Including volcanic forcing in the MiKlip prediction system has increased the prediction skill for global surface temperature (Timmreck et al., 2016). However, the regional impacts of volcanic forcing in particular on Northern Hemisphere (NH) winter climate which are controlled largely by dynamical changes are neither fully understood nor well represented in the current prediction system. ALARM-II will therefore explore and improve the representation of the climate response to aerosol perturbations caused by volcanic eruptions in the MiKlip prediction system, in order to prepare for future events and be able to forecast their effects immediately after a potential future eruption.
ALARM II consists of three workpackages and is coordinated by Dr. Claudia Timmreck (MPI-M). Dr. Hauke Schmidt (MPI-M) and Prof. Dr. Kirstin Krüger (UiO), as an external partner, contribute to the project.
A multilinear regression analysis of five historical runs with the MPI-ESM-HR and CMIP5 forcing shows that the MPI-ESM-HR model reacts qualitatively similar, in the middle atmosphere to natural and anthropogenic forcings, to the MPI-ESM-LR and the MPI-ESM-MR model (see, Schmidt et al., 2013). The temperature response to volcanic eruptions shows the typical pattern of a tropospheric cooling and a warming in the low to mid-latitude lower stratosphere. The meridional temperature signal from volcanic forcing is reflected in the westerly wind anomalies in large parts of the stratospheric high-latitudes. It is however difficult to interpret the difference between the model versions as the volcanic signal is masked by the high interannual variability in NH winter. The large ensemble (≥25) of the planned VolMIP Pinatubo simulations (Zanchettin et al., 2016) with the MPI-ESM in LR and HR resolutions will offer a great possibility to study the effect of an increased model resolution with an ensemble sufficiently large to get a significant response.
The MPI Grand Ensemble, a 100-member ensemble of historical (1850–2005) simulations with the MPI-ESM-LR, has been analyzed with the focus on the stratospheric temperature and wind response in the 1st post volcanic NH winter (Bittner et al., 2016). Approximately 15 ensemble members are needed to get a significant (95%) response of the NH polar vortex in DJF after the Pinatubo eruption. How many ensemble members are necessary for a significant response depends on the magnitude of the anomaly and the interannual variability. Including smaller eruptions to increase the sample size does not necessarily improve the detectability of the volcanic signal. Analyzing the dynamical response to volcanic eruptions in too small ensembles might therefore lead to false conclusions. Hence, the CMIP5 models do not generally fail to capture the dynamical response to tropical volcanic eruptions (Figure 1). Large uncertainties remain in the response of the real atmosphere to volcanic eruptions due to the small number of observed events.
Bittner, M. | H. Schmidt, C. Timmreck, and F. Sienz
Zanchettin, D. | M. Khodri, C. Timmreck, et al.
Toohey, M. | B. Stevens, H. Schmidt and C. Timmreck
Raible, C. C. | S. Brönnimann, R. Auchmann, P. Brohan, T.L. Frölicher, H.-F. Graf, P. Jones Phil, J. Luterbacher, S. Muthers, R. Neukom, A. Robock, S. Self, A. Sudrajat, C. Timmreck, and M. Wegmann
Kremser, S. L. W. | Thomason, M. von Hobe, M. Hermann T. Deshler, C. Timmreck, M. Toohey, A. Stenke, F. Prata, J. Schwarz, R. Weigel, S. Fueglistaler, J.-P. Vernier, B. Luo, H. Schlager, J. Barnes, J.-C. Antuna-Marrero, D. Fairlie, M. Palm, E. Mahieu, J. Notholt, M. Rex, R. Neely, C. Bingen, A. Bourassa, J. Plane, D. Klocke, S. Carn, C. Lieven, A. James, S. Borrmann, L. Rieger, T. Trickl, C. Wilson, and B. Meland