Mid-Latitude Cyclones Study Notes

A dry line indicates the boundary between air masses with different:
- A. temperatures
- B. humidity
- C. height
- D. winds

Mid-latitude cyclones are significant components of weather systems, particularly important in midlatitudes due to their role in bringing precipitation and hazardous weather conditions (e.g., winds, snow).
Early theories on cyclone formation were developed in Norway during the 1920s under the “polar front theory.”
- Prior to these theories, it was known that rain and snow were associated with areas of low pressure, but much of the atmospheric dynamics remained unexplained.
- The Bergen school introduced more detailed observational methods that contributed to the understanding of atmospheric behaviors.

Cellular Structures:
- Hadley cell
- Ferrel cell
- Polar cell
- These cells represent large scale wind patterns and associated climates.
Pressure Systems:
- Polar high
- Subpolar low
- Subtropical highs
Wind Systems:
- Polar easterlies
- Westerlies
- NE Trade winds
- SE Trade winds

Diagrams illustrating frontal systems, including:
- (a) Stationary front
- (b) Frontal wave
- (c) Open wave
The process starts with a stationary front; as it develops, cyclogenesis (the formation of a cyclone) occurs.

The process of cyclone development is termed cyclogenesis.
- Accompanies the formation of precipitation in areas surrounding the warm and cold fronts of the cyclone.

The triple point is a crucial concept in cyclone dynamics, characterized by the meeting of warm, cold, and occluded fronts.
- The development of occluded fronts as cold air overtakes warm air leads to the lifting of the warm sector.
- Eventually, cyclones undergo complete occlusion and begin to weaken, characterized by:
- Cold air on both sides of the occluded front.
- A retreat of the warm sector away from the storm center.

Midlatitude cyclones derive their energy from:
- The rising of warm air and sinking of cold air, transforming potential energy into kinetic energy.
- Latent heat released during condensation of rising air contributes to cyclone intensity.
- An increasing pressure gradient between air masses leads to heightened wind speeds.

Cyclogenesis is commonly favored in certain geographical areas:
- Gulf of Mexico
- Atlantic off Carolinas
- Eastern slopes of high mountain ranges
Explosive cyclogenesis occurs when a cyclone deepens rapidly (specifically, dropping 24 mb in a 24-hour period).

Leeward Effects: Air will expand vertically as it descends mountains, contributing to local weather patterns.

Example of the March 1993 Superstorm, recognized by its “comma” shape.
Satellite images can provide insight into real-time storm formations and movement.

Thermal Lows vs. Mid-Latitude Cyclones:
- Thermal lows are shallow and often temperature induced, whereas mid-latitude cyclones exhibit dynamic low structures that are stronger aloft.
Pressure Dynamics:
- Surface pressure correlates with the mass of air above. Air density increases with convergence—where air piles up, increasing local pressure. Conversely, divergence leads to decreased pressure.
Required Relationships: To sustain a low-pressure system, divergence aloft must exceed surface convergence.

Wind patterns around highs move more rapidly compared to lows, attributed to centrifugal force’s influence on wind speeds and resulting Coriolis forces that affect directionality.

Further exploration of how convergence (air piling up) and divergence (air spreading out) operate both at surface and aloft.
- Convergence occurs upstream of a trough, leading to greater air density and pressure increases, while divergence occurs downstream.

Jet Streak: A jet streak is an area of higher wind speeds within the jet stream influencing cyclone dynamics:
- In straight flow patterns, front left and right rear areas are divergent, while changes in velocity cause shifts in Coriolis and directional flow.
- In a curved flow, the inner patterns usually prevail.

Analysis of how upper-level winds influence the strengthening and movement of surface lows, leading to hydrodynamic interactions that support cyclone functionality.

This model elucidates different conveyor belt actions during cyclone evolution:
- Warm Conveyor Belt (red): Rises along the warm front, fostering clouds and precipitation over expansive regions.
- Cold Conveyor Belt (blue): Gains moisture and rises slowly beneath the warm air.
- Dry Conveyor Belt (orange): Moves dry, cold air downward from higher altitudes in the atmosphere.

Referenced as mid-latitude cyclones that form or intensify on the east coast or Gulf Coast before moving northeastward along the coast.

Initiated as a frontal wave off the Texas coast on March 13, growing into a deep open wave cyclone over Florida.
Notable features include:
- Dropping central pressure to 960 mb, leading to hurricane-force winds.
- Setting records for snow distribution in modern meteorological history.

Highest totals include:
- 60 in. Mt. LeConte, TN (State record for single storm)
- 50 in. Mt. Mitchell, NC (Includes 36" in 24 hours, state record)
- 43 in. Syracuse, NY (Single storm record)
- Other significant totals reported for various cities, with various records for seasonal snowfalls.

Analyze and track a low-pressure system, noting the upper-level features that influence its development.