Solar cycle effects on stratospheric temperature

1. The University of Reading Solar cycle effects on stratospheric temperature Strat Hour - July 05, 2006 Steve Rumbold Keith Shine, Lesley Gray Charlotte Pascoe (CASE, RAL) Picture: http://cloud1.arc.nasa.gov/crystalface/

2. Effect of 11 year Solar Cycle • Two main ways to affect stratospheric temperatures • Direct effect of flux change • Effect of resultant Ozone changes • 0.1 – 0.15 % on total solar irradiance (TSI) • However, large percentage effect in UV Data: www.ngdc.noaa.gov/stp/SOLAR/ Insert Ref.

3. How can the solar cycle influence the stratosphere? 1. UV effect • Large percentage effect in UV • Effects shortwave heating (O2, O3) Percentage change in spectral flux from solar min to max [data: Lean et al, 1997]. 2. Ozone effect • Change in UV has effect on O3 concentrations • This in turn has effect on heating • Magnitude and distribution of change varies between studies Percentage change in ozone from solar min to max determined from observations (annual mean) [data: SAGE satellite, Randel, 2005].

4. Approach • Determine radiative component of solar cycle effect • The model [Forster and Shine, 1997]: • Narrow band radiation code • Fixed Dynamical Heating (FDH) Description of model Blue = inputs, Pink = model, Yellow = outputs • This has been used instead of a General Circulation Model (GCM) for three main reasons: • The radiative response can be isolated. • High spectral resolution radiative calculations can be performed. • A large number of separate calculations can be run quickly.

5. Spectral sensitivity experiment (from Lean et al. 1997)

6. Comparison of “classic” data with new study Black line = Lean et al. 1997 Grey = Lean 2005 range (1s)

8. Investigating Mg II line Oct, Equator Temperature change due to the spectrally resolved irradiance changes. Note: weird units [ K / (10nm) ] Test of influence of Mg II line • To asses the importance of the Mg II line, three experiments were conducted with the FDH model: • Using actual solar cycle UV change (Black). • Same as i. but without Mg II line (Blue). • Just Mg II line change (Red). • The Mg II line has moderate importance to total solar change. ~1/6 of total effect at 1 mbar. • ii. and iii. sum linearly to reproduce i.

9. +5 km 1/e 56 km 6% -5 km 1/e Results from idealised ozone change experiment LW SW NET Change in radiative heating (max minus min) [ K / day ] (or greater) “Minimum” = Climatology – 0.5 x change “Maximum” = Climatology + 0.5 x change (or less)

10. Temperature change (max minus min) [ K ] (Oct)

11. A solar maximum minus minimum experiment • Irradiance changes only • Ozone changes only • Combining the two • Compare to other studies

12. Irradiance Changes Only Minimum = solar neutral spectra – 0.5 x change Maximum = solar neutral spectra + 0.5 x change

13. GISS – Shindell et al. (1999) Imperial College – Haigh (1994) Ozone changes solar maximum minus minimum [ % ] (annual mean) SAGE I/II Regression – Randel (2005)

14. Shibata and Kodera, 2005 Using Imperial ozone Shibata and Kodera, 2005 Using GISS ozone Reading FDHM Using SAGE I/II ozone Resulting FDH temperature changes (solar maximum minus minimum [ K ] )

15. 1.8 K 0.5 K 0.5 K ERA-40 Reanalysis Crooks & Gray (2005) Temperature change ( solar maximum minus minimum [ K ] ) (annual mean) 1.8 K Reading FDHM (SAGE ozone changes + UV irradiance changes) 0.5 K

16. Ozone effect vs. irradiance effect Bold line “50/50”. Dotted lines “irradiance wins”. Solid lines “ozone wins”