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Scientific papers

Below is the list of scientific and technical publications stemming out of PRIMAVERA, all published in open access journals.

The resolution sensitivity of Northern Hemisphere blocking in four 25‑km atmospheric global circulation models

R. Schiemann, M.-E. Demory, L. C. Shaffrey, J. Strachan, P. L. Vidale, M. S. Mizielinski, M. J. Roberts, M. Matsueda, M. F. Wehner, T. Jung • December 2016Journal of Climate • doi:10.1175/JCLI-D-16-0100.1 • View publication

Abstract. The aim of this study is to investigate if the representation of Northern Hemisphere blocking is sensitive to resolution in current-generation atmospheric global circulation models (AGCMs). An evaluation is conducted of how well atmospheric blocking is represented in four AGCMs whose horizontal resolution is increased from a grid spacing of more than 100 km to about 25 km. It is shown that Euro-Atlantic blocking is simulated overall more credibly at higher resolution (i.e., in better agreement with a 50-yr reference blocking climatology created from the reanalyses ERA-40 and ERA-Interim). The improvement seen with resolution depends on the season and to some extent on the model considered. Euro-Atlantic blocking is simulated more realistically at higher resolution in winter, spring, and autumn, and robustly so across the model ensemble. The improvement in spring is larger than that in winter and autumn. Summer blocking is found to be better simulated at higher resolution by one model only, with little change seen in the other three models. The representation of Pacific blocking is not found to systematically depend on resolution. Despite the improvements seen with resolution, the 25-km models still exhibit large biases in Euro-Atlantic blocking. For example, three of the four 25-km models underestimate winter northern European blocking frequency by about one-third. The resolution sensitivity and biases in the simulated blocking are shown to be in part associated with the mean-state biases in the models’ midlatitude circulation.

Tropical cyclone interaction with the ocean: the role of high frequency (sub-daily) coupled processes

E. Scoccimarro, P.G. Fogli. K. Reed, S. Gualdi, S.Masina, A. Navarra • December 2016Journal of Climate • doi:10.1175/JCLI-D-16-0292.1 • View publication

Abstract. Through tropical cyclone (TC) activity the ocean and the atmosphere exchange a large amount of energy. In this work possible improvements introduced by a higher coupling frequency are tested between the two components of a climate model in the representation of TC intensity and TC–ocean feedbacks. The analysis is based on the new Centro Euro-Mediterraneo per I Cambiamenti Climatici Climate Model (CMCC-CM2-VHR), capable of representing realistic TCs up to category-5 storms. A significant role of the negative sea surface temperature (SST) feedback, leading to a weakening of the cyclone intensity, is made apparent by the improved representation of high-frequency coupled processes. The first part of this study demonstrates that a more realistic representation of strong TC count is obtained by coupling atmosphere and ocean components at hourly instead of daily frequency. Coherently, the positive bias of the annually averaged power dissipation index associated with TCs is reduced by one order of magnitude when coupling at the hourly frequency, compared to both forced mode and daily coupling frequency results. The second part of this work shows a case study (a modeled category-5 typhoon) analysis to verify the impact of a more realistic representation of the high-frequency coupling in representing the TC effect on the ocean; the theoretical subsurface warming induced by TCs is well represented when coupling the two components at the higher frequency. This work demonstrates that an increased horizontal resolution of model components is not sufficient to ensure a realistic representation of intense and fast-moving systems, such as tropical and extratropical cyclones, but a concurrent increase in coupling frequency is required.

High resolution model intercomparison project (HighResMIP)

R. J. Haarsma, M. Roberts, P. L. Vidale, C. A. Senior, A. Bellucci, Q. Bao, P. Chang, S. Corti, N. S. Fučkar, V. Guemas, J. von Hardenberg, W. Hazeleger, C. Kodama, T. Koenigk, L. R. Leung, J. Lu, J.-J. Luo, J. Mao, M. S. Mizielinski, R. Mizuta, P. Nobre, M. Satoh, E. Scoccimarro, T. Semmler, J. Small, J.-S. von Storch • November 2016Geoscientifc Model Development Discussions • doi:10.5194/gmd-2016-6 • View publication

Short summary. Recent progress in computing power has enabled climate models to simulate more processes in detail and on a smaller scale. Here we present a common protocol for these high-resolution runs that will foster the analysis and understanding of the impact of model resolution on the simulated climate. These runs will also serve as a more reliable source for assessing climate risks that are associated with small-scale weather phenomena such as tropical cyclones.

Impact of ocean resolution on coupled air-sea fluxes and large-scale climate

M. J. Roberts, H. T. Hewitt, P. Hyder, D. Ferreira, S. A. Josey, M. Mizielinski, A. Shelly • October 2016Geophysical Research Letters • doi:10.1002/2016GL070559 • View publication

Abstract. Air-sea fluxes are a crucial component in the energetics of the global climate system. The largest air-sea fluxes occur in regions of high sea surface temperature variability, such as ocean boundary, frontal currents and eddies. In this paper we explore the importance of ocean model resolution to resolve air-sea flux relationships in these areas. We examine the sea surface temperature-wind stress relationship in high-pass filtered observations and two versions of the Met Office climate model with eddy-permitting and eddy-resolving ocean resolutions. Eddy-resolving resolution shows marginal improvement in the relationship over eddy-permitting resolution. However, by focussing on the North Atlantic we show that the eddy-resolving model has significant enhancement of latent heat loss over the North Atlantic Current region, a long-standing model bias. While eddy-resolving resolution does not change the air-sea flux relationship at small scale, the impact on the mean state has important implications for the reliability of future climate projections.

Designing variable ocean model resolution based on the observed ocean variability

D. V. Sein, S. Danilov, A. Biastoch, J. V. Durgadoo, D. Sidorenko, S. Harig, Q. Wang • June 2016Journal of Advances in Modeling Earth Systems • doi:10.1002/2016MS000650 • View publication

Abstract. If unstructured meshes are refined to locally represent eddy dynamics in ocean circulation models, a practical question arises on how to vary the resolution and where to deploy the refinement. We propose to use the observed sea surface height variability as the refinement criterion. We explore the utility of this method (i) in a suite of idealized experiments simulating a wind-driven double gyre flow in a stratified circular basin and (ii) in simulations of global ocean circulation performed with FESOM. Two practical approaches of mesh refinement are compared. In the first approach the uniform refinement is confined within the areas where the observed variability exceeds a given threshold. In the second one the refinement varies linearly following the observed variability. The resolution is fixed in time. For the double gyre case it is shown that the variability obtained in a high-resolution reference run can be well captured on variable-resolution meshes if they are refined where the variability is high and additionally upstream the jet separation point. The second approach of mesh refinement proves to be more beneficial in terms of improvement downstream the midlatitude jet. Similarly, in global ocean simulations the mesh refinement based on the observed variability helps the model to simulate high variability at correct locations. The refinement also leads to a reduced bias in the upper-ocean temperature.