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In atmospheric, the change of mixing ration $C_i$ of a chemical species $i$ is determined by:

$\frac{\partial C_i }{\partial t} = -\bigtriangledown (VC_i)+\frac{\partial }{\partial z}(k_z\frac{\partial C_i }{\partial z}) + (\frac{\partial C_i }{\partial z})_{dry}++ (\frac{\partial C_i }{\partial z})_{wet}+(\frac{\partial C_i }{\partial z})_{conv}+P_i-L_i+E_i$

  1. The first term represent the $Ci$ change due to horizontal and vertical advection.
  2. The fifith term on the right hand represent the $Ci$ due to the vertical convection.

I have read about this question "What exactly is the difference between advection and convection?".

The answer told, which I quoted:

Advection is the movement of some material dissolved or suspended in the fluid.
Convection is the movement of a fluid, typically in response to heat.

But when we are just talking about the chemical species. They are not in fluid form. So,how dos the convection process mean?

Update: The equation was from a phD dissertatio Climate and Air Pollution Modeling in South America focus on Megacities. Links here

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    $\begingroup$ Conv = Convective Precipitation? Wet could only mean non-convective precipitation. $\endgroup$ – daniel.neumann Mar 29 '16 at 8:33
  • $\begingroup$ Could you give a reference to the equation? $\endgroup$ – daniel.neumann Mar 29 '16 at 8:44
  • $\begingroup$ why aren't the chemical species in fluid form? aren't they subject to the same movement? $\endgroup$ – farrenthorpe Mar 30 '16 at 23:06
  • $\begingroup$ @farrenthorpe. In my opinion, chemical in particular phase were also included. $\endgroup$ – Han Zhengzu Mar 31 '16 at 5:21
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The difference between advection and convection in Chemistry Transport models (CTMs) is a question of scale:

  • Advection is driven by winds that are provided by the meteorological input dataset. Thus, the wind is resolved in the meteorological data.
  • Convection is driven by sub grid processes (e.g. temperature gradients) and is paramterized in CTMs.

See for example:

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