Bottom line is heating of the surface, Andrew. "Insolation" is the buzzword.
Over land, the amount of heat absorbed/reflected determines the amount and
rate of rising air parcels...over water, the absorption rate is pretty
constant. I'm not saying that there are no differences over water, only that
the differences are small...the jet stream plays a part in moving pressure
systems around on the face of the earth with little attention paid to the
composition of the surface.

Bob Gardner

"Andrew Sarangan" wrote in message
...
Looking at the worldwide surface analysis chart, it looks like land
areas have far more pressure variations than oceans. However, I am not
sure if this is a real effect or simply an artifact of the fact that
there aren't many observation stations on the oceans. Any thoughts?

Here is an example:
http://www.opc.ncep.noaa.gov/UA.shtml