Investigation 5: Rising Air and Stability
- Page ID
- 40379
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Some birds, such as eagles and vultures, tend not to flap their wings as much as other birds when they fly. Their flight seems effortless, almost as if they were gliding through the air. How is this possible? Figure 5.1 shows a Bonelli's eagle soaring effortlessly above a mountain range.
They use the fact that as the Sun heats the Earth's surface, warm air near the surface rises to higher altitudes. Birds such as eagles and vultures use their large wings to catch the rising air columns, called thermals, to soar high into the sky and even across mountains, much like glider aircraft. Hot air balloons also utilize the buoyancy of warm air to rise to higher altitudes, offering passengers spectacular views. (Figure 5.2).
Investigation 4 introduced the concept of saturation and cloud development in rising air. However, one thing that has yet to be covered is what allows air to rise, forming clouds in the first place. This brings us to the concept of Atmospheric Stability, which is a key weather maker. The difference between a clear, sunny day and a tornado outbreak can be determined simply by the stability of the atmosphere. The same is true between a clear day and a polluted day. Before we can determine the stability of the atmosphere, we must first explore the concept of rising and sinking air and how the temperature of the air changes as it travels in the atmosphere.
By the end of this investigation, you should be able to:
- Calculate air parcel temperature at different altitudes using lapse rates.
- Track the properties of a rising air parcel using Stüve diagrams.
- Determine atmospheric stability using measures such as CAPE and CIN.
- 5.1: Rising Air
- Adiabatic processes in the atmosphere control how rising air parcels cool and sinking ones warm. Lapse rates are introduced—10°C per 1000 m for unsaturated air (Dry Adiabatic Lapse Rate) and 6°C per 1000 m for saturated air (Moist Adiabatic Lapse Rate).
- 5.2: Charting Air Parcels
- Stüve Diagrams are used for calculating air parcel temperatures at different altitudes. Adiabats are helpful to monitor temperature changes during ascent. A practical procedure for obtaining temperatures by starting from the surface level and following the appropriate adiabat is outlined.
- 5.3: A Case Study
- Topographic lifting occurs when winds cause surface air to rise along mountains, affecting regional climates by promoting cloud formation and precipitation. Using the San Francisco Bay Area as an example, the influence of topography on rainfall is illustrated, with windward areas like Santa Cruz receiving more rainfall compared to leeward locations, such as San Jose. The concept of rain shadows is emphasized to illustrate these precipitation differences.
- 5.4: Atmospheric Stability
- Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) are introduced as they pertain to atmospheric stability, illustrating CAPE's role in rising warm air and CIN's role in sinking cooler air. Stüve diagrams are used for visualization and include a case study of severe weather in Dallas on May 20, 2019, which encourages readers to examine comparable atmospheric conditions in Topeka, Kansas, on May 29, 2019.
- 5.5: Alternative Text Descriptions for Investigation 5
- This page provides detailed text descriptions of images and charts used in Investigation 5
Thumbnail: Stable, unstable, and neutral conditions. Atmospheric Stability via the National Wildfire Coordinating Group is in the Public Domain.