What is Weather? Weather is the state or condition of the variables of the atmosphere at any given location for a short period of time.

What is Climate?  Climate is the average weather conditions of a specific region over a long time including the range of weather conditions.

Who Studies Weather?  Do you know this man?

What does a Meteorologist do?  A Meteorologist is a person who studies weather (the troposphere) and how it changes.

What are the Variables of Weather?  1) Temperature  2) Air Pressure  3) Humidity (moisture content)  4) Wind  5) Cloud Cover  6) Precipitation  7) Storms

Atmospheric Temperature (see ref. table p.13)  Air temperature is usually measured using a liquid filled glass tube called a thermometer.

What heats our atmosphere? This big ball of hydrogen fusion. You know it better as the sun.

What is Hydrogen Fusion?  Under extreme conditions of heat and pressure within the sun hydrogen nuclei join to form a helium nucleus.

Let’s see how  The Water Cycle

Insolation  Incoming  Solar  Radiation

Heating of the Atmosphere

How is Heat Transferred From One Area to Another? Convection, Conduction and Radiation

Three Ways Energy Is Transferred  1) Radiation: The amount of heat received directly from the sun by earth  2) Conduction: When molecules come into contact, energy is passed along from molecule to molecule.  3) Convection: A form of heat flow that moves both matter and energy as density currents under the influence of gravity.  4) The Coriolis Effect: Results from the rotation of Earth and wind. This causes friction where the atmosphere and Earth’s surface meet.

The Coriolis Effect  The Coriolis effect results from the rotation of Earth and wind. This causes friction and this friction produces heat some of which is absorbed from the atmosphere.

The Coriolis Effect

How do we know there is a Coriolis Effect?  The Foucault Pendulum is our proof that the the Earth rotates. The Coriolis effect is caused by Earth’s rotation.  jw/foucault_pendulum.html jw/foucault_pendulum.html jw/foucault_pendulum.html

What is Atmospheric Pressure? P.128 in your regent workbook  Atmospheric Pressure (air pressure) is the pressure due to the weight of the overlying atmosphere pushing down on any given area.  Atmospheric pressure is measured by using a barometer. There are two types of barometers: a mercury barometer and the aneroid barometer.

What does of a barometer look like?  Mercury Barometer

Aneroid Barometer

Conversions of Barometric Pressure (see p.13 in ref table)  Standard air pressure (one atmosphere) at sea level is 15.7 pounds per square inch, inches of mercury or millibars.

Effect of Temperature on Air Pressure  Changes in the temperature of the air causes changes in the air pressure.  As the temperature of air increases (gets hotter), the air expands and its density and pressure decreases.  As the temperature of air decreases (gets colder), the air compresses and its density and pressure increases.

What is Wind? Page 131 in your regent workbook Wind is horizontal movement of air parallel to Earth’s surface. Wind is a type of vector. It is a vector because it requires two measurements, magnitude (strength) and direction (where is it coming from) to totally describe it.

What tool is used to measure wind?  An instrument called an anemometer is used to measure wind speed (magnitude). Wind speed is measured in miles per hour and knots.

Wind Direction  Air (wind) moves from areas of high pressure to low pressure.  High pressure air (air low in water vapor) moves towards low pressure air (air high in water vapor).

Air Pressure Gradient  The difference in air pressure for a specific distance is called the air pressure gradient.  The closer together the isobars on a weather map, the greater (the steeper) the pressure gradient.  The greater the pressure gradient, the faster the speed.

How do we record wind?  A wind is named for the direction from which it comes from.  For example, a wind blowing from the south toward the north is a south wind. A wind blowing towards the south east is a northwest wind (the direction it is coming from).

Wind Vane  An instrument called a wind vane is often used to determine wind direction.

Formation of Waves on Surface Water  Wind blowing over bodies of water creates friction where the air and liquid water meet.  The friction transfers energy from the wind to the body of water and produces waves.  These energy waves move out from the area where they are produced and toward where the energy results in wave erosion at shorelines.

Wind Belts  Planetary Wind Patterns

Wind Pressure Belts Very Important!!!! (see p.14 of ref. table)  Wind Pressure Belts are produced in the atmosphere as a result of convection.  Low pressure belts are found at the equator and at the 60 degree North and South Latitudes.  High pressure belts are found at the 30 degree North and South Latitudes as well as at both the North and South Poles.

Location of Earth’s Pressure Belts The location of Earth’s pressure belts and the affect of Earth’s rotation determines the general position and direction of planetary wind circulation. Factors such as:  Altitude  Position relative to mountains  Position relative to bodies of water May modify the wind pattern.

Humidity and Dew Point  Humidity is the term that refers to the amount of water vapor in the atmosphere.  The amount (mass) of water vapor in each unit volume of air is called absolute humidity.  The absolute humidity (moisture capacity) increases rapidly with an increase in air temperature (gets hotter).

Hot air can hold more water vapor than cold air.  Relative Humidity  The ratio of the amount of water vapor in the air to the maximum amount it can hold (the moisture capacity).  Relative humidity is expressed as a percent therefore representing the amount of moisture the air is holding.  For example: at a relative humidity of 100% the air is holding as much moisture as it can.

Water Vapor is the Most Important Reservoir of Energy in the Atmosphere  Water vapor stores solar energy. (see p. 1 of ref. table.)  For each gram of water to change from a liquid to a gas, 2260 joules (unit for energy) must be absorbed by a water molecule.  That’s quite a bit of energy.

Relative Humidity and Temperature  As temperature increases (gets hotter) the relative humidity will decrease. This occurs because the capacity of the atmosphere to hold water increases.  As temperature decreases (gets colder) the relative humidity will increase (gets closer to 100%). As temperature gets colder there is less heat in the atmosphere and the capacity to hold water decreases.

Dew Point  Dew Point is the temperature (in degrees Celsius) at which air is saturated with water vapor.  The dew point depends on the absolute humidity and not on the relative humidity.  As the amount of water vapor in the air increases, the dew point also rises because the more water vapor in the air the closer the air is to its saturation point----the dew point.

Tools used to Measure Dew Point  Sling Psychrometer:

Parts of a Sling Psychrometer Wet Bulb and Dry Bulb Wet Bulb and Dry Bulb  The Wet Bulb has a wick (piece of gauze). This measure the temperature of evaporation. (This temperature can either be equal or less than the air temperature.)  The Dry Bulb measures the air temperature.

Tools used to Measure Dew Point (part 2)  Hygrometer

How to Find Dew Point (Use p. 12 of your reference table)  To find dew point: Subtract the wet bulb from the dry Subtract the wet bulb from the dry bulb. bulb. Go to p.12 of your reference table and line up the dry bulb temperature with the difference between the wet and dry bulbs. Remember dew point is represented in degrees per Celsius. Don’t forget your units!!!!

Cloud Cover  Clouds form by a process called condensation.  Condensation releases 2260 joules into the atmosphere as water vapor changes into tiny water droplets and ice crystals to form clouds.  *Notice Condensation is the opposite of Evaporation.

Types of Clouds  Clouds are classified into a system that uses Latin words to describe the appearance of clouds as seen by an observer on the ground /mtr/cld/cldtyp/home.rxml /mtr/cld/cldtyp/home.rxml /mtr/cld/cldtyp/home.rxml  clouds.htm

How Do Clouds Form?  1) Cooling of Air  Air must be cooled below dew point.  What happens when air expands? Expansion of a gas causes the gas to cool. If air cools below its dew point, condensation will create a cloud.

How Do Clouds Form?  2) Condensation Nuclei  When dew or frost forms this means air is below its dew point. We see dew and frost because water is condensing on a surface.  In the atmosphere those surfaces are provided by particles of solids suspended in the air. These solids are called condensdation nuclei.

Examples of Condensation Nuclei  Dust from dust storms  Fires  Exhaust from Cars  Exhaust from Homes  Exhaust from Factories  Exhaust from Power Plants

Have you ever noticed that after precipitation, there are no clouds in the sky?  Precipitation in the form of rain, snow, sleet and/or hail bring condensation nuclei to ground level.  Now, lets make a cloud. Beginning of Lab #19.

What is Precipitation? Refer to p.141 in Regent workbook Precipitation is the falling of liquid or solid water from clouds toward the surface of the Earth. Ice crystals or water droplets formed by condensation come together to become big enough so that they will fall under the influence of gravity.

How do we measure precipitation?  A rain gauge is used to measure precipitation.

What are the forms of Precipitation?  Rain: liquid precipitation, droplets are larger than 0.2 mm in diameter; may be melted snow.

Forms of Precipitation (continued)  Drizzle: Falling liquid droplets from mm in diameter. Atmospheric temperature is above 32 degrees Fahrenheit.  Snow: Falling ice crystals formed by combining cloud ice crystals. Atmospheric temperature is below 32 degrees Fahrenheit.

Forms of Precipitation (continued)  Sleet: Solid pellets of ice that form by freezing of rain drops as they fall. Temperature of the atmosphere where the clouds are is above 32 degrees Fahrenheit but at the surface of the earth the temperature is below 32 degrees Fahrenheit.

Forms of Precipitation (continued)  Freezing Rain: Rain or drizzle that freezes on contact with features of Earth’s surface.  Hail: Layers of ice, snow and water formed by many up and down movements in a thunderstorm cloud.

The States of Matter

The Heating/Cooling Curve of Water 

Lab Activity #5: Phase Changes of Water  We will now complete lab activity #5: Phase Changes of Water. You will need to complete this lab in full.

HW #5, July 19, 2010  Please complete the following:  Questions on pages in your regent review book.  Questions on p.94 in your regent review book.  Study for your quiz