TITLE: CEOP Other ARM TWP Surface Meteorology and Radiation 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 surface meteorology and radiation data from the Coordinated Energy and Water cycle Observation Project (CEOP) Reference Site operated by the Atmospheric Radiation Measurement (ARM) Program at its Tropical Western Pacific (TWP) facility. This data set includes observations from three locations. This data set covers the time period 1 October 2002 through 31 December 2009. Further information about the ARM NSA site is available at the following URL: http://www.arm.gov 1.1 Station Locations Site Elev (m) Latitude Longitude ------------------------------------------------- C1_Manus 4.0 -2.06 147.425 C2_Nauru 7.1 -0.521 166.916 C3_Darwin 29.9 -12.425 130.892 Note: The location of C3_Darwin changed on 19 May 2004. Prior to that date the location was -12.425 latitude, 130.891 longitude and 29.9 m elevation. Starting 19 May and continuing to the end of EOP-4 it was the location in the table above. 1.2 Time Period Covered by Data All stations cover the complete EOP-3 and EOP-4 period (1 October 2002 to 31 December 2009). 1.3 Temporal Resolution All data are 30-minute resolution. See the instrumentation section for further information. 2.0 INSTRUMENTATION DESCRIPTION The ARM TWP surface meteorological measurements at the TWP sites are from their Surface Meteorology (SMET) system (see section 2.1). The ARM TWP upwelling radiation measurements at the sites are from their GNDRAD system (see section 2.2) and the ARM TWP downwelling radiation measurements at the sites are from their SKYRAD system (see section 2.3). These stations provide observations of air temperature, dew point, relative humidity, specific humidity, wind speed, wind direction, U wind component, V wind component, station pressure, precipitation, incoming longwave, incoming shortwave, outgoing longwave, outgoing shortwave, net radiation, and skin temperature. None of these stations provide observations of incoming PAR, outgoing PAR, or snow depth. 2.1 SMET Sensors For complete information on the SMET instrumentation see the ARM SMET Handbook and the updated version released in March 2008 here. Highlights are provided here. 2.1.1 Wind Speed at 10 m A pair of propeller anemometers and wind vanes, R. M. Young Model 05106 Wind Monitors Precision: 0.01 m/s; Uncertainty: +/-1% for 2.5 to 30 m/s The NIST calibration uncertainty is specified as +/-1% for wind speeds from the sensor threshold to 30 m/s. The conversion error is negligible. The schedule of routine maintenance and sensor verification is designed to eliminate any long-term stability error. The sensor threshold is specified as 1 m/s. The following estimates of the range of underestimation caused by the threshold assume a normal distribution of wind speeds about the mean. When the true wind speed is 1.0 m/s, the winds will be below the threshold 50% of the time. This will result in an underestimate of 0.5 m/s. When the true wind speed is 1.5 m/s, assuming the standard deviation will be between 0.25 and 1.00 m/s, the winds will be below the threshold between 2 and 31% of the time. This will result in an underestimate between 0.02 and 0.23 m/s. When the true wind speed is 2.0 m/s with a range of standard deviations between 0.25 and 1.00 m/s, the winds will be below the threshold between 0 and 16% of the time. This will result in an underestimate between 0 and 0.12 m/s. If the reported wind speed is 0.5 m/s, an underestimate of 0.5 is probable. This would bias the measurement by -0.5. If the reported wind speed is 1.0 m/s, an underestimate of 0.19 to 0.30 m/s is possible. If the reported wind speed is 1.5 m/s, an underestimate of 0.02 to 0.20 m/s is possible. If the reported wind speed is 2.0 m/s, an underestimate of 0 to 0.10 m/s is possible. The uncertainty range with 95% confidence is approximately: +/- 1% for a reported wind speed from 2.5 to 30.0 m/s -0.12 to +0.02 m/s for a reported wind speed of 2.0 m/s -0.22 to +0.00 m/s for a reported wind speed of 1.5 m/s -0.31 to -0.20 m/s for a reported wind speed of 1.0 m/s -0.51 to -0.49 m/s for a reported wind speed of 0.5 m/s 2.1.2 Wind Direction at 10 m A pair of propeller anemometers and wind vanes, R. M. Young Model 05106 Wind Monitors Precision: 0.1 deg; Uncertainty: +/-5 deg The sensor accuracy is specified as +/-3 deg. The A-D conversion accuracy is equivalent to ± 0.7 deg over a temperature range of 0 to 40 deg C for a period of one year. I have estimated sensor alignment to true north to be accurate within +/-3 deg. The uncertainty with 95% confidence is, therefore, approximately +/-5 deg. 2.1.3 Air Temperature at 2 m Platinum RTD and RH, Vaisala Model HMP35A Temperature and Relative Humidity Probe Precision: 0.01 C; Uncertainty: +/-0.41 C The accuracy of the temperature measurement is +/-0.1 C. The long-term stability is not known. The radiation error of the aspirated radiation shield is specified as +/-0.2 C rms. The uncertainty with 95% confidence of temperature sensors in this radiation shield is, therefore, about +/-0.41 C. 2.1.4 Humidity at 2 m Platinum RTD and RH, Vaisala Model HMP35A Temperature and Relative Humidity Probe Precision: 0.1% RH; Uncertainty: +/-2% RH (0% to 90% RH), +/-3% RH (90% to 100% RH) The accuracy of the sensor is specified as +/-2% RH for 0 to 90% RH, and +/-3% RH for 90 to 100% RH. Errors considered in this accuracy are calibration uncertainty, repeatability, hysteresis, temperature dependence, and long-term stability over a period of one year. The A-D conversion accuracy is equivalent to +/-0.05% RH, which is negligible. 2.1.5 Barometric Pressure at 1 m Digital barometer, Vaisala Model PTB201A Precision: 0.01 kPa; Uncertainty: +/-0.035 kPa The manufacturer's technical data contains an uncertainty analysis. Errors included in their analysis are linearity, hysteresis, calibration uncertainty, repeatability, temperature dependence, and long-term stability over a period of one year. Because the sensor has a digital output, no conversion error occurs in the data logger. The specified uncertainty with 95% confidence is +/-0.035 kPa. Note that the pressure behaves anomalously during rain events - even very mild ones. Normally, the pressure undergoes a smooth semi-diurnal oscillation with little higher frequency variability. However, during and shortly after rain events, the pressure signal exhibits abrupt changes. 2.1.6 Precipitation Optical precipitation gauge, Scientific Technology, Inc. Model ORG-115-DA Mini-Org Precision: 0.1 mm/hr; Uncertainty: +/-0.1 mm/hr The Optical raingauge has an uncertainty of +/-0.1 mm/hr. Values that fall between -0.1 mm/hr and +0.1 mm/hr should be considered 0 mm/hr. In other words, no rainfall is ocurring. 2.1.7 System Configuration The SMET sensors are mounted on a 10-meter mast, except for the rain gauge. The wind monitor propeller anemometers produce a magnetically controlled AC output whose frequencies are proportional to the wind speed. The Wind Monitor direction vanes drive potentiometers, which are part of resistance bridges. Two Wind Monitors are mounted on a cross-arm at a height of 10 m. One is mounted slightly above the other in order to minimize interference. The higher wind monitor is designated sensor #1 and the lower wind monitor is designated sensor #2 The T-RH probe 4-lead, platinum resistance thermometer is part of a resistance bridge. The Vaisala RH circuitry produces a voltage that is proportional to the capacitance of a water vapor absorbing, thin polymer film. The T-RH probe is mounted in an R. M. Young Model 43408 Gill Aspirated Radiation Shield at a height of 2 m. The barometric pressure sensor uses a silicon capacitive pressure sensor and is housed in a water-tight enclosure along with the data logger. The optical precipitation gauge detects scintillation of an infrared beam caused by liquid water in the path. It is located near the tower. The data logger measures each input once per second except for barometric pressure, which is measured once per minute, and logs 1-min averaged data. Vapor pressure is computed from the air temperature and relative humidity. The data logger produces 1-min averages, minimums, maximums, and standard deviations of wind speed, air temperature, relative humidity, and rain rate. It also produces 1-min vector-averaged wind speed and direction, a 1-min standard deviation of the wind direction computed by an algorithm, 1-min averages and standard deviations of vapor pressure, a 1-min maximum wind gust speed, and a reading of the barometric pressure, internal temperature, and the external and internal supply voltages. The time reported for the 1-min statistics is the time of the last sample. 2.2 GNDRAD Sensors For complete information on the GNDRAD instrumentation see the ARM GNDRAD Handbook. Highlights are provided here. Upward Directed Longwave Radiation The following radiometers manufactured by The Eppley Laboratory, Inc., are used at each GNDRAD. Measurement Radiometer Mounting Typical Typical Model Arrangement Responsivity Calibration (uV/Wm-2) Uncertainty* --------------------------------------------------------------- Upwelling PSP Inverted w/o 9.0 +/-3.0% or Shortwave ventilation 10 Wm-2 Upwelling PIR Inverted w/o 4.0 +/-2% or Longwave ventilation 2 Wm-2 *Field measurement uncertainties are larger and include the uncertainties associated with instrument calibration, installation, operation and maintenance. Additional information is available from http://www.eppleylab.com, http://www.nrel.gov/srrl/, and http://rredc.nrel.gov. The skin temperature is measured using an Infrared Temperature (IRT) sensor (Heimann KT 19.85 Infrared Radiation Pyrometer) 2.3 SKYRAD Sensors For complete information on the SKYRAD instrumentation see the ARM SKYRAD Handbook. Highlights are provided here. Instrument Description Wavelength PIR2 Precision IR Radiometer, Pyrgeometer 4.0 to 50.0 um PSP Precision Spectral Pyranometer 0.285 to 2.8 um NIP Normal Incidence Pyheliometer 0.285 to 2.8 um 3.0 DATA COLLECTION AND PROCESSING 3.1 ARM Data Collection and Processing For complete information on the SKYRAD instrumentation see the ARM SKYRAD Handbook. For complete information on the GNDRAD instrumentation see the ARM GNDRAD Handbook. For complete information on the SMET instrumentation see the ARM SMET Handbook and the updated version released in March 2008 here. 3.2 NCAR/EOL Data Processing The National Center for Atmospheric Research/Earth Observing Laboratory (NCAR/EOL) converted the data from the raw format provided by ARM into the CEOP reference site 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.eol.ucar.edu/projects/ceop/dm/documents/refdata_report The SMET, GNDRAD and SKYRAD provide 1 minute measurements, the observations at the 00 and 30 minute marks of every hour are included in the final data set. 4.0 QUALITY CONTROL PROCEDURES 4.1 ARM Quality Control Procedures Data are compared to upper and lower limits and flags are reported by the data logger. The flags are described in the netcdf header of each data file. No additional flags are applied during data ingest. For complete information on the SKYRAD instrumentation see the ARM SKYRAD Handbook. For complete information on the GNDRAD instrumentation see the ARM GNDRAD Handbook. For complete information on the SMET instrumentation see the ARM SMET Handbook and the updated version released in March 2008 here. 4.2 NCAR/EOL Quality Control Procedures NCAR/EOL 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, NCAR/EOL 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, EOL conducts a manual inspection of time series plots of each parameter. 5.0 GAP FILLING PROCEDURES No gap filling procedures were applied to these data by either ARM or NCAR/EOL. 6.0 DATA REMARKS 6.1 Precipitation values less than 0.1 mm/hr During normal operation, the sensor always puts out some voltage (background noise), even during clear sky conditions. The rain rate equation that is used to convert voltage to rain rate should only be applied to voltages equal to or above a certain fixed threshold. This threshold is different for each model(ORG-815 or ORG-115-DA mini-ORG). At values below the fixed threshold the equipment will report small values (some negative) at all times. Currently, the rain rate equation is used for all voltages reported by the sensor. The rain rates that correspond to voltages below the thresholds are between -0.1 mm/hr and +0.1 mm/hr. Therefore, such values should be considered by the data user to be 0 mm/hr. It is also possible that values between -0.15 mm/hr and -0.1 mm/hr may be reported as a result of very low voltages. These values should also be considered as 0 mm/hr. If values less than -0.15 mm/hr are reported then negative voltages are being used and this is an indication of a problem with the sensor. These values should be discarded. Any value equal to and above 0.1 mm/hr that are reported are good values since positive voltages above the thresholds are being reported and the rain rate equation is valid. 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 For complete information on the SKYRAD instrumentation see the ARM SKYRAD Handbook. For complete information on the GNDRAD instrumentation see the ARM GNDRAD Handbook. For complete information on the SMET instrumentation see the ARM SMET Handbook and the updated version released in March 2008 here.