Nonlinear stratospheric variability: multifractal detrended fluctuation analysis and singularity spectra

TL;DR

This study uses multifractal detrended fluctuation analysis to characterize the complex, scale-dependent variability of the stratosphere, revealing differences between hemispheres and limitations of current models.

Contribution

It applies multifractal analysis to compare re-analysis data and models, highlighting hemispheric differences and model shortcomings in capturing stratospheric variability.

Findings

Northern Hemisphere shows a transition from multifractal to monofractal behavior around one year.

Southern Hemisphere exhibits a narrower range of multifractality.

Models reproduce low-frequency variability but miss short-term dynamics.

Abstract

Characterising the stratosphere as a turbulent system, temporal fluctuations often show different correlations for different time scales as well as intermittent behaviour that cannot be captured by a single scaling exponent. In this study, the different scaling laws in the long term stratospheric variability are studied using Multifractal de-trended Fluctuation Analysis. The analysis is performed comparing four re-analysis products and different realisations of an idealised numerical model, isolating the role of topographic forcing and seasonal variability, as well as the absence of climate teleconnections and small-scale forcing. The Northern Hemisphere (NH) shows a transition of scaling exponents for time scales shorter than about one year, for which the variability is multifractal and scales in time with a power law corresponding to a red spectrum, to longer time scales, for which the variability is monofractal and scales in time with a power law corresponding to white noise. Southern Hemisphere (SH) variability also shows a transition at annual scales. The SH also shows a narrower dynamical range in multifractality than the NH, as seen in the generalised Hurst exponent and in the singularity spectra. The numerical integrations show that the models are able to reproduce the low-frequency variability but are not able to fully capture the shorter term variability of the stratosphere.