WHAT IS WEATHER?-the short tem condition of the atmosphere at a given location, where short term generally means a few hours or days.METEOROLOGISTS:Scientists who study and predict the weather

WHAT IS THE STURCTURE OF THE ATMOSPHERE?Four Layers:

1)Troposphere, 2)stratosphere, 3)mesosphere, 4)thermosphere

*Troposphere (what we breathe)-Lowest layer

-relatively thin

-contains most of the mass of the atmosphere

Stratosphere:

Layer in which the ozone layer is present

*The upper boundaries of each layer, end with the suffix –pause, such as tropopause or stratopause

**Each boundary is identified by changing trends in temperature

BOUNDARIES BETWEEN LAYERS

CHANGES IN AIR TEMPERATURE-cyclic: lowest in the morning and warmest at mid afternoon(2 pm.)

-air temperature is created by the sun’s energy heating up objects on the surface of the earth that then radiate energy back

-Water that has cooled below its dew-point and is suspended in the air because the molecules are so small

-NOT A GAS!

Condensation nuclei-Tiny particles of dust or dirt that

provide a surface for cloud water to collect on.

-When droplets become big (heavy) enough, they fall out of the sky

-without this dust, clouds could not form

WHAT CAUSES AIR PRESSURE?-caused by the weight of the atmosphere-you can prove the air has weight by using a scale and a deflated soccer ball.

- Air pressure is greatest at the Earth’s surface, and decreases with altitude-air pressure is exerted in all directions, so we are seldom aware of it

FACTORS THAT AFFECT ATMOSPHERIC PRESSURE

-when air cools, it contracts becoming denser. This causes atmospheric pressure to rise

-when air is heated it expands becoming less dense, causing atmospheric pressure to fall

-humid air is less dense than dry air

HIGH PRESSURE SYSTEMS BRING SUNNY DAYS

AIR SINKS NEAR LOW PRESSURE CENTERS, WHICH INHIBIT PRECIPITATION AND CLOUD FORMATION. THIS IS WHY THEY OFTEN BRING SUNNY DAYS WITH CALM WEATHER

LOW PRESSURE BRINGS RAINY OR STORMY WEATHER

-AIR RISES NEAR LOW PRESSURE AREAS. AS AIR RISES, IT COOLS AND OFTEN CONDENSES INTO CLOUDS AND PRECIPITATION

-Cold air becomes more dense and sinks-This puts “high” pressure in the surface of the Earth

-warm is less dense so it rises off the ground

-this places “low” pressure on the surface of the Earth

Barometer:-instrument used to measure air pressure

-Fig 6-3 in book. P.107

Isobars: Connect places that have the same air pressure on a weather map

MOISTURE IN THE ATMOSPHERESaturation:

-When the air is holding as much water as it can hold, it is said to be saturated-the warmer the temperature,

the more moisture it can hold before it becomes saturated

Dew Point:

-The temperature to which air must be cooled to be saturated-if temperature falls below the

dew point, condensation occurs

MEASURING MOISTURE IN THE ATMOSPHERE

Sling Psychrometer:-used to determine dew point-has two thermometers-one thermometer measures the air temperature-the other is covered by a cloth wick soaked in water.

-the drier the air, the quicker water will be evaporated and the greater the difference between wet bulb temperature and air temperature

-After we swing around the sling Psychrometer and record the temperatures, we can use our dew point temperatures chart in our reference tablesSample problem:If the dry bulb temperature is 15oC and the wet-bulb temp is 5oC, find the dew point

RELATIVE HUMIDITY

-compares how much moisture the air is holding with how much it could potentially hold.

-expresses how full of moisture the air is

-expressed as a percent of saturation-For air that is saturated, it is said to have 100% relative humidity

Sample Problem-Find the relative humidity when the dry bulb temp is 20oC and the wet bulb is 14oC