11-year Solar Signalin Transient Climate SimulationsLesley Gray NCASUniversity of OxfordOxford: Dann Mitchell, Scott OspreyMet Office: Neal Butchart, Steve Hardiman, Sarah Ineson, Adam ScaifeReading: Manoj JoshiImperial: Indrani Roy

QuestionsHow well do we model solar influence on climate? - focus on Atlantic / European response

Can we use models to improve understanding of mechanisms, given that we have limited observational time records? 1. Brief description of observations of Solar Influence on Climate. 2. Summary of 3 prime mechanisms for solar irradiance influence (top-down / bottom-up influences).

3. Model analysis Analysis of very long time-varying climate runs (CMIP5)

Regression analysis of ERA dataAnnual average 1979-2008Frame and Gray 2010Gray, Rumbold and Shine 2009Regression analysis of SAGE satellite datasetAnnual average 1985-2003Soukharev and Hood 2006

ObservationsSmax minus SminSolar Maximum: More UV radiation => higher temps More ozone => higher temps (early work of Labitzke; Haigh)Temperature

Ozone

Observations: Zonal windsNCEP DJF zonally-averaged zonal winds 1979-2002Haigh,Blackburn,Simpson,Sparrow Climatology (m/s)Smax minus Smin (m/s)NCEP zonal winds/temps1979-1999windstempsKuroda and Kodera 2002StratosphereTroposphereSmax minus Smin +ve NAOPattern at surface

Roy and Haigh 2010Observations: Mean Sea Level Pressure (max-min)HadSLP2 1956-2004 Woollings et al 2010See also Ineson et al 2011

1856-1905

ERA-40 1958-2001

Response is REGIONALSolar max minus min can reach ~5-8 hPa in Atlantic but amplitude / sign varies with time => scepticism ... (min-max)

NOAA Extended Reconstructed SST Hadley Centre HadISST 1871-present

White and Liu 2008Meehl et al. 2009 Observations: Surface temperatures

Response is REGIONAL and very small ~tenths K globallyNo agreement on spatial pattern;depends on how solar max/min are defined(Roy and Haigh 2010)Zhou and Tung 2010)

Smax minus Smin temperature 2 top-down routes:Polar route: planetary waves / SSWs (only during winter)Equatorial route: synoptic-scale waves(all year round)

Mechanisms: top-downaltered planetary wave propagation = > fewer sudden stratospheric warmings (SSWs) +ve temp anomaly at stratopause+ve NAO at surface in Smax+ve temp anomaly lower strat=> increased horizontal temp grad. => altered synoptic wave propagationwesterly subtropical wind anomaly POLAR ROUTEEQUATORIALROUTESolar Maximum: More UV radiation => higher temps More ozone => higher temps

Mechanisms: bottom-up

The bottom-up mechanismthrough total solar irradiance (TSI):

Increased solar absorption during Smax in cloud-free subtropical oceans, increases evaporation;

increased moisture converges into precipitation zones, intensifies precipitation and upward vertical motions, which strengthens Hadley and Walker circulations;

stronger subsidence in subtropics gives positive feedback that reduces clouds and allows increased solar forcing. Cubasch, van Loon, Meehl, White

The MODELCoupled ocean-troposphere-stratosphere Unified model (HadGEM2-CC)

Stratosphere resolving coupled ocean-atmosphere Atmosphere: N96 1.875 x 1.25 60 levels 0-84km (high-top)Ocean: 1.0 x 0.83 40 levelsincludes non-orographic GWD scheme; interactive carbon cycle but no tropospheric or stratospheric interactive chemistry

Historical+future all-forcings CMIP5 simulations:1x ensemble 1860-21002x ensembles 1960-2100

Increasing greenhouse gases (RCP8.5); monthly ozone variations are imposed, including ozone hole development + recovery; aerosols, solar cycle.

520 years

Lean et al. up to 2005; idealised in future (average of last 4 cycles)

Spectrally partitioned based on traditional view i.e. NOT using recent SIM UV observationsSolar Irradiance VariationsCorresponding variations also imposed in ozone fields520 years = 47x 11-yr cycles

Multiple Linear Regression Analysis with autoregressive noise model (AR1) 8 regression indices: CO2, ozone, 11-year solar cycle, long-term solar trend, volcanic aerosol, ENSO 3.4 index, 2 x QBO indices

95% significance90%+95% significance95%+99%significanceTemperatureStratospheric windsTropospheric windsModel Results: Smax minus Smin

520 years

47 solar cycles95+99%confidenceModel Results: Mean sea level pressureSmax minus Smin DJFMAM

JJA

SON

ModelObservations 1956-2004 1856-1905520-year period45-year period XModel Obs Comparison: DJF Smax minus Smin in MSLP

45-year period X80%+95% confidenceAll yearsDJFWhats going on during rogue 45-periods? Possible non-linear interactions with QBO? ENSO?SONModel Zonal windsDJF

95%+99% confidenceModel Results:Surface TemperaturesSmax minus Smin520 years47 solar cyclesSONDJF

SummaryModel appears to capture both top-down mechanisms and bottom-up mechanismModel has periods where solar signal in troposphere appears to reverse similar to obs BUT overall there IS an 11-year signal in mslp (primarily NAO region) and in SSTs (Europe and tropics) Still much to be understood in terms of mechanisms especially the relative timing / lagged responses and how solar interacts with QBO and ENSO.

Additional model runs Amanda Maycock3 x ensembles 2005-2070

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