Instruments | Mesonet (2024)

The 5-minute average air temperature at a height of 1.5 meters above the ground.

• This sensor is quite rugged and accurate. Prior to 2009, the sensor was housed in a naturally-ventilated radiation shield. Such shields can create temperature errors of several degrees Celsius when the wind is calm (less than 1 m/s) and solar radiation is high.
• Since 2009, the sensor is housed in an aspirated radiation shield, which continuously draws ambient air over the sensor, while protecting it from solar radiation.

Same sensor as TAIR but positioned at 9 meters above ground level.

• This thermistor uses an unaspirated radiation shield, resulting in readings with a warm bias on calm, sunny days.

Not measured, but computed from the 1.5 meter air temperature and relative humidity.The heat index is used to provide information about possible heat stress on the human body.

Not measured, but computed from the 1.5 meter air temperature and the wind speed at 10 meters.Wind chill represents the cooling effect on the human body of low temperatures combined with wind.

The 5-minute average wind speed at a height of 10 meters above the ground. The propeller has a starting threshold of 1 m/s.

• The average wind speed is independent of the wind direction.
• When WSPD is zero, all other wind variables are set to zero.

The vector average wind direction at a height of 10 meters above the ground. Note: wind direction always describes the direction from which the wind is blowing. The vane has a starting threshold of 1.1 m/s.

• When WSPD is zero, all other wind variables are set to zero.

The maximum 3-second wind speed observed during a 5-minute interval at a height of 10 meters above ground; it is the largest value observed during the 5-minute averaging interval.

• WMAX is independent of wind direction.

The 5-minute average wind speed at 2 meters. Because of the characteristic response of the cup design, the Mesonet's dataloggers add 0.2 m/sto each observation greater than 0.2 m/s.

• The cup anemometer only counts the rotations of the sensor caused by the speed of the wind; it does not measure wind direction. Its range is from 0.5 to 50 m/sand it can withstand gusts of 60 m/s. The 2-meter wind speed mainly is used for agricultural purposes (e.g., to help estimate evapotranspiration of moisture from the soil).

The average wind velocity (speed and direction accounted for) at a height of 10 meters above the ground.

• Note that this is a vector average (i.e., the wind direction is considered). If the wind is out of the north at 10 m s^-1for 2.5 minutes and then out of the south at 10 m s^-1for 2.5 minutes, the average vector wind velocity will be zero during that 5-minute period.

The standard deviation of the wind speed at a height of 10 meters above the ground.

• This variable is a measure of the steadiness of wind speed. A small standard deviation indicates the wind generally blowing at the same speed; a large standard deviation indicates significant changes in wind speed during the 5-minute interval. The standard deviation may be large for inclement weather.

The standard deviation of the wind direction at a height of 10 meters above the ground.

• This variable is a measure of the steadiness of wind direction. A small standard deviation indicates the wind is blowing from the same direction; a large standard deviation indicates significant changes in wind direction during the 5-minute interval. The standard deviation may be large for either inclement weather or relatively light winds.

The average temperature at a depth of 10 centimeters below the ground during a 15-minute interval; the surface is not vegetated.

• Thermistor probes sheathed in stainless steel (prior to December 2013) or thermocouple sensor (December 2013 and afterward) are buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• Bare soil temperatures are useful for planting decisions under conventional tillage regimes (i.e., the vast majority of Oklahoma farms) and can be used to monitor soil conditions until a complete crop canopy develops.

The average temperature during a 15-minute interval at a depth of 5 centimeters below the ground; the surface is vegetated.

• Thermistor probes sheathed in stainless steel (prior to December 2013) or thermocouple sensor (December 2013 and afterward) are buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• Similar to 10 cm soil temperature under sod but TS05 is typically above the root level of crops.

The average temperature at a depth of 10 centimeters below the ground during a 15-minute interval; the surface is vegetated.

• Thermistor probes sheathed in stainless steel (prior to December 2013) or thermocouple sensor (December 2013 and afterward) are buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• This soil temperature reading can be very important to the vast acreage of rangeland across the state, as well as for planting decisions under reduced or no-tillage systems, for soil condition monitoring under a crop canopy, and for industries such as turfgrass.

The average temperature during a 15-minute interval at a depth of 25 centimeters below the ground; the surface is vegetated.

• Thermocouple sensor buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• This measurement began in December 2013.

The average temperature during a 15-minute interval at a depth of 60 centimeters below the ground; the surface is vegetated.

• Thermocouple sensor buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• This measurement began in December 2013.

The average temperature during a 15-minute interval at a depth of 5 centimeters below the ground; the surface is not vegetated.

• Thermistor probes sheathed in stainless steel are buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• The tower provides short duration (i.e., less than 30 minutes) intermittent shade to the soil temperature plot during late spring through early fall. In extreme instances, this shading can cause a dip in the 5-cm soil temperature of 1-2 °C.
• This measurement was discontinued in December 2013.

The average temperature during a 15-minute interval at a depth of 30 centimeters below the ground; the surface is vegetated.

• Thermistor probes sheathed in stainless steel are buried horizontally in undisturbed ground. Because the cables connecting the thermistors to the tower might conduct surface heat and divert draining rainwater, they were buried deeper than the thermistors, then angled upward.
• This measurement was discontinued in December 2013.

The total amount of rainfall measured since 0000 UTC (6 PM CST or 7 PM CDT) just above the ground; it is measured in discrete tips of the bucket (approximately 0.01 inch per tip, or 0.254 millimeters).

• The Mesonet uses an unheated tipping-bucket rain gauge with a 30.5 centimeter diameter opening 0.6 meters above the ground. The gauge works by funneling rainfall into one of two small buckets mounted on either side of a balance pivot. As each bucket fills, tips, and brings the other bucket beneath the funneled rain, the tip is counted (one tip is 0.254 millimeters or 0.01 inches of rain). Each Mesonet observation contains a running accumulation of rainfall since either 6 PM CST or 7 PM CDT. As each new evening begins, the accumulated rainfall is reset to zero.
• If the rainfall is very light, the bucket may only tip once every half hour or so. Thus, even if rain is continuous, rainfall might be recorded during every other 15-minute interval. If the rainfall is very heavy, there is a strong likelihood that rain has splashed out of the bucket. Thus, measurements during heavy rainfall periods generally underestimate the total amount of rainfall.
• Unheated gauges were chosen because of constraints on cost and power; the drawback is that unheated gauges underestimate snow or freezing rain totals. In addition, wet snow can clog the bucket while dry snow often blows away. Therefore, do not rely on the gauge observations during frozen precipitation events. Moreover, once air temperatures rise above freezing, the water equivalent of the melting precipitation is finally measured. The result is a delayed measurement of winter precipitation.
• The gauge is surrounded by a 121-cm alter shield in order to decrease wind effects.

The 5-minute average relative humidity at a height of 1.5 meters above the ground. Because of the sorption sensor's inherent inaccuracy at saturation, the mesonet restricts all readings above 100% to 100%.

• Relative humidity changes when either the moisture content of the air or the air temperature changes.

Not measured, but computed from the 1.5 m air temperature and the relative humidity.

• The dewpoint is the temperature to which the air must be cooled for it to become saturated.

The calibrated change in temperature of the soil over time after a heat pulse is introduced. From these measurements, soil water potential, fractional water index and volumetric water can be derived.

For more information, download oursoil moisture manuscript.

The calibrated change in temperature of the soil over time after a heat pulse is introduced. From these measurements, soil water potential, fractional water index and volumetric water can be derived.

For more information, download oursoil moisture manuscript.

The calibrated change in temperature of the soil over time after a heat pulse is introduced. From these measurements, soil water potential, fractional water index and volumetric water can be derived.

For more information, download oursoil moisture manuscript.

The average station pressure during the last 5-minute interval.

• A short length of tubing extends from the pressure port to outside of the datalogger enclosure in order to expose the barometer to the free atmosphere.
• Barometric pressure is not corrected for the elevation of the station above sea level. However, changes in pressure over time at any given station are very accurate measurements.

Not measured, but computed from the barometric station pressure and the station elevation.

• PALT should be used to compare pressures between two stations at different elevations. Sea level pressure is an approximation of the station's barometric pressure under a standard atmosphere if the station were located at sea level.

The average amount of downwelling global solar radiation received at the station during the last 5-minutes.

• The measurement of solar radiation does not include radiation emitted from the earth or atmosphere. However, the pyranometer will detect solar radiation which is reflected downward in the atmosphere (e.g., by molecules, clouds, etc.). Note that the sensor points upward and thus does not measure solar radiation reflected upward from the ground.
• Calibration coefficients are applied to the data in real-time during processing.
• Solar radiation measurements in the morning and evening are sensitive to obstruction (e.g., trees) on the east and west horizons. A delay of sunrise or early arrival of sunset at a particular station may be explained by examining panoramic site photos.