Example 1.

If positive, contributes to density rises.  Actually, the concept of advection is very important in many areas of synoptic analysis, in meteorology, hydrology, geophysics and oceanography.  Advection is always found by finding the product of the wind speed and the gradient of a quantity (say, temperature).

 

        

 

Figure 1:  Schematic chart illustrating density advection (wind speed constant) locally increasing the density (mass) in a fixed air column.

 

 

Example 2:

 

The divergence term measures the tendency for lateral spreading (and vertical spreading) of air to change the amount of air in the air column.

 

Figure 2:  Schematic chart illustrating wind divergence (density constant) locally decreasing density (mass) in a fixed air column.

 

 

DISCUSSION QUESTION: 

 

Given your discussions in Metr 200 and 201, can you think of one important implication of the changes in density in an air column with fixed temperature, volume and cross-sectional area?