Long-term characterisation of the vertical structure of the Saharan Air Layer over the Canary Islands using lidar and radiosonde profiles: implications for radiative and cloud processes over the subtropical Atlantic Ocean

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Á. Barreto, E. Cuevas, R. D. García, J. Carrillo, J. M. Prospero, L. Ilić, S. Basart, A. J. Berjón, C. L. Marrero, Y. Hernández, J. J. Bustos, S. Ničković, M. Yela
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Physics; QC1-999; Chemistry; QD1-999; North Atlantic
• Online Access: https://doi.org/10.5194/acp-22-739-2022; https://doaj.org/article/59d7c52bc914481f9be6196990727858

Every year, large-scale African dust outbreaks frequently pass over the Canary Islands (Spain). Here we describe the seasonal evolution of atmospheric aerosol extinction and meteorological vertical profiles on Tenerife over the period 2007–2018 using long-term micropulse lidar (MPL-3) and radiosonde observations. These measurements are used to categorise the different patterns of dust transport over the subtropical North Atlantic and, for the first time, to robustly describe the dust vertical distribution in the Saharan Air Layer (SAL) over this region. Three atmospheric scenarios dominate the aerosol climatology: dust-free (clean) conditions, the Saharan summer scenario (summer-SAL) and the Saharan winter scenario (winter-SAL). A relatively well-mixed marine boundary layer (MBL) was observed in the case of clean (dust-free) conditions; it was associated with rather constant lidar extinction coefficients ( α ) below 0.036 km −1 with minimum α ( < 0.022 km −1 ) in the free troposphere (FT). The summer-SAL has been characterised as a dust-laden layer strongly affecting both the MBL ( Δ α = + 48 % relative to clean conditions) and the FT. The summer-SAL appears as a well-stratified layer, relatively dry at lower levels ( <math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">Δ</mi><mi>r</mi><mo>∼</mo><mo>-</mo><mn mathvariant="normal">44</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="48pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="4587f555832255851f3478276c38f90d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-739-2022-ie00001.svg" width="48pt" height="10pt" src="acp-22-739-2022-ie00001.png"/></svg:svg> % at the SAL’s base, where r is the water vapour mixing ratio) but more humid at higher levels compared with clean FT conditions ( <math ...