reply to post by beaverg
oh... sorry, i did not mean to go over anyones head, i assumed and that was wrong on my part.
let me further describe what is going on.
first a stable atmosphere is one that ismost simply described as layered with the most dense on the bottom and less dense on the top. this means that
if any layer or part of the atmosphere is moved up or down it will return to its original position.
an unstable atmosphere is most simply described as one that has the most dense above and less dense below, and that means that it wants to correct
itself and the less dense will continue to rise until it reaches a state of equilibrium.
this is why we have thos big ol tall thunderclouds in an unstable atmosphere. large pockets of warmer and less dense air rise, condensing, but
remaining less dense through a latent heat process and can reach altitudes of over 50k feet.
a LEWP or line echo wind profile describes a category of radar returns that can be indicitive of strong straight line winds, and these can often be
mistaken for tornadoes and the likes.
take this picture
for example. the purple winds that are described as cold down draft
are (in the case that i am describing) coming from say 850mb or about 5k feet or so. the winds here are (normally) above the friction layer, and in
the cast of most frontal systems producing thunderstorms these winds are part of the warm belt of fast moving air that you may have heard described as
a low level jet. this is not the only case that this can happen but is merely one example.
as the line of thunderstorms develop ahead of the cold front, you get an area of higher pressure right behind the storms. this mesohigh (as it is
called) interacting with the downdraft of a thunderstorm can on occasion produce a gear like mechanism that can create an unobstructed path for the
winds associated with the llj to plummet to the ground, maintaining thier speeds, ahead of or right at the storm. this is not the same as the regular
gustfront, but can cause large amounts of wind damage. on radar this phenomenon is depicted as a weaker return behind a "bowing" linear storm
return, and is not unsimilar to what is called a "bow echo".
for gravity waves. imagine if you will a big bowl of oil and water that sets separated on a table. neither layer wants to move because they are less
dense on tp and more dense below. now imagine that you pick up this bowl off the table by say... a half inch and drop it back on the table. the fall
will cause the top layer to have a ripple effect and oscellate up and downward until all the energy caused by the gravitaional effect on the layer is
either disipated or another outside factor is introduced.
this can be seen with layers of air being propogated over shallow anticyclones or mountains and the like, and is common in stable atmosphere leeward
hope that helps.