Time Series Analysis of Particles and Fields data

1. 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: McFadden et al, THEMIS ESA instrument and calibration (Space Sci. Reviews) McFadden et al, ESA first results (Space Sci. Reviews) McFadden et al, Structure of plasmaspheric plumes (GRL) Materials in: http://www.igpp.ucla.edu/public/vassilis/ESS265/20080519 class_notes_time_series_analysis_B.ppt thm_code/thm_pot2dens.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 Time Series Analysis1

2. Potential Subtraction • Automatic subtraction: • Read spacecraft potential (Vsc) • From spheres: Vsc=-(V3+V4)/2. • Add 1V offset • Accounts for spheres drivenabove plasma potential • Correct to infinity ( x 1.15 ) • Sensor voltage is not exactly atzero+offset because Debye lengthis very large. A +15% correctionto account for plasma potentialat infinite sphere distance. • Reduce electron energies • E'elec= Eelec – Vsccorrected • 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 Ni Ne Time Series Analysis2

3. 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 Ne = Ni ;>>>>>>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 ; L2: onboard processed moms thm_load_esa,probe=sc ; L2: 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. ; eV 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' Time Series Analysis3

4. 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 ; L2: onboard processed moms thm_load_esa,probe=sc ; L2: ground processed gmoms, omni spectra thm_load_sst,level=2,probe=sc ; NOW CONSTRUCT DENSITY FROM SCPOT tinterpol_mxn,'thd_peer_t3','thd_pxxm_pot',newname='thd_peer_t3_int' get_data,'thd_pxxm_pot',data=thd_pxxm_pot,dl=dl get_data,'thd_peer_t3_int',data=thd_peer_t3_int thm_pot2dens,thd_pxxm_pot.y,thd_pxxm_potdens, $ Te=total(thd_peer_t3_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_t3',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_t3 thd_pxxm_pot thd_densities '+ $ 'thd_psef_en_eflux thd_peer_en_eflux_pot thd_peir_en_eflux' Ne = Ni Nscpot Time Series Analysis4

5. 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 >10keV electrons entering i/e aperture • Electron ESA, primaries and secondaries (below about 40eV): Ne>Ni • Primaries, grazing incidence, degraded energy • Secondaries from electron collisions with walls • Secondary electrons in ion ESA (below about 500eV): Ni > Ne • Must be >2keV to overcome post-acceleration in front of McP • 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 • > 40eV for electrons • > 100eV 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 Time Series Analysis5

6. Correct Densities: Solution ;>>>>>>density_all.pro(continued)<<<<<<<<<<<<<<<<<<<< ; CORRECT DENSITIES ; load L0 omni spectra, all ESA data in memory thm_load_esa_pkt,probe=sc ; ; PEIR MOMS/SPECTRA ; Remove radiation and integrate above 40eV 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 40eV 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_t3','thd_pxxm_pot',newname='thd_peer_t3_int' get_data,'thd_pxxm_pot',data=thd_pxxm_pot,dl=dl get_data,'thd_peer_t3_int',data=thd_peer_t3_int thm_pot2dens,thd_pxxm_pot.y,thd_pxxm_potdens, $ Te=total(thd_peer_t3_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_t3 thd_pxxm_pot thd_densities ' + $ 'thd_psef_en_eflux thd_peer_en_eflux_pot thd_peir_en_eflux' Ni requires better background removal (in progress) Time Series Analysis6

7. 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_t3','thc_pxxm_pot', $ newname='thc_peer_t3_int' get_data,'thc_pxxm_pot',data=thc_pxxm_pot,dl=dl get_data,'thc_peer_t3_int',data=thc_peer_t3_int thm_pot2dens,thc_pxxm_pot.y,thc_pxxm_potdens, $ Te=total(thc_peer_t3_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_t3',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' Nscpot > Ne=Ni Plasmasphere ! Time Series Analysis7

8. 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 • Situation is improved when Vi large • Cold ions can be detected • Ni agrees with Nscpot • When Ekinetic - eVsc > EESAmin Hot plasma (Ne=Ni=Nscpot) Time Series Analysis8

9. Cold Ion Detection, When Vi large • Situation is improved when Vi large • Cold ions can be detected • Ni agrees with Nscpot • When Ekinetic - eVsc > 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 eV ; 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'] Time Series Analysis9

10. 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 ~0.2nT over the mission Time Series Analysis10

11. Multi-spacecraft Analysis: ESA Inter-Calibration • On all spacecraft, ions and electrons • Detector anode relative efficiencies (north/south asymmetry) • 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 Analysis11

12. 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 –2keV McP pre-acceleration potential leaks through zero volt grid into detector • Collects scattered electrons, increases sensitivity of detector at low (<2keV) energies Themis, ions simulated Electrons Ions Time Series Analysis12

13. 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 McP scrubbing • Efficiency decreases due to water molecules venting • Stabilizes after few months of operations Ignore Time Series Analysis13

14. 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 • 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 ofenergy efficiency at low energies THD electrons Wind, |B| THC,THD, |B| THC,THD, Ne Wind, |B| Time Series Analysis14

15. 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 PTot PB Pi Pe Time Series Analysis15

16. Multi-spacecraft Analysis: At the magnetopause Time Series Analysis16

17. 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 Time Series Analysis17