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| Titel |
Climate variability related to the 11 year solar cycle as represented in different spectral solar irradiance reconstructions |
| VerfasserIn |
Tim Kruschke, Markus Kunze, Stergios Misios, Katja Matthes, Ulrike Langematz, Kleareti Tourpali |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134120
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| Publikation (Nr.) |
 EGU/EGU2016-14814.pdf |
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| Zusammenfassung |
| Advanced spectral solar irradiance (SSI) reconstructions differ significantly from each other
in terms of the mean solar spectrum, that is the spectral distribution of energy, and solar cycle
variability. Largest uncertainties – relative to mean irradiance – are found for the ultraviolet
range of the spectrum, a spectral region highly important for radiative heating and chemistry
in the stratosphere and troposphere.
This study systematically analyzes the effects of employing different SSI reconstructions in
long-term (40 years) chemistry-climate model (CCM) simulations to estimate related
uncertainties of the atmospheric response. These analyses are highly relevant for the next
round of CCM studies as well as climate models within the CMIP6 exercise. The simulations
are conducted by means of two state-of-the-art CCMs – CESM1(WACCM) and
EMAC – run in “atmosphere-only”-mode. These models are quite different with
respect to the complexity of the implemented radiation and chemistry schemes.
CESM1(WACCM) features a chemistry module with considerably higher spectral
resolution of the photolysis scheme while EMAC employs a radiation code with
notably higher spectral resolution. For all simulations, concentrations of greenhouse
gases and ozone depleting substances, as well as observed sea surface temperatures
(SST) are set to average conditions representative for the year 2000 (for SSTs:
mean of decade centered over year 2000) to exclude anthropogenic influences and
differences due to variable SST forcing. Only the SSI forcing differs for the various
simulations. Four different forcing datasets are used: NRLSSI1 (used as a reference in
all previous climate modeling intercomparisons, i.e. CMIP5, CCMVal, CCMI),
NRLSSI2, SATIRE-S, and the SSI forcing dataset recommended for the CMIP6
exercise. For each dataset, a solar maximum and minimum timeslice is integrated,
respectively. The results of these simulations – eight in total – are compared to each other
with respect to their shortwave heating rate differences (additionally collated with
line-by-line calculations using libradtran), differences in the photolysis rates, as well as
atmospheric circulation features (temperature, zonal wind, geopotential height,
etc.).
It is shown that atmospheric responses to the different SSI datasets differ significantly
from each other. This is a result from direct radiative effects as well as indirect
effects induced by ozone feedbacks. Differences originating from using different SSI
datasets for the same level of solar activity are in the same order of magnitude as
those associated with the 11 year solar cycle within a specific dataset. However,
the climate signals related to the solar cycle are quite comparable across datasets. |
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