Air temperature, relative humidity, and barometric pressure are measured at 30-minute intervals at three locations on the experimental forest - two upland locations (S2 and S5) and one bog location (S2 Bog). Data reported at the S5 (North) upland site are from 2015 to the present, while data from the South and S2 bog sites are from 2017 to the present. The North and South sites are separated by about 5 km. The South and S2 bog site are separated by about 0.175 km.
The air temperature and relative humidity sensors are located inside standard National Weather Service shelters. The shelters are 107 cm (42 inches) off the ground, have louvered sides, vented bottoms, double roofs and are painted white for protection against direct solar radiation. Shelters at the upland sites are in open areas with grass that is mowed at least every 2-3 weeks when growing. Optimally, the forest clearings are maintained with a 45-degree opening from the height of the thermometers. However, there were periods when this site condition was not adequately maintained.
At both North and South, the surrounding upland forest was last harvested during the 1910s. During the early 1960s, the sites were initially cleared to establish the meteorological stations and since then have been unmanaged to allow natural regeneration and succession of the surrounding forests. The upland forest currently is dominated by aspen (Populus tremuloides), white birch (Betula papyrifera), red maple (Acer rubrum), and balsam fir (Abies balsamea), with some red oak (Quercus rubra), and basswood (Tilia americana). There has been an observable shift in the dominance of aspen over the last 10 to 15 years as aspen have died. Gaps in aspen have opened to growth of red maple, balsam fir, red oak, and basswood into the canopy.
The measurement station in the S2 bog (a northern peatland) is beneath a black spruce (Picea mariana) forest canopy. Sphagnum and low ericaceous shrubs (Rhododendron groenlandicum, Chamaedaphne calyculata, Vaccinium angustifolium) grow under and around the sensor shelter. The organic soil (peat), which is less than 3 m deep where air temperature is measured, is not stable for data recorders. Therefore, the shelter is mounted on three treated posts that extend below the maximum frost depth. Water tables are at or near the peat surface.
Vaisala (Louisville, Colorado) HMP60 temperature and humidity probes (https://s.campbellsci.com/documents/us/manuals/hmp60.pdf) were installed at all three locations. The first measurements were recorded on 2020-08-11 at South, 2015-08-15 at North, and 2017-08-29 at S2 bog. Air temperature values are accurate to 0.6 degree Celsius and rounded to the nearest 0.1 degree Celsius for reporting. Relative humidity values are accurate to 3 – 5 percent and are rounded to the nearest tenth of a percent. Values are not normalized to sea level. Relative humidity has not been calibrated and we rely solely upon manufacturer calibration. Relative humidity values between 100 and 108 percent are recorded as 100 percent. HumiCap relative humuididty chips were replaced at South and S2 bog on 2024-02-13 and at North on 2024-02-14.
Barometric pressure is recorded using Apogee SB-100 sensors (https://www.apogeeinstruments.com/content/SB-100-manual.pdf). The first measurements were recorded on 2017-08-15 at South, 2017-08-29 at S2 bog, and 2015-08-15 at North. Barometric pressure is reported in kiloPascals (kPa) and is accurate to 1.5 kPa. The barometers at South and North are in the base of a co-located precipitation gage along with a Campbell Scientific Inc. (Logan, Utah) CR1000 datalogger. Since 2020-10-07 the barometer at S2 bog is located inside the shelter with the air temperature/relative humidity sensor. Prior to that it was in a sealed shelter approximately 15 feet from the NWS shelter.
Measurements are recorded at 30 minute intervals. Time is recorded in Central Standard Time. Air temperature data from the S2 bog site prior to 2020-01-01 were suspicious at air temperatures at or below -18 degree Celsius and were changed to NA. Missing values are not gap-filled.
We request courtesy notification to stephen.sebestyen@usda.gov if the data are used in a publication, that this data release be fully cited, and that the Northern Research Station of the USDA Forest Service be acknowledged for funding the long-term research and monitoring program at the MEF. Contact the lead author for more information or when seeking guidance on research regarding these data. The Forest Service MEF research team welcomes collaborative engagement regarding these and other MEF data.
The MEF is operated and maintained by the USDA Forest Service, Northern Research Station. The S2 catchment is located on US federal government land that is part of the Chippewa National Forest.
