# Meteorology Part 2: Weather Variables

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Meteorology Part 2: Weather Variables
Earth Science Golodolinski/Black 2009

Part II: Weather Variables
Temperature Air Pressure Relative Humidity

Weather Variables 1. Temperatures Measured in °F Fahrenheit °C Celsius
The measure of the average kinetic energy How fast the molecules move Instrument used to measure temperature: Thermometer ESRT: Temperature conversion chart on p. 13 Measured in °F Fahrenheit °C Celsius °K Kelvin

1. Temperatures Shown on a weather map with:
Isotherms- Lines that connect places of equal temperature

ESRT: Temperature conversion chart on p. 13 & Chart Blank p. 183

ESRT: Temperature Conversion Chart on p. 13 Chart Answers p. 183

ESRT: Temperature Conversion Chart on p. 13 Temperature Chart Blank p

ESRT: Temperature Conversion Chart on p. 13 Temperature Chart Answers p. 183

Weather Variables 2. Air Pressure The weight of Earth’s Atmosphere
Changes depending on the temperature Instrument used to measure pressure: Barometer Measured in inches and milibars

2. Air Pressure Shown on a weather map with:
Isobars- Lines that connect places of equal barometric pressures

2. Air Pressure Mercury barometer
As the air pressure pushes on the surface of the mercury in the dish, the mercury travels up the tube. As pressure increases, the mercury rises in the tube. Cool air sinks- causes higher pressure As the pressure decreases, the mercury sinks out of the tube. Warm air rises- causes lower pressure

ESRT: Pressure Conversion Chart p. 13

ESRT: Pressure Conversion Chart p. 13 Blank Chart p. 184

ESRT: Pressure Conversion Chart p. 13 Answer Chart p. 184

2. Air Pressure State the relationship between altitude and air pressure. As the altitude increases, the pressure decreases Draw the relationship on the graph.

Weather Variables 3. Relative Humidity
A ratio between the amount of moisture is in the atmosphere and how much moisture the atmosphere can hold Measured in % When the air is holding as much water vapor as it can, the air is saturated. When saturated, warm air contains more water vapor than cold saturated air. When the air is saturated, the relative humidity is 100% To summarize, when the water-vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity.

3. Relative Humidity Temperature & Relative Humidity
The warmer the temperature is, the more moisture it can hold State the relationship between temperature and relative humidity: As the temperature increases, relative humidity decreases Draw the relationship on the graph.

3. Relative Humidity- Insturements

3. Relative Humidity Dew Point Temperature
The temperature in which the air is saturated 100% relative humidity

Determining Relative Humidity and Dew Point Temperatures
Dry bulb Air temperature Wet bulb Temperature an air parcel cooled by evaporation of water (wet cloth) When given the wet bulb and dry bulb temperatures, you can determine the dew point temperature and relative by follow directions provided and using ESRT p. 12

ESRT: Dew Point Temp. p. 12

ESRT: Relative Humidity p. 12

Example 1 p. 186

Example 2 p. 186 p. 187 chart and #1-5

Practice Dew Point & Relative Humidity p. 187

Practice Dew Point & Relative Humidity p. 187 Answers

Practice Dew Point & Relative Humidity p. 187 #1-5

Condensation Gas to liquid
Change of phase from water vapor (gas) to liquid vapor (water) Examples: Water on cold glass of water, water on mirror after a shower, dew on grass, fog, clouds Evaporation Liquid to gas

3 Things Needed for Condensation to Occur
Water vapor must be present Air must be separated (relative humidity 100%) Condensation nuclei (ex. dust particles)

Density of Air Warm air rises because it is less dense
Cold air sinks because it is more dense

Formation of Clouds Warm moist air rises
Air expands and cools due to the dew point Air becomes saturated Water droplets form on dust particles Clouds consist of water droplets and ice crystals

Cloud Classification

Adiabatic Cooling The cooling of a parcel of air as it rises through the atmosphere Dry adiabatic lapse rate rate of cooling or heating that applies only to unsaturated air. dry air cools faster Wet adiabatic lapse rate rate of adiabatic temperature change in saturated air. moist air cools slower

Precipitation Cloud particles (any form of water) too heavy to remain suspended in the air fall to Earth from a cloud Examples: rain, hail, sleet, snow, freezing rain What does precipitation do for the environment? Cleans the air ESRT p. 13 Present Weather

Forms of Precipitation
The type of precipitation that reaches Earth’s surface depends on the temperature profile in the lower few kilometers of the atmosphere. Rain & Snow In meteorology, the term rain means drops of water that fall from a cloud and have a diameter of at least 0.5 mm. At very low temperatures (when the moisture content of air is low) light fluffy snow made up of individual six-sided ice crystals forms. Sleet is the fall of clear-to-translucent ice. Hail is produced in cumulonimbus clouds.

ESRT p. 13 Present Weather

Wind The horizontal movement of air
Caused by the uneven heating of Earth’s surface Differences in air temperature cause differences in air pressure The greater the difference in air pressure, the faster the wind

Wind Named by the direction in which they come from Isobars
Ex. North wind comes from the North Isobars Connect places of equal barometric pressure on a weather map

Wind Instruments Anemometer Wind vane Measures wind speed
Determines wind direction

Sea Breeze Water heats up slower than land:
High specific heat Cooler temperatures Air sinks *HIGH pressure* Land heats up faster than water: Low specific heat Warmer temperatures Air rises *LOW pressure*

Land Breeze Water cools down slower than land (stays warmer)
High specific heat Warmer temperatures at night Air rises Land cools down faster than water Low specific heat Cooler temperatures at night Air sinks

Sea and Land Breezes

Coriolis Effect The deflection of winds and ocean currents caused by the rotation of Earth Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

Weather Factors Associated with Different Pressure Areas
High Pressure Cool/ cold air Air sinks/ goes down Air moves outward Clockwise No clouds No precipitation Low Pressure Warm air Air rises Air moves inward Counter clockwise Clouds Precipitation likely

ESRT: Planetary Winds p. 14

Planetary Winds p. 191 Weather Changes- adobe

Weather Changes p. 191

Weather Changes

Air Masses Large region of the atmosphere with uniform temperature and humidity ESRT p. 13: Air Masses

Air Masses Table

Air Masses Map

Fronts The boundary between 2 air masses ESRT p. 13 Front Symbols

Cold Front Cold air pushes the warm, moist air upward
Cold air is located behind the front The greater the differences in temperatures, the more likely there will be a major storm Usually pass quickly Brings colder but clear weather conditions

Warm Front Warm air gently rolls over the colder air
Warm air is located behind the front Conditions are usually cloudy and rainy for several hours Usually pass slowly Brings warmer but rainy weather conditions

Occluded Front Occurs when a cold air mass overtakes a warm mass and overtakes another cold air mass Precipitation is possible but not definite Very slight temperature change

Stationary Front Notice no arrows to show direction in the weather map symbols Stationary means the front is not moving Final direction of the movement is difficult to predict Winds are blowing in opposite directions on each side of the front Clouds can last for days

Fronts are usually associated with…
Clouds Precipitation Change in temperature Change in wind direction p.195 Station Models- Adobe

Station Models On a station model, barometric pressure is ALWAYS written in a three-digit format Converting from millibars: Drop the 9 or 10 in the front of the number and loose the decimal point Millibars Station Model mb 093 984.2 mb mb

Station Models Station Model Millibars 146 1014.6 mb 457 986
Converting from the station model format to milibars First: If the first number on the station model is 0-4, place a 10 in front of the number If the first number on the station model is 5-9, place a 9 in front of the number Second: Place a decimal point between the last 2 numbers Station Model Millibars 146 mb 457 986 p. 195

ESRT: Weather Map Symbols

Weather Stations

Draw a weather station using the following information:

Need to know: Dew Point & Air Temperature
The closer the air temperature is to the dew point temperature, the greater the chance for precipitation.

Determining Weather Station Values
6 stations on p. 197; Weather Map practice p #1-31; More questions p #1-22