Time Series Analysis of Particles and Fields data

Time Series Analysis of Particles and Fields data • • Potential subtraction Density computation from three sources (Ne, Ni, scpot) Cold plasma detection Next opportunity: – Velocity, pressure corrections from SST – Waves analysis Suggested reading: Mc. Fadden et al, THEMIS ESA instrument and calibration (Space Sci. Reviews) Mc. Fadden et al, ESA first results (Space Sci. Reviews) Mc. Fadden et al, Structure of plasmaspheric plumes (GRL) Materials in: http: //www. igpp. ucla. edu/public/vassilis/ESS 265/20080519 class_notes_time_series_analysis_B. ppt thm_code/thm_pot 2 dens. pro, thm_part_dist. pro, thm_part_moments. pro (for cleanup) esa_particles/get_th? _pe? r. pro potential_correction. pro; density_all. pro; cold_ions. pro ESS 265 Time Series Analysis 1

Potential Subtraction • Automatic subtraction: – Read spacecraft potential (Vsc) • From spheres: Vsc=-(V 3+V 4)/2. – Add 1 V offset • Accounts for spheres driven above plasma potential – Correct to infinity ( x 1. 15 ) • Sensor voltage is not exactly at zero+offset because Debye length is very large. A +15% correction to account for plasma potential at infinite sphere distance. Ni – Reduce electron energies • E'elec= Eelec – Vsccorrected Ne – Increase ion energies • E'ion= Eion + Vsccorrected – Cannot do if EFI is not deployed • Right hand side is an example • Must do manually – Determine Vsc from spectrum – Manually correct potential ESS 265 Time Series Analysis 2

Potential Subtraction • Manual scpot subtraction: – When EFI not deployed: • Read scpot value (~0) • Correct based on spectra • Recompute moments – Use full or reduced distributions » From peef get N, V, T » From peer (6 angles): N, T ; >>>>>>potential_correction. pro<<<<<<<<<<<<<< timespan, '7 11 07/10', 2, /hours sc='a‘ thm_load_state, probe=sc, /get_support thm_load_fit, probe=sc, data='fgs', coord='gsm', suff='_gsm' thm_load_fit, probe=sc, data='fgs', coord='dsl', suff='_dsl' thm_load_mom, probe=sc ; L 2: onboard processed moms thm_load_esa, probe=sc ; L 2: ground processed gmoms, omni spec ; ; Modify sc potential thm_load_esa_pkt, probe=sc get_data, 'tha_pxxm_pot', data=tha_pxxm_pot, dlim=dlim tha_pxxm_pot. y(*)=10. ; e. V store_data, 'tha_pxxm_pot_corr', $ data={x: tha_pxxm_pot. x, y: tha_pxxm_pot. y}, dlim=dlim ; ; Recompute moments thm_part_moments, probe = sc, instrum = 'peer', $ scpot_suffix = '_pxxm_pot_corr', $ mag_suffix = '_fgs_dsl', tplotnames = tn options, 'tha_peer_density', 'colors', ['b'] options, 'tha_peim_density', 'colors', ['r'] store_data, 'tha_pexm_density', $ data='tha_peer_density tha_peim_density' options, 'tha_pexm_density', 'colors', ['b', 'r'] options, 'tha_pe? m_density', yrange=[0, 2] options, 'tha_pexm_density', ylog=0 tplot, 'tha_fgs_gsm tha_pexm_density tha_pe? r_en_eflux' ESS 265 Ne = Ni Time Series Analysis 3

Density from S/C Potential, Other ; >>>>>>density_all. pro<<<<<<<<<<<<<< timespan, '8 1 16/14: 00', 6, /hours sc='d' thm_load_state, probe=sc, /get_supp thm_load_fit, probe=sc, data='fgs', coord='gsm', suff='_gsm' thm_load_fit, probe=sc, data='fgs', coord='dsl', suff='_dsl' thm_load_mom, probe=sc ; L 2: onboard processed moms thm_load_esa, probe=sc ; L 2: ground processed gmoms, omni spectra thm_load_sst, level=2, probe=sc ; NOW CONSTRUCT DENSITY FROM SCPOT tinterpol_mxn, 'thd_peer_t 3', 'thd_pxxm_pot', newname='thd_peer_t 3_int' get_data, 'thd_pxxm_pot', data=thd_pxxm_pot, dl=dl get_data, 'thd_peer_t 3_int', data=thd_peer_t 3_int thm_pot 2 dens, thd_pxxm_pot. y, thd_pxxm_potdens, $ Te=total(thd_peer_t 3_int. y, 2)/3. ; New code, in class materials store_data, 'thd_pxxm_potdens', $ data={x: thd_pxxm_pot. x, y: thd_pxxm_potdens}, dl=dl ; NOW PLOT UNCORRECTED DENSITIES store_data, 'thd_peer_en_eflux_pot', data='thd_peer_en_eflux thd_esa_pot' options, 'thd_fgs_gsm', yrange=[-150, 150] options, 'thd_peer_density', colors=['r'] options, 'thd_peir_density', colors=['b'] options, 'thd_pxxm_potdens', colors=['g'] options, 'thd_pxxm_potdens', ylog=1 options, 'thd_peer_t 3', ylog=0 options, 'thd_pxxm_pot', ylog=0 options, 'thd_pe? r_en_eflux*', yrange=[7. , 25000. ] store_data, 'thd_densities', $ data='thd_peir_density thd_peer_density thd_pxxm_potdens' tplot, 'thd_fgs_gsm thd_peer_t 3 thd_pxxm_pot thd_densities '+ $ 'thd_psef_en_eflux thd_peer_en_eflux_pot thd_peir_en_eflux' ESS 265 Time Series Analysis 4 Ne = Ni Nscpot

Correct Densities: Issues • Photoelectrons on Ne: – Have been corrected already, as EFI operating – Both on board and through ground processing • Primary and secondary electrons from >10 ke. V electrons entering i/e aperture – Electron ESA, primaries and secondaries (below about 40 e. V): Ne>Ni • Primaries, grazing incidence, degraded energy • Secondaries from electron collisions with walls – Secondary electrons in ion ESA (below about 500 e. V): Ni > Ne • Must be >2 ke. V to overcome post-acceleration in front of Mc. P – When significant flux of energetic electrons is present • See 16: 00 and 16: 30 UT injections on THD, 2008 -01 -16 • Can result in either Ne>Ni or Ni>Ne depending on – Scattered flux relative to electron/ion fluxes – Correct by integrating density above secondaries • > 40 e. V for electrons • > 100 e. V for ions • Background radiation near radiation belts – – Penetrates ESA walls Produces constant background eflux as function of energy Most evident in ions which have lower flux Correct by removing constant eflux background at all energies ESS 265 Time Series Analysis 5

Correct Densities: Solution ; >>>>>>density_all. pro(continued)<<<<<<<<<< ; CORRECT DENSITIES ; load L 0 omni spectra, all ESA data in memory thm_load_esa_pkt, probe=sc ; ; PEIR MOMS/SPECTRA ; Remove radiation and integrate above 40 e. V to remove scattered electrons thm_part_moments, probe = sc, instrum = 'peir', scpot_suffix = '_pxxm_pot', $ trange=['8 1 16/14: 00', '8 1 16/20: 00'], erange=[0, 31], $ mag_suffix = '_fgs_dsl', tplotnames = tn, verbose = 2, $ /bgnd_remove ; names are output into tn New code, in class materials ; ; PEER MOMS/SPECTRA ; Remove radiation and integrate above 40 e. V to remove scattered electrons thm_part_moments, probe = sc, instrum = 'peer', scpot_suffix = '_esa_pot', $ trange=['8 1 16/14: 00', '8 1 16/20: 00'], erange=[0, 24], $ mag_suffix = '_fgs_dsl', tplotnames = tn, verbose = 2, $ /bgnd_remove ; names are output into tn New code, in class materials ; ; scpot determination of density, with (now/see above) better temperature ; tinterpol_mxn, 'thd_peer_t 3', 'thd_pxxm_pot', newname='thd_peer_t 3_int' get_data, 'thd_pxxm_pot', data=thd_pxxm_pot, dl=dl get_data, 'thd_peer_t 3_int', data=thd_peer_t 3_int thm_pot 2 dens, thd_pxxm_pot. y, thd_pxxm_potdens, $ Te=total(thd_peer_t 3_int. y, 2)/3. store_data, 'thd_pxxm_potdens', $ data={x: thd_pxxm_pot. x, y: thd_pxxm_potdens}, dl=dl ; tplot, 'thd_fgs_gsm thd_peer_t 3 thd_pxxm_pot thd_densities ' + $ 'thd_psef_en_eflux thd_peer_en_eflux_pot thd_peir_en_eflux' ESS 265 Ni requires better background removal (in progress) Time Series Analysis 6

Cold Ion Detection, Using Nscpot ; >>>>>>cold_ions. pro<<<<<<<<<< timespan, '7 6 8/21: 00', 3, /hours & sc='c' thm_load_state, probe=sc, /get_supp thm_load_fit, probe=sc, data='fgs', coord='gsm', suff='_gsm' thm_load_fit, probe=sc, data='fgs', coord='dsl', suff='_dsl' thm_load_mom, probe=sc thm_load_esa, probe=sc ; NOW CONSTRUCT DENSITY FROM SCPOT tinterpol_mxn, 'thc_peer_t 3', 'thc_pxxm_pot', $ newname='thc_peer_t 3_int' get_data, 'thc_pxxm_pot', data=thc_pxxm_pot, dl=dl get_data, 'thc_peer_t 3_int', data=thc_peer_t 3_int thm_pot 2 dens, thc_pxxm_pot. y, thc_pxxm_potdens, $ Te=total(thc_peer_t 3_int. y, 2)/3. store_data, 'thc_pxxm_potdens', $ data={x: thc_pxxm_pot. x, y: thc_pxxm_potdens}, dl=dl ; NOW PLOT DENSITIES (NO SCATTER/NO RADIATION) store_data, 'thc_peer_en_eflux_pot', $ data='thc_peer_en_eflux thc_pxxm_pot' options, 'thc_fgs_gsm', yrange=[-70, 100] options, 'thc_peer_density', colors=['r'] options, 'thc_peir_density', colors=['b'] options, 'thc_pxxm_potdens', colors=['g'] options, 'thc_pxxm_potdens', ylog=1 options, 'thc_peer_t 3', ylog=0 options, 'thc_pxxm_pot', ylog=0 options, 'thc_pe? r_en_eflux*', yrange=[7. , 25000. ] store_data, 'thc_densities', data='thc_peir_density ' + $ thc_peer_density thc_pxxm_potdens' tplot, 'thc_fgs_gsm thc_peir_velocity_gsm thc_densities ‘+ $ thc_psef_en_eflux thc_peer_en_eflux_pot thc_peir_en_eflux' ESS 265 Time Series Analysis 7 Nscpot > Ne=Ni Plasmasphere !

Cold Ion Detection, Issues • • • – – – When Vscpot > Vthion then Cold ions cannot overcome barrier Ni < Vscpot When Vscpot < EESAmin then: Electrons are missed Cold electrons missed: Ne < Ni Hot plasma (Ne=Ni=Nscpot) Situation is improved when Vi large • Cold ions can be detected Ni agrees with Nscpot ESS 265 When Ekinetic - e. Vsc > EESAmin Time Series Analysis 8

Cold Ion Detection, When Vi large • Situation is improved when Vi large –Cold ions can be detected –Ni agrees with Nscpot • When Ekinetic - e. Vsc > EESAmin ; >>>>>>cold_ions. pro (continued)<<<<<<<<<< ; tvectot, 'thc_peir_velocity_gsm', $ newname='thc_peir_velocity_gsmt' tvectot, 'thc_peir_velocity_gsm', tot='thc_peir_velocity_t‘ ; tinterpol_mxn, 'thc_peir_velocity_t', $ 'thc_pxxm_pot', newname='thc_peir_velocity_tint' get_data, 'thc_peir_velocity_tint', data=thc_peir_velocity_tint get_data, 'thc_pxxm_pot', data=thc_pxxm_pot ; eflow=1000. *(thc_peir_velocity_tint. y/310. )^2 - $ thc_pxxm_pot. y; in e. V ; store_data, 'thc_eflow', data={x: thc_peir_velocity_tint. x, y: eflow} store_data, 'thc_peir_en_eflux-n-flow', $ data='thc_peir_en_eflux thc_eflow' options, 'thc_peir_en_eflux*', yrange=[7. , 25000. ] ; tplot, 'thc_fgs_gsm thc_peir_velocity_gsmt thc_densities ', $ thc_psef_en_eflux thc_peer_en_eflux_pot thc_peir_en_eflux-n-flow' tlimit, ['7 6 8/22: 00', '7 6 8/22: 30'] ESS 265 Time Series Analysis 9

Multi-spacecraft Analysis: Calibration • • – – – – ESA instruments received first an absolute calibration In the sheath, avoid unmeasured plasmaspheric cold ions, electrons, or solar wind beam Correct for energy dependent efficiencies Detector anode relative efficiencies (north/south asymmetry) Electron-ion relative efficiencies (based on density, account for solar wind composition) FGM calibration was done independently for each spacecraft Spin plane offsets determined routinely In the solar wind determine spin axis offsets Spin axis offset variation ~0. 2 n. T over the mission ESS 265 Time Series Analysis 10

Multi-spacecraft Analysis: ESA Inter-Calibration – – • • On all spacecraft, ions and electrons Detector anode relative efficiencies (north/south asymmetry) ESS 265 Sort ions and electrons separately in pitch-angle Apply low-order polynomial fit to pitch angle Determine anode efficiency that minimizes variance (a 1 -2% effect) Large angle variance (systematic asymmetry) checked further – Look at systematic flows during times expected to have zero » Found none for ions in the magnetosphere » Adjusted electron asymmetry (1 -3%) in the sheath such that Vi = Ve Time Series Analysis 11

Multi-spacecraft Analysis: ESA Inter-Calibration – • • Detector energy relative efficiency Based on published data, private communications and simulations Main effect on ions is increase in g-factor due to fringe fields at grid – – Field from – 2 ke. V Mc. P pre-acceleration potential leaks through zero volt grid into detector Collects scattered electrons, increases sensitivity of detector at low (<2 ke. V) energies Themis, ions simulated Electrons ESS 265 Ions Time Series Analysis 12

Multi-spacecraft Analysis: ESA Cross-Calibration THC was the trailblazer (EFI out); used as reference • THC Electron sensor selected as reference • THC Ion sensor cal’ed for energy, anode efficiency • THC Ion sensor g-factor adjusted to match electron • All other spacecraft also internally calibrated • Cross-calibration as follows • – – – Use early string of pearls configuration Adjust Ni/Ne (0. 99) based on WIND/SWE ~4% alphas Adjust THD/THC electron densities to match Adjust THE/THC … etc. For THA Time varying calibration • • ESA Mc. P scrubbing Efficiency decreases due to water molecules venting Stabilizes after few months of operations Ignore ESS 265 Time Series Analysis 13

Multi-spacecraft Analysis: ESA Absolute Calibration THC electrons THC and THD electrons versus WIND-SWE • – – • • • Time-shift WIND data WIND has plasma waves WIND density calibrated from plasma frequency THD electrons Five intervals found in summer of ’ 07 – – Correct deficiency due to scpot below Emin Extend Maxwellian spectra to low energies Themis g-factors scaled to ~70% in Fall’ 07 In retrospect, were due to overestimate of energy efficiency at low energies Wind, |B| THC, THD, Ne Wind, |B| ESS 265 Time Series Analysis 14

Multi-spacecraft Analysis: Calibration verification Find magnetopause crossings and sheath waves • Expect quasi-static pressure balance • Determine total pressure • – Ptotal = Pion + Pelectron + PB Show total pressure is constant across Method shows that pressure balance is observed Calibration is working, at least at low energies Higher energy component has been less tested ESS 265 PTot PB Pi Pe Time Series Analysis 15

Multi-spacecraft Analysis: At the magnetopause ESS 265 Time Series Analysis 16

Homework • • • Find a THEMIS 2 -4 hour interval of your interest Use at least two satellites Plot ion and electron density Plot density derived from spacecraft potential Explain the differences ESS 265 Time Series Analysis 17