Southern Hemisphere winter cyclone activity under recent and future climate conditions in multi‐model AOGCM simulations

Abstract

This article investigates extratropical winter cyclone activity in the Southern Hemisphere (SH) in a multimodel ensemble (MME) of coupled atmosphere-ocean general circulation model (AOGCM) simulations of recent and potential future climate conditions. Most individual models and also the ensemble mean yield good reproductions of the typical cyclone characteristics found in reanalysis data, although some individual models show peculiarities, and a large inter-model spread in terms of quantity of identified cyclone tracks is found. We use a scaling approach to combine the cyclone statistics from different models into a MME. In the future climate simulations, the total number of SH cyclones is reduced, whereas an increased number of strong cyclones is found in most models and in the ensemble mean. The long term trend with respect to all cyclones is a robust feature throughout the simulations. It is associated with a general poleward shift, shown to be related to both tropical upper tropospheric warming and shifting meridional sea surface temperature gradients in the Southern Ocean. The magnitude of increased strong cyclone activity has a focus on the Eastern Hemisphere. It is clearly influenced by natural variability and thus depends on specific time periods considered.

Evaluating the representation of Australian East Coast Lows in a regional climate model ensemble

“…Compared to the reanalyses, the GDD systematically shows too few cyclones that are too weak, too short and too large. A general underestimation of the intensity of cyclones by coarse resolution datasets was also found by Zappa et al (2013) and Grieger et al (2014), especially when considering the coarsest horizontal resolutions GCMs. Figure 3 shows the relative frequency of events as a function of the event-mean intensity for high-resolution reanalyses, individual RCM simulations and GDDs.…”

Impact of Identification Method on the Inferred Characteristics and Variability of Australian East Coast Lows

“…The cyclone identification and tracking scheme described in Murray and Simmonds (1991) is one of the more widely used low identification methods in the literature (e.g., Lim and Simmonds 2002;Pezza and Ambrizzi 2003;Pinto et al 2005;Allen et al 2010;Kouroutzoglou et al 2011;Grieger et al 2014), and has recently been applied to the Australian ECL in Pepler and Coutts-Smith (2013). This approach first identifies a maximum in the Laplacian of the pressure, before employing an iterative technique to identify a corresponding pressure minimum from a spline-fitted pressure field.…”

Meteorology and oceanography of the Atlantic sector of the Southern Ocean—a review of German achievements from the last decade

“…5) diagnose an increased number of extremely strong ETCs. This general change is associated with a poleward shift related to upper tropospheric tropical warming and shifting meridional sea surface temperature gradients in the Southern Ocean (Grieger et al 2014). The largest increase of strong cyclone activity was found in the eastern hemisphere.…”

“…Nevertheless, a large model-to-model variability is revealed with respect to the quantity of simulated ETCs. Grieger et al (2014) used a new scaling approach to account for these systematic biases. Applying the SRES A1B scenario (e.g.…”

“…These results illustrate a counteraction of different climate drivers (enhanced sea-surface temperatures due to climate change and recurring springtime ozone hole), leading to a two-way impact on the characteristics of SH extra-tropical waves with a more or less pronounced enhancement of synoptic heat transport. However, more impacts have to be taken into account to fully explain the observed recent Antarctic surface changes, such as reduced radiative input due to cloud Grieger et al 2014) cover changes with increased cyclone activity, or changes in regional wind systems, such as katabatic winds.…”