Protons - Part Two. Remodelling the Models

Transcription

1 Protons - Part Two Remodelling the Models

2 Quick Recap Three types of fluxes we regularly see in astronomy Light Neutrinoes Particles The last one is the most important to me

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4 The Westmorland Gazette goes New Scientist

5 Particles hitting the Earth

6 How Do Protons Interact? Ionisation removal of an electron Charge exchange as ionisation, but one of the interactors gains the electron from the other Excitation energetic and electronic Dissociation The tearing apart of a molecule

7 The ICE Interactions

8 The DICE Interactions

9 The RIDE Interactions

10 What are the differences between Electron and Proton Interactions? Mass difference proton closer to the average mass of atmospheric particles than e - Charge difference one +ve, one ve e - cannot undergo charge exchange and leave the flux tube during its journey it is confined

11 Do protons matter? They are less likely to lead to light being produced in the aurora than e - They carry less energy in They are usually represented by an additional e - flux in general models But they do act differently than an e - flux and some of the implications are discussed in the following paper

12 The Paper Ionisation by Energetic Protons in Thermosphere-Ionosphere Electrodynamics General Circulation Model M. Galand R. G. Roble D. Lummerzhein

13 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 more precise computing 5. Discussion and summary did it work? Was it all worth it? Where did it fail?

14 1.0 How to build an atmosphere Choose your favorate atmospheric particles 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

15 But there s more To expand, take account of the winds, the different pressures and all other factors that alter the atmospheric and ionospheric compositions over the surface of the Earth The first example gives you a 1D Global Mean Model The Second example gives a Global Circulation Model, or GCM

16 This paper The authors examine, using two models and a parameterisation of the precipitation code, how the proton aurora affects the atmosphere. In particular, the production of Nitric Oxide, which has been observed with the Student Nitric Oxide Explorer SNOE satellite to be linked with the aurora.

17 2.0 Parameterizations Monte Carlos or Boltzmann? Monte Carlos more precise takes up far more computational time This paper compares the GCM transport model with a parameterization of that model

18 But parameterise what? Proton interactions produce a Bragg peak of ionisation, a characteristic shape of how the rate changes with depth The depth in the atmosphere the peak appears at is determined by the energy of the incoming protons The area under the peak is determined by the flux of the protons

19 The Bragg Peak

20 Boltzmann Transport Equatiobns One way to model the Bragg curve is to use Boltzmann s Equation to model the coupled transport of a beam of Hydrogen atoms and Protons, this requires a number of approximations They can be grouped together by saying this models the centre of a large beam of high-flux protons below a certain altitude

21 Further simplifications In order to parameterise the transport equations, the rate of ionisation was stated as proportional to energy loss Loss function determined as a power-law Power laws for neutral species N 2, O 2 and O added together, wieghted according to crosssections, masses and energy loss factors taken from the larger model Average energy loss per electron-ion pair production event then worked out as a function of total energy loss

22 Secondaries are put in by assuming a lower energy requirement for production of ion electron pairs Even more

23 Depends on whether or not you believe the original model here s the results compared to that Note how energy and flux change the shape of the curve KE = 1,5,15keV Normalised to 1 erg s -1 Does it work?

24 Does it work? Ionisation is done in two stages the first is from the method described for general ionisation, the second is to use fragmentation ratios to determine how many ions come from dissociation, itself proportional to ionisation here Breakdown of curve:

25 3.0 Application part 1 1-D in space Thermosphere-Ionosphere Global Mean Model Just a latitudanally averaged atmosphere, with chemical balance models solved for ions, neutrals and excitated states O +,NO +,O 2+,N 2+,N + N 2,O 2,O NO,N( 2 D),N( 4 D) required for Nitric Oxide production and loss chemistry

26 Higher e - density Second ionisation peak when compared to e - assumption Definitely shows difference between proton and electron behaviours Proton peak higher More secondaries! Results - 1

27 4.0 Application part 2 3-D in space Thermosphere-Ionosphere Electrodynamics Global Circulation Model 3D, time dependant model for upper atmosphere from km O +,NO +,O 2+,N 2+,N + N 2,O 2,O NO,N( 2 D),N( 4 S),He,Ar

28 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 and thermodynamics Inputs include solar irradiance, auroral flux, e- potential at poles and tides and gravity waves from below

29 What they did Ran the model with slow electron precipitation Ran it with fast precipitation Ran it with precipitation from both electrons and protons Compared results Each time for one simulated day e -,O 2+,NO + and NO densities modelled

30 What they found NO enhancement at the altitude of the new proton peak, 130km, as well as enhancements at that altitude of the other monitored ions NO spread out from precipitation area as it was produced Ions and electrons only enhanced in area of precipitation due to short lifetime Extra NO destroyed by solar irradiance later on Therefore changes in minor species and ion densities

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33 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 NO densities affecting minor species chemistry

34 Their problems No high energy protons included, but desired Spatial structure highly simplified auroral ovals too oval No information on higher regions heating by the protons before they begin ionisation

35 My Problems - 1 Aurora aren t always continuous large beams H - kept out, as it may complicate results No mag fields? No redistribution? Crosssections? How proportional to ionisation rate is emission?

36 My Problems - 2 Seems too geared to producing a certain result Secondaries peak? Both models exceed upper limit of parameterization assumptions! What about the decrease in ionisation below how does the shift of emphasis affect things? Better chemical models required!

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