Convection (velocity $v_0$ ) is responsible for the overall bulk displacement, determining how far the mass pulse travels down the domain. Conversely, diffusion (coefficient $D$ ) dictates the pulse's shape and integrity, causing it to spread, widen, and ultimately decrease in peak concentration over time. This dynamic is perfectly illustrated by the difference between Case 2, where high convection and low diffusion allow the pulse to travel a great distance while retaining a sharp, concentrated peak, and Case 1, where high diffusion causes the mass to disperse quickly, resulting in a low, almost flat profile that is barely detectable after 100 seconds.
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