1 / 37

Mid-latitude Cyclones

Chapter 12. Mid-latitude Cyclones. Polar Front Theory. Polar front is a semi-continuous boundary separating cold, polar air from more moderate mid-latitude air Mid-latitude cyclone (wave cyclone) forms and moves along polar front in wavelike manner

hallam
Download Presentation

Mid-latitude Cyclones

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 12 Mid-latitude Cyclones

  2. Polar Front Theory • Polar front is a semi-continuous boundary separating cold, polar air from more moderate mid-latitude air • Mid-latitude cyclone (wave cyclone) forms and moves along polar front in wavelike manner • Frontal wave, warm sector, mature cyclone, triple point, secondary low, family of cyclones

  3. Where do mid-latitude cyclones tend to form? • Lee-side lows (cyclogenesis) • Nor’easters • Hatteras low • Alberta Clipper • Explosive cyclogenesis, bomb

  4. Where do mid-latitude cyclones tend to form? • Topic: Northeasters • Mid-latitude cyclones that develop or intensify off the eastern seaboard of North America then move NE along coast

  5. Vertical Structure of Deep Dynamic Lows • Dynamic low = intensify with height • When upper-level divergence is stronger than surface convergence (more air is taken out of the top than the bottom) surface pressure drops and low formation • Topic: Convergence and divergence • Convergence between ridge and trough, divergence between trough and ridge

  6. Upper Level Waves and Mid-latitude Cyclones • Longwaves and shortwaves • Barotropic vs. baroclinic • Cold and warm air advection

  7. The Necessary Ingredients for Development of Mid-latitude Storm • Baroclinic instability • Upper-Air Support: the overall effect of differential temperature advection is to amplify the upper level wave; cut-off low • Role of the Jet Stream: the polar jet stream removes air from surface cyclone and supplies air to surface anti-cyclone

  8. The Necessary Ingredients for Development of Mid-latitude Storm • Topic: Jet Streaks and Storms • Entrance and exit regions associated with divergence and convergence, right exit allows divergence. • Conveyor Belt Model: air constantly glides through storm; warm, cold, and dry conveyor belts • March Storm of 1993

  9. Vorticity, Divergence and Development of Cyclones • Vorticity is a measure of the spin of small air parcels • Positive: cyclonic, negative: anticyclonic • Divergence aloft causes and increase in the cyclonic vorticity of surface cyclones = cyclogenesis and upward air movement

  10. Vorticity on a Spinning Planet • Earth’s vorticity always positive • Relative vorticity: curvature + shear, trough: cyclonic, ridge: anticyclonic • Absolute vorticity = Earth + relative • An increase in absolute vorticity is related to upper level convergence • A decrease in absolute vorticity is related to upper level divergence • Vorticity maxima/minima

  11. Vorticity on a Spinning Planet • Topic: Vorticity and Longwaves • Longwaves develop in upper-levels due to the conservation of absolute vorticity. • Putting It All Together • Forecasters review 200mb, 500mb, and surface maps to examine pressure, convergence, vorticity, and advection

  12. Polar Lows • Storms that develop over water behind (poleward of) main polar front. • Comma cloud, eye • Warm central core, strong winds, heavy showery precipitation. • Arctic front = baroclinic instability

More Related