Weather & Pressure Flashcards
A barometer should be adjusted to mean sea level pressure because (2)
- Pressure decreases rapidly in vertical direction.
- If not, subtle changes related to highs and lows would be swamped, leading to a contour map where important weather disturbances would be hidden.
High pressure = strong winds =
Steep pressure gradient, with isobars close together on a map. This results in strong winds and gales.
Horizontal pressure gradient (HPG) is the
Rate at which barometric pressure changes with distance.
HPG = ………./………
= difference in pressure between two points / distance between two points
Pressure falls by a factor of 2 for every 5500 m ascended
Eg - 16500 m ascent = 2^3 = 2x2x2 = 8
Therefore the pressure drops by a factor of 8
Measuring surface variables - humidity
Vapour pressure
Wet bulb
Relative
Specific
Measuring surface variables - wind speed
Anemometer
Measuring surface variables - barometric pressure
Mercury barometer
Measuring surface variables - wind direction
To the nearest 10’ from true north
Measuring surface variables - temperature
Dry bulb
Max and me thermometers
Relative humidity:
The ratio (%) of
Absolute humidity : Saturation value of absolute humidity.
Specific humidity:
Mass mixing ratio of water vapour in air, usually in
g kg-1
Wetbulb thermometer:
A DB thermometer with a permanently wet muslin bag of its mercury bulb.
Inside a weather screen, used to calculate humidity.
If the ELR is greater than the SALR then
Conditions are unstable and convection can take place. Emitted IR can be absorbed in the air above and as the air rises, the energy is carried away as thermal energy.
