Robust thermodynamic signatures of the Indian ocean high during DJF: A Monte Carlo-based correlation and composite analysis

Abstract

This study investigates the role of the Indian Ocean High Pressure (IOHP) system in modulating surface turbulent heat fluxes—specifically latent heat flux (LHF) and sensible heat flux (SHF)—across the southeastern Indian Ocean during the austral summer (DJF) over the 1988-2017 period. The IOHP is characterized using a center-of-action (COA) framework to quantify its intensity, latitudinal extent, and pressure magnitude. Our findings show that LHF exhibits a statistically significant long-term decline during 1988-2017, whereas SHF demonstrates only weak interannual variability with no consistent trend. This contrasting behavior highlights that evaporative cooling dominates the long-term flux changes, while SHF remains secondary. Long-term analysis reveals a statistically significant downward trend in LHF, closely linked to reductions in IOHP pressure and spatial coverage. In contrast, SHF exhibits weaker variability with no consistent trend. Composite diagnostics based on high and low IOHP phases show suppressed LHF and SHF across 15-30º S and 65-95º E during intensified IOHP years, indicating enhanced atmospheric stability and reduced surface moisture flux. These results are supported by Monte Carlo significance testing. Further, scatterplots illustrate strong inverse relationships between IOHP pressure and LHF (r ≈ –0.93), underscoring the IOHP’s control on evaporation processes. Detrended correlation analyses with dominant teleconnections—including El Niño-Southern Oscillation, the Indian Ocean Dipole, the Southern Annular Mode, and the South Pacific High—highlight mode-specific interactions, with the IOHP acting as a regional mediator of broader climate variability. This work demonstrates that a weakening and contraction of the IOHP could exacerbate surface warming and reduce ocean-atmosphere coupling, with potential implications for regional hydroclimate and energy balance over western Australia.