The impact of solar variability and Quasibiennial Oscillation on climate simulations

1. The impact of solar variability and Quasibiennial Oscillation on climate simulations Fabrizio Sassi (ESSL/CGD) with: Dan Marsh and Rolando Garcia (ESSL/ACD), Gokhan Danabasoglu (ESSL/CGD), Hanli Liu (ESSL/HAO)

2. Introduction • Solar variability has a large effect on the thermal structure and composition of the upper atmosphere (z>50 km) where most of the short wavelength (highly energetic) photons are absorbed. • Longer wavelength (less energetic photons) are absorbed below 50 km. There they can affect ozone in the stratosphere, a radiatively active minor constituent. • In the lowermost stratosphere (z<30 km), detection of solar signals is more difficult, partly because of the presence of other signals (ENSO). • The interactions among solar radiation, hydrological cycle and dynamics has been suggested to result in a solar signature on tropospheric climate. • The observational record is short and contaminated by other forcing, both natural and anthropogenic. Modeling studies – like this one - are necessary to determine the effects of solar variability combined with the tropical QBO.

3. CCSM/WACCM Simulations • CCSM3.5 (beta19) configured with a WACCM atmosphere (lid @ ~150 km) • 2 degrees atmosphere with 66 vertical levels; 1 degree ocean with 40 levels • Fully interactive chemistry, but composition is held constant to 1995 • Spectrally varying solar cycle as in Garcia et al. (repeated in time) • Quasi-biennial oscillation: based on obs, tropical zonal winds between ~17 km and ~40 km (repeated in time)

4. Regression Formula Sea Srfc Temp Solar var. Eq. Zonal wind @ 20mb Eq. Zonal wind @ 50mb U(EQ,20mb) and U(EQ,50mb) are ~90° out of phase

5. Regression of T (ann-avg) vs. F107(K per max-min F107 range) 87 years 120 years

6. Solar Influence • The influence of solar variability is largest in the upper atmosphere • Significant response is calculated also in the lower stratosphere at high latitudes in both hemispheres, which could affect the troposphere • What is the seasonal cycle of this regression? In which month does it maximizes in the lower stratosphere?

7. Regression of T vs F107 by month

8. What is the role of the QBO? • Several studies (e.g. Labitzke, van Loon, Gray) have suggested that the response of the extra-tropical stratosphere to solar cycle is affected by the phase of the QBO.

9. Composite difference (Smax – Smin) stratified by the QBO 10 hPa

10. 10 hPa  Sea level pressure difference between 2xCO2 and present day (WACCM w/ mixed layer ocean) -3 hPa • The response in sea level pressure is comparable, if not larger, than that predicted by a doubling of CO2

11. Composites of Weak Vortex Events PC1 of Geopotential Height CCSM/WACCM w/ QBO Baldwin and Dunkerton, 2001

12. Summary • Solar variability and QBO interact to produce significant anomalies that affect the near surface 30-60 days after stratospheric events • The presence of the QBO is important in order to represent correctly the downward propagation of stratospheric anomalies