CTM-10.04-circulació-general-atmosférica

Circulation of Winds in the Atmosphere

Overview of Atmospheric Circulation

• The video discusses general wind circulation in the atmosphere, particularly in the troposphere, focusing on the formation of anticyclones and depressions, prevailing wind directions, and their impact on climate distribution.

Earth's Axial Tilt and Insolation

• Earth's axis is tilted at approximately 23 degrees relative to its orbital plane around the sun, affecting insolation patterns across hemispheres.

• At mid-latitudes (e.g., 45°N and 45°S), solar rays strike more perpendicularly in the Northern Hemisphere, leading to higher absorption and lower albedo compared to oblique angles in the Southern Hemisphere.

Temperature Distribution

• Maximum insolation occurs between the equator and tropics, while minimum insolation is near the poles; thus, temperatures are highest at the equator and lowest at polar regions.

• As latitude increases, solar radiation becomes less direct, resulting in cooler temperatures due to increased albedo effects.

Wind Patterns in Troposphere

• Air temperature variations lead to pressure differences: warmer air near the equator creates low-pressure zones while colder air at poles results in high-pressure areas (anticyclones).

• This theoretical model suggests a convective cell between polar anticyclones and tropical depressions; however, Earth's rotation complicates this ideal scenario.

Coriolis Effect on Wind Circulation

• The Coriolis effect causes winds to deflect clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. This deviation disrupts theoretical convective cells between high and low-pressure areas.

• In intertropical regions, rising air reaches tropopause before moving poleward but is deflected leftward by Coriolis effect around 30° latitude leading to high-pressure zones forming instead of completing a full convective cycle.

Formation of Additional Convective Cells

• High-pressure systems near poles generate surface winds directed towards equatorial regions but also experience leftward deflection due to Coriolis effect around 60° latitude creating additional low-pressure zones there.

• A third convective cell forms between 30° anticyclones and 60° depressions completing atmospheric circulation with three distinct cells per hemisphere rather than one theoretical model.

Jet Streams Dynamics

• Due to Earth’s axial tilt, anticyclones and depressions shift about 23 degrees toward poles during summer months while moving back toward equator during winter months.

Understanding Tropical and Polar Wind Circulation

Characteristics of Tropical Cells

• The convergence of tropical cells in the Northern and Southern Hemispheres creates a wind pattern known as the tropical jet stream, which flows from east to west.

• Each convective cell exhibits distinct wind circulation patterns between the surface and the tropopause due to variations in temperature and density.

Polar Front Dynamics

• The polar tropopause is located at approximately 89 km, while that of the Ferrel cell ranges from 10 to 12 km. At around 60 degrees latitude, cold polar winds meet warm subtropical winds, forming a contact zone called the polar front.

• Winds at this front ascend towards the tropopause and are deflected eastward by the Coriolis effect, creating a high-speed jet stream known as the polar jet stream.

Pressure Systems and Wind Patterns

• High-pressure zones at poles generate winds directed toward the equator but veer left due to Coriolis forces; these winds reach about 60 degrees latitude where they ascend convectively.

• Anticyclonic systems at around 30 degrees latitude produce clockwise winds in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, leading to varied wind characteristics that interact at fronts.

Equatorial Calm Zones

• Winds from subtropical anticyclones converge towards low-pressure areas near the equator, resulting in calm conditions where warm, humid air rises convectively, leading to vertical cloud development and heavy rainfall.

Influence of Polar Jet Stream on Weather Patterns

• The polar anticyclone generates northeast or southeast winds that diverge towards both poles and equator; these create westerlies moving eastward and trade winds (northeast in NH & southeast in SH).

• Both northern and southern trade winds converge at a low-pressure area known as the Inter-Tropical Convergence Zone (ITCZ), characterized by convective uplift.

Seasonal Variations Affecting Climate

• In mid-latitudes like those found in our country, climate is influenced by changes in intensity within circumpolar vortexes formed by subpolar low-pressure zones and polar jets; these can shift due to continental distribution or seasonal changes.

Evolution of Polar Front Dynamics

• When northeastern polar wind intensity matches that of southwestern tropical wind, it maintains a straight front; however, if cold polar air intensifies more than tropical air, it causes southward descent of fronts leading to undulations.

Cold Front Interaction with Warm Air Masses

Understanding Subtropical Anticyclones and Tropical Depressions

Dynamics of Atmospheric Pressure Systems

• The discussion highlights the alignment and undulation of atmospheric pressure systems, particularly around the polar front at approximately 30 degrees latitude, where subtropical anticyclones are prevalent.

• Near the equator, the text references tropical depressions found in the Intertropical Convergence Zone (ITCZ), emphasizing their significance in global weather patterns.

Seasonal Displacement of Weather Systems

• It is noted that both anticyclones and tropical depressions experience seasonal shifts; they move poleward during summer months and return towards the equator in winter.