Daily maximum and minimum temperatures are measured at three locations on the experimental forest. Daily air temperatures are available for two upland locations (S2 and S5) and one bog location (S2 Bog). Data collection at the S2 (South) upland site began in 1961 to the present, while data collection at the S5 (North) upland site began in 1962. Data collection at the S2 bog site began in July 1989.
The shelters at the upland sites are in open areas with grass that is mowed at least every 2 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 clearings are surrounded by mature aspen (Populus tremuloides, P. balsamifera, and P. grandidentata) stands. Though hardwood forest stands near snow course transects have not been managed, forest cover is shifting from overstory dominance of aspen to balsam fir (Abies balsamea), red maple (Acer rubrum), basswood (Tilia americana) and red oak (Quercus rubra). 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 shelter 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 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.
All three sites had Belfort model 594-1 hygrothermographs (data resolution 1-degree Fahrenheit) through 2019-012-31. Each site also has a US Weather Bureau style maximum and minimum thermometers (hereafter, max min thermometers) mounted on a Townsend Support (National Weather Service 2014). The instruments are housed in 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. The sites have been visited weekly and charts are changed during visits.
The max min thermometers were read weekly and reset during site visits. The weekly readings were recorded on charts. In the Grand Rapids Forestry Sciences Laboratory, the weekly maximum and minimum values were used to calibrate the hygrothermograph temperature recorder and to prorate the chart values if they differed. The daily maximum and minimum values were written on charts.
If the hygrothermograph malfunctioned (e.g. clock stops, pen stops inking, other mechanical issues), the daily temps were estimated from the max min thermometer readings and the chart from one of the other sites. A HOBO external temperature data logger (Onset Corporation, Part no. H08-031-08) has been paired with each hygrothermograph and records air temperature at 15-minute resolution. The Hobo sensors were installed during 1997 at the North and South sites, and September 1, 1999 at the S2 bog site. The HOBO data were used to gap-fill any missing max/min values through 2020-01-01. Gap-filled values during this period are not flagged. Beginning 2008-01-01, daily max/min data from the South station was recorded with the HOBO instead of the hygrothermograph. Hygrothermograph malfunctions were uncommon and never more than 1-7 days were affected since the sites were visited weekly. Hygrothermographs have been cleaned and lubricated on a yearly basis, or more frequently if subjected to an extreme dust, pollen, or insect event. Max min thermometers are calibrated with a distilled water ice bath.
Values were recorded in degrees Fahrenheit on paper tally sheets before the mid-1990s, and entered into Microsoft Excel spreadsheets thereafter. All entries were verified and data plots were observed to detect any suspicious values. The daily maximum and minimum entries were then converted to metric units and stored in a summary spreadsheet. All values are presented in degrees Celsius.
Beginning as early as 2015, Campbell Scientific HMP60 thermistors were installed in each National Weather Service shelter. They recorded the instantaneous air temperature at 30-minute intervals. Digital sensors and hygrothermographs were operated in the same shelter for an overlap period of at least one full year at all stations. The transition from hygrothermograph to HMP60 sensors occurred on 2020-01-01 at the North and S2 bog stations. Data are still recorded by the HOBO sensor at the South station. Adjustments for changes in sensor technology were not necessary. Beginning 2020-01-01, missing values are estimated according to linear regression with the best matched location and are indicated with a flag.
Prior to the transition, values recorded in Fahrenheit were converted to Celsius and rounded to the nearest whole degree Centigrade. After the transition, values are rounded to the nearest 0.5 degree Centigrade.
The sites and methods are described in further detail in the publication:
Sebestyen, S.D., C. Dorrance, D.M. Olson, E.S. Verry, R.K. Kolka, A.E. Elling, and R. Kyllander (2011). Chapter 2: Long-Term Monitoring Sites and Trends at the Marcell Experimental Forest. In Randall K. Kolka, Stephen D. Sebestyen, Elon S. Verry, and Kenneth N. Brooks (Ed.). Peatland Biogeochemistry and Watershed Hydrology at the Marcell Experimental Forest (pp 15-71). CRC Press, Boca Raton, FL. https://www.fs.usda.gov/treesearch/pubs/37979.
Citations:
National Weather Service (2014), National Weather Service manual 10-1315: Cooperative station observations and maintenance, 130 pp, National Weather Service.
