Much of the early climatological measurements on the Andrews Forest were associated with the investigation of the initial small watersheds experiment (Watersheds 1, 2, 3). The Climatic Station on WS 2 was installed in 1956 to measure precipitation and a hygrothermograph was added in 1958. The High-15 station was established to measure precipitation in 1964 in conjunction with small watersheds 6, 7, 8, and has evolved into a secondary meteorological station. A more general set of modeling needs led to the installation of the Primary Meteorological Station in 1972 to characterize the meso-scale environment. Originally, solar radiation, air temperature, dew point temperature, and windspeed were collected. Along with precipitation from the climatic station on WS 2, these were the primary climatic variables needed for the models predicting the rates at which materials accumulate or move through ecosystems (Waring et al., 1978). Significant improvements to the station were made in 1975, 1979, and 1988, as the station evolved from chart recorders to state-of-the-art digital data loggers (Bierlmaier and McKee, 1989). The Vanilla Leaf Met Station was installed in 1987. The primary intent was to provide micro- meteorological data for a study of seedling survival following clearcut and shelterwood logging at high elevation. Ultimately, the shelterwood site was discontinued and the clearcut site has evolved as a primary high elevation meteorological station.
Four Benchmark Meteorological Stations (BMS) and two second-level stations are included in the MS001 database. The Primary Meteorological and Vanilla Leaf Meteorological BMS are retained. Two new BMS are installed. In 1994, the Upper Lookout Meteorological Station was established at high elevation (4200 ft, ENE aspect) on clearcut L708 in the SE Andrews. In 1995 the Central Meteorological BMS was established at a centrally located site on clearcut L351 (3300 ft, WSW aspect) in the east-central Andrews. A GIS analysis of elevation and aspect indicated the average elevation (3170 ft., 966 m) and average aspect (267 degrees) of the Andrews Forest, and the Central Met Station was located to represent these general averages. Modifications are made to the Primary and Vanilla Leaf Stations to standardize measured variables, temporal resolution, methods, and instrumention across all BMS. Sites will be cleared and required openings maintained following standards of the National Weather Service, the LTER network, and where appropriate, the NADP network. Telemetering of all BMS was completed in 1996. Second-level stations (SLS) at the Hi-15 and WS 2 Climatic Station will continue to be maintained for measurement of precipitation, temperature, and other data to maintain continuity of historical records. These sites also follow established procedural standards.
The BMS include meteorological measurement of air and soil temperature, relative humidity, calculated dew point temperature and vapor pressure deficit, wind speed and direction measurement, incoming solar radiation, photosynthetically active radiation (PAR), soil moisture, snow melt, and snow moisture and depth.
The follow link describes data collection methods (by date range and resolution) that have been used by each unique probe. Results are filtered by database code, sitecode, parameter, and probe.
https://andlter.forestry.oregonstate.edu/MethodCode/View_History.aspx
Please follow this link to view climate data collection methods that have been used over time at select stations. Results can be filtered by parameter, climate station, and date range. A general text search is also available.
https://hjandrews.shinyapps.io/im_methods_history/
Temperature data has been measured with a variety of instruments:
Probes were housed in locally designed PVC radiation shields from the 1980s until the mid 2000s. Gill radiation shields replaced the PVC shields at all of the benchmark sites after a significant concurrent comparison was made. Aspirated shields are also now in use. The original 1.5 meter Primary Met Station sensor was housed in a Cotton Region Shelter. Historical methods included Rustrak strip charts with thermister where air temperature is measured by a Yellow Springs Instruments linear thermistor in a standard Cotton Region Shelter and continuously recorded on a separate 30-day Rustrak strip chart scaled from -10 degrees C to 40 degrees C.
Data loggers are typically Campbell Scientific (CR10, CR21X, CR500, or CR23X). Early data loggers used in the 1980s are Interface Instrument models M-2, M-3, and M-4.
Dew Point is calculated from air temperature and relative humidity every sampling interval (generally every 15 seconds) and output hourly using Tetens Equation for the relation between temperature and the partial pressure of water vapor (see http://andrewsforest.oregonstate.edu/data/studies/ms01/dewpt_vpd_calculations.pdf). This is calculated for independent pairs of air temperature and relative humidity probes at 150 and 450 cm heights for all benchmark stations (except CS2MET which only has sensors at 150 cm height).
Historical methods at PRIMET used a heated lithium-chloride dew point sensor with a thermistor that recorded continuously on a separate 30-day Rustrak strip chart throughout the 1970s. An Interface Instrument hygrometer with linear thermister was used to measure dew point indirectly with a heated Interface Instrument lithium-chloride hygrometer with a linear thermistor from 1979 until 1988. The PRIMET early dew point sensors and subsequent air temperature and relative humidity sensors used to calculate dew point were located in the 150 cm height cotton shelter until May 2000. The cotton shelter was discontinued for dew point calculation and replaced with use of the 450 cm probe on the PRIMET tower.
Generally, relative humidity is output hourly and is measured at heights of both 150 and 450 cm at these benchmark stations using Vaisala sensors with Campbell data loggers. Early records at CS2MET employed a hygrothermograph sensor to record daily max-min relative humidity from within a Cotton Region shelter on a recording chart from 1958 to 1998. Standard maximum and minimum thermometers on a Townsend support and a sling psychrometer were used to make weekly corrections to the hygrothermograph chart readings.
Vapor pressure deficit values are calculated and output hourly from air temperature and relative humidity probes that sample every 15 seconds. Values are output in millibars and are collected at 150 and 450 cm heights at each of the four benchmark stations (PRIMET, CENMET, UPLMET, VANMET). The earliest hourly calculations were started at PRIMET in 1988 from air temperature and relative humidity sensors located in the 150 cm cotton shelter based on sampling every 15 seconds (in millibars). Please see the following for calculation details: http://andrewsforest.oregonstate.edu/data/studies/ms01/dewpt_vpd_calculations.pdf
Providing calculated vapor pressure deficit values was discontinued 9/30/2021.
Dewpoint and vapor pressure deficit equations can be found at:
http://andrewsforest.oregonstate.edu/data/studies/ms01/dewpt_vpd_calculations.pdf
A description of the early processing history and instrumentation for the Primary Meteorological Station (PRIMET), 1972-1989, is posted here:
http://andrewsforest.oregonstate.edu/data/studies/ms01/ms001_primet_1972_1989.pdf
