A simple subtropical high‐pressure system index over the South Atlantic

• Published in: Atmospheric science letters 2024-11, Vol.25 (11), p.n/a
• Main Authors: Quagraine, Kwesi A., Hewitson, Bruce, Nkrumah, Francis, Quagraine, Kwesi T., Egbebiyi, Temitope S.
• Format: Article
• Language: English
• Subjects: Annual variations; Centroids; climate; Climate change; Climate science; Climate variability; Climatic indexes; Computation; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Flexibility; High pressure; high pressure index; La Nina; Position measurement; Precipitation; Rain; regional climate; Regional climates; Sea level; Sea level pressure; Seasonal variations; Southern Oscillation; Subtropical climates; subtropical highs; synoptic; Winter
• ISSN: 1530-261X; 1530-261X
• DOI: 10.1002/asl.1266

This research introduces a novel index for the South Atlantic High Pressure (SAHP) system to enhance understanding of regional climate variability and change. Subtropical highs significantly influence regional climates, yet comprehensive indices to measure their behaviours are lacking. Utilizing ERA5 reanalysis data from 1940 to 2023, the proposed index estimates a weighted centroid of the area surrounding the maximum sea level pressure within a 3 hPa range. This method ensures robustness and flexibility in contiguous area estimation specific to subtropical high events. Results showed the index effectively reflects the position and intensity of the SAHP. The study reveals that latitudinal variability of the SAHP has a strong unimodal structure, whereas longitudinal variability exhibits a bimodal structure. Seasonal patterns of the index show noticeable changes, with winter (JJA) and spring (SON) months having relatively high index values compared to summer (DJF) and autumn (MAM) months, underscoring the intra‐annual variability of the SAHP index. During ENSO events, the mean centroid position of the SAHP shifts significantly, moving westwards and polewards during El Niño and showing greater stability during La Niña. The index, with minimal computation requirements and flexibility, can be applied across diverse datasets, aiding in the assessment of future subtropical high changes. The spatially contiguous seasonal climatologies of the high‐pressure area within 3 hPa of the domain maximum (shading) with centroid position (red triangle) for the period 1940–2023. Cx and Cy denote the corresponding seasonal climatological centroid longitude and latitude for the spatially contiguous area.