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Frontal zone – strong T gradient

Fronts. How to identify fronts on a weather map?. Frontal zone – strong T gradient. Thickness. A measurement of how warm (high value) or cold (low values) a layer of the atmosphere is. Thickness gradient can be used to find fronts (strong gradient region). -- Hypsometric equation. Thickness.

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Frontal zone – strong T gradient

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  1. Fronts • How to identify fronts on a weather map? • Frontal zone – strong T gradient

  2. Thickness • A measurement of how warm (high value) or cold (low values) a layer of the atmosphere is. • Thickness gradient can be used to find fronts (strong gradient region). -- Hypsometric equation

  3. Thickness

  4. Cold Fronts • Cold Front (http://www.suu.edu/faculty/colberg/hazards/weather/05_cnWfronts.html) • A transition zone where a cold air mass is replacing a warm air mass Air is pushed up rapidly. Front quickly passes. Stormy! Moving speed of a front at the developing stage is ~ 25 knots (12.5 m/s) and the speed is reduced as the front "matures“. The slope of the front (the ratio of the vertical to the horizontal scale) is about 1/50 to 1/100

  5. cold warm Cold Fronts • Cold Front • A transition zone where a cold air mass is replacing a warm air mass Or blue line Front symbol is located at the warm air edge of the temperature gradient. Large temperature contrast across it (10 oC across 100 km)

  6. Cold Fronts Ci: Cirrus Cs: Cirrostratus Cb: Cumulonimbus Cu: Cumulus mediocris Cu Cs Ci Cb

  7. Warm Fronts • Warm Front (http://www.suu.edu/faculty/colberg/hazards/weather/05_cnWfronts.html) • A transition zone where a warm air mass is replacing a cold air mass Or red line Air is pushed slowly. Rainfall is generally more gentle and extended in duration. The slope of the front (the ratio of the vertical to the horizontal scale) is about 1/200 Moving speed is about 8 m/s (slower than cold fronts).

  8. Warm Fronts Ci: Cirrus Cs: Cirrostratus As: Altostratus Ns: Nimbostratus Sc: Stratocumulus St: Stratus St Ns Sc As

  9. 56 52 49 46 .. 39 37 cold air mass direction of propagation 32 31 ** L cold front warm air mass warm front . 992 996 988 Cyclone, Cold Front, and Warm Front

  10. Fronts Cold front Warm front

  11. cold warm Occluded and Stationary Fronts • Occluded Front • when a cold front overtakes a warm front. (Cold fronts moves faster than warm fronts) Or purple line Or red-blue line • Stationary Front • A front that moves very slow

  12. Occluded Front Formation of a warm front type occlusion Formation of a cold front occlusion From http://atmoz.org/blog/2007/06/10/the-warm/cloud-occluded-front-explained/

  13. Occluded, Warm, and Cold Fronts

  14. Isobars Thickness Frontogenesis Winds deflect to the right in the Northern hemisphere due to the Coriolis force

  15. Frontogenesis to (Extratropical) Cyclone Formation C Frontogenesis W C Front W C Draw the front at the warm side of the front Cyclone L W

  16. Isobars Thickness Initial Cyclone Formation The strong thickness gradient zone (TGZ) passing the center of the cyclone. Draw at the warm side Draw at the warm side

  17. Isobars Thickness Mature Cyclone The strong TGZ is away from the center of the cyclone (occluded front)

  18. Isobars Thickness Decaying Cyclone

  19. Cold Front 1 3 2 4

  20. Fronts

  21. Fronts

  22. What stage of the cyclone’s life cycle? Mature Cyclone http://www.youtube.com/watch?v=OBkf3TItuWQ (animation)

  23. Where are fronts? What’s the Stage of the Cyclone? Initial cyclone formation

  24. Dry line • A boundary separates a moist air mass from a dry air mass (sharp dew point gradient). Occurs in the spring and early summer seasons around Texas, New Mexico, Oklahoma, Kansas, and Nebraska. If there is enough moisture and instability in the warm air, severe storms can occur. Subsidence warming – dry and hot Warm, moist air Td : 50’s to 70’s T: 70’s to 80’s Hot, dry air Td : 20’s to 30’s T: 80’s to 90’s Dry line Rocky Mountains

  25. Dry line Dew points

  26. Dry line • Some people like to chase dryline storms! • It propagates eastward in the morning, then stalls by mid-afternoon, and retreats back to high plans by early evening as the hot dry side is destroyed by radiative cooling.

  27. dry air Cumulus stage (Developing stage) Mature stage Dissipation stage Thunderstorms • Occurs when atmosphere has a lot of energy (how do you know?). • Rain, hail, thunder, lightning, flash flood, and gust wind • Unstable atmosphere – using indices to help check.

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