Relative Roles of Cloud, Radiative, and Solar–Geomagnetic Processes in Modulating Convective Available Potential Energy across Nigerian Climate Zones

Abstract

This study examines the effects of cloud properties, solar thermal radiation, and solar–geomagnetic indices on convective available potential energy (CAPE) across Nigeria’s tropical rainforest (Af), tropical monsoon (Am), and tropical savanna (Aw) climate zones from 1994 to 2024. Daily reanalysis and satellite-derived datasets were aggregated into climatological means. Statistical relationships were analyzed using lag-correlation and Normalized information flow (NIF), based on transfer entropy, was used to quantify directional causal influence among variables to quantify directional influences among variables. Mean CAPE values are highest in the Af and Am zones, frequently exceeding 2000–3000 J kg⁻¹ during peak convective periods, while the Aw zone exhibits lower and more seasonal CAPE, typically ranging from 500 to 1800 J kg⁻¹. Cloud fraction remains persistently high in the Af and Am zones (>0.60), coinciding with enhanced convective precipitation (CONPRE) and pronounced CAPE variability. Solar thermal radiation downward (STRD) contributes indirectly through surface heating, with shortwave fluxes of approximately 220–260 W m⁻² during the dry season, particularly influencing CAPE in the Aw zone. In contrast, solar and geomagnetic indices, including F10.7obs (FL) and Ap, show low mean values and weak correlations with CAPE. Information flow analysis indicates that cloud and precipitation processes account for more than 60% of CAPE variability, whereas solar and geomagnetic parameters contribute less than 10%. Collectively, CAPE variability acrossNigeria is dominated by internal atmospheric processes, with limited direct modulation by external solar–geomagnetic forcing.