Inferring the Structure of the Solar Corona and Inner Heliosphere during the Maunder Minimum using MHD simulations

Transcription

1 Inferring the Structure of the Solar Corona and Inner Heliosphere during the Maunder Minimum using MHD simulations Pete Riley, Roberto Lionello, Jon Linker, and Zoran Mikic Predictive Science, Inc. (PSI), San Diego, CA, USA

2 Overview The MHD Model: CORHEL Observational constraints on the model for Maunder Minimum (MM) period Possible scenarios for the structure of the solar wind during the MM period

3 REALITY CHECK Models can be poor approximations to reality, even when they match observations.

4 CORHEL Magnetic Maps: MDI, MWO, NSO/KP, NSO/GONG, NSO/SOLIS, WSO Smoothing, Flux balance, Pole Fitting Input Models Output Validation WSA Coronal Model Choices: MHD (MAS) (Polytropic) MHD (MAS) (Thermodynamic) Vr, Br, open/closed Coronal Solution Coronal Solution Radiative Outputs (EUV, X-Rays) Observational Validation (Coronal Holes) Empirical prescription Empirical prescription White Light Cone Model CME Heliospheric Model Choices: Enlil MAS Observational Validation (White Light, EUV, X-rays, coronal holes) Observational Validation (In Situ Measurements, STEREO Heliospheric Imaging)

5 REALITY CHECK Boundary conditions (Br at the base of the corona) represent a major uncertainty in the model.

6 Synoptic Maps: CR2071 (June 9 - July 6, 2008) Sin(Latitude) MDI Synoptic Map: 1080x3600 points distributed as sin(latitude) Longitude Poles filled with flag values (-3200G) Interpolated Br map: 180x360 points distributed as latitude Latitude Longitude

7 How do you Fill in the Poles?

8 Fits to Polar Fields Range of Polar Field Strengths: Gauss in the North Gauss in the South

9 Synoptic Maps: CR2071 (June 9 - July 6, 2008) Latitude Interpolated Br map: 180x360 points Poles fit with polynomial to lower m modes Longitude Interpolated Br map: 150x360 nonuniform cells (code mesh) Field smoothed with diffusive operator Flux Balanced Latitude Longitude 9

10 REALITY CHECK Model formalisms (i.e., approximations) represent the remaining substantial uncertainties.

11 RESISTIVE MHD EQUATIONS (POLYTROPIC MODEL) B = 4π c J E = 1 c B t E + 1 c v B = ηj ρ t + (ρv) = 0 ρ ( v t + v v) = 1 c p t J B p + ρg + (νρ v) + (pv) = (γ 1)( p v + S) γ = 1.05, S = ηj 2 +νρ v: v (S frequently neglected)

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13 CORHEL ON THE WEB 13

14 CORHEL Simulations for CR2060: Different Results for Different Observatories Stanford/Wilcox Simulations using NSO/SOLIS and SOHO/MDI are similar, predict 1 stream 770km/s 280km/s Simulations using 280km/s NSO/GONG and Wilcox predict 2 streams 770km/s 14

15 Comparison of Polar fields from model with OMNI data

16 Comparison of model fields at 1 AU in ecliptic plane with OMNI data

17 Jack Eddy s speculation on the solar wind during the Maunder minimum: The solar wind would have blown steadily and isotropically, and possibly at gale force, since high- speed streams of solar wind are associated with the absence of closed structure in the solar corona.

18 Steve Suess s speculation on the solar wind during the Maunder minimum: Firstly, C- 14 data indicate an enhanced cosmic ray intensity, with the conclusion that the interplanetary magne@c field was smooth and perhaps of low intensity. Secondly, the apparent absence of a corona during eclipses requires low coronal density, sugges@ng an absence of closed magne@c loops. Thirdly, the absence of sunspots eliminates the possibility of a solar maximum type of corona of low emission intensity and implies a low large- scale photospheric field intensity. Finally, the absence of mid- la@tude aurorae implies either that the solar wind speed or the IMF intensity, or both, were low and not irregular.

19 POSSIBLE MAUNDER MINIMUM SCENARIOS The MM interval was driven by a photospheric magne@c field configura@on that was: Similar to the recent (2008/9) solar minimum (scenario 1) Similar in structure, but substan@ally less than 2008 values (10%, 50%?) (scenario 2) Devoid of any ARs, but with a unipolar polar field (scenario 3) Devoid of any ARs or large- scale polar fields (i.e., parasi@c polari@es only) (scenario 4) Zero (scenario 5)

20 OBSERVATIONAL CONSTRAINTS ON THE MAUNDER MINIMUM Eclipse observations Auroral observations Cosmic ray modulation MAUNDER MINIMUM SUN? Sunspot observations Reconstructions of the heliospheric flux

21 Scenario 1: Similar to the recent (2008/9) solar minimum

22 Scenario 1: The Maunder Minimum was just like the last minimum -2.5G -> +2.5 G

23 Scenario 1: The Maunder Minimum was just like the last minimum

24 Scenario 1: The Maunder Minimum was just like the last minimum

25 Scenario 1: The Maunder Minimum was just like the last minimum

26 Scenario 1: The Maunder Minimum was just like the last minimum Observations in favor of this scenario Observations against this scenario Modulation of GCRs Interplanetary field too large (open flux = 1.05nT) Eclipse observations would show strong K corona with ample structure Auroral activity would be too high? Sunspots would have been visible

27 Scenario 2:A photospheric field similar in structure to the recent minimum, but substantially less than 2008 values (10%, 50%?)

28 Scenario 5:A photospheric field similar in structure to the recent minimum, but substantially less than 2008 values (10%, 50%?) -2.5G -> +2.5 G -0.25G -> G

29 Scenario 5:A photospheric field similar in structure to the recent minimum, but substantially less than 2008 values (10%, 50%?)

30 Scenario 5:A photospheric field similar in structure to the recent minimum, but substantially less than 2008 values (10%, 50%?) Observations in favor of this scenario Observations against this scenario Modulation of GCRs Substantial coronal structure => Noteworthy eclipses? low interplanetary field (open flux = 0.2 nt) Auroral activity would be lower (CMEs if present would be slow, IMF low) Sunspots would might not be visible

31 Scenario 4: A photospheric field devoid of any ARs or large-scale dipolar fields

32 Scenario 3: A photospheric field devoid of any ARs or large-scale dipolar fields -10G -> +10 G

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36 Scenario 4: A photospheric field devoid of any ARs or large-scale dipolar fields Observations in favor of this scenario Observations against this scenario Modulation of GCRs (Complex HCS and open flux = 0.36 nt) Would require dynamo to stop completely to allow polar fields to disappear A lack of coherent coronal structure Auroral activity would be lower (CMEs if present would be slow, IMF low) No sunspots

37 Summary It is difficult to constrain the structure/properties of the solar wind during the MM based on the limited observations It is unlikely that the MM corona was: like the 2008/2009 minimum magnetic-free An intriguing scenario, which is consistent with most observations, is one where the solar wind is driven by a corona consisting only of small-scale randomly oriented polarities The most probable scenario, however, is that of a scaled version of solar minimum conditions