scholarly journals Sensitivity of the WRF-Chem (V3.6.1) model to different dust emission parametrisation: assessment in the broader Mediterranean region

2017 ◽  
Vol 10 (8) ◽  
pp. 2925-2945 ◽  
Author(s):  
Emmanouil Flaounas ◽  
Vassiliki Kotroni ◽  
Konstantinos Lagouvardos ◽  
Martina Klose ◽  
Cyrille Flamant ◽  
...  

Abstract. In this study we aim to assess the WRF-Chem model capacity to reproduce dust transport over the eastern Mediterranean. For this reason, we compare the model aerosol optical depth (AOD) outputs to observations, focusing on three key regions: North Africa, the Arabian Peninsula and the eastern Mediterranean. Three sets of four simulations have been performed for the 6-month period of spring and summer 2011. Each simulation set uses a different dust emission parametrisation and for each parametrisation, the dust emissions are multiplied with various coefficients in order to tune the model performance. Our assessment approach is performed across different spatial and temporal scales using AOD observations from satellites and ground-based stations, as well as from airborne measurements of aerosol extinction coefficients over the Sahara. Assessment over the entire domain and simulation period shows that the model presents temporal and spatial variability similar to observed AODs, regardless of the applied dust emission parametrisation. On the other hand, when focusing on specific regions, the model skill varies significantly. Tuning the model performance by applying a coefficient to dust emissions may reduce the model AOD bias over a region, but may increase it in other regions. In particular, the model was shown to realistically reproduce the major dust transport events over the eastern Mediterranean, but failed to capture the regional background AOD. Further comparison of the model simulations to airborne measurements of vertical profiles of extinction coefficients over North Africa suggests that the model realistically reproduces the total atmospheric column AOD. Finally, we discuss the model results in two sensitivity tests, where we included finer dust particles (less than 1 µm) and changed accordingly the dust bins' mass fraction.

2017 ◽  
Author(s):  
Emmanouil Flaounas ◽  
Vassiliki Kotroni ◽  
Konstantinos Lagouvardos ◽  
Martina Klose ◽  
Cyrille Flamant ◽  
...  

Abstract. In this study we aim to assess the WRF-Chem model capacity to reproduce dust transport over the eastern Mediterranean. For this reason, we compare the model aerosol optical depth (AOD) outputs to observations, focusing on three key regions: North Africa, the Arabian Peninsula and the eastern Mediterranean. Three sets of four simulations have been performed for the six-month period of spring and summer 2011. Each simulation set uses a different dust emission parametrisation and for each parametrisation, the dust emissions are multiplied with various coefficients in order to tune the model performance. Our assessment approach is performed across different spatial and temporal scales using AOD observations from satellites and ground-based stations, as well as from airborne measurements of aerosol extinction coefficients over the Sahara. Assessment over the entire domain and simulation period shows that the model presents temporal and spatial variability similar to observed AODs, regardless of the applied dust emission parametrisation. On the other hand, when focusing on specific regions, the model skill varies significantly. Tuning the model performance by applying a coefficient to dust emissions may reduce the model AOD bias over a region, but may increase it in other regions. In particular, the model was shown to realistically reproduce the major dust transport events over the eastern Mediterranean, but failed to capture the regional background AOD. Further comparison of the model simulations to airborne measurements of vertical profiles of extinction coefficients over North Africa suggests that the model realistically reproduces the total atmospheric column AOD. Finally, we discuss the model results in two sensitivity tests, where we included finer dust mode (less than 1 μm) and changed accordingly the dust bins mass fraction.


2016 ◽  
Author(s):  
Emmanouil Flaounas ◽  
Vassiliki Kotroni ◽  
Konstantinos Lagouvardos ◽  
Martina Klose ◽  
Cyrille Flamant ◽  
...  

Abstract. In this study we aim at optimizing the WRF-Chem model performance for the purpose of operational forecasting of dust transport over the eastern Mediterranean. For this reason, we compare the model output to observations in order to assess its capacity to realistically reproduce the aerosol optical depth (AOD), focusing on three key regions: North Africa, the Arabian Peninsula and the eastern Mediterranean. Three sets of four simulations each have been performed for the six-month period of spring and summer 2011. Each simulation set uses a different dust emission parametrisation and for each parametrisation, the dust emissions are multiplied with various coefficients in order to tune the model performance. Our approach is based on the model assessment across spatial and temporal scales by comparing its outputs to AOD observations from satellites and ground-based stations, as well as airborne measurements of aerosol extinction coefficients over the Sahara. Tuning the model performance by applying a coefficient to dust emissions may reduce the model AOD bias over a region, but may increase it in other regions. Concerning dust transport over the eastern Mediterranean, the model was shown to realistically reproduce the major transport events, however failing to capture the regional background AOD. Model assessment over the entire domain and simulation period shows that the model presents temporal and spatial variability similar to observed AODs, regardless of the applied dust emission parametrisation. However, when focusing on specific regions, the model’s skill may vary significantly. Further comparison of the model simulations to airborne measurements of the vertical profiles of extinction coefficients over North Africa suggests that the model may realistically reproduce the total atmospheric column AOD. Finally, we show that the inclusion of a finer dust mode (less than 1 μm) in the model presents the advantage of relaxing unrealistically large atmospheric dust loads and yet reproducing realistic AOD values.


2010 ◽  
Vol 10 (18) ◽  
pp. 8821-8838 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
L. R. Leung ◽  
B. Johnson ◽  
S. A. McFarlane ◽  
...  

Abstract. A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate mineral dust and its shortwave (SW) radiative forcing over North Africa. Two dust emission schemes (GOCART and DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in simulations to investigate the modeling sensitivities to dust emissions and aerosol size treatments. The modeled size distribution and spatial variability of mineral dust and its radiative properties are evaluated using measurements (ground-based, aircraft, and satellites) during the AMMA SOP0 campaign from 6 January to 3 February of 2006 (the SOP0 period) over North Africa. Two dust emission schemes generally simulate similar spatial distributions and temporal evolutions of dust emissions. Simulations using the GOCART scheme with different initial (emitted) dust size distributions require ~40% difference in total emitted dust mass to produce similar SW radiative forcing of dust over the Sahel region. The modal approach of MADE/SORGAM retains 25% more fine dust particles (radius<1.25 μm) but 8% less coarse dust particles (radius>1.25 μm) than the sectional approach of MOSAIC in simulations using the same size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11% higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more negative) SW dust radiative forcing at the surface than MOSAIC over the Sahel region. In the daytime of the SOP0 period, the model simulations show that the mineral dust heats the lower atmosphere with an average rate of 0.8 ± 0.5 K day−1 over the Niamey vicinity and 0.5 ± 0.2 K day−1 over North Africa and reduces the downwelling SW radiation at the surface by up to 58 W m−2 with an average of 22 W m−2 over North Africa. This highlights the importance of including dust radiative impact in understanding the regional climate of North Africa. When compared to the available measurements, the WRF-Chem simulations can generally capture the measured features of mineral dust and its radiative properties over North Africa, suggesting that the model is suitable for more extensive simulations of dust impact on regional climate over North Africa.


2018 ◽  
Author(s):  
Sandra L. LeGrand ◽  
Chris Polashenski ◽  
Theodore W. Letcher ◽  
Glenn A. Creighton ◽  
Steven E. Peckham ◽  
...  

Abstract. Airborne particles of mineral dust play a key role in Earth's climate system and affect human activities around the globe. The numerical weather modeling community has undertaken considerable efforts to accurately forecast these dust emissions. Here, for the first time in the literature, we thoroughly describe and document the Air Force Weather Agency (AFWA) dust emission scheme for the GOCART aerosol model within the Weather Research and Forecasting Chemistry (WRF-Chem) model and compare it to the other dust emission parameterizations available in WRF-Chem. The AFWA dust emission scheme addresses some shortcomings experienced by the earlier GOCART-WRF parameterization. Improved model physics are designed to better handle emission of fine dust particles by representing saltation bombardment. Model performance with the improved parameterization is evaluated against observations of dust emission in southwest Asia and compared to emissions predicted by the other parameterizations built into the WRF-Chem GOCART model. Results highlight the relative strengths of the available schemes, indicate the reasons for disagreement between the models, and demonstrate the need for improved soil source data.


2010 ◽  
Vol 10 (4) ◽  
pp. 9753-9799 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
L. R. Leung ◽  
B. Johnson ◽  
S. A. McFarlane ◽  
...  

Abstract. A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate mineral dust and its shortwave (SW) radiative forcing over North Africa. Two dust emission schemes (GOCART and DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in simulations to investigate the modeling sensitivities to dust emissions and aerosol size treatments. The modeled size distribution and spatial variability of mineral dust and its radiative properties are evaluated using measurements (ground-based, aircraft, and satellites) during the AMMA SOP0 campaign from 6 January to 3 February of 2006 (the SOP0 period) over North Africa. Two dust emission schemes generally simulate similar spatial distributions and temporal evolutions of dust emissions. Simulations using the GOCART scheme with different initial (emitted) dust size distributions show that the difference of initial dust size distributions can result in significant difference (up to ~50%) in simulating SW dust heating and SW dust radiative forcing at the surface over the Sahel region. The modal approach of MADE/SORGAM retains 25% more fine dust particles (radius <1.25 μm) but 8% less coarse dust particles (radius >1.25 μm) than the sectional approach of MOSAIC in simulations using the same size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11% higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more negative) SW dust radiative forcing at the surface than MOSAIC over the Sahel region. In the daytime of the SOP0 period, the model simulations show that mineral dust heats the lower atmosphere (1–3 km) with a maximum rate of 0.8±0.5 K day−1 below 1 km and reduces the downwelling SW radiation at the surface by up to 58 W m−2 over the Sahel region. This highlights the importance of including dust radiative impact in understanding the regional climate of North Africa. When compared to the available measurements, the WRF-Chem simulations can generally capture the measured features of mineral dust and its radiative properties over North Africa, suggesting that the model is suitable for more extensive simulations of dust impact on regional climate over North Africa.


2012 ◽  
Vol 12 (21) ◽  
pp. 10209-10237 ◽  
Author(s):  
K. Wang ◽  
Y. Zhang ◽  
A. Nenes ◽  
C. Fountoukis

Abstract. The US Environmental Protection Agency's (EPA) Community Multiscale Air Quality (CMAQ) modeling system version 4.7 is further developed to enhance its capability in simulating the photochemical cycles in the presence of dust particles. The new model treatments implemented in CMAQ v4.7 in this work include two online dust emission schemes (i.e., the Zender and Westphal schemes), nine dust-related heterogeneous reactions, an updated aerosol inorganic thermodynamic module ISORROPIA II with an explicit treatment of crustal species, and the interface between ISORROPIA II and the new dust treatments. The resulting improved CMAQ (referred to as CMAQ-Dust), offline-coupled with the Weather Research and Forecast model (WRF), is applied to the April 2001 dust storm episode over the trans-Pacific domain to examine the impact of new model treatments and understand associated uncertainties. WRF/CMAQ-Dust produces reasonable spatial distribution of dust emissions and captures the dust outbreak events, with the total dust emissions of ~111 and 223 Tg when using the Zender scheme with an erodible fraction of 0.5 and 1.0, respectively. The model system can reproduce well observed meteorological and chemical concentrations, with significant improvements for suspended particulate matter (PM), PM with aerodynamic diameter of 10 μm, and aerosol optical depth than the default CMAQ v4.7. The sensitivity studies show that the inclusion of crustal species reduces the concentration of PM with aerodynamic diameter of 2.5 μm (PM2.5) over polluted areas. The heterogeneous chemistry occurring on dust particles acts as a sink for some species (e.g., as a lower limit estimate, reducing O3 by up to 3.8 ppb (~9%) and SO2 by up to 0.3 ppb (~27%)) and as a source for some others (e.g., increasing fine-mode SO42− by up to 1.1 μg m−3 (~12%) and PM2.5 by up to 1.4 μg m−3 (~3%)) over the domain. The long-range transport of Asian pollutants can enhance the surface concentrations of gases by up to 3% and aerosol species by up to 20% in the Western US.


2007 ◽  
Vol 7 (6) ◽  
pp. 15955-15987 ◽  
Author(s):  
K. Yumimoto ◽  
I. Uno ◽  
N. Sugimoto ◽  
A. Shimizu ◽  
Z. Liu ◽  
...  

Abstract. A four-dimensional variational (4D-Var) data assimilation system for a regional dust model (RAMS/CFORS-4DVAR; RC4) is applied to a heavy dust event which occurred between 20 March and 4 April 2007 over eastern Asia. The vertical profiles of the dust extinction coefficients derived from NIES LIDAR observation network are directly assimilated. We conduct two experiments to evaluate impacts of selections of observation sites: Experiment A uses five Japanese observation sites located only downwind of dust source regions; the other Experiment B uses these sites together with two other sites near source regions (China and Korea). Validations using various observation data (e.g., PM10 concentration, MODIS AOT, OMI Aerosol Index, and the dust extinction coefficient derived by space-based LIDAR NASA/CALIPSO) are demonstrated. The modeled dust extinction coefficients are improved considerably through the assimilation. Assimilation results of Experiment A are consistent with those of Experiment B, indicating that observations of Experiment A can capture the dust event correctly and include sufficient information for dust emission inversion. Time series of dust AOT calculated by modeled and LIDAR dust extinction coefficients show good agreement. At Seoul, Matsue, and Toyama, assimilation reduces the root mean square errors of dust AOT by 31–32%. Vertical profiles of the dust layer observed by CALIPSO are also compared with assimilation results. The dense dust layer was trapped between θ=280–300 K and elevated higher toward the north; the model reproduces those characteristics well. The modeled dust AOT along the orbit paths agrees well with the CALIPSO dust AOT, OMI AI, and the coarse mode AOT retrieved from MODIS; especially the modeled dust AOT and the MODIS coarse mode AOT are consistent quantitatively. Assimilation results increase dust emissions over the Gobi Desert and Mongolia considerably; especially between 29 and 30 March, emission flux is increased by about 2–3 times. The heavy dust event is caused by the heavy dust uplift flux over the Gobi Desert and Mongolia during those days. We obtain the total optimized dust emissions of 57.9 Tg (Experiment A; 57.8% larger than before assimilation) and 56.3 Tg (Experiment B; 53.4% larger).


2012 ◽  
Vol 12 (5) ◽  
pp. 13457-13514 ◽  
Author(s):  
K. Wang ◽  
Y. Zhang ◽  
A. Nenes ◽  
C. Fountoukis

Abstract. The US Environmental Protection Agency (EPA)'s Community Multiscale Air Quality (CMAQ) modeling system version 4.7 is further developed to enhance its capability in simulating the photochemical cycles in the presence of dust particles. The new model treatments implemented in CMAQ v4.7 in this work include two online-dust emission schemes, nine dust-related heterogeneous reactions, an updated aerosol inorganic thermodynamic module ISORROPIA II with an explicit treatment of crustal species, and the interface between ISORROPIA II and the new dust treatments. The resulting improved CMAQ (referred to as CMAQ-Dust), offline-coupled with the Weather Research and Forecast model (WRF), are applied to the April 2001 dust storm episode over the trans-Pacific domain to examine the impact of new model treatments and understand associated uncertainties. WRF/CMAQ-Dust produces reasonable spatial distribution of dust emissions and captures the dust outbreak events, with the total dust emissions of ∼111 and 223 Tg when the erodible fraction is assumed to be 0.5 and 1.0, respectively, for the April 2001 episode. The model system can reproduce well observed meteorological and chemical concentrations, with significant improvements for suspended particulate matter (PM), PM with aerodynamic diameter of 10 μm and aerosol optical depth than default CMAQ v4.7. The sensitivity studies show that the inclusion of crustal species reduces the concentration of PM with aerodynamic diameter of 2.5 μm (PM2.5) over polluted areas. The heterogeneous chemistry occurring on dust particles acts as a sink for some species (e.g., as a lower limit estimate, O3 by up to 3.8 ppb (∼9%) and SO2 by up to 0.3 ppb (∼27%)) and as a source for some others (e.g., fine-mode SO42− by up to 1.1 μg m−3 (∼12%) and PM2.5 by up to 1.4 μg m−3 (∼3%) over the domain. The long-range transport of Asian pollutants can enhance the background concentrations of gases by up to 3% and aerosol species by up to 20% in the US.


2020 ◽  
Author(s):  
Lamei Shi ◽  
Jiahua Zhang ◽  
Fengmei Yao ◽  
Da Zhang

&lt;p&gt;The breakdown of nocturnal low-level jets (NLLJs), West African heat low (WAHL), and Harmattan Surges (HS) have been proved to be important meteorological drivers of the seasonal variation of dust emissions over North Africa. This study further investigated their relative contributions to the interannual variation of dust emissions from 1980 to 2018. Dust emissions from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), precipitation data from TerraClimate, and wind speed, temperature, and geopotential from the European Centre for Medium-Range Weather Forecasts (ECMWF) were used to examine the roles of precipitation and wind speed in the dust emission trend as well as the spatiotemporal characteristics of the contributions of those three meteorological factors to the interannual variation of dust emissions. Results indicated that the dust emissions over Sahel and the southern coast of Mediterranean were more sensitive to precipitation rather than wind speed, while areas that were not influenced by rainfall were highly correlated with the cube of the wind speed at 10 m above surface with p &lt; 0.001. The regional difference in the contribution of the three meteorological factors was significant. HS was the main contributor for dust emissions over the northern North Africa primarily in winter and spring. NLLJs primarily controlled the southern part (south of 20&amp;#176;N) in almost all seasons especially in winter and spring, while they contributed more to dust emissions north of 20&amp;#176; N from June to August. The contribution of WAHL started from the south of the Hoggar-Tibesti channel and the lee of Ethiopian Highlands in winter, then it moved northwestward in spring and reached their strongest states in summer.&lt;/p&gt;


2008 ◽  
Vol 8 (11) ◽  
pp. 2869-2884 ◽  
Author(s):  
K. Yumimoto ◽  
I. Uno ◽  
N. Sugimoto ◽  
A. Shimizu ◽  
Z. Liu ◽  
...  

Abstract. A four-dimensional variational (4D-Var) data assimilation system for a regional dust model (RAMS/CFORS-4DVAR; RC4) is applied to an adjoint inversion of a heavy dust event over eastern Asia during 20 March–4 April 2007. The vertical profiles of the dust extinction coefficients derived from NIES Lidar network are directly assimilated, with validation using observation data. Two experiments assess impacts of observation site selection: Experiment A uses five Japanese observation sites located downwind of dust source regions; Experiment B uses these and two other sites near source regions. Assimilation improves the modeled dust extinction coefficients. Experiment A and Experiment B assimilation results are mutually consistent, indicating that observations of Experiment A distributed over Japan can provide comprehensive information related to dust emission inversion. Time series data of dust AOT calculated using modeled and Lidar dust extinction coefficients improve the model results. At Seoul, Matsue, and Toyama, assimilation reduces the root mean square differences of dust AOT by 35–40%. However, at Beijing and Tsukuba, the RMS differences degrade because of fewer observations during the heavy dust event. Vertical profiles of the dust layer observed by CALIPSO are compared with assimilation results. The dense dust layer was trapped at potential temperatures (θ) of 280–300 K and was higher toward the north; the model reproduces those characteristics well. Latitudinal distributions of modeled dust AOT along the CALIPSO orbit paths agree well with those of CALIPSO dust AOT, OMI AI, and MODIS coarse-mode AOT, capturing the latitude at which AOTs and AI have high values. Assimilation results show increased dust emissions over the Gobi Desert and Mongolia; especially for 29–30 March, emission flux is about 10 times greater. Strong dust uplift fluxes over the Gobi Desert and Mongolia cause the heavy dust event. Total optimized dust emissions are 57.9 Tg (Experiment A; 57.8% larger than before assimilation) and 56.3 Tg (Experiment B; 53.4% larger).


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