•Upper
tropospheric flows are characterized by trough (low pressure; isobars dip southward) and
ridge (high pressure; isobars bulge northward).
•The winds are in
gradient wind balance at the bases of the trough and ridge and are slower and
faster, respectively, than the geostrophic winds.
•Therefore, convergence and divergence are created at
different parts of the flow patterns, which contribute
to the development of the low and high systems.