TITLE: CEOP EOP-3 and EOP-4 GAPP ARM SGP Meteorological Tower Data Set CONTACT: Raymond McCord Building 1507 PO Box 2008, MS 6407 Oak Ridge, TN 37831-6407 Telephone: (865) 574-7827 Fax: (865) 574-4665 E-Mail: firstname.lastname@example.org 1.0 DATA SET OVERVIEW 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: http://www.arm.gov 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. 2.0 INSTRUMENTATION DESCRIPTION The ARM 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. 3.0 DATA COLLECTION AND PROCESSING 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: http://www.joss.ucar.edu/ghp/ceopdm/refdata_report/ceop_met_tower_format.html UCAR/JOSS took the 30-minute data values provided by ARM without change. 4.0 QUALITY CONTROL PROCEDURES 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 . 30 MINUTE DATA: 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 summaries 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. 5.0 GAP FILLING PROCEDURES No gap filling procedures were applied to these data by either ARM or UCAR/JOSS. 6.0 DATA REMARKS 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 period. 6.5 25 and 60 m Air Temperature, RH, dewpoint, and specific humidity incorrect 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. 7.0 REFERENCE REQUIREMENTS To support the continuation of this program, please include the following 'credit line' in the acknowledgments of your publication: "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." 8.0 REFERENCES 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: http://www.arm.gov/instruments/static/towert.stm.