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

Emmanouil Flaounas,Vassiliki Kotroni,Konstantinos Lagouvardos,Cyrille Flamant,Martina Klose,Theodore M Giannaros

doi:10.5194/gmd-10-2925-2017

Abstract

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.

Highlights

The geographical belt composed by North Africa and the Arabian Peninsula constitutes the largest desert in the world (Tsvetsinskaya et al, 2002)
Given that our motivation is to assess the WRF-Chem performance especially in reproducing dust transport over the eastern Mediterranean, in Fig. 8 we provide an example of the model performance in simulating a dust episode that took place on 23 July of 2011
To gain more confidence in that the 0.2 value of aerosol optical depth (AOD) background in AERONET is due to dust, we compared the MODIS AOD retrievals with the AERONET measurements

Summary

Introduction

The geographical belt composed by North Africa and the Arabian Peninsula constitutes the largest desert in the world (Tsvetsinskaya et al, 2002). This region is a major dust source, emitting annually large loads into the atmosphere and has a global impact on climate and air quality (Huneeus et al, 2011). While both North Africa and the Arabian Peninsula emit remarkable amounts of particulate matter, it is the Saharan desert that constitutes the worldwide main source of dust. Dryan et al (1991) showed that dust intrusions in the eastern Mediterranean from the Arabian Peninsula have a short duration (of the order of a day) and take place within shallow atmospheric layers of up to 2 km a.s.l., while African dust intrusions persist longer (2–4 days of duration) and transport takes place at atmospheric layers over 3 km of altitude.

Objectives

Findings

Discussion

Conclusion