Piecewise Evolutionary Spectra: A Practical Approach to Understanding Projected Changes in Spectral Relationships Between Circulation Modes and Regional Climate Under Global Warming
Creators: name: Putrasahan, D. A.
name: Von Storch, J.‐S.
Publisher: name: FID GEO
Year: 2021

description: Regional climate variability is strongly related to large‐scale circulation modes. However, little is known about changes in their spectral characteristics under climate change. Here, we introduce piecewise evolutionary spectra to quantify time‐varying variability and co‐variability of climate variables, and use ensemble periodograms to estimate these spectra. By employing a large ensemble of climate change simulations, we show that changes in the variability and relationships of the North Atlantic Oscillation (NAO) and regional surface temperatures are disparate on individual timescales. The relation between NAO and surface temperature over high‐latitude lands weakens the most on 20‐year timescales compared to shorter timescales, whereas the relation between NAO and temperature over subtropical North Africa strengthens more on shorter timescales than on 20‐year timescales. These projected evolution and timescale‐dependent changes shed new light on the controlling factors of circulation‐induced regional changes. Accounting for them can lead to the improvement of future regional climate predictions.
description: Plain Language Summary: Large‐scale atmospheric circulation modes influence regional climate variability. For example, the North Atlantic Oscillation (NAO) is a circulation mode closely linked to surface temperatures variations over Europe, Africa, and North America. However, under global warming, changes in regional climate variability and their relation to circulation modes (co‐variability) can evolve differently and disparately depending on timescales. Here, we use the theory of evolutionary spectra to quantify these nonstationary changes and present a novel approach to estimate such changes on various timescales. The estimation approach is based on a large ensemble of climate change simulations. We show that changes in the NAO and regional surface temperature variability and their relationships evolve differently on individual timescales. On 20‐year timescales, co‐variability between NAO and surface temperature weakens over high‐latitude lands surrounding the northern North Atlantic, whereas the corresponding co‐variability on shorter timescales strengthens over subtropical North Africa. These differing evolution and timescale‐dependent changes shed new light on the controlling factors of circulation‐induced regional changes. Taking them into account can lead to the improvement of future regional climate predictions.
description: Key Points: We define piecewise evolutionary spectra (special case of evolutionary spectra) to quantify time‐varying second moments in a warming climate. We introduce ensemble periodograms derived from a large ensemble as consistent estimators of piecewise evolutionary spectra. We find time‐dependent and timescale‐dependent changes in relations between NAO and surface temperature.
description: EU Commission Horizon 2020: PRIMAVERA
description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
description: Max‐Planck‐Gesellschaft http://dx.doi.org/10.13039/501100004189