Interaction of Dust Aerosols with Land/Sea Breezes over the Eastern Coast of the Red Sea from LIDAR Data and High-resolution WRF-Chem Simulations

Abstract

<jats:p>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 with a high temporal resolution. KAUST is located on the east coast of the Red Sea (22.3° N, 39.1° E), and currently hosts the only operating LIDAR system in the Arabian Peninsula. We use the data from this LIDAR together with other collocated observations and high-resolution WRF-Chem model simulations to study the following aspects of aerosols, with a focus on dust over the Red Sea Arabian coastal plains. Firstly, we investigate the vertical profiles of aerosol extinction and concentration in terms of their seasonal and diurnal variability. Secondly, we evaluate how well the WRF-Chem model performs in representing the vertical distribution of aerosols over the study site. 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. We found a substantial variation in the vertical profile of aerosols in different seasons. We also discovered a marked difference in the daytime and nighttime vertical distribution of aerosols at the study site, as revealed by the LIDAR data. The LIDAR data also identified a prominent dust layer at ∼5–7 km during the nighttime, which represented the long-range transported dust brought to the site by the easterly flow from remote inland deserts. The vertical profiles of aerosol extinction in different seasons were largely consistent between the LIDAR, MERRA-2 reanalysis, and CALIOP data, as well as in the WRF-Chem simulations. 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, which eventually collide with the dust-laden northeasterly trade winds coming from nearby inland deserts, causing elevated dust maxima at a height of ∼1.5 km above sea level over the mountains. Moreover, the sea and land breezes intensified dust emissions from the coastal region during the daytime and nighttime, respectively. The WRF-Chem model successfully captured the onset, demise, and height of a large-scale dust event that occurred in 2015, compared to LIDAR data. 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. </jats:p>

Synergy processing of diverse ground-based remote sensing and in situ data using GRASP algorithm: applications to radiometer, lidar and radiosonde observations

“…Higher values as well as differences could be observed above 6 km, where the concentration of aerosol is negligible and therefore higher AE errors 1125 are expected. Higher values of AE at ~6 km also supports the findings that the aerosols at this height consist of fine-mode transported dust (Parajuli et al, 2020).…”

“…The aerosol 700 layer on the top (~7500 m) is similar to those observed on 5 and 11 of August 2015, which is not identified by MPL data but consistently shown by the radiosonde data in all three days. It should be noted that a similar aerosol layer (~6000-8000 km) was reported by Parajuli et al, (2020) in summer while analyzing the nighttime MPL data and which was attributed to the dust transported from remote inland deserts. Unfortunately, the amount of available data does not allow us to conduct a robust conclusion about the reason for such differences or a nature of the high-altitude layers observed at night.…”

“…The size distribution changes significantly overnight with higher concentration of coarse particles in the morning than in the evening. This could be explained by the diurnal-scale sea breezes becoming stronger by late morning, which mobilizes dust 620 locally over the study site (Parajuli et al, 2020). At the same time, nighttime retrieval, which largely depends on inter-pixel temporal constraints due to the low sensitivity of backscatter observations to a detailed size distribution, shows a shape that is somewhat between evening and morning retrievals, although closer to the evening one.…”

“…The KAUST site is located at the campus of King Abdullah University of Science and Technology, Thuwal, Saudi Arabia (22.3º N, 39.1º E) on a seashore 565 of the Red Sea next to a relatively big city (Jeddah). The site observes strong dust activity due to its proximity to Arabian desert (Parajuli et al, 2020). Altogether 10 radiosonde flights were performed during the campaigns.…”

“…The lack of quality COBALD data on 12/08/15 and photometric data on 605 08/08/16 makes the combined retrieval impossible since information about vertical aerosol distribution is missing. It is worth mentioning that a large-scale dust storm swept over KAUST site on August 8-9, 2015, which affected AERONET measurements (Parajuli et al, 2020). Other cases (marked in italic) were processed using only one sun-photometer dataset available but their analysis is less interesting and not included in the article.…”