Atmospheric Temperature and Pressure

Chapter 16 By Jimmy Dougherty

Temperature in the Atmosphere

• Temperature – Measure of average-speed atoms or molecules

• Greater speed, higher the temperature• Cold winter day—movement slower, lower

temperature• Movement of molecules– Kinetic energy • Higher kinetic energy, higher temperature

Temperature in the Atmosphere(continued)

• Temperature measured with a thermometer • Fahrenheit: – Freezing 32 F, boiling point 212 F

• Celsius– Freezing 0 C, boiling point 100 C– Most of world uses Celsius scale

Distribution of Heat on Earth

• Unequal heating caused by: – Earth’s tilted axis – Length of time Earth exposed to radiation • Changes during year

– Rotation of Earth itself • Leads to unequal distribution

• Unequal distribution called heat gradient

Distribution of Heat on Earth (continued)

• Temperature flows from high temperature to low

• Flow leads to distribution of heat by: – Radiation – Conduction – Convection – more dynamic • Convection cell—circular movement

– Hot rising fluid and descending cooler fluid

Radiative Cooling

• Radiative cooling transfers heat in the atmosphere

• During day insolation is absorbed– Causes surface temperature to rise

• Throughout day – Surface is continually heated • Heat conducted or radiated back into atmosphere

– Eventually surface cools and heating stops

Radiative Cooling (continued)

• Can cause rapid decline of atmospheric temperature

• Extreme radiative cooling on cloudless nights– Coldest temperatures occur at night during the

winter• Cloudy nights trap heat and slow cooling– Cloudy nights warmer in winter than cloudless

The Greenhouse Effect

• Infrared radiation absorbed by gases in atmosphere

• Causes the greenhouse effect – shortwave infrared radiation absorbed in

greenhouse – Solid material radiation long-wave infrared

radiation back – Long-wave radiation trapped causing temperature

to rise

The Greenhouse Effect (continued)

• Atmospheric gases act like glass in greenhouse – Absorbed long-wave radiation heating the planet – Called greenhouse gases• Water vapor • Carbon dioxide • Methane

Pressure in the Atmosphere

• Weight pressing down at a specific level • Atmosphere is invisible but has mass • Closer to Earth, the higher the air pressure • At sea level, force is 14.7 lbs./sq. inch.• Farther away from Earth, pressure decreases • Extremely low in upper stratosphere

Measuring Atmospheric Pressure

• Measure using a barometer – Weight of air at a specific point – Measured using inches of mercury and millibars • Inches of mercury is oldest method • One standard atmosphere is 29.92 inches • Most common measurement unit is the millibar• Used in meteorology and weather forecasting

High and Low Atmospheric Pressure

• Low Pressure at the surface associated with:– Warmer, lighter, less dense air

• Warm air rises• Begins to expand and cool– Called adiabatic cooling

• Cooler air becomes more dense • Sinks back to Earth’s surface

High and Low Atmospheric Pressure (continued)

• Dense air sinks causing high atmospheric pressure

• Warm air associated with low pressure • Cool air associated with high pressure • Low pressure indicates poor weather • High pressure indicates good weather

Atmospheric Pressure and Moisture

• Air pressure – Influenced by amount of water vapor in the air

• More moisture, less dense • Lighter, less dense moist air rises – Results is lower atmospheric pressure

• Drier air weighs more and is denser – Sinks toward Earth’s surface—forms high pressure