Identification and discrimination of patterns of dynamical influences within the climate system by means of complex network approaches

Abstract:

Complex network theory provides a powerful toolbox for studying the structure of statistical interrelationships between multiple time series. In this work, we demonstrate how networks constructed from fields of climatological observables like surface air temperatures, geopotential height or vertically integrated moisture divergence can be used for characterizing the evolving spatio-temporal correlation structure of the Earth’s climate system and the time-dependent coupling between different variables.

As a first application, we study the temporal variability of several network characteristics based on global surface air temperature data. The corresponding evolving climate network properties provide a functional discrimination between different large-scale climatological situations associated with different phases of the El Nino Southern Oscillation (ENSO), as well as reorganizations of dynamical similarity patterns following localized perturbations of the global climate system after strong volcanic eruptions. As a particular application, we demonstrate the distinction between the two previously known El Nino types based on global climate network properties and discuss implications for the possible existence of different La Nina types.

A second example concerns the spatio-temporal organization of strong evapotranspiration events over South America. By constructing climate networks based on the synchronicity of extreme values in the vertically integrated moisture flux at different locations, we obtain distinct spatial patterns associated with the organization of strong atmospheric upwelling events. Again, our results exhibit a distinct imprint of the phasing of ENSO.

Finally, we demonstrate how the climate network approach can be extended to studying the interaction structure between two climatological fields. As an example, we discuss the cross-linkage structure of mid-to-high latitude northern hemispheric ocean-atmosphere interactions during summer and winter season, which displays some interesting spatial structures not previously reported.