2/9/10MET 61 topic 02 1 MET 61 Topic 2 Atmospheric Dynamics

2/9/10MET 61 topic 02 2 Goal(s)… Main goal = investigate motions = winds –Wind = air in motion 1.What causes air motions? –What causes any object to move? –A force! –“F = ma” –All we need to do is indentify forces in the atmosphere → ideas about why air moves

2/9/10MET 61 topic What air motions result? –Range from “simple” to highly complex –e.g., geostropic wind is a simple wind that we can derive –Sometimes a good approximation to real (observed) winds 3.How can we characterize air motions? –What properties of air motions are useful to know?

2/9/10MET 61 topic 02 4 Kinematics of large-scale flows VIP note: we will focus on flows with 1)horizontal scales O(1000 km +) e.g., not a tornado 2)vertical scales O(10 km) E.g., not a Cu cloud 3)time scales O(one day +) e.g., not a tornado “on the order of”

2/9/10MET 61 topic 02 5 Properties are listed in Table 7.1 Need to understand: Physics what the property is what information this conveys Math how to express / compute the property

2/9/10MET 61 topic 02 6 Shear Physically A change in wind speed or direction in space Example: Winds across a front

2/9/10MET 61 topic 02 7 Example: Associated with a thunderstorm Microburst example  A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage.straight-line windstornadoes

2/9/10MET 61 topic

2/9/10MET 61 topic 02 9 Math We invent and use natural coordinates Flow-following coordinates Fig. 7.1 s = direction along the flow n = direction  to flow (and to the left) Lower cases!

2/9/10MET 61 topic Math Thus: Here, V = wind speed (scalar) Wind direction is tracked via the coordinate system!