WeatherInstrumentsAssignment (1)
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LAB 6: WEATHER INSTRUMENTS 100 points
Due at the beginning of lab next week.
LEARNING OUTCOMES
At the end of this lab, you will be able to
1.
Describe atmospheric properties and their influence on weather.
2.
Measure atmospheric processes and calculate weather indexes.
3.
Identify relationships between atmospheric properties.
4.
Discover and download atmospheric.
INTRODUCTION
This lab will introduce you to ways of measuring atmospheric properties. Radiation
Energy, in the form of shortwave radiation, from the Sun is the ultimate driving force of weather. Most shortwave radiation passes through the atmosphere and reaches the surface; however, some is reflected into space (albedo). The reflected shortwave radiation that does make it passed the atmosphere is absorbed and re-emitted as longwave radiation hours later. Radiation is measured with a radiometer. This device measures the radiation received by a sensor pointed in the direction of incoming light. The amount of light energy received is then displayed in numerical form. Temperature Temperature is the average kinetic energy of molecules in a substance such as the atmosphere. There are three temperature scales used worldwide: Fahrenheit (°F), Celsius (°C), and Kelvin (K). Scientists work with Celsius and Kelvin and measure these values with thermometers. Mathematical equations are used to convert between the scales:
°F = (°C * 1.8) + 32
°C = (°F – 32) / 1.8
K = °C + 273.15 °C = K – 273.15
Atmospheric
Moisture
Water vapor in the atmosphere is a function of temperature. As air temperature decreases, the amount of water vapor it can hold decreases. The opposite occurs when it gets hotter. Atmospheric moisture is commonly measured in two ways: relative humidity and dew point. 1
Relative humidity is the ratio of the amount of moisture in the air to the amount of moisture the
air can hold reported as a percent (0 – 100%). It describes how close the atmosphere is to being completely saturated. The higher the value, the closer the air is to total saturation. Dew point is the temperature at which saturation occurs. Therefore, the closer dew point and air temperature are to one another, the higher the relative humidity. Combining relative humidity and air temperature yields a “feels like” temperature known as the heat index. There are many ways to measure atmospheric moisture, but you will use a sling-psychrometer then calculate relative humidity and dew point. The sling-psychrometer contains two thermometers. One of the thermometers contains a wetted sock or sleeve on its bulb. Hence, this thermometer is known as the wet-bulb. The other thermometer is your normal, unmodified
thermometer, and it is known as the dry-bulb. The wet-bulb aids in the measurement of the air’s moisture content by measuring the cooling effect of water evaporating from the sleeve. The more moisture there is in the atmosphere, the less water evaporates from the sleeve, resulting in a relatively higher the wet-bulb temperature than if the humidity were lower.
Barometric Pressure and Wind
Air has mass and weight. The weight of air leads to air pressure and is directly related to temperature. Because the Sun does not heat the surface of the Earth evenly, we see differences in air pressure. These differences in air pressure cause movement of the air (wind), and the larger the pressure differences, the faster the wind blows. Combining air temperature and wind speed yields a “feels like” temperature known as the wind chill index. Air always moves from areas of higher pressure to areas of lower pressure. The common term for describing the difference in pressures is the pressure gradient, which includes both the magnitude of the difference as well as the distance between the measurements. Pressure gradients can describe pressure conditions in three dimensions and is not only measured horizontally. Low pressure air is relatively light (less dense and often warmer) and ascends in the
atmosphere taking any water vapor with it. If this water vapor cools to the dew point, then clouds and precipitation will develop. Air at high pressure is relatively heavy (denser = more air molecules in a given volume) and descends in the atmosphere. This warming dries the air, and normally allows for clear conditions. Therefore, low pressure systems tend to bring cloudy/wet weather, while high-pressure systems tend to bring clear/dry conditions.
Air pressure is measured with a barometer. Wind speed and/or direction are measured with several devices. The first of which is called an anemometer, it only measures the wind speed. The second device is termed a wind vane, and it only measures wind direction. The third device can measure both speed and direction and is termed the aerovane. The aerovane is widely used
today in most weather stations.
2
LAB 9: WEATHER INSTRUMENTS Name: _________Brian Griffith_________
Section: _____________________________
Take measurements, perform the following calculations, and answer the questions [100 pts].
Part I – Weather Measurements
In this part of the lab exercise, you will go outside and take measurements with a psychrometer to measure air moisture. Dip the sock/sleeve located on one of the thermometers into a cup of water. Travel outside, and one person per group gets the privilege of slinging/twirling the psychrometer around with the other keeping time. Sling the psychrometer for one minute and take preliminary temperature readings on the thermometers. Sling the psychrometer for an additional 30 seconds and again take the wet-bulb reading. If there is no change, you may stop and record your final values for both dry- and wet-bulb readings. If the reading is still changing, then continue slinging the psychrometer for 30 seconds until it is steady and record wet and dry
readings when the temperatures have stabilized. [4 pts] Record your preliminary dry-bulb and wet-bulb temperatures below (time = 60 seconds): 1.
Initial Wet-bulb Temperature (°F): ____68_____________
2.
Dry-bulb Temperature (°F): ____________82.4______
[6 pts] Record your second wet-bulb temperatures below after an additional 30 seconds (time = 90 seconds). Record additional measurements only if the temperature changes drastically between your first and second readings
:
3.
Second Wet-bulb Temperature (°F):
________68_________
Additional Wet-bulb T (
if needed
, °F): _______na_____
Additional Wet-bulb T (
if needed
, °F): _________na___
[2 pts] Use the radiometer to make measurements about the amount of radiation coming towards the Earth’s surface from the Sun:
4.
Incoming Energy (direct sun): ___13.5________________
5.
Incoming Energy (shade/covered area): _.5__________________
[2 pts] Use the anemometer to measure the wind speed and direction:
6.
Wind speed (mph): ___________.8______
7.
Wind Direction: _______________south___ 3
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[2 pts] Use the barometer to measure air pressure:
8.
Air pressure (inches of mercury): ______790 mm___________________
Part II – Weather Calculations
Using your weather measurements, determine the relative humidity with Table 1 and the dew point with Table 2. Calculate the final wet-bulb depression, where the wet-bulb depression is found by subtracting the wet-bulb temperature from the dry-bulb temperature (i.e., wet-bulb depression = T
dry
- T
wet
).
9.
[4 pts] Wet-Bulb Depression (°F): __________14.4________
10. [4 pts] Relative Humidity (%) _________________51%_____
11. [4 pts] Dew Point (°F): ______________________62_____
4
Table 1: Use this table to obtain a relative humidity
value. The measurements of air temperature (i.e., the dry-bulb temperature) and the wet-bulb depression set which row and column representing the relative humidity of the air.
5
Table 2: Use this table to obtain a dew point temperature
in degrees Fahrenheit. Use your measurement of air temperature (i.e., the dry-bulb temperature) and the calculated relative humidity to find the approximate dew point temperature.
With values you have measured and calculated, determine the heat index using Table 3, and answer the following questions about heat index. If a heat index does not exist for your data, explain why instead of providing a heat index value.
12. [4 pts] Heat Index (°F): _______________
6
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13. [2 pts] If the relative humidity is 30% and the air temperature is 100°F, what is the heat index in °F?
102
14. [2 pts] If the relative humidity is 60% and the air temperature is 91°F, what is the heat index in °F?
100-105
Table 3: Use this table to find the heat index
. First, determine whether the temperature is below 80°F. A heat index is not calculated for temperatures below 80°F. If the temperature is at or above 80°F, then use the air temperature (i.e., the dry-bulb temperature) and the relative humidity to identify the approximate heat index value in degrees Fahrenheit. With measurements of the temperature and wind speed, we could calculate the wind chill index
using Table 4. Determine the wind chill index, if it exists for your measurements, and the answer
the questions about wind chill index. Otherwise, explain why a wind chill index cannot be calculated for your data. Please use a local weather source to approximate the current wind speeds (e.g., weather app on your phone).
15. [1 pt] Current approximate wind speed (mph): ___6 mph_______________
[1 pt] Source: 16. [4 pts] Wind Chill Index (°F): ______80____________
7
17. [2 pts] If the wind speed is 24 mph and the air temperature is 20°F, what is the wind chill
index in °F?
3
18. [2 pts] If the wind speed is 33 mph and the air temperature is 15°F, what is the wind chill
index in °F?
-6 to -7
8
Table 4: Use this table to calculate the wind chill index
. Wind chill indices are not calculated for temperatures greater than 40°F. If the temperature is at or below 40°F, then use the air temperature (i.e., the dry-bulb temperature) and the wind speed to determine the approximate wind chill index value in degrees Fahrenheit.
9
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Part 3 – Measurement interpretation
Research the current weather data for Fayetteville, AR using the Drake Field weather station:
National Weather Service : Observed Weather for past 3 Days : Fayetteville, Drake Field
(This is weather data for Drake Field in Fayetteville)
19. [20 pts] Compare the current weather data obtained on the Internet for Drake Field to your observations from the UA campus. Are there any differences in temperature (current, maximum, and minimum), dew point, air pressure, wind speed and direction? Why might there be differences? Include these measurements in your answer.
10
Around 2:53 P.M. on October 10", the temperature at Drake Field was 77°F and the dry bulb temperature was 82.4°F and the wet bulb temperature recorded was 68°F. The wind speed that the NWS recorded was 8.06 mph and the wind speed that we found was 6 mph. We found a dew point of 62°F and the NWS had a dew point of 48.9°F. There are differences in our answers because of various factors such as cloud cover, humidity levels, wind speed, and temperature that vary because of different locations. Drake Field is 4.2 miles south of the University of Arkansas campus, so weather conditions can be different there.
[34 pts] Use what you have learned about temperature and moisture to answer the following questions. 20. [5 pts] What time of day should usually have the highest relative humidity?
The mornings around sunrise are generally the highest humidity because of the cooler air temperatures.
21. [2 pts] What time of day is usually the hottest?
Generally the hottest time of the day is between 3-4:30 and will vary with wind and cloud conditions.
22. [2 pts] Would you expect a concrete walkway or a flower garden to result in a higher albedo? Why?
I would expect the walkway to have a higher albedo since it is probably a light solid surface that reflects like very well, since most visible light is reflected by it. Unlike a flower garden that absorbs much more light for photosynthesis, but also just has a lot more colors to absorb lights, instead of the majority of it being deflected like the concrete walkway. So therefore the walkway would have the higher albedo. 23. [5 pts] Describe weather that often occurs when relative humidity is 100%.
11
When humidity reaches 100% the air is full of moisture so it will either be rain, snow, hail, fog, or
dew.
24. [5 pts] Convert 212°F to °C? Show your work.
212-32=180/1.8=100 degrees Celsius
25. [5 pts] Convert 25°C to °F? Show your work.
25*1.8=45+32=77
26. [5 pts] Convert 300K to °C. Show your work.
300-273.15=26.85 Celsius
27. [5 pts] Which of these temperatures is hotter: 100°F, 100°C, or 100K? Why? (Use a common scale to support your answer)
100 degrees Celsius is the hottest temperature. 100 degrees Celsius equals 212 degrees Fahrenheit so it is hotter than 100°F and 100K is like colder than like anything for the most part.
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