Angela M. Maharaj

Multiple westward propagating signals in South Pacific sea level anomalies

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.

Observed variability of the South Pacific westward sea level anomaly signal in the presence of bottom topography

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.

Unravelling Eastern Pacific and Central Pacific ENSO Contributions in South Pacific Chlorophyll- a Variability through Remote Sensing

Abstract: El Nino—Southern Oscillation (ENSO) is regarded as the main driver of phytoplankton inter-annual variability. Remotely sensed surface chlorophyll -a (Chl- a ), has made it possible to examine phytoplankton variability at a resolution and scale that allows for the investigation of climate signals such as ENSO. We provide empirical evidence of an immediate and lagged influence of ENSO on SeaWiFS and MODIS- Aqua derived global Chl- a concentrations. We use 13 years of Chl- a remotely sensed observations along with sea surface temperature (SST) observations across the Tropical and South Pacific to isolate and examine the spatial development of Chl -a anomalies during ENSO: its canonical or eastern Pacific (EP) mode, and El Nino Modoki or central Pacific (CP) mode, using the extended empirical orthogonal function (EEOF) technique. We describe how an EP ENSO phase transition affects Chl -a , and identify an interannual CP mode of variability induced spatial pattern. We argue that when ENSO is analysed as a propagating signal by the EEOF, CP ENSO is found to be more influential on Chl