Post on 14-Jan-2016
description
Steve Rumbold
Keith Shine, Lesley Gray Charlotte Pascoe (CASE, RAL)
Picture: http://cloud1.arc.nasa.gov/crystalface/
Strat Hour - July 05, 2006
The University of Reading
Solar cycle effects on stratospheric temperature
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
Insert Ref.
Data: www.ngdc.noaa.gov/stp/SOLAR/
How can the solar cycleinfluence the stratosphere?
• 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].
1. UV effect
2. Ozone effect
Percentage change in ozone from solar min to max determined from observations (annual mean) [data: SAGE satellite, Randel, 2005].
• Change in UV has effect on O3 concentrations
• This in turn has effect on heating
• Magnitude and distribution of change varies between studies
Approach
Description of modelBlue = inputs, Pink = model,
Yellow = outputs
• Determine radiative component of solar cycle effect
• The model [Forster and Shine, 1997]: • Narrow band radiation code• Fixed Dynamical Heating (FDH)
i. The radiative response can be isolated.
ii. High spectral resolution radiative calculations can be performed.
iii. A large number of separate calculations can be run quickly.
• This has been used instead of a General Circulation Model (GCM) for three main reasons:
0)(
DTQt
T
Spectral sensitivity experiment
(from Lean et al. 1997)
Black line = Lean et al. 1997Grey = Lean 2005 range (1
Comparison of “classic” data with new study
Test of influence of Mg II line
• To asses the importance of the Mg II line, three experiments were conducted with the FDH model:
i. Using actual solar cycle UV change (Black).ii. Same as i. but without Mg II line (Blue).iii.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.
Oct, Equator
Investigating Mg II lineTemperature change due to the spectrally resolved irradiance changes.
Note: weird units[ K / (10nm) ]
LW SW NETChange in
radiative heating(max minus min)
[ K / day ]
(or greater)
(or less)
Results from idealised ozone
change experiment
6%56 km
+5 km
-5 km1/e
1/e
“Minimum” =Climatology – 0.5 x change
“Maximum” =Climatology + 0.5 x change
Temperature change(max minus min)
[ K ](Oct)
A solar maximum minus minimum experiment
• Irradiance changes only
• Ozone changes only
• Combining the two
• Compare to other studies
Irradiance Changes Only
Minimum = solar neutral spectra – 0.5 x change
Maximum = solar neutral spectra + 0.5 x change
Ozone changes solar maximum minus minimum [ % ](annual mean)
SAGE I/II Regression – Randel (2005)
GISS – Shindell et al. (1999) Imperial College – Haigh (1994)
Resulting FDH temperature changes
(solar maximum minus minimum [ K ] )
Shibata and Kodera, 2005Using GISS ozone
Shibata and Kodera, 2005Using Imperial ozone
Reading FDHMUsing SAGE I/II ozone
ERA-40 ReanalysisCrooks & Gray (2005)
Reading FDHM(SAGE ozone changes+ UV irradiance changes)
Temperature change ( solar maximum minus minimum [ K ] )(annual mean)
0.5 K 0.5 K
1.8 K
1.8 K
0.5 K
Ozone effect vs. irradiance effectBold line “50/50”. Dotted lines “irradiance wins”. Solid lines “ozone wins”