Properties of the Atmosphere Unit #6 Properties of the Atmosphere

Vocabulary Weather Meteorology Atmosphere The short-term conditions of the atmosphere Meteorology The study of the atmosphere and its properties Atmosphere Blanket of gas that surrounds the Earth

Gas of the atmosphere Earth Science Reference Table page 11 Nitrogen Oxygen Carbon dioxide Water Vapor Methane

Structure of the Atmosphere ESRT page 14 Decreases 0 km Stratosphere and thermosphere Troposphere Greenhouse gases http://www.epa.gov/globalwarming/kids/version2.html

Air Pressure à  Caused by the weight of the air molecules in the atmosphere à  The atmosphere extends kilometers above the Earth’s surface à  The weight of the air exerts a pressure of nearly 15 lbs/in2 à  The air pressure is greatest at the surface and decreases with altitude  Since, the pressure is exerted in every direction we are seldom aware of it.

Air pressure is seen when: 1) Drinking through a straw

Effects of air pressure Macro-scale

Measuring Air Pressure Air pressure can be measured with a barometer. Two types of barometers: 1) Mercury barometer uses mercury in a column an measures the change in air pressure

2) Aneroid Barometer  air pressure causes changes to the metal cover on a air tight box, which is translated to an dial.

Air pressure is measured in: Millibars Inches of mercury Convert pressures by reading across the scale 1000.0 mb = 29.53 inches of Hg

Points of equal pressure are connected by isobars. Isobars – connect points of equal pressure

How does air pressure affect us? 1) Airplane travel many kilometers above the surface, since the air is very thin, the cabins are pressurized 2) Mountaineers often take along oxygen on very high mountains because the air is thin at high elevations

Factors affecting Atmospheric Pressure 1) Temperature à When air cools it contracts and becomes more dense, increasing pressure. à When air is heated it expands and becomes less dense, decreasing pressure. à This is an inverse relationship.

Factors affecting Atmospheric Pressure 2) Moisture à Water has a mass of 18 AMU à Nitrogen has a mass of 28 AMU  If there is more moisture (water) in the air, the air will be lighter and decrease the pressure.

Moisture in the Atmosphere  Water Vapor: water in the gas form  Air has the ability to hold to hold water vapor  Think of air as a container, which can only hold a limited amount of moisture.

Unsaturated Saturated

Unsaturated vs. Saturated Unsaturated Air: air that is not holding as much water vapor as possible Saturated Air: air that is holding as much water vapor as possible à water vapor will start to condensate to form droplets of water Water vapor can not be seen, water droplets can be seen (clouds)

Ways to make air saturated: 1) Add more water vapor to the air 2) Lower the temperature of the air à  lowering temperature air has a reduced ability to hold moisture 60 deg. F unsaturated 40 deg. F saturated

Dew point The temperature to which the air must be cooled to become saturated, condensation will occur

Measuring Moisture in the Atmosphere  Moisture is determined by measuring the amount of evaporation. Evaporation causes cooler temperatures. Lower temperature, due to evaporation Measures the air temperature, Higher temperature

The amount of moisture is determined by measuring the difference in temperature caused by evaporation and the air temperature. Psychrometer  tool used to measure the air temperature and the temperature after evaporation.

Relative Humidity à expresses the amount of moisture in the air, compared to how much it can hold. 50% Humidity 25% Humidity

Influences of humidity: à High humidity can make the air uncomfortable     When the relative humidity is 100%, the dew point is reached and condensation occurs

Wind à Movement of air due to convection currents, temperature and densities changes  Uneven heating of the Earth causes differences in air pressure Wind moves from areas of high pressure to areas of low pressure Anemometer  tool used to measure wind speed

Determining Wind Strength Winds strength is determined by the pressure gradient Pressure gradient  change in pressure over a distance à larger gradient = stronger winds à smaller gradient = slower winds

Sea Breeze Low Pressure High Pressure

Land Breeze High Pressure Low Pressure

Land heats and cools faster than water creating Low pressure during the day Water heats and cools slower, creating low pressure at night

Prevailing Winds and Ocean Currents Notice how both the maps generally match. Winds are the major factor in moving the surface waters of the oceans. Winds are moving between areas of high and low pressure, but notice: The winds follow a curved path this is due to the Coriolis Effect

Coriolis Effect: (song) Due to the Earth’s rotation, freely moving object like wind and water, will follow a curved path, à  curving to the right in the Northern Hemisphere à curving to the left in the Southern Hemisphere

Large Scale

Small Scale Rotate Counter clockwise Rotate Clockwise

When air moves from High to Low pressure wind is created. (song) Vertical Movement Rising Sinking Horizontal Movement Into the center Out of the center Cause Less dense are rising More dense air sinking Effect Cooling, condensation and cloud formation Warming, drying clear skies Also known as Convergence Zone Divergence Zone

High and Low Pressure

Where will clouds form? Formation of clouds requires: Water vapor Lower temperatures Condensation nuclei Clouds form when water vapor condensates As air rises, the temperature decreases due to expansion and lower pressures Condensation nuclei  tiny dust particles suspended in the air on which condensation can occur. Air rises, cools & condensates within a Low pressure system When the air temperature cools to the dew point, condensation will occur and a cloud will form

If air temperature and dew point are not the same at the surface, how can they cool to the same temperature in the troposphere? The air temperature will cool faster than the dew point temperature

Cloud height chart Use the air temperature & dew point

Temperature is 30 C and the dew point is 20 C, what is the cloud height?

How do clouds form and cause precipitation? Clouds form when rising air is cooled below its dew point.  As air rises, the air cools due to expansion and condensation occurs. Condensation nuclei tiny particles of dust upon which condensation will occur. Rain Drops get larger as smaller drops of water bump into each other. Clouds  mass of liquid water droplets suspended in air. Precipitation  water fall from the sky

Large cloud droplet drizzle droplet Cloud droplet Condensation nuclei Large rain drop

Types of Precipitation Type of Precipitation Description Rain Water droplets falling from the sky Snow Frozen water crystals Sleet Partially frozen mixture of rain and snow Hail Ice balls created from repeated freezing and thawing

Temperature and Atmospheric Pressure  As temperature increases, the pressure will decrease because the air is less dense.  As the temperature decreases the pressure will increase because the air is more dense.  Inverse relationship

Temperature and Relative Humidity  As the temperature increases the relative humidity will decrease because the air has a greater ability to hold moisture.  As the temperature decreases the relative humidity will increase because the air has a lower ability to hold moisture.  Inverse relationship