Publications


The benefits of global high-resolution for climate simulation: process-understanding and the enabling of stakeholder decisions at the regional scale.

Bulletin of the American Meteorological Society (2018)

MJ Roberts, PL Vidale, C Senior, HT Hewitt, C Bates, S Berthou, P Chang, HM Christensen, S Danilov, M-E Demory, SM Griffies, R Haarsma, T Jung, G Martin, S Minobe, T Ringler, M Satoh, R Schiemann, E Scoccimarro, G Stephens, MF Wehner


Improving Weather Forecast Skill through Reduced-Precision Data Assimilation

MONTHLY WEATHER REVIEW 146 (2018) 49-62

S Hatfield, A Subramanian, T Palmer, P Duben


Can bias correction and statistical downscaling methods improve the skill of seasonal precipitation forecasts?

CLIMATE DYNAMICS 50 (2018) 1161-1176

R Manzanas, A Lucero, A Weisheimer, JM Gutierrez


The impact of stochastic parametrisations on the representation of the Asian summer monsoon

CLIMATE DYNAMICS 50 (2018) 2269-2282

K Strommen, HM Christensen, J Berner, TN Palmer


Seasonal predictability of onset and cessation of the east African rains

Weather and Climate Extremes (2018)

D MacLeod

© 2018 The Author Advanced warning of delayed onset or early cessation of the rainy seasons would be extremely valuable information for farmers in east Africa and is a common request from regional stakeholders. Such warnings are beginning to be provided, however forecast skill for these metrics has not been demonstrated. Here the forecast skill of the ECMWF seasonal hindcasts is evaluated for onset and cessation forecasts over east Africa. Correlation of forecast with observed long rains anomalies only above a 95% statistical significance level for a small part of the domain, whilst short rains are significance a large part of the region. The added value of updating the forecast outlook with the extended range 46 day forecast is assessed and this gives a small improvement. For the short rains detection of early onset is better near the coast, and late onset detection is better over northwestern Kenya. During exceptionally dry years the method to detect onset and cessation fails. Using this as a definition of a failed season, the model shows significant skill at anticipating long rains season failure in the northwest of Kenya, and short rains failure in Somalia and northeast Kenya. In addition the strength of the correlation between long rains cessation and seasonal total is shown to be particularly weak in observations but too strong in the hindcasts. Predictability of onset and cessation for both seasons appears to arise primarily from the link with seasonal total and it is unclear that the model represents variability in onset and cessation beyond this. This has important implications for operational forecasting: any forecast of season timing which is ‘inconsistent’ with seasonal total (e.g. an early onset but low total rainfall) must be treated with caution. Finally links with zonal winds are investigated. Late onset is correlated with easterly (westerly) anomalies during the long (short) rains, though the strength and spatial pattern of the relationship is not well represented in the model. Early cessation is correlated with easterly anomalies in both seasons for most of the region in both observations and hindcasts. However for the long rains the sign of the correlation is reversed along the coast in observations but not in the hindcasts. These dynamical inconsistencies may have a negative impact on forecast skill and have the potential to inform process-based development of climate modelling in the region.


Transforming climate model output to forecasts of wind power production: how much resolution is enough?

METEOROLOGICAL APPLICATIONS 25 (2018) 1-10

D MacLeod, V Torralba, M Davis, F Doblas-Reyes


OPTIMAL-TRANSPORT-BASED MESH ADAPTIVITY ON THE PLANE AND SPHERE USING FINITE ELEMENTS

SIAM JOURNAL ON SCIENTIFIC COMPUTING 40 (2018) A1121-A1148

ATT Mcrae, CJ Cotter, CJ Budd


Impact of Gulf Stream SST biases on the global atmospheric circulation

Climate Dynamics (2018) 1-19

RW Lee, TJ Woollings, BJ Hoskins, KD Williams, CH O Reilly, G Masato

© 2018 The Author(s) The UK Met Office Unified Model in the Global Coupled 2 (GC2) configuration has a warm bias of up to almost (Formula presented.) in the Gulf Stream SSTs in the winter season, which is associated with surface heat flux biases and potentially related to biases in the atmospheric circulation. The role of this SST bias is examined with a focus on the tropospheric response by performing three sensitivity experiments. The SST biases are imposed on the atmosphere-only configuration of the model over a small and medium section of the Gulf Stream, and also the wider North Atlantic. Here we show that the dynamical response to this anomalous Gulf Stream heating (and associated shifting and changing SST gradients) is to enhance vertical motion in the transient eddies over the Gulf Stream, rather than balance the heating with a linear dynamical meridional wind or meridional eddy heat transport. Together with the imposed Gulf Stream heating bias, the response affects the troposphere not only locally but also in remote regions of the Northern Hemisphere via a planetary Rossby wave response. The sensitivity experiments partially reproduce some of the differences in the coupled configuration of the model relative to the atmosphere-only configuration and to the ERA-Interim reanalysis. These biases may have implications for the ability of the model to respond correctly to variability or changes in the Gulf Stream. Better global prediction therefore requires particular focus on reducing any large western boundary current SST biases in these regions of high ocean-atmosphere interaction.


Skilful Seasonal Predictions of Summer European Rainfall

GEOPHYSICAL RESEARCH LETTERS 45 (2018) 3246-3254

N Dunstone, D Smith, A Scaife, L Hermanson, D Fereday, C O'Reilly, A Stirling, R Eade, M Gordon, C Maclachlan, T Woollings, K Sheen, S Belcher


Changes in European wind energy generation potential within a 1.5 degrees C warmer world

ENVIRONMENTAL RESEARCH LETTERS 13 (2018) ARTN 054032

JS Hosking, D MacLeod, T Phillips, CR Holmes, P Watson, EF Shuckburgh, D Mitchell


Flow dependent ensemble spread in seasonal forecasts of the boreal winter extratropics

Atmospheric Science Letters (2018)

D Macleod, C O'Reilly, T Palmer, A Weisheimer

© 2018 Royal Meteorological Society. Flow-dependent spread (FDS) is a desirable characteristic of probabilistic forecasts; ensemble spread should represent the expected forecast error. However this is difficult to estimate for seasonal hindcasts as they tend to have a relatively small sample size. Here we use a long (110year) seasonal hindcast dataset to evaluate FDS in forecasts of boreal winter North Atlantic Oscillation (NAO) and Pacific North American pattern (PNA). A good FDS relationship is found for interannual variations in both the NAO and PNA, with mild underdispersion for negative NAO and PNA events and slight overdispersion for positive NAO. Decadal-scale variability is seen in forecast errors but not in ensemble spread, which shows little variation on this timescale. Links between forecast errors and tropical heating anomalies are also investigated, though no strong links are found. However, a weak link between strong El Niño warming in the East Pacific and reduced PNA error is suggested.


Challenges and opportunities for improved understanding of regional climate dynamics

NATURE CLIMATE CHANGE 8 (2018) 101-108

M Collins, S Minobe, M Barreiro, S Bordoni, Y Kaspi, A Kuwano-Yoshida, N Keenlyside, E Manzini, CH O'Reilly, R Sutton, S-P Xie, O Zolina


The Gulf Stream influence on wintertime North Atlantic jet variability

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 143 (2017) 173-183

CH O'Reilly, S Minobe, A Kuwano-Yoshida, T Woollings


Reliable low precision simulations in land surface models

Climate Dynamics (2017) 1-10

A Dawson, PD Düben, DA MacLeod, TN Palmer

© 2017 The Author(s) Weather and climate models must continue to increase in both resolution and complexity in order that forecasts become more accurate and reliable. Moving to lower numerical precision may be an essential tool for coping with the demand for ever increasing model complexity in addition to increasing computing resources. However, there have been some concerns in the weather and climate modelling community over the suitability of lower precision for climate models, particularly for representing processes that change very slowly over long time-scales. These processes are difficult to represent using low precision due to time increments being systematically rounded to zero. Idealised simulations are used to demonstrate that a model of deep soil heat diffusion that fails when run in single precision can be modified to work correctly using low precision, by splitting up the model into a small higher precision part and a low precision part. This strategy retains the computational benefits of reduced precision whilst preserving accuracy. This same technique is also applied to a full complexity land surface model, resulting in rounding errors that are significantly smaller than initial condition and parameter uncertainties. Although lower precision will present some problems for the weather and climate modelling community, many of the problems can likely be overcome using a straightforward and physically motivated application of reduced precision.


Potential applications of subseasonal-to-seasonal (S2S) predictions

METEOROLOGICAL APPLICATIONS 24 (2017) 315-325

CJ White, H Carlsen, AW Robertson, RJT Klein, JK Lazo, A Kumar, F Vitart, EC de Perez, AJ Ray, V Murray, S Bharwani, D MacLeod, R James, L Fleming, AP Morse, B Eggen, R Graham, E Kjellstrom, E Becker, KV Pegion, NJ Holbrook, D McEvoy, M Depledge, S Perkins-Kirkpatrick, TJ Brown, R Street, L Jones, TA Remenyi, I Hodgson-Johnston, C Buontempo, R Lamb, H Meinke, B Arheimer, SE Zebiak


On the use of scale-dependent precision in Earth System modelling

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 143 (2017) 897-908

T Thornes, P Duben, T Palmer


Single Precision in Weather Forecasting Models: An Evaluation with the IFS

MONTHLY WEATHER REVIEW 145 (2017) 495-502

F Vana, P Duben, S Lang, T Palmer, M Leutbecher, D Salmond, G Carver


Universal continuous transition to turbulence in a planar shear flow

JOURNAL OF FLUID MECHANICS 824 (2017) ARTN R1

M Chantry, LS Tuckerman, D Barkley


A study of reduced numerical precision to make superparameterization more competitive using a hardware emulator in the OpenIFS model

JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 9 (2017) 566-584

PD Duben, A Subramanian, A Dawson, TN Palmer


Impact of stochastic physics on tropical precipitation in the coupled ECMWF model

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 143 (2017) 852-865

A Subramanian, A Weisheimer, T Palmer, F Vitart, P Bechtold

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