WEATHE R (part #2)
Mr. Sammartano Hommocks Middle School- Room S301
Name: ______Period: ______
1 M. Sammartano 2008 Moisture in the Atmosphere (Dew- point) • When the air is holding as much moisture, or water vapor, as it can, it is said to be saturated.
• Hotter air is able to hold much more moisture than colder air. As air warms, for every 10°C increase in temperature, the air can hold twice as much moisture.
• If you take an unsaturated air mass and cool it, it will eventually become saturated. The temperature at which it becomes saturated is known as the dew-point. Measuring Moisture in the Atmosphere
• A sling psychrometer is used to measure the amount of moisture in the air.
• To calculate the dew point, you must also use the “Dew-point Temperatures” ESRT.
• A sling psychrometer is made of two thermometers connected together on a handle that allows them to be swung through the air. One thermometer has a wet piece of cloth over the bulb (known as the wet-bulb), the other is dry (known as the dry-bulb). As you swing the psychrometer around the water on the wet-bulb will evaporate, removing heat energy from the air causing that thermometer to record a lower temperature. The dry-bulb simply records the actual air temperature. The wet-bulb temperature will always be lower than the dry-bulb temperature.
•To find the dew-point, record the dry and wet- bulb temperatures. Find the dry-bulb temperature on the left side of the “Dew-point Temperatures” ESRT, then find the diference between the wet and dry-bulbs, also known as the wet-bulb depression, on the top of the chart. Where these rows meet, you will see the dew-point.
• The drier the air, the further the dew-point will be from the actual temperature.
2 M. Sammartano 2008 • The more moisture in the air, the closer the dew-point will be to the air temperature.
• When the dew-point equals the air temperature, the air is saturated, clouds will form and precipitation is likely.
3 M. Sammartano 2008 Absolute and Relative Humidity •Absolute humidity refers to the measured amount of moisture in the air (i.e. 50 ml)
•Relative humidity refers to how full of moisture the air is.”
•It is a comparison of how much moisture there is in the air, compared to how much it would take for the air to be saturated at that temperature.
•Remember! Warmer air can hold more moisture than cooler air.
•When air is saturated, it is said to have a relative humidity of 100%.
•If the relative humidity is 50%, it means the air is holding half as much moisture as it is capable of at that temperature.
•Generally speaking, as temperature decreases, relative humidity will go up because colder air has less available “space” to hold the moisture.
•Both the amount of moisture and the temperature afect the relative humidity.
•As the temperature of the air drops closer to the dew-point, the relative humidity approaches 100%. Calculating Relative Humidity
•Determining the relative humidity is the same process as determining dew-point, except you must use the relative humidity chart instead of the dew point chart.
•Refer to the “Relative Humidity”
4 M. Sammartano 2008 chart in the ESRTs
5 M. Sammartano 2008 Use the “Dew-point” and “Relative humidity” charts to fill in the following table.
Relative Dry-bulb Wet-bulb Wet-bulb Depression Dew-point Humidity
1 12°C 7°C
2 22°C 20°C
3 18°C 12°C
4 6°C 5°C
5 21°C 1°C 20°C
6 16°C 4°C 66%
7 19°C 19°C
8 17°C 13°C 4°C 63% 10°C
9 86 F 77 F
10 64 F 54 F
11 26°C 24°C
12 16°C 12°C
13 30°C 21°C
14 0°C -2°C
15 25°C 21°C
16 11°C 6°C
17 26°C 15°C
18 8°C 4°C
19 1°C 14°C
20 16°C -1°C
6 M. Sammartano 2008 Use this packet and the ESRTs to answer the following questions.
1. Which weather variable can be determined by using a psychrometer? (1) barometric pressure (2) cloud cover (3) relative humidity (4) wind speed
2. Large oceans moderate the climatic temperatures of surrounding coastal land areas because the temperature of ocean water changes (1) rapidly, due to water’s low specific heat (2) rapidly, due to water’s high specific heat (3) slowly, due to water’s low specific heat (4) slowly, due to water’s high specific heat
3. Which component of Earth’s atmosphere is classified as a greenhouse gas? (1) oxygen (2) helium (3) carbon dioxide (4) hydrogen
4. If the base of a cloud is located at an altitude of 2 kilometers and the top of the cloud is lo- cated at an altitude of 8 kilometers, this cloud is located in the (1) troposphere, only (2) stratosphere, only (3) troposphere and stratosphere (4) stratosphere and mesosphere
5. The diagram below shows a sling psychrometer.
Based on the dry-bulb temperature and the wet-bulb temperature, what is the relative humid- ity? (1) 66% (2) 51% (3) 58% (4) 12%
6. Which process transfers energy pri-
7 M. Sammartano 2008 marily by electromagnetic waves? (1) radiation (2) conduction (3) evaporation (4) convection
7. Which two gases have been added to Earth’s atmosphere in large amounts and are be- lieved to have increased global warming by absorbing infrared radiation? (1) neon and argon (2) chlorine and nitrogen (3) hydrogen and helium (4) methane and carbon dioxide
8. Which type of land surface would probably reflect the most incoming solar radiation? (1) light colored and smooth (2) light colored and rough (3) dark colored and smooth (4) dark colored and rough
9. The tropopause is approximately how far above sea level? (1) 12 mi (2) 60 mi (3) 12 km (4) 60 km
10. Which form of electromagnetic radiation has a wavelength of 1.0 x 10–3 centimeter? (1) ultraviolet (2) radio waves (3) infrared (4) microwaves
8 M. Sammartano 2008 What Causes Air Pressure? •Air Pressure is caused by the weight of the air pushing down on the Earth’s surface.
•Air pressure decreases as you go higher up in the atmosphere.
Measuring Air Pressure •Air pressure, also called barometric pressure, is measured with an instrument called a barometer.
•The weight of the air pushes down on the liquid causing it to rise in the column. The higher the air pressure, the higher the column will rise.
•High air pressure generally means good weather (dry/clear) and low pressure generally means bad weather (wet/cloudy).
•Pressure is measured in either millibars or inches of mercury. Conversions between the two can be made using the “Pressure” diagram on the ESRTs.
Factors that Afect Air Pressure •Altitude- The higher you are above the surface, the lower the air pressure
•Temperature- Cool air is dense causing air pressure to be higher, warm air is not dense, causing air pressure to be lower.
•Humidity- Water vapor is lighter than air; so the more moisture in the air, the lower the pressure, the drier the air, the higher the air pressure.
9 M. Sammartano 2008 Use the “Pressure” chart to answer the following questions.
Millibars Inches
1040.0
973.0
1013.2
Convert the following from 1000.0 millibars to inches.
1013.0
969.0
1005.0
Inches Millibars
30.50
30.00
29.40
Convert the following from 28.70 inches to millibars.
29.30
29.90
30.20
10 M. Sammartano 2008 What Causes the Wind? • Because the Earth is unevenly heated, there are significant diferences in air pressure in diferent locations.
• Cool, dry air is more dense than warm, moist air so cooler places generally have higher pressure air and warmer places generally have lower pressure air.
• To try and even out air pressure on Earth, winds transport air from areas of high pressure to areas of low pressure. Winds always blow from high to low pressure.
• Winds will blow fastest between areas that have a large diference in air pressure, or a steep pressure gradient. These areas can be located on maps by examining isobars. Isobars are isolines that connect points of equal air pressure. They are read the same way contour lines are read.
Wind direction will be impacted by several • Steep pressure gradi- factors including the rotation of the Earth. This ent = high wind speed is called the Coriolis Efect.
• Winds curve to the right in the Northern hemisphere, and to the left in the Southern hemisphere due to the rotation of the Earth. Winds are always curved relative to their direction of travel.
• The efects of the Coriolis Efect can be seen on the map of global wind patterns on page 14 of the ESRTs.
• Remember, one of the best pieces of evidence we have that supports the idea that the Earth is spinning is the observation of curved winds, or the Coriolis Efect.
• Wind speed is measured with an anemometer and wind direction is measured with a wind vane.
11 M. Sammartano 2008 Global Winds
90°N
60°N
30°N
equator
30°S
60°S
90°S
12 M. Sammartano 2008 Land and Sea Breezes • Small scale breezes form due to diferences in heating of land and water.
• During the day, the land heats faster than the sea. Warm air over the land rises due to it’s lower density. It then cools and sinks over the water. Along the surface the air rushes from the sea to the land to replace the rising air over the warmer land. This surface breeze coming from the sea is called a sea breeze.
• Over night, the land cools quickly while the water remains warm. Warm air over the water now rises due to it’s lower density. It then cools and sinks over the land. Along the surface the air rushes from the land to the sea to replace the rising air over the warmer water. This surface breeze coming from the land is called a land breeze.
• Land warms and cools much quicker than water because it has a lower specific heat. Remember, water takes a long to time heat up and a long time to cool down.
13 M. Sammartano 2008 Sea Breeze
Land Breeze
14 M. Sammartano 2008 Winds and Air Pressure • Winds will always flow from areas of high pressure to areas of low pressure.
• In the northern hemisphere, winds are deflected to the right because of the Coriolis efect. In the southern hemisphere, winds are deflected to the left
• As a result, winds blow out from high pressure areas and in a clockwise motion. Winds blow towards low pressure and in a counter-clockwise motion.
HIGH LOW
From above... H L
From the side... H L
Characteris- tics
15 M. Sammartano 2008 The Jet Stream • A “river” of wind in the upper atmosphere that drives weather systems.
• Jet streams do not follow the same patters as surface winds. They generally flow from west to east in the mid-latitudes
Ocean Currents • Ocean currents are large flows of water within the ocean caused mainly by surface winds.
• Look at the Surface Ocean Currents map on page 4 of the ESRTs.
16 M. Sammartano 2008 Air Masses • A large body of air that has relatively consistent temperature and pressure conditions.
• There are several types of air masses described using the following terms:
•Continental: dry, formed over land
•Maritime: moist, formed over water
•Arctic, Polar: Cold, formed far to the north or south of the equator
•Tropical: Hot, formed near the equator
•cP Continental Polar
•cA Continental Arctic
•cT Continental Tropical
•mP Maritime Polar
•mT Maritime Tropical
cA
17 M. Sammartano 2008 Clouds • A cloud is a large object made up of billions a tiny droplets of water that are too small to fall through the atmosphere.
•Clouds form when air rises, expands, cools to it’s dew point where all water vapor condenses back into these liquid water droplets.
•For clouds to form, there must be condensation nuclei, or small dust particles for the water vapor to condense on to.
•Air rises because of:
•Diferences in density (convection)
•Mountains (orographic lifting)
•Fronts
•Air cools as it expands because there is less friction between the molecules as they slow down and move farther from each
other. Precipitation
• When drops of water in a cloud crash together, they may combine and grow large enough to fall to the ground under the pull of gravity. When this mositru falls to the Earth, we call it precipitation.
• Types of precipitation include rain, snow, sleet, and hail
18 M. Sammartano 2008 19 M. Sammartano 2008 Fronts
• Fronts are the leading edges of air masses. They are named for the temperature changes that they bring. For example, a cold front passing over you will bring cold air.
• There are four types of fronts:
• Warm fronts- the boundary between a mass of warm air and the colder mass it is replacing.
•Cold fronts- the boundary between a mass of cold air and the warmer mass it is replacing.
•Stationary fronts- the boundary between two air masses that are not moving.
•Occulded fronts- A boundary where warm air is forced to rise between two approaching cold air masses.
•All fronts are labeled with specific symbols on weather maps. These symbols can be found on the ESRTs.
•Fronts are important because they signify changes in the weather.
•Fronts are often associated with precipitation, winds, and temperature changes.
20 M. Sammartano 2008 Type of Symbol Side-view What happens... Front
Warm
Cold
Stationary
Occluded
21 M. Sammartano 2008 Review of Weather Fronts • When large masses of warm air and cold air meet, they do not mix. Instead, they form a front, usually hundreds of miles long. When a front passes, the weather changes. The chart describes the four main types of fronts and the weather changes each type brings.
22 M. Sammartano 2008 Orographic Lifting
• Mountains act as barriers to air, forcing it to rise.
• When air rises, it expands and cools. If it reaches it’s dew point, clouds and precipitation will form.
• You can always tell where the wind is coming from by looking at the vegetation on a mountain. The side facing the winds will be wet and covered with plants (this is called the windward side). The other side will be dry and desolate (this is called the leeward side).
• This is an example of an adiabatic temperature change, or a change in temperature without adding or taking energy away. Another example would be releasing the air from a tire. The air is rapidly expanding and cooling, though no energy was taken away.
23 M. Sammartano 2008 The Mid-Latitude Cyclone
• A mid-latitude cyclone is a large storm that forms normally in the middle-latitude locations (like the United States).
• The process of formation includes four steps:
1. A wave on the front will form as an upper level disturbance embedded in the jet stream moves over the front. The front develops a "kink" where the wave is developing. Precipitation will begin to develop with the heaviest occurrence along the front
2. As the wave intensifies, both cold and warm fronts become better organized.
3. The wave becomes a mature low pressure system, while the cold front, moving faster than the warm front, "catches up" with the warm front. As the cold front overtakes the warm front, an occluded front forms.
4. As the cold front continues advancing on the warm front, the occlusion increases and eventually cuts of the supply of warm moist air, causing the low pressure system to gradually dissipate.
24 M. Sammartano 2008 The Mid-Latitude Cyclone
25 M. Sammartano 2008 Hurricanes
• A hurricane is a tropical low Typical Hurricane Paths Affecting the United pressure system that forms from low pressure coming of the coast of Africa. As it travels over the warm waters of the ocean, it gains strength until afecting the Caribbean and Gulf of Mexico.
• Hurricanes die when the move over land or over cool water and lose their source of energy.
Tornadoes
• A tornado is a small cyclone of high winds spawned by a thunderstorm.
• They are common in “Tornado Alley” in the Spring and early Summer.
Emergency Preparations
• Listen to radio or TV for storm announcements
• Have an emergency plan
• Keep supplies like food and water available
• Stay inside away from windows and doors, preferably in the basement or a closet or bathroom
• Be careful of downed power lines and damaged trees.
26 M. Sammartano 2008 Station Models
• A station model is a small symbol used to summarize weather variable for a particular location. The details of a station model can be seen on the ESRTs.
• Notice that barometric pressure values are simplified by dropping the first 9 or 10 and dropping the decimal point.
• For example: •An air pressure of 998.4 mb would be simplified as 984 •An air pressure of 1013.5 would be simplified as 135
• To convert back from the simplified version, follow these rules: •If the simplified number is more than 500, add a 9 before it and a decimal point. •For example, 743 would become 974.3 mb •If the simplified number is less than 500, add a 10 before it and a decimal point. •For example 328 would become 1032.8 mb
•Also, add a decimal when calculating barometric trend. •For example +19/ would mean that pressure has increased by 1.9 mb over the last 3 hours.
27 M. Sammartano 2008 Air Temperature Air Temperature
Dew Point Dew Point
Wind Speed Wind Speed
Wind Direction Wind Direction
Precipitation Precipitation
Cloud Cover Cloud Cover
Pressure Pressure
Air Temperature 93 Air Temperature 42
Dew Point 77 Dew Point 41
Wind Speed 5 Wind Speed 35
Wind Direction East Wind Direction Northwest
Precipitation None Precipitation Rain
Cloud Cover Clear Cloud Cover Overcast
Pressure 1014.6 mb Pressure 985.6 mb
28 M. Sammartano 2008 Climate
• The average weather conditions (temperature and moisture) for a larger region over a long period of time.
• Factors afecting climate include:
• Latitude- The higher your latitude, the colder your climate.
• Altitude- The higher your altitude, the colder your climate.
• Mountain ranges- On the windward side of a mountain, your climate will be wet, on the leeward side of a mountain, your climate will be dry.
• Oceans/Large Bodies of Water- The closer you are to water, the less extreme your climate (warmer winters and cooler summers).
• Ocean Currents- Locations near warm water currents will have warmer climates, locations near cold water currents will have colder climates.
• Planetary Wind Belts- On-shore winds will cause wet climates, of-shore winds will cause dry climates (monsoon winds).
29 M. Sammartano 2008 30 M. Sammartano 2008 Key Concepts
✓As temperature increases, air pressure decreases.
✓As humidity (moisture content of the air) increases, air pressure decreases.
✓As altitude/elevation increases, air pressure decreases.
✓High Pressure = sinking air, dry conditions, little to no clouds.
✓Low Pressure = rising air, moist conditions, increase in clouds
✓Wind occurs due to diferences in air pressure.
✓Wind always moves from regions of high pressure to regions of low pressure perpendicular to the isobars. Isobars close together = steep pressure gradient = high wind speeds.
✓Wind is named by the direction it is coming from.
✓Surface High Pressure (anticyclones) = Clockwise and divergent winds.
✓Surface Low Pressure (cyclones) = Counterclockwise and convergent winds.
✓The closer the dew point temperature gets to the air temperature the greater the chance for precipitation.
✓Dew point = Air temp ➙ brings 100% humidity!!
✓In the middle latitudes (U.S.), weather moves from the west to the east (northeast). Prevailing Westerlies.
✓Precipitation occurs when: warm, moist air rises, expands, cools, reaches the dew point temp., condensation occurs (on condensation nuclei), the droplets collect in masses (cloud formation), when the drops are large enough = precipitation.
✓Air cools adiabatically as it rises due to expansion from the higher atmospheric pressure at low elevations to the lower atmospheric pressures at higher elevations.
✓Air warms adiabatically as it sinks due to compression by the heavier atmospheric pressure at lower elevations.
✓Air masses are characterized by their TEMPERATURE and MOISTURE characteristics.
✓The leading edge of the air mass is called the FRONT.
✓Mountains force air up the windward ( cool/moist) side and down the leeward (warm/dry) side (the Orographic Efect).
✓Large bodies of water moderate coastal climates, (warmer winters, cooler summers). 31 M. Sammartano 2008