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Warren B. White and Neil J. Cherry

Abstract

Autumn–winter temperature and precipitation records at 34 stations over New Zealand from 1982 to 1995 are found by empirical orthogonal function (EOF) analysis to fluctuate together with 3–6-yr quasi periodicity similar to that associated with the Antarctic Circumpolar Wave (ACW), which propagates slowly eastward past New Zealand in its global traverse around the Southern Ocean. By allowing these EOF time sequences to represent New Zealand temperature and precipitation indices, both the positive temperature index related to warm sea surface temperature (SST) anomalies around New Zealand and the positive precipitation index related to warm (cool) SST anomalies north and east (south and west) of New Zealand are found. These warm (cool) SST anomalies are associated with poleward (equatorward) meridional surface wind (MSW) anomalies, the same as observed in association with the ACW. When warm (cool) SST and poleward (equatorward) MSW anomalies are located north (south) of New Zealand, then anomalous low-level wind convergence occurs over New Zealand, and when they are located east (west) of New Zealand, then anomalous cyclonicity occurs over New Zealand, both during years of anomalously high autumn–winter precipitation over New Zealand. Regular eastward propagation of the ACW past New Zealand suggests that covarying SST and MSW anomalies (and New Zealand autumn–winter temperature and precipitation) can be predicted 1–2 yr into the future. The authors test for this by utilizing the eastward propagation of the ACW contained in the dominant extended EOF mode of SST anomalies upstream from New Zealand to predict SST indices in the western South Pacific that are linked statistically to New Zealand temperature and precipitation indices. At 0-yr lead, this statistical climate prediction system nowcasts the observed sign of New Zealand temperature (precipitation) indices 12 (12) years out of the 14-yr record, explaining 50% (62%) of the interannual variance for each index. At 1-yr lead, it hindcasts the observed sign of New Zealand temperature (precipitation) indices 12 (13) years out the 14-yr record, explaining 24% (74%) of the interannual variance. At 2-yr lead, hindcasting is insignificant. This hindcast skill at 1-yr lead suggests that prediction of interannual climate variability over New Zealand may depend more upon predicting the amplitude and phase of the ACW than upon predicting it for tropical ENSO.

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John A. Church, Allan J. Clarke, Neil J. White, Howard J. Freeland, and Robert L. Smith

Abstract

No abstract available.

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John A. Church, Neil J. White, Allan J. Clarke, Howard J. Freeland, and Robert L. Smith

Abstract

The Australian Coastal Experiment (ACE) was designed to test coastal-trapped wave (CTW) theory and the generation of coastal-trapped waves by the wind. For the ACE dataset, we use CTW theory to attempt to hindcast the observed alogshelf currents and coastal sea levels at locations remote from the upstream (in the CTW sense) boundary of the ACE region. Local (in the ACE region) wind forcing is responsible for only about a quarter of the CTW energy flux at Stanwell Park (the center of the ACE region), and the remainder enters the ACE region from the south and propagates northward through the ACE region. Including the second-mode CTW improves the correlation between the hindcast and the observed near-bottom currents on the upper slope at Stanwell Park, but the use of the third-mode CTW cannot be justified. A linear bottom drag coefficient of r = 2.5 × 10−4 m s−1 works better than a larger drag coefficient, and simplifying the CTW equations by assuming the modes are uncoupled does not detract from the quality of the hindcasts. The hindcast and observed coastal sea levels are correlated at greater 2 than the 99% significance level. For the nearshore locations at Stanwell Park, the hindcast and observed alongshelf currents are correlated at greater than the 99% significance level, and the CTW model can account for about 40% of the observed variance. On the shelf at Stanwell Park, we find the hindcasts agree with the observations only if direct wind forcing within the ACE region and the correct (nonzero) upstream boundary conditions are included. However, even after attempting to remove the effects of the eddies and the East Australian Current, the CTW model is not useful for predicting the currents on the slope at Stanwell Park and on the shelf and slope at Newcastle (the northern boundary of the ACE region). The currents at these locations are dominated by the effect of the East Australian Current and its eddies.

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John A. Church, Neil J. White, Richard Coleman, Kurt Lambeck, and Jerry X. Mitrovica

Abstract

TOPEX/Poseidon satellite altimeter data are used to estimate global empirical orthogonal functions that are then combined with historical tide gauge data to estimate monthly distributions of large-scale sea level variability and change over the period 1950–2000. The reconstruction is an attempt to narrow the current broad range of sea level rise estimates, to identify any pattern of regional sea level rise, and to determine any variation in the rate of sea level rise over the 51-yr period. The computed rate of global-averaged sea level rise from the reconstructed monthly time series is 1.8 ± 0.3 mm yr−1. With the decadal variability in the computed global mean sea level, it is not possible to detect a significant increase in the rate of sea level rise over the period 1950–2000. A regional pattern of sea level rise is identified. The maximum sea level rise is in the eastern off-equatorial Pacific and there is a minimum along the equator, in the western Pacific, and in the eastern Indian Ocean. A greater rate of sea level rise on the eastern North American coast compared with the United Kingdom and the Scandinavian peninsula is also found. The major sources of uncertainty are the inadequate historical distribution of tide gauges, particularly in the Southern Hemisphere, inadequate information on tide gauge signals from processes such as postglacial rebound and tectonic activity, and the short satellite altimeter record available to estimate global sea level covariance functions. The results demonstrate that tide gauge records will continue to complement satellite altimeter records for observing and understanding sea level change.

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Susan E. Wijffels, Josh Willis, Catia M. Domingues, Paul Barker, Neil J. White, Ann Gronell, Ken Ridgway, and John A. Church

Abstract

A time-varying warm bias in the global XBT data archive is demonstrated to be largely due to changes in the fall rate of XBT probes likely associated with small manufacturing changes at the factory. Deep-reaching XBTs have a different fall rate history than shallow XBTs. Fall rates were fastest in the early 1970s, reached a minimum between 1975 and 1985, reached another maximum in the late 1980s and early 1990s, and have been declining since. Field XBT/CTD intercomparisons and a pseudoprofile technique based on satellite altimetry largely confirm this time history. A global correction is presented and applied to estimates of the thermosteric component of sea level rise. The XBT fall rate minimum from 1975 to 1985 appears as a 10-yr “warm period” in the global ocean in thermosteric sea level and heat content estimates using uncorrected data. Upon correction, the thermosteric sea level curve has reduced decadal variability and a larger, steadier long-term trend.

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