This article examines the influence of El Niño Southern Oscillation (ENSO), Southern Annular Mode (SAM) and Interdecadal Pacific Oscillation (IPO) on the synoptic weather types over New Zealand. The effects of ENSO (indicated by the Southern Oscillation Index, SOI), SAM and IPO on the occurrence of synoptic types are estimated in a holistic framework using the maximum likelihood method via applications of generalized linear models, both annually and by seasons. The average within‐class variations in the intensity and air‐mass characteristics (as expressed in the Auckland Airport meteorological variables) of synoptic systems were examined for individual types at the annual level. The results show that ENSO, SAM and IPO have significant effects on the probability of occurrence and to lesser degree the intensity and air‐mass characteristics of some synoptic types. The effects vary considerably with seasons, synoptic types and phases of SOI, SAM and IPO and it is the confounding effects of different large‐scale modes that lead to the observed changes in the type frequencies. The findings, with respect to ENSO and SAM in all cases and for IPO at the seasonal level, are in good agreement with the literature. However, the annual changes in type frequencies associated with the 1976/1977 IPO phase shift do not support the observed changes in the strength of anomalous southwesterly windflows over New Zealand, and the influence of the recent negative IPO phase also appears different from what we expect based on the existing research. It appears that the interaction between IPO and ENSO is important for understanding the observed climatic effects of IPO on New Zealand's weather and climate. This aspect deserves further attention in future studies. The findings from this work have important methodological and practical implications for New Zealand climate research. Copyright © 2012 Royal Meteorological Society

Ozone and particle pollution are of concern for the Sydney basin, in particular during warm months (November to March) when pollution levels can exceed national standards. Previous studies on the relationship between synoptic circulation and air quality focused on high pollution days or aggregated air quality conditions over the region as a whole. This study provides both temporal and spatial analyses of the synoptic processes affecting warm‐month ozone and particle pollution in Sydney. A warm‐month synoptic catalogue was developed by applying the self‐organising map method to the NCEP/NCAR geopotential height reanalysis for south‐east Australia. The catalogue was linked to mesoscale meteorological features such as drainage flows and sea breezes, and subsequently to the spatial variability in air quality across the Sydney basin. The typical synoptic types commonly associated with high or low ozone and PM₁₀ levels, as well as variations in visibility, were identified. The results suggest that, due to Sydney's subtropical coastal‐basin environment, the interaction between meso‐ and synoptic‐scale features determine local air quality conditions in the region, rather than the synoptic conditions alone. Emissions from bushfires appear to have considerable impacts on the synoptic modulation to visibility and PM₁₀ levels, with such impacts tending to be more at a local scale. In contrast, no comparable impacts were found for ozone pollution. For ozone and visibility, the probability for an exceedance day under some synoptic types varied considerably over time, implying that there might have been a shift in the role of synoptic modulation to local air quality associated with changes in air emissions profiles. This study provides a leap in our understanding of the relationship between synoptic circulation and air quality in a coastal‐basin environment. The results are useful for improving air quality forecasting in Sydney, with the methodology developed readily applicable to similar regions elsewhere.

Synoptic weather typing depends on the method and its implementation. This paper demonstrates the utility of a 2‐phase batch self‐organising map procedure (CP2) in comparison with a procedure (CP1) consisting of T‐mode principal component analysis followed by convergent K‐means clustering, for classifying the synoptic weather types over east Australia. Four classifications were obtained for the 52‐year NCEP/NCAR dataset, one from CP1 and three from CP2. These classifications were examined in terms of grouping quality, mean type maps, type frequencies, lifetime and transitions, and in relation to the Southern Oscillation Index (SOI).The results showed that the classifications derived from different procedures are inter‐confirmative and capture a similar set of major synoptic situations influencing east Australia, each having counterparts in previous studies and conforming well to local synoptic experience. In particular, this study demonstrates that CP2 is a promising tool for the purpose of weather typing with a two‐fold utility: CP2 can perform data projection (neighbourhood width > = 1) and provide a flexible means for visualising the broad distribution of the daily weather patterns in the dataset; and the procedure can also conduct cluster analysis (neighbourhood width = 0) and produce results equivalent to those from CP1. It was found that performing data clustering or data projection may affect the inference associated with type frequencies. While focusing on methodology, the analysis has also shown that the frequency of synoptic weather types fluctuates on the seasonal, interannual, and decadal scales. From the 1970s to 1995 there was a decline in the occurrence of a few weather types associated with an east‐coast trough extending over New South Wales from the north, and a slight increase in the activity of some anticyclonic types. Significant correlations were also identified between SOI and frequencies of synoptic weather types on the annual and seasonal timescales. Copyright © 2011 Royal Meteorological Society

An analysis of temperature variability and trends in the South Pacific, mainly in the twentieth century, using data from 40 island stations and optimally interpolated sea surface and night marine air temperature data is presented. The last-named dataset is new and contains improved corrections for changes in the height of thermometer screens as ships have become larger. It is shown that the South Pacific convergence zone plays a pivotal role in both variability and trends in all three datasets. Island, collocated sea surface temperature, and night marine air temperature time series for four large constituent regions are created and analyzed. These have been corrected for artificial changes in variance due to changes in the availability of constituent island stations whose intrinsic variance varies from station to station. The method is described in detail. Objective estimates of uncertainty in the sea surface temperature data are also provided. The results extend previous work, showing that annua... Abstract An analysis of temperature variability and trends in the South Pacific, mainly in the twentieth century, using data from 40 island stations and optimally interpolated sea surface and night marine air temperature data is presented. The last-named dataset is new and contains improved corrections for changes in the height of thermometer screens as ships have become larger. It is shown that the South Pacific convergence zone plays a pivotal role in both variability and trends in all three datasets. Island, collocated sea surface temperature, and night marine air temperature time series for four large constituent regions are created and analyzed. These have been corrected for artificial changes in variance due to changes in the availability of constituent island stations whose intrinsic variance varies from station to station. The method is described in detail. Objective estimates of uncertainty in the sea surface temperature data are also provided. The results extend previous work, showing that annua...

As with many urban centres around the world, nitrogen dioxide (NO₂) is of concern in Auckland, New Zealand because of its possible link to respiratory and heart disease. It has also been associated with the frequent occurrence of brown haze in the region. This article examines quantitatively the differential effects of the local‐, synoptic‐ and large‐scale (El Niño‐Southern Oscillation—ENSO, Southern Annular Mode—SAM) climate conditions on daily NO₂ concentrations in urban Auckland under the framework of generalized linear models. The local meteorology is found to be the most important driver of the daily NO₂ concentrations in Auckland, primarily through the coupling of local‐scale atmospheric flow and stability conditions with local emissions and chemical processes. Both the synoptic circulation and large‐scale climate modes play significant roles in determining the local air pollution. Synoptic circulations, even after controlling for the local meteorological conditions, modulate the daily NO₂ at a regional level via two main mechanisms: (1) blocking types facilitate the transport of clean oceanic air over the Auckland landmass, leading to generally low NO₂ concentrations; (2) westerly cyclonic types contribute to region‐wide increases in NO₂ concentrations due to the enhanced mixing‐in and/or downward transport of ozone (O₃) from the upper troposphere or stratosphere. The large‐scale climate modes, ENSO and SAM, modulate the regional air quality through changing the frequency of occurrence and air‐mass characteristics of synoptic systems over New Zealand. Overall, this study demonstrates a holistic approach to understand how atmospheric circulations of different scales affect local air quality and thus provides useful information for the formulation of effective public health management and planning strategies in response to future climate variability and change.