Contact: Hauke Schmidt, Stergios Misios, Jens Kieser

The Sun is the energy source that drives the whole atmospheric dynamics. The energy and particle flux from the Sun varies 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 potential influence of these variations on Earth’s climate is discussed in the scientific community for decades, yet no satisfactory answer has been given. 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, MAECHAM5/MPIOM) are developed and applied to address the various physical aspects of Sun-Earth connections. E.g., in the framework of the ARTOS project, the impact of variable UV, TSI radiation and precipitating particles on the dynamics and composition of the whole atmosphere has been studied. Some results from recent simulations are highlighted below. A complete list of publications is given at the bottom of this page.

While previous studies demonstrated remarkable changes of atmospheric conditions due to solar proton events, our simulations with HAMMONIA support a supplementary contribution of precipitating electrons. In contrast, precipitating α-particles play a minor only role. Moreover, particle precipitation leads to a substantial temperature increase in a large regions of the thermosphere while a remarkable cooling in the lower polar thermosphere in summer is simulated (right figure). It is found that particle precipitation strengthens chemical and Joule heating leading to a temperature increase, while negative temperature anomalies arise when the effects of radiative cooling by nitric oxide and dynamical cooling exceed the warming effects.

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).

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.

Schmidt, H. and G. P. Brasseur (2006). "The response of the middle atmosphere to solar cycle forcing in the hamburg model of the neutral and ionized atmosphere." Space Science Reviews 125(1-4): 345-356

Schmidt, H., G. P. Brasseur, 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., G. P. Brasseur, et al. (2010). "Solar cycle signal in a general circulation and chemistry model with internally generated quasi-biennial oscillation." Journal of Geophysical Research-Atmospheres 115