GHY 104 1st Edition Lecture 10Pressure Gradient- High Pressure- Air that is descending from above- Air that is therefore diverging at the surface- Low Pressure- Air that is ascending from below - Air that is therefore converging at the surface- Coriolis Force - Apparent deflection of objects- Coriolis is therefore maximum at the poles and non-existent at the equator- Southern Hemisphere – left turns- Northern Hemisphere – right turns- Earth’s rotation adds the Coriolis force and a “twist” to air movements. High-pressure and low pressure areas develop a rotary motion, and wind flowing between highs and lows flows parallel to isobars.- Geostrophic Winds- Anticyclone – High pressure- Cyclone – Low pressure- Note areas of convergence aloft and divergencealoft– upper atmosphere conditions at 500-mb level support surface cyclones and anticyclones.Primary High and Low Pressure Areas- Equatorial low-pressure trough (clouds and rain) – ITCZ(Inter Tropical Conversion Zone)- Large amounts of energy in region = lighter, less dense, ascending air = full of moisture & latent heat.- As air rises, it cools and condenses = heavy rain (vertical cloud formation)- Where winds converge together, and have no place to go but up = low pressure- Intense heating = Convectional uplif = low pressure- ITCZ (bands of clouds associated with conv. Of winds along equator)- Northeast Tradewindsin the Northern Hemisphere- Southeast Tradewindsin the Southern Hemisphere- Subtropical High Pressure (hot, dry, desert air)- Bermuda High or Azores High- Pacific High or Hawaiian High- Subtropical High Pressure = STHP- Wind belt = Westerliesin the Midlatitudes- Subpolar low-pressure cells (cool and moist air)- Aleutian low (winter; weaken in summer)- Icelandic low (winter; weaken in summer)- Subpolar Low Pressure (SPLP)- Polar front – area of contrast between cold and warm air - Polar high-pressure cells (frigid, dry deserts)- Weak because atmosphere mass is small - Winds = Polar Easterlies- Polar (Arctic and Antarctic) High Pressure (PHP)- Siberian High (winter)High pressure = RidgeLow pressure =
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