Climate models predict an upward trend of the Southern Annular Mode (SAM) in response to increasing atmospheric CO2 concentration, however the consequential impact of this change on oceanic circulation has not been explored. Here we analyse the outputs of a series of global warming experiments from the CSIRO Mark 3 climate model. We show that although for the zonal wind stress change the maximum is located at approximately 60°S, in terms of the change in surface wind stress curl, the maximum is situated at approximately 48°S. This change in the wind stress curl causes a spin‐up of the entire southern midlatitude ocean circulation including a southward strengthening of the subtropical gyres, particularly the East Australia Current (EAC). The intensified EAC generates a warming rate in the Tasman Sea that is the greatest in the Southern Hemisphere (SH) with significant implications for sea level rise. The pan‐Southern Ocean scale suggests a broad impact on the marine ecosystem of the entire southern midlatitude ocean.

Since 1950, there has been an increase in rainfall over North West Australia (NWA), occurring mainly during the Southern Hemisphere (SH) summer season. A recent study using 20 th century multi-member ensemble simulations in a global climate model forced with and without increasing anthropogenic aerosols suggests that the rainfall increase is attributable to increasing Northern Hemisphere aerosols. The present study investigates the dynamics of the observed trend toward increased rainfall and compares the observed trend with that generated in the model forced with increasing aerosols.We find that the observed positive trend in rainfall is projected onto two modes of variability. The first mode is associated with an anomalously low mean sea level pressure The modeled rainfall trend, however, is generated by a different process. The model suffers from an equatorial cold-tongue bias: the tongue of anomalies associated with El Niño-Southern Oscillation extends too far west into the eastern Indian Ocean.Consequently, there is an unrealistic relationship in the SH summer between Australian rainfall and eastern Indian Ocean SST: the rise in SST is associated with an increasing rainfall over NWA. In the presence of increasing aerosols, a significant SST increase occurs in the eastern tropical Indian Ocean. As a result, the modeled rainfall increase in the presence of aerosol forcing is accounted for by these unrealistic relationships. It is not clear whether, in a model without such defects, the observed trend can be generated by increasing aerosols. Thus, the impact of aerosols on Australian rainfall remains an open question.3

The dynamics of El Niño‐Southern Oscillation (ENSO) cycles has previously been interpreted in terms of discharge and recharge of mass and heat in the equatorial Pacific. Some of the ENSO discharge/recharge signals transmit into the Indian Ocean, but the pathway is yet to be fully established. This study reveals a previously un‐noticed subtropical North Pacific (NP) pathway. NP Rossby waves associated with ENSO impinge on the western boundary and move equatorward along the “ray‐path” of Kelvin‐Munk waves, and reflect as equatorial Kelvin waves. En‐route to the equator, the waves are reinforced by wind stress anomalies associated with ENSO. The reflected equatorial Kelvin waves impinge on the Australasian continent and move poleward along the northern western Australia (WA) coast as coastally‐trapped waves, radiating Rossby waves into the south Indian Ocean. In this way, some 55% of the total interannual variance of the WA thermocline is linked to the subtropical NP Rossby waves.

[1] The majority of climate models project a winter rainfall reduction over south-eastern Australia (SEA), while some show a tendency for a summer rainfall increase. The dynamics for these rainfall changes are not clear. Using outputs from a climate model, we show that a summer rainfall increase is consistent with a large Tasman Sea warming promoting convection, and an upward trend of the Southern Annular Mode (SAM) promoting onshore flows; these processes dominate over a rainfall decrease from an El Niño-like warming pattern. In winter, similar effects from a Tasman Sea warming and an upward SAM trend operate along Australia's east coast, however, the rain-reducing impact of an Indian Ocean Dipole-like warming pattern dominates. In both seasons, the upward SAM trend causes a rainfall reduction over southern Australia. Summer rainfall over north-western Australia is projected to decrease, due to an unrealistic relationship with the El Niño-Southern Oscillation. Possible uncertainties are discussed.

[1] Over the past decades surface warming in the southern subtropical Indian Ocean (IO) has been greater than that in other oceans. The warming penetrates to a depth of 800 m, in contrast to the off-equatorial surface warming which coexists with subsurface cooling. We examine the dynamics for this rich structure. Results from the 20th century experiments of the Intergovernmental Panel on Climate Change (IPCC) confirm that the southern subtropical IO surface-to-800 m warming is greater than that in the Pacific and Atlantic Oceans. Outputs from two targeted ensemble sets of coupled model experiments, one with and one without increasing anthropogenic aerosols, show that increasing aerosols strengthen the global Conveyor, and generate a greater poleward shift and intensification of the Agulhas outflow and its retroflection; the process increases the warming rate in the subtropics, and takes heat out of the off-equatorial region generating a cooling. Citation: Cai, W., T. Cowan, M. Dix, L. Rotstayn, J. Ribbe, G. Shi, and S. Wijffels (2007), Anthropogenic aerosol forcing and the structure of temperature trends in the southern Indian Ocean, Geophys. Res. Lett., 34, L14611,

Previous studies have suggested that the observed winter rainfall reduction since the late 1960s over southwest Western Australia (SWWA) is consistent with what is expected from greenhouse forcing but the relative importance of potential causes is not conclusive. Here, we investigate the possibility of the rainfall reduction being a part of multidecadal variability using outputs of the CSIRO Mark 3 climate model. We find that multidecadal‐long drying trends comparable to the observed exist in an experiment without climate change forcing. The model multidecadal‐long rainfall decline manifests as a reduction in high‐intensity rainfall events and is accompanied by an upward trend of the southern annular mode (SAM) with an increasing midlatitude mean sea level pressure (MSLP). Thus, multidecadal variability could primarily be responsible for the observed winter rainfall reduction, and could potentially superimpose on a greenhouse‐induced drying trend to generate an even greater reduction than what has been observed thus far.

Since 1980, transmission of El Niño‐Southern Oscillation (ENSO) signals into the Indian Ocean involves an equatorial, and a subtropical North Pacific (NP) Rossby wave pathway. We examine the robustness of the amount of energy that leaves the Pacific via each of the pathway using the Simple Ocean Data Assimilation with the Parallel Ocean Program (SODA‐POP) reanalysis and a multi‐century coupled model control experiment. We find that in the pre‐1980 period, little ENSO signal is transmitted to the Indian Ocean and does not involve the subtropical NP pathway. Such multidecadal variability is periodically produced by the climate model. Examinations reveal that when ENSO is weak as determined by Niño3.4, their meridional extent is narrow, the associated discharge‐recharge does not involve the subtropical NP pathway; further, weak ENSO events have a low signal‐to‐noise ratio, making the transmission hard to detect. The dynamics of multidecadal variability in ENSO strength awaits further investigation.

Harvesting ambient vibration energy using piezoelectric elements is a popular energy harvesting technique. Energy harvesting efficiency is the research focus. Using synchronous electric charge extraction technology in piezoelectric energy harvesting systems can greatly improve the energy harvesting efficiency. This article presents a self-powered efficient synchronous electric charge extraction circuit for piezoelectric energy harvesting systems, in which four self-powered switch circuits are used to optimize the time sequence of charge extraction so that the rectifier bridge circuit used in traditional synchronous electric charge extraction can be saved. The effect of phase lag on extraction efficiency, system energy, and loss of overall circuit is analyzed. A piezoelectric vibration experimental platform is built for testing the power generation performance of the self-powered efficient synchronous electric charge extraction and those published energy harvesting circuits. The experimental results accord with the theoretical analysis. Moreover, the harvesting energy of the proposed self-powered efficient synchronous electric charge extraction is about three times more than those of the standard energy harvesting circuit under its maximum power point and the self-powered synchronized switch harvesting on inductor in most cases. The energy harvesting efficiency of self-powered efficient synchronous electric charge extraction remains at a high level (>80%) in most cases, and the maximum energy harvesting efficiency is up to 85.1%.