State of the Atmosphere

Temperature Temperature – a measure of the movement of molecules Greater number of molecules or faster the movement = hotter the temperature Lower number of molecules or slower the movement = colder the temperature Measured by thermometer

Heat Heat is the transfer of energy that occurs due a difference in temperature Direction of heat flow depends on temperature Heat flows from hotter objects to cooler objects

Heat VS Temperature Heat transfers energy that fuels atmospheric processes, while temperature measures the heat energy Temperature is measured in Farenheit, Celsius, and Kelvin Prefer measurements of temperature in Celsius for weather temperature, because convenient for freezing point (0C) and boiling point (100C)

Dew Point Dew point is the temperature at which air must be cooled at constant pressure to reach saturation Saturation = point at which air holds as much water vapor as it can Until air is saturated, condensation cannot occur Condensation = occurs when matter changes state from a gas to a liquid

South American Gray Fox Dew Point Important for desert animals whose only source of water comes from dew left on plants South American Gray Fox Kangaroo Rat

Vertical Temperature Changes In the troposphere, temperature decreases as altitude increases Why? As altitude increases, move away from source of heat (Earth’s surface)

Vertical Temperature Changes Air pressure decreases as altitude increases As air mass moves upward, pressure decreases and the air mass expands as a result Molecules are further apart, and collisions between molecules decrease, causing temperature to decrease If air continues to rise, will eventually cool to condensation temperature and form clouds Height at which condensation occurs is called lifted condensation level (LCL)

Air Pressure and Density Just like water, air exerts pressure on our bodies Gravity from Earth pulls air particles toward the center of Earth We don’t feel air pressure because adapted to it Density of air related to the number of particles occupying a particular space Gases from upper layers of atmosphere push down on lower layers to compress particles and increase density

Wind Wind occurs when air moves from areas of high pressure to areas of lower pressure Cool air is denser than warm air, and sinks and forces warmer air upward Air moves in response to density imbalances caused by unequal heating and cooling of Earth’s surface Wind measured in miles/hour or ships at sea measure wind in knots 1 knot = 1.85 km/hr

Wind Wind changes with height in altitude Near Earth’s surface, wind encounters friction that results from contact with trees, water, hills, sand, etc As you get further from Earth’s surface, less friction encountered by wind, so wind speeds increase

On surface of sand dunes? Wind Would you expect wind speeds to be faster or slower… On surface of sand dunes? On surface of water?

Relative Humidity Amount of water vapor in air is called humidity Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor Relative humidity varies with temperature Warm air holds more humidity than cold air Expressed as a percentage