ESS228
Prof. Jin-Yi Yu
Quasi-Geostrophic Approximation
http://snowball.millersville.edu/~adecaria/ESCI445/esci445_10_filtered_equations_files/image002.gif
§Quasi-geostrophic approximation use the geostrophic wind for the actual wind everywhere except when computing divergence. 
§The Q-G approximation eliminates both sound and gravity waves as solutions to the equations of motion.