1 wsa model and forecasts nick arge space vehicles directorate air force research laboratory
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WSA Model and ForecastsWSA Model and Forecasts
Nick ArgeNick ArgeSpace Vehicles Directorate
Air Force Research Laboratory
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Source Surface
PFSS Model
Schatten Current Sheet Model
5-30 Rs
2.5 Rs
Plot courtesy Sarah McGregor (BU/CISM)
Solar Wind Model
(e.g., 1D Kinematic
model, ENLIL, HAF)
(5-30Rs to 1AU)
WSA Coronal & Solar Wind ModelWSA Coronal & Solar Wind Model
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PFSSPFSS++SCS MODEL (R = 5.0 SCS MODEL (R = 5.0 RR)) Predicted Solar Wind Speed at 5.0 Predicted Solar Wind Speed at 5.0 RR
(New Empirical Relationship )(New Empirical Relationship )
5.3
5.7θ1
3/1
3
6.18.51
5.1265θ,
b
ef
fVs
bskm s-1
Where:
fs = Magnetic field expansion factor.
θb = Minimum angular distance that an open field footpoint lies from nearest coronal hole boundary (i.e., Angular depth inside a coronal hole)
WSA Model Coronal OutputWSA Model Coronal OutputC
oron
al H
oles
Cor
onal
Fie
ld (
5.0R
)
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IMF directed radially toward from Sun.
IMF directed radially away from Sun.
Solar Wind Speed and IMF Polarity in the Ecliptic Solar Wind Speed and IMF Polarity in the Ecliptic Driven by Daily Updated Photospheric Field MapsDriven by Daily Updated Photospheric Field Maps
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Solar Wind Speed Predictions & ObservationsSolar Wind Speed Predictions & Observations IMF Polarity Predictions & ObservationsIMF Polarity Predictions & Observations
Predictions & Observations:Near Solar MaximumPredictions & Observations:Near Solar Maximum
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Solar Wind Speed Predictions & ObservationsSolar Wind Speed Predictions & Observations
Predictions & ObservationsPredictions & Observations
Solar Wind Speed Predictions & ObservationsSolar Wind Speed Predictions & Observations
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Validated 8 years of WSA predictions Event-based approach: high speed enhancements (HSE):
Captures more than 72% of the observed HSE events Most of the false HSEs are small Missed HSEs: are small events or transients Timing of HSEs shows no offset. Slight underestimation of magnitude
of fastest events – probably due to transients
Observed
HSE No HSE
Model
HSE 166 36
No HSE 64 -
Contingency Tables
Missed
False
Observed
Model
Boston University Boston University ValidationValidation of WSA Event-Based of WSA Event-Based Approach: (High Speed Events)Approach: (High Speed Events)
( Owens et al., JGR 2005)( Owens et al., JGR 2005)
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Corrections that often need to be applied to photospheric field maps (depending on the observatory):
• Line-of-sight fields need to be converted to radial orientation (including effects due to the Solar b angle).
• Observational evidence suggests this is generally true except in strong active regions!
• Monopole moment needs to be removed.
• Polar fields need to be corrected and filled (when necessary).
• Can use historical data for retrospective studies.
• Field corrected (when necessary) for magnetic field saturation effects.
• Flux transport processes (differential rotation, meridional flow, diffusion, etc.)
Solar Wind Model Driver:Solar Wind Model Driver:Photospheric Field Synoptic MapsPhotospheric Field Synoptic Maps
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Modeling Results With & Without Polar Field Modeling Results With & Without Polar Field Corrections AppliedCorrections Applied
Polar Fields Not Corrected Polar Fields Corrected
Der
ived
Cor
onal
Hol
es
Der
ived
Cor
onal
Hol
es
Solar Wind Speed Predictions (WSA Model) and Observations
Poles NOT Corrected
Poles Corrected
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Monopole Moments in Synoptic MapsMonopole Moments in Synoptic Maps
Split bi-polar Region
Corresponding Negative polarity missing
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Time Evolution of Photospheric & Time Evolution of Photospheric & Coronal FeaturesCoronal Features
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Observed & Predicted IMF Polarity
Observed & Predicted Solar Wind Speed
Solar Wind Sources Near & Far From Active RegionsSolar Wind Sources Near & Far From Active RegionsWSA Model Predictions & Observations: CR2027WSA Model Predictions & Observations: CR2027
+ / — = Outward/(Inward) Footpoint Field Polarity
Cor
onal
Hol
esC
oron
al F
ield
(5.
0R)
Ph
otos
ph
eric
Fie
ld &
Cor
onal
Hol
e B
oun
dar
ies
NSO/SOLIS
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Observed & Predicted IMF Polarity
Observed & Predicted Solar Wind Speed
Solar Wind Sources Near & Far From Active RegionsSolar Wind Sources Near & Far From Active RegionsWSA Model Predictions & Observations: CR2028WSA Model Predictions & Observations: CR2028
+ / — = Outward/(Inward) Footpoint Field Polarity
NSO/SOLIS
Cor
onal
Hol
esC
oron
al F
ield
(5.
0R)
Ph
otos
ph
eric
Fie
ld &
Cor
onal
Hol
e B
oun
dar
ies
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Observed & Predicted IMF Polarity
Observed & Predicted Solar Wind Speed
+ / — = Outward/(Inward) Footpoint Field Polarity
NSO/SOLIS
Cor
onal
Hol
esC
oron
al F
ield
(5.
0R)
Ph
otos
ph
eric
Fie
ld &
Cor
onal
Hol
e B
oun
dar
ies
Solar Wind Sources Near & Far From Active RegionsSolar Wind Sources Near & Far From Active RegionsWSA Model Predictions & Observations: CR2029WSA Model Predictions & Observations: CR2029
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1) The WSA model predicts ambient solar wind speed and IMF polarity 1-7 days in advance at L1.
Model validated using 8 years (~1 solar cycle) of predictions & the results are VERY encouraging.
2) Careful handing of the input photospheric magnetic field data is essential for improving the predictive success of the model. In particular,
• Monopole moments.• Polar fields.• Radial field Assumption.• Flux transport processes.
3) The ability of the WSA model to successfully predict solar wind speed appears to be a function of the proximity of its source regions to strong active regions. That is
If the source region is close to (far from) a strong active region, then the model’s speed predictions are generally poor (good).
Possible reasons why the model performs less well when the solar wind source lies near an active region.
- Fields near active regions are not potential, as the WSA model assumes. (MHD and/or Force Free coronal model could help here).
- The model assumes that the photospheric field is radial everywhere.
Observational evidence suggests this is generally true except in strong active regions! (Direct measurement of radial fields needed in active regions).
- A different empirical solar wind speed relationship is required near active regions.
SummarySummary
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WSA Coronal - ENLIL MHD Solar Wind WSA Coronal - ENLIL MHD Solar Wind Model Coupling Model Coupling (A (A Joint AFRL-CISM Effort)Joint AFRL-CISM Effort)
Output of WSA MODEL Output of WSA MODEL (R = 21.5 (R = 21.5 RR))
Coronal Field Strength
Solar Wind Speed
ENLIL 3D MHD Solar Wind ModelENLIL 3D MHD Solar Wind Model
Output of ENLIL MODEL at 1AUOutput of ENLIL MODEL at 1AU
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Schatten Current Sheet Model (SCS): 2.5 – 21.5 R
Potential Field Source Surface Model (PFSS): 1.0 – 2.5 R
Coupled Model: PFSS+SCSCoupled Model: PFSS+SCS
Schatten, 1971; Wang and Sheeley 1995
2.5 R
21.5 R
Solar Wind Model
(e.g., 1D Kinematic
model, ENLIL, HAF)
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LOS B Field Remapped to Heliographic Coordinates
Model InputModel Input Magnetic Field Measurements at the PhotosphereMagnetic Field Measurements at the Photosphere
Courtesy Mount Wilson Solar Observatory
LOS Disk Image: Magnetograms
LOS B Field Remapped to Heliographic Coordinates & Converted to Radial
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• Validated 8 years of WSA predictions • Mean Squared Error (MSE)
• 3 day old magnetograms give optimal prediction• No systematic time lag• Skill scores low on average (<10%)
Boston University Validation of WSA Boston University Validation of WSA ( Owens et al., JGR 2005)( Owens et al., JGR 2005)
MSE(A) < MSE(B)(Same for correlation coefficients)
Hypothetical Example
Courtesy Matt Owens (BU/CISM)
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Validating Coronal Models Using Coronal HolesValidating Coronal Models Using Coronal Holes
Solar Minimum Solar Maximum Short After Solar Maximum
MAS/SAIC
de Toma, Arge, and Riley (2005)
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Photospheric Field Synoptic Map TypesPhotospheric Field Synoptic Map Types
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Solar Wind Speed Predictions & ObservationsSolar Wind Speed Predictions & Observations IMF Polarity Predictions & ObservationsIMF Polarity Predictions & Observations
Predictions & Observations:Near Solar MinimumPredictions & Observations:Near Solar Minimum
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A Technique For Filling Missing Polar RegionsA Technique For Filling Missing Polar Regions
Boundary Values used to Fill Poles
•Pole
Equator
• Pole
Weighted mean of boundary values used to fill the poles. The weighting is function of inverse distance raised to some power.
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Daily-Updated Synoptic Map With Poles FilledDaily-Updated Synoptic Map With Poles Filled
Pole filled using a “noisy” boundary.*
Pole filled using a “trimmed” boundary.*
*Note, the synoptic maps shown here are NOT from CR1921 or 1922 but illustrate well why filling the poles needs to be done very carefully!
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Synoptic Map TypesSynoptic Map Types
DAILY UPDATED MAP
Longitude
Latitude
+90º
360º250º 250º
FULL CARRINGTON MAP
-90º
Cut fromPrevious
Map
0º
0º347º
DAILY UPDATED MAP
New Magnetogram
Weighting Functions ~13º
Latitude
-90ºLongitude
+90º
347º 360º
Latitude
0º Longitude
+90º
360º-90º
347º
DAILY UPDATED FRAME MAP
Merged Field Data
Unmerged Field Data From Latest
Magnetogram
347º
Zhao Frame Method
(a)
(b)
(c)
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Solar Wind Speed Predictions & Observations
IMF Polarity Predictions & Observations
Solar Wind Speed Predictions & Observations
IMF Polarity Predictions & ObservationsICME ICME
Solar Wind Predictions Using Photospheric Field Maps Solar Wind Predictions Using Photospheric Field Maps With Different Grid ResolutionsWith Different Grid Resolutions
5 Degree 2.5 Degree
Arge et al. 2005Arge et al. 2004
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Observed & Predicted IMF Polarity
Observed & Predicted Solar Wind Speed
NSO/SOLIS
WSA Model Predictions & Observations: CR2018WSA Model Predictions & Observations: CR2018
+ / — = Outward/(Inward) Footpoint Field Polarity
Cor
onal
Hol
esC
oron
al F
ield
(5.
0R)
Ph
otos
ph
eric
Fie
ld &
Cor
onal
Hol
e B
oun
dar
ies