atmosphere,with chemical balance models solved forions, neutrals and excitated states

• O+,NO+,O2+,N2

+,N+

• N2,O2,O• NO,N(2D),N(4D) – required for Nitric Oxide

production and loss chemistry

Results - 1

• Higher e- density• Second ionisation

peak when comparedto e- assumption

• Definitely showsdifference betweenproton and electronbehaviours

• Proton peak higher• More secondaries!

4.0 Application part 2

• 3-D in space Thermosphere-IonosphereElectrodynamics Global Circulation Model

• 3D, time dependant model for upperatmosphere from 95-800km

• O+,NO+,O2+,N2

+,N+

• N2,O2,O

• NO,N(2D),N(4S),He,Ar

Dynamics of NCAR TIE-GCM

• Atmosphere calculates:• Continuity, momentum and thermodynamic

equations for neutral gas and plasma• State equation for ideal gas• Coupled dynamics, associated e-fields and

currents, plus feedback on motions andthermodynamics

• Inputs include solar irradiance, auroral flux, e-potential at poles and tides and gravity wavesfrom below

What they did

• Ran the model with ‘slow’ electronprecipitation

• Ran it with fast precipitation

• Ran it with precipitation from bothelectrons and protons

• Compared results

• Each time for one simulated day

• e-,O2+,NO+ and NO densities modelled

What they found

• NO enhancement at the altitude of the newproton peak, 130km, as well as enhancementsat that altitude of the other monitored ions

• NO spread out from precipitation area as it wasproduced

• Ions and electrons only enhanced in area ofprecipitation due to short lifetime

• Extra NO destroyed by solar irradiance later on• Therefore changes in minor species and ion

densities

Conclusions

• Don’t confuse your ps and e-s• Protons peak higher, with more 2ndries• Protons carry less energy in and dump it

quicker• Protons have a short term, immediate area

affect on ionisation rates in the E-region,and a slightly longer affect on NOdensities – affecting minor specieschemistry

Their problems

• No high energy protons included, butdesired

• Spatial structure highly simplified – auroralovals too oval

• No information on higher regions – heatingby the protons before they begin ionisation

My Problems - 1

• Aurora aren’t always continuous largebeams

• H- kept out, as it may ‘complicate’ results

• No mag fields? No redistribution? Cross-sections?

• How proportional to ionisation rate isemission?

My Problems - 2

• Seems too geared to producing a certainresult

• Secondaries peak?• Both models exceed upper limit of

parameterization assumptions!• What about the decrease in ionisation

below – how does the shift of emphasisaffect things?

• Better chemical models required!