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Periodic Report Summary 1 - ATLANTIC CLIMATE (Variability and Trends in Atlantic Climate)

Project overview:

The North Atlantic Oscillation (NAO) is affected by processes internal to the troposphere, and by “external” effects from the stratosphere above. In today’s climate, it is not understood what fraction of NAO variability is attributable to the stratosphere. Understanding future climate—how the NAO will change, how jets and storm tracks will shift—is a difficult research challenge. However, it is an important challenge, because without a fundamental understanding of the physical processes involved, and without models that realistically simulate these changes over time, we are left with low confidence in climate projections—especially how climate will change over the large European sector. This topic is highly relevant to society.

Summary description of the project objectives,:

1) To exploit recent advances in our understanding of stratospheric influence on the NAO to quantify the coupling in observational data;
2) To define indices using climate model output (e.g., IPCC-class models) from standard publically-available model output;
3) To quantify and compare the degree to which climate models simulate the observed vertical coupling;
4) To extend the above results to movement of the tropospheric jet streams and associated storm tracks, with emphasis on regional changes (e.g., over Europe);
5) The final goal of this research is to identify climate model characteristics that affect the realism of both the vertical coupling and the shifts in jets and storm tracks.

Description of work performed and main results achieved so far

1: Process Observational Data.
Extend detailed study of stratosphere–troposphere coupling with current data sets. Initially, the calculations will be performed using the same observational reanalysis data (ERA-40) used for Figure 2. These calculations will be updated with the much higher resolution ERA-Interim data (Dee et al., 2011). One advantage of these reanalyses is that the desired fields (e.g., potential vorticity) are available at high spatial resolution and time resolution of daily or better.

2: Process climate model data.
Goal: Extend results of Step 1 to climate models.
Testing our ideas on climate model runs (e.g., IPCC CMIP5), extending to ~2100, will allow the examination of how a changing climate will affect both stratospheric variability, the mean stratospheric circulation, and coupling to the troposphere. Model runs have been obtained from on-line archives. Models must do credible job of simulating 1) wave propagation and breaking, and 2) a realistic residual circulation and temperature anomalies. We have also processed several runs from a “dry dynamical core.” We are presently trying to understand these results.
Some climate models match the observations very well. Others produce too little tropospheric amplification, while other models amplify stratospheric effects too much. A key final project goal is to understand why. We have developed and tested a metric of stratosphere–troposphere coupling, which is straightforward to compute from nearly any model (or observations).
Expected final results and their potential impact and use (including the socio-economic impact and the wider societal implications of the project so far).

According to the latest Intergovernmental Panel on Climate Change report, the Mediterranean basin represents one of the most important hot spots of climate change in the world, with recent trends toward a hotter and drier climate being related to changes in atmospheric circulation patterns. The North Atlantic Oscillation (NAO) exerts a clear influence throughout the year, although with stronger intensity and extension during winter. As discussed in a recent workshop, socio-economic impacts of NAO variability include (1) natural hazards, including droughts, severe precipitations, floods, heat waves, and cold spells; (2) vegetation activity and agriculture production; (3) natural ecosystems and environment, including forest dynamics, fisheries, dynamics of animal populations, and air quality; (4) geomorphology, including landslides and debris flows, erosivity mechanisms, and surface erosion processes; and (5) renewable energies production, including hydraulic, and solar .
A dynamical understanding of stratosphere–troposphere coupling is an important component of understanding the sources of future climate change. Without such an understanding, we do not know which (if any) IPCC climate models are accurately simulating the stratospheric contribution to climate change during the rest of this century. We propose to derive diagnostics that are metrics of how well individual models simulate stratosphere–troposphere coupling.

Reported by

United Kingdom


Life Sciences
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