The
figure to the right shows how satellite data can be used to monitor
the north-south, or meridional, transport of water vapor (qv). In
this figure, southward moisture transport is indicated in yellow
and red, while northward transport is in green and blue. Seasonal
mean qv for an 18 month period (6 seasons) spanning the
1987-88 El-Nino Southern Oscillation may be viewed by clicking
on the image to the right. The meridional moisture transport is useful in determining where the mean position of large-scale atmospheric ridges and troughs are located in the subtropics and midlatitudes. This is well illustrated over the United States where the line at which qv = 0 separates northward from southward transport and thus indicates the mean position of a ridge or trough axis. Notice the trough axis extending southwest-northeast just south of the Great Lakes. Often in the deep tropics the "0" line coincides with regions where tropical convection (and thus upper-level divergence) is observed in satellite imagery.