Seasonal simulations of summer aerosol optical depth over the Arabian Peninsula using WRF‐Chem: Validation, climatology, and variability

Abstract

This study investigates the climatology and variability of summer aerosol optical depth (AOD) over the Arabian Peninsula (AP) using a long-term high-resolutionWeather Research and Forecasting model coupled with the chemistry module (WRF-Chem) simulation, available ground-based and satellite observations, and reanalysis products from 2008 to 2018. The simulated spatial distribution of the summer AOD agrees well with the satellite observations and reanalysis over the AP, with spatial correlation coefficients of 0.81/0.83/0.89 with MODIS-A/MODIS-T/MERRA-2, respectively. Higher values of summertime AOD are broadly found over the eastern AP regions and the southern Red Sea and minima over the northern Red Sea and northwest AP, consistent with observational datasets. The WRF-Chem simulation suggests that the two regions of high AOD are associated with dust advected from the Tigris-Euphrates by the northwesterly summer Shamal wind in the eastern AP and from the African Sahara via Sudan by westerly winds through the Tokar Gap for the southern AP. The high AOD over the south-central east AP is due to locally generated dust by the action of northerly winds, modulated by variations in relative humidity, vertical motion, soil moisture, and soil temperature over the desert regions. The vertical extent of this dust is primarily driven by upward motion triggered by thermal convection over the local source region. In terms of interannual variability, summer AOD exhibits significant yearto-year variations over the AP region. In particular, enhanced (reduced) AOD over the southern AP (Persian Gulf) is observed during La Niña conditions, favoured by stronger (weaker) Tokar westerly (northwesterly summer Shamal) winds. HighlightsThis study evaluated the long-term simulations of AOD using high resolution WRF-Chem model over the AP. WRF-Chem successfully simulated the summer AOD climatology and its variability.

Investigation of Dust‐Induced Direct Radiative Forcing Over the Arabian Peninsula Based on High‐Resolution WRF‐Chem Simulations

“…The mean seasonal spatial distributions of MODIS level‐2 DOD pixels over the three seasons displayed in Figure 2 indicate that the highest dust loadings are located over the southern parts of the AP and along the northeastern AP. The high dust loading in the southern parts of the AP is mainly due to dust emissions from the Rub’ Al Khali, as well as dust that is advected from the Iraq and Sudan regions (Karumuri et al., 2021; Kunchala et al., 2018). Among the three seasons in focus, strong dust loading is noticeable during the dust season of 2012, which is also captured by the WRF‐Chem simulations, as seen in the highest dust loadings over the AP in 2012 (Figures 2a and 2d).…”

“…WRF‐Chem has been widely used to investigate and predict aerosols, air quality, and dust storms, and accounts for the aerosol effect on radiation at regional scales (Grell et al., 2011; Karumuri et al, 2021; Karumuri, Ghude, et al., 2019; Marelle et al., 2017). For our experiments, WRF‐ChemV4.2.1 was configured with a single domain covering the AP region (20°−70°E and 0°−40°N) at 0.1° horizontal resolution and with 50 vertical levels up to model 10 hPa.…”

Impact of COVID-19 lockdown on the ambient air-pollutants over the Arabian Peninsula

“…The spatial distribution of AOD and surface winds from WRF-Chem are compared against those of MODIS satellite and ERA-5 reanalysis, respectively (Figure 5). The AP is one of the world's largest dust source regions (Ginoux et al, 2001) and experiences the highest dust concentrations between March to September due to frequent passages of dust storms (e.g., Kunchala et al, 2018Kunchala et al, , 2019Dasari et al, 2019;Gandham et al, 2020Gandham et al, , 2022Karumuri et al, 2022). The spatial distribution of MODIS AOD exhibits high values over the southern Red Sea and central AP during PLD (Figure 5A), mainly associated with the presence of an anticyclonic circulation over the central AP.…”

Using Satellite‐Derived Fire Arrival Times for Coupled Wildfire‐Air Quality Simulations at Regional Scales of the 2020 California Wildfire Season

“…In general, it is difficult for WRF-Chem simulations to reproduce MODIS AOD. Balzarini et al (2015) found that WRF-Chem/MODIS AOD relationships can be a strong function of the chemical mechanism for both gas and aerosol phases, and Karumuri et al (2022) found that the relative bias between WRF-Chem and MODIS AOD can vary regionally within the simulation domain. However, some studies have had success reproducing MODIS AOD with WRF-Chem simulations (e.g., Chen et al, 2014;Siméon et al, 2021).…”