Solar Irradiance Variations
During Solar Cycle 24
Slow Rise
in SC 24 ?
Low Minimum
in 2008 ?
Tom Woods
LASP / University of Colorado
tom.woods@lasp.colorado.edu
With Contributions / Data from: Gary Chapman, Angie Cookson, Steven
Dewitte, Leonid Didkovsky, John Emmert, Georg Fuelner, Claus Fröhlich,
Andrew Jones, Greg Kopp, Judith Lean, Stan Solomon, Dick Willson
Summary - 1
 Low, long minimum between solar cycle (SC) 23 and 24
 Early warning in 2003: polar magnetic fields (PMF) are 40% lower
 Open magnetic field is lower, and declining since 1985
 Solar extreme ultraviolet is 10% lower, along with less dense
thermosphere density
1996 MIN
•Lower polar magnetic fields in 2003
•Reversal for SC 24 started in 2009.
•Solar Max expected in 1-2 years
(Wilcox PMF)
2008 MIN
1986 MIN
2
Summary - 2
 Is the Total Solar Irradiance (TSI) lower in 2008 than in 1996?
 Perhaps – up to 200 ppm, but the results have large uncertainty.
+100
Measurement
Model / Proxy
0
-100
-200
100 ppm
uncertainty
-300
-400
ppm = parts per million
SSA = SunSpot Area
SFO = San Fernando Observatory
PMOD = Phys.-Met. Obs. Davos
ACRIM = Active Cavity Radiometer
Irradiance Monitor
RMIB = Royal Met. Inst. Belgium
3
What does this mean for Maunder Minimum?
 Because SC 23/24 minimum was three years wide, Schrijver et al. (GRL,
2011) suggests 2008 magnetic fields, and thus TSI level, are possibly as
low as Maunder Minimum levels.
 Even if baseline minimum did not change for Maunder Minimum, Feulner’s
climate model (GRL, 2011) shows that this scenario is still viable for a
colder period. Why?
 The solar cycle amplitude was near zero for decades and there are
other contributions from volcanic aerosols and natural CO2 changes
4
Lingering Question ?
 Is the solar cycle maximum more important than the irradiance
variation from minimum-to-minimum?
 If so, then longer time scales of solar forcing (namely the ocean
effects) on climate needs to be considered
 and the solar forcing / feedback factor might be larger than the
factor of 2 that some climate-atmosphere models indicate (GISS,
NCAR models)
5
Summary - 3
 Solar cycle 24 is off to a slow start
 Sunspot record looks like Gleissberg Minimum in the early 1900s
 X-ray flares are smaller, but still frequent. Both SC 23 and 24
have fewer flares than previous cycles (SC 21 and 22).
 SC 24 maximum is expected to be low and in 2013.
SC
Minimum
(shifted)
SC 24 is more than a factor of 2 slower
than all previous F10.7 cycles (19-23).
6
Thanks for participating in the
9th SORCE science meeting
1st GSFC-LASP Sun Climate Research Center Meeting
Let us know if we can
put your presentation
on the SORCE web site.
Lowell Observatory
Bell Rock, Sedona, AZ
Meeting Overview
Did we answer the questions?
Meeting Question #1
 What can we learn about decadal climate response and climate sensitivity
using the solar cycle as a well-specified external radiative forcing?
 Quasi 2-year periods in ocean and atmosphere oscillations (ENSO, NAO,
and QBO) may have link to solar variations, but in complicated and nonlinear ways. Solar maximum and declining phase appear more clearly.
 Both bottom-up (surface/ocean heating) and top-down (UV atmosphere
heating) contribute to the solar influence on climate.
NSIDC press release yesterday about
second lowest Arctic sea ice area in 2011
(Serreze)
ENSO – Ruzmaiken, Misios
Oscillations, Oscillations, Oscillations …
QBO - Labitzke
Ozone - Hood
9
Meeting Question #2
 What is current understanding of the amplitude of
solar spectral variability and the response of the
Earth’s atmosphere and climate system?
 Solar Spectral Irradiance (SSI) short-term (27-day
rotation) variability is understood well, but there is much
to do towards resolving differences between
measurements and models
 SORCE SSI validation workshop in 2012 !
What is going on for 200-400 nm?
Dudok de Wit
Lean
For More UV in SC-23
For Less UV / Vis In-Phase
SORCE SOLSTICE & SIM Obs.
(Harder, Snow)
UARS SUSIM & SBUV Obs.
(Morrill, DeLand)
SFO Red-Blue Solar Images
(Preminger)
NRLSSI, SATIRE Models
(Lean, Unruh)
Atmosphere Ozone and OH
(Li, Wang, Haigh, Cahalan)
Sun-like Stars
(Radick, Metcalfe)
SORCE SOLSTICE & SIM indicate more
UV variations than SUSIM and NRLSSI
model.
10
Meeting Question #3
 How does total solar irradiance vary over the solar cycle and
what are the implications for climate modeling to recent
refinements in its magnitude?
 There has been great progress in resolving the TSI level.
 TSI variations clearly include sunspot darkening and faculae
brightening components and perhaps a longer term component.
Validate, Validate, Validate …
TSI Radiometric Facility (TRF)
provides first irradiance
calibrations and validation for
lower TSI level.
Kopp, Willson, Schmutz
11
Meeting Question #4
 How do comparisons with Sun-like stars improve our
understanding of solar variability?
 The Sun appears to be much like other older G stars and yet it
appears somewhat unique.
 Stellar dynamo modeling is in a new phase of dazzling results
with high end computing and yet the solar dynamo is elusive.
Dynamo ?, Dynamo ?, Dynamo ?…
Reversal in
physics-based
Dynamo Model
Sun
Brown
Sun-like
Stars
Radick
Metcalfe
12
Meeting Question #1
 How can solar and climate models be advanced to better
reproduce decadal variability and improve forecast capabilities?
 Better understanding of the complex climate system is expected to
lead to improving forecast accuracy
 Some challenges are clouds and aerosols (large uncertainties) and
energy imbalance / missing energy
 Recent solar cycle minimum challenges Maunder Minimum results
Forecasting climate change
for IPCC AR5
Trentberth – energy imbalance and missing energy
Swanson- regime shifts
Dessler, Soden - feedbacks
13
Next Meeting Ideas
2012: Solar Spectral Irradiance (SSI) Validation Workshop
2012 ? : 1-day session about Sun-Climate at Decadal Variability Meeting
Fall 2013: Solar Cycle 24 Maximum:
Was it low as predicted? How did the climate respond?
Harpers Ferry
National Park
West Virginia
Backup Slides
for
Woods Solar Cycle 24 Talk
Is the solar Modern Maximum over?
Modern
Maximum
Maunder
Minimum
Dalton
Minimum
Gleissberg
Minimum
 F10.7 and other solar activity
1%
Accuracy
(K. Tapping)
indicators suggest lowest
solar minimum for the past 50
or more years [e.g. Russell et
al., Rev. Geophys., 2009]
 F10.7 cycle minima trend
indicates decline since 1996
and perhaps even since 1985
16
What does the sunspot record tell us?
 SSN Minimum Level
 Lowest since 1920s
 (3 of 24 are lower)
 SC Period Length
 Longest since 1900
 (4 of 24 are longer)
 Minimum Duration
 Widest since 1920s
 (7 of 24 are wider)
For more comparisons, see Russell
et al., Rev. Geophys., 2010.
17
Solar Magnetic Open Flux is Low in 2008
 Lockwood et al. (JGR, 2009) indicates decline in solar open flux since 1990
 Lockwood et al., (P.R.S.A, 2010) suggest that TSI variation is linearly
related to solar magnetic open flux
 They estimates lower TSI level by 270 ppm in 2008 than in 1996
TSI 1364 5.34 FS 1015Wb
Note that similar idea is
used to estimate solar
irradiance during the
Maunder Minimum using
magnetic activity derived
from tree rings and ice
cores.
18
Lower Solar EUV Irradiance
 SOHO SEM 26-34 nm is about
10% less in 2008 than in 1996
 Uncertainty is ~6%
 Solomon et al. (GRL, 2010)
 Thermospheric density at 400
km is about 28% lower in 2008
than in 1996
 Emmert et al. (GRL, 2010)
 ~3% is from long-term CO2
10%
increase (IR cooling)
trend
from
CO2
28%
19
Is the Total Solar Irradiance (TSI) lower in 2008 than in 1996?
 Perhaps:
TSI might be Lower by about 200 ppm (0.3 W/m2)
 PMOD Composite: 188 ppm lower in 2008 (140 ppm in Fröhlich, A&A, 2009)
 ACRIM Composite: 224 ppm lower in 2008
 RMIB Composite: 48 ppm higher in 2008
 SORCE TIM record does not extend back to previous minimum
Composite TSI Trends
Uncertainty of ~100 ppm
(~10 ppm/year)
PMOD = Physikalisch-Meteorlogisches
Observatorium Davos
RMIB = Royal Meteorological Institute of
Belgium
ACRIM = Active Cavity Radiometer
Irradiance Monitor
SORCE = Solar Radiation and Climate
Experiment mission
TIM = Total Irradiance Monitor
20
Is the Total Solar Irradiance (TSI) lower in 2008 than in 1996?
 Maybe Not: some models indicate little change in 2008
 Lean TSI 2-component Model based on SORCE TIM indicates no significant
change (Kopp & Lean, GRL, 2011)
 San Fernando Observatory (SFO) TSI model shows 4 ppm less in 2008 than in
1996 (Chapman et al., Solar Phy., 2011). They assume constant quiet Sun.
Residual having solar cycle variation suggests
that the model needs 3rd component (QS varies?)
Lean TSI Model
SFO TSI Model with TIM TSI 21
What If ?
 If the residual from the SFO TSI model indicates quiet Sun variation, then the
limit for the quiet Sun variation is 100 ppm over the solar cycle.
 If solar cycle TSI variation is related to solar magnetic fields, then the Wilcox
mean magnetic field time series provides an estimate of 50 ppm lower TSI in
2008 than in 1996.
 And if there is zero mean magnetic field during Maunder Minimum, then the
Maunder Minimum TSI level is perhaps only about 50 ppm lower than 2008.
This estimate and Schrijver et al. (2011)
are in contrast with larger reductions of
TSI during Maunder Minimum of 3001100 ppm [Wang et al., 2005; Tapping et
al., 2007, Krivova et al., 2011].
Magnetic Field is lower
in 2008 than in 1996
22
SC 24 Activity: Lots of Flares in February – March 2011
96 Flares (> C4) during Feb. 13 – Mar. 15, 2011
Only 64 Flares > C4 from SC Min (Oct. 2008) thru Jan. 2011 (59 of those in 2010)
Are intense solar storm periods normal
during SC rising phase?
The intense solar storms do not
usually start until 2 years after
cycle minimum.
Comparison Results
1. SC 24 has slower start
2. SC 24 & 23 are similar
3. Lower activity started in SC 23
24
Solar cycle 24 is off to a slow start
 Sunspot number (SSN) also shows slow rise.
 SC-24 appears similar to Gleissberg Minimum in early 1900s
but faster than the Dalton Minimum in early 1800s
A Slow Rise also means
Low Maximum is
expected
25
Next Solar Cycle Maximum is expected to be Low
Prediction with Post-MIN Slope
SSN Max: 94 ± 10
Consistent with NOAA Prediction
(last updated May 8, 2009)
SSN Max: 90 ± 10 in May 2013