Existence of a second structural break in the variance of F_ovS (ORAS5)

Ascertain whether a second structural break exists in the variance of the ORAS5‑derived F_ovS time series, as suggested by the cumulative sum of squared trend residuals analysis, and determine if this putative break reflects a real change in variability.

Background

Using the ORAS5 product for F_ovS (1958–2022), the paper applies an HP‑filter to estimate the trend and examines the cumulative sum of squared residuals to assess variance changes. A clear structural break is identified in the late 1990s, with higher variance thereafter.

The author notes a possible second change—likely a variance decrease—visible in the cumulative plot, but states it is too early to conclude whether this apparent break is real, leaving its existence as an open question.