Costas Varotsos Discusses Ozone & Temperature Analyses

Emerging Research Fronts Commentary, August 2011

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Costas VarotsosTherefore we have started our analysis by asking if the ozone concentration in the atmosphere at a given instant has any correlation with the ozone value at a later time (even after many years). This would enable us to provide forecasts of future ozone concentrations for input into climate models. If ozone values at different times are correlated, then the ozone time series exhibits long-range correlations (displaying scaling dynamics). The latter has the following meaning: a correctly rescaled subset of the original ozone time series resembles the original ozone time series (persistence).

The novel aspect of this study is that the basic global climate-forming parameters (e.g., ozone concentration and air temperature) obey scaling dynamics with opposite behavior in their temporal evolution, notably: for ozone fluctuations, persistence at long time scales is strongest in tropics, but weaker in mid-latitude, while temperature fluctuations show strong persistence in mid-latitudes, and random noise in the tropics.

We sought to understand various mechanisms that might account for the persistence found in ozone and temperature. Stronger persistence is, in general, a result of either stronger positive feedbacks or larger inertia. Thus, the reduced temperature persistence in the tropics at long time scales, compared to that in the mid-latitudes could be connected to the poleward increase in climate sensitivity (due to latitude-dependent climate feedbacks) predicted by the global climate models.

Nowadays, although many coupling mechanisms between ozone and temperature are known, the net effect of the interactions and feedbacks is only poorly understood and quantified.

"The inclusion into the Intergovernmental Panel on Climate Change models of the scaling behavior of the climate system components can offer rich insight into the climate temporal evolution dynamics and may also give us key information about the unknown interactive mechanisms."

This work thus suggests a new way of thinking about the climate change dynamics, contributing to the growing body of evidence that confidence in the predictions of the climate-forming factors by the long-term climate and atmospheric dynamics modeling would be improved.

SW: How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?

I became involved in this research on my sabbatical leave as Visiting Professor to the Department of Atmospheric and Oceanic Science, University of Maryland, College Park, USA. My first paper on the subject entitled: "Power-law correlations in column ozone over Antarctica," (International Journal of Remote Sensing 26[16]: 3333–42, 20 August 2005) had been my first effort to explore the intrinsic dynamics in column ozone, illustrating the role of planetary waves in the scaling characteristics of the spatio-temporal variability of the Antarctic ozone hole.

The pioneer work done by the group of S. Lovejoy (e.g., "Area-perimeter relation for rain and cloud areas," Science 216[4542]: 185–7, 1982) on scaling analysis of atmospheric data was my first challenge on this field. Later on, Tuck and Hovde ("Fractal behavior of ozone, wind and temperature in the lower stratosphere," Geophys. Res. Lett. 26: 1271–4, 1999) by applying a measure from fractal geometry to time series of airborne observations of ozone and meteorological quantities in the lower stratosphere suggested that ozone and horizontal wind speed behave as random, self-affine fractals (having anisotropic scaling, in distinction from isotropic scaling in self-similarity).

In addition, they found that horizontal wind direction behaves persistently (positive correlation among neighboring time intervals), being thus a candidate for multifractality.

A particular challenge in this work for me was the necessity to contemplate in an interdisciplinary manner. Along the way, and while experimenting with long-range correlations on a global scale, I thought to use chaos, fractals, and complexity theory to solve difficult problems in climate physics with amazing simplicity. Building on pioneering work done by many other people on the other scientific fields, I studied the temporal evolution of the complex climate system by employing the detrended fluctuation analysis (DFA) with the help of some of my colleagues. The most challenging aspect was responding to the open question that the multi-complexity of the climate system physics could be solved as a scaling problem.

SW: Where do you see your research leading in the future?

Despite the progress in climate science dynamics, a number of related problems remain unsolved so far and there is a necessity for a more comprehensive and integrative consideration of the complexity of all interactive processes, including the chemistry and dynamics of the atmosphere.

In order to reduce the level of existing uncertainties, the modeling of nature-society interaction is urgently required with long-term, non-linear changes in the climate system taken into account. In addition, various advances in different branches of modern physics, which are now occasionally used in climate research, would systematically need to be employed, in order to explore unknown features of the climate non-linear dynamics.

For instance, one of the main uncertainties is whether CO2 observations remain residually correlated with one another even after many years (long-range dependence). We have made progress on this front suggesting, among others, that the fluctuations of carbon dioxide concentrations exhibit long-range power-law correlations with lag times ranging from four months to eleven years, which correspond to 1/f noise (mean DFA slope is unity).

We have shown that this scaling comes from the time evolution and not from the values of the CO2 data. Therefore the long-range correlations in the atmospheric CO2 can help in recognition of anthropogenically induced changes caused by increased CO2 emissions to the atmosphere on the background of natural atmosphere changes.

Recently, we also proved that the global tropopause (assumed as fingerprint of human effects on climate), exhibits scaling behavior. It introduces a level of complexity that requires a new level of thinking to resolve climate change problems.

" intriguing future direction for my group is to thoroughly investigate the mechanisms by which the persistence in the global ozone sphere prevails through the inclusion of additional variables in the analysis "

On the basic research side, one intriguing future direction for my group is to thoroughly investigate the mechanisms by which the persistence in the global ozone sphere prevails through the inclusion of additional variables in the analysis. This will be done in the frame of our major concern to give a better understanding of the self-organized criticality in the global change dynamics.

SW: Do you foresee any social or political implications for your research?

Indirectly "yes," by helping to improve the climate models which are used as a basis for advice to decision makers on global warming/climate change.

Climatologists can compare the simulated data from the available climate models with the actual experimental data from different facilities, on the basis of the observed long-range correlations. These comparisons will help climatologists to better understand the meaning of the experimental data and distinguish the interesting effects of the unknown geophysics from the complicated effects of the known geophysical processes.

For instance, models that hope to predict global climate parameters over long time scales should be able to duplicate the long-range correlations of these parameters shown with modern tools of Statistical Physics (e.g. DFA analysis). Successful simulation of the DFA curves of observed data would be a versatile tool to enhance confidence in model climate predictions.

The Intergovernmental Panel on Climate Change (IPCC) makes extensive use of the outputs from such models in producing its reports, which are intended to guide policymakers at national and international levels, although there are people who are critical of the IPCC and its heavy reliance on modeling projections. The inclusion into the IPCC models of the scaling behavior of the climate system components can offer rich insight into the climate temporal evolution dynamics and may also give us key information about the unknown interactive mechanisms.End

Professor Costas Varotsos
University of Athens, Faculty of Physics
Department of Applied Physics, Laboratory of Upper Air
University of Athens Climate Research Group
Athens, Greece

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  • Read a New Hot Paper Commentary (Mar. 2006) by Costas Varotsos.

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