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 BASIC METEOROLOGY EXPERIMENTS

METEOROLOGIST JEFF HABY

The following experiments are meant to be low cost and relatively easy to do but have a high meteorology principle value.

EXPERIMENT #1: Temperature and Heat Transfer

Supplies: mercury glass thermometer, glass cup, ice, water

Process: Record the air temperature of the room. Fill a glass half way with hot water. Place the thermometer in the glass of water and wait 5 minutes. After the 5 minutes, Each 2 minutes thereafter record the temperature of the water. Continue recording the temperature until the water is the same temperature as the air in the room. Next, pour ice cubes into the water. Record the temperature each 2 minutes until the temperature of the ice-water mixture stays the same.

Scientific principles: 1. Heat travels from warmer toward colder objects, 2. The freezing-thawing point of water is 32 F (0 C), 3. It takes time for a system to come into thermal equilibrium. It takes time for the thermometer to adjust to a new temperature. It takes time for heat transfer between neighboring objects to produce the same temperature of those objects, 4. The temperature of the water remains constant when latent heat absorption of melting occurs (as the ice melts the temperature stays at 32 F).

EXPERIMENT #2: Evaporation Rate

Supplies: White hand towel, clothes pins

Process: Determine a quantity of water that will wet a hand towel without any water dripping away from it. Record the temperature, relative humidity and wind of outside air. Label wind as light (5 mph or less), moderate ( 6 to 14 mph) or strong (greater than 14 mph). Wet the hand towel with a specific quantity of water and hang it outside with clothes pins in the shade. Always use the same amount of water on the towel and use the same towel on every trial. Check the towel every 5 minutes until it is completely dry. Determine relationships between drying time and the temperature, relative humidity and wind speed outside. It will take many trials to determine these relationships.

Scientific principles: The following general relationships should be discovered:

a. At a similar temperature and relative humidity, drying time should be less as wind speed increases. A stronger wind removes water vapor molecules away from the towel at a higher rate. This keeps the vapor gradient between the towel and the air high and thus promotes a faster evaporation rate as compared to lighter wind.

b. At a similar temperature and wind speed, drying time should be less as the relative humidity decreases. When the relative humidity is 100% then the towel will not be able to dry since the air is already saturated with water vapor. As the relative humidity decreases, the vapor gradient between the saturated towel and air increases and thus evaporation increases.

c. At a similar relative humidity and wind speed, drying time should be less as the temperature increases. Warmer air can evaporate more moisture into it than cooler air can. Thus, when the relative humidity and wind speed is the same, warmer air will be able to evaporate moisture from the towel at a faster rate.

EXPERIMENT #3: Supercooled Water

Supplies: Bowl, salt, ice, small plastic cup, thermometer

Process: Fill a bowl half way with water. Dissolve as much salt as possible into the water. Next, add ice and wait a few minutes. Measure the temperature of the ice/salt/water mixture. The temperature should be below 32 F. Place a small amount of water into a plastic cup. Try to use as pure of water as possible in the plastic cup and make sure the plastic cup in completely clean. Float the plastic cup with the water in the bowl of ice/salt/water making sure not to touch the experiment once the plastic cup is placed in the salty ice water. Wait about 10 minutes. The water in the plastic cup will come into thermal equilibrium with the ice/salt/water and thus the pure water will be supercooled. Next, drop a few grains of dust or other small matter into the pure supercooled water. You should notice the water immediately turn to all or mostly ice.

Scientific principles: 1. Water will not freeze until it has a condensation nuclei to freeze on. The plastic is not a good condensation nuclei but the small particles of matter dropped into the supercooled water will be. Typically, liquid cloud drops in the troposphere that have temperatures between 0 and -10 C will be supercooled. 2. Salt water has a lower freezing point than pure water. 3. As the supercooled water turns to ice, the latent heat release will warm the water back to 32 F (0 C).

EXPERIMENT #4: Helium Balloon Experiment

Supplies: 2 Helium balloons, freezer

Process: Get two Helium balloons that are the same size. Place one in the freezer for 20 minutes and keep the other at room temperature. Take the balloon out of the freezer and compare it to the size of the one at room temperature. Next and quickly, take both balloons outside and release them and see which one rises at the quickest rate.

Scientific principles: 1. Colder air is more dense than warmer air. The Helium balloon in the freezer should contract since the air inside the balloon will become more dense as it cools. 2. The rate a balloon rises will be a function of the density difference between the air in the balloon and the air outside. The balloon that was placed in the freezer will not rise as quickly as the balloon at room temperature. The buoyancy of the balloon placed in the freezer will be reduced since the air is made more dense by cooling it. 3. Helium is a lighter gas than the air outside, thus a Helium balloon has positive buoyancy and will rise as a result. As the Helium is cooled, the rate it rises will be reduced.

EXPERIMENT #5: Finding Dewpoint

Supplies: Cup, ice-water, warm-water, any type of syringe, mercury in glass thermometer

Note: For this experiment to work best the dewpoint needs to be well above freezing. If the dewpoint is below freezing, salt water or a liquid that stays unfrozen below the freezing point of water would need to be used in place of the ice-water and cold water would be used to start instead of warm-water. If the dewpoint is below freezing, frost instead of condensation will occur on the cup when doing the experiment.

Process: Take a metal, hard plastic or glass cup (metal works best) and fill it up a third of the way with warm water that is around 85 F. Place the thermometer into the warm water. Have another cup with you that is filled with ice-water. Gradually place small amounts cold water into the warm water with the syringe. Place enough cold water to drop the temperature of the water a degree or 2 each time some cold water is added. Ice cubes may need to be added if the dewpoint is near the freezing point. Do this until condensation starts to form on the outside of the cup. When condensation on the outside of the cup starts to develop then the dewpoint temperature has been reached.

Scientific principles: 1. Dewpoint is the temperature that air needs to be cooled to in order for condensation to occur. You have probably noticed that on warm/humid days that lots of condensation will develop of the outside of a cup that has an icy cold beverage in it. If the cup temperature is below the dewpoint temperature, moisture will condense out of the air since the maximum amount of moisture that can be in the air decreases as temperature decreases. 2. Dewpoint gives a meteorologist as assessment of the amount of moisture in the air. As dewpoint increases, the amount of moisture in the air increases.

EXPERIMENT #6: Pressure Change and Weather

Supplies: barometer (or use website)

Note: Experiment works best in the mid-latitudes at a location that was weather variability due to mid-latitude cyclones and fronts. Pressure value will be given in millibars or inches of mercury. The use of either will suffice.

Process: Every 6 hours take note of the barometric pressure or sea level barometric pressure and the magnitude that the pressure rose or fell over the last 6 hours. Do this from several days up to as long as needed. Take note of the cloud and precipitation conditions at each observation. Note if over the last 6 hours there was a trend toward more fair weather or more cloudy/precipitation weather. Also, look at a current weather map to see positions of high pressure systems, low pressure systems and fronts in relation to where you are located. Develop a descriptive relationship between pressure change and the expected weather.

NWS website for barometric pressure can be found here. Click on a state, then click hourly report or click the city.

Surface map can be found here.

Scientific principles: 1. As a front or low pressure system approaches the area, the barometric pressure will tend to decrease. This is because rising air lowers the surface pressure. As a front or low pressure system moves away from the area the barometric pressure will tend to increase. This is because sinking air raises the surface pressure. As a high pressure system moves into the area the pressure will tend to increase.

EXPERIMENT #7: Albedo and Temperature

Supplies: Large piece of white construction paper and a large piece of black construction paper, 2 thermometers

Process: On a sunny day with light wind, place a piece of white and black construction paper on the ground a few feet away from each other in direct sunlight. Place a thermometer on each piece of construction paper and position the thermometers in the same manner on both. After 20 minutes, read the temperature of each thermometer. Best results will be on a day with a high sun angle (summer) and light winds.

Scientific principles: 1. A substance with a high albedo will reflect a significant portion of incoming solar radiation. Since less radiation absorbs into the object, the object tends to not warm up as much. A substance with a low albedo will absorb a significant portion of incoming solar radiation. Since more radiation absorbs into the object, the object tends to be warmer. The white piece of construction paper has a high albedo while the black piece has a low albedo. Thus, the black piece of construction paper should be warmer than the white piece. 2. Land cover on the earth' surface will influence the surface air temperature since different land covers have different albedoes. 3. An object is black to the human eye when a lack of reflection occurs off an object; An object is white to the human eye when all colors are reflected off an object. All colors together make up white light; When a color of blue is seen, it means blue light is reflected while the other colors are not.

EXPERIMENT #8: Non-Buoyant Helium Balloon

Supplies: Helium, Balloon

Process: It will take several trials to perfect the method. First, place some Helium into a balloon. Next, fill the rest of the balloon up with your breath. With the right combination of Helium and regular air within the balloon, the balloon will neither rise or fall when you let it go. The balloon will appear to defy gravity. Make sure there are no air current such as air conditioning to disrupt the experiment.

Scientific principles: 1. A balloon with only regular air in it will fall to the surface since the membrane of the balloon makes it heavier than the surrounding air. The higher pressure of the air inside the balloon also gives it a higher density. A balloon with only Helium will rise since the Helium overcomes the weight of the balloon membrane and because Helium is much lighter than regular air. The key to the experiment is to have the right amount of Helium in the balloon to balance the density of the air outside the balloon. The Helium produces an updraft directed buoyancy force while the balloon membrane produces a downward directed buoyancy force. Balloon will have neutral buoyancy when: density of air inside balloon + density of balloon membrane = density of air surrounding the balloon.

A Helium balloon will gradually lose Helium over time. As the balloon gradually loses buoyancy, there will be a time when it will be neutrally buoyant. I noticed one such Helium balloon at Walmart that was suspended in midair about 12 feet off the ground and drifting very slowly horizontally.

EXPERIMENT #9: SNOW TO LIQUID RATIO

Supplies: Long cylinder can with water proof bottom, ruler

Process: After a snowfall pick a place of snow on the ground that represents the average snow depth of the event. Gently place the can upside down and push it down over the snow until it reaches the surface. Cap the bottom of the can with a method you see fit. Place the can upright not letting any snow escape. The accumulation of snow in the can should be similar to that on the ground. Measure the snow depth of the snow on the ground very close to where the sample was taken in the can. Next, take the can inside and let the snow melt. After the snow melts then measure the depth of the liquid water. Next, develop the ratio. For example, if it snows 7 inches and 0.5 inches of liquid water results after melting, then the snow to liquid ratio will be 14:1 (14 inches of snow for every inch of liquid water).

Do this same process for several snow events. Examine the nearest sounding to your location closest to the time of the snow event: http://weather.unisys.com/upper_air/skew/

Relate the temperature profile of the lower troposphere to the snow to liquid ratio that occurs in each event.

Scientific Principles: 1. Snow tends to be wetter and more dense when the temperature profile in the lower troposphere (surface to 700 millibars) is at or below freezing BUT near freezing. Ratios in this case will be 10:1, 9:1 or less. 2. Snow tends to be drier and less dense when the temperature profile is well below freezing in the lower troposphere. Ratio is this case will be 11:1, 12:1 or greater and can even be as high as 40:1 in extreme cases. 3. The average ratio is generally 10:1 for all events across the U.S.

EXPERIMENT #10: Making Thunder

Supplies: Balloon

Process: Blow up a balloon to close to the maximum holding capacity of air. Place balloon on the floor. Step on the balloon with your shoe. Feel the thunder!

Scientific Principles: 1. The noise is caused by a rapid expansion of air. The air pressure inside the balloon is higher than the air pressure outside the balloon. When the membrane of the balloon breaks, air rushes through the breaking membrane. The friction of the air expanding through the membrane gives off noise. 2. When lightning occurs it warms the air along the current of electricity by thousands of degrees in a very small amount of time. The air then rapidly cools. This rapid expansion and contraction of the air produces violent friction between air molecules and thus the noise is produced.