TITLE: CEOP EOP-3 and EOP-4 GAPP ARM SGP Meteorological Tower Data Set


Raymond McCord
Building 1507
PO Box 2008, MS 6407
Oak Ridge, TN 37831-6407

Telephone: (865) 574-7827
Fax: (865) 574-4665

E-Mail: mccordra@ornl.gov


This data set contains 30-minute resolution meteorological tower data 
from the Coordinated Enhanced Observing Period (CEOP) Global Energy 
and Water Cycle Experiment (GEWEX) Americas Prediction Project (GAPP) 
Reference Site operated by the Atmospheric Radiation Measurement (ARM) 
Program at its Southern Great Plains (SGP) facility in Kansas and 
Oklahoma.  This data set includes meteorological tower observations 
from one location.  This data set covers the time period 1 October 2002 
through 31 December 2004.  Further information about the ARM SGP site is 
available at the following URL: 

1.1  Station Locations

Site       State    Elev (m)  Latitude  Longitude   Surface Type
C1_Lamont   OK        314     36.607 N   97.489 W   Pasture & Wheat

1.2 Time Period Covered by Data

Site           Start Date       End Date
C1_Lamont      1 October 2002   31 December 2004

1.3  Temporal Resolution

All data are 30-minute resolution.  See the instrumentation section for
further information.



Tower Handbook contains complete information.  Highlights from that document
are included here.

The ARM SGP surface meteorological measurements are from the 60 m
tower at the central facility.  Air temperature and moisutre parameters are
measured at the 25 and 60 m levels of the tower.

2.1.1 Expected uncertainties

Temperature: +/-2 degrees C
Relative Humidity: +/-2% (0-90% RH); +/-3% (90-100% RH)

2.1  Sensors

West Elevator:

Air temperature: Platinum Resistance Temperature Detector (PRTD), 
100 ohm, Minco Products Inc., Model S853PD60X72; Detection Limits -30 to 
40 deg C; Operating Temperature Range -40 to 50 deg C; 
Accuracy +/- 0.2 deg C.

Relative Humidity: Vaisala Inc. HMP35D or HMP45D; Humicap capacitive 
relative humidity element; Detection Limits 0% to 100% RH; 
Accuracy +/- 2% (0-90% RH) and +/- 3% (90-100%) over a temperature range 
of -20 to 50 degrees C; uncertainty of RH calibration +/- 1%.

Motor Aspirated Radiation Shield:Qualimetrics, Inc. Model 8151-B with 
flow sensor; nominal ventilation rate 1.83 m per sec into inlet; 
radiation error 0.05 degree C; operating temperature range -40 to 55 
degrees C. Wind speeds over 10 m per second, particularly from the south 
can reduce the ventilation rate in the radiation shield; uncertainties 
are thought to be negligible due to this effect as radiation errors from 
heating of the radiation shield are reduced in high wind speeds.

Flow Sensor: Qualimetrics Model T450009; this sensor is a heated element 
type sensor that detects changes in air flow via a relay sensing of a 
gap that is dependent on the maintenance of a particular temperature in 
a coil.

Southeast Elevator:

Temperature and Relative Humidity: Vaisala Inc. HMP35D or HMP45D;

Air Temperature: Platinum Resistance Temperature Detector (PRTD), 
100 ohm; Detection Limits -30 to 40 deg C; Operating Temperature Range 
-40 to 50 deg C; Accuracy +/- 0.2 deg C.

Relative Humidity: Humicap capacitive relative humidity element; 
Detection Limits 0% to 100% RH; Accuracy +/- 2% (0-90% RH) and +/- 3% 
(90-100%) over a temperature range of -20 to 50 degrees C; uncertainty 
of RH calibration +/- 1%.

Motor Aspirated Radiation Shield:R. M. Young Model 43408/43482 ; nominal 
ventilation rate 3 m per sec into inlet; radiation error 0.05 degree C;
operating temperature range -40 to 55 degrees C. Uncertainties are 
thought to be negligible. 


3.1  ARM Data Collection and Processing

Duplicate sets of instrumentation are used at heights of 25 m and 60 m 
on the SGP CART Central Facility 60 m tower. The probes and aspirated 
radiation shields are mounted on both the west and southeast elevator 
systems. A separate Campbell CR10X datalogger (previously, CR21X 
datalogger) is used for each level on the west elevator to measure 
sensor outputs, perform conversions to engineering units, and provide 
serial output for the remote collection of data from the datalogger 
memory. The same functions are accomplished for both levels on the 
southeast elevator with one CR10X. The meteorological measurements 
made with the system are:

    Air temperature at two heights (25 m and 60 m)
    Relative humidity at two heights (25 m and 60 m)
    Aspiration status (west elevator only)

3.2  UCAR/JOSS Data Processing

The University Corporation for Atmospheric Research/Joint Offfice for
Science Support (UCAR/JOSS) converted the data from the raw format
provided by ARM into the CEOP EOP-3 data format agreed to by
the CEOP Scientific Steering Committee.  This format is described
in detail as part of the CEOP Reference Site Data Set Procedures
Report which is available at the following URL:


UCAR/JOSS took the 30-minute data values provided by ARM without change.


4.1  ARM Quality Control Procedures

For detailed information on tower quality control procedures please
see the ARM
Tower Handbook.

Some automated data quality checks are included in the processed Tower netCDF
files. Specifically, QC flags are included in the files for the 30-minute data,
but not in the files for the 1-minute and daily data. Explanation of these flags
is given below .


Variable: temp; min = -50 deg. C, max = 50 deg. C.

Explanation: The minimum and maximum bracket a range of temperature that is
greater than what is expected at either the 25 or 60 meter levels of the tower
during any season. Temperatures outside of this range should be compared with
other local temperature measurements (SMOS, EBBR) to determine if the tower
temperatures are reasonable.

Variable: rh; min = 0%, max = 102%.

Explanation: Relative humidities outside of this range are not natural. The
capacitive relative humidity element is subject to an offset drift of up to 0.04
per year; this results from aging of the element materials and from contamination
by soil, etc. The max QC flag alerts the user to the possibility that an offset
drift has occurred. The drift is most easily quantified during saturated (100% RH)
conditions, by the excess over 100. It is not always possible to determine when
saturated conditions occur at 25 and 60 meters from SMOS and EBBR measurements at
the surface. However, relative humidity measurements from those systems may
indicate periods when saturation at 25 and 60 meters is possible. Normally it is
not too difficult to see saturation periods, as the relative humidity will remain
at the same high value for multiple 30 minute periods.

Variable: vap_pres; min = 0 kPa, max = 10 kPa.

Explanation: Vapor pressure values outside of this range are not natural. The
vapor pressure is a calculated quantity and may be outside of the range because
temperature or relative humidity (from which vapor pressure is calculated) are
incorrect. SMOS vapor pressure measurements may be consulted to help determine if
the tower vapor pressures are correct.

Variable: aspirator; min = 90, max = 100.

Explanation: Aspiration values below 90 (west elevator system only) may indicate
insufficient aspiration to produce accurate temperature and relative humidity
measurements, during at least part of the 30 minute averaging period. The one
minute data may be used to better determine periods of low aspirator status values
during a 30 minute period. Values above 100 are not real and may indicate failure
of the flow sensor in the aspirated radiation shield. Values less than or equal to
zero may indicate failure of the aspirator fan, and thus indicate that no
aspiration was present in the aspirator radiation shield.

The 60-m Tower Instrument Mentor (David Cook) performs a number of tasks to assure
the quality of its data.  Data quality control procedures for this system are
considered to be mature.

QC frequency: Once per week
QC delay: Not specified
QC type: Data flags; graphical plots, comparisons to BBSS data
Inputs: Data plots; printouts of tables of 1- and 30-min tower data; metadata
Outputs: DQRs; summary report to SGP Site Scientist Team
Reference: N/A

The instrument mentor attempts to inspect the tower T and RH data weekly. He
reports data deficiencies to data users via DQRs and to site operators via DQPRs,
and periodically sends status reports to the SGP Data Quality Office.

He inspects data plots on the SGP Data Quality Health and Status website to look
for obvious problems and identify approximate times of problems. Printouts of
tables of 1- and 30-min tower data provide detailed information. Periodic
comparison with the BBSS data also helps in interpreting problems. The mentor uses
computer programs to compare some of the tower data to data from the SMOS and EBBR
at the Central Facility. He reads DQPR entries and other metadata to determine
when and how preventative and corrective maintenance responds to work requests,
and instances when the carriages are not at their normal parked levels. 

4.2  UCAR/JOSS Quality Control Procedures

UCAR/JOSS converted the ARM QC flags into the CEOP QC flags in the 
following manner.  If a parameter failed one of the ARM QC checks it was 
flagged as Questionable/Dubious ("D") and if it failed two or more ARM 
QC checks it was flagged as Bad ("B").  Additionally, ARM issues Data
Quality Reports (DQRs) anytime problems are noticed within the data stream
(e.g. failing instruments, calibration periods, etc).  UCAR/JOSS has
examined the DQRs issued by ARM over this time period (over 140 DQRs were
issued) and determined when the parameters included within this data set
may have been impacted and flagged the data either "D" or "B" based on the
description of the problem included in the DQR.  The ARM DQR's are provided
as part of the data set:

Additionally, UCAR/JOSS conducted two primary quality assurrance/control
procedures on the reference site data.  First the data has 
been evaluated by a detailed QA algorithm that verifies the format is 
correct, examines any QC flags, and conducts basic checks on data 
values.  Second, JOSS conducts a manual inspection of time series 
plots of each parameter.  Additional data quality flags are applied
during this stage.


No gap filling procedures were applied to these data by either


Temperature comparisons between the southeast and west sensors can show 
some differences. Strong solar heating can cause the west temperatures 
to be slightly higher than the southeast temperatures. This is most 
frequently seen during the summer.

6.1  60 m RH biased high (dew point and specific humidity also suspect)

08/02/2002 1913 UTC to 10/25/2002 1806 UTC

The 60 m RH was biased high during this period, but only when the RH
was above 65%.

6.2 25 and 60 m Air Temp and RH (and Dew Point/Specific Humidity) Incorrect

Start Date   Start Time	End Date	End Time
07/25/2002   1722	07/25/2002	1724
07/25/2002   1932	07/25/2002	1934
07/31/2002   2300	07/31/2002	2331
08/01/2002   1300	08/01/2002	1910
08/02/2002   1354	08/02/2002	1913
08/09/2002   2000	08/09/2002	2010
08/30/2002   1342	08/30/2002	1416
09/03/2002   1847	09/03/2002	1851
09/03/2002   1937	09/03/2002	2032
09/10/2002   1734	09/10/2002	1843
09/23/2002   1931	09/23/2002	1946
10/02/2002   1723	10/02/2002	1741
10/09/2002   1426	10/09/2002	1510
10/24/2002   1418	10/24/2002	1436
10/25/2002   1806	10/29/2002	2155
10/29/2002   2155	10/31/2002	1621
10/31/2002   1914	10/31/2002	0229

The CF Tower 25M and 60M Southeast (10X) T, RH, VP were Incorrect during the periods
indicated for a variety of reasons, some known and some unknown, including:

08/01/02 - 08/02/02 Tower Maintenance and Annual T/RH calibrations/checks
10/24/02 - MFR repairs
10/25/02 - T/RH replacement
10/25/02 - 10/31/02 Jumper not on 60M T/RH sensor

Half hour values just after the end time of these periods may also be incorrect; a 
separate DQR has not been submitted for these.

6.3  25 and 60 m Air Temp and RH (and Dew Point/Specific Humidity) incorrect

The SGP 60 m Tower carriages were lowered or other
maintenance performed that caused the 25 m and 60 m
T/RH/VP data to be incorrect.  30 minute data ending
at the half hour after the end times are suspect.

6.4  25 m Air Temperature (and Dew Point/Specific Humidity) Incorrect

12/21/2002  0128	12/21/2002	0140

The southeast side Temperature at 25 m was unchanging for a long

6.5  25 and 60 m Air Temperature, RH, dewpoint, and specific humidity

12/22/2002	0809	12/22/2002	1029

The measurements on both sides of the Tower were basically unchanging
during the period.

6.6  60 m RH, dewpoint and specific humidity suspect

12/13/2002	0820	12/13/2002	0944

After a period of saturation conditions, the 60 m SE RH 
did not recover immediately, and therefore produced RH and Vapor Pressuer measurements 
that are too high during this period.

6.7  60 m Air Temperature, dewpoint, specific humidity suspect

12/09/2002	0409	12/09/2002	0456
12/09/2002	0641	12/09/2002	0655
12/09/2002	1224	12/09/2002	1256
12/10/2002	0408	12/10/2002	0700
12/10/2002	0850	12/10/2002	0858
12/20/2002	1222	12/20/2002	1311
12/21/2002	0507	12/21/2002	1320
12/24/2002	0422	12/24/2002	0714
12/24/2002	1331	12/24/2002	1425
12/25/2002	2106	12/25/2002	2218
12/26/2002	1810	12/26/2002	1826
12/29/2002	0334	12/29/2002	0440
12/29/2002	0455	12/29/2002	0528
12/29/2002	0551	12/29/2002	0610
01/02/2003	1214	01/02/2003	1245
01/03/2003	0819	01/03/2003	1338

During these periods the Southeast side 60 m Temperature was unchanging
(flat).  This can occur for several consecutive minutes, but not for as long as occurred 
here. Therefore the Temperature and Vapor Pressure measurements

6.8  25 and 60 m air temp, dew point, relative/specific humidity

01/30/2003	1655	01/30/2003	1814
02/21/2003	1955	02/21/2003	2057
02/22/2003	1917	02/22/2003	2110
03/17/2003	1622	03/17/2003	1740
03/21/2003	1825	03/21/2003	2027

Temperature, relative humidity, and vapor pressure were
incorrect during maintenance on systems on the SE elevator.


To support the continuation of this program, please include the
following 'credit line' in the acknowledgments of your

"Data were obtained from the Atmospheric Radiation Measurement
(ARM) Program sponsored by the U.S. Department of Energy, Office
of Science, Office of Biological and Environmental Research,
Environmental Sciences Division."


Further information on ARM SGP tower instrumentation (including QC, calibration,
maintenance, theory of operation, and references) can be found at the
ARM 60-m tower web page: