Lagrangian ocean analysis: Fundamentals and practices

OCEAN MODELLING 121 (2018) 49-75

E van Sebille, SM Griffies, R Abernathey, TP Adams, P Berloff, A Biastoch, B Blanke, EP Chassignet, Y Cheng, CJ Cotter, E Deleersnijder, K Doos, HF Drake, S Drijfhout, SF Gary, AW Heemink, J Kjellsson, IM Koszalka, M Lange, C Lique, GA MacGilchrist, R Marsh, CGM Adame, R McAdam, F Nencioli, CB Paris, MD Piggott, JA Polton, S Ruehs, SHAM Shah, MD Thomas, J Wang, PJ Wolfram, L Zanna, JD Zika

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


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

Frazil-ice growth rate and dynamics in mixed layers and sub-ice-shelf plumes

The Cryosphere Copernicus Publications (2018)

D Rees Jones, A Wells

Stochastic representations of model uncertainties at ECMWF: state of the art and future vision


M Leutbecher, S-J Lock, P Ollinaho, STK Lang, G Balsamo, P Bechtold, M Bonavita, HM Christensen, M Diamantakis, E Dutra, S English, M Fisher, RM Forbes, J Goddard, T Haiden, RJ Hogan, S Juricke, H Lawrence, D MacLeod, L Magnusson, S Malardel, S Massart, I Sandu, PK Smolarkiewicz, A Subramanian, F Vitart, N Wedi, A Weisheimer

THE GLOBAL AEROSOL SYNTHESIS AND SCIENCE PROJECT (GASSP): Measurements and Modeling to Reduce Uncertainty


CL Reddington, KS Carslaw, P Stier, N Schutgens, H Coe, D Liu, J Allan, J Browse, KJ Pringle, LA Lee, M Yoshioka, JS Johnson, LA Regayre, DV Spracklen, GW Mann, A Clarke, M Hermann, S Henning, H Wex, TB Kristensen, WR Leaitch, U Poeschl, D Rose, MO Andreae, J Schmale, Y Kondo, N Oshima, JP Schwarz, A Nenes, B Andersrson, GC Roberts, JR Snider, C Leck, PK Quinn, X Chi, A Ding, JL Jimenez, Q Zhang

Storm-Track Shifts under Climate Change: Toward a Mechanistic Understanding Using Baroclinic Mean Available Potential Energy


C Mbengue, T Schneider

Eddy saturation and frictional control of the Antarctic Circumpolar Current


DP Marshall, MHP Ambaum, JR Maddison, DR Munday, L Novak

A family of super congruences involving multiple harmonic sums

International Journal of Number Theory 13 (2017) 109-128

M McCoy, K Thielen, L Wang, J Zhao

Processes Maintaining Tropopause Sharpness in Numerical Models

Journal of Geophysical Research: Atmospheres 122 (2017) 9611-9627

L Saffin, SL Gray, J Methven, KD Williams

©2017. The Authors. Recent work has shown that the sharpness of the extratropical tropopause declines with lead time in numerical weather prediction models, indicating an imbalance between processes acting to sharpen and smooth the tropopause. In this study the systematic effects of processes contributing to the tropopause sharpness are investigated using daily initialized forecasts run with the Met Office Unified Model over a three-month winter period. Artificial tracers, each forced by the potential vorticity tendency due to a different model process, are used to separate the effects of such processes. The advection scheme is shown to result in an exponential decay of tropopause sharpness toward a finite value at short lead times with a time scale of 20–24 h. The systematic effect of nonconservative processes is to sharpen the tropopause, consistent with previous case studies. The decay of tropopause sharpness due to the advection scheme is stronger than the sharpening effect of nonconservative processes leading to a systematic decline in tropopause sharpness with forecast lead time. The systematic forecast errors in tropopause level potential vorticity are comparable to the integrated tendencies of the parametrized physical processes suggesting that the systematic error in tropopause sharpness could be significantly reduced through realistic adjustments to the model parametrization schemes.

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


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

Emergent eddy saturation from an energy constrained eddy parameterisation

OCEAN MODELLING 112 (2017) 125-138

J Mak, DP Marshall, JR Maddison, SD Bachman

The statistical nature of turbulent barotropic ocean jets

OCEAN MODELLING 113 (2017) 34-49

TW David, DP Marshall, L Zanna

Constraining the instantaneous aerosol influence on cloud albedo.

Proceedings of the National Academy of Sciences of the United States of America 114 (2017) 4899-4904

E Gryspeerdt, J Quaas, S Ferrachat, A Gettelman, S Ghan, U Lohmann, H Morrison, D Neubauer, DG Partridge, P Stier, T Takemura, H Wang, M Wang, K Zhang

Much of the uncertainty in estimates of the anthropogenic forcing of climate change comes from uncertainties in the instantaneous effect of aerosols on cloud albedo, known as the Twomey effect or the radiative forcing from aerosol-cloud interactions (RFaci), a component of the total or effective radiative forcing. Because aerosols serving as cloud condensation nuclei can have a strong influence on the cloud droplet number concentration (Nd ), previous studies have used the sensitivity of the Nd to aerosol properties as a constraint on the strength of the RFaci. However, recent studies have suggested that relationships between aerosol and cloud properties in the present-day climate may not be suitable for determining the sensitivity of the Nd to anthropogenic aerosol perturbations. Using an ensemble of global aerosol-climate models, this study demonstrates how joint histograms between Nd and aerosol properties can account for many of the issues raised by previous studies. It shows that if the anthropogenic contribution to the aerosol is known, the RFaci can be diagnosed to within 20% of its actual value. The accuracy of different aerosol proxies for diagnosing the RFaci is investigated, confirming that using the aerosol optical depth significantly underestimates the strength of the aerosol-cloud interactions in satellite data.

Impact of Atmospheric Blocking on South America in Austral Summer

JOURNAL OF CLIMATE 30 (2017) 1821-1837

RR Rodrigues, T Woollings

Grand European and Asian-Pacific multi-model seasonal forecasts: maximization of skill and of potential economical value to end-users

Climate Dynamics (2017) 1-20

A Alessandri, MD Felice, F Catalano, JY Lee, B Wang, DY Lee, JH Yoo, A Weisheimer

© 2017 Springer-Verlag GmbH Germany Multi-model ensembles (MMEs) are powerful tools in dynamical climate prediction as they account for the overconfidence and the uncertainties related to single-model ensembles. Previous works suggested that the potential benefit that can be expected by using a MME amplifies with the increase of the independence of the contributing Seasonal Prediction Systems. In this work we combine the two MME Seasonal Prediction Systems (SPSs) independently developed by the European (ENSEMBLES) and by the Asian-Pacific (APCC/CliPAS) communities. To this aim, all the possible multi-model combinations obtained by putting together the 5 models from ENSEMBLES and the 11 models from APCC/CliPAS have been evaluated. The grand ENSEMBLES-APCC/CliPAS MME enhances significantly the skill in predicting 2m temperature and precipitation compared to previous estimates from the contributing MMEs. Our results show that, in general, the better combinations of SPSs are obtained by mixing ENSEMBLES and APCC/CliPAS models and that only a limited number of SPSs is required to obtain the maximum performance. The number and selection of models that perform better is usually different depending on the region/phenomenon under consideration so that all models are useful in some cases. It is shown that the incremental performance contribution tends to be higher when adding one model from ENSEMBLES to APCC/CliPAS MMEs and vice versa, confirming that the benefit of using MMEs amplifies with the increase of the independence the contributing models. To verify the above results for a real world application, the Grand ENSEMBLES-APCC/CliPAS MME is used to predict retrospective energy demand over Italy as provided by TERNA (Italian Transmission System Operator) for the period 1990–2007. The results demonstrate the useful application of MME seasonal predictions for energy demand forecasting over Italy. It is shown a significant enhancement of the potential economic value of forecasting energy demand when using the better combinations from the Grand MME by comparison to the maximum value obtained from the better combinations of each of the two contributing MMEs. The above results demonstrate for the first time the potential of the Grand MME to significantly contribute in obtaining useful predictions at the seasonal time-scale.

Scale-aware deterministic and stochastic parametrizations of eddy-mean flow interaction

Ocean Modelling 111 (2017) 66-80

L Zanna, PGL Porta Mana, J Anstey, T David, T Bolton

© 2017 The Authors The role of mesoscale eddies is crucial for the ocean circulation and its energy budget. The sub-grid scale eddy variability needs to be parametrized in ocean models, even at so-called eddy permitting resolutions. Porta Mana and Zanna (2014) propose an eddy parametrization based on a non-Newtonian stress which depends on the partially resolved scales and their variability. In the present study, we test two versions of the parametrization, one deterministic and one stochastic, at coarse and eddy-permitting resolutions in a double gyre quasi-geostrophic model. The parametrization leads to drastic improvements in the mean state and variability of the ocean state, namely in the jet rectification and the kinetic-energy spectra as a function of wavenumber and frequency for eddy permitting models. The parametrization also appears to have a stabilizing effect on the model, especially the stochastic version. The parametrization possesses attractive features for implementation in global models: very little computational cost, it is flow aware and uses the properties of the underlying flow. The deterministic coefficient is scale-aware, while the stochastic parameter is scale- and flow-aware with dependence on resolution, stratification and wind forcing.

The link between eddy-driven jet variability and weather regimes in the North Atlantic-European sector


E Madonna, C Li, CM Grams, T Woollings

Drivers of uncertainty in simulated ocean circulation and heat uptake

Geophysical Research Letters 44 (2017) 1402-1413

MB Huber, L Zanna

©2017. The Authors. The impact of uncertainties in air-sea fluxes and ocean model parameters on the ocean circulation and ocean heat uptake (OHU) is assessed in a novel modeling framework. We use an ocean-only model forced with the simulated sea surface fields of the CMIP5 climate models. The simulations are performed using control and 1% CO 2 warming scenarios. The ocean-only ensemble adequately reproduces the mean Atlantic Meridional Overturning Circulation (AMOC) and the zonally integrated OHU. The ensemble spread in AMOC strength, its weakening, and Atlantic OHU due to different air-sea fluxes is twice as large as the uncertainty range related to vertical and mesocale eddy diffusivities. The sensitivity of OHU to uncertainties in air-sea fluxes and model parameters differs vastly across basins, with the Southern Ocean exhibiting strong sensitivity to air-sea fluxes and model parameters. This study clearly demonstrates that model biases in air-sea fluxes are one of the key sources of uncertainty in climate simulations.

Seasonal Climate Prediction: A New Source of Information for the Management of Wind Energy Resources


V Torralba, FJ Doblas-Reyes, D MacLeod, I Christel, M Davis