Stochastic weather and climate models

Nature Reviews Physics Springer Science and Business Media LLC 1 (2019) 463-471

TN Palmer

The ECMWF ensemble prediction system: Looking back (more than) 25 years and projecting forward 25 years

Quarterly Journal of the Royal Meteorological Society (2018)

T Palmer

© 2018 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. This paper has been written to mark 25 years of operational medium-range ensemble forecasting. The origins of the ECMWF Ensemble Prediction System are outlined, including the development of the precursor real-time Met Office monthly ensemble forecast system. In particular, the reasons for the development of singular vectors and stochastic physics – particular features of the ECMWF Ensemble Prediction System - are discussed. The author speculates about the development and use of ensemble prediction in the next 25 years.

The Sensitivity of Euro-Atlantic Regimes to Model Horizontal Resolution

Geophysical Research Letters American Geophysical Union (2019)

K Strommen, I Mavilia, S Corti, M Matsueda, P Davini, JV Hardenberg, P-L Vidale, R Mizuta

There is growing evidence that the atmospheric dynamics of the Euro-Atlantic sector during winter is driven in part by the presence of quasi-persistent regimes. However, general circulation models typically struggle to simulate these, with e.g. an overly weakly persistent blocking regime. Previous studies have showed that increased horizontal resolution can improve the regime structure of a model, but have so far only considered a single model with only one ensemble member at each resolution, leaving open the possibility that this may be either coincidental or model-dependent. We show that the improvement in regime structure due to increased resolution is robust across multiple models with multiple ensemble members. However, while the high resolution models have notably more tightly clustered data, other aspects of the regimes may not necessarily improve, and are also subject to a large amount of sampling variability that typically requires at least three ensemble members to surmount.

Seasonal Predictability of the Winter North Atlantic Oscillation From a Jet Stream Perspective


T Parker, T Woollings, A Weisheimer, C O'Reilly, L Baker, L Shaffrey

Estimates of flow-dependent predictability of wintertime Euro-Atlantic weather regimes in medium-range forecasts


M Matsueda, TN Palmer

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


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

The Impact of Tropical Precipitation on Summertime Euro-Atlantic Circulation via a Circumglobal Wave Train

JOURNAL OF CLIMATE 31 (2018) 6481-6504

CH O'Reilly, T Woollings, L Zanna, A Weisheimer

The scaling and skewness of optimally transported meshes on the sphere

Journal of Computational Physics Elsevier 375 (2018) 540-564

CJ Budd, ATT McRae, CJ Cotter

In the context of numerical solution of PDEs, dynamic mesh redistribution methods (r-adaptive methods) are an important procedure for increasing the resolution in regions of interest, without modifying the connectivity of the mesh. Key to the success of these methods is that the mesh should be sufficiently refined (locally) and flexible in order to resolve evolving solution features, but at the same time not introduce errors through skewness and lack of regularity. Some state-of-the-art methods are bottom-up in that they attempt to prescribe both the local cell size and the alignment to features of the solution. However, the resulting problem is overdetermined, necessitating a compromise between these conflicting requirements. An alternative approach, described in this paper, is to prescribe only the local cell size and augment this an optimal transport condition to provide global regularity. This leads to a robust and flexible algorithm for generating meshes fitted to an evolving solution, with minimal need for tuning parameters. Of particular interest for geophysical modelling are meshes constructed on the surface of the sphere. The purpose of this paper is to demonstrate that meshes generated on the sphere using this optimal transport approach have good a-priori regularity and that the meshes produced are naturally aligned to various simple features. It is further shown that the sphere's intrinsic curvature leads to more regular meshes than the plane. In addition to these general results, we provide a wide range of examples relevant to practical applications, to showcase the behaviour of optimally transported meshes on the sphere. These range from axisymmetric cases that can be solved analytically to more general examples that are tackled numerically. Evaluation of the singular values and singular vectors of the mesh transformation provides a quantitative measure of the mesh aniso...

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


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

Forcing Single-Column Models Using High-Resolution Model Simulations.

Journal of advances in modeling earth systems 10 (2018) 1833-1857

HM Christensen, A Dawson, CE Holloway

To use single-column models (SCMs) as a research tool for parameterization development and process studies, the SCM must be supplied with realistic initial profiles, forcing fields, and boundary conditions. We propose a new technique for deriving these required profiles, motivated by the increase in number and scale of high-resolution convection-permitting simulations. We suggest that these high-resolution simulations be coarse grained to the required resolution of an SCM, and thereby be used as a proxy for the true atmosphere. This paper describes the implementation of such a technique. We test the proposed methodology using high-resolution data from the UK Met Office's Unified Model, with a resolution of 4 km, covering a large tropical domain. These data are coarse grained and used to drive the European Centre for Medium-Range Weather Forecast's Integrated Forecasting System (IFS) SCM. The proposed method is evaluated by deriving IFS SCM forcing profiles from a consistent T639 IFS simulation. The SCM simulations track the global model, indicating a consistency between the estimated forcing fields and the true dynamical forcing in the global model. We demonstrate the benefits of selecting SCM forcing profiles from across a large domain, namely, robust statistics, and the ability to test the SCM over a range of boundary conditions. We also compare driving the SCM with the coarse-grained data set to driving it using the European Centre for Medium-Range Weather Forecast operational analysis. We conclude by highlighting the importance of understanding biases in the high-resolution data set and suggest that our approach be used in combination with observationally derived forcing data sets.

On the Dynamical Mechanisms Governing El Nino-Southern Oscillation Irregularity

JOURNAL OF CLIMATE 31 (2018) 8401-8419

J Berner, PD Sardeshmukh, HM Christensen

A Simple Pedagogical Model linking Initial-Value Reliability with Trustworthiness in the Forced Climate Response.

Bulletin of the American Meteorological Society (2017)

TN Palmer, A Weisheimer

Impact of Gulf Stream SST biases on the global atmospheric circulation

CLIMATE DYNAMICS 51 (2018) 3369-3387

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

Skilful Seasonal Predictions of Summer European Rainfall


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

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


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

Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

CLIMATE DYNAMICS 51 (2018) 3333-3350

CH O'Reilly

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