Current
Data
Current data
reported on our weather web server are given by default in English units
of measure. We do this to allow users who are uncomfortable with the
metric system to view current conditions on familiar terms. Historic data
can be viewed in either metric or English units. By accessing the NOAA
Conversion page (link in the page header) you can easily convert these data
to metric units.
Plots of data with
time intervals longer than 1 week do not include all data points. In order
to get the plots to display in a reasonable time, we plot very large data sets
as data averages. For the most part, data are presented as daily
averages. All data are archived on our main webpage and are available for
download as tab delimited text files. If you are interested in the
complete data set you can access these files by month at
http://www.clayhillforest.org/weather/weatherdata.html by clicking on any of the three archived data links.
Temperature and
Relative Humidity
Temperature sensors are accurate to ± 0.7 ºC. Air temperature sensors are mounted in sun-shielded plastic container located approximately 2 meters
above the surface of the ground. Soil temperature probes are located at a
depth of 20 cm.
The relative humidity
sensors are housed in the sun shields. These
sensors are accurate to ± 3 %.
Soil Moisture Content
We
measure soil moisture with ECH2O ® Dielectric Aqua Meter Probes located approximately 20 cm below the surface of the
soil. These sensors measure
the amount of water in soil relative the total amount of water possible at
saturation and report this value as m3 H2O/ m3soil. The range of this
sensor is from slightly less than 0.0- to 0.405 m3 H2O/ m3soil with smaller values
indicating dryer soil. Soil moisture
spikes following rainfall events and then declines rapidly.
Solar Radiation
We measure light using Silicon Pyranometer Sensors. These sensors use a silicon photo diode to
measure solar power in watts/meter2/second. The sensors respond to radiation ranging in wavelength from 300-1100
nm. This range includes visible light as
well as some ultraviolet and infrared radiation. The sensor range is from 0-1280 W/m2/sec. Its accuracy is ± 10 W/m2/sec. These sensors respond rapidly to cloud cover,
precipitation and fog with reduced readings. On days with scattered clouds, the readings will spike up and down. In late evening and early morning, when the
sun is low in the sky, similar spikes can be observed as the sun is temporally
blocked by objects near the ground. This is
particularly true for light sensors at forest stations where trees often temporarily
block light.
Visible Light (PAR)
Our second light sensor responds to light in the visible
spectrum, particularly light which can cause photosynthesis ( wavelengths from
400-700 nm). PAR stands for Photosynthetically Active
Radiation. In photosynthesis light is measured
in units called photons. When of
photon of correct energy level (wavelength) strikes a chlorophyll molecule, the
process of photosynthesis is initiated. The PAR sensors measure the number of photons striking one square meter of
surface in a second. The actual unit is
µmol/ m2/sec (micromoles per meter square per second). The PAR sensors range from 0-2500 µmol/ m2/sec
and are accurate to ± 5 µmol/ m2/sec. PAR sensors are located on each of our
weather stations. The unit is abbreviated
as µE.
Barometric Pressure
Our main weather sensor is equipped with an air pressure
sensor. This sensor measures barometric
pressure also commonly known as atmospheric pressure. Our sensor reports data from 660-1070 mb
(millibar). The millibar is a metric unit
of air pressure and 1 mb = 0.01450377 pounds/square inch. Barometric pressure is a useful indicator of
the passage of weather fronts. When the
remnants of hurricanes Katrina and Rita passed across Clay Hill in September
of 2005, the barometric pressure dropped markedly. With Katrina, pressure plummeted to one of the
lowest values we have recorded. You can view this event by plotting the
data for that month.
Rainfall
We monitor precipitation with a tipping bucket
rain gauge
capable of recording up to 10- cm (~4 inches) of rainfall/ hour. Each tip of the bucket measures 0.01 inches
or 0.2 mm of precipitation. The gauge is
accurate to ± 1 %. Anomalies may occur with snowfall as this will not be
recorded until melting.
Wind Speed and
Direction
Our meter measures wind above 0.5 meters/second or 1.1
miles/hour. The instrument continuously
records wind speeds and directions and records averages of these data over
15-minute intervals. The accuracy of
wind speed measurements varies from ± 3-4% being more accurate at slower wind
speeds than at high wind speeds. Maximum
recordable wind speed is 99 mph.
In addition to measuring averages, our
sensor records maximum
gust speed during each 15-minute interval.
Wind direction is measured as azimuth or compass
direction. 360º or 0º is due north, 90º is east, 180º is south, and 270º is west. The accuracy of any directional measurement is ~±5º.
Additional information including
technical reports and complete specifications is available for all of our
sensors on the Onset Computer website.
HOME
