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Select Lesson:

1. Comparing Observations

Objectives:

Weather variables such as temperature, dew point, wind, and rainfall can vary with both space and time. Scientists have shown that rainfall can significantly vary over distances as short as 3 feet! Sites within the SchoolNet8 network measure all of the weather variables mentioned above. Your SchoolNet8 site is located close to some other sites, yet relatively far away from other sites. The purpose of this lesson is see how we can use SchoolNet8 data to see how weather differs from place to place.

SchoolNet8.com Online Resources:

SchoolNet8.com provides many ways to view current and historical weather data for your site and others in the SchoolNet8 network. One of these ways is your site's homepage found here:

Questions:

  1. For our first question, we will compare your site's weather data to a site nearby. From your My SchoolNet8 Site page, select another site in the SchoolNet8 network by choosing it from the pull-down menu found near the lower righthand side of the page. Be sure to click the 'Compare Station' box to ensure that the comparison is made. What differences do you notice in variables like temperature?
  2. Many factors can influence temperatures reported by your SchoolNet8 site. Here are a few:
    • Clouds tend to prevent temperatures from warming during the day by restricting the amount of solar energy that reaches the ground. They also tend to keep temperatures warmer at night by providing a blanket to prevent heat from escaping into space.
    • Winds can bring warmer or colder air into Iowa by a process called advection. By moving warmer or colder air into the state, it can locally raise or lower our temperatures. For Iowans, we know that winds from the north tend to bring colder air into the state and winds from the south bring warmer air. You can probably remember a cold winter day with a strong Northwest wind.
    • Snow cover: Sites with snow cover versus sites without snow cover can produce different temperatures during the daytime and nighttime. Snow acts to reflect solar energy away from the Earth's surface during the day, which keeps us colder. At night, this colder daytime temperature combined with the long winter nights result in even colder nighttime temperatures.
    • Elevation: Although not that important in Iowa, differences in elevation, or height above sea level, can lead to differences in air temperatures. This often occurs during the early evening and overnight. Cold air is more dense than warm air, so it tends to sink to lower elevations. A site located in a valley compared with a site on a hill will often have cooler temperatures at night, yet have similar temperatures during the day.
    • Rainfall: Especially during the summer, locations that recieve rainfall during the day will be cooler than those without rain. Rainfall cools the air by evaporating as it falls from the clouds.
    • Urban Areas are often warmer than rural areas during the day and night. All of the buildings, concrete, and human activity tend to trap heat in the urban areas during the day and night. This is commonly called a 'Urban Heat Island'.

    Looking at the above list. Can you guess which factors are contributing to any differences you are noticing with your comparison?
  3. Do you notice any differences when you compare your site to sites near to you and when you compare against sites far away?

Possible Answers:

  1. Differences in any weather variable will depend on when you make the comparison. In general, differences should exist during windier and sunnier days.
  2. The cause of these differences will be highly dependent on the day you are making the comparison. If a difference seems too large to believe, it may be due to an error with one of the sensors.
  3. In general, the differences in weather variables should increase with distance between the observing sensors. Variables like solar radiation and precipitation can be highly variable over short distances.

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