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The response of the troposphere and surface to the 11-yr solar cycle variability in idealized ensemble simulations Stergios Misios, Hauke Schmidt and Kleareti Tourpali Aristotle University of Thessaloniki, Greece Max Plank Institute for Meteorology, Germany 11-yr solar signals in the troposphere and surface Increased solar activity is (possibly) related to: warmer troposphere (Labitzke and van Loon, 1995; Coughlin and Tung, 2004) weakening and poleward expansion of the mid-latitude jets (Haigh, 2003) poleward shift of the Hadley circulation (Gleisner and Thejll, 2003) stronger Walker circulation (Meehl et al., 2008) cooling (or warming?) of the tropical Pacific (van Loon et al., 2007, Meehl et al., 2008, White et al., 1997) excess precipitation over the convergence zones (van Loon et al., 2004; van Loon et al., 2007) Solar cycle signals appear in local scales!!! Examples of possible solar signals Tropospheric jets (Haigh 2005) Climatology (m/s) Tropical Pacific sea surface temperature La Nina-like cooling (Meehl et al., 2009) Solar MAX-MIN (m/s) El Nino-like warming (White et al., 2008) weakening and poleward expansion of the mid-latitude jets Warming or Cooling ? UV Total solar irradiance: 1 W/m2 at the top of the atmosphere translates to 0.18 W/m2 at the surface Energy balance models predict ~0.1 K global-mean warming ! VIS Suggested mechanisms Stratosphere Spectral solar irradiance: Affects ozone Stratospheric warming of about 1 K Two main mechanisms: Top-down Bottom-up ? ? Troposphere ? 30°S Ocean 30°N Adapted from Gray et al. 2010 Questions and our toolbox Question 1: Is numerical modeling supporting aspects of the observed solar signals at the surface and troposphere? Question 2: Does the tropospheric response to solar cycle depend on the solar signal on the ocean surface? Our toolbox Middle Atmosphere version of ECHAM5/MPIOM Detailed stratospheric dynamics: internal QBO Present-day greenhouse gas concentrations Sinusoidal spectral solar irradiances of realistic amplitude (14 cycles) (Lean et al., 2000) Solar-induced ozone anomalies from HAMMONIA 10.7 cm radio flux (F10.7) (Schmidt et al., 2010) Experiments CENS: fully coupled ensemble (10 members, T31L90/GR30L40) MENS: mixed layer ensemble (10 members, T31L90 ) Response of the tropical oceans: MSSA filtering MSSA (Multichannel singular spectrum analysis) •Attempts to incorporate both the spatial and temporal correlations and to extract oscillations (Ghil et al., 2001) Coupled ensemble (CENS) sea surface temperature •Several oscillations indentified in SSTs: 3.6 yrs, 4.9 yrs, 10 yrs, … Characteristics of the filtered signal at decadal scale: • Basin-wide weak warming • Stronger in the west side • Lags the forcing by 1 year The observed solar cycle (1955-2006) gives similar responses in the model study of Misios and Schmidt 2012, J. Clim. Response of the tropical oceans: Linear regression Linear regression shows: • A basin-wide warming, with stronger anomalies in the west • MENS shows stronger warming Lag 1 year Mixed layer ensemble (MENS) sea surface temperature Lag 2 years Solar cycle/Temperature Lag: CENS +1 year MENS +2 years Coupled ensemble (CENS) sea surface temperature Κ/100 sfu Response of the tropical troposphere: Temperature Coupled ensemble solar leads solar lags Mixed layer ensemble solar leads solar lags Atmosphere-only ensemble solar leads solar lags Κ/100 sfu • The lower stratosphere responds instantaneously to the solar cycle. • A time lag between the stratosphere and troposphere. This suggests links to the surface. • Weak tropospheric signals when SSTs and SICs climatologies are specified. Response of the tropical troposphere: Walker cell Reg. coef. zonal winds (5S-5N) Mixed layer ensemble m/s/100 sfu Coupled ensemble • Walker cell weakens and shifts eastward in solar MAX. • Consistent responses both in CENS and MENS. What we learned from the model simulations Our simulations with MAECHAM5/MPIOM showed: 1) A warmer tropical Pacific in solar maxima, which peaks +1 year after the forcing. This is similar to observational analysis of White et al., 1997. 2) The tropospheric temperature response lags the stratospheric. 3) The Walker circulation weakens and shifts eastward. Can similar signals be detected in observations? Troposphere-stratosphere lag in observations? Reg. coef. of zonal mean temperature (25S-25N) Coupled ensemble ERA-40 (1958-2001) Κ/100 sfu • Traces of similar responses? • Signal is noisy. Weakening /eastward shift of the Walker cell? Reg. coef. zonal winds (5S-5N) ERA-40 (1958-2001) m/s/100 sfu Coupled ensemble Positive zonal wind anomalies are seen over the western Pacific. Summary Question 1: Is numerical modeling supporting aspects of the observed solar signals at the surface and troposphere? Yes, MAECHAM5/MPIOM indicates a warmer tropical Pacific in solar MAX as in observations. Question 2: Does the tropospheric response to 11-yr solar cycle forcing depend on the solar signal on the ocean surface? The tropospheric response in MAECHAM5/MPIOM is mainly related to the surface. In solar MAX we find: • Warmer tropical Pacific Ocean, lagging the forcing by 1 to 2 years. • A warmer tropical troposphere, directly related to the surface warming. • A weaker and eastward displaced Walker circulation.