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) 120 years87 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. The response in sea level pressure is comparable, if not larger, than that predicted by a doubling of CO 2 10 hPa -3 hPa  Sea level pressure difference between 2xCO2 and present day (WACCM w/ mixed layer ocean)

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

12. Stratospheric/Tropospheric anomalies result from a combination of solar variability and QBO phase: Are these anomalies producing a different variability at high northern latitudes during winter? Stratospheric Sudden Warming (SSW): composite behavior

13. Winter time variability - CCSM/WACCM: SSW Frq = 0.30 Frq = 0.33 Sudden Stratospheric Warming are natural events that produce a large warming of the polar stratosphere during winter The associated perturbations propagate downward to the lowermost stratosphere and it is argued that SSW anomalies may reach the troposphere The two panels on the rhs show the composite geopotential height, between 60 days before and 60 days after each event, using the SSWs simulated in the two CCSM-W simulations

14. 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