Modulation of Australian Summer Surface Heat Fluxes by Coupled Indian and South Pacific Highs
Observational Evidence and Composite Analysis of Coupled Highs
Keywords:
Subtropical highs, IOHP, SPH, Latent Heat Flux, Sensible Heat Flux, DJF, Ocean-Atmosphere interaction, SAM, IOD, ENSO, Composite AnalysisAbstract
This study investigates the combined influence of the Indian Ocean High Pressure (IOHP) and South Pacific High Pressure (SPH) systems on summer (DJF) surface heat fluxes and regional thermal conditions over the southeastern Indian Ocean and eastern Australia during 1988–2017. Using the Center of Action (COA) framework, years were classified into combined phases, identifying six HH (high IOHP–high SPH) and six LL (low IOHP–low SPH) years. Composite analyses reveal that HH years exhibit drier air, suppressed evaporation, and reduced latent heat flux (LHF), alongside moderate increases in sensible heat flux (SHF), enhancing near-surface warming. Thermodynamic anomalies (Qa, Qs, Ta, Ts) overlaid with wind vectors indicate enhanced boundary-layer stability and strengthened easterly to southeasterly flow, limiting onshore moisture transport and confirming weaker air–sea interaction during HH phases. Correlation analyses show a significant negative association between IOHP and LHF (r = –0.38, p < 0.05) and positive spatial coupling between IOHP longitude and SPH pressure (r = 0.40, p < 0.05), highlighting the role of subtropical highs in modulating surface fluxes. Detrended spatial correlations further indicate IOHP–SPH as primary drivers of LHF and SHF variability, while broader climate modes—SAM, IOD, and ENSO (Niño 3.4, Niño 4)—exert secondary, regionally modulated influences on surface fluxes and seasonal skin temperature. Spatial trend analyses reveal declining LHF across the subtropical southeast Indian Ocean, heterogeneous SHF patterns, and subtle sea level pressure increases, suggesting potential IOHP intensification. Monte Carlo and bootstrapped tests confirm the robustness of these results. Overall, coupled subtropical highs dominate regional ocean–atmosphere energy exchange and surface heating patterns, providing a process-level understanding of how circulation anomalies amplify summer climate extremes in a warming climate.
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