Awoleye et al. (2025) Moisture and dust in motion: the dual role of integrated vapour transport over West Africa

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-11-21
• Authors: Peace Olubukunmi Awoleye, Adeyemi A. Adebiyi, Babatunde J. Abiodun, Ifeoluwa Adebowale Balogun, Ademola Akinbobola, Ayodeji Oluleye, Vincent O. Ajayi
• DOI: 10.1007/s00704-025-05913-1

Research Groups

• Department of Meteorology and Climate Science, Federal University of Technology, Akure, Nigeria
• University of California, Merced, USA
• Climate System and Analysis Group, Department of Environmental and Geographical Sciences, University of Cape Town, South Africa
• Nansen-Tutu Research Centre for Marine Environment, Department of Oceanography, University of Cape Town, South Africa
• Department of Geography, Geoinformatics and Meteorology, University of Pretoria, South Africa
• West Africa Science Service Centre on Climate Change and Adapted Land-use DRP-WACS, Federal University of Technology, Akure, Nigeria

Short Summary

This study comprehensively evaluates Integrated Vapour Transports (IVTs) over West Africa during the 2024 monsoon season, revealing their dual role as significant drivers of rainfall patterns and key regulators of atmospheric dust dynamics through wet scavenging.

Objective

• To assess the dynamical structure, seasonality, and impacts of Integrated Vapour Transports (IVTs) over West Africa during 2024.
• To examine the dynamics, intensity, and spatial attributes of IVT over West Africa.
• To investigate the association of IVT with rainfall patterns and monsoonal influence.
• To analyze the influence of IVT on dust aerosol dynamics, including optical depth, surface concentration, and wet deposition.

Study Configuration

• Spatial Scale: West Africa, geographically defined between 20° W to 20° E and 0° N to 20° N.
• Temporal Scale: The 2024 West African monsoon season, specifically the wet season from May to October.

Methodology and Data

• Models used:
  • Integrated Vapour Transport (IVT) computation: $$IVT=\frac{1}{g}\sqrt{{\left({\int\:}{{p}{top}}^{{p}{surface}}q.udp\right)}^{2}+{\left({\int\:}{{p}{top}}^{{p}{surface}}q.vdp\right)}^{2}}$$ where (q) is specific humidity (kg/kg), (u) and (v) are zonal and meridional wind components (m/s), (p) is pressure (Pa), and (g=9.81\:{m/s}^{2}). Vertical integration was performed from 1000 hPa to 200 hPa.
  • IVT detection: Percentile-based approach using the 85th percentile (approximately ≥ 250 kg m⁻¹ s⁻¹) for events persisting at least 24 hours.
  • IVT categorization: Moderate (250–550 kg m⁻¹ s⁻¹), Strong (550–750 kg m⁻¹ s⁻¹), and Extreme (> 750 kg m⁻¹ s⁻¹).
  • IVT-linked precipitation estimation: $$P{IVT\%}=\left(\frac{\sum\:{i=1}^nP{{IVT}i}}{\sum\:{j=1}^NPj}\right)\times\:100$$
  • Dust wet deposition linked to IVTs: $$D{wet,IVT}=\left(\frac{\sum\:{i=1}^{n}{D}{{IVT}{i}}}{\sum\:{j=1}^{N}{IVT}{j}}\right)$$
  • Percentage of dust scavenged by IVTs: $$D{scav\%}=\left(\frac{D{wet,IVT}}{L_{dust}}\right)\:\times\:100$$
• Data sources:
  • Meteorological fields (specific humidity, wind components, vertical velocity, potential velocity, specific rainwater content, vapour flux): Fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5).
  • Dust and total aerosol extinction coefficients: Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2).
  • Vertically integrated dust mass concentration and wet deposition flux: ECMWF Copernicus Atmosphere Monitoring Service (CAMS) reanalysis.
  • Aerosol Optical Depth (AOD) at 550 nm: Moderate Resolution Imaging Spectro-radiometer (MODIS) dark target product.
  • Precipitation data: Climate Hazards Group Infrared Precipitation with Station data (CHIRPS).
  • All datasets were harmonized and re-gridded to a spatial resolution of 0.25° x 0.25°.

Main Results

• IVT frequency and intensity over West Africa exhibit a strong seasonal signal, peaking between June and September, particularly over the Guinean and southern Sudano-Sahelian zones.
• Extreme IVT events (≥ 750 kg m⁻¹ s⁻¹) are characterized by distinct structures, strong zonal wind cores at 700 hPa, and vertically coupled moisture fluxes that enhance organized convection and upward motion.
• Moderate IVTs (250–500 kg m⁻¹ s⁻¹) contribute significantly to daily rainfall in coastal regions, accounting for over 60% of total precipitation in some areas.
• Extreme IVTs (≥ 750 kg m⁻¹ s⁻¹) deliver intense, spatially focused precipitation in the Sahel, contributing over 65% of rainfall in targeted zones despite their rarity.
• A strong positive correlation (r = 0.81) was found between IVT intensity and precipitation.
• Periods of extreme IVTs are associated with strong negative correlations with aerosol optical depth and dust concentrations, alongside increased dust wet deposition.
• Dust scavenging efficiency peaks around an IVT threshold of approximately 300 kg m⁻¹ s⁻¹, suggesting that beyond this point, rainfall variability, rather than moisture flux alone, becomes the dominant factor for aerosol removal.
• IVTs preferentially align with the southern flank of the African Easterly Jet (AEJ) and are associated with Tropical Easterly Jet (TEJ)-entrance ascent, which deepens the moist column.

Contributions

• This study is among the first to explicitly characterize the dual role of IVTs in simultaneously modulating precipitation and dust dynamics over tropical West Africa.
• It expands the understanding of integrated vapour transport in a tropical context, highlighting IVTs as dynamically coupled systems with deep vertical structures, embedded ascent, and jet-level wind maxima.
• The findings provide critical insights for climate diagnostics, seasonal weather variability, air quality, and convective organization across the West African monsoon belt.
• It establishes IVTs as key synoptic-scale systems that shape both West African rainfall patterns and aerosol dynamics, linking the region's hydrological and atmospheric composition cycles.

Funding

Not explicitly stated in the provided text.

Citation

@article{Awoleye2025Moisture,
  author = {Awoleye, Peace Olubukunmi and Adebiyi, Adeyemi A. and Abiodun, Babatunde J. and Balogun, Ifeoluwa Adebowale and Akinbobola, Ademola and Oluleye, Ayodeji and Ajayi, Vincent O.},
  title = {Moisture and dust in motion: the dual role of integrated vapour transport over West Africa},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05913-1},
  url = {https://doi.org/10.1007/s00704-025-05913-1}
}