ENVIR SCI 1A03 February 24, 2014
Winds and Pressure
What are Winds?
• Air moving horizontally relative to the Earth’s surface
• Caused by: unequal heating of Earth’s atmosphere, which leads to
differences in pressures
• Differences in pressure drive winds
• Pressure gradient: difference in pressure between regions
• One is colder and has lower pressure, one is warm and has higher
pressure: net movement towards low pressure
• High temp to low temp
How is Pressure mapped?
• Constant height: plot variations in air pressure on a constant elevation
o Aka sea-level temperature
o On maps: isobars connect points of equal pressure
o Air pressures need to be adjusted for differences in altitude – need
to calculate the actual pressure at sea-level to compare equal
o Isobars are universal
o Rule is approximately add 10 hPa per 10 m but on a hot day, the
pressure will be slightly lower because
• What are Constant Height Maps?
o Lines of isobars: bend and turnaround areas of High (H) and Low
o Maps are smoothed to account for potential errors and altitude
• Constant height charts can be used to show variations in pressure at any
• What are Constant Pressure Maps?
o Show variations in altitude at constant pressure using average
height of a certain pressure surface
o Aka upper level charts, isobaric charts
o With warmer air – high altitude, cold air – lower altitude for a certain