9. Predicting turbulence – improved weather forecasts and £1.25 million annual savings for MoD
Submitting InstitutionUniversity of Leeds
Unit of AssessmentEarth Systems and Environmental Sciences
Summary Impact TypeTechnological
Research Subject Area(s)
Earth Sciences: Atmospheric Sciences
Engineering: Maritime Engineering, Interdisciplinary Engineering
Summary of the impact
Research carried out at the University of Leeds has led to the
development of a system for predicting severe air turbulence at airports
and elsewhere. The research modelled highly localised `rotor streaming'
turbulence which is too small-scale to predict using today's numerical
weather prediction models. The Met Office now uses the highly efficient
3DVOM computer prediction model, based on the Leeds research, to improve
its operational weather forecasting, especially for providing warnings of
`gustiness' to the public and airports and to highlight risks of
overturning of high-sided vehicles. In addition, the model is used by
forecasters to predict dangerous turbulence at Mount Pleasant Airport in
the Falkland Islands, and has led to the prevention of around five flight
diversions per year at an estimated cost saving of £1.25 million.
Certain airports, especially those located in the lee of a hill or
mountain, are prone to a particular type of atmospheric turbulence often
called `rotor streaming' by meteorologists. Strong winds passing over and
around a hill generate pockets of highly turbulent `spinning' air, which
are dangerous for aircraft. When atmospheric conditions for rotor
streaming occur, flights may be diverted to a safer airport.
Although rotor streaming has been recorded many times since the 1950s,
meteorologists have had limited success in predicting this phenomenon.
Even the high-resolution weather models of the UK's Met Office, which run
on supercomputers, have been unable to resolve the details of these
turbulent eddies, which typically are very small (a few hundred metres) in
In 1999 the Ministry of Defence (MoD) commissioned a Leeds team led by Stephen
Mobbs to develop a new forecasting system for turbulence at the new
Mount Pleasant Airport (MPA), Falkland Islands, which suffered from
problems of expensive flight diversions. The work was funded on the basis
of Mobbs' expertise on airflows over mountains (e.g. ).
Following a successful first phase, the MoD continued to support the
development of the forecasting model in three additional phases over a
period of about four years (1999-2004), and the research was further
supported by funding from the Natural Environment Research Council (NERC)
between 2002 and 2007.
Mobbs and colleagues from Leeds spent two years taking atmospheric
measurements in the Falkland Islands and in Scotland [2,3]. Some
of this work required the team to modify the design of sensitive
barographs so they could measure the effect of lee waves on the drag force
on hills. These instruments were deployed in the Falklands and in the UK;
readings from these instruments helped the researchers to understand the
parameters and dynamics of rotor streaming and diagnose the physical
processes that were the cause of the severe turbulence at MPA.
Such detailed ground-based and aircraft observations generated a detailed
understanding of this localised turbulence which allowed the researchers
to develop a computer prediction model, later called 3D Velocities Over
Mountains (3DVOM) . Analysis of this data over several years
also led to new and more detailed understanding of turbulent airflow over
Model refinement, testing and validation
As part of the wider development of the predictive model, Mobbs
and his colleagues carried out an 18-month experiment in collaboration
with the Met Office. The study focused on the Pennines in northern England
to address turbulence encountered by flights to and from the chain of MoD
airfields in North Yorkshire, as well as wind hazards on the A1 trunk road
. Both the Leeds research group and the Met Office team
contributed equally to the collection of field data and modelling using
3DVOM. The team also studied capabilities of the 3DVOM system to forecast
turbulence in steeper mountains, carrying out experiments in Switzerland
in 2003 . This work demonstrated that techniques developed for
the Falkland Islands could be effectively adapted to similar turbulence
By 2007, 3DVOM had been integrated into the Met Office's suite of
forecasting models; the Met Office was able to improve its turbulence
forecasting to airports using the new technology (see Section 4).
Stephen Mobbs, Professor of Atmospheric Dynamics (1995-present) in
the School of Earth and Environment, University of Leeds.
References to the research
1. Vosper, S.B., Castro, I.P., Snyder, W.H., and Mobbs, S.D.
(1999) Experimental studies of strongly stratified flow past
three-dimensional orography, Journal of Fluid Mechanics, 390, pp.
2. Burton, R.R., Vosper, S.B. and Mobbs, S.D. (2006) Underlying
structures in orographic flow: An analysis of measurements made on the
Isle of Arran, Quarterly Journal of the Royal Meteorological Society,
132, 457-1466. DOI: 10.1256/qj.05.192.
3. Mobbs, S.D., Vosper, S.B., Sheridan, P.F., Cardoso, R.,
Burton, R.R. and Arnold, S.J. (2005) Observations of downslope winds and
rotors in the Falkland Islands, Quarterly Journal of the Royal
Meteorological Society, 131, 329-351. DOI: 10.1256/qj.04.51.
4. Ross, A.N., Arnold, S., Vosper, S.B., Mobbs, S.D., Dixon, N.
and Robins, A.G. (2004) A comparison of wind-tunnel experiments and
numerical simulations of neutral and stratified flow over a hill, Boundary-Layer
Meteorology, 113, 427-459. DOI: 10.1007/s10546-004-0490-z.
5. Sheridan, P.F., Horlacher, V., Rooney, G.G., Hignett, P., Mobbs,
S.D. and Vosper, S.B. (2007) Influence of lee waves on the near surface
flow downwind of the Pennines, Quarterly Journal of the Royal
Meteorological Society, 133, 1353-1369. DOI: 10.1002/qj.110.
6. Lewis, H.W., Mobbs, S.D. and Lehning, M. (2008) Observations
of cross-ridge flows across steep terrain, Quarterly Journal of the
Royal Meteorological Society, 134, 801-816. DOI:
Key funding and grants
The research outputs listed above were funded from a variety of sources,
including the following key grants (NERC grants are awarded on the basis
of rigorous peer review):
• Natural Environment Research Council (NERC): £77,355 for "Flow over
complex terrain using adaptive numerical methods" (1997-2000).
• Royal Society: £9916 for "Measurement of Orographic Drag" (1997-1998).
• NERC: £162,831 for "Stable boundary layer flow over hills" (1998-2002).
• NERC: £9,016 for "A microbarograph array for detection of travelling
internal gravity waves" (1997-2000).
• Ministry of Defence: £325,082 for "Rotor forecasting at MPA"
• Ministry of Defence: £78,985 for "Rotor forecasting at MPA"
• Ministry of Defence: £48,000 for "Development of a rotor forecasting
• Ministry of Defence (via Met Office): £48,950 for "Rotor forecasting at
• NERC: £133,693 for "Unsteady flow over complex terrain" (2002-2005).
• NERC: £203,610 for "Observations and Modelling of Rotors" (2003-2007).
All grants were awarded to Mobbs as Principal Investigator. The
MoD does not provide evaluations of its commissioned research; however,
the repeated funding is indicative of the quality of the Leeds research
and its application to the MoD's requirements.
Details of the impact
Improved weather forecasts — protecting people
The 3DVOM predictive computer model is now fully integrated into the
operational forecasting of the Met Office in the UK, aided by the transfer
of Dr Simon Vosper (Research Fellow, 1995-2001) from Mobbs' Leeds
research group to the Met Office in 2004-05. It provides meteorologists
with predictions of vertical wind speed, which they can integrate into
The 3DVOM software was initially deployed in 2005 for forecasting
hazardous turbulence in the Falkland Islands, especially around MPA.
However, following additional studies and testing by the Leeds group, the
Met Office extended its operational use of 3DVOM to four UK meteorological
domains: south-west England (Dartmoor and Bodmin moor), north Wales
(Snowdonia), northern England (the Pennines and the Lake District) and
eastern Scotland (the Grampians) [A1,A2]. In 2007 the domains of
Northern Ireland and eastern Ireland were added. Since this application of
3DVOM to the UK, duty forecasters have been able to use the model's output
to produce warnings of hazardous turbulence for both the MoD and civil
aviation authorities across the country, allowing them to adjust flight
plans accordingly [B].
Since 2010 the 3DVOM system has been run four times per day serving 5 UK
areas, Eire and the Falklands, giving forecasters refreshed model
predictions every six hours. Direct users include all the Aviation and
Defence forecasters within the Met Office Head Quarters (Exeter), all the
outstations (e.g. Falkland Island) and within the Defence sites (c.5).
3DVOM predictions for low- level winds, combined with outputs from other
forecasting models, are also used by forecasters to assess the risk of
overturning for high-sided vehicles on exposed routes, such as the A1
trunk road to the east of the Pennines. Forecasts of `gusts' in public
weather forecasts and warnings issued by the Met Office are based on 3DVOM
Commercial benefits — reducing costly diversions from Mount Pleasant
MPA was constructed in the Falkland Islands in the 1980s following the
conflict there to service the military garrison. It is often afflicted by
severe turbulence, which prevents incoming aircraft from landing. Aircraft
from the UK fly to MPA via Ascension Island, over seven hours flying time
away. If flights to MPA are unable to land they are diverted to distant
airports in South America, at least three hours away. Here the crew must
rest for more than 12 hours and the passengers must be accommodated during
this time. Such diversions are costly: rough estimates suggest diversion
costs for a flight are somewhere around £250,000, based on additional
aviation fuel costs, airport charges and unscheduled overnight
accommodation for 300 passengers [C,D].
Clearly it is preferable for flights to remain at Ascension until weather
conditions at MPA improve; ideally accurate weather and turbulence
forecasts are required at least 12 hours in advance of take-off from the
Ascension stopover. Since the implementation of 3DVOM for Falkland Islands
forecasting by the Met Office in 2005, the system has helped to avoid
approximately five diversions per year, with a cost saving to the MoD of
around £1.25 million per year [B,D].
The 3DVOM turbulence forecasts have also helped to protect military
personnel at MPA, for example in a case described by the Principal Met
Officer at MPA: "I did have a case last year when a VVIP was on board
the airbridge, and I advised all in this region that the vertical motion
was of great concern as we were forecasting very strong cross winds and
rotors during the usual airbridge arrival time. I briefed CBF [Chief of
British Forces] along with many operators, and we managed to delay the
aircraft until the wind backed westerly, to reduce any diversion risk"
Sources to corroborate the impact
A. Papers to the Met Office Working Group for the Operational Suite
(WGOS): A1 Proposed implementation of the 3DVOM lee-wave forecasting
system, 2006. A2 Implementation of two additional 3dVOM domains,
This report pre-dates the REF assessment, but is included to provide
evidence that the program was integrated within the MET Office
B. Letter from MET Office (dated 01/02/2013) detailing the Met Office
usage of 3DVOM.
C. Letter from MET Office (dated 13/06/2013) regarding requests for
clarification on savings estimates. Within this letter, the MET Office
provides an extract from email correspondence between MET Office personnel
and the Senior Operational Meteorologist at Met Office Falkland Islands
dated 11 April 2013: "I'm not sure if you're interested or not but the
last few runs of the 3DVOM for the Falklands has produced some very
strong signals. In all my time forecasting down here, I don't think I've
ever seen a signal that was in essence "off the scale" in terms of
strengths of up/down drafts. As a result of the output from the 3DVOM
and a recent air bridge encounter with severe up/down drafts, nobody is
willing to take chances and as such the airfield is essentially now
closed to all aircraft until 0300Z tomorrow morning, when the wind
becomes westerly and the risk has diminished."
D. Further corroboration can be obtained from the Head of Atmospheric
Processes and Parameterizations, Met Office.