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”