Middle Latitude Cyclones a storm that forms at middle and high latitudes, outside of the tropics.

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Susanna Norris
5 years ago
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warm sub tropical air (our old friend from the three cell model of global atmospheric circulation) Stationary front Frontal wave the initial kink that forms on the polar

It consists of: the central low pressure (low, which is deepening with time) overrunning of warm air over the warm front cold air surging southward behind the cold front

precip also generates energy for the storm as Latent Heat is released Warm sector warm air mass located between the cold and warm fronts (c, d, and e) Mature cyclone

1 Middle Latitude Cyclones a storm that forms at middle and high latitudes, outside of the tropics. Polar Front Theory a theory that explains the life cycle of mid latitude cyclones and their associated fronts Polar Front the boundary that separates cold polar air from warm sub tropical air (our old friend from the three cell model of global atmospheric circulation) Stationary front Frontal wave the initial kink that forms on the polar front (b) Apr 21 7:27 AM Open wave fully developed cyclone (c) A fully developed "wave cyclone" is seen hours from its inception. It consists of: the central low pressure (low, which is deepening with time) overrunning of warm air over the warm front cold air surging southward behind the cold front wide spread precip ahead of the warm front narrow band of precip along the cold front Wind speeds continue to get stronger as the low deepens The production of clouds and precip also generates energy for the storm as Latent Heat is released Warm sector warm air mass located between the cold and warm fronts (c, d, and e) Mature cyclone (initial occlusion) (d) As the cold front moves swiftly eastward, the systems starts to occlude. Storm is most intense at this stage have an occluded front trailing out from the surface low triple point/occlusion is where the cold, warm and occluded fronts all intersect Apr 21 8:36 AM 1

has been lifted upward The cold air is at the surface stable situation. Apr 21 9:10 AM Mid latitude cyclones can produce a wide variety of precipitation types.

2 Advanced Occlusion (e) the warm sector diminishes in size as the systems further occludes. The storm has used most all of its energy and dissipates All of the APE has been utilized and the KE has dissipated into turbulence cloud/precip production has diminished The warm sector air has been lifted upward The cold air is at the surface stable situation. Apr 21 9:10 AM Mid latitude cyclones can produce a wide variety of precipitation types. Precipitation types include: rain, freezing rain, hail, sleet, snow pellets, and snow. Frozen forms of precipitation (except hail) are common with storms that occur in the winter months. Hail is associated with severe thunderstorms that form along or in front of cold fronts during spring and summer months. Apr 21 8:40 AM 2

Apr 21 8:54 AM Where do mid latitude cyclones

northeastern United States) storms that form

3 Apr 21 8:54 AM Where do mid latitude cyclones tend to form? Named after the region where they form Nor easters (a favorite of weather fans in the northeastern United States) storms that form along the eastern seaboard of the US and then move northeastward Apr 21 8:56 AM 3

Developing Mid latitude Cyclones and Anticyclones Cyclogenesis development or strengthening of a mid latitude cyclone What causes mid latitude cyclones and anticyclones to

So, we can change surface pressure by changing the amount of air over a certain location.

4 Developing Mid latitude Cyclones and Anticyclones Cyclogenesis development or strengthening of a mid latitude cyclone What causes mid latitude cyclones and anticyclones to develop? (or how can we change the air pressure at the surface?) Remember, air pressure is just the weight of the overlying air. So, we can change surface pressure by changing the amount of air over a certain location. The secret lies in convergence and divergence Convergence, divergence, and vertical motions associated with surface pressure systems. Notice that for the surface storm to intensify, the upper trough of low pressure must be located to the left (or west) of the surface low. Apr 21 9:14 AM Another view Apr 21 9:19 AM 4

Meteorology Ch 8 Day 2.notebook Long waves in the upper level flow Long waves are a fundamental feature on an unevenly heated rotating spherical planet.

current long wave positions Apr 21 9:20 AM Short waves in the upper level flow Short waves (short wave troughs) are embedded in the long waves move quickly to the east weaken when move to a long wave

5 Meteorology Ch 8 Day 2.notebook Long waves in the upper level flow Long waves are a fundamental feature on an unevenly heated rotating spherical planet. also referred to as Rossby waves usually are 4 6 of them around the globe at a given time wavelength varies between km are generally stationary or move very slowly east or west Here are the current long wave positions Apr 21 9:20 AM Short waves in the upper level flow Short waves (short wave troughs) are embedded in the long waves move quickly to the east weaken when move to a long wave ridge strengthen when they move to a long wave trough Short waves are readily observable at mid levels (e.g., 500 mb chart) Short waves are an important ingredient for the development and intensification of a mid latitude cyclone through baroclinic instability Apr 21 9:23 AM 5

Apr 21 9:26 AM Jet streak core of strongest jet stream Areas of upper level convergence and divergence Therefore, jet streaks are also important in the development of mid latitude

24 (a) As the polar jet stream and its area of maximum winds (the jet streak or MAX), swings over a developing mid latitude cyclone, an area of divergence D draws warm surface air

6 Apr 21 9:26 AM Jet streak core of strongest jet stream Areas of upper level convergence and divergence Therefore, jet streaks are also important in the development of mid latitude cyclones. Figure 8.24 (a) As the polar jet stream and its area of maximum winds (the jet streak or MAX), swings over a developing mid latitude cyclone, an area of divergence D draws warm surface air upward, and an area of convergence (C) allows cold air to sink. The jet stream removes air above the surface storm, which causes surface pressures to drop and the storm to intensify. (b) When the surface storm moves northeastward and occludes, it no longer has the upper level support of diverging air, and the surface storm gradually dies out. Apr 21 9:26 AM 6

Air Masses of North America cp and ca air masses Air mass characterized by very cold and dry conditions

Air Masses of North America cp and ca air masses Air mass characterized by very cold and dry conditions Chapter 8: Air Masses, Fronts, and Middle-Latitude Cyclones Air masses Fronts Middle-latitude cyclones Air Masses Air mass an extremely large body of air whose properties of temperature and humidity are