Friday 20 min Centennial Variations of Near-Earth IMF and ...
From Maunder Minimum to the recent Grand Solar Maximum 11:45 Tuesday November 18 auditorium Roger Session: 6. Key solar observables for assessing long-term changes of the Geospace Time allowed 25 min From Maunder Minimum to the recent Grand Solar Maximum Mike Lockwood, C.J. Scott, M.J. Owens, & L. Barnard (Department of Meteorology, University of Reading, & Space Science and Technology Department, STFC/Rutherford Appleton Laboratory ) 11th European Space Weather Week, Liege, 18th November 2014
Session: 6. Key solar observables for assessing long-term changes of the Geospace Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width The future Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width
The future Sunspot numbers and cosmogenic isotope records Annual means of corrected sunspot number, RC & group sunspot number, RG (Lockwood et al, 2014) 22-year means of year means of RC & RG with 22 22-year means of year means of modulation potential
from 14C (14C) & 10Be (10Be) and the mean of the two, 22 = <14C>22+<10Be>22)/ 2 Sunspot numbers on a logarithmic scale Annual means of corrected sunspot number, RC & group sunspot number, RG Top: RC & RG on loge scale along with 11-year means of year means
of RG in black -year means of highlights the Maunder minimum. Bottom: RC & RG to the power e, along with 11-year means of year means of Rce -year means of highlights the Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width
The future Millennial Variation composite (22-year means) from cosmogenic isotope 10Be cores by Steinhilber et al. (2008) Solar Modulation Potential, (MV) MV) ) 1000 800 we have just left the most recent grand maximum, defined by 600 MV 600
400 200 0 = 168 MV -6000 -4000 -2000 Year AD 0 2000
Maunder minimum composite from Solanki et al., 2004; Vonmoos et al., 2006 & Muscheler et al., 2007 Distribution of over 9300 years (22-year means) from cosmogenic isotope 10Be cores by Steinhilber et al. (2008) Red lines are at 168 MV and 600 MV, near deciles of distribution (50 of 424 samples (12%) have 600 MV and 12% have 168 MV
Using 600 MV defines 24 grand maxima Using 168 MV defines 22 grand minima Low point of Maunder minimum = 123 MV Peak of recent grand maximum = 694 MV
Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width The future Dependence of different geomagnetic activity indices on IMF B(VSW)n interplanetary data (annual means) all indices depend on B but depend
on (VSW)n with different n We use pairings with different n to reconstruct B and VSW best fit aaC n = 1.70.8 r = 0.961 best fit IHV) n = 1.60.8 r = 0.952 best fit IDV) (MV) 1d) n = 0.11.1 r = 0.919
best fit IDV) n = 0.11.1 r = 0.908 Geomagnetic Reconstructions of near-Earth IMF, B, solar wind speed, VSW, and the Open Solar Flux (OSF), FS Sunspot number, R near-Earth IMF, B near-Earth solar wind speed, VSW
Open Solar Flux (OSF) (from Lockwood et al., Annales Geomagnetic Reconstructions of near-Earth IMF, B, solar wind speed, VSW, and the Open Solar Flux (OSF), FS note that first calibrated magnetometer made in 1832 available reliable continuous and
usable data starts in 1844 need models based on sunspot number to get back to Maunder minimum Geomagnetic Reconstructions of near-Earth IMF, B, solar wind speed, VSW, and the Open Solar Flux (OSF), FS systematic difference only before 1870 when IDV index
(the IDV-aaC combination is in red) is not IDV at all but is Bartels q index which is both different & inhomogeneous Geomagnetic Reconstructions of near-Earth IMF, B, solar wind speed, VSW, and the Open Solar Flux (OSF), FS the minima in annual mean VSW at 1878 and 1900 are only
slightly greater than the lowest hourly means in the satellite data suggests slow and fast solar wind speeds the same but Earth continuously in slow solar wind Solar wind speed at Earth and the streamer belt width: concept streamer belt comprises dipole streamers (DS) and pseudostreamers (PS) and is filled with slow solar wind
during the solar cycle streamer belt width varies thinnest around sunspot minimum so Earth spends more time solar in continuous fast solar wind of polar coronal holes We infer it was thicker when solar activity was low so Earth remained almost continuously in slow solar wind Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width The future Streamer belt width: a model
Divides total open flux into coronal hole and streamer belt components: FS = FCH + FSB Applies Solanki et al (2000) continuity concept to both FCH & FSB All new open flux emerges into streamer belt and that emergence is dominated by CMEs emergence rate quantified as a function of sunspot number by Owens et al. (2011) Streamer belt flux that escapes disconnection transfers to Solar wind speed at Earth and the streamer belt width: model Disconnection of streamer belt flux such that fractional loss rate varies over the solar cycle with current sheet tilt as predicted by Owens et al. (2012) and found by Owens and Lockwood (2013) Disconnection of coronal hole flux occurs at a constant fractional rate
Ratio FSB/(FCH + FSB) gives streamer belt width Model results: total open solar flux (one free fit parameter) Reproduces total open solar flux FS from reconstructions very well with just two free fit parameters (the ratio of HCS tilt to the streamer belt fractional loss rate and the coronal
hole fractional loss rate) Model results: streamer belt width in recent cycles (3 free fit parameters) Top: modelled coronal hole flux FCH (in blue) consistent with polar field from date from magnetographs (in red) Model results: streamer belt width in recent cycles (3 free fit parameters)
Bottom: modelled streamer belt width (in blue) consistent with streamer belt from magnetograph data (Owens et al., 2012) and from eclipse images (cyan dots) Note model has captured the variation in width at sunspot minimum Model results: streamer belt width since
the Maunder minimum Lower panel shows streamer belt width modelled for corrected sunspot number composite RC (in black) and group sunspot number RC (in mauve) Model results: streamer belt width since the Maunder minimum Model matches SB widths from eclipse images (dots: coloured dots relating to the
examples shown for sunspot minimum along the top and sunspot maximum along bottom) Grey dots are from the catalogue of Loucif & Koputchmy (1989) Open circles are from written reports Model results: streamer belt width since the Maunder minimum Model predicts streamer belt was broader at all phases
of remnant cycles during the Maunder minimum such that Earth would have remained continuously within streamer belt and seen only slow solar wind Solar change on timescales of days to millennia The past 400 years The past 9300 years Use of geomagnetic data Streamer belt width
The future Superposed epoch study of the end of grand maxima Solar Modulation Parameter, (MV) MV) ) (MV) 24 previous events in 9300 yrs) end of grand solar maximum 800 600 400 200
0 -80 -40 0 40 80 time after end of grand maximum (MV) yrs) Recent grand solar maximum (GSMax, 600MV)
ended in 2006 Recent descent faster than in all previous 24 cases 5% chance another GSMax starts in 50 years 15% chance a GSMin (168MV) starts in 50 years Modulation Potential, (MV) Probabilities of after the end of a Grand Solar Maximum This century
GSMax 1941-2006 GSMin Years after end of GSMax Predictions for the future: Probabilistic analogue forecasts from cosmogenic isotope data by Barnard et al. (2011) Sunspot number, R Near-Earth IMF, B Oulu neutron
monitor GCR counts aa geomagnetic index as cycle 24 develops all are following the blue lines: i.e. in the top 5-15% most rapid descents seen in the last 9300 years Sunspot number, R Near-Earth IMF, B Oulu neutron monitor GCR counts
aa geomagnetic index Conclusions 1941-2006 formed a grand solar maximum (GSMax defined by 600MV) Variation between Maunder minimum and this GSMax seen in several reconstructed solar and heliospheric parameters Solar wind speed lower when open solar flux is low, suggests a broader streamer belt Small (5%) chance of another GSMax within 50 years but decline in parameters thus far is as expected for a new GSMin in 50 years time (15% chance)
Space Weather Implications Not known! Past experience from the space age may be of limited value Lower heliospheric fields may allow greater SEP escape from inner heliosphere but may also limit SEP acceleration Effect on solar wind number density, Alfvn speed & Alfvn Mach number of events? Many Ground Level Events have been seen when solar activity is lower (e.g. in the 1940s)
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