Showing papers by "Andrew Lorrey published in 2014"

State of the Climate in 2013

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The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach

Abstract: Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of −0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the ‘HSE’-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the ‘T’- and ‘SW’-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Nino-Modoki in the tropical Pacific and negative Southern Annular Mode activity.

A reconstruction of extratropical Indo-Pacific sea-level pressure patterns during the Medieval Climate Anomaly

Abstract: Subtropical and extratropical proxy records of wind field, sea level pressure (SLP), temperature and hydrological anomalies from South Africa, Australia/New Zealand, Patagonian South America and Antarctica were used to reconstruct the Indo-Pacific extratropical southern hemisphere sea-level pressure anomaly (SLPa) fields for the Medieval Climate Anomaly (MCA ~700–1350 CE) and transition to the Little Ice Age (LIA 1350–1450 CE). The multivariate array of proxy data were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data. The mean SLP and SLP anomaly patterns derived from these analogues illustrate the evolution of low frequency changes in the extratropics. The Indo-Pacific extratropical mean climate state was dominated by a strong tropical interaction with Antarctica emanating from: (1) the eastern Indian and south-west Pacific regions prior to 1100 CE, then, (2) the eastern Pacific evolving to the central Pacific La Nina-like pattern interacting with a +ve SAM to 1300 CE. A relatively abrupt shift to –ve SAM and the central Pacific El Nino-like pattern occurred at ~1300. A poleward (equatorward) shift in the subtropical ridge occurred during the MCA (MCA–LIA transition). The Hadley Cell expansion in the Australian and Southwest Pacific, region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported Hadley Cell expansion in the North Pacific and Atlantic regions, and suggests that bipolar climate symmetry was a feature of the MCA.

An ex‐tropical cyclone climatology for Auckland, New Zealand

Abstract: Auckland, New Zealand, is influenced by ex-tropical cyclones (ETCs); however, there is no established climatology for these weather systems at present. In this study, we present a climatology of ETCs for Auckland and investigate whether their spatio-temporal traits are influenced by large-scale climate modes such as the El Ni˜ no-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). We utilize the South Pacific Enhanced Archive for Tropical Cyclone research (SPEArTC) to establish a climatology that covers the high-quality TC data period from 1970 to 2010. ETCs have entered a region within 550km of Auckland city regardless of ENSO or SAM phase, and on average one event per year occurs. Peak ETC season for Auckland is during March, preceded by an increase in activity during February, with a wide-range of meteorological impacts. Regional circulation patterns, including reduced blocking in the southwest Pacific and synoptic type presence, allow ETCs into the Auckland sector of the southwest Pacific while guiding them either to the east or west of the city.

Identifying New Zealand, Southeast Australia, and Southwest Pacific historical weather data sources using Ian Nicholson's Log of Logs

Abstract: Historical meteorological data are essential for increasing the level of understanding about past, present, and future climates. In the Northern Hemisphere, a significant amount of research has been dedicated to rescuing climate data from historical sources such as ship logbooks (e.g. RECLAIM, CLIWOC, and ICOADS). However, limited research in this field has focused on New Zealand, Southeast Australia, and the Southwest Pacific. Because these regions were colonized recently by Europeans (~200 years ago), only 50–100 years of land-based meteorological data exist for many locations. However, meteorological information contained in ship logbooks may extend and reinforce the existing historical climate record for these regions. The Log of Logs is a catalogue of ships that visited Australia, New Zealand, and surrounding waters in the th and 20th centuries of the Common Era. These volumes provide a record of the location of ship logbooks. This study extracted information from the Log of Logs for New Zealand, Southeast Australia, and the Southwest Pacific for 1786–1900. The purpose of this was to locate ship logbooks that may contain meteorological data. The next stage of this project is to gather, image, digitize, and to analyse the data from the prioritized logbooks. These data have application for local climate reconstruction, extension of regional circulation indices, and augmentation of the extended reanalysis without radiosondes effort.

Australasia: An Overview of Modern Climate and Paleoclimate during the Last Glacial Maximum

Abstract: Australasia is a collection of landmasses inclusive of the large Australian continent, the microcontinent of New Zealand, Pacific islands within the Indonesian archipelago, and most islands within Melanesia.1 Australasia encapsulates a wide range of terrestrial climates, with several ecological zones, from the equatorial tropical zone to the temperate middle latitudes.

AUS2K meeting: Australasia's past climate variability

Abstract: Strengths drawn from palaeoclimate and model data over the last 2000 years. An open workshop incorporating the pages AUS2K working group and Australian Climate Change Science Program (ACCSP) palaeoclimate data-climate model comparison project variability of Australian Climate over the last 1000 years in coupled model simulations and proxy data.

Australasia's past climate variability—strengths drawn from palaeoclimate and model data over the last 2,000 years

Abstract: Pandora Hope, Joelle Gergis, Nerilie Abram, Josephine Brown, Steven J. Phipps, Russell Drysdale, Benjamin J. Henley, Andrew M. Lorrey, Heidi Roop, Jonathan Tyler Australian Bureau of Meteorology; 2 School of Earth Sciences, University of Melbourne, Australia; 3 Research School of Earth Sciences, Australian National University; 4 ARC Centre of Excellence for Climate System Science, Climate Change Research Centre, University of New South Wales, Australia; 5 Climate Change Research Centre, University of New South Wales, Australia; 6 National Institute of Water and Atmospheric Research, New Zealand; 7 GNS Science and Antarctic Research Centre, Victoria University of Wellington, New Zealand; 8 School of Earth and Environmental Science, University of Adelaide, Australia.