Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 4 Atmospheric and Oceanic Circulation Atmospheric & Oceanic Circulation Major things you need to know: • What causes wind to happen • Global pressure areas and wind patterns, and explanations for them • What causes ocean currents • Global ocean current geography Air Pressure: the weight of a column of air at a location • Air pressure decreases with altitude, as there is less “weight” of air above Forces Creating and Affecting Air Movement • • • • Pressure Gradient Force Coriolis Force Friction Force Gravity Primary Cause of Wind: difference in pressure between two places (pressure gradient). Closer spacing of isobars indicates stronger presssure gradient. one example of how pressure gradients are created: At the surface, cold air, located next to warm air, is denser and has higher pressure. Pressure Gradient Fig. 4.7 The Coriolis Effect • Explanation: earth rotation “deflects” movement to the right in the N. Hemisphere, to the left in S. Hem. • Effect is greater at higher latitudes • Friction reduces wind velocity, thus reduces Coriolis Effect • In upper atmosphere with negligible friction, wind flows nearly parallel to isobars (geostrophic wind) • Merry-go-round analogy Coriolis Force Figure 4.9 Pressure + Coriolis + Friction Figure 4.8 Global High Pressure and Low Pressure Areas - Why they Develop: 1. 2. Thermal (heating or cooling) – Great amounts of solar radiation promote heating, low pressure, and convergence (example: circum-equatorial area of low pressure known as “Inter -Tropical Convergence Zone” or ITCZ, or “Equatorial Low”) – Minimal or no solar radiation promotes cooling, high pressure, and divergence (Polar Highs) Dynamic (mechanical forcing) results from movements of air masses (result in Subtropical Highs, Sub Polar Lows) animation: http://www.geography.hunter.cuny.edu/tbw/wc.notes/7.circ.atm/animations/GlobalWind.html The Basic Oversimplified Model of Global Wind, Ignoring the Coriolis Effect: • The hot Equator and the cold Poles would create Equatorial low pressure (thermal low), Polar Highs (thermal high) • Surface winds would flow from poles to equator • Rising air at the Equator would flow to the north & south in the atmosphere and descend at the poles…BUT But the Coriolis Effect will not allow this model to work • Winds from polar areas are deflected, becoming Easterlies rather than remaining northerlies – thus they never make it to the Equator to replace the warm, rising air there. Therefore, a more complex model is needed… This is your model to learn - worth at least 15 pts on exam: Barometers Figure 4.2