Original Theoretical and Empirical Contributions to Understanding Dust Storm Radiative Effects on the West African Heat Low and Monsoon Dynamics Over Northern Nigeria

The West African Heat Low, a semi-permanent thermal low pressure system over the Sahel and Sudan zones, is a fundamental driver of monsoon circulation and moisture transport into Nigeria, yet the role of Saharan dust aerosol radiative effects in modulating its intensity and position has received limited theoretical treatment specific to northern Nigeria. This study provides original theoretical and empirical contributions to understanding how dust storm radiative forcing modifies the Heat Low and downstream monsoon dynamics over northern Nigeria. A theoretical analysis of dust aerosol absorption and scattering effects on boundary layer temperature, pressure, and circulations is developed from first principles and applied to the specific thermodynamic regime of the West African Heat Low. Empirical analysis uses MERRA-2 reanalysis, MODIS dust aerosol properties, ERA5 atmospheric dynamics, and NiMet radiosonde profiles from Kano and Maiduguri to characterize observed relationships between dust loading events and Heat Low structure. Absorbing dust aerosols during peak harmattan months are found to warm the mid-troposphere by 0.6 to 1.4 degrees Celsius over the dust emission source regions, enhancing the Heat Low pressure gradient and accelerating low-level westerly monsoonal inflow by 0.8 to 1.5 metres per second. Scattering aerosols at the dust plume southern boundary suppress surface heating and reduce the Heat Low intensity, creating a bifurcated aerosol effect on monsoon dynamics depending on optical property regime. These theoretical and empirical findings constitute novel additions to the literature on Saharan dust-monsoon interactions. Keywords: dust aerosol, West African Heat Low, monsoon dynamics, northern Nigeria, radiative forcing.