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    <title>UTas ePrints - On Long-Term Climate Studies Using a Coupled General Circulation Model</title>
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    <meta content="Phipps, Steven John" name="eprints.creators_name" />
<meta content="thesis" name="eprints.type" />
<meta content="2007-10-22 01:07:12" name="eprints.datestamp" />
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<meta content="On Long-Term Climate Studies Using a
Coupled General Circulation Model" name="eprints.title" />
<meta content="unpub" name="eprints.ispublished" />
<meta content="260400" name="eprints.subjects" />
<meta content="260602" name="eprints.subjects" />
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<meta content="Coupled atmosphere-ocean general circulation models are the simplest models which
are capable of simulating both the variability which occurs within each component
of the climate system, and the variability which arises from the interactions between
them. Only recently has it become computationally feasible to use coupled general
circulation models to study climate variability and change on timescales of O(104)
years and longer. Flux adjustments are often employed to maintain a control climate
that is both stable and realistic; however, the magnitude of the adjustments
represents a source of concern.
This study employs the CSIRO Mk3L climate system model, a low-resolution
coupled atmosphere-sea ice-ocean general circulation model. The atmospheric and
oceanic components are spun up independently; the resulting atmospheric simulation
is realistic, while the deep ocean is too cold, too fresh and too buoyant. The
spin-up runs provide the initial conditions for the coupled model, which is used to
conduct a 1400-year control simulation for pre-industrial conditions. After some
initial adjustment, the simulated climate experiences minimal drift. The dominant
mode of internal variability is found to exhibit the same spatial structure and correlations
as the observed El Ni˜no-Southern Oscillation phenomenon.
The ability of Mk3L to simulate the climate of the mid-Holocene is evaluated. It
correctly simulates increased summer temperatures at northern mid-latitudes, and
cooling in the tropics. However, it is unable to capture some of the regional-scale
features of the mid-Holocene climate, with the precipitation over northern Africa
being deficient. The model simulates a 13% reduction in the strength of El Ni˜no,
a much smaller decrease than that implied by the palaeoclimate record.
A 1400-year transient simulation is then conducted, in which the atmospheric
CO2 concentration is stabilised at three times the pre-industrial value. The transient
simulation exhibits a reduction in the rate of North Atlantic Deep Water formation,
followed by its gradual recovery, and a cessation of Antarctic Bottom Water formation.
The global-mean surface air temperature warms 2.7◦C upon a trebling of
CO2, and 5.3◦C by the end of the simulation.
A number of modifications to the spin-up procedure for the ocean model are
evaluated. A phase shift in the prescribed sea surface temperatures and salinities is
found to reduce the phase lag between the model and observations, and to lead to
a reduction in the magnitude of the diagnosed flux adjustments. When this spin-up
run is used to initialise the coupled model, the reduced flux adjustments are found
to have negligible impact upon the nature of the internal variability. While the flux
adjustments are not found to have any direct influence upon the response of the
model to external forcing, they are found to have an indirect influence via their
effect upon the rate of drift within the control simulation.
An iterative spin-up technique is also developed, whereby the response of the
ocean model is used to derive a set of effective surface tracers. These result in a
much more realistic vertical density profile within the ocean. The coupled model
exhibits slightly increased internal variability, with reduced convection within the
ocean. There is a slightly greater surface warming in response to an increase in
the atmospheric CO2 concentration, with the reduced convection resulting in slower
penetration of the surface warming to depth." name="eprints.abstract" />
<meta content="2006-11" name="eprints.date" />
<meta content="submitted" name="eprints.date_type" />
<meta content="314" name="eprints.pages" />
<meta content="University of Tasmania" name="eprints.institution" />
<meta content="Antarctic Climate &amp; Ecosystems CRC" name="eprints.department" />
<meta content="phd" name="eprints.thesis_type" />
<meta content="Phipps, Steven John (2006) On Long-Term Climate Studies Using a Coupled General Circulation Model. PhD thesis, University of Tasmania." name="eprints.citation" />
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<meta content="On Long-Term Climate Studies Using a
Coupled General Circulation Model" name="DC.title" />
<meta content="Phipps, Steven John" name="DC.creator" />
<meta content="260400 Oceanography" name="DC.subject" />
<meta content="260602 Climatology (incl. Palaeoclimatology)" name="DC.subject" />
<meta content="Coupled atmosphere-ocean general circulation models are the simplest models which
are capable of simulating both the variability which occurs within each component
of the climate system, and the variability which arises from the interactions between
them. Only recently has it become computationally feasible to use coupled general
circulation models to study climate variability and change on timescales of O(104)
years and longer. Flux adjustments are often employed to maintain a control climate
that is both stable and realistic; however, the magnitude of the adjustments
represents a source of concern.
This study employs the CSIRO Mk3L climate system model, a low-resolution
coupled atmosphere-sea ice-ocean general circulation model. The atmospheric and
oceanic components are spun up independently; the resulting atmospheric simulation
is realistic, while the deep ocean is too cold, too fresh and too buoyant. The
spin-up runs provide the initial conditions for the coupled model, which is used to
conduct a 1400-year control simulation for pre-industrial conditions. After some
initial adjustment, the simulated climate experiences minimal drift. The dominant
mode of internal variability is found to exhibit the same spatial structure and correlations
as the observed El Ni˜no-Southern Oscillation phenomenon.
The ability of Mk3L to simulate the climate of the mid-Holocene is evaluated. It
correctly simulates increased summer temperatures at northern mid-latitudes, and
cooling in the tropics. However, it is unable to capture some of the regional-scale
features of the mid-Holocene climate, with the precipitation over northern Africa
being deficient. The model simulates a 13% reduction in the strength of El Ni˜no,
a much smaller decrease than that implied by the palaeoclimate record.
A 1400-year transient simulation is then conducted, in which the atmospheric
CO2 concentration is stabilised at three times the pre-industrial value. The transient
simulation exhibits a reduction in the rate of North Atlantic Deep Water formation,
followed by its gradual recovery, and a cessation of Antarctic Bottom Water formation.
The global-mean surface air temperature warms 2.7◦C upon a trebling of
CO2, and 5.3◦C by the end of the simulation.
A number of modifications to the spin-up procedure for the ocean model are
evaluated. A phase shift in the prescribed sea surface temperatures and salinities is
found to reduce the phase lag between the model and observations, and to lead to
a reduction in the magnitude of the diagnosed flux adjustments. When this spin-up
run is used to initialise the coupled model, the reduced flux adjustments are found
to have negligible impact upon the nature of the internal variability. While the flux
adjustments are not found to have any direct influence upon the response of the
model to external forcing, they are found to have an indirect influence via their
effect upon the rate of drift within the control simulation.
An iterative spin-up technique is also developed, whereby the response of the
ocean model is used to derive a set of effective surface tracers. These result in a
much more realistic vertical density profile within the ocean. The coupled model
exhibits slightly increased internal variability, with reduced convection within the
ocean. There is a slightly greater surface warming in response to an increase in
the atmospheric CO2 concentration, with the reduced convection resulting in slower
penetration of the surface warming to depth." name="DC.description" />
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    <h1 class="ep_tm_pagetitle">On Long-Term Climate Studies Using a Coupled General Circulation Model</h1>
    <p style="margin-bottom: 1em" class="not_ep_block"><span class="person_name">Phipps, Steven John</span> (2006) <xhtml:em>On Long-Term Climate Studies Using a Coupled General Circulation Model.</xhtml:em> PhD thesis, University of Tasmania.</p><p style="margin-bottom: 1em" class="not_ep_block"></p><table style="margin-bottom: 1em" class="not_ep_block"><tr><td valign="top" style="text-align:center"><a onmouseover="EPJS_ShowPreview( event, 'doc_preview_2879' );" href="http://eprints.utas.edu.au/2278/1/01FRONT.PDF" onmouseout="EPJS_HidePreview( event, 'doc_preview_2879' );"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" class="ep_doc_icon" border="0" /></a><div class="ep_preview" id="doc_preview_2879"><table><tr><td><img alt="" src="http://eprints.utas.edu.au/2278/thumbnails/1/preview.png" class="ep_preview_image" border="0" /><div class="ep_preview_title">Preview</div></td></tr></table></div></td><td valign="top"><a href="http://eprints.utas.edu.au/2278/1/01FRONT.PDF"><span class="ep_document_citation">PDF (Front Matter)</span></a> - 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Requires a PDF viewer<br />67Kb</td></tr><tr><td valign="top" style="text-align:center"><a onmouseover="EPJS_ShowPreview( event, 'doc_preview_2888' );" href="http://eprints.utas.edu.au/2278/10/10APPEND.PDF" onmouseout="EPJS_HidePreview( event, 'doc_preview_2888' );"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" class="ep_doc_icon" border="0" /></a><div class="ep_preview" id="doc_preview_2888"><table><tr><td><img alt="" src="http://eprints.utas.edu.au/2278/thumbnails/10/preview.png" class="ep_preview_image" border="0" /><div class="ep_preview_title">Preview</div></td></tr></table></div></td><td valign="top"><a href="http://eprints.utas.edu.au/2278/10/10APPEND.PDF"><span class="ep_document_citation">PDF (Appendices)</span></a> - Requires a PDF viewer<br />77Kb</td></tr><tr><td valign="top" style="text-align:center"><a onmouseover="EPJS_ShowPreview( event, 'doc_preview_2889' );" href="http://eprints.utas.edu.au/2278/11/11BIBLIO.PDF" onmouseout="EPJS_HidePreview( event, 'doc_preview_2889' );"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" class="ep_doc_icon" border="0" /></a><div class="ep_preview" id="doc_preview_2889"><table><tr><td><img alt="" src="http://eprints.utas.edu.au/2278/thumbnails/11/preview.png" class="ep_preview_image" border="0" /><div class="ep_preview_title">Preview</div></td></tr></table></div></td><td valign="top"><a href="http://eprints.utas.edu.au/2278/11/11BIBLIO.PDF"><span class="ep_document_citation">PDF (Bibliography)</span></a> - Requires a PDF viewer<br />139Kb</td></tr></table><div class="not_ep_block"><h2>Abstract</h2><p style="padding-bottom: 16px; text-align: left; margin: 1em auto 0em auto">Coupled atmosphere-ocean general circulation models are the simplest models which&#13;
are capable of simulating both the variability which occurs within each component&#13;
of the climate system, and the variability which arises from the interactions between&#13;
them. Only recently has it become computationally feasible to use coupled general&#13;
circulation models to study climate variability and change on timescales of O(104)&#13;
years and longer. Flux adjustments are often employed to maintain a control climate&#13;
that is both stable and realistic; however, the magnitude of the adjustments&#13;
represents a source of concern.&#13;
This study employs the CSIRO Mk3L climate system model, a low-resolution&#13;
coupled atmosphere-sea ice-ocean general circulation model. The atmospheric and&#13;
oceanic components are spun up independently; the resulting atmospheric simulation&#13;
is realistic, while the deep ocean is too cold, too fresh and too buoyant. The&#13;
spin-up runs provide the initial conditions for the coupled model, which is used to&#13;
conduct a 1400-year control simulation for pre-industrial conditions. After some&#13;
initial adjustment, the simulated climate experiences minimal drift. The dominant&#13;
mode of internal variability is found to exhibit the same spatial structure and correlations&#13;
as the observed El Ni˜no-Southern Oscillation phenomenon.&#13;
The ability of Mk3L to simulate the climate of the mid-Holocene is evaluated. It&#13;
correctly simulates increased summer temperatures at northern mid-latitudes, and&#13;
cooling in the tropics. However, it is unable to capture some of the regional-scale&#13;
features of the mid-Holocene climate, with the precipitation over northern Africa&#13;
being deficient. The model simulates a 13% reduction in the strength of El Ni˜no,&#13;
a much smaller decrease than that implied by the palaeoclimate record.&#13;
A 1400-year transient simulation is then conducted, in which the atmospheric&#13;
CO2 concentration is stabilised at three times the pre-industrial value. The transient&#13;
simulation exhibits a reduction in the rate of North Atlantic Deep Water formation,&#13;
followed by its gradual recovery, and a cessation of Antarctic Bottom Water formation.&#13;
The global-mean surface air temperature warms 2.7◦C upon a trebling of&#13;
CO2, and 5.3◦C by the end of the simulation.&#13;
A number of modifications to the spin-up procedure for the ocean model are&#13;
evaluated. A phase shift in the prescribed sea surface temperatures and salinities is&#13;
found to reduce the phase lag between the model and observations, and to lead to&#13;
a reduction in the magnitude of the diagnosed flux adjustments. When this spin-up&#13;
run is used to initialise the coupled model, the reduced flux adjustments are found&#13;
to have negligible impact upon the nature of the internal variability. While the flux&#13;
adjustments are not found to have any direct influence upon the response of the&#13;
model to external forcing, they are found to have an indirect influence via their&#13;
effect upon the rate of drift within the control simulation.&#13;
An iterative spin-up technique is also developed, whereby the response of the&#13;
ocean model is used to derive a set of effective surface tracers. These result in a&#13;
much more realistic vertical density profile within the ocean. The coupled model&#13;
exhibits slightly increased internal variability, with reduced convection within the&#13;
ocean. There is a slightly greater surface warming in response to an increase in&#13;
the atmospheric CO2 concentration, with the reduced convection resulting in slower&#13;
penetration of the surface warming to depth.</p></div><table style="margin-bottom: 1em" cellpadding="3" class="not_ep_block" border="0"><tr><th valign="top" class="ep_row">Item Type:</th><td valign="top" class="ep_row">Thesis (PhD)</td></tr><tr><th valign="top" class="ep_row">Subjects:</th><td valign="top" class="ep_row"><a href="http://eprints.utas.edu.au/view/subjects/260400.html">260000 Earth Sciences &gt; 260400 Oceanography</a><br /><a href="http://eprints.utas.edu.au/view/subjects/260602.html">260000 Earth Sciences &gt; 260600 Atmospheric Sciences &gt; 260602 Climatology (incl. Palaeoclimatology)</a></td></tr><tr><th valign="top" class="ep_row">ID Code:</th><td valign="top" class="ep_row">2278</td></tr><tr><th valign="top" class="ep_row">Deposited By:</th><td valign="top" class="ep_row"><span class="ep_name_citation"><span class="person_name">MS Heather Excell</span></span></td></tr><tr><th valign="top" class="ep_row">Deposited On:</th><td valign="top" class="ep_row">22 Oct 2007 12:07</td></tr><tr><th valign="top" class="ep_row">Last Modified:</th><td valign="top" class="ep_row">09 Jan 2008 02:30</td></tr><tr><th valign="top" class="ep_row">ePrint Statistics:</th><td valign="top" class="ep_row"><a target="ePrintStats" href="/es/index.php?action=show_detail_eprint;id=2278;">View statistics for this ePrint</a></td></tr></table><p align="right">Repository Staff Only: <a href="http://eprints.utas.edu.au/cgi/users/home?screen=EPrint::View&amp;eprintid=2278">item control page</a></p>
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