Preprints
https://doi.org/10.5194/os-2021-94
https://doi.org/10.5194/os-2021-94

  28 Sep 2021

28 Sep 2021

Review status: this preprint is currently under review for the journal OS.

Passive tracer advection in the equatorial Pacific region: statistics, correlations, and a model of fractional Brownian motion

Imre M. Jánosi1,2, Amin Padash1, Jason A. C. Gallas1,3, and Holger Kantz1 Imre M. Jánosi et al.
  • 1Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden, Germany
  • 2Department of Water and Environmental Policy, Faculty of Water Sciences, University of Public Service, Ludovika tér 2, H-1083 Budapest, Hungary
  • 3Instituto de Altos Estudos da Paraíba, Rua Silvino Lopes 419-2502, 58039-190 João Pessoa, Brazil

Abstract. Evaluating passive tracer advection is a common tool to study flow structures, particularly Lagrangian trajectories ranging from molecular scales up to the atmosphere and oceans. Here we report on numerical experiments in the region of equatorial Pacific (20° S–20° SN), where 6600 tracer parcels are advected from a regular initial configuration during periods of one year, 25 years altogether. We demonstrate that the strength of the advection exhibits a surprisingly large year by year variability. Furthermore an analysis of cross-correlations between advection strength and El-Niño and Southern Oscillation Indices (SOI) reveal a significant anti-correlation between advection intensity and ONI (Oceanic Niño Index) and a weaker positive correlation with SOI, both with a time lag of about 3 months (the two indices are strongly anti-correlated near real-time). The statistical properties of advection (first passage time, and mean squared displacement) suggest that the westward moving tracers can be mapped into a simple 1D stochastic process, namely fractional Brownian motion. We fit the model parameters and show by numerical simulations of the fractional Brownian motion model that it is able to well reproduce the observed statistical properties of the tracers' trajectories.

Imre M. Jánosi et al.

Status: open (until 23 Nov 2021)

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Imre M. Jánosi et al.

Imre M. Jánosi et al.

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Short summary
Spectacular climatic phenomena such as El Nino – La Nina oscillations are connected with large scale rearrangement of the oceanic surface flow patterns. In order to get a better insight into the dynamics of such changes, we performed numerical experiments on the advection of 6600 water parcels in the focus area. Surface flow fields are from the the AVISO data bank. One of the findings is that the marked changes in drifts occur after the onset of an El Nino period with a time lag of 3 months.