I am trying to estimate the residence time of dust aerosol over the MENA region. I have tried to compute it using the equation T=fct(radius, normalized_radius,Twet). But, Twet varies with the meteorology (3*1e5, 6.91*1e5). From literature, residence time of dust is : 1) varying between ~2 and 8 days, 2) varying between ~2.4 and 12.9 days, 3) global mean is ~2.7 days, 3) average of ~4days, …
Anyone can suggest more precise season specific residence time for the MENA region.
You help is greatly appreciated.
Dear Imen, I am afraid that there is no simple answer. The MENA region is very large with various climates. Dust in UAE has not the same properties than dust in Lybia and the meteorological systems differ, too. My answer does not help much but means that there is a variety of scales. Maybe, you can restrict your domain by looking at the scales of interest.
Residence time is a quantity associated with the mechanisms for losses or sinks of atmospheric species. In the case of dust, if you think of the main sink being deposition, the residence time would be the inverse of its deposition velocity times the depth of the mixing layer. You should keep in mind that the height of the boundary layer varies with the amount of insolation and so, with the time of the day. Also, if the terrain is not flat but complex, the evolution and height of the PBL in time will depend on topography too. You should also keep in mind that deposition velocity will depend on the size of particle that you are considering and the seasonality of meteorological factors that contribute to particles being suspended in the air. I would suggest finding out experimental data for deposition velocities and proper parametrization for the evolution of the boundary layer in your region. Good luck!
My approach is pretty different as this is a Lagrangian discrete particle is entrained in a continuous Eulerian fluid (air) subjected to buoyancy forces and gravitational forces with a particle trajectory coupled with the conditions of the continuous flow within the atmospheric boundary layer. Your mathematical prediction is functional model and your constrains needs to be explicitly stated such as the terrain type, the mean velocity, the mean particle size, the mean temperature, humidity etc. Therefore given these data a miso scale simulation can be carried out to answer you more vividly. But I am afraid that this project on its own.
Just a simple comment, you can try Calipso data which provide the vertical profile of the atmosphere. It has a product of aerosol sub-types, based on it, you can see where the dust located on daily bases.
This may not helpful, but it can be a good hint.
http://www-calipso.larc.nasa.gov/products/lidar/browse_images/show_calendar.php
I would skip any calculations, and just use the NAAPS daily dust mapping data, and for the UAE the maps are at http://www.nrlmry.navy.mil/shared-bin/display_image.cgi?URL=/aerosol_web/globaer/ops_01/india/current.gif and the index along with the archives that go back about a decade is at http://www.nrlmry.navy.mil/aerosol//
Have you noticed that you have a more or less permanent dust cloud over your part of the world, that I call the "Arabia-Pakistan Dust Cloud" cause by grazing of the deserts of Arabia? I have been suggesting setting aside large areas where the Dust Cloud originates, to allow the bare soil to regrow a native grass cover, at http://www.ecoseeds.com/cool.html.
I am asking several questions about your Dust Cloud on Research gate, if you check at https://www.researchgate.net/search.Search.html?type=question&query=dust+cloud. For example, has anyone other than myself, given a name to the "Arabia-Pakistan Dust Cloud"?
As long as the soil is bare in Arabia, little rain will fall, and the Dust Cloud will continue to hover, causing extreme heat and suffering. Allowing the local native vegetation to cover the soil, that will lower the heat, no dust any more, and a major increase in annual rainfall, maybe as much as a meter a year. The lakes and rivers would flow again, that have been dry for about 5,500 years.
That is exactly what the USA had to do in the 1930s ]during the Dust Bowl to stop the dust storms, replant the bare soil to keep it from getting airborne. It took many millions of dollars and about a decade in the USA and I believe the same approach could be done for all of Arabia over a couple of generations.
- Badges
- Science topic
- Similar topics
- Geoscience
- Atmospheric Sciences