![Why dust is good?
• Dust cycle is an important part of
the Earth System.
• Dust scatters and absorbs SW and
LW radiation thus regulates climate
and environment
• Mineral dust acts as a fertilizer (P,
Fe) for terrestrial/marine
ecosystem1.
• Dust is a key player of
long-term climate
(paleoclimate).
1[Koren, et al., 2006]](https://image.slidesharecdn.com/talkondust-rainfallconnections-220326070837/85/Dust-rainfall-connections-5-320.jpg)
![When is dust a problem?
• Dust became an air-quality issue after
increased human activity, which
generated anthropogenic dust
• Anthropogenic dust generated from
agricultural/disturbed lands and
construction: finer particles and may
contain environmental pollutants
• Its ageing, or interaction with other
pollutant aerosols and gases makes it a
threat.
• Anthropogenic pollutants typically
have higher concentration of PM2.5.
• Dust can act as a medium to transmit
human/plant diseases1.
1[Kellogg and Griffin 2006]](https://image.slidesharecdn.com/talkondust-rainfallconnections-220326070837/85/Dust-rainfall-connections-7-320.jpg)
![When is dust a problem?
• Dust storms affect daily life activities,
hinders air/ground traffic operation.
• Affects the efficiency of solar panels and
wind turbines.
• Corrodes historical monuments and
buildings
• Anthropogenic dust can affect coral
health: bleaching
• Wind erosion removes soil nutrients (e.g.
soil organic carbon)1 thus affects
agricultural productivity
• Severe dust storms can bring economic
disaster: dust bowl of the 1930s.
1[Li et al., 2008]](https://image.slidesharecdn.com/talkondust-rainfallconnections-220326070837/85/Dust-rainfall-connections-8-320.jpg)
Dust-rainfall connections
- 1. Effect of dust on rainfall over the Red Sea coast from WRF-Chem simulations - Sagar Parajuli March, 2022
- 2. A few questions to ponder • What is dust? • Is dust good or bad? • Is there a difference between natural and anthropogenic dust?
- 3. Interesting facts about dust/aerosols • Sand dunes are dynamic system that reorganize constantly -- moving at the rate of about 8-12 feet per year. • Sand from sand dunes cannot be used for construction. • Dust is the smallest building block of entire physical existence that can be physically measured (dust emission/deposition can be measured directly) • The Solar System was formed from a large, rotating cloud of interstellar dust and gas called the solar nebula
- 4. • Without dust or aerosols there would be no rainfall1, can you imagine? • Measurements in high Cirrus clouds show that Mineral dust dominantly forms IN2 • Dust from China can affect precipitation in California, USA3 2Cziczo et al., 2013 Interesting facts about dust/aerosols 3Creamean et al., 2013 1J. Aitken (18th century)
- 5. Why dust is good? • Dust cycle is an important part of the Earth System. • Dust scatters and absorbs SW and LW radiation thus regulates climate and environment • Mineral dust acts as a fertilizer (P, Fe) for terrestrial/marine ecosystem1. • Dust is a key player of long-term climate (paleoclimate). 1[Koren, et al., 2006]
- 6. Why dust is good? • Dust affects rainfall: modifies cloud microphysical properties by forming IN/CCN. • Most dust particles are coarse in size, so dust is not a big problem itself for air- quality. • People have lived in the desert regions since ages, natural dust/sand was not an air-quality threat.
- 7. When is dust a problem? • Dust became an air-quality issue after increased human activity, which generated anthropogenic dust • Anthropogenic dust generated from agricultural/disturbed lands and construction: finer particles and may contain environmental pollutants • Its ageing, or interaction with other pollutant aerosols and gases makes it a threat. • Anthropogenic pollutants typically have higher concentration of PM2.5. • Dust can act as a medium to transmit human/plant diseases1. 1[Kellogg and Griffin 2006]
- 8. When is dust a problem? • Dust storms affect daily life activities, hinders air/ground traffic operation. • Affects the efficiency of solar panels and wind turbines. • Corrodes historical monuments and buildings • Anthropogenic dust can affect coral health: bleaching • Wind erosion removes soil nutrients (e.g. soil organic carbon)1 thus affects agricultural productivity • Severe dust storms can bring economic disaster: dust bowl of the 1930s. 1[Li et al., 2008]
- 9. Pollution is a regional environmental problem • Anthropogenic dust in Tigris- Euphrates region affects air quality in the downwind region: e.g., Kuwait, UAE, Saudi Arabia • Depleted Uranium was used heavily in the Tigris-Euphrates region during Gulf War (1991). • The U.S. Navy’s mesoscale meteorological system COAMPS1 was used for real-time dust forecasts during Operation Iraqi Freedom (OIF) in 2003. • Regional cooperation is essential for mitigating the adverse effects of air pollution 1Coupled Ocean/Atmosphere Mesoscale Prediction System Tigris-Euphrates region
- 10. Health aspects of air pollution • Long-term exposure of PM2.5 and finer particles can cause severe cardiovascular diseases • COVID-19 deaths are associated with the level of background air pollution 1https://www.latestgkgs.com/science-technology-5467-a 2https://academic.oup.com/cardiovascres/article/116/14/2247/5940460?login=true
- 11. Dust effect on rainfall • Water is essential for plant and animal life • Rainfall affects the distribution of surface and ground water resources, which are constantly declining over the MENA1 1Joodaki et al., 2014 why study?
- 12. • Irregular rainfall patterns: causes floods and droughts • Also increase water-borne diseases such as malaria and diarrhea2 • Understanding how dust affects the regional rainfall pattern is crucial, particularly in regions with high atmospheric dust loads such as MENA Dust effect on rainfall: why study? 2Trinh et al., 2020
- 13. WRF-Chem model domain The study area over the Red Sea coast (d03) showing nested domains (d01 and d02) used in WRF-Chem model simulations.
- 14. Summary of WRF-Chem model configuration • Cloud-resolving simulations at 1.5 × 1.5 km – thanks to Shaheen supercomputer • Simulations carried for the month of August from 2006-2015 • We calibrated dust amount and size distribution to obtain realistic AOD and aerosol sizes • MOSAIC 8-bin sectional aerosol scheme • Double-moment microphysics scheme (Morrison) • Boundary conditions from high- resolution ECMWF operational analysis with SST updates
- 15. Model experiments The total effect (ΔTot), indirect effect (ΔIndir), and direct effect (Δdir) of dust is then given by, Δtot = F1-F2 (1) Δindir = F3-F4 (2) Δdir = ΔTot-ΔIndir = (F1-F2)-(F3-F4) (3) Aerosol species Experiments with both direct and indirect effects Experiments with indirect effects only F1 all_aer F2 no_dust F3 all_aer, no_direct F4 no_dust, no_direct Dust yes no yes no Sea salt yes yes yes yes Anthrop- ogenic yes Yes yes Yes
- 16. Validation Abha Field Campaign August 2009 Micropulse Lidar (MPL)
- 17. Results
- 18. How does the model perform?
- 19. How does the model perform? Daily- accumulated rainfall Diurnal wind profile at KAUST.
- 20. How does the model perform KAUST lies slightly out of the ‘Rain Zone’.
- 21. How does model perform?
- 22. Dust effect on rainfall • Over the study region, rainfall is very much predictable • The daily maximum rainfall occurs exactly at 15:00 UTC (6pm local time), at the same place -- over the mountains. • It is because the moisture availability is governed by sea breezes which are recurring feature.
- 23. Rain processes over the Red Sea coast Diurnal rainfall due to warm- cloud processes Profile of cloud water mixing ratio
- 24. CCN and aerosol size comparisons • Comparison with data from Abha field campaign: August 2009 • CCNs are generally overestimated by up to a factor of two.
- 25. CCN comparisons with VIIRS Satellite data • The # of activated CCN in a convective cloud base is a function of cloud drop effective radius Re, which can be retrieved from a satellite imager with high-resolution wave bands1. • Similarly, the cloud base updraft speeds is a linear function of cloud- base height2. • Again, the model overestimates CCNs • Although large, difference is reasonable for microphysical parameters given their high uncertainty VIIRS satellite-retrieved CCN # concentrations, August 2015 1Rosenfeld et al., 2014 2Yue et al., 2019
- 26. Dust contribution on CCN # concentration • There is up to ten-fold increase of CCN, making dust the major contributor • Although overestimated, CCN #s much closer to observations with dust. • Rainfall amount well simulated -- CCN is not a limiting factor for rain formation. • Cloud growth does not strongly depend on CCNs, unlike in other aerosol-limited areas1 CCN # concentrations at 0.2% at a cloud-level height (570 hPa) averaged at 15:00 UTC for August, 2015 1Koren et al., 2014
- 27. Dust effect on radiative balance • Indirect effect very small, total effect governed by direct effect • Decreases SW radiation and increases LW radiative fluxes at the surface • Δtot (top row) • Δindir (middle row) • Δdir (bottom row)
- 28. Dust effects • 2-m air temp. • 10-m winds • 2-m water vapor mixing ratio • Black dots: statistically significant areas • Δtot (top row) • Δindir (middle row) • Δdir (bottom row)
- 29. Direct effects • Warming and high moisture over the lands due to enhanced breeze circulation • Δtot (top row) • Δindir (middle row) • Δdir (bottom row) direct effects only experiments direct effects only but without SW absorption (SW refractive index changed from 0.003 to 0)
- 30. Physical mechanisms: direct effect • Well understood • Dust induces land surface cooling (warming) by SW scattering (absorption) • Land cooling (warming) ultimately weakens (strengthens) the sea breeze circulation, thus reducing (increasing) the landward moisture transport.
- 31. Physical mechanisms: indirect effects • Indirect effects have higher uncertainty because aerosol effects on clouds and rainfall process less understood • During the early 21st century, research showed that aerosols suppress rainfall1 • Current understanding: aerosols suppress rainfall initially but enhances during the later stage of the convection, through a process called aerosol invigoration2 2(Koren et al., 2012) 1(Rosenfeld et al., 2000)
- 32. Results: Dust effects on rainfall Normal rainfall events Extreme rainfall events Indirect effect (%) Direct effect (%) Total effect (%) Indirect effect (%) Direct effect (%) Total effect (%) 4.76 -5.78 -1.02 4.54 1.51 6.05 Yes Yes Yes Yes No Yes • Dust enhances extreme rain events but suppresses normal rain events. • Consistent with previous studies (e.g., Alizadeh-Choobari, 2018; Li et al., 2011): dust increases (decreases) rainfall in high (low) rainfall conditions. Significant?
- 33. Summary • In summary, dust enhances rainfall for extreme-rainfall events but suppresses rainfall for normal-rainfall events. • For normal-rainfall events, the suppressing direct effect is strong and significant, which is governed by the weakening of the sea breezes in response to SW cooling by dust. • The extreme rainfall events are governed by diverse synoptic processes and breezes do not play significant role in the effect.
- 34. Broader implications • Dust and dust storms are considered as problems from an air quality perspective, but our study highlights their positive contribution in modulating rain • Managing of regional water resources1, in the context of Saudi Green Initiative – planting 10 billion trees • Understanding of extreme rainfall events: minimize the risk of heavy flooding and loss of public property • Implications for cloud seeding -- regional rain enhancement efforts. Presence of background dust aerosols must be considered in the dusty regions. 1(Mostamandi et al., 2020)