Cold air drainage transect studies at the Andrews Experimental Forest, 2002 to Present

CREATOR(S): Christopher Daly
ORIGINATOR(S): Christopher Daly
OTHER RESEARCHER(S): Joseph I. Smith, Adam M Kennedy, Greg M Cohn, David Rupp
20 Jul 2007
13 Dec 2019
Long-Term Ecological Research (LTER), meteorology, climatology, climate change, air temperature, topography, forest ecosystems
These data are being used to inform methods for downscaling regional climate maps using PRISM ( Specifically, data from these transects reveal patterns of cold air drainage and pooling in mountain valleys, and their relationships with regional weather conditions, topographic position, and the spatial scale of the valleys.
Experimental Design - MS036:
Description: Observed temperatures on “cold air” transects at 34 locations within the HJ Andrews Forest. The lower Lookout Creek transect (10 stations) is located just to the west of the concrete bridge, and intersects RS10. The upper Lookout Creek transect (11 stations) extends north from the north slope of Lookout Mountain, across Lookout Creek, and ends below the CENMET benchmark station. East of the upper transect, there is a short, 4-station transect across Cold Creek, a tributary of Lookout Creek. North of the upper transect, a 5-station cluster samples locations near a stream channel, above and below a spring. Single sensors are located downslope from the Roads End rain gauge near the southern border of the forest (high elevation, but locally low topographic position), and near the summit of Carpenter Mountain, on the northern border of the forest (high elevation, high topographic position, exposed to the free atmosphere). Two sensors will located temporarily in and above a sink northeast of the CENMET benchmark station. The upper and lower Lookout Creek transects were established in 2002, with others placed at later dates.
Field Methods - MS036:
Description: Data are sampled every 15 minutes with Hobo portable sensors mounted on rebar approximately 1.5 m above ground. Radiation shields are the “HJA short” type, which is made from PVC tubing, cut lengthwise and mounted above the sensor; sensors are open to the ground. Most sensors are located under dense forest canopy, with little solar radiation exposure. Many sensors also record illumination, which is useful in quantifying light exposure. Data are downloaded from the Hobo two times per year.
Processing Procedures - MS036:

Daily maximum and minimum temperature values for entity 1 are generated from the raw 15-min HOBO data files. The data are subjected to a series of QC checks including range, rate of change, sufficient number of observations, standard deviation, and multi-day persistence checks. For range checks, the values are compared to the state monthly record. If a value falls outside of 2.8 degree C buffer, the value is removed from further consideration. For the rate of change check, if the current temperature is not missing and within one hour of the previous valid temperature, the difference between the temperatures is calculated. If the temperature difference exceeds 10 degrees C, the current temperature is removed from further consideration. At this point, the maximum and minimum of all non-missing temperatures for the day become the daily maximum and minimum temperatures. To check if there were a sufficient number of observations for the day, if there were valid observations in less than 18 of the 24 hours in the day, the daily maximum and minimum temperatures are flagged as an insufficient number of hourly observations to generate a valid daily observation. The standard deviation of all observations for the day is calculated and if the standard deviation is less than 0.1 degrees C, the daily observations are flagged as having too little variation over the day to be considered valid. Finally, the daily observations are checked for multi-day persistence. The difference between successive daily observations is calculated and if the difference is 0.4 degrees C or less for more than 10 successive observations, all observations in the sequence (not already flagged by previous checks) are flagged as being too many days with the same value. There can be no more than two missing days between successive observations before the sequence is reset. The 0.4 degree C threshold was chosen to identify occurrences of drift in automated sensors. Maximum and minimum temperatures are tested for multi-day persistence independently to account for issues that affect only one end of the temperature range, or where maximum and minimum temperatures are measured independently.

The 15-minute QC'd data in entity 2 was a one-time process to create this dataset for publication and is separate from the processing of data in entity 1. The raw 15-minute data are first run through an R program that concatenates the separate files from the HOBO datalogger into a single, uniformly formatted, time series with time gaps filled with blank records. The concatenated data are then run through a Python program (hja_hobo_clean) created for the purpose of data quality assurance and quality control of HOBO temperature sensor data collected at the Andrews Forest. The program flags data based on user-specified parameters. The program can also remove flagged data (clean) and fill in missing data with regressed data from other sites, but these procedures where not used for these data. Visual inspection was also done of the data from some sites - those on the Lower Lookout (LL) and Upper Lookout (UL) transects only. Visual inspection consisted of comparing all sensors within a transect to identify suspect data (e.g., a sensor whose reading were clearly inconsistent with others and with its own previous patterns). For all sites, field notes were also used to identify data when a sensor may have been on ground and/or its radiation shield was broken. Lastly, data are run through a second R program that flags data based on results from the visual inspection and field notes.

Quality Assurance - MS036:
Description: The flags set for daily minimum and maximum data are single-station QC (SSQC) flags. Spatial consistency QC (SPQC) tests have not been applied to these data. If a daily value fails an SSQC test, the value is retained, but it is not passed to PRISM for use in modeling, as it has been determined that the value does not meet minimum requirements for inclusion. Users of these data should be aware of these short-comings with the flagged data.
Sites are selected along transects to represent elevational change moving in lateral directions away from a stream, or are clustered above or below a spring or depression. Two single points are selected at high elevations to represent one low and one high topographic position.
HJ Andrews Experimental Forest
Ground condition