From the start, the measurement of daily maximum and minimum air temperature within one hour of local solar noon has been a key GLOBE protocol. The low cost approach was to use a U-tube thermometer housed in a wooden instrument shelter facing away from the equator. The U-shaped tube contained mercury with pins on either side of the mercury. As the air temperature warmed the pin on one side would move while the other pin stayed in place; when the air cooled, the pin on the other side would be pushed up. The pins were held in place by magnetized strips behind the thermometer tube so that they would only move when pushed by the column of mercury. The bottom of each pin indicated the maximum or minimum air temperature. After each day’s reading a magnet was used to move the pins down so that they were in contact with the mercury.
As GLOBE students took measurements day after day for years, the resetting of the pins using the magnet gradually demagnetized the strip that held the pins in place. Sometimes the pins would move down with the mercury resulting in bad data. The GLOBE scientist responsible for this protocol Dr. Susan Postaeko and her research team uncovered this problem. GLOBE worked with Taylor, the thermometer supplier, to develop a replacement – the digital, multi-day max/min thermometer. This is now the thermometer for GLOBE schools to use in instrument shelters.
This thermometer has features designed to make it more useful to GLOBE participants. The thermometer can store maximum and minimum temperatures for up to 7 consecutive 24-hour periods. So if schools initiate the thermometer within one hour of local solar noon, they can collect readings over weekends and short holidays when no one is at school to take the measurements, The thermometer comes with 2 probes so that the second one can be used to measure soil temperatures. This enables students to investigate the relationship between air and soil temperatures at their sites. A second copy of the thermometer may be used to collect soil temperatures at two other depths. This experience illustrates the power of citizen science and massive data collection. The problem was subtle and only occurred after prolonged use of the U-tube thermometers. It is impressive that the group at the University of Oklahoma caught it. It also illustrates the strength of the GLOBE partnership among teachers, students, and scientists – a partnership that is open to other citizen scientists who wish to contribute data to the Program. Taylor was strongly supportive in developing the still affordable improved instrument required. The solution opened the door to measurements with which one aspect of Earth’s energy cycle – a key component of Earth as a system – can be studied.