LabWorksheet04_ExploringWeatherData-1 (4)

Name: ________Nicole Brunel ___________ Lab 4: Exploring Weather Data GEOG 5, Instructor: Joy Fritschle This lab has 3 parts, each of which are designed to enhance your understanding of weather data. In part 1, you will calculate Relative Humidity and Dew Point Temperature; in part 2, you will interpret and predict weather maps; and in part 3, you will explore the National Weather Service web mapping service. Part 1: Relative Humidity and Dew Point Temperature When we discuss the “humidity of the air,” we are typically talking about a calculated value referred to as relative humidity. There are two main variables that are considered when calculating relative humidity. These include specific humidity and the maximum water vapor of the air. Specific humidity refers to the actual, measurable amount of water vapor in the air. It is the amount of water (in the form of a gas) that would be found if we were able to isolate each of the different types of gasses in the air. The value is usually reported in grams of water vapor per kilogram of air (g H 2 O/kg air). The maximum water vapor of the air parcel must also be considered. Think of an air parcel as a small box of the atmosphere that is distinct from the atmosphere surrounding it in terms of temperature and humidity. How much water can this air parcel hold? The ability of an air parcel to hold water vapor is a function of the temperature of the air parcel. Warmer air has a greater capacity for holding water vapor, while colder air has a lower capacity. Similar to specific humidity, the maximum water vapor is reported in grams of water vapor per kilogram of air (g H 2 O/kg air). The table below shows the max water vapor (g H 2 0/kg air) that is possible for air parcels at different temperatures (°C): Temperature °C (°F) Max. Water Vapor g H 2 0/kg air -10°C (14°F) 2 0°C (32°F) 3.5 5°C (41°F) 5 10°C (50°F) 7 15°C (59°F) 10 20°C (68°F) 14 25°C (77°F) 20 30°C (86°F) 26.5 35°C (95°F) 35 40°C (104°F) 47 The more commonly used relative humidity (RH) is simply the ratio (expressed as a percentage) of the amount of water in an air parcel (the specific humidity), compared to the amount of water an air parcel can hold (the maximum water vapor). The equation used to calculate the relative humidity is as follows:

Relative Humidity = (Specific Humidity / Maximum Water Vapor) X 100 Use the table and formula above to answer the following questions. 1. Just before sunrise, the temperature is 15 ° C (59°F) with a specific humidity of 8.5 g H 2 O/kg air. What is the relative humidity? (0.5 pts) Temperature: 15°C (59°F), Specific Humidity: 8.5 g H2O/kg air Relative Humidity = (8.5 g/kg / 10 g/kg) x 100 Relative Humidity = 85% 2. By 10 am, the temperature has risen to 25 ° C (77°F). Assume that the specific humidity remains at 8.5 g H 2 O/kg air. What is the relative humidity? (0.5 pts) Temperature: 25°C (77°F), Specific Humidity: 8.5 g H2O/kg air Relative Humidity = (8.5 g/kg / 20 g/kg) x 100 Relative Humidity = 42.5% 3. When the heat of the day strikes at 2 p.m., the temperature has risen to 35 ° C (95°F). Assume that the specific humidity remains at 8.5 g H 2 O/kg air. What is the relative humidity? (0.5 pts) Temperature: 35°C (95°F), Specific Humidity: 8.5 g H2O/kg air Relative Humidity = (8.5 g/kg / 35 g/kg) x 100 Relative Humidity = 24.29% (rounded to 2 decimal places) 4. Assuming the actual amount of water vapor in the air stays the same, what is the relationship between temperature and relative humidity (as demonstrated by the previous three questions)? (1 pt) As the temperature increases, assuming the actual amount of water vapor in the air remains the same (specific humidity stays constant), the relative humidity decreases. This inverse relationship between temperature and relative humidity is a fundamental concept in meteorology. Warmer air can hold more water vapor, so as it warms up, the same amount of water vapor becomes a smaller fraction of the air's capacity, resulting in lower relative humidity. Relative humidity can only reach a maximum of 100%. At this point, the air parcel can no longer hold the same amount of water vapor (an invisible gas) and so water droplets begin to form (suspended water droplets in the form of fog or clouds are created by condensation). The temperature at which relative humidity reaches 100% is called the dew point temperature . In order to calculate the dew point temperature, you will still need to know the specific humidity of the air parcel, but your goal is to determine at what temperature the maximum water vapor will be the same as the specific humidity. The equation used to calculate the dew point temperature is as follows: