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El Nino-Southern Oscillation (ENSO) plays a dominant role in interannual climate variability in Pacific island countries, directly affecting lives there. Many countries show different rainfall responses depending on the sea surface temperature (SST) structure of different types of El Nino events. El Nino events are classified into three types based on previous studies: those with strongest SST anomalies in the eastern Pacific Cold Tongue region (CTE), in the Western Pacific Warm Pool region (WPE), and those in between, a “Mixed” El Nino (MxE), and results from 30 CMIP5 models are investigated. These models accurately reproduce observed SST and precipitation anomalies for the three El Nino types and La Nina. CMIP5 models simulate much larger ranges in the strength of ENSO events than observed. Results clarify the roles of both the different structures of El Nino SST anomalies and their magnitudes on rainfall in the Pacific, and demonstrate that each of the three El Nino types has different impacts on rainfall in the region. These impacts vary with location, with WPE and CTE producing very different impacts in most Pacific island countries. There is a linear intensification of both the mean and maximum rainfall anomalies in the equatorial Pacific as the events become stronger. Equatorial rainfall shifts eastward in CTE and MxE, westward in La Nina. Both the South Pacific and Intertropical Convergence Zones (SPCZ and ITCZ) shift equatorward in El Nino and poleward in La Nina, the shifts increasing as events strengthen. WPE show different behaviour to other events, with little east-west shift in equatorial rainfall, and the orientation angle of the convergence zones increases. Identification of models with no erroneous westward bias in SST anomalies has clarified the effect of strong CTE events producing “zonal” SPCZ and shifting rainfall away to the east from western equatorial countries.

Understanding how the South Pacific convergence zone (SPCZ) may change in the future requires the use of global coupled atmosphere–ocean models. It is therefore important to evaluate the ability of such models to realistically simulate the SPCZ. The simulation of the SPCZ in 24 coupled model simulations of the twentieth century is examined. The models and simulations are those used for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The seasonal climatology and interannual variability of the SPCZ is evaluated using observed and model precipitation. Twenty models simulate a distinct SPCZ, while four models merge intertropical convergence zone and SPCZ precipitation. The majority of models simulate an SPCZ with an overly zonal orientation, rather than extending in a diagonal band into the southeast Pacific as observed. Two-thirds of models capture the observed meridional displacement of the SPCZ during El Niño and La Niña events. The four models that use ocean heat flux adjustments simulate a better tropical SPCZ pattern because of a better representation of the Pacific sea surface temperature pattern and absence of cold sea surface temperature biases on the equator. However, the flux-adjusted models do not show greater skill in simulating the interannual variability of the SPCZ. While a small subset of models does not adequately reproduce the climatology or variability of the SPCZ, the majority of models are able to capture the main features of SPCZ climatology and variability, and they can therefore be used with some confidence for future climate projections.

The coastal region of the Antarctic continent is renowned for the frequent, intense blizzards and associated extreme weather that affect it, creating treacherous conditions that place human activities there in often perilous situations. The understanding and prediction of these events are therefore vital for continued safe operations on the continent. Severe wind events are investigated at two Australian coastal sites, Casey and Mawson. A summer case study at Casey and then the climatology of the events at the two stations are studied using station observations and atmospheric analyses. All events are found to be associated with extratropical cyclones that move close to the stations and lead to strong winds and heavy cloud cover. Most events see the passage of a high pressure ridge over the station ahead of the cyclone that blocks the cyclone, forcing it to move farther south close to the coast, thus intensifying the effect of the cyclone on the coastal weather. The ridge also produces calm, clea...

Strong wind events occurring near Casey (Antarctica) in a long July GCM simulation have been studied to determine the relative roles played by the synoptic situation and the katabatic flow in producing these episodes. It has been found that the events are associated with strong katabatic and strong gradient flow operating together. Both components are found to increase threefold on average for these strong winds, and although the geostrophic flow is the stronger, it rarely produces strong winds without katabatic flow becoming stronger than it is in the mean. The two wind components do not flow in the same direction; indeed, there is some cancellation between them, since katabatic flow acts in a predominant downslope direction, while the geostrophic wind acts across slope. The stronger geostrophic flow is associated with higher-than-average pressures over the continent and the approach of a strong cyclonic system toward the mast and a blocking system downstream. The anomalous synoptic patterns lea...