The original intention of this thesis was to investigate Climate
Change (CC), in particular the meteorological impacts of CC on
New Zealand (NZ). Succinctly, “to understand what NZ’s future
weather may entail”. However, as the research progressed it
has led to the larger circulation and has highlighted the teleconnections that are present and the importance of the wider
circulation and to NZ . It is apparent that the larger scale circulation needs to be considered in conjunction with, if not before,
the synoptic scale. Thus, in order to understand NZ’s future
weather first we must understand the Southern Hemisphere
and the circulation within it.
CC is often described in a broad global scale and it is difficult to
translate and relate these mechanisms into day to day weather
terms, which have the advantage of being commonly understood. Synoptic Climatology (SC) can bridge this gap by simplifying the wide variety of weather into a small grouping of types, and thus can provide an understandable alternative.
To undertake this research an existing SC scheme known as
the Kidson Types (KTs) was extended with the use of General
Circulation Model (GCM) output. The KTs have been widely
used in NZ, thus work detailing their future would be advantageous. The GCMs were able to reproduce the observed frequencies of occurrence of the KTs during the late 20th century. Future
projections for the late 21st century surprisingly showed little
change in annual type frequencies. To investigate this further
a sensitivity study was undertaken, which revealed that the
methodology was insensitive to annual type frequency change.
The range of response from the GCM projections also inhibited
determining significant changes in KT frequencies. Additionally,
trend analysis using four realisations from one GCM noted both
positive and negative trends in some of the types. This also highlights the difficulty in using GCM output, as a larger ensemble can diffuse results and in a small ensemble individual
GCMs can unduly bias the results.
Further scrutiny of the KT was then undertaken. An investigation of the KTs to ascertain their influence in the wider circulation using the ERA Interim (ERA-I) reanalysis and trends within
the KT using a long term reanalysis data set, the Twentieth Century Reanalysis (20CR). Due to the high year to year variability
in the KTs, significant trends were only determined in the 20CR
with a reduction in the Zonal Regime representing the occurrence of strong westerly flows over NZ. A composite analysis
was also undertaken to evaluate the KTs within the Southern
Hemisphere (SH). A positive pressure anomaly was detected
far from the Kidson domain, which is defined over NZ, during
the SW type. This motivated another study on SH Blocking.
Blocking is a large scale phenomena that can influence the paths
of synoptic systems and thus potentially cause or exacerbate
adverse weather events. Blocking is an area of climate research
that requires further work, as there is a deficit of GCM studies in
the SH. This study utilised a Persistent Positive Anomaly (PPA)
methodology which is advantageous as the spatial pattern, latitude and longitude, of the Blocking Events (BEs) is determined.
To our knowledge, this is the first study to use GCM output
using the PPA methodology in the SH and this is also the first
blocking study using Coupled Model Inter-comparison Project
(CMIP)5 GCM output in the SH. A reduction of BEs was observed
over the South Pacific Ocean (SPO) region during summer and
spring, in the GCM projections between 2041-2070 and 2071-
2100. The Southern Annular Mode (SAM) has been suggested
as an influence on blocking frequency in previous work and
this relationship was studied. A high negative correlation between SAM + and BEs was observed in summer with the reanalysis and GCM historical output. This correlation was reduced in
21st century. However, further work is needed in this study in
order to gain an understanding of the mechanisms and linkages
between SAM and the BEs.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/10248 |
| Date | January 2015 |
| Creators | Parsons, Simon |
| Publisher | University of Canterbury. Physics and Astronomy |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Simon Parsons, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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