| Other weather measurements: |
Temperature, humidity, wind and solar radiation are all important aspects of climate and are recorded at Hubbard Brook in the interest of tracking local long-term climatic conditions that may help explain observed changes in the ecosystem. Modelers also use this Hubbard Brook climate data to create models that estimate how forests use water.
1.
Temperature and relative humidity
2.
Wind
3.
Solar radiation
4.
See the data
1. Temperature
and relative humidity
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Temperature and humidity are recorded at only eight locations in the Hubbard Brook valley, none of which happens to be in Watershed 6, but we will talk about it here anyway. The instruments are housed in a standard Stevenson screen, mounted 5 feet off the ground and oriented to face north. The screen is painted white to reflect the sunlight, and the slats allow ventilation of the interior so that the air inside the screen is as similar as possible to the air outside.
Temperature and relative humidity are measured and recorded with a Belfort hygrothermograph. The sensors for each parameter are attached to a pen which moves up and down as temperature or humidity changes, recording the results on a rotating chart. Both sensors rely on the movement of a shrinking and expanding material to move the pen--metal for temperature, and horse hair for humidity. The data is retrieved and the chart paper replaced once a week. Maximum and minimum daily temperatures are read manually from the chart and recorded, along with a daily mean, in the long term database.
In addition to the hygrothermograph, a standard thermometer and maximum and minimum thermometers are also housed in the Stevenson screen. These are present mostly to verify that the hygrothermograph is working properly. They are read and recorded weekly during the station visit, but generally the "official" data is taken from the hygrothermograph.
Here are the
highest and lowest recorded temperatures in the Hubbard Brook valley since
the late 1950s:
| Highest maximum temperature |
|
1994 |
(elev 830 ft) |
| Lowest minimum temperature |
|
1980 |
(elev 2450 ft) |
| Greatest temperature change in one day |
to 32ºC (90ºF) |
1979 |
(elev 1600 ft) |
Wind speed and direction is measured at the Forest Service
Headquarters with an anemometer and weathervane mounted three meters above
the ground. The anemometer, on the right, consists of three equally
spaced cups attached to a free spinning ring on the post. Any slight
wind will cause the ring to spin and the rate of spinning is proportional
to the wind speed. A weathervane is mounted on the left side of the
post in the photo. It swings freely and points in the direction from
which the wind is coming. Before 1981, the data was recorded continuously
with a strip chart recorder, but since that time the data has been recorded
with an automatic data logger. In actuality, wind speed is not recorded
as an instantaneous rate, but as the total kilometers of wind that have
passed by the anemometer over a given time period. Every hour a message
is sent electronically to the data logger, indicating the
total kilometers logged by the anemometer over that hour and the
average compass direction of the weathervane. For each cardinal compass
direction, the total kilometers are summed for each day. A second
totalizing anemometer, seen slightly below the first in the photo, records
total kilometers of wind movement, regardless of direction. This
is read every workday, and is used as a backup to the automated anemometer.
The windiest
day on record occurred on January 7, 1973 with 462 km/day.
Until 1981, solar radiation was measured at the Forest Service Headquarters with a pyranograph, which is the white box on the left in the photo above. When the weather station was automated in 1981, a LI-COR pyranometer was installed. The pyranograph now remains as a back up instrument.
The pyranograph measures changes in solar radiation by a mechanism similar to that in the hygrothermograph. The differential shrinking and expanding of two bimetallic strips causes a pen to move up or down against a rotating drum, recording changes in solar radiation. Both strips are exposed to the ambient air temperature, but one strip is shielded from the direct rays of the sun and the other is exposed. The pen moves when the temperature of the exposed strip increases beyond that of the shielded strip, i.e. when direct radiation from the sun causes it to heat up and expand. The pen does not move when both strips are changing temperature at the same rate in response to changes in the ambient air temperature. In effect, the shielded strip is the baseline and solar radiation is measured as any change in the exposed strip that exceeds that baseline.
The LI-COR
pyranometer is a more sophisticated electrical instrument that measures
incoming solar radiation with a silicon photodiode sensitive to the relevant
electromagnetic wavelengths of the sun's radiant energy. Average
solar radiation is recorded hourly in calories per cm2
to a data logger.
Check the Datasets for over 40 years of weather data at Hubbard Brook.