This dataset contains one-minute resolution surface meteorological data in University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) Quality Control (QC) format from stations within the following networks:
Section 2.0 contains a detailed description of the
instrumentation, siting, and algorithms used by the source network to collect
the data. Section 2.1 contains a detailed
description of the format of the composite dataset. See
Section 2.2 for information on data processing, and
Section 3.0 below for the quality control processing performed by UCAR/JOSS
on this dataset. Section 4.0 contains references.
The Automated Surface Observing System (ASOS) is an automated observing
system that is sponsored by the Federal Aviation Administration, National
Weather Service (NWS) and the Department of Defense (DOD). ASOS provides
weather observations which include: temperature, dew point, wind,
altimeter setting, visibility, sky condition, and precipitation.
ASOS stations are installed at airports throughout the country. All 41
stations that are in the IHOP area of interest are included in this IHOP
2002 One Minute Surface Composite.
The Automated Surface Observing Systems are designed to provide airport
weather observations in real time. The observing systems work nonstop,
updating observations every minute, 24 hours a day, every day of the year.
Aviation weather parameters are measured in the runway touchdown zone on
the airport.
The ASOS data are acquired by UCAR/JOSS via modem and a dial-in telephone
system. We typically called each station every 8 hours.
The ASOS uses a chilled mirror to determine the dew point
temperature. Once per day the mirror is heated to recalibrate
the reference reflection expected from a dry mirror (since a
clean mirror needs relatively less indirect light to determine
when dew has formed than a dry mirror). This procedure compensates
for a possible dirty or contaminated mirror and redefines adaptive
criterion value used to determine when dew or frost has occurred.
This once per day recalibration nominally takes about 15 min (
ASOS Users Guide, 1998
[ PDF]).
The occurrence time of this recalibration varies
from station to station. Some stations also vary the occurrence time of
the recalibration on about weekly intervals. In an effort to remove
the most extreme effects of this recalibration, JOSS has set to
missing any occurrence of dew point temperatures 5 degF or more
higher than the air temperature. There are often still a minute
or two of abnormally high dew points (mostly at sites in the drier
western portion of the IHOP domain), but these are typically flagged as bad by the
JOSS Horizontal Quality Control procedure ( Section 3.0).
This recalibration and reset to missing affects all ASOS stations.
There are three station pressures reported at each station for each time
period. The lowest sensor pressure value obtained, whose pressure difference from
either of the other sensors is 0.04 inch or less, is the designated ASOS pressure to
be reported at the end of the minute. If no two sensors are within 0.04 inch of each
other, then the station pressure is set to missing for that time period. (
ASOS Users Guide, 1998 Section 3.3.2
[ PDF])
All Automated Surface Observing System sites are commissioned.
For more information on ASOS data and instrumentation, see the
National Weather Service Automated Surface
Observing System web site
(NWS, 2003),
Federal Aviation Administration
Automated Surface Observing System web site
(FAA, 2003), or the
ASOS Users Guide, 1998
[ PDF].
For information on the calculation of parameters derived by UCAR/JOSS from the
raw parameters available, see Section 2.2.
The Department of Energy (DOE) Atmospheric Radiation Measurement (ARM)
Southern Great Plains (SGP) Surface Meteorological Observation System
(SMOS) [ARMSFC] stations are located at many of the ARM SGP Extended
Facilities in southern Kansas and northern Oklahoma. There are 15 SMOS station
included within this IHOP 2002 One Minute Surface Composite.
Instrumentation
The SMOS mostly uses conventional in situ sensors to obtain one-minute
averages of surface wind speed, wind direction, air temperature, relative
humidity, barometric pressure, and precipitation at the central facility
and many of the extended facilities of the SGP Clouds and Radiation Testbed
(CART) site. UCAR/JOSS
computes the dewpoint temperature from station pressure, temperature, and
relative humidity using the formula from Bolton
(1980). SMOSes have not
been installed at extended facilities located within about 10 km of
existing surface meteorological stations such as those of the Oklahoma
MESONET.
The SMOS stations directly measure:
Wind speed at 10 m, Precision: 0.01 m/s; Uncertainty: +/-1% for 2.5 to 30
m/s (see Assessment of System Uncertainties for Primary
Quantities Measured
for wind speeds below 2.5 m/s)
Wind speed and direction sensor: Propellor anemometer and wind vane, R. M.
Young Model 05103 Wind Monitor
Wind direction at 10 m, Precision: 0.1 deg; Uncertainty: +/-5 deg
Wind speed and direction sensor: Propellor anemometer and wind vane, R. M.
Young Model 05103 Wind Monitor
Air temperature at 2 m, Precision: 0.01 C; Uncertainty: a function of wind
speed (see Assessment of System Uncertainties for Primary
Quantities Measured)
Temperature and relative humidity sensor: Thermistor and Vaisala RH,
Campbell Scientific Model HMP35C Temperature and Relative Humidity Probe
Relative humidity at 2 m, Precision: 0.1% RH; Uncertainty: +/-2.06% RH (0%
to 90% RH), +/-3.04% RH (90% to 100% RH)
Temperature and relative humidity sensor: Thermistor and Vaisala RH,
Campbell Scientific Model HMP35C Temperature and Relative Humidity Probe
Barometric pressure at 1 m, Precision: 0.01 kPa; Uncertainty: +/-0.035 kPa
Barometric pressure sensor: Digital barometer, Vaisala Model PTB201A
Precipitation, Precision: 0.254 mm; Uncertainty: +/-0.254 mm (unknown
during strong winds and for snow)
Precipitation: Electrically heated, tipping bucket precipitation gauge,
Novalynx Model 260-2500E-12 Rain/Snow Gage
The data logger is a Campbell Scientific Model CR10 Measurement & Control
Module and Model SM716 Storage Module, Precision: A function of input type
and range, Uncertainty: 0.2% of Full Scale Range for Analog Inputs
2.0 Detailed Data Description
2.0.1 Automated Surface Observing System (ASOS) Algorithms
2.0.2 DOE ARM SMOS Surface Meteorological Data (ARMSFC) Algorithms
| +/- 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 |
Wind Direction
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.
Temperature
The accuracy of the temperature measurement is specified as +/-0.4 C. Included in this accuracy are sensor interchangeability, bridge resistor precision, and polynomial curve fitting errors. The long-term stability is not known. The radiation error of the naturally aspirated multi-plate radiation shield used for all stations, except for the central facilities SMOS, is specified as +/-0.4 C rms at 3 m/s, +/-0.7 C rms at 2 m/s, and +/-1.5 C rms at 1 m/s.
The uncertainty with 95% confidence of temperature sensors in naturally aspirated radiation shields is approximately:
| +/-0.45 C | when the wind speed is 6 m/s or greater |
| +/-0.89 C | when the wind speed is 3 m/s |
| +/-1.46 C | when the wind speed is 2 m/s |
| +/-3.07 C | when the wind speed is 1 m/s |
The radiation error of the aspirated radiation shield used at the Central Facility is specified as +/- 0.2 C rms. The uncertainty with 95% confidence of temperature sensors in this radiation shield is, therefore, +/- 0.57 C.
Relative Humidity
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 +/-0.5% RH.
The uncertainty with at least 95% confidence is, therefore,
| +/-2.06 % RH, 0 to 90 % RH |
| +/-3.04 % RH, 90 to 100 % RH |
The UNCERTAINTY of +/-2.06% RH (0% to 90% RH) or +/-3.04% RH (90% to 100% RH) is for a calibrated probe. The RH values reported by the probe normally drift slowly upward over time. Whenever a probe falls outside the range of uncertainty for a SIX-MONTH SENSOR VERIFICATION or reports values exceeding 104% RH, the probe is replaced by one that has been recently calibrated. Occasionally, a sensor will report values that are suspiciously low. A work order is then issued to perform a verification check and replacement if needed. A data quality report is issued for known erroneous data.
Barometric Pressure
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 Campbell data logger.
The specified uncertainty with 95% confidence is +/-0.035 kPa.
Precipitation
The tipping-bucket rain gauge produces a pulse output. The data logger counts the pulses for the period of integration. The uncertainty is, therefore, a minimum of one full bucket or 0.254 mm. For rain rates less than 75 mm per hour with light to moderate winds, the collection efficiency of the gauge is 99 to 100%. During heavy rain or strong, gusty winds, the collection efficiency is reduced. Manufacturers have not attempted to specify accuracies for these conditions.
Although Alter shields are used to increase the efficiency of snow collection, the efficiency of collection is variable and usually well below 100%. Furthermore, the heater does not melt snow at temperatures below -10 deg C. Thus the data user should use the water-equivalent estimates for snowfall with a great deal of skepticism. At best, the readings are only a rough indicator that snow occurred, for temperatures above -10 C. If snow occurred at -10 C or below and the temperature increased to above -10 C hours later, then some melting would occur and an incorrect time of precipitation would be reported.
Site maps are available at: http://www.arm.gov/docs/sites/sgp/maps.html
Algorithms
Description of System Configuration and Measurement Methods of all SMOS stations except at E21, Okmulgee, OK
The SMOS sensors are mounted on a 10 meter, triangular tower, except for the rain gauge.
The wind monitor propeller anemometer produces a magnetically controlled AC output whose frequency is proportional to the wind speed. The Wind Monitor direction vane drives a potentiometer, which is part of a resistance bridge. The Wind Monitor is mounted on a cross-arm at a height of 10 m.
The T-RH probe thermistor 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. For all SMOSes except, the one at the central facility, the T-RH probe is mounted in a naturally aspirated R. M. Young Model 41002 Gill Multi-plate Radiation Shield. The central facilities (E13) T-RH probe is mounted in an R. M. Young Model 43408 Gill Aspirated Radiation Shield. The Radiation Shields are mounted at a height of 2 m on the southwestern leg of the tower.
The barometric pressure sensor uses a silicon capacitive pressure sensor and is housed in a weatherproof enclosure along with a data logger, a storage module, and serial communications equipment, all mounted on the tower at a height of 1 m.
The rain-snow gauge has a 12-inch orifice and is located near the tower. A thermostatically controlled heater melts frozen precipitation. The water is funneled to a tipping bucket, which triggers a magnetic reed switch. An Alter Shield is used to increase the reliability of rain collection in high winds and of snow collection.
The data logger measures each input once per second except for barometric pressure, which is measured once per minute. The data logger produces one-minute averages of wind speed, vector-averaged wind direction, air temperature, and relative humidity. The one-minute output includes the barometric pressure reading and total precipitation during the minute.
Description of SMOS at E21, Okmulgee, OK
The same sensors that are used on the other SMOS stations are used on the E21 SMOS. Since this SMOS is in a forested site, the sensors are mounted on a 20 m tower which extends above the top of the forest canopy. During the summer of 1999 the canopy height was estimated to be 47 feet or 14.3 m. The air temperature and relative humidity probe is mounted at 17.0 m or approximately 2.7 m above the average canopy height facing North. The wind speed and direction sensor is mounted at 18 m or approximately 3.7 m above the average canopy height on a boom 10ft out from the tower facing North. The barometric pressure sensor is mounted at 19 m or approximately 4.7 m above the average canopy height. New booms for sensor mounting were installed in July 2002. The two sensors affected are the wind speed and direction sensor and the T/RH probe. The height of the wind speed and direction sensor did not change, it is still 18 m or approximately 3.7 m above the average canopy height. The orientation of the wind speed and direction sensor did change and it is now facing West on a boom 15ft out from the tower. The date of the wind speed and direction sensor change was July 16, 2002 at 18:44 GMT. Both the orientation and the height of the T/RH probe changed. It is now 19.25 m above the surface or 4.95 m above the average canopy height and is facing Northeast. The date of the T/RH probe change was July 15, 2002 at 22:36 GMT.
Precipitation Measurements Questionable
Since the height of the tower at E21 extends above the forest canopy it has become a favorite roosting area for turkey vultures. The birds roosting on the tower has caused considerable amounts of bird droppings on the equipment, tower & sensors. The precipitation gage is frequently clogged with bird droppings during the time period that the vultures are in the area. The turkey vultures are migratory but are generally in the area from early April through sometime in November. Precipitation data during these times should be investigated closely to determine if the precipitation gage data is consistent with other nearby sites. Typically when the raingage is clogged a stairstep pattern in the data can be noticed.
Theory of Operations
Each of the primary measurements of wind speed, wind direction, air temperature, relative humidity, barometric pressure, and rainfall are intended to represent self-standing data streams that can be used independently or in combinations. The theory of operation of each of these sensors is similar to that for sensors typically used in other conventional surface meteorological stations. Some details can be found under Algorithms - Description of System Configuration and Measurement Methods but further, greatly detailed description of theory of operation is not considered necessary for effective use of the data for these rather common types of measurements. The SMOS instrument mentor or the manufacturer can be contacted for further information. Contact information can be found on the SMOS web page given at the bottom of this section 2.0.2.
Instrument Mentor Quality Control Checks
Data quality control procedures for this system is mature.
Graphical displays are generated at ANL and inspected on a weekly basis for the following parameters: relative humidity, temperature, wind speed, wind direction and barometric pressure. Any one of these parameters acquired on any one day for up to 4 SMOS stations are viewed on a single display to compare data from relatively close extended facilities. This procedure does not verify accuracy, but does help identify suspected drifts in the sensors. When any of the graphed data are suspect, a work request for investigation and/or sensor verification by SGP site operations personnel is issued. Every six months the aforementioned SMOS sensors are compared to secondary references. Given adequate funding, every two years the wind monitors are replaced and the removed sensors are returned to the manufacturer for preventative maintenance and, if necessary, re-calibration. Summary reports are sent weekly to the SGP site scientist team. Precipitation data are not visually inspected due to the site-specific nature of these parameters. It is left to the user to determine the validity and accuracy of these values.
Additional checks on the temperature and relative humidity probes, and rain gauges are accomplished every two weeks during routine maintenance. The temperature and relative humidity probes are compared to secondary standards (hand-held meters). The secondary standards are calibrated in a humidity generator chamber at the SGP facility every 7 to 10 days. The rain gauges are checked for proper operation, the screens are cleaned if necessary, and tip tests are done. The rain gauges are also inspected for being level and at the proper height for the Alter wind-screen. Adjustments are made at the time of inspection.
Data acquisition and processing is disabled whenever sensors are being tested.
One problem currently persists. The rain gauges on the SMOS and on the SWATS are tested biweekly. Data acquisition and processing can be disabled on the SMOS stations but not on the SWATS. Whether data acquisition and processing is disabled or false counts appear in the data, a Data Quality Report (DQR) should be issued. A method to automatically search the MDS and issue DQR's when rain gauge testing is performed is being considered by SMOS.
Calibration and Maintenance
Calibration Theory
The SMOSs are not calibrated as systems. The sensors and the data logger (which includes the analog-to-digital converter) are calibrated separately. All systems are installed using components that have a current calibration. The sensor calibrations are checked every six months in the field by SGP site operations personnel by comparison to calibrated references. Any sensor that fails a field check is returned to the manufacturer for recalibration. The Wind Monitors are returned to the manufacturer for recalibration after two years of use per manufacturer suggestion and given adequate funding. Therefore, it is possible that in some years the wind monitors are not sent back to the manufacturer for the 2 year recalibration and preventative maintenance. Overall, this should not lead to a problem, as the sensors rarely go out of calibration and are checked every 6 months.
Wind speed calibration is checked by rotating the propellor shaft at a series of fixed rpm's using an R. M. Young Model 18810 Anemometer Drive. The reported wind speeds are compared to a table of expected values and tolerances. If the reported wind speeds are outside the tolerances for any rate of rotation, the sensor is replaced by one with a current calibration.
Wind direction calibration is checked by using a vane angle fixture, R. M. Young Model 18212, to position the vane at a series of angles. The reported wind directions are compared to the expected values. If any direction is in error by more than 5 degrees, the sensor is replaced by one with a current calibration.
Air temperature and relative humidity calibrations are checked by comparison with a reference Vaisala Model HMI31 Digital Relative Humidity and Temperature Meter and HMP35 Probe. If the reported temperature and relative humidity vary by more than the sensor uncertainty from the reference, the probe is replaced by one with a current calibration.
Barometric pressure calibration is checked by comparison with a reference Vaisala PA-11 Barometer. If the reported pressure varies by more than the sensor uncertainty from the reference, the sensor is replaced by one with a current calibration.
Precipitation calibration is checked by allowing 500 ml of water to slowly pass through the sensor. If the reported number of tips varies by more than one from the expected value, the rain gauge is replaced by one with a current calibration.
The ARM SMOS web site contains a complete calibration History, as well as information on instrumentation, data collection and processing (ARM, 2005). General information on ARM data quality (ARM, 2003b) can be found as well. Or see the ARM Program homepage (ARM, 2003a).
For information on the calculation of parameters derived by UCAR/JOSS from the
raw parameters available, see Section 2.2.
These data contain one-minute resolution surface meteorological data from the
Atmospheric Boundary Layer Experiments (ABLE). ABLE is a research initiative
devoted to atmospheric research. This project has been developed by the
Atmospheric Section of Argonne National Laboratory. The ABLE is located on the
lower Walnut Watershed, mostly in Butler County east of the city of Wichita,
Kansas. This location is within the existing boundaries of DOE's Atmospheric
Radiation Measurement (ARM) Southern Great Plains (SGP) Clouds and Radiation
Testbed (CART) site. The ABLE Automated Weather Station (AWS) Network consists
of five stations.
Instrumentation
The AWS stations directly measure:
Wind speed at 10 m, Precision: 0.01 m/s; Uncertainty: +/-1% for
2.5 to 30 m/s, increases to +/-0.5 m/s when 0.5 m/s is reported.
Propellor anemometer and wind vane, R. M. Young Model 05103 Wind Monitor
Wind direction at 10 m, Precision: 0.1 deg; Uncertainty: +/-5 deg
Air temperature at 2 m, Precision: 0.01 C; Uncertainty: +/-0.7 C
(This will eventually improve when an aspirated reference is obtained.)
Thermistor and Vaisala RH, Campbell Scientific Model HMP35C Temperature and
Relative Humidity Probe
Relative humidity at 2 m, Precision: 0.1% RH; Uncertainty: +/-2.06% RH
(0% to 90% RH), +/-3.04% RH (90% to 100% RH)
Thermistor and Vaisala RH, Campbell Scientific Model HMP35C Temperature and
Relative Humidity Probe
Barometric pressure at 1 m, Precision: 0.01 kPa; Uncertainty: +/-0.035 kPa
Digital barometer, Vaisala Model PTB201A
Precipitation, Precision: 0.254 mm; Uncertainty: +/-0.254 mm (unknown
during strong winds and for snow)
Electrically heated, tipping bucket precipitation gauge, MetOne Model 385
Rain/Snow Gage
The data logger is a Campbell Scientific Model CR10X-1M Measurement &
Control Module with 1 MByte memory; Precision: A function of input type
and range, Uncertainty: 0.2% of Full Scale Range for Analog Inputs
Topo maps and aerial photos are available at:
http://gonzalo.er.anl.gov/ABLE/sitelatlon.html
Data Collection and Processing
The AWS sensors are mounted on a 10 meter, triangular tower,
except for the rain gauge.
The wind monitor propeller anemometer produces a magnetically
controlled AC output whose frequency is proportional to the wind speed.
The Wind Monitor direction vane drives a potentiometer, which is part
of a resistance bridge. The Wind Monitor is mounted on a cross-arm
at a height of 10 m.
The T-RH probe temperature sensor, a thermistor, is connected into 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 Mode l43408 Gill
Aspirated Radiation Shield. The Radiation Shield is mounted at a height
of 2 m on the southern face of the tower.
The barometric pressure sensor uses a silicon capacitive pressure
sensor and is housed in a weatherproof enclosure along with a data logger,
a storage module, and serial communications equipment, all mounted on the
tower at a height of 1 m.
The rain-snow gauge has a 12-inch orifice and is located near the
tower. A thermostatically controlled heater melts frozen precipitation. The
water is funneled to a tipping bucket, which triggers a magnetic reed
switch. An Alter Shield is used to increase the reliability of rain
collection in high winds and of snow collection.
The data logger measures each input once per second except for
barometric pressure, which is measured once per minute. The data logger
produces one-minute averages of wind speed,
vector-averaged wind direction, air temperature, and relative humidity
The one-minute output includes the barometric pressure reading and total
precipitation during the minute.
More information on ABLE AWS can be found on the
ABLE Home Page (
ANL, 2003a).
For information on the calculation of parameters derived by UCAR/JOSS from the
raw parameters available, see Section 2.2.
This dataset contains supplemental data from NCAR's Meteorological
Stations. Data includes pressure, temperature, humidity, wind speed and
wind direction for the IHOP_2002 time period. Five stations are
represented in this dataset. The algorithms used to produce the NCAR
Supplemental Surface Meteorological station data from NCAR/ATD are not
currently available.
Note that ventilation fans failed on all stations during this project
at sometime between May 18th (julian 138) and June 6th (julian 157) on the
day they were replaced. There were no further failures from that date until
the end of the project. (J 177) Users should note that sensor arm heating
may have occurred when wind speeds were low and daytime temperatures were
high during this period.
For information on the calculation of parameters derived by UCAR/JOSS from the
raw parameters available, see Section 2.2.
The Integrated Sounding System (ISS) was developed jointly by the Surface and Sounding
Systems Facility of the National Center for Atmospheric Research Atmospheric
Technology Division and the Aeronomy Laboratory of the National Oceanic and
Atmospheric Administration. The ISS combines various measurement systems, both in situ
and remote, to take advantage of the positive attributes of each.
The ISS sites are housed in a standard 20-foot sea container modified to serve as an
equipment shelter and laboratory for project scientists and engineers. The modified
sea container houses the Sun workstation. The surface meteorological instrumentation
and Campbell datalogger are outside away from the container.
During IHOP 2002, a single ISS site was located at the "Homestead" or
"Profiling Site", near Elmwood in the Oklahoma panhandle, approximately 16km east of
the S-Pol site.
Instrumentation
At each ISS site, a ten-meter tower is instrumented with wind velocity sensors as well
as pressure, temperature, and humidity sensors. A rain gauge is mounted independently.
An anemometer is mounted on the top of a ten-meter tower. Temperature and humidity
sensors are mounted on the end of a one-meter boom attached to the ten-meter tower at
two meters above the surface. The temperature and humidity sensors are aspirated and
protected with a radiation shield. The pressure sensor is housed in the box containing
the Campbell CR 10x datalogger. That box is mounted on the ten-meter tower at one
meter above the surface and a "pressure port" is connected and mounted at 2 meters.
The "pressure port" reduces noise in the pressure sensor do to the venturi effect from
the wind.
The output from all the sensors is directed to the Campbell datalogger for processing.
The Campbell datalogger, which is independently programmable, typically generates
one-minute average data which are sent via RS-232 to the ISS Sun workstation. The data
input to the Campbell datalogger are five-second sample data.
Data Collection and Processing
Pressure Measurement
The surface pressure sensor used in the ISS installation is either a Vaisala PTA427
or PTA427A pressure sensor. The PTA427 sensor pressure range is 800 to 1060mb while
the PTA427A sensor pressure range is 600 to 1060mb. These sensors have an accuracy of
+/- 0.5mb and +/- 0.8mb respectively. They are both silicon capacitive pressure
sensors patented by Vaisala. Both are temperature compensated and produce a linear
voltage output over the full operating range. In order to interface with the Campbell
datalogger, a 2:1 voltage divider is incorporated into the cable from the pressure
sensor.
Temperature and Humidity Measurement
The temperature and humidity sensors are contained in a Vaisala 50Y humitter which has
been carefully calibrated with a curve fit. The actual sensors are a PRT and a Vaisala
"humicap" capacitive relative humidity sensor. The temperature sensor accuracy is +/-
0.4 degrees C over the range -33 to +48 degrees C. The accuracy of the humidity sensor
against field references is approximately +/- 2% with a long term stability of better
than 1% RH per year. These specifications for accuracy are achieved by internal
calibration at ATD and data curve fitting in real time. The 50Y humitter sensor probe
is protected and ventilated by an RM Young aspirated radiation shield model number
43-408 and external high flow aspiration fan.
Wind Measurement
Wind speed and direction are measured with an R.M. Young 05103 Wind Monitor. The
monitor is a propeller wind vane with a 0.9 m/s threshold for wind speed and a 60 m/s
maximum. Wind direction is measured using a 360 degree mechanical precision conductive
potentiometer. Direction measurements have a threshold of 1.0 m/s at a 10 degree
displacement and 1.5 m/s at a 5 degree displacement. The potentiometer is 10 K-ohm,
with a life expectancy of 50 million revolutions and has a 0.25% linearity through the
entire range.
Rain Measurement
A Texas Electronics TE525 tipping bucket rain gauge is used at all land based ISS
sites for measurement of rainfall. The rain gauge resolution is 0.254 mm. The gauge is
typically positioned 1.5 meters above the ground about 7 or 8 meters from the
ten-meter tower.
For more information, see the
ISS web page
(NCAR/ATD, 2003a) or the
NCAR/ISS Home Page for
IHOP_2002 (NCAR/ATD, 2003b)
For information on the calculation of parameters derived by UCAR/JOSS from the
raw parameters available, see Section 2.2.
The IHOP 2002 One Minute Surface Composite observation data
contains ten metadata parameters and 38 data parameters and flags. The
metadata parameters describe the station location and time at which the
data were collected. The time of observation is reported both in Universal
Time Coordinated (UTC) Nominal and UTC actual time. For this one minute
surface composite, reported nominal time and actual time are the same.
Days begin at UTC 0100 and end at UTC 0000 the following day. The table
below details the data parameters in each record. Several data parameters
have an associated Quality Control (QC) Flag Code which are assigned by the
Joint Office for Science Support (JOSS). For a list of possible QC Flag
values see the Quality Control Section 3.0.
This dataset contains only one minute observations for the IHOP 2002
domain and time period. The component datasets from which this dataset was
compiled are available on-line in native format via the
IHOP 2002 Master
Table of Datasets (UCAR/JOSS, 2003)
Calculated Sea Level pressure is computed from station pressure,
temperature, dewpoint, and station elevation using the formula of
Wallace and Hobbs (1977).
When not present in the raw data, the dewpoint temperature was
computed by UCAR/JOSS from station pressure, temperature, and relative
humidity using the formula from Bolton (1980). This
calculation was done for the following networks: ABLE_AWS, ARMCART, NCAR_supp,
ISS.
This IHOP 2002 One Minute Surface Composite does not contain any Sea Level
Pressures.
The IHOP 2002 One Minute Surface Composite was formed
from several datasets:
During the JOSS Horizontal Quality Control (JOSS HQC) processing,
station observations of pressure, temperature, dew point, wind speed and
wind direction were compared to "expected values" computed using an
objective analysis method adapted from that developed by
Cressman (1959) and
Barnes (1964). The JOSS HQC method allowed for short term (>/= 30 day)
variations by using 30 day standard deviations computed for each parameter
when determining the acceptable limits for "good", "questionable", or
"unlikely" flags. "Expected values" were computed from inverse distance
weighted station observations within a 200 km Radius Of Influence (ROI)
centered about the station being quality controlled (the station being
quality controlled was excluded); i.e.;
theta_e = < theta(i)/w(i) > / < w(i) >
Where theta_e is the "expected value" of the parameter at the site in
question, theta(i) is the observed value of the parameter at site i, w(i)
is the weighting factor for site i (here the inverse of the distance
between site i and the station being quality controlled), and <...> is
the sum over all stations "i" in the current ROI that have valid
observations of the parameter at the time in question. Data were
always compared at like solar times.
To determine an observation's HQC flag setting, the difference between
the actual observation and its "expected value" was compared to that
parameter's normalized standard deviation. Normalizing factors (also
called the sensitivity coefficients) were chosen to control the "good",
"questionable", and "unlikely" flag limits for each parameter. See
Table 3-1 for IHOP 2002 normalizing factors. Table 3-2
contains the HQC flag limit ranges derived from the normalizing factors
given in Table 3-1 and estimated standard deviations for each parameter
so that 95% of the QC limits applied to the IHOP 2002 data
fell within these ranges. For example, 95% of the observed station
pressure values that were flagged as "good" were within 1.2 mb of the
expected value. The significant overlap of the ranges seen in
Table 3-2 was partially due to seasonal and station differences in
standard deviations. The actual HQC limits applied at any particular
time depended upon the dynamic nature of the particular station's
parameter values over time.
Data were never changed, only flagged.
HQC was only applied to station pressure, sea level pressure,
calculated sea level pressure, temperature, dew point, wind speed and
wind direction. If the calculated sea level pressure quality control
information was available, its flag was applied to the station and
sea level pressures. If the calculated sea level pressure could not
be quality controlled, the sea level pressure quality control flag
was applied to the station pressure. If the sea level pressure could
not be quality controlled, the station pressure quality control flag
was not overridden.
The squall/gust wind speed data were not quality controlled.
There were no Sea Level Pressure values in this
IHOP 2002 One Minute Surface Composite.
General consistency checks were also applied to the dry bulb
temperature, wind direction, and the relationship between precipitation and
cloud amount/cloud cover. If the dew point temperature was greater than the
dry bulb temperature both values were coded "questionable". Also, wind
direction for observed "calm" winds was given the same QC code as the wind
speed. If precipitation was reported, but the cloud amount was "none" or
"clear", then both the cloud amount and precipitation values were coded
"questionable".
Several impossible values were also checked. Negative wind speeds
were coded "unlikely". Negative squall/gust wind speeds were coded
"unlikely". Wind directions of less than 0 degrees or greater than 360
degrees were coded "unlikely". If these consistency checks would have
upgraded the quality control flags previously set by HQC or gross limit
checks, then they were not applied. However, if these consistency checks
would have degraded the previously set QC flags, they were applied.
The JOSS HQC scheme relied on spatial and temporal continuity to
flag the data. It has been shown that this method works very well for
temperature, dew point, pressure, and wind speed, but is not a very good
scheme for the wind direction. The flags appear to be overly lax and
perhaps could be tightened.
Gross limit checks were also used to determine the quality of the
precipitation values. The gross limits are shown in Table 3-3. Certain
"questionable" and "unlikely" data values were also manually inspected.
After inspection, the quality control flag may have been manually modified
to better reflect the physical reasonableness of the data. Data were never
modified, only flagged. Negative precipitation was also coded "unlikely".
See Table 3-4 for a list of the possible quality control flags and their
meanings.
Argonne National Laboratory, cited 2003a: ABLE Automatic Weather Station
(AWS) [Available online from
http://www.atmos.anl.gov/ABLE/aws.html]
Argonne National Laboratory, cited 2003b: ABLE Site Latitude/Longitude
[Available online from:
http://gonzalo.er.anl.gov/ABLE/sitelatlon.html]
ARM, cited 2003a: Atmospheric Radiation Measurement Program [Available online
from http://www.arm.gov/]
ARM, cited 2003b: Data Quality HandS Explorer [Available online from
http://dq.arm.gov/cgi-bin/dqmenu.pl]
ARM, cited 2005: Surface Meteorological Observation System Instruments
for SGP (SMOS) [Available
online from
http://www.arm.gov/instruments/instrument.php?id=36]
ARM, cited 2003d: SGP CART Site Maps [Available online from
http://www.arm.gov/docs/sites/sgp/maps.html]
ASOS User's Guide, 1998, ASOS Project Office, NOAA, National Weather Service,
Washington D.C., June 1998. [Available online from
http://www.nws.noaa.gov/asos/aum-toc.pdf]
Barnes, S. L., 1964: A technique for maximizing details in numerical
weather map analysis. J. Appl. Meteor., 3, 396-409.
Bolton, D., 1980: The computation of equivalent potential temperature.,
Mon. Wea. Rev., 108, pp 1046-1053.
Cressman, G. P., 1959: An operational objective analysis system.
Mon. Wea. Rev., 87, 367-374.
FAA, cited 2003: Automated Surface Observing System [Available online from
http://www2.faa.gov/asos/asosinfo.htm]
NCAR/ATD, cited 2003a: Integrated Sounding System (ISS) [Available online from
http://www.atd.ucar.edu/rtf/facilities/iss/iss.html]
NCAR/ATD, cited 2003b: NCAR/ISS Home Page for IHOP_2002 [Available online from
http://www.atd.ucar.edu/rtf/projects/ihop_2002/iss/]
NWS, cited 2003: Automated Surface Observing System [Available online from
http://www.nws.noaa.gov/asos]
UCAR/JOSS, cited 2003: IHOP Master Table of Datasets [ Available online from
http://www.joss.ucar.edu/ihop/dm/archive/index.html]
Wallace, J.M., P.V. Hobbs, 1977: Atmospheric Science, Academic Press,
467 pp.
World Meteorological Organization (WMO), 1988: Manual on Codes
Volume I, Part B - Binary Codes. WMO, Geneva, Switzerland.
2.0.3 DOE ABLE AWS Algorithms
2.0.4 NCAR/ATD Supplemental Surface Meteorological data Algorithms
2.0.5 NCAR/ATD Homestead ISS Algorithms
2.1 Detailed Format Description
Parameters Units
---------- -----
Date of Observation UTC Nominal
Time of Observation UTC Nominal
Date of Observation UTC Actual
Time of Observation UTC Actual
Network Identifier Abbreviation of platform name
Station Identifier Network Dependent
Latitude Decimal degrees, South is negative
Longitude Decimal degrees, West is negative
Station Occurrence Unitless
Station Elevation Meters
Station Pressure, QC flag Hectopascals (mb)
Reported Sea Level Pressure, QC flag Hectopascals (mb)
Computed Sea Level Pressure, QC flag Hectopascals (mb)
Dry Bulb Temperature, QC flag Celsius
Dew Point, QC flag Celsius
Wind Speed, QC flag m/s
Wind Direction, QC flag Degrees
Total Precipitation, QC flag mm
Squall/Gust Indicator Code Value
Squall/Gust Value, QC flag m/s
Present Weather, QC flag Code Value
Visibility, QC flag Meters
Ceiling Height (first layer) Hundreds of feet
Ceiling Flag (first layer), QC flag Code Value
Cloud Amount (first layer), QC flag Code Value
Ceiling Height (second layer) Hundreds of feet
Ceiling Flag (second layer), QC flag Code Value
Cloud Amount (second layer), QC flag Code Value
Ceiling Height (third layer) Hundreds of feet
Ceiling Flag (third layer), QC flag Code Value
Cloud Amount (third layer), QC flag Code Value
The list of code values for the Present Weather is too large to reproduce
in this document. Refer to WMO, 1988 for a complete
list of Present Weather codes.
The code values for the Squall/Gust Indicator are:
Code Definition
---- ----------
blank No Squall or Gust
S Squall
G Gust
The code values for the ceiling flag Indicator are:
Code Definition
---- ----------
0 None
1 Thin
2 Clear below 12,000 feet
3 Estimated
4 Measured
5 Indefinite
6 Balloon
7 Aircraft
8 Measured/Variable
9 Clear below 6,000 feet (AUTOB)
10 Estimated / Variable
11 Indefinite / Variable
12 12-14 reserved
15 Missing
The code values for the Cloud Amount Indicator are:
Code Definition
---- ----------
0 0 ( or clear)
1 1 okta or less, but not zero or 1/10 or less, but not zero
2 2 oktas or 2/10-3/10
3 3 oktas or 4/10
4 4 oktas or 5/10
5 5 oktas or 6/10
6 6 oktas or 7/10-8/10
7 7 oktas or more, but no 8 oktas or 9/10 or more, but not 10/10
8 8 oktas or 10/10 (or overcast)
9 Sky obscured by fog and/or other meteorological phenomena
10 Sky partially obscured by fog and/or other meteorological
phenomena
11 Scattered
12 Broken
13 13-14 Reserved
15 Cloud cover is indiscernible for reasons other than fog or
other meteorological phenomena, or observation is not made.
2.2 Data Remarks
3.0 Quality Control Processing
These IHOP 2002 One Minute Surface Composite datasets
were collected over the IHOP 2002 domain (i.e., 32N to 42N latitude and
90W to 105W longitude) and time period (13 May 2002 through 25 June 2002)
and were combined to form a surface composite. The composite was quality
controlled to form the final IHOP 2002 One Minute Surface Composite.
Table 3-1 Normalizing factors used for IHOP 2002 One Minute
Surface Composite
Parameter Good Questionable Unlikely
--------- ---- ------------ --------
Station Pressure 0.2 0.2 0.5
Calculated SLP 0.4 0.4 1.0
Dry Bulb Temperature 0.5 0.5 1.0
Dew Point Temperature 0.5 0.5 1.0
Wind Speed 2.25 2.25 4.0
Wind Direction 1.22 1.22 2.2
Table 3-2 Ranges of HQC flag limit values for IHOP 2002
One Minute Surface Composite
Parameter Good Questionable Unlikely
--------- ---- ------------ --------
Station Pressure (mb) < 1.2 [0.6-2.9] > 1.5
Calculated SLP (mb) < 3.3 [1.3-8.2] > 3.2
Dry Bulb Temperature (deg.C) < 3.4 [1.4-6.8] > 2.8
Dew Point Temperature (deg.C) < 2.9 [1.0-5.7] > 2.0
Wind Speed (m/s) < 8.3 [2.8-14.7] > 4.9
Wind Direction(degrees) < 120.5 [57.9-180.0] >104.4
Table 3-3 - Precipitation Gross Limit Values
Parameter Good Questionable Unlikely
--------- ---- ------------ --------
1 Minute Precip < 3.0 mm >= 3.0 mm >= 6.0 mm
Table 3-4 - Quality Control Flags
QC Code Description
------- -----------
U Unchecked
G Good
M Normally recorded but missing.
D Questionable
B Unlikely
N Not available or Not observed
X Glitch
E Estimated
C Reported value exceeds output format field size or
was negative precipitation.
T Trace precipitation amount recorded
I Derived parameter can not be computed due to
insufficient data.
4.0 References