Left entrance region:ConvergenceSinking motionIncreasing surface pressureLeft exit region:DivergenceRising motionDecreasing surface pressureRight entrance region:DivergenceRising motionDecreasing surface pressureRight exit region:ConvergenceSinking motionIncreasing surface pressureMovement from trough to ridge:Air speeds upDivergenceRising motionDecreasing surface pressureMovement from ridge to trough:Air slows downConvergenceSinking motionIncreasing surface pressureCHAPTER 10 EXTRATROPICAL CYCLONES FORMING EAST OF THE ROCKY MTS.Where will a low-pressure system center form at the surface relative to an upper air trough and ridge? On the EAST side of the trough under the LEFT EXIT region of the jetstreakConsider a situation in which upper level divergence exceeds low-level convergence:There is a surface low that is weakening  Left entrance region: Convergence Sinking motion Increasing surface pressure Left exit region: Divergence Rising motion Decreasing surface pressure Right entrance region: Divergence Rising motion Decreasing surface pressure Right exit region: Convergence Sinking motion Increasing surface pressure 1 Movement from trough to ridge: Air speeds up Divergence Rising motion Decreasing surface pressure Movement from ridge to trough: Air slowsdown Convergence Sinking motion Increasing surface pressure Both curvature and jetstreak influence flowEffects of Heating and cooling on development of highs and lows“Diabatic processes” involve heating and cooling, usually dude to solar heating1. Conduction (contact with surface)2. Convection (rising plumes)3. Radiation4. Latent heat release2Warming of the atmosphere will lead to the formation of low pressure at the surface Cooling of the surface will lead to the formation of high pressure at the surfaceLow-pressure centers over the ocean tend to be stronger then low-pressure centers over continents- More evaporation occurs over the oceans then over land, leading to more latent heating in the could and a reduction in surface pressure- Friction is reduced over water, so frictional dissipation of the low occurs at a slower rateIf an air column is heated through latent heat release, how will the surface pressure change? The surface pressure will LOWER when an air column is heated.When air pressure is rising due to a surface low pressure system any latent heat release will INTENSIFY the surface low.SUMMARY1. Divergence/Convergence (wind speed and direction) in upper level flow2. Cyclonic/Anticyclonic flowa. Cyclonic = counter clockwise and slower then geostrophic3. Curvature effect, flow around troughs/ridgesa. Direction of divergence/convergence4. Role of friction, surface low is diverted towards low pressureDevelopment of High and Low Pressure CentersDynamic processes (curvature, jetstreaks, and friction) and thermodynamic processes (heating and cooling) cause a redistribution of mass in the atmosphere and create high and low pressure centers.• We need to consider all of these processes (curvature, jetstreaks, friction, heating, and cooling) to understand why high and low pressure centers form in a particular location.• Low pressure at the surface usually forms initially due to upper level features such as troughs and jetstreaks• High pressure at the surface usually forms due to cooling of the airAir flows in towards a low pressure center at the surface and rises. This rising air is associated with clouds and precipitation. The air then diverges at upper levels of the troposphere.• Air flows outward from a high pressure center at the surface, leading to sinking motion above the high pressure center. This sinking motion is typically associated with clear skies. At upper levels air often converges above a high pressure center.3- Curvature effect will result in CONVERGENCE at A- Curvature effect will result in CONVERGENCE at E- Curvature effect will result in N/A at F- Curvature effect will result in DIVERGENCE at C- Jetstreak effect will result in CONVERGENCE at A- Jetstreak effect will result in N/A atB- Jetstreak effect will result in DIVERGENCE at C- Jetstreak effect will result in CONVERGENCE at G- C will have maximum UPPER LEVEL DIVERGENCE- A will have maximum UPPER LEVEL CONVERGENCE- C will develop a surface LOW- A will develop a surface HIGHConvergence is a net INFLOW of air molecules into a region of the atmosphere, and is associated with an INCREASE of surface pressureAssuming that the spacing between height contours remain constant an air parcel will SLOW DOWN as it move from a ridge to a trough at 300mb leading to CONVERGENCE between the ridge and trough Convergence of air at the surface will result in RISING MOTION in an air column, which is associated with CLOUDS/PRECIPITATION For a straight jetstreak at 300mb you would expect a sinking motion in the LEFT ENTRANCE REGION AND RIGHT EXIT REGION How does surface friction modify the pressure at the center of low and high-pressure systems? Surface friction causes air to flow into lows increasing the central pressure and out of highs decreasing their central pressure. The pressure gradient force is strongest in the entrance region and the Coriolis forceis strongest in the exit region of jetstreaksMore evaporation occurs over the oceans than over land, leading to more latent heating in the clouds and a reduction in surface pressure.Friction is reduced over water so frictional dissipation of the low over water occurs at a slower rate4Geostrophic Balance = horizontal PGF + Coriolis ForceAbove the boundary layer the atmosphere is also close to being in geostrophic balanceFor exact balance isobars must be straight and parallel and air flows parallel to isobarsA surface low has formed in SE Colorado. Where is the trough/jetstreak that formed this low located? West of the low, near Rockies Air masses are least likely to develop along coastlinesA surface low has formed in a given location. For this low to intensify, of for its pressure to decrease further, where should the trough axis be relative to this low? West Prior to a cyclone 4 distinct air masses exist, reflecting a temperature gradient between the equator and the poleInitial development of a cyclone- Small wave introduces curvature, jet streak can form, enhancing divergence east of troughCyclones for preferentially in 5 locations in North America5Extratropical Cyclones- Form along the jet stream-