Solar variability and its impact on climate Laura Balmaceda 4 th El Leoncito Solar Physics School November, 2008

Outline Global warming The climate system Solar signal in climate records Solar variability Solar irradiance variations

Global warming

Climate records IPCC (2001) Other climate records suggesting that the climate has been changing over the past century include: - the retreat of mountain glaciers - sea level rise - thinner Arctic ice sheets - an increased frequency of extreme precipitation events

The Earth climate system

… going back in time Proxy data: provide information about weather conditions at a particular location through records of a physical, biological or chemical response to these conditions. Dendrochronology:

… going back in time Analysis of oxygen isotopes in ice cores obtained from Greenland and Antarctica.

Solar variability

Solar signal on climate records

Solar signal on climate records: century scale Lassen & Friis-Christensen (1991) Laut & Gundermann (2000)

Solar signal on climate records: solar cycle scale atmosphere below 24 km troposphere

Cosmic rays – cloud coverage Marsh & Svensmark (2000) Gray et al. (2005)

… and more signal at solar cycle scales

Solar variability – climate: possible mechanisms.... Forcing factorGeneric mechanism Total solar irradiance (variations due to orbital variations or to variable solar emission) Radiative forcing of climate. Direct impact on sea surface temperatures and hydrological cycle. Solar UV irradianceHeating the upper and middle atmosphere, dynamical coupling down to troposphere. Middle and lower atmosphere chemistry and composition; impacts temperature structure and radiative forcing. Solar energetic particlesIonisation of upper and middle atmosphere; impact on composition and temperatures. Magnetosphere – ionosphere – thermosphere coupling. Galactic cosmic rays Ionisation of lower atmosphere; impact on electric field. Impact on condensation nuclei.

Total solar irradiance

The variation in TSI over the past two 11-year cycles shows approximately 0.08% ( ∼ 1.1 Wm –2 ) peak-to-peak over the solar cycle.

Why irradiance change?

Irradiance variations: dark sunspots

Irradiance variations: bright faculae

F( ) - quiet Sun flux (Fontenla et al. 1993) F s ( ) - sunspot flux; separate umbra/penumbra (cool Kurucz models) F f ( ) - facular flux (modified P-model; Fontenla et al. 1993; Unruh et al. 2000)  s (t) - filling factor of sunspots (MDI continuum)  f (t) - filling factor of faculae (MDI magnetograms) Modeling solar irradiance variations

Studying irradiance variations: short term reconstructions Wenzler et al. (2005)

The model for magnetic flux

Total magnetic flux Solanki et al. (2002)

Total magnetic flux

Magnetic flux in long-term scales

Open flux – secular change

Irradiance variations on long timescales DI = 1.3 W/m 2

Long-term irradiance variation

Comparison with other models

The contribution of the UV irradiance variations to the total irradiance change is very high: about 60% of all TSI variations originate below 400 nm. Spectral irradiance variations Krivova et al. (2006)

Reconstruction of spectral irradiance variations The spectral composition of solar irradiance is important in determining at what altitudes it is absorbed and produces local heating. Krivova et al. (2006)

Solar activity in the last years Solanki et al. (2004)

Summary There is some statistical evidence for solar influence on various meteorological parameters on all timescales. Changes in total solar irradiance impact on the energy balance of Earth’s atmosphere. Changes in spectral irradiance may have impact on the thermal structure and composition of the middle atmosphere. A lot of work to be done!!!!!

Some links: Solar variability and climate change: is there a link? Sami K Solanki Astronomy & Geophysics Volume 43, Issue 5, Pages