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Weather Stations

Weather Stations Data[LB]

Weather Stations Microclimate Description [PH]

Differences in climate within small geographic areas or even between the top and bottom of a leaf are important to a variety of organisms. For instance, deer on the Mt. Holyoke Campus use a White Pine stand as a wintering rest and sleep area, because the evergreen covers buffers wind and extremes in daily temperatures. To investigate differences in microclimate due to differences in forest cover, three new weather stations have been installed on the Mount Holyoke campus. These stations are among the stops in the CE’s new Curricular Trail. All three stations are located on Prospect Hill. The first weather station is in an open field on the North side of Prospect Hill. The second station is in a hemlock stand on the west side of Prospect Hill and the third weather station is near the top of Prospect Hill in a deciduous stand that includes maple, birch and oak trees. In addition to the weather stations described here, Al Werner of the Earth and Environment Department has been running a weather station off of the top of Clapp for several years.


Location of weather stations on MHC campus

Data from these weather stations are used in both class lab projects and group projects, and by students doing independent or thesis work on campus. We expect to find differences in microclimate due to variations in the ability of various types of vegetation to hold heat and buffer wind. In addition, the Hemlock stand is currently in decline due to an infestation by the Whooly Adelgid. As the Hemlock stand declines, we expect to see changes in the microclimate within that stand.

Datalogger in the Hemlock stand
Datalogger in the Hemlock stand.
Weather Station in the open site
Side view of the weather station in the open site.

Datalogger console inside the weatherproof enclosure.

The weather stations are the Davis Instruments Vantage Pro. They record a variety of parameters including the following- barometric pressure, evapotranspiration, outside humidity, dew point,
rainfall (daily, storm, monthly, yearly), rain rate, solar radiation, outside temperature,
heat index, UV index,
UV dose, wind direction,
wind speed, and wind chill.

The stations collect data every ten minutes using a cable that links the Vantage Pro console to the Integrated Sensor Suite (ISS). The ISS unit has the following components-
Rain collector, Anemometer vane, Wind cups, UV and solar radiation sensors.

A work-study student downloads the data from the each weather station once a week. She visits each site, removes the debris from the rain collector, and takes the consoles back to the CE where the data is moved from the console to a desktop computer. Once the data is downloaded it is permanently removed from the console. When the console is disconnected from the ISS it continues to collect data as long as the console is within approximately ten meters from the ISS. Each time the console is taken back to the CE, approximately twenty to thirty minutes of data are lost.

Explanation of Weather Parameters [PH] [LB]

Barometric pressure is the pressure exerted on the earth by air in the atmosphere. This is essentially atmospheric pressure, however barometric pressure accounts for the variability in atmospheric pressure that can be attributed to altitude. Barometric pressure is greater in lower altitudes because there is room for air in the atmosphere here than in an alpine environment, for example. In other words, between the Earth and the ceiling of the atmosphere, there is more space for air thus more air pressure where the elevation of the Earth’s surface is lower.

Evapotranspiration is a measurement of the amount of water vapor returned to the air in a given area. Moisture is put into the air from evaporation (the process by which water becomes a vapor suspended in air molecules) and from transpiration (the active exhalation of water through plant skin). This is essentially the opposite of rainfall.

Outside humidity is the amount of water in the air outside of the box in which the console is contained. Relative humidity is an expression of the amount of water held in the air in relation to the amount of water that the air can hold, which is affected by temperature and air pressure. Relative humidity and evapotranspiration are closely related because if the relative humidity is close to its holding capacity, plants’ ability to evapotranspire may be inhibited.

Dew point is the temperature at which air must be cooled for saturation (100% relative humidity) to occur. Dew point can be used to predict minimum overnight temperature and the likelihood of fog, for example. Dew point is an expression of vapor content.

Daily, storm, monthly, yearly rainfall is measured every ten minutes in 0.01in increments.

Solar radiation is a measure of the intensity of the sun’s radiation reaching a horizontal surface. This is an expression of direct radiation and reflected radiation. It is expressed in Watts per square meter.

Outside temperature is measured in degrees Fahrenheit.

Heat index is a measure of how hot or cold it feels. This is affected by the relative humidity and temperature of the outside air and is explained by evapotranspiration. In the summer, for example, it may feel hotter if humidity is high. It feels hotter because evapotranspiration is low. That is, your perspiration that holds your body’s expelled heat does not evaporate as quickly.

UV dose is a measure of the sun’s energy. This energy reaches the Earth as visible, infrared, and ultraviolet rays (UV). The latter may be dangerous to human health. The console measures UV in two forms. The first form Minimum Erythemal Dose (MED) is an index of the relationship between UV exposure and the extent of congestion of small capillaries in skin that redden the skin’s appearance. The MED scale is in whole number units and is presented in relation to a person’s skin type.

The second measurement derived form the UV index is a scale from 1 to 16 that expresses exposure in terms of "likeliness to cause sunburn."

Wind direction is measured using a compass display and Wind speed is measured in miles per hour.

Wind chill is measure of how hot or cold it feels in relation to the temperature and the wind speed. A person’s body releases heat; when it is undisturbed this heat remains near to one’s body affecting one’s perception of the outside temperature. When it is windy this heated air is literally blown away from the body causing one to feel colder. This is measured in a scale related to wind speed (mph).

The depth of soil probes (soil moisture and soil temperature):
  #1 = 5 cm
  #2 = 20 cm
  #3 = 50 cm

The specifications for each weather parameter

Function

Resolution

Range

Accuracy
(+/-)

Barometric Pressure

0.01"Hg

26" to 32" Hg

0.03" Hg

Evapotranspiration

0.01"

Daily to 99.99"
Monthly & Yearly to 199.99"

greater of 5%
or 0.01"

Outside Humidity

1%

0 to 100%

3%RH
4% above 90%

Dew Point

1° F

-105° to + 130°

3° F

Daily & Storm Rainfall

0.01"

To 99.99"

greater of 4%
or 1 tip

Monthly & Yearly Rainfall

0.01"

To 199.99"

greater of 4%
or 1 tip

Rain Rate

0.01"

To 100"/hr

greater of 5%
or 0.04"

Solar Radiation

1W/m2

0 to 1800 W/m2

5% of full scale

Outside Temperature

0.1° F

-40° to + 150°

1° F

Heat Index

1° F

-40° to + 135°

3° F

UV Index

0.1 Index

0 to 16

5% of full scale

UV Dose

0.1 for 0-20
1 MED > 20

0 to 199 MEDS

5%

Wind Direction

1mph/1 kt

0 to 360°

7°

Wind Speed

1mph/1 kt

2 to 150 mph;
2 to 130 kts

greater of 5%
or 2mph/kts

Wind Chill

1° F

1° F

2° F

 

Credits:
Page designed, created and maintained by Leszek Bledzki
Peter Houlihan – text and pictures marked [PH]
Leszek A. Bledzki – text and pictures marked [LB]

Center for the Environment
Talcott Greenhouse South
50 College Street
Mount Holyoke College
South Hadley, MA 01075
Phone: 413-538-3091

Copyright © 2006 Mount Holyoke College. This page created and maintained by Center for the Environment. Last modified on April 16, 2006.