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Day 1 - Atmospheric science

Title: Who needs a stratosphere? Predicting downward influences on weather and climate

Presenter: Damian Murphy

Australian Antarctic Division

Authors: Damian J Murphy and Andrew R Klekociuk

Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050 Australia

Abstract

The remoteness of the polar stratosphere does little to isolate it from global processes. Its thermal and dynamical state is strongly influenced by hemisphere-scale circulations driven by large and small scale waves, and plays a role in modulating ozone depletion processes. The remoteness of the polar stratosphere also does little to isolate us from its influence. It is now clear that surface climate at mid- and high-southern latitudes is strongly influenced by the state of the southern polar stratosphere.

During the past 3 decades, the Antarctic lower stratosphere has undergone significant cooling in austral spring and summer as a result of anthropogenic ozone loss associated with the ozone hole. This cooling has accelerated the eastward circumpolar stratospheric flow, and strengthened the stratospheric vortex. Ozone-induced circulation changes have played a major role in trending the Southern Annular Mode (SAM) during summer towards a preferred high-index polarity state. The observed trend in the SAM during summer has been directly linked to changes in various aspects of SH climate with influences across latitudes from Antarctica to Australia.

During the next several decades, the ozone hole will decrease in severity due to controls on ozone depleting substances. However, the emerging effects of greenhouse gas (GHG) increases are likely to extend the reach of stratospheric influence across seasons and decades.

Two AAP projects are underway to assess the influence of ozone on the climate system and to ensure we can reliably predict future climate. “Polar FORCeS: Polar Feedbacks between Ozone Recovery and Climate in the Southern hemisphere” will quantify feedbacks and changes in the climate due to ozone variability and trends using models and observations. “Gravity wave drag parameterisation in climate models” will improve the representation of small-scale waves in model dynamics to ensure the state of the southern polar stratosphere is accurately reproduced in climate models. Both projects will act to ensure that the Antarctic polar stratosphere does not go unnoticed.

Title: ACCESS polar modelling – plans and opportunities for collaboration

Presenter and Author: Anthony Hirst (on behalf of the ACCESS modelling team)

Centre for Australian Weather and Climate Research (a partnership between CSIRO and the Bureau of Meteorology), CSIRO Marine and Atmospheric Research, PMB 1, Aspendale 3195, tony.hirst@csiro.au

Abstract

The Antarctic region plays a key role in the climate system, in terms of global ocean circulation and deep water mass formation, southern hemisphere climate, ocean-atmosphere carbon exchange, atmospheric chemistry, and sea level change. In addition, Australian research activities in the Antarctic region are significantly weather affected. Consequently, there is benefit in state-of-science modelling of components of the earth system for this region to facilitate local short term prediction (e.g., weather, sea ice) and longer term prediction/projection of climate variability and change more broadly.

The Australian Community Climate and Earth System Simulator (ACCESS) is an initiative aiming for a national approach to weather and climate modelling, including the Antarctic. Principal partners are the Bureau of Meteorology and CSIRO, through CAWCR, and participating universities, in particular through the Centre of Excellence for Climate System Science. A major focus of the initiative is to support applications across a range of time scales from numerical weather prediction (NWP), seasonal-to-decadal, and to centennial-scale projection of change, in climate, carbon cycle and atmospheric chemistry. The initiative has recently provided Bureau operations with a new NWP system operating at both regional and global scales, and has contributed multi-century coupled model simulations to the Coupled Model Intercomparison Project phase 5 (CMIP5) in support of the IPCC 5th Assessment Report (AR5). Comparisons with other CMIP5 models show that ACCESS is one of the top performing models in terms of the Antarctic sea ice making it suitable for further analysis of the Antarctic climate system.

This talk will briefly present the status of current ACCESS modelling systems and then discuss plans for further model development work, focussing on aspects relevant to application and simulation of processes in the Antarctic region. Major drivers over the next several years will be requirements for further improvement in short-term prediction (days, weeks), application to seasonal prediction and preparation for contribution to CMIP6 in support of the anticipated IPCC AR6. The potential for collaboration between institutions under the framework of the Australian Antarctic Science Strategic Plan will be considered.

Title: Antarctic and Southern-Hemisphere Climate Change: The Role of Chemistry-Climate Models

Presenter: Olaf Morgenstern

National Institute of Water and Atmospheric Research Lauder

Authors: Olaf Morgenstern1, Guang Zeng1, Sam Dean2, Graham Rickard2, Adrian McDonald3, Kane Stone4, Robyn Schofield4, David Karoly4, Andrew Klekociuk5

1 - NIWA Lauder, New Zealand, Olaf.morgenstern@niwa.co.nz, guang.zeng@niwa.co.nz

2 - NIWA Wellington, New Zealand, Sam.dean@niwa.co.nz, graham.rickard@niwa.co.nz

3 - Dept. of Physics and Astronomy, U. Canterbury, Christchurch, New Zealand, Adrian.mcdonald@canterbury.ac.nz

4 - Dept. of Earth Sciences, U. Melbourne, Victoria, K.stone4@student.unimelb.edu.au, robyn.schofield@unimelb.edu.au, dkaroly@unimelb.edu.au

5 - Australian Antarctic Division, Kingston, Tasmania, Andrew.klekociuk@aad.gov.au

Abstract

The Antarctic Peninsula has been amongst the most rapidly warming regions on the planet during the past few decades, with associated loss of ice shelves and sea ice. By contrast, some of the Antarctic interior has been cooling during the same period. In both developments, and more widely in recent climate change across the Southern Hemisphere, the Antarctic ozone hole is thought to have played a major role. In the future, under the terms of the Montreal Protocol, the ozone layer is anticipated to recover; at the same time, climate change associated with other greenhouse gas emissions will continue apace. Over Antarctica, these two developments will force climate in opposite directions, complicating predictions of near-term climate change. Past assessments of climate change have typically relied on climate models which use prescribed, zonally symmetric ozone fields. This means that zonal asymmetries of ozone and feedbacks between climate and ozone are not accounted for. Consequently, lacking or inadequate ozone feedback is a candidate for explaining the widespread failure of climate models to represent regional climate change, e.g., the changes in sea ice cover around Antarctica. At present, a new generation of coupled climate models, comprising both ozone chemistry and a deep ocean, is being used for the Chemistry-Climate Modelling Initiative (CCMI). We will present first results from this activity, with a particular focus on the New Zealand and Australian contributions to CCMI.

Title: Identifying vortex air using Carbon Monoxide Observations

Presenter and Author: Adrian McDonald

Department of Physics and Astronomy, University of Canterbury

Abstract

This study uses observations of carbon monoxide (CO) from the MLS instrument to quantify transport in the winter polar region. In particular, we use the probability distribution function (PDF) of the CO data to delineate CO concentrations characteristic of the interior of the vortex core as a function of space and time without additional information. This is achieved by fitting two Gaussian distributions to the PDF for a specific period and altitude, pressure or isentropic level. These Gaussian fits are then examined to determine whether two chemically distinct regions exist by inspecting the intersection area between the Gaussians relative to their individual areas. When chemically distinct regions exist, the values of the fitted mean CO concentrations are representative of the interior and exterior of the polar vortex. To prove this point, a domain filling analysis is performed to produce high resolution maps. Comparison of these maps with the vortex edge derived using the equivalent latitude technique shows that the statistical methodology detailed can be used to characterize measurements made in the interior of the vortex during periods when the regions are chemically distinct. Statistical analysis for a number of years and a range of isentropic levels also unambiguously shows that the fitting scheme can be used to characterize measurements made inside the Southern hemisphere vortex during periods when the regions are chemically distinct. Given the weaknesses of reanalyses at high altitudes, this technique potentially provides a simple alternative to the dynamically derived calculation of values characteristic of the vortex interior.


Title: What the READER and the homogenised radiosonde data sets reveal about the seasonality of multi-decadal temperature trends in the Antarctic troposphere and stratosphere

Presenter: Ian Simmonds

The University of Melbourne

Authors: I Simmonds1, J Screen2

1 - The University of Melbourne

2 - University of Exeter, UK

Abstract

In situ measurements in the Antarctic region are very valuable, and can provide a reference against which model products and reanalyses can be assessed over this complex and challenging region of the globe. Five decades of Antarctic radiosonde data are now available through the SCAR ‘READER’ project. The data deposited in this database has undergone basic (although intensive) quality control, and no attempt was made to remove temporal inconsistencies such as those associated with changes in radiosonde technology or observing practice over time. Such changes have the potential to lead to discontinuities in radiosonde temperature records and induce artificial trends. In attempts to alleviate this possibility several projects have reprocessed the (global) radiosonde records and attempted to remove temporal inconsistencies with statistical approaches, resulting in ‘homogenized’ data sets. Five of these are used here.

Trend analyses of these 50 years of data reveals a complex spatial pattern of change. However, when averaged across all the stations used, a robust vertical profile of half-century temperature change emerged, characterized by mid-tropospheric warming and stratospheric cooling. Statistically significant Antarctic-mean 500 hPa warming (0.1 to 0.2oC per decade) is found in all seasons. In the lower stratospheric cooling was diagnosed primarily in spring and summer (-1.0 to -2.0oC per decade). We show sizeable differences in the trends diagnosed in the homogenized sets, and the READER tends to sit in the middle of these. Our analysis indicates that the READER set can be used with some confidence.



Title: The impact of the Southern Annular Mode on Southern Ocean physics and biogeochemistry

Presenter and Author: Peter Strutton

Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, 7001, Tasmania, Australia
peter.strutton@utas.edu.au

Abstract

The Southern Annular Mode (SAM) is the dominant mode of climate variability in the southern hemisphere. In recent decades, its mostly positive phase has been associated with a strengthening and southerly migration of the westerly winds over the Southern Ocean. These winds drive the large scale overturning circulation and therefore modulate vertical fluxes of nutrients and dissolved inorganic carbon, which fuel Southern Ocean productivity. The satellite ocean colour data record is now long enough (1997 to present) to document circumpolar and regional trends in surface ocean productivity, in response to the SAM. This presentation documents interannual and spatial variability in winds, sea surface temperature (SST), mixed layer depths and surface chlorophyll as a function of the SAM. The analysis indicates that the winds are indeed shifting poleward and intensifying in response to the increasingly positive SAM. In some regions this results in cool SST anomalies, which can be attributed to enhanced Ekman upwelling. The response in both satellite chlorophyll and satellite based primary productivity is statistically significant in only a few small patches. A region of particular interest is the southeast Pacific, where the wind stress curl pattern is different to the Atlantic and Indian, and the cool SST anomalies may be caused by deeper mixing as opposed to enhanced upwelling. If so, this region could be trending in the direction of a source of CO2 to the atmosphere, but a satellite-based model of surface ocean CO2 suggests otherwise.

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    20 Jun 2013

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Key dates

  • 11th June 2013
    Registrations close
  • 21st June 2013
    Registrations at the AAD open for staff
  • 24th June 2013
    Registrations at the venue open
  • 24th June 2013
    Conference commences
  • 26th June 2013
    Conference concludes

More key dates…

This page was last modified on 6 June 2013.