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Minute and daily data from the meteorological tower at the Smithsonian Environmental Research Center (SERC)

We have published two data files that contain minute-scale meteorological data and aggregations of those data at the daily scale. This document describes the basic collection and processing of the data, the variables used, and some of the filters and interpolation strategies used to gap-fill and correct the data. A more detiailed exposition of this workflow can be found in the Updater markdown file, where the code that actually processes the data is presented and described. The original data and unfilled data are available on request if a user wishes to use their own gap-filling algorithms.

Sensors and data description

Description of sensors used to collect the data SERC collects weather data using various instruments located on top of a 40 m tower, located at 38.89 N, 76.56 W (NAD27), near the Mathias Laboratory on the SERC campus. Additional observations are made at a forest floor (below canopy) site located ~30 m to the west of the tower. Meteorological observations at the tower site began in 2002. Previously, routine observations were made at ground level location near the Schmidt Center also near the Mathias Laboratory.

For a full description of instrumentation see file from this instrument description document which describes the instrumentation deployed by the SERC Photobiology Lab.

Climate variables collected and calculated There are six data files published in this collection, described in Table 1. Data collected from the sensors include observed variables, such as temperature and relative humidity, and calculated variables, such as vapor pressure deficit (VPD). Table 2 presents the variables for minute file, while Table 3 for daily files, along with their units. Most users would want to use daily or minute data without gaps–these are provided by gap-filling with climatic averages described below. The percentage of data missing before this gap-filling is presented in Table 4 & Table 5.

Filtering, corrections, and gap-filling

Missing data Note that significant gaps exist in the data for Temperature and Relative Humidity. Forest Floor Temperature and Relative Humidity readings are problematic from August 1, 2013 until end of 2014. For Tower Top they are problematic from Jan 2015 through March 9, 2017 (new sensor unit was installed 3/9/2017).

Over any long data gathering period, instruments change. That is the case with this data. Most importantly, instruments degrade and are replaced or re-calibrated. For a full account of instrument changes and data adjustment issues see Updater markdown file and documentation from the SERC Photobiology lab.

Filtering In the minute data, Temp.tower is removed when RH.tower > 100 during January-01-2015 to November-13-2015 and February-08-2016 to March-09-2017. RH.tower is flagged in column tower.RH.Flag as 0 from January-01-2015 to November-13-2015 (records ~ 6% lower RH), while from February-08-2016 to March-09-2017 RH.tower is removed. RH.floow and RH.tower values < 10 are also removed.

Beyond the imposed limits in Table 2, seasonally removals of daily data were made according to the following:

Temperatures < 4 \(^\circ\)C in summer (doy > 150 & doy < 270) Temp < 4 \(^\circ\)C in summer (doy > 150 & doy < 270) are also removed. Temp < 4 \(^\circ\)C in summer (doy > 150 & doy < 270) are also removed.

In daily summary data RHmax in summer (doy > 150 & doy < 330) below 30%, RHmin below 10%, Tmax below 4 deg C and Tmin below 0 deg C are considered unacceptable and removed.

Replacing seasonally unacceptable extremes

RHmax in summer below 30 looks unacceptable RHmax.floor[Julian >150 & Julian < 330 & RHmax.floor < 30] <- NA RHmax.tower[Julian >150 & Julian < 330 & RHmax.tower < 30] <- NA RHmin in summer below 10 looks unacceptable RHmin.floor[Julian > 130 & Julian < 330 & RHmin.floor < 10] <- NA RHmin.tower[Julian > 130 & Julian < 330 & RHmin.tower < 10] <- NA

Tmax in summer below 4 looks unacceptable Tmax.floor[Julian > 150 & Julian < 270 & Tmax.floor < 4] <- NA Tmax.tower[Julian > 150 & Julian < 270 & Tmax.tower < 4] <- NA Tmin in summer below 0 looks unacceptable Tmin.floor[Julian > 150 & Julian < 270 & Tmin.floor < 0] <- NA Tmin.tower[Julian > 150 & Julian < 270 & Tmin.tower < 0] <- NA

Gap-filling Daily summaries of missing data as well as data removed as above, —for Forest Floor alone– are gap-filled from green-house data. Remaining gaps in daily data are filled with climatalogical means (doy means). All gaps in minute data are filled with climatalogical means (doy-minute means).

-See figures below to get a general sense of raw data issues, variables and periods covered in the package datasets, data gaps therein, trends over the years and between Tower Top and Forest Floor.

-This package is updated using file Updater markdown file

-This data should be cited as: Chitra-Tarak, Rutuja, Sean M. McMahon, Patrick J. Neale. Smithsonian Online Libraries. A data-package for the Smithsonian Environmental Research Center, Maryland high resolution meteorological tower data. 2002-2019.v1. DOI: 10.25573/data.9981506

Table 1 Data products in this package

Files are provided in both .Rda and .h5 formats.

S.N.	Data product object	Description	Variables & Units	Details
1	SERC.daily.data	This is daily mettower from either SERC_daily_data.Rda or SERC_daily_data.h5 data gap-filled with climatic means for the DOY.	See Table 3
2	SERC.minute.data	This is minute mettower data from either SERC_minute_data.Rda or SERC_minute_data.h5 gap-filled with climatic means for DOY-minute, or minute of the year	See Table 21	met_minute

Table 2: Minute data in minute scale datasets

This refers to the files SERC_minute_data.Rda and SERC_minute_data.h5.

Limits for time variables are the ranges in the data as they are–included to show the available date range, limits for other variables are imposed for cleaning. Saturated Vapour Pressure (SVP) is derived using temperature (Temp) based on Buck’s equation: SVP = 0.61121 x exp((18.678 - Temp/234.84) * (Temp/(257.14 + T))). Vapour Pressure Deficit (VPD) is derived using SVP and relative humidity (RH) as VPD = SVP x (1 – RH/100).

Column Header	Variable	Lower limit	Upper limit	Units/format
Year	Year	2002	2019	“YYYY” format
Month	Month	1	12	“MM” numeric format
Julian	Day of Year (DOY)	1	366	Numeric Day of Year
Hour	24 Hour format	1	24	24 Hour format
Date	Date	2002-01-15	2019-09-04	“YYYY-MM-DD” format
date.time	Date and time stamp	2002-01-15 10:03:00	2019-09-04 00:00:00	“YYYY-MM-DD hh:mm:ss EST/EDT” format
Precip.tower	Precipitation	0	300	mm
Ws.tower	Wind speed measured at tower height	0	50	m/s
Bp.tower	Barometric Pressure	90	104	kPa
Rs.floor	Incoming Solar Radiation (total short wave 290-2800 nm) at Forest Floor	-10	1500	W/m2
Rs.tower	Incoming Solar Radiation (total short wave 290-2800 nm) at Tower Top	-10	1500	W/m2
Temp.floor	Temperature at Forest Floor	-25	50	degree Celsius
Temp.tower	Temperature at Tower Top	-25	50	degree Celsius
RH.floor	Relative Humidity at Forest Floor	10	100	%
RH.tower	Relative Humidity at Tower Top	10	100	%
tower.RH.Flag	0 if RH falls in problematic date-range 2015-01-01 to 2015-11-13 (records ~ 6% lower RH yet retained), else 1
SVP.floor	Saturated Vapor Pressure at Forest Floor	0	20	kPa
SVP.tower	Saturated Vapor Pressure at Tower Top	0	20	kPa
VPD.floor	Vapor Pressure Deficit at Forest Floor	NA	NA	kPa
VPD.tower	Vapor Pressure Deficit at Tower Top	NA	NA	kPa

Table 3: Daily summaries in daily scale datasets

This refers to variables in the objects from either SERC_daily_data.Rda or SERC_daily_data.h5.

Column Header	Variable	Unit/format
Date	Date	“YYYY-MM-DD” format
Year	Year	“YYYY” format
Month	Month	“MM” numeric format
Julian	Day of Year (DOY)	Numeric Day of Year
Precip.tower	Daily Total Precipitation	mm
Ws.tower	Daily Mean wind speed measured at tower height	m/s
Bp.tower	Daily Mean Barometric Pressure	kPa
Rs.floor	Daily Total Incoming Solar Radiation at Forest Floor	KW/m^2
Rs.tower	Daily Total Incoming Solar Radiation at Tower Top	KW/m^2
Tmax.floor	Daily Maximum Temperature at Forest Floor	degree Celsius
Tmax.tower	Daily Maximum Temperature at Tower Top	degree Celsius
Tmin.floor	Daily Minimum Temperature at Forest Floor	degree Celsius
Tmin.tower	Daily Minimum Temperature at Tower Top	degree Celsius
RHmax.floor	Daily Maximum Relative Humidity at Forest Floor	%
RHmax.tower	Daily Maximum Relative Humidity at Tower Top	%
RHmin.floor	Daily Minimum Relative Humidity at Forest Floor	%
RHmin.tower	Daily Minimum Relative Humidity at Tower Top	%
tower.RH.Flag	0* = if day that contains at least one minute datum that falls in problematic date-range 2015-01-01 to 2015-11-13 (records ~ 6% lower RH yet retained), else 1
SVPmax.floor	Daily Maximum Saturated Vapor Pressure at Forest Floor	kPa
SVPmax.tower	Daily Maximum Saturated Vapor Pressure at Tower Top	kPa
VPDmax.floor	Daily Maximum Vapor Pressure Deficit at Forest Floor	kPa
VPDmax.tower	Daily Maximum Vapor Pressure Deficit at Tower Top	kPa

Figure 1. Mettower daily data gap-filled with climatic means.

Figure 2. Daily Met data at Tower Top after cleaning (using ‘met_daily.Rda’). Remaining eorroneous data can be spotted here. As described in Table 2 seasonal cutoffs are used, currently: Temp < 4 deg c in summer (doy > 150 & doy < 330) are removed.

Figure 3. Daily Forest Floor data after cleaning as well as gap-filling from Green house station (using ‘metbottom.filled.Rda’). Remaining eorroneous data can be spotted here. As described in Table 2 seasonal cutoffs are used, currently: Temp < 4 deg c in summer (doy > 150 & doy < 330) removed.

Figure 4. Seasonal contrast between Tower Top and Forest Floor. Daily data are shown after cleaning and, additionally for forest floor, after gap filling from SERC Greenhouse station (using ‘metbottom.filled.Rda’).

Figure 5. Seasonal contrast between Tower Top and Forest Floor. Daily climatic mean +- SE are shown after cleaning and, additionally for forest floor, after gap filling from SERC Greenhouse station (using ‘clim.Rda’).

Figure 6. Annual summary met data for Met Tower Top and Forest Floor afer cleaning (using ‘metbottom.filled.Rda’).

Table 4 Percent gaps in minute data (met_minute.Rda) before gap-filling with climatic means

var	percent_missing
date.time	0.00
Year	0.00
Month	0.00
Julian	0.00
Hour	0.00
date	0.00
Temp.floor	15.43
RH.floor	15.29
Precip.tower	7.33
Ws.tower	7.33
Bp.tower	7.46
Temp.tower	10.24
RH.tower	11.05
Rs.floor	7.82
Rs.tower	7.48
tower.RH.Flag	7.33
SVP.tower	8.68
SVP.floor	15.04
VPD.tower	11.99
VPD.floor	15.29

Table 5 Percent gaps in daily data (metbottom.filled.Rda) before gap-filling with climatic means

var	percent_missing
date.time	0.00
Year	0.00
Month	0.00
Julian	0.00
Hour	0.00
date	0.00
Temp.floor	15.43
RH.floor	15.29
Precip.tower	7.33
Ws.tower	7.33
Bp.tower	7.46
Temp.tower	10.24
RH.tower	11.05
Rs.floor	7.82
Rs.tower	7.48
tower.RH.Flag	7.33
SVP.tower	8.68
SVP.floor	15.04
VPD.tower	11.99
VPD.floor	15.29