1. ~130 Years of Solar Wind Data: The Floor and More
E.W. Cliver
Space Vehicles Directorate
Air Force Research Laboratory
AGU
27-30 May 2008

2. Outline Long-term solar wind reconstruction: Emerging consensus
Floor in the IMF: Then & Now
Secular variation of solar wind speed
Entering a Gleissberg Minimum?

3. Long-term Solar Wind Magnetic Field Reconstruction:2 2
2005 1 3 4 1 5
Br = 0.56Btot
Long-term Solar Wind Magnetic Field Reconstruction:
Emerging Consensus

4. (Svalgaard & Cliver, JGR, 110(12), 2005)
The IDV index has the useful property of being highly correlated with B
and independent of V

5. Long-term Solar Wind Magnetic Field Reconstruction: 2 4 3 2
2005 1 3 5 4 2 1 5
Long-term Solar Wind Magnetic Field Reconstruction:
Emerging Consensus (Exception: McCracken, 2007)

6. - Annual averages of B show evidence for a floor ~ 4.5 nT
- The sharp drop from in the McCracken time series
does not appear in geomagnetic data
- The low value in 1901 from RL&F is in error (APR, priv. comm.)

7. Floor in the Solar Wind Magnetic Field:
Direct Observations (27-Day Averages)

8. Floor in the Solar Wind Magnetic Field: Recent Direct Observations
Last 13 rotations similar to 1901, 1902, 1913
Floor in the Solar Wind Magnetic Field:
Recent Direct Observations

9. Floor in the Solar Wind Magnetic Field: Cosmogenic Nuclei / long-term
(Muscheler et al., 2005)
(Caballero-Lopez et al., 2004)
Since SSN ~ 0 during MM, would expect B to be at floor level. Direct from C-L (parameterized). For M, modulation parameter vs. IDV-based B; IDV-based B vs. SSN
Floor in the Solar Wind Magnetic Field:
Cosmogenic Nuclei / long-term

10. Interpretation of Floor: Baseline Open Magnetic Flux
SSW + HSS + CME
º SSW + HSS
* SSW
B (nT) M
~250 μT M
245 μT M
200 μT M
115 μT
(Fisk et al., 1999;
Owens & Crooker,
2006)
Year
Interpretation of Floor: Baseline Open Magnetic Flux

11. Svalgaard & Cliver, ApJ Lett. 661, L203, 2007 B(nT) = 0.27R½ + 4.6
For SSN = 0
Then: B Total (ecliptic) = 4.6 nT; B RADIAL (all latitudes) = 3.0 nT
Now: B Total (ecliptic) ~ 4 nT; B RADIAL (all latitudes) ~ 2 nT

12. ~15% increase in solar wind speed during the last ~120 years
Floor
(Rouillard et al., 2007; Svalgaard & Cliver, 2007)
~15% increase in solar wind speed during the last ~120 years

13. Plea for Help to Magnetospheric Physicists
Open Question:
Effect of ~10% decrease of Earth’s dipole
since ~1850 on geomagnetic activity?
- Siscoe et al. (2002)  Decrease in activity
(ISM model & Hill M/I coupling models)
- Glassmeier et al. (2004)  Weak/no effect
(scaling relationships between
magnetospheric parameters & M)

14. A Coming Gleissberg Minimum? Cycle 24 may be smallest in ~100 years
Test of Long-term Reconstructions,
Precursor Prediction Technique, Dynamo Models, …
164.5
158.5
120.8
75?
(Svalgaard, Cliver, & Kamide, 2005)

15. Conclusions Consensus long-term B & V / Validation of IDV
Floor in IMF in ecliptic Btot ~4 nT & Br ~ 2 nT (SSN = 0)
~15% increase in solar wind V since 1872?