Unformatted text preview: Winds: Winds: Global Systems Global This chapter discusses: 1. Models to examine general circulation of the Models atmosphere with average wind, precipitation, and pressure patterns pressure 1. Ocean - atmosphere interactions and global Ocean oscillations including El Nino oscillations Single-Cell Circulation Model Single-Cell
The basis for The average air flow around the earth can be examined using a nonusing rotating, non-tilted, rotating, ocean covered earth. earth. Heating is more Heating intense at the equator, which triggers Hadley cells to redistribute rising heat from the tropical low to the polar highs. the Figure 11.1A A rotating earth rotating breaks the single cell into three cells. into Three Cell Circulation Model Three The Hadley cell The extends to the subtropics, the reverse flow Ferrel cell extends over the mid latitudes, and the Polar cell extends over the poles. the The Coriolis force The generates westerlies and NE trade winds, and the polar front redistributes cold air. redistributes Figure 11.2A Observed Winds in January Observed
Observed average Observed global pressure and winds have increased complexity due to continents and the tilted earth. tilted Differential Differential ocean-land heating creates areas of semiareas permanent high permanent and low pressure that guide winds and redistribute heat. heat. Figure 11.3A Observed Winds in June Observed
Global pressure Global and wind dynamics shift as the Northern Hemisphere tilts toward the sun, bringing the interthe tropical tropical convergence zone, the Pacific high, and blocking highs in the southern oceans northward. northward. Figure 11.3B North American Winter Weather North
Semipermanent permanent highs redirect North American winds, such as cold interior southerly flow from the Canadian high. Canadian The Polar front The develops a wave like pattern as air flows around lows. lows. Figure 11.4 Global Precipitation Patterns Global
Global low pressure Global zones around the equator and 60° latitude generate convergence at the surface, rising air and cloud formation. formation. Zones of high Zones pressure at 30° and the Poles experience convergence aloft with sinking, drying air. air. Figure 11.5 Coastal Summer Weather Coastal Figure 11.6 The semi-permanent Pacific high blocks moist maritime winds and The rain from the California coast, while the Bermuda high pushes moist tropical air and humidity over the eastern states. moist Coastal Winter Weather Coastal
During winter During months, the Pacific high migrates southward and allows for maritime winds with moisture and rains to reach California. reach On the east On coast, precipitation is rather even throughout the year. year. Figure 11.7 January Winds Aloft January Land-sea Land-sea temperature differences trigger ridges and troughs in the isobaric surface. surface. Figure 11.8A June Winds Aloft June Horizontal Horizontal temperature gradients establish pressure gradients that cause westerly winds in the mid latitudes. mid Figure 11.8B Jet Stream Jet Figure 11.10 Figure 11.9 High velocity Polar and subtropical jet stream winds are located High in the lower tropopause, and they oscillate along planetary ridges and troughs. and 300 mb Winds & Jets 300 300 mb pressure 300 surface maps illustrate lines of equal wind speed (isotachs) as the jets meander. jets Jet streaks are Jet the maximum winds, exceeding 100 knots. 100
Figure 11.11 Simulation of Clear Turbulence Simulation Figure 11.12 Clear turbulence is created by steep gradients of changing wind Clear speed near the jet, called shearing winds, which generate fast flowing particles in this simulation. flowing Polar Jet Formation Polar
Steep gradients of Steep temperature change at the Polar front trigger steep pressure gradients, which then forces higher velocity geostrophic winds. winds. This is the trigger This for jet stream flow. flow.
Figure 11.13A Winds & Angular Momentum Winds
Angular momentum Angular is the product of mass, velocity, and the radius of curvature and it must be conserved. be As northwardflowing air flowing experiences a smaller radius, it increases in velocity and augments the jet stream flow. stream
Figure 11.14 Surface Ocean Currents Surface
Surface winds Surface cause ocean water drift, a piling up, and creation of pressure differences that generates ocean circulation. circulation. Major ocean Major currents are categorized as warm or cold, and help to redistribute heat. heat. Figure 11.15 Gulf Stream Warmth Gulf Color enhanced Color imagery shows an oceanic front at the edge of the warm Gulf Stream current, where eddies redistribute heat into cooler waters. waters. Figure 11.16 Cold Water Upwelling Cold Maps of west coast Maps sea surface temperature indicate regions of significantly cooler water that has up welled from below. welled Figure 11.17 Eckman Spiral & Upwelling Eckman Figure 11.18 Figure 11.19 The Coriolis force directs surface water to the right of The southward blowing winds along California's coast. southward This creates an Eckman spiral of ocean transport which This removes water from the coast, and is then replaced by the upwelling of deeper water. upwelling Ocean Oscillations Ocean Figure 11.20A In the southern Pacific Ocean, high pressure in the east pushes In surface winds, and waters, toward the low in the west. surface This Walker Circulation becomes disrupted during El Nino events, This which impacts upwelling and rains. which El Nino Kelvin Wave El Figure 11.21 Satellite imagery shows the eastward movement of higher ocean Satellite levels, or Kelvin wave, in white and red colors, caused by the reversal of the Walker Circulation and El Nino event. reversal El Nino Ocean Temperature El Figure 11.22A Satellite data of Satellite sea surface temperature (SST) illustrate the difference between a nonbetween El Nino year, El with cool easterly waters, and the warmer SST El Nino year. year. ENSO Index ENSO Figure 11.23 El Nino Southern Oscillation (ENSO) intensity has been tracked El using 6 parameters, including air and sea temperature, sea level pressure, wind speed and direction, and cloudiness. pressure, A graph of the ENSO index shows eastern Pacific warm El Nino and graph cool La Nina years. cool US El Nino Impacts US Figure 11.24A US Winter weather is impacted by El Nino & La Nina events. During El Nino, a persistent trough of low pressure in the north During Pacific steers wet weather in the southern US, while La Nina brings a blocking high south of Alaska that pushes the cold weather of the Polar jet into the western states. Polar Global El Nino Impacts Global
The El Nino The Southern Oscillation (ENSO) is part of a planetary oceanoceanatmosphere atmosphere interaction, and can take several years to run its course. course. ENSO causes ENSO abnormalities around the globe. around Figure 11.25 Pacific Decadal Oscillation Pacific Figure 11.26A Scientists recently discovered a 20 to 30 year sea surface temperature (SST) reversal in a more northern section of the Pacific. section During the warm, positive, phase, SSTs are warmer off During the Pacific Northwest coast, which strengthens the Aleutian low and generates warmer winters. Aleutian During a cool phase, Pacific Northwest coastal SSTs During are cooler, causing colder winters. are ...
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This note was uploaded on 03/15/2010 for the course ATOC ATOC 250 taught by Professor Gyakum during the Spring '09 term at McGill.
- Spring '09