pressure and density and the temperature distribution met 10
TRANSCRIPT
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• 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:Three temperature scales:•KelvinKelvin•CelsiusCelsius•FahrenheitFahrenheit
•What does temperature What does temperature mean physically?mean physically?
•What does 0 K mean?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
• Rain
• Snow
• Sleet
• Hail
• Feezing Rain