RAIN

Rainfall since 0000 UTC

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 centimeter alter shield in order to decrease wind effects.
Type Sensor Used Standards Units Accuracy
Standard - Primary Met One Tipping-Bucket Rain Gauge millimeters of water per day, PDF ±5% over the range of 0 to 5 centimeters per hour.

Met One Tipping-Bucket Rain Gauge Sensor

TDEW

Dewpoint Temperature

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.
Sensor Used Standard Units
Thermometrics Air Temperature (for Air Temperature), PDF degrees Celsius
Vaisala HMP45C (for Relative Humidity), PDF  

Vaisala HMP45C Sensor

Thermometrics Air Temperature Sensor

RELH

Relative Humidity (1.5 m)

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.
Type Sensor Used Standards Units Accuracy
Standard - Primary Vaisala HMP45C, PDF described as a percentage ±3% for 10 - 98

Vaisala HMP45C Sensor

TR05

TR05: Calibrated Delta - T (5 cm)

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 our soil moisture manuscript.

Type Sensor Used Standard Units
Standard - Secondary Campbell Scientific 229 - L degrees Celsius

Campbell Scientific 229 - L Sensor

TR25

TR25: Calibrated Delta - T (25 cm)

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 our soil moisture manuscript.

Type Sensor Used Standard Units
Standard - Secondary Campbell Scientific 229 - L degrees Celsius

Campbell Scientific 229 - L Sensor

TR60

TR60: Calibrated Delta - T (60 cm)

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 our soil moisture manuscript.

Type Sensor Used Standard Units
Standard - Secondary Campbell Scientific 229 - L degrees Celsius

Campbell Scientific 229 - L Sensor