GGY 130 1st Edition Lecture 6 Oceanic Circulation Subtropical gyres: east to west movement; leaves eastern continental coastlines warm and western continental coastlines cool; equator mild Equatorial currents: east to west Equatorial countercurrents: west to east *Arctic (ice) circle is wider in the North Pacific than in the North Atlanticdue to “continental blocking” of oceanic currents; more blockage results in less warm water reaching the Arctic ice Circle and melting it.Chapter 5: Atmospheric Pressure and Wind  Atmospheric Pressure Pressure is the force exerted by gas molecules At sea level, pressure is approximately one kilogram per cubic centimeter Pressure goes down as altitude increases as the gas molecules are more compact closer to the Earth’s surface Factors influencing Atmospheric Pressure  Air Density:  Denser air results in higher pressure  Less dense air results in lower pressure High altitude results in lower pressure  Low altitude results in higher pressure Air Temperature: High temperatures result in low pressure  Low temperatures result in high pressure Air Movement:  Descending air results in higher pressure Ascending air results in lower pressure Mapping Pressure Barometer Millibar; Average pressure at sea level is 1013.25 mb Isobars  Ridge and Trough High Pressure (Anticyclone) Air descends into center of the high pressure system and diverges Clear skies, fair weather Low Pressure (Cyclone) Air converges into the center of the low pressure system and ascends  Cloudy skies, precipitation Adiabatic Cooling and Warming Adiabatic – changes in temperature caused by the expansion/compression of air as it rises/descends Adiabatic cooling- rising air(expansion) Adiabatic warming- descending air (compression) Wind  Wind movement: insolation causes the unequal heating of the Earth’s surface  Wind direction: determined by three factors: Pressure Gradient force- Wind blows from high to low pressure- Steep pressure gradient results in fast winds - Gentle pressure gradient results in slow winds Coriolis effect : deflection of wind direction due to the rotation of the Earth- Direction: deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere- Magnitude: Maximum at the poles and no deflection at the equator Friction: force that slows wind speed over rough surfaces- Wind speed in North America:o Average wind speed in North America is six to twelve knots o Highest wind speeds in North American found in the Great Plains to near lack of friction Wind Measurements Use Anemometer to measure speed Use Compass to measure direction Global Circulation Features 1)Hadley Cells and the ITCZ (Inter-Tropical Convergence Zone)- Characterized by radiation surplus, rising air, low pressure, and heavy precipitation- Hadley cells are formed by the warm rising air flowing away from the equator as it rises and the cool air descending back towards the equator in a cycle- The low air flowing towards the equator at the bottom of the Hadley cell are the trade winds - The high air flowing away from the equator at the topof the Hadley cell are the antitrade winds - The area between the Hadley cells marked by heavy precipitation is the ITCZ; this shifts as the seasons