Abstract

Wintertime Saharan dust plumes in the vicinity of Barbados are investigated by means of airborne lidar measurements. The measurements were conducted in the framework of the EUREC4A field experiment (Elucidating the Role of Cloud-Circulation Coupling in Climate) upstream the Caribbean island in January/February 2020. The combination of the water vapor differential absorption and high spectral resolution lidar techniques together with dropsonde measurements aboard the German HALO (High Altitude and Long-Range) research aircraft enable a detailed vertical and horizontal characterization of the measured dust plumes. In contrast to summertime dust transport, mineral dust aerosols were transported at lower altitudes and were always located below 3.5 km. Calculated backward trajectories affirm that the dust-laden layers have been transported in nearly constant low-level altitude over the North Atlantic Ocean. Only mixtures of dust-particles with other aerosol species, i.e. biomass burning aerosol from fires in West Africa and marine aerosol, were detected by the lidar. No pure mineral dust regimes were observed. Additionally, all the dust-laden airmasses that were observed during EUREC4A came along with enhanced water vapor concentrations compared to the free atmosphere above. Such enhancements have already been observed during summertime and were found to have a great impact on radiative transfer and atmospheric stability.

Highlights

  • Mineral dust aerosol is known to be a major contributor to the Earth’s aerosol mass burden (Cakmur et al, 2006) and is 15 estimated to contribute between 25 % and 30 % to the total aerosol optical depth (Tegen et al, 1997; Kinne et al, 2006)

  • While during the summer months Saharan dust particles are predominantly transported westwards in Saharan air layers (SALs) at altitudes as great as 6 km (e.g. Prospero and Carlson, 1972; Prospero et al, 2010), Saharan dust transport in the winter months happens at lower atmospheric levels (Chiapello et al, 1995)

  • This agrees well with the findings in this study, as mineral dust particles were never observed in altitudes higher than ∼ 3.5 km

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Summary

Introduction

Mineral dust aerosol is known to be a major contributor to the Earth’s aerosol mass burden (Cakmur et al, 2006) and is 15 estimated to contribute between 25 % and 30 % to the total aerosol optical depth (Tegen et al, 1997; Kinne et al, 2006). From a comparison of 15 global aerosol models, Huneeus et al (2011) derived annual dust emissions from North Africa that range from 400 to 2200 Tg a−1. This makes up roughly 50 % of the total global annual dust emission (1000 to 4000 Tg a−1). Once injected into the atmosphere, Saharan dust particles can be transported far away from their origin. While only 15 % of 20 the total emitted dust load is transported north- and eastwards towards the Mediterranean and the Middle East (e.g. Shao et al., 2011), almost 85 % of the dust burden gets carried south- and westwards over the Atlantic Ocean.

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