Pressure and Density and the Temperature Distribution

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Pressure and Density and the Temperature
Distribution

• Met 10

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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!

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Pressure

• Gravity causes the atmosphere to exert a downward
  force on the surface.
• Simply put, its the weight of air above you.
• Pressure falls off rapidly w/ height, so it
  doesnt take long until air is very thin.
• E.g. Whats the pressure in Lake Tahoe and Death
  Valley?? Look at a places 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
• Its the pressure differences we care about,
  since these are what cause winds!

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Pressure is commonly measured using a Barometer.
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Pressure extremes
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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
  doesnt take long until air is very thin.

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Vertical structure of pressure and density
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Pressure changes with height
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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. pVnRT

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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

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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

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• Three temperature scales
• Kelvin
• Celsius
• Fahrenheit
• What does temperature mean physically?
• What does 0 K mean?

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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

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Climatological temperature variability
Latitudinal

• A places climate depends on its latitude
• Whats 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

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Precipitation Types

• Rain
• Snow
• Sleet
• Hail
• Feezing Rain