| NATS 101 Lecture 20 Global Circulation |
| Supplemental References for TodayÕs Lecture |
| Aguado, E. and J. E. Burt, 2001: Understanding Weather & Climate, 2nd Ed. 505 pp. Prentice Hall. (ISBN 0-13-027394-5) | |
| Lutgens, F. K. and E. J. Tarbuck, 2001: The Atmosphere, An Introduction to the Atmosphere, 8th Ed. 484 pp. Prentice Hall. (ISBN 0-13-087957-6) | |
| Review |
| Global Energy Balance (from long ago!) | |
| Thermally Direct Circulations AGAIN! |
| Annual Energy Balance |
| Heat transfer done by winds and ocean currents | |
| Differential heating drives winds and currents | |
| Global Energy Budget |
| Averaged over entire earth, incoming solar radiation is equal to outgoing IR | |
| Tropics absorb more solar radiation than they emit IR to space | |
| Surplus of radiant energy in tropics | |
| Poles absorb less solar radiation than they emit IR to space | |
| Deficit of radiant energy in poles |
| Global Circulation |
| To balance the inequalities in the global energy budget, energy must be transported from the tropics to the poles. | |
| 40% of transport is done by oceans | |
| 60% of transport is done by atmosphere | |
| Thermally Direct Circulation |
| Global Circulation |
| Winds throughout the world are averaged over a long period of time (over many winters) | |
| Local wind patterns vanish | |
| Distinct patterns in the prevailing winds emerge | |
| Driven by the unequal heating of the earthÕs surface |
| Consider Waterworld A Simple Model |
| Earth uniformly covered by water | |
| Land-Sea heating difference isnÕt factor | |
| Sun is always directly over the equator | |
| No seasons | |
| Earth doesnÕt rotate Use average daily sun | |
| No diurnal cycle and É ? |
| Waterworld Single Equator to Pole Cell |
| Consider a Rotating Waterworld |
| Equator-to-Pole temperature difference and rotation of Earth produce 3 circulation cells | |
| Hadley Cell (Strong Thermally Direct) | |
| Ferrel Cell (Indirect: Forced by Hadley & Polar) | |
| Polar Cell (Weak Thermally Direct) |
| Rotating Waterworld Prevailing Winds |
| Major Surface Pressure Zones |
| ITCZ |
| Inter-Tropical Convergence Zone | |
| Near equator Northeast Trades (N.H.) Converge with Southeast Trades (S.H.) along this zone. | |
| Is not evident as a continuous band around the globe on a day-to-day basis. | |
| Jet Streams |
| Why Jet Streams in
Mid-Latitudes? Strong Thermal Contrast |
| Mid-Latitude Westerlies |
| Real World Circulation |
| Land-Ocean heating difference, along with the difference between tropics and poles, and rotation of earth. | |
| Sun not always directly over the Equator (cause of the seasons). | |
| Expect high pressure over cold land in the winter. | |
| Expect low pressure over warm land in the summer. |
| Slide 19 |
| Slide 20 |
| Pacific High, Bermuda High |
| Pacific High, Bermuda High |
| Global Circulation - Precipitation |
| Summary |
| Global Circulation | |
| Differential Heating Between Tropics and Poles | |
| Three Cells | |
| Mid-Latitude Westerlies | |
| Patterns shift slightly with seasons | |
| Precipitation | |
| Major Deserts occur under Sub-Tropical High | |
| Mid-latitude storms occur along Polar Front |
| Next Lecture |
| Topic- Atmosphere-Ocean Interactions | |
| El Nino and La Nina | |
| Reading - Ahrens pg 189-197 | |
| Problems - 7.17, 7.18 |