The temperature of the air is a measure of how quickly the molecules are moving. The more energy of motion the molecules have, the higher the temperature you feel in the air. Air temperature is measured with thermometers. Common thermometers consist of a glass rod with a very thin tube in it.
The tube contains a liquid that is supplied from a reservoir, or "bulb," at the base of the thermometer. Sometimes the liquid is mercury, and sometimes it is red-colored alcohol. Each wire, when excited with 12V DC, vibrates with a frequency relative to the weight in the collection bucket.
The station datalogger measures the frequency of each vibrating wire and converts it to a gauge depth in mm every five minutes. Its data are not quality controlled and are not considered official USCRN precipitation readings, but can assist in cases where the Geonor unit fails during warm conditions.
These probes use reflected electromagnetic radio waves at 50 MHz to determine the dielectric permittivity of the soil in which the probe is inserted, which can be converted to volumetric soil moisture units m3m-3 by use of a calibration equation. The probe also contains a thermistor to measure ambient temperature in the face plate pressing against the soil. All 15 probes are interrogated every two minutes and their measurements averaged over 5-minute periods for output purposes.
An Apogee Instruments infrared temperature sensor measures the infrared ground surface temperature in degrees Celsius at each station. The datalogger samples the sensor every two seconds. Every five minutes these two-second samples are averaged to obtain 5-minute values. A Met One Model A anemometer measures wind speed in meters per second at each station. The datalogger samples the anemometer every two seconds. The capacitance of the film is related to relative humidity by a calibration equation that converts the flow of electricity to relative humidity.
These values are averaged over 5-minute periods to produce final data for this variable. In addition to the above elemental observations, the hourly data stream from each station includes measurements from a disdrometer, or wetness sensor.
The former is used to provide information at least two times every 5 minutes as to whether precipitation is falling. In addition to the above elemental observations, the hourly data stream from each station includes the following values:.
Precipitation Each station has a weighing precipitation gauge which is equipped with three load cell sensors to provide three independent measurements of depth change in millimeters at 5-minute intervals. For temperature readings to be accurate and meaningful, thermometers should be located five to six feet above the ground ideally not over a paved surface to minimize the effect that the underlying ground itself might have on temperature.
Thermometers also should not be exposed to direct sunlight. The bimetallic strip or "bulb" of a liquid-in-glass thermometer absorbs solar radiation more efficiently than surrounding air, so exposure to direct sunlight causes it to measure a temperature that's higher than the surrounding air. To truly measure air temperature, a thermometer should be in the shade, where the temperature of the thermometer itself should be the same as the air temperature.
Finally, thermometers shouldn't be located too close to buildings since warmth from buildings via emitted radiation or the escape of air through vents, etc. In order to accomplish proper thermometer "siting" at many of the nearly 10, official U. Cooperative Observer COOP Network sites, thermometers are placed in "cotton-region shelters," shown below which are also known as "Stevenson Screens" named after their designer, the father of author Robert Louis Stevenson.
Cotton-region shelters sit roughly five feet above ground atop a base, and have open vents on the sides to allow air to flow freely through the shelter and contact the thermometers. To maximize the reflection of incoming solar radiation, cotton-region shelters are painted white, and in addition to protecting the thermometers from direct solar radiation, cotton-region shelters also protect the instruments inside from falling precipitation.
Other official temperature measurements taken via the Automated Surface Observing System ASOS , mostly located at airports, have shields that serve the same basic function of a cotton-region shelter , and if you have ever purchased a home weather station, its thermometer should have come with a shield to attempt to protect it from direct solar radiation, yet still allow for free air flow.
So, now that you know how temperature should be measured, what's the problem with temperatures measured by bank thermometers, car thermometers, or "on the field" at sporting events? For starters, bank thermometers are often housed very close to or are attached to buildings. Furthermore, they're often exposed to direct sunlight, or are encased in a dark-colored shelter, which maximizes the absorption of solar radiation.
So, when you see a really high temperature on a bank thermometer on a sunny day, don't buy it! How we measure grass minimum temperature For many years the grass minimum temperature has been defined as the lowest overnight temperature measured by a thermometer, fully exposed to the open sky, suspended horizontally over an area covered with short cropped turf and in contact with the tips of grass blades.
How we measure concrete minimum temperature Concrete minimum temperature is measured by a thermometer in contact with a concrete slab, as shown in the image above.
How we measure soil minimum temperature At many stations with automatic systems soil temperature is measured at a depth of 10 cm, 30 cm and cm below the ground surface by platinum resistance thermometers. You might also like. Read more. Sunshine is measured using either Campbell-Stokes sunshine recorders or modern sunshine sensors.
A pyranometer is used for measuring global radiation. Related links How weather forecasts are created How we measure cloud How we measure wind How we measure rainfall How we measure snow depth How we measure visibility How we measure atmospheric pressure How we measure sunshine and radiation The UK land observation network.
Help us improve our website Take our short survey.
0コメント