as new observational techniques were developed. As upper air soundings became
more widespread and frequent, it was observed that frontal zones could exist for long
periods of time without becoming unstable and that strong cyclonic disturbances
could occur without preexisting frontal zones.
f i g u re 17. centrifugal force affects wind around high pre s s u re and low pre s s u re diff e re n t l y
figure 18. mid-latitude cyclones tend to develop in the shaded area
LLHHCe CoPGF
CoGradient Wind with Force Ce PGFSee Horizontal Divergence in
figure 18 for surface low.