Transcript Global
http://www-news.uchicago.edu/releases/05/050601.fultzlab.shtml Global atmospheric circulation http://www.ssec.wisc.edu/data/composites.html Objectives 1. 2. 3. 4. List/describe factors that shape global atmospheric circulation 1. Tilt 2. Rotation 3. Land/water differences 4. Coriolis Force Describe/draw components of the three-cell model Explain how components shape regional patterns of climate Explain the function of the global atmospheric circulation system Circulation without rotation (no Coriolis Force) on a uniform surface (no land/water differences) and no tilt (no differential heating between hemispheres) Circulation with rotation on a uniform surface with no tilt Circulation with rotation, on non-uniform surface, and tilt (the 3-cell model) Global atmospheric circulation redistributes heat from the tropics to the poles Intertropical convergence zone (ITCZ) • Belt of low air pressure around equator • Forms from surface heating • Associated with clouds and rain • Current position Subtropical high pressure • Semi-permanent high pressures along 20 - 35 degrees N and S latitude Atlantic and Pacific STHP The Atlantic Bermuda STHP can bring drought conditions to the southeastern US when it moves closer to the North American continent. The Atlantic Bermuda STHP can bring rainfall is its location is sufficiently offshore from North America to allow its winds to pick up moisture and become unstable. Tradewinds and westerlies • Air descending from the STHP forms – Northeast tradewinds – Westerlies Polar high • Deep, cold high pressure • Descending air forms the polar easterlies Polar front • Zone of collision between westerlies and the easterlies Polar front • Very changeable weather • Location of polar jet stream Polar jet stream Midlatitude cyclones, storm system of the polar front Midlatitude cyclones Subtropical jet stream Pacific subtropical jet Branch of subtropical jet stream that brings moisture up from tropics to enhance precipitation within mid-latitude cyclones Components of global circulation shift throughout the year California coast (32 – 42 N) San Francisco (37 N) • Winter wet – Pacific STHP diminishes and high pressure shifts south and offshore – Midlatitude cyclones bring precipitation • Summer dry – Pacific STHP dominant – Dry conditions – Track of cyclones along polar jet stream is further north 1. Pacific Northwest coast (40 – 50 N) Pacific Northwest coast (40 – 50 N) • Greater year-round influence of polar front • More rainfall, more evenly distributed all seasons • Winter wet from midlatitude cyclones • Summer becomes wetter to the north • Weaker influence of STHP moving north 2. Baja Peninsula (22 – 35 N) • Dry all year but seasonal variability in rainfall along peninsula N C S Baja Peninsula (22 – 35 N) • North: winter wet from midlatitude cyclones and summer dry from STHP • Central: dry all year from STHP • Southern: winter dry from STHP, summer wet from ITCZ Kentucky weather and climate and their global controls • Winter – MLCs create alternating periods of cold and dry then warmer and humid conditions. Rainfall in winter is derived from the fronts in the MLCs • Summer – weather and climate under more local controls, fewer MLCs. Rainfall from locally generated convective thunderstorms with the occasional enhancement due to weak cold fronts and polar jet stream support