Notes on Occluded Cyclones and Atmospheric Dynamics: Lecture 4/21

Introduction to Occluded Cyclones

• Discussed the research on occluded cyclones, highlighting the need for objective identification approaches.
• Collaboration with experts around the country to leverage a large dataset (10-11 years) to better understand these systems.
• Importance in climate models, particularly concerning precipitation changes in future climates.

Pressure and Atmosphere Layers

• Top of Atmosphere (TOA) denoted at 0 millibars, with a standard atmospheric pressure at ground level being around 1000 millibars.
• Pressure at a given height relates to the weight of the air column above it.
• Pressure decreases with increasing height.
• Example: Accumulated air mass in a column explains pressure changes and how half the mass would exert half the pressure.

Air Density and Temperature Relationship

• Comparing two columns of air with identical mass but different densities; column A with higher density than column B.
• If pressures are equal, lower density indicates higher temperature in column B.
• Thicker layers of warm air have more temperature, which affects cyclone structure characteristics.

Cyclone Structure and Dynamics

• Mid-latitude cycles typically characterized by a cold core and temperature gradients affecting pressure and wind speeds.
• Coldest air is usually found at the center of a cyclone, supporting the idea of cold air within these systems.
• Observations of cyclone behavior provide insights into their development and life cycle.

Isotherms and Pressure Gradients

• Detailed diagrams illustrating pressure gradients at various levels to show how isotherm distances affect wind speed and cyclone intensity.
• The steeper the pressure gradient, the stronger the wind.
• Understanding how pressures and temperatures interact is crucial for predicting cyclone development.

Geostrophic vs. Surface Winds

• At surface levels, friction influences wind patterns leading to zones of divergence (air flowing away).
• The relationship between upper level convergence and surface divergence impacts cyclone strength and life cycle stages.
• Illustrations used to exemplify how surface low pressure systems develop and relate to higher-level flows.

Western Tilt of Cyclones

• Mid-latitude cyclones exhibit a westward tilt that becomes significant during their development.
• The tilt is reinforced by the upper-level features and impacts the storm's evolution and intensity.
• As a storm ages, this tilt diminishes, affecting the storm dynamics as convergence occurs throughout the structure.

Cyclone Life Cycle

• As a cyclone matures, the tilt lessens, and when the surface pressure and upper-level systems align closely, the cyclone weakens.
• Emergency buildup in surface mass due to convergence can lead to increased ground pressure, signaling the end of the cyclone's life cycle.

Conclusion and Questions

• Emphasizing the integrated nature of cyclone dynamics, the importance of understanding the principles discussed, and readiness for further exploration in upcoming weeks.
• Encouragement for students to ask questions and deepen their understanding of cyclone behavior and meteorological concepts as part of their learning process.