Solar Variability

Contact: Opens window for sending emailHauke Schmidt, Opens window for sending emailKatharina Meraner

The Sun is the fundamental energy source that drives Earth’s climate. The Sun warms our planet by heating the ground, oceans and atmosphere. In this sense, it is fundamental to all life on this planet. The energy and particle fluxes from the Sun vary over a large range of time scales: from the secular changes of total irradiance to the coronal mass ejections that last for hours or a few days. The influences of these variations on Earth’s climate are discussed in the scientific community for decades, yet many questions remain open. A quantification of the influence of solar activity on the climate system is a prerequisite in order to separate anthropogenic and natural causes of the observed climate trends.

In our group chemistry-climate and coupled ocean-atmosphere general circulation models (HAMMONIA, MPI-ESM,
ICON) are developed and applied to address the various physical aspects of Sun-Earth connections. The impacts of variable UV, TSI radiation and energetic particle precipitation on the dynamics and composition of the whole atmosphere have been studied. Some results from recent simulations are highlighted below. A list of selected publications is given at the bottom of this page.

Energetic particle precipitation

Energetic particles enter the Earth’s atmosphere near the magnetic poles altering the chemistry of the middle and upper atmosphere. Energetic particle precipitation (EPP) is the major source of nitrogen oxides (NOx) and hydrogen oxides (HOx) in the polar middle and upper atmosphere. Both components are powerful ozone destroyers. The impact of HOx on ozone is limited to the mesosphere, because HOx has a short chemical lifetime (up to hours). In contrast, NOx can persist up to several months in the winter polar middle atmosphere and can be transported downward to the stratosphere. Models covering the middle and upper atmosphere underestimate this downward transport. This may lead to an underestimation of potential climate effects from energetic particle precipitation.

We have studied the polar winter transport from the lower thermosphere to the stratosphere and quantified, for the first time, the contribution of advection, eddy diffusion and molecular diffusion for the transport through the mesopause. Advection and molecular diffusion dominate the transport through the mesopause. This leaves advection being responsible for the underestimation of the downward transport. Gravity waves are the key driver for the advective downwelling in the polar winter mesosphere. We showed that weakening gravity waves enhances the mesospheric transport bringing it close to satellite observations. The altitude of the mesospheric momentum deposition is identified to be key for the polar downwelling (Meraner and Schmidt 2016; Meraner et al. 2016).

Furthermore, we analyzed the climate impact of winter polar mesospheric and stratospheric ozone losses due to EPP. Recently, it has been inferred from observations that energetic particle precipitation can cause significant long-term mesospheric ozone variability. Satellites observe a decrease in mesospheric ozone by up to 34% between EPP maximum and EPP minimum. Using radiative transfer modeling, we find that the radiative forcing of a mesospheric ozone loss during polar night is small. Hence, climate effects of a mesospheric ozone loss due to energetic particles seem unlikely. A stratospheric ozone loss due to energetic particles warms the winter polar stratosphere and subsequently weakens the polar vortex (see figure below). However, those changes are small, and few statistically significant changes in surface climate are found (Meraner 2017; Meraner and Schmidt 2017).

Atmospheric and oceanic response to 11-year solar cycle

Simulations with HAMMONIA have examined the interaction between the signals of the 11-yr solar cycle and the stratospheric quasi-biennial oscillation (QBO). As in observations, the simulated response of the stratospheric polar vortex to solar cycle forcing depends on the QBO phase. Moreover, the assumption that the solar signal is propagated from the stratosphere to the troposphere is supported by the simulations. As a consequence, dynamically driven positive temperature and ozone anomalies at the lower stratosphere are also simulated. For more details see Schmidt et al., (2010, 2013).

Stratospheric changes such us the lower stratospheric heating during increased solar activity have the potential to modify tropospheric circulation and subsequently the sea surface temperature. We have conducted tailor-made simulations with the MAECHAM5/MPIOM to investigate how the tropical oceans, particularly the Pacific Ocean, respond to the 11-yr solar cycle forcing. Our simulations refute earlier suggestions about an eastern Pacific cooling in peak years of solar activity. Instead, a basin-wide warming is simulated. The animation on the right shows the simulated solar signal after a spatiotemporal filter is applied. The apparent eastward propagation underlines the importance of coupled atmosphere-ocean dynamics. For more details see Misios and Schmidt (2012).

Furthermore, we have studied the role of observed SST patterns for observed atmospheric circulation changes attributed to solar forcing. So far, it had been assumed that the observed poleward shift of the subtropical jets under solar maxima is related to a downward propagation of signals from the stratosphere. Using reanalysis data and specific model simulations we have shown that the same jet shift can be produced by the observed anomalies in sea surface temperatures which are co-varying with the solar cycle (Misios and Schmidt, 2013).


Selected publications:

Meraner, K. and H. Schmidt (2017): Climate Impact of Polar Mesospheric and Stratospheric Ozone Losses due to Energetic Particle Precipitation, Atmos. Chem. Phys. Discuss., in review.

Meraner, K. (2017): Towards modeling climate effects of energetic particle precipitation. Phd-Thesis, Universität Hamburg, Hamburg. Berichte zur Erdsystemforschung, 190.

Meraner, K., Schmidt, H., Manzini, E., Funke, B. and A. Gardini (2016): Sensitivity of simulated mesospheric transport of nitrogen oxides to parameterized gravity waves. Journal of Geophysical Research-Atmospheres, 121, 12,045-12,06.

Meraner, K. and H. Schmidt (2016): Transport of Nitrogen Oxides through the winter mesopause in HAMMONIA. Journal of Geophysical Research-Atmospheres, 121, 2556-257.

Misios, S., D. M. Mitchell, L. J. Gray, K. Tourpali, K. Matthes, L. Hood, H. Schmidt, G. Chiodo, R. Thieblemont, E. Rozanov, and A. Krivolutsky (2015): Solar Signals in CMIP-5 Simulations: Effects of atmosphere-ocean coupling, Quart. J. Roy. Met. Soc.

Misios, S. and H. Schmidt (2013): The role of the oceans in shaping the tropospheric response to the 11-year solar cycle, Geophys. Res. Lett, 40, 6373-6377.

Misios, S. and H. Schmidt (2012). "Mechanisms involved in the amplification of the 11-yr solar cycle signal in the tropical Pacific Ocean." J. Climate, 25(14), 5102-5118.

Schmidt, H. et al. (2006): "The HAMMONIA chemistry climate model: Sensitivity of the mesopause region to the 11-year solar cycle and CO2 doubling." Journal of Climate, 19(16): 3903-3931.

Schmidt, H., S. Rast, F. Bunzel, M. Esch, M. Giorgetta, S. Kinne, T. Krismer, and M. Walz (2013): "The response of the middle atmosphere to anthropogenic and natural forcing in the CMIP5 simulations with the MPI‐ESM". J. Adv. Model. Earth Syst., 5, 98-116.