Bolide falling to earth

Lake effect snow over the Great Lakes

Hurricane tracks

I. Weather is the condition of the atmosphere at any point in time.

A. Weather Variables are individual pieces of information that describe specific conditions of the atmosphere.

B. Weather stations are locations that record weather data that is shared with other stations, from which a weather map may be created.

C. Weather maps provide a picture of the conditions of the atmosphere at a moment in time. These provide meteorologists with information to make predictions.

Link to current

Comparing Warm and Cold Air

– Water vapor enters the atmosphere due to evaporation from surface water and ice.

– Energy is required for evaporation, which takes heat away from the surface.

– Warm air has more energy, and can therefore cause more evaporation.

– Cold air cannot cause as much evaporation, so the water vapor tends to condense or sublimate.

– Condensation releases heat back into the air.

C. Dewpoint temperature

– The dewpoint temperature is the temperature at which water vapor will CONDENSE to become drops of water or SUBLIMATE to become ice crystals.

– The air must be cooled for this to happen.– The dewpoint depends on the amount of water vapor in

the air. It DOES NOT depend on the air temperature. It indicates how humid air is.

– A sling psychrometer, shown on page 501 text, compares a ‘wet’ bulb to a ‘dry’ bulb.

– A high dewpoint indicates a high concentration of water vapor. Dry air has a low dewpoint.

D. Relative Humidity

– Relative humidity is a percent.– It compares the amount of water vapor in the air,

(humidity), to the amount of water vapor the air can hold at the present air temperature.

– Water vapor requires ENERGY. Warm air has more energy than does cold air.

– The relative humidity indicates the likelihood of dew or frost or fog forming.

– 100% RH indicates that fog is probably forming. This means that the air is saturated with vater vapor.

– Clouds are always at 100% RH.

IV. Weather Variables

A. Air pressure is the weight of air at any particular point. It is also called barometric pressure.– The units are given in the ESRT in millibars and

inches of mercury and as atmospheres.– A barometer is a device used to measure pressure,

and one type is shown on page 523 text. – Air pressure depends on how tightly packed the

molecules are and how heavy they are.

Comparing Weather variables

Heavy Air: (high pressure)

– cold, because the molecules are closer together.

– Dry, because nitrogen and oxygen are heavier than water vapor.

– Calm, because moving air is less dense than calm air.

Light Air: (low pressure)

– warm; the molecules have more energy and are farther apart.

– Humid, because water vapor is a very light molecule.

– Windy

E. Wind speed and direction

– Wind is the horizontal movement of air.

– Since air is fluid, it can flow, just as water can.

– Wind occurs when heavy air moves along the surface, pushing lighter air out of its way.

– The greater the difference in air pressure, the faster the wind will move. Speed is given in mph or in knots.

– Wind is always named for the direction from which it comes.

– An anemometer measures wind speed and weather vanes, or socks, show direction.

B. Air temperature

– Temperature is the measure of the average kinetic energy of the molecules. Heat causes molecules to move faster and expand.

– Liquid thermometers measure temperature as the liquid becomes less dense when heated, causing it to rise in the glass, or more dense when cooled, causing it to drop in the glass.

– Temperature is measured in degrees Celsius, degrees Fahrenheit and Kelvin.

– ALL MOLECULES have heat.

II. The atmosphere

A. The atmosphere is the ocean of gases, held in by gravity, that surrounds our planet. It is a mixture of gases.– Page 14 of the ESRT has a graph of the

characteristics that change with altitude.– Page 10 shows us that the lowest level, called the

troposphere, is primarily nitrogen and oxygen.– Water vapor is found ALMOST only in the

troposphere, which is where ‘weather’ occurs.

III. The atmosphere A. Using the page of the ESRT, notice the following:

– the atmosphere is divided according to the way in which temperature CHANGES with altitude.

– Atmospheric pressure steadily decreases with altitude. The greatest pressure is at sea level, due to the weight of overlying molecules.

– Pressures are given as negative exponents.– Water vapor concentrations are greatest at sea

level, and almost nonexistent above the tropopause.

B. The levels of the atmosphere.– The troposphere has the greatest concentration of water

vapor and the greatest pressure.– The stratosphere contains ozone, which absorbs

ultraviolet (uv) rays, causing it to warm with increases in altitude.

– Ozone is a form of oxygen, O3 very different than breathable oxygen,O2.

– Ultraviolet light is a form of very powerful electromagnetic energy.

Practice

– What is the temperature range of each of the layers?

– What is the altitude of the tropopause?– In what layer is the air pressure 10-3?– What is the pressure at sea level?– What is the temperature at a height of 25 miles?