Impact of solar vs. volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum
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2013-11-04
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Working Paper
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Abstract
The aim of this work is to elucidate the impact of changes in solar irradiance and en-ergetic particles vs. volcanic eruptions on tropospheric global climate during the Dal-ton Minimum (DM, 1780–1840 AD). Separate variations in the (i) solar irradiance inthe UV-C with wavelengthsλ<250 nm, (ii) irradiance at wavelengthsλ>250 nm, (iii)5in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed sepa-rately, and (v) in combination, by means of small ensemble calculations using a cou-pled atmosphere-ocean chemistry-climate-model. Global and hemispheric mean sur-face temperatures show a significant dependence on solar irradiance atλ>250 nm.Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decrease10global mean temperature by up to 0.5 K for 2–3 yr after the eruption. However, whilethe volcanic effect is clearly discernible in the southern hemispheric mean tempera-ture, it is less significant in the Northern Hemisphere, partly because the two largestvolcanic eruptions occurred in the SH tropics and during seasons when the aerosolswere mainly transported southward, partly because of the higher northern internal vari-15ability. In the simulation including all forcings, temperatures are in reasonable agree-ment with the tree-ring-based temperature anomalies of the Northern Hemisphere.Interestingly, the model suggests that solar irradiance changes atλ<250 nm and inenergetic particle spectra have only insignificant impact on the climate during the Dal-ton Minimum. This downscales the importance of top-down processes (stemming from20changes atλ<250 nm) relative to bottom-up processes (fromλ>250 nm). Reductionof irradiance atλ>250 nm leads to a significant (up to 2 %) decrease of the ocean heatcontent (OHC) between the 0 and 300m of depth, whereas the changes in irradianceatλ<250 nm or in energetic particle have virtually no effect. Also, volcanic aerosolyields a very strong response, reducing the OHC of the upper ocean by up to 1.5%.25In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 yr after volcanic eruption, while the solar signal and the different volcanic eruptionsdominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had asignificant impact on the precipitation patterns caused by a widening of the Hadley celland a shift of the intertropical convergence zone.
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9 (6)
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6179 - 6220
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Copernicus
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03517 - Peter, Thomas (emeritus) / Peter, Thomas (emeritus)
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Is previous version of: https://doi.org/10.3929/ethz-b-000084962