Weather and Climate Unit Investigative Science

* Meteorologists describe properties of the atmosphere using the following descriptors: * Temperature * Dew Point * Air Pressure * Temperature Inversions * Wind * Relative Humidity

* Temperature is the measurement of the average kinetic energy of the particles. * More/faster moving molecules = higher temperature * Fewer/slower moving molecules = lower temperature

* Temperature is measured in Celsius, Fahrenheit, or Kelvin. * In the United States, Fahrenheit is the most common unit to measure temperature. * Celsius is the unit used in most textbooks and by scientists. It measures the difference between the freezing (0 o C) and boiling (100 o C) points of water. * Kelvin is the SI unit for temperature. It is not measured in degrees, just numbers. The zero point in Kelvin is absolute zero—the lowest temperature any substance can have!

* Heat is the total amount of energy contained in an object. * Heat can flow from a warmer object to a colder object. * Heat is the transfer of energy that fuels weather systems on Earth. * Temperature is used to measure and record that energy.

* Dew Point: the temperature to which air must be cooled at constant pressure to reach saturation. * Saturation occurs when the air holds as much water vapor as possible and condensation occurs. * Condensation is when water vapor turns into liquid water.

* The Dew Point is often called the Condensation Temperature. This is because condensation occurs when water molecules cool to the point where water droplets form. * Air gets cooler, the further away from Earth’s surface you go. Eventually, it is cool enough for water vapor to condense and form clouds. The height above the Earth where condensation occurs is called the Lifted Condensation Level (LCL). This corresponds to the bottom level of clouds.

* The density of air increases as you get closer to the surface of the Earth (the bottom of the atmosphere). * As you go higher in the atmosphere, air pressure and density decreases as the mass of air above you decreases.

* In a closed system, if temperature increases, pressure increases (particles are hitting each other more often and with more force). * In the atmosphere, if the temperature increases, air particles move outward, which decreases its density and pressure.

* Typically, as you move up in the atmosphere, temperatures decrease (because there are fewer particles hitting each other). Cold air is on top of warm air at the surface. * However, sometimes, certain conditions exist where the temperature INCREASES as you move up in the atmosphere. * This is a Temperature Inversion. In other words, warm air is over cold air. The relationship is inverse (or turned upside down).

* Example of temperature inversion: when there is a rapid cooling of land on a cold, clear winter night when the air is calm. The land does not radiate heat, so the air above the land gets very cold. * By contrast, the air above this layer of cold air is relatively warmer. This leads to fog, or very low-level clouds. It definitely gets very hazy and can trap smog/pollution close to Earth’s surface.

* The atmosphere works much like an air-conditioned building. When entering an air conditioned building, cold, dense air rushes out to the warm (less dense) air outside.

* In the atmosphere, cold air, being more dense, sinks and forces warm, less dense air upward. * Wind can be though of as air moving from an area of high pressure and density to an area of low pressure and density.

* Wind close to the surface of the Earth is slowed by friction—it hits buildings, objects, mountains, etc. and slows down. * High up in the atmosphere, there is little friction to slow it down and wind speeds increase.

* Humidity is the amount of water vapor in the atmosphere at a given location on Earth’s surface. * Relative humidity is the amount of water vapor in a volume of air relative to the amount of water vapor needed for that volume of air to reach saturation (when the air has reached the maximum amount it can hold).

* Relative humidity is expressed as a percentage. * If a certain volume of air is holding as much water vapor as it possibly can, then its relative humidity is 100% * If that same volume of air is holding half as much water vapor as it can, its relative humidity is 50%.