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| Titel |
Future Weather Patterns in New Zealand using Synoptic Climatology: Kidson Types and a Simple Synoptic Classification System |
| VerfasserIn |
S. Parsons, A. J. McDonald, J. Renwick |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064666
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| Zusammenfassung |
| Understanding climate change and variability at a regional level is a significant challenge for
the current generation of global climate models. In particular, circulation patterns at the
synoptic scale need to be well resolved. The ability of synoptic climatology to translate
complex climate information into a simple format is one advantage of this technique, as this
allows easier communication, thereby aiding policy/decision makers. The goal of this study is
to explore and understand regional climate variability over New Zealand, by determining if
weather patterns are changing, using synoptic classification schemes applied to reanalyses
and IPCC AR4 data.
We apply the synoptic classification system described in Kidson (2000) to identify
changes in the “Kidson types”. The frequency of the present day synoptic scale features (the
12 Kidson Types) are first derived using reanalysis data sets (NCEP/NCAR and ERA40), and
are compared against the frequency of types derived using IPCC AR4 GCM simulations
(20c3m, A1B and A2 emission scenarios) over New Zealand (domain of latitude 25Ë S-55Ë S
and longitude 160Ë E-175Ë W).
Initial results show that the GCMs 20c3m runs echo the reanalysis data and reinforce the
results of previous studies. Results from the NCAR CCSM3.0 GCM surprisingly show no
significant future change in annual type frequency, under the A1B & A2 emission
scenarios. Investigation has revealed that the annual type frequency derived using the
Kidson methodology appears to be relatively insensitive to the changes observed in
the domain. In particular, a sensitivity study in which the geographical domain
was shifted in the meridional direction displayed limited variations in some of the
type frequencies observed until the shift was of the order of 10 degrees in latitude
(equivalent to the same shift of the jet position relative to New Zealand). While
there is no significant variation in the annual type frequency, there may be some
seasonal variation. Inter-run variability, 4 runs from the NCAR CCSM3.0 GCM,
also increases the uncertainties. Therefore additional results, incorporating a larger
ensemble of AR4 GCM models and investigation of the seasonal type variation, are also
presented.
To determine whether the complexity of the Kidson classification scheme causes this
sensitivity issue we have also applied a Simple Synoptic Classification System (SSCS, based
on Lund’s, “Map-Pattern Classification by Statistical Methods”) to the same data. This
provides an independent methodology, which can then be compared to the Kidson results.
Both methods are in general agreement, with limited annual change of type frequency. |
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