dynamicists versus modellers: a growing divide?
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eavy
rain
fall
in lo
ng t
ime
seri
es
throughout the Ryedale record, and for more
heavy rain days to occur in summer than in
other seasons. When compared with the
most recent period (2001–2008), higher fre-
quencies of heavy rain days and a greater
proportion of annual rainfall falling on heavy
rain days occurred in the 1930s.
The composite record which has been con-
structed for Ryedale in this study has enabled
heavy rainfalls and seasonal trends to be
assessed over a 93-year period in an upland
area. The conclusion that recent heavy rain-
fall events, particularly in summer, are not as
rare as may first have been thought clearly
illustrates the importance of using long-term
climatic monitoring and associated records
to put recent weather events into context.
Acknowledgements
We gratefully acknowledge use of the British
Atmospheric Data Centre and also the use of
a synoptic chart (both UK Met Office), and
the use of the Digimap service and Strategi®
map data. Jeff Warburton also acknowledges
support from NERC (Award NE/D005744/1).
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© Royal Meteorological Society, UK
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Dynamicists versus modellers: a growing divide?Meeting reportThis meeting, on 18 November 2009, was
organised by the Society’s History Group
and was held at the University of Reading.
It was advertised with what was described
during the meeting as a deliberately pro-
vocative abstract, asking whether the mete-
orological community has forgotten the
pioneering principles of Rossby and Charney
and whether today’s modellers are really
computer scientists who ‘tweak’ models
without fully understanding them.
In his introduction, Malcolm Walker (Chair
of the History Group) introduced the cast of
characters (Rossby, Charney, Sutcliffe et al.)
whose classic papers in the 1940s laid the
foundations of dynamical meteorology, and
whose experiments with numerical weather
prediction (NWP) led to the first computer-
based weather forecasting systems. The sec-
ond speaker, John Methven (University of
Reading), gave an introduction to the early
theories of the development of extratropical
weather systems, beginning with the Bergen
School and the development of the polar
front theory of cyclones and ending with
the independent development of quasi-
geostrophic theory by Rossby and Charney.
The point was stressed that what both
Rossby and Charney sought, and indeed
found, was a mathematically closed theory
for the evolution of synoptic-scale cyclones.
The initial NWP systems were based on
quasi-geostrophic equations, keeping a
close link with theory. With increases in
computing power, and the realisation that
accurate prediction at finer resolution
required greater knowledge of the unbal-
anced flow, NWP moved to the primitive
equations and the link to theory began to
weaken. The talk ended with a Monty
Python inspired question: what has quasi-
geostrophic theory ever done for us? John’s
answer: It has given us the ability to under-
stand the evolving flow and develop intel-
ligent diagnostics for analysing the output
from numerical simulations.
Next, Lennart Bengtsson (University of
Reading) gave a summary of the initial
development of NWP. His first point fol-
lowed directly from John Methven’s talk: the
fundamental requirement for the inception
95
Weather –
April 2010, Vol. 65, No. 4
of NWP was the theoretical basis provided
by Charney and Rossby. He noted that the
first operational NWP forecasts began in
December 1954; they were for the North
Atlantic region and were based on the baro-
tropic model developed by the Stockholm
group led by Rossby. The BESK computer
used for these initial forecasts had only a
512-word memory and could perform a sin-
gle operation approximately every 50
microseconds. Lennart pointed out that the
huge improvements in computer technol-
ogy since those first operational forecasts
have led to models becoming so complex
that it is difficult for users to know how to
interact with them. The next speaker, Brian
Golding (Met Office), sought in his presenta-
tion to answer the question: NWP since the
1960s: A triumph of numerical analysis or
meteorological science? He drew a distinc-
tion between NWP and meteorology: the
former is based on the numerical solution
of known physical laws and the latter is the
study of emergent weather phenomena. He
noted that there have been great improve-
ments in the skill of NWP, due to improve-
ments in the numerical models and the use
of observations to initialise the forecasts,
with current four-day forecasts as accurate
as one-day forecasts were around 1975. But
he stressed that these improvements could
only be judged and guided by comparison
with the observed emergent weather
phenomena.
The final speaker, Andy White (Met Office),
began with his favourite equation (the zonal
momentum equation on the sphere), stat-
ing that there are two options when faced
with it: you either immediately proceed to
a numerical solution or you carefully analyse
the equation discarding small terms and
reducing it to a simpler, more easily under-
stood, form. Both options have merits and
drawbacks. In the first, you obtain an accu-
rate solution but little understanding, whilst
in the second, understanding comes at the
expense of accuracy. He felt there was a
creative tension between those who prefer
each option, which is beneficial to both.
A panel and audience discussion followed
and was chaired by Brian Hoskins (University
of Reading/Grantham Institute for Climate
Change), and a lively debate centred on the
question: Is there a growing divide? The
large variety of opinions expressed indi-
cated that scientists in general are always
ready to talk to each other, even if they
cannot reach a consensus. On the one hand,
many were of the opinion that the sheer
size and complexity of modern computers
and models is such that there is inevitably
a larger number of computer technicians
and programmers who may have only a
limited understanding of dynamical mete-
orology. Some felt that modellers should be
dynamicists at heart, and voiced their con-
cern over the fact that new generations of
scientists increasingly use models without
developing an understanding of the under-
lying dynamics. One member of the panel
felt that some dynamical concepts, such as
group velocity, have simply been forgotten
and one audience member went so far as
to state that dynamicists were a dying breed.
Others were not so pessimistic, with some
feeling that NWP models have become
important tools which are used by dynami-
cists for knowledge generation. Some felt
that the divide was greater in the early days
of NWP, in part because of a divide that
existed between dynamicists and forecast-
ers. Several people raised the issue that the
increased emphasis on climate and statisti-
cal analysis has led to a reduction in the
amount of dynamical meteorology research
being performed, so that the real divide was
between dynamicists/modellers and statis-
ticians. Some felt that the sheer complexity
of the interaction between the dynamics
and physics included in modern NWP mod-
els means that no single person is capable
of understanding them as a whole, and that
the future of dynamical meteorology lies in
guiding our understanding of the increas-
ingly complex model world by the develop-
ment of intelligent diagnostics.
Whatever its future within NWP, it was
clear from the discussion that all agreed
that an understanding of dynamical mete-
orology should remain a key objective in
the education of young atmospheric
scientists.
Correspondence to: Thomas H. A. Frame, Meteorology Department,University of Reading,PO Box 243, Earley Gate, Reading RG6 6BB, UK.
© Royal Meteorological Society, 2010
DOI: 10.1002/wea.567
The long road aheadMeeting reportThis is a report of the joint RMetS and Royal
Society meeting on The Science of UK Climate
Projection: UKCP09 and Beyond, held on 15
October 2009 at the Royal Society.
While international political negotiations
seek to limit emissions of greenhouse gases,
climate change is already happening and
some level of future climate change will be
inevitable. How do we plan for the future?
This meeting discussed how to provide
information about regional climate change
on scales relevant for local and national
responses.
Because we require information at local
scales, and because we are interested in how
climate change will affect phenomena such
as rainfall, storms, heatwaves, etc., it is natural
to turn to complex climate models which are
designed to simulate the interactions
between the different processes that deter-
mine local climate. Despite the extensive use
of climate models in research and in putting
the scientific case for anthropogenic climate
change so far, imperfections in models mean
that projections are uncertain; different mod-
els produce different futures.
Recognising that we are not in possession
of a perfect model of the climate system,
and because there are natural fluctuations
in climate that cannot be deterministically
predicted, the most recent set of UK Climate
Projections, UKCP09, is presented in the
form of probabilities (http://ukclimatepro-
jections.defra.gov.uk; Street et al., 2009). The
method on which UKCP09 is based involves
exploring the input parameter space of a
model, in this case HadCM3, to find model
versions which simulate historical climates
consistent with available observations of
the climate system and their uncertainties.
The input parameters are those which con-
trol many of the physical processes and
feedbacks in the model, together with forc-
ing parameters, such as increasing green-
house gases. The model versions which best
simulate historical climate are used to form
probability distribution functions (PDFs) of
future climate change.
Despite this relatively simple concept,
implementation of the UKCP09 projections
is very complex. Limitations on computer
resources mean that the projections are
constructed from a fairly limited number of
samples of the model input parameter
space – even though those 400 or so
ensemble simulations took a team of Hadley
Centre scientists over eight years to pro-
duce. Considerable effort is required to turn
this ensemble into a more comprehensive
sample of model input parameter space
that can be compared with the available
observations, including fitting statistical
models called emulators to mimic the out-
put of HadCM3. In many cases, quantitative
estimates of uncertainty or errors in obser-
vations are not available, so assessing the
extent to which model versions actually
compare to the real world is a challenge.
Some assumptions have to be made in the
implementation of the UKCP09 algorithm
for reasons of expediency; nevertheless,
the sensitivity of the final PDFs to many
Meeting report