The El Nino-Southern Oscillation is a quasi-periodic climate pattern with irregular cycles of 2-7 years. Standard visualization — time series plots, spectral analysis, phase space diagrams — represents it in visual dimensions. Sonification converts it to sound (arXiv:2602.14560).
The researchers mapped 154 years of ENSO temperature data onto two traditional Javanese musical scales: pelog (seven tones, uneven intervals) and slendro (five tones, roughly equal intervals). Four compositional strategies were tested: single mode, alternating modes, polyphonic, and sequential. Recurrence-based diagnostics, convex hull geometry, and coupling analysis measured how well each sonification preserved the oscillation's dynamical structure.
Alternating modes captured ENSO's oscillatory character most faithfully. The mode switching — pelog for warm phases, slendro for cool phases, or vice versa — encoded the phase transition that is ENSO's defining feature. Polyphonic arrangements explored broader acoustic space but smeared the phase distinction. Single modes preserved temporal structure but lost the binary character of the oscillation.
The two scale families — pelog and slendro — produced opposite relationships between spectral brightness and energy. The same data, filtered through different tonal systems, emphasized different dynamical features. The scale is not a neutral medium; it's a filter that selects which aspects of the data become perceptible.
The structural insight: a musical scale is a discretization scheme with built-in biases. Pelog's uneven intervals create different sensitivities at different parts of the temperature range. Slendro's even intervals treat all ranges equally. The choice of scale is a modelling decision disguised as an aesthetic one. Sonification doesn't just represent data audibly — it projects data through a tonal filter that can amplify or suppress structural features. The medium is not transparent. The gamelan hears the climate differently than a piano would.