WeatherInstrumentsAssignment

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University of Arkansas *

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MISC

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Geography

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Dec 6, 2023

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docx

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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: _____________________________ 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): _________________ 2. Dry-bulb Temperature (°F): __________________ [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): _________________ Additional Wet-bulb T ( if needed , °F): ____________ Additional Wet-bulb T ( if needed , °F): ____________ [4 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): ___________________ 5. Incoming Energy (shade/covered area): ___________________ 6. What probably has a higher albedo (reflects more energy), the grass or the sidewalk?: __________________. 3
[2 pts] Use the anemometer to measure the wind speed and direction: 7. Wind speed (mph): _________________ 8. Wind Direction: __________________ [2 pts] Use the barometer to measure air pressure: 9. Air pressure (inches of mercury): _________________________ 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 ). 10. [4 pts] Wet-Bulb Depression (°F): __________________ 11. [4 pts] Relative Humidity (%) ______________________ 12. [4 pts] Dew Point (°F): ___________________________ 4
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