Previous literature has suggested that multiple peaks in sea level anomalies (SLA) detected by twodimensional Fourier Transform (2D-FT) analysis are spectral components of multiple propagating signals, which may correspond to different baroclinic Rossby wave modes. We test this hypothesis in the South Pacific Ocean by applying a 2D-FT analysis to the long Rossby wave signal determined from filtered TOPEX/Poseidon and European Remote Sensing-1/2 satellite altimeter derived SLA. The first four baroclinic mode dispersion curves for the classical linear wave theory and the Killworth and Blundell extended theory are used to determine the spectral signature and energy contributions of each mode. South of 17°S, the first two extended theory modes explain up to 60% more of the variance in the observed power spectral energy than their classical linear theory counterparts. We find that Rossby wave modes 2-3 contribute to the total Rossby wave energy in the SLA data. The second mode contributes significantly over most of the basin. The third mode is also evident in some localized regions of the South Pacific but may be ignored at the large scale. Examination of a selection of case study sites suggests that bathymetric effects may dominate at longer wavelengths or permit higher order mode solutions, but mean flow tends to be the more influential factor in the extended theory. We discuss the regional variations in frequency and wave number characteristics of the extended theory modes across the South Pacific basin.

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[1] This study investigates the behavior of westward propagating sea level anomalies across the South Pacific Ocean, with a focus on the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS satellite altimeter data. An evaluation of the energy variability of the signal using a two-dimensional Radon Transform analysis suggests that Rossby waves interact with both ridges and seamounts at various locations across the basin. Anomalously slow Rossby wave phase speeds are found over steep, isolated bathymetric features in the tropical South Pacific and over the plateau around New Zealand. Interaction with ridges increases the energetic variability, range of dominant propagation speeds, and meridional deviations in the Rossby wave signal.

[1] The characteristics of multiple westward propagating signals in the satellite observed South Pacific sea level anomalies (SLA) between 10°S and 50°S are analyzed using the two-dimensional Radon transform (2D-RT). We test the hypothesis that these signals are most likely to be the signature of the first few baroclinic Rossby wave modes. This involves a comparison of the estimated phase speeds of the 2D-RT peaks against the first four baroclinic mode Rossby wave speeds predicted from the extended theory. The 2D-RT analysis typically identified up to three propagating signals in the SLA and very occasionally, a fourth. The first Radon transform (RT) peak phase speeds corresponded very well with first baroclinic mode Rossby wave phase speed estimates from linear theory between 15°S and 25°S and the extended theory phase speed estimates poleward of 25°S. RT peak 2 speeds were less coherent but fell within the range of extended theory estimates of the first four baroclinic Rossby wave modes, consistent with large-scale Rossby wave dynamics. The relationship between peaks 3 and 4 and the extended theory higher-order baroclinic mode speed estimates varied markedly across the basin. Regional variability in the spectral characteristics of the peaks suggests that different dynamical regimes dominate north and south of 30°S in the South Pacific basin. The presence of secondary peaks in the middle to high latitudes suggests that higher-order modes may play a role in these regions.

We introduce a simple but effective means of removing ENSO-related variations from the Indian Ocean Dipole (IOD) in order to better evaluate the ENSO-independent IOD contribution to Australian climate-specifically here interannual variations in Australian region tropical cyclogensis (TCG) counts. The ENSO time contribution is removed from the Indian Ocean Dipole Mode index (DMI) by first calculating the lagged regression of the DMI on the sea surface temperature anomaly (SSTA) index NINO3.4 to maximum lags of 8 months, and then removing this ENSO portion. The new ENSO-independent time series, DMI NOENSO , correlates strongly with the original DMI at r = 0.87 (significant at [99% level). Despite the strength of the correlation between these series, the IOD events classified based on DMI NOENSO provide important differences from previously identified IOD events, which are more closely aligned with ENSO phases. IOD event composite maps of SSTAs regressed on DMI NOENSO reveal a much greater ENSO-independence than the original DMI-related SSTA pattern. This approach is used to explore relationships between Australian region TCG and IOD from 1968 to 2007. While we show that both the DMI and DMI NOENSO have significant hindcast skill (on the 95% level) when used as predictors in a multiple linear regression model for Australian region annual TCG counts, the IOD does not add any significant hindcast skill over an ENSO-only predictor model, based on NINO4.Correlations between the time series of annual TCG count observations and ENSO ? IOD model cross-validated hindcasts achieve r = 0.68 (significant at the 99% level).

High-quality, standardized urban canopy layer observations are a worldwide necessity for urban climate and air quality research and monitoring. The Schools Weather and Air Quality (SWAQ) network was developed and distributed across the Greater Sydney region with a view to establish a citizen-centred network for investigation of the intra-urban heterogeneity and inter-parameter dependency of all major urban climate and air quality metrics. The network comprises a matrix of eleven automatic weather stations, nested with a web of six automatic air quality stations, stretched across 2779 km2, with average spacing of 10.2 km. Six meteorological parameters and six air pollutants are recorded. The network has a focus on Sydney’s western suburbs of rapid urbanization, but also extends to many eastern coastal sites where there are gaps in existing regulatory networks. Observations and metadata are available from September 2019 and undergo routine quality control, quality assurance and publication. Metadata, original datasets and quality-controlled datasets are open-source and available for extended academic and non-academic use.

Oceanic Rossby waves can propagate climate signals over considerable distances over long timescales. Using a long simulation from a coupled climate model, we examine oceanic and mixed atmosphere‐ocean teleconnections to the south‐western Indian Ocean (SWIO) associated with Rossby waves excited by the El Niño‐Southern Oscillation (ENSO). Reconstruction of propagating ENSO‐induced sea‐level anomalies from the simulation using an optimized linear wave model with dissipation highlights the prominent role of baroclinic, rather than barotropic, Rossby waves in modulating sea‐surface heights. Between 9.5° and 18.5°S, El Niño‐associated anomalous anticyclonic wind‐stress fields initiate downwelling Rossby waves, potentially influencing SWIO regional climate around 1–4 seasons after El Niño peak, while also destructively interfering with upwelling waves triggered on the eastern boundary by oceanic teleconnections. Further south, weaker ENSO winds, dissipation, non‐linear processes, and interference from higher‐mode Rossby waves limit ENSO influences in the SWIO. In the model, ENSO‐associated predictability is therefore constrained by the “atmospheric” rather than “oceanic” bridge.

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