13 Apr 2023
 | 13 Apr 2023
Status: this preprint is currently under review for the journal NPG.

Superstatistical analysis of sea surface currents in the Gulf of Trieste, measured by HF Radar, and its relation to wind regimes, using the maximum entropy principle

Sofia Flora, Laura Ursella, and Achim Wirth

Abstract. Two years (2021–2022) of High Frequency Radar (HFR) sea surface current data in the Gulf of Trieste (Northern Adriatic Sea) are analysed. Two different time scales are extracted using superstatistical formalism: a relaxation time and a larger timescale over which the system is gaussian. A new analytical universality class of Probability Density Functions (PDFs) is proposed for ocean current data combining a gaussian PDF for the fast fluctuations and a convolution of exponential PDFs for the slowly evolving variance of the gaussian. The Gaussian PDF has maximum entropy for real-valued variables with a given variance. If a positive variable, as is a variance, has a specified mean, the maximum entropy solution is an exponential PDF. Here it is the sum of two exponentials, reflecting the two spatial degrees of freedom.

In the Gulf of Trieste there are three distinct main wind forcing regimes: Bora, Sirocco and low wind, leading to a succession of different sea current dynamics on different time scales. The universality class PDF successfully fits the observed data over the two observation years and also for each wind regime separately with a different variance of the variance PDF, which is the only free parameter in all the fits.

Sofia Flora et al.

Status: open (until 08 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on npg-2023-9', Anonymous Referee #1, 22 May 2023 reply
  • RC2: 'Comment on npg-2023-9', Anonymous Referee #2, 23 May 2023 reply

Sofia Flora et al.

Sofia Flora et al.


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Short summary
Increasing amount of data allows us today to move from considering low order moments of fluctuating observations to their Probability Density Functions (PDFs). We found a new analytic form of the PDF for two years of sea surface current increments data in the Gulf of Trieste (Northern Adriatic Sea) using the maximum entropy principle twice: in a short timescale and in a longer one. The data for the different wind forcings follow the same analytic PDF form, pointing towards a universal behaviour.