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In order to understand the effects aerosols has on clouds, we will first have to know how
the radiative energy is behaving with and without the presence of an aerosol.
1. The sun is the earth`s energy source. Clip 1 demonstrates the way the sun`s electromagnetic radiation is distributed in our atmosphere: part of the energy is scattered in the air, while most of it reaches the surface. Then, some is absorbed and the rest is reflected back.
2. When aerosol particals are present in the
atmosphere, they affect the way the photons behave.
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This is called the Direct radiative effect of aerosols in the atmosphere.
In Clip 2 the aerosol blocks part of the energy, by absorbing it or reflecting it back to space, therefor lessening the energy flow to the earth, which means cooling the atmosphere and ground underneath.
3. Now, what happens when a cloud is added to this system? - first we must remember that a cloud is made out of droplets of different sizes. These droplets are created by the condensation of water vapor around cloud condensation nucleaes (ccn), which are aerosols. In normal conditions, the droplets grow either by diffusion, in which a micron sized droplet sofahat more water vapor, or by colision coalesence, which happens while a growing droplet that gathers wheight descends and bumps into other droplets. The Indirect radiative effect of aerosols is their first effect on clouds. In Clip 3 a regular dripping cloud which contacts aerosol is suddenly full with new CCN`s, which automatically reduces the size of the droplets and equalizes it, causing any rain to stop.
4. This is not the only outcome of a cloud-aerosol interaction. As a result of the radiation absorbtion of the aerosol, (as shown on clip 2), the aerosol itself gathers energy and becomes warmer than it`s surroundings, therefor emiiting heat to the air near it. This emission produces the Semi direct radiative effect, which is shown on Clip 4. The cloud that iteracts with the aerosol finds itself in a warmer surrounding, which results in it`s evaporation. this has a more larger scale effect since the reduction of clouds affects the amount of global warming. Therefor, man-made aerosols which reduce clouds have a direct effect on the worlds global warming.
