1st Edition ATMS 120 Lecture 9 Outline of Last Lecture I Doppler effect and radar II Radar operation modes III Radar estimated precipitation IV Extra tropical cyclones A Characteristics B Origins and tracks Outline of Current Lecture I Coriolis effect II Development of high and low pressure systems III The jet stream IV Troughs and ridges V Constant pressure maps sloping pressure surfaces VI Air flow alof VII Curvature effects Current Lecture I The Coriolis accounts for large storms hurricanes cyclones In the northern hemisphere these storms rotate counter clockwise In the southern hemisphere they rotate clockwise This does not happen on a smaller scale in toilet bowls for instance If the Coriolis effect were observed on a human scale people in the northern hemisphere would be falling to the right and people in the southern hemisphere would be falling to the lef The Coriolis effect has no effect on the equator and maximum effect on the poles If there were no Coriolis effect high pressure systems would all move straight into low pressure systems Instead in the northern hemisphere these pressures are pushed inward and rotate to the right at the same time creating a counter clockwise spin II Main idea To increase the surface pressure put more air molecules in a column To decrease the surface pressure remove some air molecules from the column This is accomplished by convergence and divergence These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute For a high pressure system to strengthen convergence alof must be greater than divergence at the surface There is a net gain of air molecules in the column weight of air over area on surface increases For a low pressure system to strengthen divergence alof must be greater than convergence at the surface There is a net loss of air molecules in the column weight of air over area on surface decreases III The jet stream a band of strong winds that encircle the earth in a wave like pattern that moves from the west to the east Exists where warm air meets cold Creates and destroys high and low pressure systems The whole point of understanding winds in the context of force balances is to understand what happens when they are not in balance Specifically when they are not in balance the development of surface high and low pressure systems are the result Jet streams can be 200 300 miles wide and as large as 1 mile thick They can be thousands of miles long and extend vertically from the tropopause down to 500mb at the furthest For their location in their wave like pattern they can vary between 30 degrees N to 80 degrees N Jet streaks regions of the jet stream with exceptionally fast winds IV If the jet stream is north of your location it will be warm there If the jet stream is south of your location it will be cold there Ridges when the jet stream bends to the north Synonymous with warm weather Troughs when the jet stream dips to the south Synonymous with cold weather Troughs occur when one area is cooled and the others are warmed Ridges occur when one area is warmed and the others are cooled This winter California has been under a semi permanent ridge They have been experiencing warm weather This winter Champaign IL has been under a semi permanent trough We have been experiencing cold weather V Key idea the thickness of a layer in the atmosphere is governed by the mean air temperature between the top and bottom of the layer Troughs cold temperatures low surface pressure Ridges warm temperatures high surface pressure VI Key feature fast around the ridge slow around the trough The air flow in the jet stream slows down afer a ridge and piles up convergence The air flow in the jet stream speeds up afer a trough and spreads apart divergence If air converges high temperature If air diverges low temperature VII How the jet stream creates low pressure When air flow slows down top of lef column air converges and sinks it diverges clockwise onto the surface creating high pressure When surface pressure is low bottom of right column air converges counter clockwise and rises and divergence in the jet stream increases speeds up Convergence happens afer a ridge and before a trough Divergence happens afer a trough and before a ridge Remember troughs are associated with cold weather ridges are associated with warm weather