Analysis of the mid-latitude weather regimes in the 200-year control integration of the SINTEX model

S Gualdi S Gualdi,A Navarra A Navarra,S Corti S Corti

doi:10.4401/ag-3386

Abstract

Recent results indicate that climate predictions require models which can simulate accurately natural circulation regimes and their associated variability. The main purpose of this study is to investigate whether (and how) a coupled model can simulate the real world weather regimes. A 200-year control integration of a coupled GCM (the «SINTEX model») is considered. The output analysed consists of monthly mean values of Northern Hemisphere extended winter (November to April) 500-hPa geopotential heights. An Empirical Orthogonal Function (EOF) analysis is first applied in order to define a reduced phase space based on the leading modes of variability. Therefore the principal component PDF in the reduced phase space spanned by two leading EOFs is computed. Based on a PDF analysis in the phase space spanned by the leading EOF1 and REOF2, substantial evidence of the nongaussian regime structure of the SINTEX northern winter circulation is found. The model Probability Density Function (PDF) exhibits three maxima. The 500-hPa height geographical patterns of these density maxima are strongly reminiscent of well-documented Northern Hemisphere weather regimes. This result indicates that the SINTEX model can not only simulate the non-gaussian structure of the climatic attractor, but is also able to reproduce the natural modes of variability of the system.

Highlights

Previous studies have assumed that anthropogenic climate change can be understood in terms of a linear superposition of a response to external forcing on unchanging background variability
Taking into account the limitations imposed by the «coarse» atmospheric horizontal resolution, the overall performance of the SINTEX model in simulating the leading patterns of the Northern Hemisphere low-frequency variability is quite accurate
It was found that the SINTEX model can simulate the non-gaussian structure of the climatic attractor, but is able to reproduce the natural modes of variability of the system

Summary

Introduction

Previous studies have assumed that anthropogenic (and natural) climate change can be understood in terms of a linear superposition of a response to external forcing on unchanging background variability While this may be an adequate description of large-scale temperature changes, there is evidence that changes in atmos-. This new conceptual model has important implications both for the interpretation of the observed signal and for future climate change Considering this nonlinear perspective, the prediction of anthropogenic climate change require models which can simulate accurately natural circulation regimes and their associated variability, even though the dominant timescale of such variability may be much shorter than the climate change signal itself.

Simulation of the wintertime climatology

Weather regimes in the SINTEX model

Findings

Concluding remarks