•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.