The Atmosphere Structure and Temperature

Atmosphere Characteristics  Weather: the state of the atmosphere at a given time and place; “snapshot” in time  Climate: based on weather observations over many years (typically 30 years)  Weather properties: air temperature; humidity; type and amount of precipitation; air pressure; wind speed and direction  Weather: the state of the atmosphere at a given time and place; “snapshot” in time  Climate: based on weather observations over many years (typically 30 years)  Weather properties: air temperature; humidity; type and amount of precipitation; air pressure; wind speed and direction

Atmospheric Composition  Mixture  “Others”: Argon, CO2, water vapor, traces of other gases  Water vapor: source of clouds and precipitation; absorbs heat from Earth and solar radiation  Condensation nuclei (particulates) : dust, pollen salt, soot, smoke (necessary for cloud formation as provides water with something to condense onto)  Mixture  “Others”: Argon, CO2, water vapor, traces of other gases  Water vapor: source of clouds and precipitation; absorbs heat from Earth and solar radiation  Condensation nuclei (particulates) : dust, pollen salt, soot, smoke (necessary for cloud formation as provides water with something to condense onto)

Height and Structure  Atmosphere thins with increased altitude (gravity concentrates air at surface)  Temperature decreases with altitude in Troposphere (where weather occurs) and Mesosphere  Temperature increases with altitude in Stratosphere (ozone) and Thermosphere (O and N absorb short-wave, high energy solar radiation)  Atmosphere thins with increased altitude (gravity concentrates air at surface)  Temperature decreases with altitude in Troposphere (where weather occurs) and Mesosphere  Temperature increases with altitude in Stratosphere (ozone) and Thermosphere (O and N absorb short-wave, high energy solar radiation)

The Atmosphere

Altitude and Pressure  Air pressure is simply the weight of the air above you  The higher the altitude, the fewer the air particles  Fewer particles exert less pressure, thus pressure decreases with an increase in altitude  Air that rises from the surface moves into layers with less pressure. This makes the air parcel expand and cool, forming clouds (adiabatic cooling).  Air pressure is simply the weight of the air above you  The higher the altitude, the fewer the air particles  Fewer particles exert less pressure, thus pressure decreases with an increase in altitude  Air that rises from the surface moves into layers with less pressure. This makes the air parcel expand and cool, forming clouds (adiabatic cooling).

Adiabatic  Describes a change in temperature resulting from the expansion or compression of air  Air that rises will expand (due to less pressure from surrounding particles) and will cool adiabatically  Air that descends will compress (due to more pressure from surrounding particles) and will warm adiabatically  Describes a change in temperature resulting from the expansion or compression of air  Air that rises will expand (due to less pressure from surrounding particles) and will cool adiabatically  Air that descends will compress (due to more pressure from surrounding particles) and will warm adiabatically

Earth-Sun Relationships  Solar energy is not distributed evenly over Earth’s surface  Varies with latitude, time of day, and season of the year  Unequal heating creates winds and drives ocean currents  Winds and ocean currents transport heat from warmer to colder regions in an attempt to balance energy differences  Solar energy is not distributed evenly over Earth’s surface  Varies with latitude, time of day, and season of the year  Unequal heating creates winds and drives ocean currents  Winds and ocean currents transport heat from warmer to colder regions in an attempt to balance energy differences

Earth’s Orientation  Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels its orbit.  Due to the Earth’s tilt (23.5º) and revolution around the sun, energy received at given latitudes changes with time. This creates our seasons as well as seasonal variations in severe weather.  Seasons ARE NOT due to changes in distance from the sun. (We have summer when farthest from the sun, and winter when closest.)  Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels its orbit.  Due to the Earth’s tilt (23.5º) and revolution around the sun, energy received at given latitudes changes with time. This creates our seasons as well as seasonal variations in severe weather.  Seasons ARE NOT due to changes in distance from the sun. (We have summer when farthest from the sun, and winter when closest.)

Heating the Atmosphere  Heat is the energy transferred from one object to another because of a difference in their temperatures.  When energy is transferred to the gas atoms and molecules in the air, particles move faster and air temperature increases.  When air transfers energy to a cooler object, its particles move slower and air temperature decreases.  Three mechanisms of heat transfer: conduction, convection and radiation  Heat is the energy transferred from one object to another because of a difference in their temperatures.  When energy is transferred to the gas atoms and molecules in the air, particles move faster and air temperature increases.  When air transfers energy to a cooler object, its particles move slower and air temperature decreases.  Three mechanisms of heat transfer: conduction, convection and radiation

Conduction  Transfer of heat through matter by molecular activity  Energy of molecules transferred by collisions from one to another  Heat flows from higher to lower temperatures  Air is a poor heat conductor, so conduction only occurs between land and air in direct contact with it  Transfer of heat through matter by molecular activity  Energy of molecules transferred by collisions from one to another  Heat flows from higher to lower temperatures  Air is a poor heat conductor, so conduction only occurs between land and air in direct contact with it

Convection  Transfer of heat by mass movement or circulation within a substance  Takes place in fluids (ocean and air) and solids (mantle)  Air warmed at surface rises (less dense), cools adiabatically and sinks (more dense)  Most heat transfer within the atmosphere is due to convection.  Transfer of heat by mass movement or circulation within a substance  Takes place in fluids (ocean and air) and solids (mantle)  Air warmed at surface rises (less dense), cools adiabatically and sinks (more dense)  Most heat transfer within the atmosphere is due to convection.

Radiation  All objects (hot or cold) emit radiant energy, although hotter objects emit more total energy  Hottest radiating bodies produce the shortest wavelengths of maximum radiation  Solar energy reaches earth by radiation  Some energy (depending on wavelength) is scattered, some reflected and some absorbed at the Earth’s surface.  All objects (hot or cold) emit radiant energy, although hotter objects emit more total energy  Hottest radiating bodies produce the shortest wavelengths of maximum radiation  Solar energy reaches earth by radiation  Some energy (depending on wavelength) is scattered, some reflected and some absorbed at the Earth’s surface.

Temperature and Wind  Temperature differences (due to unequal heating of the Earth’s surface) create pressure differences. (Colder air is “heavier” so it exerts greater pressure.)  Wind is the result of pressure differences. Wind flows from areas of HIGH pressure to areas of LOW pressure in an attempt to make the atmosphere more uniform.  Temperature differences (due to unequal heating of the Earth’s surface) create pressure differences. (Colder air is “heavier” so it exerts greater pressure.)  Wind is the result of pressure differences. Wind flows from areas of HIGH pressure to areas of LOW pressure in an attempt to make the atmosphere more uniform.

Factors Affecting Wind  If Earth did not rotate and friction between air and Earth didn’t exist, air would flow in a straight line from high to low pressure. However…  Three factors combine to control wind: pressure differences, the Coriolis effect, and friction.  If Earth did not rotate and friction between air and Earth didn’t exist, air would flow in a straight line from high to low pressure. However…  Three factors combine to control wind: pressure differences, the Coriolis effect, and friction.

Pressure Differences  The greater the difference in pressure, the greater the wind speed.  Isobars connect places of equal air pressure. The closer the isobars, the faster the wind speed.  Pressure Gradient: amount of pressure change occurring over a given distance  The greater the difference in pressure, the greater the wind speed.  Isobars connect places of equal air pressure. The closer the isobars, the faster the wind speed.  Pressure Gradient: amount of pressure change occurring over a given distance

Coriolis Effect  Describes how Earth’s rotation affects moving objects.  All free-moving objects or fluids (including the wind) are deflected to the RIGHT of their path in the N.H. and to the LEFT of their path in the S. H.  Wind actually moves in a straight line, but the Earth rotates beneath it, giving the “illusion” of bending.  Describes how Earth’s rotation affects moving objects.  All free-moving objects or fluids (including the wind) are deflected to the RIGHT of their path in the N.H. and to the LEFT of their path in the S. H.  Wind actually moves in a straight line, but the Earth rotates beneath it, giving the “illusion” of bending.

Earth’s Rotation and Weather Systems

Friction  Important only within a few kilometers of Earth’s surface.  Acts to slow air movement, which changes wind direction.  When air is above friction layer, the pressure gradient causes air to move across the isobars. At that time, the Coriolis effect acts at right angles to this motion. The faster the wind, the greater the deflection.  Important only within a few kilometers of Earth’s surface.  Acts to slow air movement, which changes wind direction.  When air is above friction layer, the pressure gradient causes air to move across the isobars. At that time, the Coriolis effect acts at right angles to this motion. The faster the wind, the greater the deflection.

Pressure Centers and Winds  Cyclones (low pressure centers)  Pressure decreases from outer isobars to center  Winds flow counterclockwise into system  Associated with overcast skies and rain  Cyclones (low pressure centers)  Pressure decreases from outer isobars to center  Winds flow counterclockwise into system  Associated with overcast skies and rain  Anticyclones (high pressure centers)  Pressure increases from outer isobars to center  Winds flow clockwise out of system  Associated with fair weather and blue skies  Anticyclones (high pressure centers)  Pressure increases from outer isobars to center  Winds flow clockwise out of system  Associated with fair weather and blue skies

Weather and Air Pressure  Low pressure at surface causes air to convergence and rise. Rising air cools adiabatically and forms clouds.  High pressure at surface causes air to diverge (air subsides from aloft and warms adiabatically) creating clear, blue skies.  Low pressure at surface causes air to convergence and rise. Rising air cools adiabatically and forms clouds.  High pressure at surface causes air to diverge (air subsides from aloft and warms adiabatically) creating clear, blue skies.

Global Winds  Recall that a non-rotating Earth would create two main convection cells with air flowing from the poles to the equator (high to low)  The Earth’s rotation breaks this convection into smaller cells  The behavior of winds within these cells produce global wind belts.  Recall that a non-rotating Earth would create two main convection cells with air flowing from the poles to the equator (high to low)  The Earth’s rotation breaks this convection into smaller cells  The behavior of winds within these cells produce global wind belts.

El Nino  Under normal conditions, trade winds and a strong equatorial ocean current flows toward the west.  Flow encourages upwelling of cold nutrient- filled water from below as water above “pushed away” from the wind.  Food source for fish  Under normal conditions, trade winds and a strong equatorial ocean current flows toward the west.  Flow encourages upwelling of cold nutrient- filled water from below as water above “pushed away” from the wind.  Food source for fish

More on El Nino…  At irregular intervals of three to seven years, these warm countercurrents become unusually strong and replace normally cold offshore water with warm equatorial waters (El Nino)  Produces abnormal weather patterns for Ecuador and Peru (excessive rainfall).  Fishing industry impacted.  At irregular intervals of three to seven years, these warm countercurrents become unusually strong and replace normally cold offshore water with warm equatorial waters (El Nino)  Produces abnormal weather patterns for Ecuador and Peru (excessive rainfall).  Fishing industry impacted.

La Nina  Opposite of El Nino  Occurs when surface temperatures in the eastern Pacific are colder than average  Distinctive set of weather patterns  Colder than normal air over Pacific Northwest and northern Great Plains, but warmer over much of the rest of the United States  Greater precipitation over Northwest than usual  Can increase hurricane activity; hurricane damages 20X greater in U.S. during La Nina years  Opposite of El Nino  Occurs when surface temperatures in the eastern Pacific are colder than average  Distinctive set of weather patterns  Colder than normal air over Pacific Northwest and northern Great Plains, but warmer over much of the rest of the United States  Greater precipitation over Northwest than usual  Can increase hurricane activity; hurricane damages 20X greater in U.S. during La Nina years