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Note to readers: This chapter, taken from The Physical Environment: A New Zealand Perspective, edited by Andrew Sturman and Rachel Spronken‐Smith, South Melbourne, Vic. ; Auckland [N.Z.] : Oxford University Press, 2001, has been reproduced with the kind permission of Oxford University Press (OUP). OUP maintain copyright over the typography used in this publication. Authors retain copyright in respect to their contributions to this volume. Rights statement: http://library.canterbury.ac.nz/ir/rights.shtml
The Physical Environment
A New Zealand Perspective Edited by
Andrew Sturman and Rachel Spronken-Sm ith
OXFORD UNIVERSITY PRESS
OXFORD UNIVERSITY PRESS
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First published 2001 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means , without the prior permission in writing of Oxford University Press. Within New Zealand, exceptions are allowed in respect of any fair dealing for the purpose of research or private study, or criticism or review, as permitted under the Copyright Act 1994, or in the case of repro graphic reproduction in accordance with the terms of the licences issued by Copyright Licensing Limited. Enquiries concerning reproduction ou tside these term s and in other countries should be sent to the Rights Department, Oxford University Press, at the address above . ISBN 0 19 558395 7 Edited by Richard King Indexed by Russell Brooks Cover and text designed by Derrick I Stone Design Typeset by Derrick I Stone Design Printed through Bookpac Production Services, Singapore
Atmosph eric processes ope rate ove r a range of sca les from globa l to mi cro . The synoptic scale refers to those processes that operate over a spatial scale of hundreds to a few thousand ki lo metres, with a time sca le ranging from a day to about a week. Weather systems of this scale a re the most familiar pub lic representation of the a tmosphere, as they appear daily in both newspapers and o n telev ision. They also tend to be the most relevant for llIany users of weather information, as people tend to plan their working or leisure activities on the basis of forecasts of synoptic weather activity. They are also of equal sign ificance to both physical and human aspects of the environment, as individual weather systems control such th ings as the input of rainfall to a catch ment, the effect of wind on plants, as wel l as the we ll-be ing of members of the public and the livel ihood of such primary producers as farmers and fishers.
The origin of synoptic weather systems As described in Chapter 4, the types of synoptic weather system dominant in a given part of the world are controlled by the global atmospher ic circu lation. This macroscale circulation determines the major cl imate zones of the world, including the tropical circulation to the north of New Zealand, the ring of subtropical anticyclones (or highs) that stradd les the country, and the circumpo lar region of dep ressions (or lows) to the south (Figure 5.1). The synoptic weather systems that affect New Zealand play a particular role in the globa l circu lation, as described in C hapter 4. For example, sub· tropical anticyclones are created by the subsidence of a ir fro m the trop ics on the po leward limb of the tropical Had ley Cell, whi le mid·latitude depressions develop as the result of the meeting of warm trop ical air with cold polar air further south . It is the contrasting air-mass characteristics that provide much of the energy that drives the weather experienced over N ew Zealand. The weather systems themselves are the means by which the globa l energy budget is maintained in equilibrium. However, a distinctive characteristic of the N ew Zealand region is that it is dominated by oceanic effects, which moderate the effects of synoptic weather syste ms. The result is that the climate is neither extremely hot nor cold , although weather can v,ary significantly from day to day.
Synoptic Control s on the Weather
9I
A brief history of weather forecasting Between the seventeenth and nineteenth centuries, meteorology involved developing instruments and making observations, although the first permanent national observing network was not establish ed until 1855 (in France). However, only retrospective analysis of weather patterns cou ld be undertaken using the data, and it was not until communications systems improved that forecasting could be undertaken seriously. It was also quickly realised that international cooperation wou ld be required to ensure adequate data coverage and exchange across the globe. Most of the early activity took place in the Northern Hemisphere, although basic observations were initiated in New Zealand during the late 1860s. The New Zealand Meteorological Department was established in 188 1 with 37 stations making 9 a.m . observations, which were transmitted by telegraph, allow ing da ily weather maps to be constructed . During the twentieth century the development of commercia l av iation increased interest in meteorology, although significant progress was not made until World War II, when the strategic importan ce of accurate weather forecasts became paramount. At this time there was an increase in upper-a ir observations and the invention of radar. Since the war two major developments have been the weather satellite and the electronic computer. The first provided a uniquely different and informative view of weather systems, while the latter allowed rapid manipulation of data and the development of numerical weather prediction techniques that now form the basis of modern forecasting. Both of these advances are of particular sign ificance to the New Zealand region because of the lack of observations made over the oceans. A summary of the history of the New Zealand Meteorological Service is provided in Table 5.1. Table 5.1
1867
1879 1881
I882 1926 1927 1929 1930 1934
History of the New Zealand Meteorological Service.
New Zealand Institute Act provides for the establishment of a federal scientific body to oversee the national scientific effort including collection of meteorological statistics. New Zealand participates in the first Intercolonial Meteorological Conference. Meteorological Department and Weather Signal Department combined into one Meteorological Department and first telegraphic weather reports received from Australia. Commencement of publication of weather maps and basic forecasts in daily newspapers. Meteorological Department of the Marine Department comes under control of DSIR and is renamed Meteorological Service. Dr Edward Kidson named Director of the New Zealand Meteorological Service. Regular pilot balloon observations of upper winds commence in Wellington and Christchurch. Opening of the first pu rpose-built national Meteorological Office at Kelburn, Wellington. Fi rst New Zealand radiosonde flights to determine upper-air temperatures made at Kelburn, becoming routine in 1942.
92
Th e Atm osph e ric Envi ronm e nt
1942 1943
Meteorological Service incorporated into the RNZAF for duration of the war. Radar wind soundings to replace pilot balloon observations commence at Ohakea. 1947 Meteorological Service comes under the control of the Air Departme nt (later C ivil Aviation). 195 1 New Zealand Meteorological Service begins regu lar ozone observat ions. 1957 Meteorological observations begin at Scott Base, Antarctica as part of the International Geophysical Year (lGY). 1960 First weather satell ite information becomes avai lable in coded form. 1961 Introduction of facsim ile equ ipment to distribute material to branch offices; fi rst television weather forecasts. 1966 Fi rst limited numerical weather prediction output available for guidance o f forecasters. 1968 O peni ng of the new Meteorological Office at Kelburn. 1970 Fi rst satellite I-ece iving station install ed. 1978 Inst al latio n o f the Meteorological Service computer; pilot natio nal netwo rk of automatic weather stations commissio ned to provide data from remote, un manned locations. 1980 O pening of t he new satell ite-receiving term inal at Kelburn, allowing reception of visible and infra-red imagery from the Geostationary Met eorological Sat ell ites. 1982 Meteorological radio-facsimi le broadcasts begin with 5 I charts each day to users. 1984 First four-day forecasts based on European Centre for Medium-Range Weather Forecasting (ECMWF) model output issued. 1987-90 Introductio n of'usel- pays' and majol- funding cuts in t he Meteorological Service 1992 Major split of forecasting and research components of the New Zealand Meteorological Service , with t he forecasting component incorporated into Meteoro logical Service Lt d. and the research com ponent into t he National Institute of Water and Atmospheric Research (N IWA).
Sturman and Tapper 1996
It is clear that weather forecast ing has become reliant on the application of sophisticated numerical modell ing techniques requiring increasingly fast computers. It is anticipated that future generations of computers will allow the development of models of significantly greater resolution and sophistication . Figure 5.1 5 illustrates the increase in supercomputer pelformance over the 20 years to 199 1. However, there is a limit to the predictability of atmospheric ph enomena, because of the element of chaos that is inherent in the system. There are also significant problems owing to the lack of good data coverage over much of the Southern Hemisph ere. It will therefore n ever be possible to forecast exactly what the weather situation will be beyond a few days ahead of the present. In spite of the limi tations to short-term fo recasting, it may become possible to make more generalised forecasts several months in advance on the bas is of improved knowledge of teleconnections that exist in global atmospheric circu lation . These wou ld be particu larly useful for the farming industry.
Synoptic Controls on the Weather 100000
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Summary This chapter first considered the origin of synoptic weather systems. The mean sealevel isobaric map was described in detail, since it is a useful tool for understanding and forecasting weather. The three-dimensional aspects of weather were then discussed, followed by a description of the major synoptic weather features, including mid-latitude depressions, subtropica l anticyclones, and tropical cyclones. The impact of these synoptic weather systems on New Zealand weather was then described, and the chapter concluded with a consideration of weather forecasting developments both internationally and within New Zealand. Further reading Brensu'um, E. 1998, The New Zealand Weather Book, Craig Potton, Nelson. Neale, AP. 1993, A Practical Guide to Weather Forecasting in New Zealand, GP Publications, Wellington. Sturman, AP. & Tapper, N .] . 1996, The Weather and Climate of Australia and New Zealand, Oxford University Press, Melbourne.
