Stratospheric interannual variability influences weather and climate on the decadal time scale, hence ignoring stratospheric variability increases the uncertainty of decadal predictions. The provision of reliable and robust decadal climate predictions requires proper representation of decadal stratospheric variability, its interaction with tropospheric weather and the feedback with the oceans.

Major factors with decadal impact have been identified in the MiKlip precursor project STRATO. It was shown that the consideration of stratospheric processes leads to an improvement of the prediction of decadal climate variations (Dameris, 2015). Relevant stratospherical processes in terms of solar activity (11-year solar cycle), as well as the internal variability of the stratosphere on decadal time scales were identified. Regarding stratospheric dynamics at a decadal time scale, the so called quasi-biennial-oscillation (QBO) in the tropics and the polar vortex in winter are dominating stratospheric variability. This was clearly visualised with the decadal power-spectra-analysis (PSA) (figure 1). The analysis of the representation of the variability induced by the solar cycle in the preceding development stages of the MiKlip models showed a clear overestimation, e. g. the solar signal in the short-wave heating rates was too strong. Short wave heating waves are significantly characterised by the prescribed ozone field of the models (figure 2).

Aims

The aim of STRATO-II is to validate and improve the performance of the MiKlip prediction system with respect to the representation of stratospheric decadal variability due to solar forcing, climate change and ozone recovery, and its implications on European climate.
STRATO-II will allow for a detailed evaluation of the MiKlip prediction system including a risk assessment and determination of uncertainties with respect to stratospheric effects. Results derived from the MiKlip prediction system will be evaluated with corresponding results from the Chemistry-Climate Model (CCM) EMAC. An innovative aspect is the consideration of chemistry-climate feedbacks. For example, the role of stratospheric water vapor fluctuations (on short- and long-term) and the variability of the stratospheric ozone layer including the expected recovery due to the regulation of Chlorofluorocarbons (CFC) (according to the Montreal protocol) are explicitly considered in EMAC, and can therefore be studied in detail. Climate-chemistry feedbacks and in particularly ozone feedbacks will be analysed in cooperation with the project FAST O3 II. In the future, opposite regional trend patterns are anticipated, e.g. a decrease of tropical ozone and an increase of ozone in the extra-tropics, which are affected by climate change (depending on the assumed future greenhouse gas scenarios; see Scientific Assessment of Ozone Depletion: 2014, WMO (2014)). Here, we will investigate possible impacts for the European sector, i.e. assessing the climate change and (direct and indirect) effects for Europe, and its consequence on the decadal timescale.
 

Progress so far

During STRATO-II, the analyses of STRATO-I have been continued successfully. In this framework, we focused on the evaluation of the latest versions of the MiKlip prediction system, with respect to the solar signal in the North Atlantic sector. To evaluate the near surface signals (such as anomalies of the surface pressure) which are associated to the 11-year solar cycle, historical ensemble simulations have been analysed. The findings suggest, that the HR version shows a better representation of the observed solar signal compared to the LR and MR model versions. Further analysis will investigate possible reasons for the model improvement, for instance the transfer mechanisms of the solar signal between the middle atmosphere and the troposphere.