Stergios Misios, Hauke Schmidt and Kleareti Tourpali 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) Tropical Pacific sea surface temperature La Nina-like cooling (Meehl et al., 2009) El Nino-like warming (White et al., 2008) Warming or Cooling ? Climatology (m/s) Solar MAX-MIN (m/s) weakening and poleward expansion of the mid-latitude jets

? ? ? Suggested mechanisms 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 ! Spectral solar irradiance: Affects ozone Stratospheric warming of about 1 K Two main mechanisms: Top-down Bottom-up VIS UV Stratosphere Stratosphere ? ? Troposphere 1 w/m2 increase from solar minimum to solar maximum at the TOA translates to 0.18 W/m2 at the surface, if the sphericity and the global albedo of the earth is accounted. Straight forward calculations with EBM predict 0.1 K global mean warming. However, local feedbacks could amplify the response manifold. In the tropical Pacific, for instance atmosphere-ocean feedbacks could amplify any weak response. I focus on the tropical oceans and particularly on the tropical pacific because solar signals in the tropical Pacific can be felt globally through atmospheric teleconnections. This a schematic of the stratosphere, troposhere the ocean over the tropics. One would expect warmer tropical oceans with increased total solar irradiance, but it is explained later that analyses of observations do not give a clear answer. The combined effect of higher UV and ozone levels warms the upper tropical stratosphere. Satellite observations suggest warming of about 1 K and model simulation with chemistry schemes to account for ozone photochemistry have given consistent results. It has been suggested that solar signals in the stratosphere can propagate downward inducing changes in the tropical troposphere. Changes in the troposphere, may in turn affect ocean circulation. This pathway is commonly called, the top-down mechanism. In the opposite direction, if the response of the tropical oceans to the 11-yr solar cycle is strong enough, then it could induce changes in the troposphere and even in the stratosphere. This pathway is commonly called the bottom up-mechnism. These two mechanisms are not well represented in previous modeling attempts for different reasons and we don’t know how these mechanisms effect the surface or the stratosphere. ? Ocean 30°S 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 (Schmidt et al., 2010) 10.7 cm radio flux (F10.7) Experiments CENS: fully coupled ensemble (10 members, T31L90/GR30L40) MENS: mixed layer ensemble (10 members, T31L90 )

Coupled ensemble (CENS) sea surface temperature 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) Several oscillations indentified in SSTs: 3.6 yrs, 4.9 yrs, 10 yrs, … Coupled ensemble (CENS) sea surface temperature 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 Coupled ensemble (CENS) sea surface temperature Solar cycle/Temperature Lag: CENS +1 year MENS +2 years 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 Κ/100 sfu

Response of the tropical troposphere: Temperature Mixed layer ensemble Atmosphere-only ensemble Coupled ensemble solar leads solar lags solar leads solar lags 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) Coupled ensemble Mixed layer ensemble m/s/100 sfu 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: 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. The tropospheric temperature response lags the stratospheric. The Walker circulation weakens and shifts eastward. Can similar signals be detected in observations?

Reg. coef. of zonal mean temperature (25S-25N) 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) Coupled ensemble ERA-40 (1958-2001) m/s/100 sfu 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.