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:
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
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Time Series Analysis1

2. Potential Subtraction
Automatic subtraction:
Read spacecraft potential (Vsc)
From spheres: Vsc=-(V3+V4)/2.
Add 1V 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.
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
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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,' /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'
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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
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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,
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
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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
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], $
; 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)
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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 !
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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)
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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']
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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
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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
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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
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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
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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 of energy efficiency at low energies
THD electrons
Wind, |B|
THC, THD, |B|
THC, THD, Ne
Wind, |B|
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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
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Time Series Analysis15

16. Multi-spacecraft Analysis: At the magnetopause
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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
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Time Series Analysis17