GEOG 1900 STUDY GUIDE WINTER SEM 2024
● What is air pressure?
○ Atmospheric pressure→ the weight of the column of air above a given unit area of the Earth’s
surface
○ Exerted equally in all directions
● How do we measure it? What units do we use? Describe different instruments.
○ SI unit→ pascal (Pa), in US→ millibar (mb) = 100 Pa, in Canada→ kilopascal (kPa) = 1000 Pa= 10
mb
○ Mercury barometer→ avg. height of column at sea level = 76 cm
○ Aneroid barometer→ spring in flexible evacuated chamber
● How does pressure vary in the atmosphere vertically? Draw a profile through the atmosphere.
○ Pressure always decreases with altitude
○ Decrease NONlinearly because air is compressible→ rate of decrease is larger at lower altitudes
and smaller at higher altitudes
○ Horizontal pressure changes are very minimal
● What is Dalton’s law of partial pressures?
○ Total pressure exerted = sum of partial pressures
● What is the ideal gas law? Write it down and explain the variables.
○ Equation of state:
○ P= ρ*R*T
■ Where P = pressure in pascals
■ Ρ (rho) = density
■ T = temperature
■ R=287 J/kg K (← constant)
● Density is inversely proportional to temperature
● How is pressure related to temperature?
○ Increase in temperature leads to increase in pressure; they are proportional
● Re-write the equation of state to define density. Now, describe how density changes with an air parcel’s
temperature, if pressure is held constant.
○ ρ = P / (R * T )
○ As temperature increases, density decreases→ they are inversely proportional
● What are lines of equal pressure on a weather chart called? → ISOBARS
,● What is the pressure gradient? How is this seen on a weather chart?
○ Pressure gradient= rate of change in pressure
○ Spacing of isobars indicates strength of the pressure gradient→ dense clustering of isobars
indicates a steep pressure gradient ( a rapid change in pressure with distance)
● What drives all wind? Explain how.
○ THE PRESSURE GRADIENT→ gives rise to pressure gradient force that sets air in motion
○ If the air over one region exerts a greater pressure than the air over the adjacent region, the higher-
pressure air will spread out toward the zone of lower pressure as wind (always moves from high to
low pressure)
○ Greater the PGF, stronger the wind
● Explain the hydrostatic equilibrium.
○ Vertical pressure gradient force and the force of gravity are normally of nearly equal value and
operate in opposite directions (so the atmosphere doesn’t explode away or get sucked down to the
very surface of the Earth)
● How does the vertical change in pressure differ between columns of warmer and colder air?
○ Cool air has a greater vertical pressure gradient because the warm column of air has the same mass
of air, but expands upwards, thus, to reach the same pressure in each column, you have to go up
higher in the warmer column of air
● Why do we care about the 500 mb heights, and how do we map these?
○ Look similar to isobars but they are telling us lines of equal height and at what height the pressure
is 500 mb, this allows us to determine the pressure gradient force
● Explain how 500 mb heights reflect the relative density of air.
○ The lower the 500 mb height, the denser the air, and vice versa.
● What forces affect the speed and direction of wind?
○ Unequal distribution of air across the globe establishes the horizontal pressure gradient that
initiate movement of air as wind
○ Planetary rotation alters direction of wind (Coriolis Force)
○ Friction slows the speed of the wind
● Describe the Coriolis force and how it changes with respect to latitude, and hemisphere.
○ Apparent deflection of path of objects moving on Earth due to Earth’s rotation; the Earth is
spinning fastest at the equator
○ The intensity of the deflection is proportional to the speed of movement
○ At the equator, the CF = 0, and it increases with higher latitudes
○ In the NH, wind will be deflected to the right
○ In the SH, wind will be deflected to the left
● How does friction impact wind speed and direction?
○ Friction reduces wind speed and the lower wind speeds reduce the Coriolis force and thereby
prevent the the flow from becoming gradient or geostrophic
○ Winds cross the isobars at an angle as they blow from high to low pressure
● Explain geostrophic winds. Where do they occur? How do they differ between hemispheres?
○ If pressure gradient and Coriolis force are equal, then a geostrophic wind occurs.
○ Non-Accelerating flow→ geostrophic flow
■ Flows to right in NH and left in SH
● What is gradient flow?
○ Close to geostrophic.
○ Small accelerations because isobars are not straight
○ Continual mismatch between pressure gradient and Coriolis force
, ● Under what surface pressure conditions do winds converge and diverge near the surface, and why?
○
● What is an anticyclone? Cyclone? Draw the relative motion of winds for each, in both Northern and
Southern Hemispheres.
○ Anticyclone→ enclosed areas of high pressure marked by roughly circular isobars or height
contours; wind rotates clockwise around ACs in NH because of Coriolis force
○
○ cyclones→ closed low-pressure systems; air at surface spirals counterclockwise into cyclones
in NH
● What is air pressure?
○ Atmospheric pressure→ the weight of the column of air above a given unit area of the Earth’s
surface
○ Exerted equally in all directions
● How do we measure it? What units do we use? Describe different instruments.
○ SI unit→ pascal (Pa), in US→ millibar (mb) = 100 Pa, in Canada→ kilopascal (kPa) = 1000 Pa= 10
mb
○ Mercury barometer→ avg. height of column at sea level = 76 cm
○ Aneroid barometer→ spring in flexible evacuated chamber
● How does pressure vary in the atmosphere vertically? Draw a profile through the atmosphere.
○ Pressure always decreases with altitude
○ Decrease NONlinearly because air is compressible→ rate of decrease is larger at lower altitudes
and smaller at higher altitudes
○ Horizontal pressure changes are very minimal
● What is Dalton’s law of partial pressures?
○ Total pressure exerted = sum of partial pressures
● What is the ideal gas law? Write it down and explain the variables.
○ Equation of state:
○ P= ρ*R*T
■ Where P = pressure in pascals
■ Ρ (rho) = density
■ T = temperature
■ R=287 J/kg K (← constant)
● Density is inversely proportional to temperature
● How is pressure related to temperature?
○ Increase in temperature leads to increase in pressure; they are proportional
● Re-write the equation of state to define density. Now, describe how density changes with an air parcel’s
temperature, if pressure is held constant.
○ ρ = P / (R * T )
○ As temperature increases, density decreases→ they are inversely proportional
● What are lines of equal pressure on a weather chart called? → ISOBARS
,● What is the pressure gradient? How is this seen on a weather chart?
○ Pressure gradient= rate of change in pressure
○ Spacing of isobars indicates strength of the pressure gradient→ dense clustering of isobars
indicates a steep pressure gradient ( a rapid change in pressure with distance)
● What drives all wind? Explain how.
○ THE PRESSURE GRADIENT→ gives rise to pressure gradient force that sets air in motion
○ If the air over one region exerts a greater pressure than the air over the adjacent region, the higher-
pressure air will spread out toward the zone of lower pressure as wind (always moves from high to
low pressure)
○ Greater the PGF, stronger the wind
● Explain the hydrostatic equilibrium.
○ Vertical pressure gradient force and the force of gravity are normally of nearly equal value and
operate in opposite directions (so the atmosphere doesn’t explode away or get sucked down to the
very surface of the Earth)
● How does the vertical change in pressure differ between columns of warmer and colder air?
○ Cool air has a greater vertical pressure gradient because the warm column of air has the same mass
of air, but expands upwards, thus, to reach the same pressure in each column, you have to go up
higher in the warmer column of air
● Why do we care about the 500 mb heights, and how do we map these?
○ Look similar to isobars but they are telling us lines of equal height and at what height the pressure
is 500 mb, this allows us to determine the pressure gradient force
● Explain how 500 mb heights reflect the relative density of air.
○ The lower the 500 mb height, the denser the air, and vice versa.
● What forces affect the speed and direction of wind?
○ Unequal distribution of air across the globe establishes the horizontal pressure gradient that
initiate movement of air as wind
○ Planetary rotation alters direction of wind (Coriolis Force)
○ Friction slows the speed of the wind
● Describe the Coriolis force and how it changes with respect to latitude, and hemisphere.
○ Apparent deflection of path of objects moving on Earth due to Earth’s rotation; the Earth is
spinning fastest at the equator
○ The intensity of the deflection is proportional to the speed of movement
○ At the equator, the CF = 0, and it increases with higher latitudes
○ In the NH, wind will be deflected to the right
○ In the SH, wind will be deflected to the left
● How does friction impact wind speed and direction?
○ Friction reduces wind speed and the lower wind speeds reduce the Coriolis force and thereby
prevent the the flow from becoming gradient or geostrophic
○ Winds cross the isobars at an angle as they blow from high to low pressure
● Explain geostrophic winds. Where do they occur? How do they differ between hemispheres?
○ If pressure gradient and Coriolis force are equal, then a geostrophic wind occurs.
○ Non-Accelerating flow→ geostrophic flow
■ Flows to right in NH and left in SH
● What is gradient flow?
○ Close to geostrophic.
○ Small accelerations because isobars are not straight
○ Continual mismatch between pressure gradient and Coriolis force
, ● Under what surface pressure conditions do winds converge and diverge near the surface, and why?
○
● What is an anticyclone? Cyclone? Draw the relative motion of winds for each, in both Northern and
Southern Hemispheres.
○ Anticyclone→ enclosed areas of high pressure marked by roughly circular isobars or height
contours; wind rotates clockwise around ACs in NH because of Coriolis force
○
○ cyclones→ closed low-pressure systems; air at surface spirals counterclockwise into cyclones
in NH
