BA CLIMATOLOGY Planetary and Local Winds.pptx

BA GEOGRAPHY 3RD SEMESTER

1. Planetary and Local Winds Explore the fundamental drivers and diverse manifestations of atmospheric circulation, from global patterns to localized phenomena.

2. Agenda • Atmospheric Dynamics & Wind Fundamentals • Global Circulation: Cells & Wind Belts • The Coriolis Effect & Pressure Gradients • Key Global Wind Systems (e.g., Jet Streams) • Local Wind Phenomena & Topographic Influence

3. The Dynamic Atmosphere Atmospheric movement, fundamentally driven by differential heating and pressure gradients, manifests as wind. This continuous air circulation is crucial for global energy redistribution, transferring heat from equatorial regions towards the poles. Such dynamic processes regulate Earth's climate system.

4. Wind: Air in Motion Wind is defined as the horizontal movement of air, driven by pressure gradients. Air flows from regions of high atmospheric pressure to areas of lower pressure. This fundamental principle explains phenomena like sea breezes, where cool air from the ocean moves inland towards warmer, lower-pressure land.

5. Unequal Heating: The Driver All atmospheric winds, global and local, fundamentally arise from Earth's unequal solar heating. This differential insolation creates temperature gradients, directly inducing atmospheric pressure variations. For instance, the equator's intense sunlight generates warm, low-pressure air, driving global circulation.

6. Global Winds Local Winds Global winds are large-scale, persistent wind patterns that circulate across the Earth's surface. They are driven by the planet's differential heating between the equator and poles, coupled with the Coriolis effect. Examples include the Trade Winds, Westerlies, and Polar Easterlies, forming distinct atmospheric circulation cells. Local winds are smaller-scale atmospheric movements influenced primarily by regional topography and localized temperature variations. These winds arise from specific pressure gradients created by the uneven heating or cooling of land and water bodies or terrain. Common examples include sea breezes, land breezes, and mountain-valley winds.

7. Solar Radiation Distribution Solar radiation strikes Earth at varying angles, causing differential heating across latitudes. Near the equator, direct insolation concentrates energy per unit area. Conversely, at the poles, oblique angles spread energy over larger areas, resulting in less intense heating and driving global temperature gradients.

8. Atmospheric Pressure Gradients Differential solar heating creates temperature variations across Earth's surface. Warmer air expands and rises, forming low-pressure zones, while cooler, denser air sinks, creating high-pressure zones. This pressure imbalance generates a pressure gradient force, driving air from high to low pressure, as seen in sea breezes.

9. The Coriolis Effect The Coriolis effect is an apparent force arising from Earth's rotation, causing moving objects to deflect from their initial path. In the Northern Hemisphere, this deflection is to the right of the object's motion, while in the Southern Hemisphere, it is to the left. This phenomenon is crucial for understanding the large-scale circulation patterns of both planetary winds and ocean currents.

10. Coriolis and Wind Direction • Pressure Gradient Force initiates wind from high to low pressure. • Coriolis effect deflects air right (NH) or left (SH). • Forces balance at high altitudes, creating geostrophic flow. • Geostrophic winds flow parallel to isobars.

11. Idealized Global Circulation On an idealized, non-rotating Earth, solar heating drives a simple thermal circulation. Warm air rises at the equator, flows poleward aloft, sinks at the poles, and returns equatorward near the surface. This forms a single, large Hadley cell in each hemisphere, illustrating the fundamental heat transport mechanism.

12. Three-Cell Model: Overview The three-cell model describes global atmospheric circulation through distinct Hadley, Ferrel, and Polar cells in each hemisphere. These interconnected cells fundamentally distribute heat from the equator towards the poles, mitigating temperature extremes. For example, the Hadley cell efficiently transports warm, moist air poleward from tropical regions.

13. The Hadley Cell The Hadley Cell is a fundamental tropical atmospheric circulation cell driven by solar heating. It originates with intense insolation at the equator, causing warm, moist air to rise and form the Intertropical Convergence Zone (ITCZ). This air then flows poleward in the upper troposphere, cools, and descends around 30 degrees latitude, completing the cell as it returns to the equator as surface trade winds.

14. Intertropical Convergence Zone (ITCZ) • Equatorial low-pressure belt, intense solar heating. • Convergence zone of Northern and Southern Hadley Cells. • Characterized by strong convection and heavy precipitation. • Historically known as the "doldrums" due to calm winds.

15. Subtropical Highs Subtropical high-pressure systems form around 30° latitude as the upper-level air from the Hadley cells descends, warms, and dries. This subsidence suppresses cloud formation and precipitation, creating Earth's major desert belts, such as the Sahara and Australian deserts. These persistent high-pressure zones are crucial for global atmospheric circulation.

16. The Ferrel Cell The Ferrel cell is an indirect atmospheric circulation cell located between approximately 30° and 60° latitude in each hemisphere. Unlike the Hadley and Polar cells, it is not primarily driven by direct thermal forcing but rather by the momentum and energy exchange from these adjacent cells. This complex interaction leads to the prevailing surface westerlies observed in the mid-latitudes, significantly impacting global weather systems.

17. The Polar Cell The Polar Cell forms as cold, dense air sinks at the poles. This air flows equatorward along the surface, then rises around 60 degrees latitude. It subsequently returns poleward aloft, completing this thermally direct circulation.

18. Trade Wind Origin and Flow Coriolis Effect and Naming Trade winds are persistent surface winds that originate from the subtropical high-pressure belts, approximately 30 degrees north and south latitudes. They flow equatorward, driven by the pressure gradient force towards the low-pressure Intertropical Convergence Zone (ITCZ). This consistent flow makes them a fundamental component of the global atmospheric circulation. As these winds move towards the equator, the Coriolis effect deflects them. In the Northern Hemisphere, they are deflected to the right, becoming the Northeast Trade Winds. In the Southern Hemisphere, they are deflected to the left, forming the Southeast Trade Winds. Their easterly component gives them the common name 'Easterlies', historically crucial for maritime trade routes.

19. Global Wind Belts: Westerlies Westerlies are the prevailing winds found in the mid-latitudes, blowing from west to east between approximately 30° and 60° latitude. Their direction is primarily influenced by the Coriolis effect acting on air within the Ferrel cell. For instance, these winds drive most weather systems across North America and Europe.

20. Global Wind Belts: Polar Easterlies Polar Easterlies are cold, dry winds originating from the high-pressure polar regions, flowing towards the mid-latitudes. Driven by the Polar cell's descending air and deflected westward by the Coriolis effect, they bring frigid conditions. For instance, these winds contribute significantly to the extreme cold experienced in Siberia or northern Canada.

21. Upper-Level Winds: Jet Streams Jet streams are narrow, fast-flowing air currents found in the upper troposphere, typically at altitudes of 7-16 km. Their formation is driven by significant latitudinal temperature gradients, which create strong pressure gradients, coupled with the Coriolis effect deflecting the air. These powerful currents profoundly influence global weather patterns, steering storm systems and impacting regional climate variability.

22. Local Wind Systems: Introduction Local wind systems are atmospheric movements occurring over relatively small geographic areas. They are primarily driven by localized temperature and pressure gradients, often significantly influenced by topography. Examples include sea breezes and land breezes, which result from differential heating between land and water.

23. Land and Sea Breezes Land and sea breezes are mesoscale wind systems driven by the differential heating and cooling capacities of land and water. During the day, land heats faster than water, creating a thermal low over land and a relatively higher pressure over the cooler sea, resulting in an onshore sea breeze. Conversely, at night, land cools more rapidly, establishing a thermal high, while the warmer sea maintains lower pressure, driving an offshore land breeze.

24. Mountain and Valley Breezes Mountain and valley breezes are thermally driven local wind systems resulting from differential heating and cooling. During the day, sun-warmed mountain slopes heat the adjacent air more rapidly than the valley floor, creating an upslope flow known as a valley breeze. Conversely, at night, the slopes cool more quickly, causing the denser, cooled air to descend into the valley as a mountain breeze.

25. Foehn/Chinook Winds Foehn (Alps) and Chinook (Rockies) winds are warm, dry downslope winds that occur when stable air descends the leeward side of a mountain range. As air ascends the windward side, it cools moist adiabatically, often precipitating, before warming at the dry adiabatic lapse rate upon descent. This adiabatic warming results in significantly higher temperatures and lower relative humidity on the leeward side.

26. Synthesizing Wind Dynamics • Solar radiation drives global pressure differences. • Earth's rotation deflects winds (Coriolis effect). • Topography modifies local wind patterns significantly. • These interactions create Earth's complex wind systems.

27. How Do Global Winds Shape Our World? Beyond local effects, how do global wind systems interconnect with and profoundly influence Earth's climate, weather, ocean currents, and human societies?

28. Resources https://www.youtube.com/watch?v=Ye45DGkqUkE&pp=0gcJCfwAo7VqN5tD https://www.youtube.com/watch?v=my74aDv0QP8 https://www.youtube.com/watch?v=HjTqdVuEEPo https://www.youtube.com/watch?v=-8GNi-8Xwpk

29. Conclusion • Atmospheric circulation is fundamentally driven by differential solar insolation and resulting pressure gradients. • The Coriolis effect critically modifies wind direction, leading to complex global circulation patterns. • Global wind belts (e.g., Trades, Westerlies, Polar Easterlies) and upper-level jet streams are products of interconnected atmospheric cells. • Localized wind systems arise from mesoscale thermal contrasts and significant topographic influence. • The interplay of these forces creates Earth's dynamic wind systems, vital for climate regulation and energy redistribution.