Transcript Pressure and Density and the Temperature

Pressure and Density and the
Temperature Distribution
Met 10
Introduction
– Temperature, density and pressure are some of the most
important variables in meteorology
– Knowing all of these quantities at all times and places
would make understanding and forecasting weather
events much easier
– Linked together via the gas law
• pV = nRT
– Pressure differences cause winds, which are caused by
the uneven heating at the surface!!!!
– So, the uneven heating of the surface causes the
weather!
Pressure
- Gravity causes the atmosphere to exert a downward force on
the surface.
- Simply put, it’s the weight of air above you.
- Pressure falls off rapidly w/ height, so it doesn’t take long until
air is very thin.
- E.g. What’s the pressure in Lake Tahoe and Death Valley??
Look at a place’s elevation.
- Pressure does not change as much in the horizontal
- However, these changes are the high and low-pressure systems
that may bring certain types of weather events
- So these are most important to meteorologists
- It’s the pressure differences we care about, since these are what
cause winds!
Pressure is
commonly
measured using a
Barometer.
Pressure
extremes
Density
- # of air molecules per volume
- Physically, it is mass per unit volume
- E.g. population density
- Density falls off rapidly w/ height, so it doesn’t take
long until air is very thin.
Vertical
structure
of
pressure
and
density
Pressure
changes with
height
Temperature
 Definition: Averagre speed of molecules
 Faster speed is synonymous with warmer
temperatures, and vice versa.
 Can also be thought of as energy.
– Hotter objects have more energy associated.
– Colder “
less energy”
• E.g. Warmer areas are areas of more energy.
 Changes in temperature/energy can lead to
changes in pressure and volume, via the gas law.
pV=nRT
Temperature Scales
• Fahrenheit: created 18th century physicist
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freezing point of water = 32°
Boiling point = 212°
0° is the lowest temperature he could reach using Salt, Ice and Water
F = 9/5C + 32
• Celsius: Used worldwide
• Made 0° the freezing point
• 100 ° boiling point
• C = 5/9(F - 32)
• Kelvin: Absolute temperature scale
• At 0 K, all molecular movement stops!
• K = C + 273.15 °
Thermometers
 Thermometers work because substances
(like mercury) expand and contract with
changes in temperature.
 Warmer temperature, fluid expands
 Colder temperature, fluid contricts
 Mercury not used much anymore
Three temperature scales:
•Kelvin
•Celsius
•Fahrenheit
•What does temperature
mean physically?
•What does 0 K mean?
Vertical temperature structure
• 4 levels
– troposphere, stratosphere, mesosphere, thermosphere
• we look mostly at the troposphere, where weather happens
– 80% of all mass, nearly all vapor, clouds/precipitation
• a little at the stratosphere, where ozone is at max and explains
warming in stratosphere
– In stratosphere: Ozone layer: O3 absorbs solar energy and
waves.
– lapse rate: How temperature changes with height
• Not constant in the atmosphere
• Typically, it cools 3 - 5 degrees per 1000 ft
• Depends on how much moisture is in the air
Climatological temperature
variability: Latitudinal
• A place’s climate depends on it’s latitude
– What’s latitude?
– Poles, mid-latitudes, tropics?
• Polar/high latitudes: 60-90º
• Mid-latitudes: 30-60º
• Tropical/low latitudes: 0-30º
• The temperature differences (gradient) between
poles and equator are twice as large in their winter
season.
– This causes mid-latitude weather systems like
cold/warm fronts and high and low-pressure areas
Precipitation Types
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Rain
Snow
Sleet
Hail
Feezing Rain