Abstract
Abstract. With advances in modeling approaches and the application of satellite and ground-based data in dust-related research, our understanding of the dust cycle has significantly improved in recent decades. However, two aspects of the dust cycle, namely the vertical profiles and diurnal cycles, are not yet adequately understood, mainly due to the sparsity of direct observations. Measurements of backscattering caused by atmospheric aerosols have been ongoing since 2014 at the King Abdullah University of Science and Technology (KAUST) campus using a micro-pulse lidar (MPL) with a high temporal resolution. KAUST is located on the eastern coast of the Red Sea and currently hosts the only operating lidar system in the Arabian Peninsula. We use the data from the MPL together with other collocated observations and high-resolution simulations (with 1.33 km grid spacing) from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to study the following three aspects of dust over the Red Sea coastal plains. Firstly, we compare the model-simulated surface winds, aerosol optical depth (AOD), and aerosol size distributions with observations and evaluate the model performance in representing a typical large-scale dust event over the study site. Secondly, we investigate the vertical profiles of aerosol extinction and concentration in terms of their seasonal and diurnal variability. Thirdly, we explore the interactions between dust aerosols and land/sea breezes, which are the most influential components of the local diurnal circulation in the region. The WRF-Chem model successfully reproduced the diurnal profile of surface wind speed, AOD, and dust size distributions over the study area compared to observations. The model also captured the onset, demise, and height of a large-scale dust event that occurred in 2015, as compared to the lidar data. The vertical profiles of aerosol extinction in different seasons were largely consistent between the MPL data and WRF-Chem simulations along with key observations and reanalyses used in this study. We found a substantial variation in the vertical profile of aerosols in different seasons and between daytime and nighttime, as revealed by the MPL data. The MPL data also identified a prominent dust layer at ∼5–7 km during the nighttime, which likely represents the long-range transported dust brought to the site by the easterly flow from remote inland deserts. The sea breeze circulation was much deeper (∼2 km) than the land breeze circulation (∼1 km), but both breeze systems prominently affected the distribution of dust aerosols over the study site. We observed that sea breezes push the dust aerosols upwards along the western slope of the Sarawat Mountains. These sea breezes eventually collide with the dust-laden northeasterly trade winds coming from nearby inland deserts, thus causing elevated dust maxima at a height of ∼1.5 km above sea level over the mountains. Moreover, the sea and land breezes intensify dust emissions from the coastal region during the daytime and nighttime, respectively. Our study, although focused on a particular region, has broader environmental implications as it highlights how aerosols and dust emissions from the coastal plains can affect the Red Sea climate and marine habitats.
Highlights
The aforementioned sea breezes cause these wind peaks in the afternoon. Note that these sea breezes originate at sea and advance landward to reach the coast only later in the afternoon (Estoque et al, 1961), where they are measured at our station
We investigated the vertical distribution of aerosols over the eastern coast of the Red Sea
We used data collected from the only operating lidar in the region, located on the King Abdullah University of Science and Technology (KAUST) campus, together with other collocated observations and high-resolution WRF-Chem model simulations, to explore three main aspects of dust aerosols
Summary
Dust aerosols, which mainly originate from natural deserts and disturbed soils such as agricultural areas, have implications for air quality (Prospero, 1999; Parajuli et al, 2019) and the Earth’s climate (Sokolik and Toon, 1996; Mahowald et al, 2006; Jish Prakash et al, 2015; Bangalath and Stenchikov, 2015; Kalenderski and Stenchikov, 2016; Di Biagio et al, 2017). Understanding the vertical structure is important because the vertical distribution of aerosols affects the radiative budget (Johnson et al, 2008; Osipov et al, 2015) and surface air quality (Chin et al, 2007; Wang et al, 2010; Ukhov et al, 2020b). Understanding the diurnal cycle of aerosols is important because aerosols scatter and absorb radiation (Sokolik and Toon, 1996; Di Biagio et al, 2017), which affects the land and sea breezes in coastal areas. Land and sea breezes, which are the key diurnal-scale atmospheric processes over the Red Sea coastal plain, can affect the distribution and transport of aerosols (Khan et al, 2015) and their composition (Fernández-Camacho et al, 2010; Derimian et al, 2017)
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