| NATS 101-05 Lecture 14 Monsoons & Global Circulation |
| Supplemental References for TodayŐs 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) | |
| Monsoon |
| SEASONAL Reversal of Prevailing Wind | |
| Wind shift often accompanied by | |
| Major Change in Weather | |
| Summer Rains - Often Abrupt Onset | |
| Winter Dryness | |
| Major Monsoon occurs over Asia | |
| Weaker Monsoon occurs in North America |
| Monsoon |
| Land mass is colder than ocean in winter | |
| Land-sea temp contrast reverses in summer | |
| Wind forced by seasonal changes in PGF Higher SLP over land in winter FOffshore flow at Surface | |
| Lower SLP over land in summer FOnshore flow at Surface |
| Monsoon |
| Onshore flow leads to surface convergence | |
| FRising motion over land during summer | |
| Offshore flow leads to surface divergence | |
| FSinking motion over land during winter | |
| Monsoon is Thermally Direct Circulation | |
| FWarm Air Rises - Cold Air Sinks |
| Slide 6 |
| Slide 7 |
| Asian Winter |
| Asian Summer |
| Monthly Average Rain Cherrapunji |
| Geography of Our Monsoon Region |
| January |
| July |
| Terrain |
| Terrain (300 m) | |
| Steep slopes of Sierra Madre Occidental | |
| Warm Waters |
| Yecora & Moctezuma PWV 2004 Monsoon Onset |
| Pre-monsoon event |
| Monthly Rainfall |
| Mexican Monsoon | |
| Similar onset | |
| Similar behavior butÉ | |
| Much less intense | |
| than Asian Monsoon |
| Percentage of Annual Rainfall |
| Accounts for up to 70% total rain in monsoon core | |
| Tucson ~50% | |
| Phoenix ~40% |
| July minus June Rainfall |
| Monsoon Evolution from Satellite |
| CCT < -38oC Frequency | |
| Centered over W. Mexico | |
| June start over Mexico | |
| AZ at northern fringes of heart of monsoon | |
| Rains reach SE Arizona by July |
| June-July 500 mb Flow |
| July 900 mb Flow |
| Diurnal Winds 450 m AGL |
| Summary |
| Monsoons | |
| Differential Heating Between Land and Oceans | |
| Seasonal Reversal of Wind | |
| Summer Rain - Winter Aridity | |
| Thermally-Direct Circulation | |
| Regions | |
| Major Monsoon Occurs over SE Asia | |
| Weaker Monsoon Occurs over North America | |
| West Africa in NH | |
| Australia, South America in SH |
| now Global
CirculationÉ. But first Review |
| Global Energy Balance | |
| 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 earthŐs surface |
| Consider Waterworld A Simple Model |
| Earth uniformly covered by water | |
| Land-Sea heating difference isnŐt factor | |
| Sun is always directly over the equator | |
| No seasons | |
| Earth doesnŐt 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 evident as a band around the globe on a day-to-day basis. | |
| IR movie | |
| 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 40 |
| Slide 41 |
| Pacific High, Bermuda High |
| Pacific High, Bermuda High |
| Global Circulation - Precipitation |
| Global Circulation - Seasonal Precipitation |
| Summary |
| Global Circulation | |
| Differential Heating Between Tropics and Poles | |
| Three Cells | |
| Mid-Latitude Westerlies | |
| Patterns shift somewhat 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 192-200 | |
| Problems - 7.17, 7.18 |