the impact of solar variability and quasibiennial oscillation on climate simulations

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)

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.

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)

Regression Formula

U(EQ,50mb)*U(EQ,20mb)*107F*NINO34* 43210 TT

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

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

120 years87 years

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?

Regression of T vs F107 by month

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.

Composite difference (Smax – Smin) stratified by the QBO

10 hPa

• The response in sea level pressure is comparable, if not larger, than that predicted by a doubling of CO2

10 hPa

-3 hPa

Sea level pressure difference between 2xCO2 and present day (WACCM w/ mixed layer ocean)

Composites of Weak Vortex Events PC1 of Geopotential Height

Baldwin and Dunkerton, 2001

CCSM/WACCM w/ QBO

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