Understanding Atmospheric Pressure and Wind Dynamics

These flashcards cover key concepts related to atmospheric pressure levels, wind dynamics, air mass characteristics, and meteorological phenomena, providing a comprehensive review for the exam.

850 hPa

This pressure level, typically around 1.5 \, \text{km} above sea level, is crucial for assessing low-level temperature conditions, temperature advection, and the presence of inversions, often indicating the boundary layer's top.

700 hPa

Located approximately 3 \, \text{km} above sea level, this pressure level is used to evaluate mid-level relative humidity, cloud cover, and the potential for precipitation, providing insights into atmospheric moisture content and stability.

500 hPa

At an altitude of roughly 5.5 \, \text{km}, this pressure level is fundamental for assessing vorticity (the rotation of air), identifying the steering currents for weather systems, and locating the mid-latitude low pressure centers that drive cyclonic activity.

200 and 300 hPa

These upper-level pressure levels, found at approximately 12 \, \text{km} and 9 \, \text{km} respectively, are vital for analyzing wind patterns, locating and determining the strength of the jet stream, and understanding upper-level divergence and convergence, which influence surface weather systems.

Pressure Gradient Force (PGF)

The force that initiates air movement, driving it from areas of higher atmospheric pressure to areas of lower pressure. It acts perpendicular to isobars and its strength is directly proportional to the magnitude of the pressure gradient.

Coriolis Force (CF)

An apparent force resulting from the Earth's rotation that deflects moving objects, including air parcels. In the Northern Hemisphere, it deflects objects to the right of their motion, and to the left in the Southern Hemisphere. Its strength depends on the object's speed and latitude.

Geostrophic Wind

An idealized wind that results from a perfect balance between the Pressure Gradient Force (PGF) and the Coriolis Force (CF). This wind blows parallel to straight isobars and is typically a good approximation for winds in the upper atmosphere, where friction is minimal.

Gradient Wind

A theoretical wind model that describes air flow along curved paths, such as around high or low-pressure centers. It accounts for the balance between the Pressure Gradient Force (PGF), the Coriolis Force (CF), and the centrifugal force due to the curved motion.

Conservation of Mass

A fundamental principle stating that in the atmosphere, the total mass of air is conserved. This implies that the rate of change of mass within a volume is equal to the net mass flowing into or out of that volume, which is expressed by the continuity equation and impacts vertical motion.

Convergence

The atmospheric condition where air flows inward and

Divergence

The spreading out or outward flow of air in a particular region. In the upper atmosphere, divergence often leads to sinking air (subsidence) to conserve mass, which is associated with high pressure systems, clear skies, and stable conditions at the surface.

Monsoon

A large-scale seasonal wind system characterized by a dramatic change in wind direction between seasons. Monsoons are primarily driven by the differential heating between land and ocean, leading to distinct wet (summer) and dry (winter) seasons in affected regions, particularly in Asia and parts of Africa.

El Nino

A periodic climate pattern characterized by an anomalous warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean, typically occurring every 2-7 years. It is associated with a weakening of the trade winds and a shift in atmospheric circulation (Walker Circulation), leading to significant global weather impacts.

La Nina

A climate pattern in the tropical Pacific Ocean characterized by unusually cool sea surface temperatures in the central and eastern equatorial Pacific. It represents an intensification of the typical Pacific pattern, with stronger trade winds and increased upwelling of cold water, often leading to opposite global weather impacts compared to El Niño.

Pacific Decadal Oscillation (PDO)

A long-term ocean oscillation pattern in the North Pacific Ocean that affects sea surface temperatures. Its phases (warm or cool) typically last for 20-30 years, influencing regional climate and marine ecosystems along the Pacific Rim, and is distinct from the shorter-term El Niño-Southern Oscillation (ENSO).

North Atlantic Oscillation (NAO)

An atmospheric phenomenon characterized by fluctuations in the difference of atmospheric pressure at sea level between the Icelandic Low and the Azores High. The NAO affects the strength and direction of westerly winds and storm tracks across the North Atlantic, significantly influencing winter weather patterns in Europe and eastern North America.

Air Masses

Extensive bodies of air, often several thousand square kilometers in extent, which acquire relatively uniform temperature and moisture characteristics from their source regions. They are typically classified based on their temperature (e.g., polar, tropical) and moisture content (e.g., continental, maritime).

Cold Front

A leading edge of an advancing mass of colder, denser, and typically drier air, displacing warmer, moister air. Cold fronts are often characterized by a relatively steep slope, leading to rapid uplift of warm air, resulting in a narrow band of intense precipitation, thunderstorms, a sharp temperature drop, and a wind shift.

Warm Front

The leading edge of an advancing mass of warm, moist air that moves over a colder, denser air mass. Warm fronts typically have a gentle slope, leading to a gradual uplift of warm air, which often produces widespread, light precipitation (drizzle, snow), a gradual temperature rise, and a wind shift.

Dryline

A sharp atmospheric boundary separating two air masses with distinct moisture content, but often similar temperatures. Commonly found in the Great Plains of the United States, it separates moist maritime tropical air from dry continental tropical air and is a frequent focus for severe weather initiation due to strong density differences and convective uplift.

UTC Time

Coordinated Universal Time, the primary time standard by which the world regulates clocks and time. It is a 24-hour time system used universally in meteorology and aviation to ensure consistent global communication and to avoid confusion arising from local time zones and daylight saving changes.