DEW POINT OR DEWPOINT TEMPERATURE (TDEW)

TYPE: Derived parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: Not measured, but computed from the 1.5-meter air temperature (TAIR) and relative humidity (RELH).

SENSOR USED: None

NOTES: The dewpoint temperature is a more revealing measure of the moisture content in the air than is the relative humidity.

HEAT INDEX (HEAT)

TYPE: Derived parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: Not measured, but computed from the 1.5-meter air temperature (TAIR) and relative humidity (RELH).

SENSOR USED: None

NOTES: The heat index is used to provide information about possible heat stress on the human body.

PRESSURE, ATMOSPHERIC OR BAROMETRIC PRESSURE (PRES)

TYPE: Core parameter

STANDARD UNITS: Millibars

DESCRIPTION: The average station pressure during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Barometer

NOTES: The average pressure reading is accurate to 0.4 millibars for temperatures between -30 deg and 50 deg Celsius, and for pressures between 700 and 1100 millibars. Interestingly, some pressure events smaller than 0.4 millibars, such as gravity waves, can nevertheless be tracked with Mesonet barometers. The key is to note trends and times of occurrence visible in the data rather than count on individual readings being precise to the nth degree.

Barometric pressure is not corrected for the elevation of the station above sea level. Caution must be used when calculating pressure gradients or correcting station pressure to a reference height. For theoretical wind calculations, an error is induced that is proportional to the distance between the two stations. However, changes in pressure over time at any given station are very accurate measurements.

RAINFALL (RAIN)

TYPE: Core parameter

STANDARD UNITS: Millimeters of water per day

DESCRIPTION: The total amount of rainfall measured since 0000 GMT [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).

SENSOR USED: Tipping-Bucket Rain Gauge

NOTES: 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 the 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.

RELATIVE HUMIDITY (RELH)

TYPE: Core parameter

STANDARD UNITS: Described as a percentage

DESCRIPTION: The average relative humidity at a height of 1.5 meters above the ground during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Sorption Sensor

NOTES: Relative humidity changes when either the moisture content of the air or the air temperature changes. This sensor can detect relative humidity between 0 and 100%. The error for readings of 0 - 90% RH is 2%, while readings of 90 - 100% RH have a 3% error. A dew-point sensor of the chilled-mirror type was considered for the Mesonet, but was less reliable for use in field conditions, more expensive to purchase, and required more power.

SEA LEVEL PRESSURE (PALT)

TYPE: Derived parameter

STANDARD UNITS: Millibars

DESCRIPTION: Not measured, but computed from the barometric station pressure (PRES) and the station elevation.

SENSOR USED: None

NOTES: Sea level pressure should be used to compare pressures between two stations at different elevations. Sea level pressure is an approximation of the station's barometric pressure if the station were located at sea level. Because pressure readings can be approximated for sea level, differences in sea level pressure between stations are related to differences in the air mass above the two stations.

SOIL TEMPERATURE, UNDER BARE SOIL (5 CM) (TB05)

TYPE: Supplemental parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average temperature during a 15-minute interval at a depth of 5 centimeters below the ground; the surface under which the measurement is taken is not vegetated.

SENSOR USED: Thermistor

NOTES: Similar to 10 centimeters soil temperature under bare soil (TB10) but TB05 is typically above the root level of crops.

The thermistor at 5 centimeters is able to detect the passage of the solar panel's shadow on some days.

SOIL TEMPERATURE, UNDER BARE SOIL (10 CM) (TB10)

TYPE: Core parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average temperature at a depth of 10 centimeters below the ground during a 15-minute interval; the surface under which the measurement is taken is not vegetated.

SENSOR USED: Thermistor

NOTES: Bare soil temperatures are useful for planting decisions under conventional tillage regimes (the vast majority of Oklahoma farms) and can be used to monitor soil conditions until a complete crop canopy develops. This temperature reading also is valuable during freezing rain and snow events when soil temperatures play a critical role in determining how much winter precipitation might accumulate.

SOIL TEMPERATURE, UNDER SOD (5 CM) (TS05)

TYPE: Supplemental parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average temperature during a 15-minute interval at a depth of 5 centimeters below the ground; the surface under which the measurement is taken is vegetated.

SENSOR USED: Thermistor

NOTES: Similar to 10 centimeters soil temperature under sod (TS10) but TS05 is typically above the root level of crops.

The thermistor at 5 centimeters is able to detect the passage of the solar panel's shadow on some days.

SOIL TEMPERATURE, UNDER SOD (10 CM) (TS10)

TYPE: Core parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average temperature at a depth of 10 centimeters below the ground during a 15-minute interval; the surface under which the measurement is taken is vegetated.

SENSOR USED: Thermistor

NOTES: 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.

SOIL TEMPERATURE, UNDER SOD (30 CM) (TS30)

TYPE: Supplemental parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average temperature during a 15-minute interval at a depth of 30 centimeters below the ground.

SENSOR USED: Thermistor

NOTES:

SOLAR RADIATION (SRAD)

TYPE: Core parameter

STANDARD UNITS: Watts per square meter

DESCRIPTION: The average amount of solar radiation received at the sensor during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Pyranometer

NOTES: A tripod supports the sensor at a height of 1.8 m at the southern end of the site, a position selected to avoid reflections from the tower and to ensure that as few shadows as possible fall upon the sensor.

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.). Therefore, the pyranometer can be used to determine if there are clouds, but only during daylight hours. Note that the sensor points upward and thus does not measure solar radiation reflected upward from the ground.

TEMPERATURE, AIR (1.5 M) OR AIR TEMPERATURE AT 1.5 METERS (TAIR)

TYPE: Core parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: The average air temperature at a height of 1.5 meters above the ground during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Thermistor

NOTES: This sensor can have temperature errors of several degrees Celsius when the wind is calm (less than 1 meter per second) and radiation is strong (more than 800 Watts per square meter). Radiation at high sun angles near 70 degrees seem to induce the worst errors.

For design reasons, this sensor is mounted within the same membrane shell as the relative humidity sensor. As a result, the response time of the TAIR is somewhat longer than would be the case for free air exposure.

TEMPERATURE, AIR (9 M) OR AIR TEMPERATURE AT 9 METERS (TA9M)

TYPE: Supplemental parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: Same as air temperature at 1.5 meters (TAIR) but faster response temperature sensor and positioned at 9 meters.

SENSOR USED: Thermistor

NOTES: In combination with the 1.5-meter air temperature, these data have potential value in monitoring the stability of the near-surface atmosphere, turbulence and temperature inversions (including frost protection applications). This thermistor has the same warm bias on calm, high-radiation days as does the 1.5 meter thermistor.

WIND CHILL (CHIL)

TYPE: Derived parameter

STANDARD UNITS: Degrees Celsius

DESCRIPTION: Not measured, but computed from the 1.5-meter air temperature (TAIR) and the wind speed at 10 meters (WSPD).

SENSOR USED: None

NOTES: Wind chill represents the cooling effect on the human body of low temperatures combined with wind.

WIND DIRECTION, AVERAGE OR VECTOR AVERAGE WIND DIRECTION (WDIR)

TYPE: Core parameter

STANDARD UNITS: Described in degrees in a circle (from North), where north is 0 degrees, east is 90 degrees, south is 180 degrees, and west is 270 degrees.

DESCRIPTION: The vector average wind direction at a height of 10 meters above the ground during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour). Note: wind direction always describes the direction from which the wind is blowing and not toward which the wind is blowing.

SENSOR USED: Propeller Vane Anemometer

NOTES: When WSPD is zero, WDIR and other 10-meter wind parameters are set to zero.

WIND DIRECTION STANDARD DEVIATION
(WDSD)

TYPE: Core parameter

STANDARD UNITS: Degrees from north

DESCRIPTION: The standard deviation of the wind direction at 10 meters.

SENSOR USED: Pyranometer

NOTES: This parameter is a measure of the steadiness of wind direction. A small standard deviation indicates the wind was generally blowing from the same direction; a large standard deviation indicates significant changes in wind direction during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour). The standard deviation may be large for either inclement weather or relatively light winds.

WIND SPEED AT 2 METERS (WS2M)

TYPE: Supplemental parameter

STANDARD UNITS: Meters per second

DESCRIPTION: Same as average wind speed for 10 meters except the anemometer is positioned at 2 meters.

SENSOR USED: Cup Anemometer

NOTES: The cup anemometer only counts the rotations of the sensor caused by the speed of the wind; it does not measure wind direction. This sensor is a three cup unit mounted at the end of a short boom, and has a starting threshold of 0.5 meters per second. Its range is from 0.5 to 50 meters per second and it can withstand gusts of 60 meters per second. The 2-meter wind speed mainly is used for agricultural purposes (e.g., to help estimate evapotranspiration of moisture from the soil).

WIND SPEED, AVERAGE (10 M)
OR
AVERAGE WIND SPEED AT 10 METERS
(WSPD)

TYPE: Core parameter

STANDARD UNITS: Meters per second

DESCRIPTION: The average wind speed without regard to direction at a height of 10 meters above the ground during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Propeller Vane Anemometer

NOTES: The average wind speed is independent of the wind direction during the 5-minute averaging interval. The parameter is the arithmetic average speed.

The propeller has a range of 1 to 60 meters per second, and can withstand gusts of 100 meters per second. A wind speed of 1 meter per second is necessary to start the propeller.

WIND SPEED, MAXIMUM (WMAX)

TYPE:Core parameter

STANDARD UNITS: Meters per second

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

SENSOR USED: Propeller Vane Anemometer

NOTES: This parameter is independent of wind direction. The propeller can withstand gusts of 100 meters per second.

WIND SPEED STANDARD DEVIATION
(WSSD)

TYPE: Core parameter

STANDARD UNITS: Meters per second

DESCRIPTION: The standard deviation of the wind speed at 10 meters.

SENSOR USED: Propeller Vane Anemometer

NOTES: This parameter 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 last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour). The standard deviation may be large for inclement weather.

WIND SPEED, VECTOR AVERAGE
OR
VECTOR AVERAGE WIND SPEED
(WVEC)

TYPE: Core parameter

STANDARD UNITS: Meters per second

DESCRIPTION: The average wind velocity (speed and direction accounted for) at a height of 10 meters above the ground during the last 5-minute interval before the time designated on the file (usually 00, 15, 30, or 45 minutes after the hour).

SENSOR USED: Propeller Vane Anemometer

NOTES: This is a vector average (i.e., the wind direction is considered). If the wind is out of the north at 10 meters per second for 2.5 minutes and then out of the south at 10 meters per second for 2.5 minutes, the average vector wind velocity will be zero during that 5-minute period.