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Types of Fronts and their Characteristics in Atmospheric Sciences

This refresher course provides an overview of the four main types of fronts (warm front, cold front, stationary front, occluded front) and their associated changes in temperature, dew point, wind direction, pressure, and cloudiness. It also explains the vertical structure of fronts and their connection to low-pressure systems. The course highlights the typical cloud progression before and after frontal passage, as well as the concept of occluded fronts. Additionally, it covers the evolution of cyclones and the energy source of midlatitude cyclones.

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Types of Fronts and their Characteristics in Atmospheric Sciences

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  1. Fronts Atmospheric Sciences 101 Winter 2019

  2. Refresher A front is a boundary between relatively uniform warm air and a zone in which temperatures cools rapidly

  3. Four Main Types of Fronts

  4. Warm Front

  5. Stationary Fronts

  6. Occluded Front (a hybrid)

  7. As a front passes there are changes in: • Temperature • Dew point • Wind direction • Pressure • Cloudiness

  8. Fronts are associated with troughs of low pressure

  9. Fronts are associated with bands of clouds

  10. Vertical Structure of Fronts

  11. Cold Front • Slope 1:50, moves fast (20-30 mph), convection on leading edge

  12. Warm Front • Smaller slope (1:200), slower (1—15 knots), more stratiform clouds

  13. Stationary Front: similar structure to warm front, but without movement

  14. There is a typical progression of clouds as cold and warm fronts approach and pass by • Cirrus • Cirrostratus • Altostratus • Nimbostratus • Cumulus after cold front

  15. There is another type of front: the occluded front • But to understand this this front, you need to learn about the life cycle of fronts and cyclones.

  16. For much of the 20th century the dominant paradigm for cyclone/frontal evolution has been the Norwegian Cyclone Model (Bergen School) Bjernkes, 1919

  17. Concept of Evolution of CyclonesBjerknes and Solberg1922

  18. Stationary Polar Front Wave Forming on Polar Front

  19. Wave Amplifies Occlusion as Cold Front Catches Up to Warm Front

  20. Occlusion Lengthens and System Weakens

  21. Warm and Cold Occlusions

  22. In the real world, only the warm occlusion is observed

  23. During the 1930s-1950s we learned the relationship between cyclones and fronts and upper level flow • Upper troughs associated with surface lows. Usually lagging to the west. • Upper ridges asociated with surface highs. Usually lagging to the west.

  24. Active fronts are generally in front of (east of) upper level troughs

  25. https://atmos.washington.edu/~ovens/wxloop.cgi?h500_slp+/-168//https://atmos.washington.edu/~ovens/wxloop.cgi?h500_slp+/-168//

  26. What is the energy source of midlatitude cyclones?

  27. The answer: warm air rising and cold air sinking

  28. Warm (less dense) air rising and cold (more dense) air sinking lowers the center of gravity of the atmosphere • Like dropping a weight. • Potential energy (energy inherent in being aloft) is converted to kinetic energy (energy of moving air)

  29. The conversion to kinetic energy is enhanced by having large differences of temperatures (large horizonal temperature gradients)

  30. No accident that cyclones grow in regions of large temperature gradients

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