IHOP 2002 Five Minute Surface Composite

1.0 General Description

This dataset contains five-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:

The 5 Minute surface data extract contains five one-minute networks: Automated Surface Observing System (ASOS), Department Of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Surface Meteorological Observation System (SMOS) [ARMSFC], DOE Atmospheric Boundary Layer Experiments (ABLE) Automatic Weather Station (AWS), National Center for Atmospheric Research Atmospheric Technology Division (NCAR/ATD) Supplemental Surface Meteorological data (NCAR_supp), and the NCAR/ATD Homestead Integrated Sounding System (ISS) observation stations.

Data for the International H2O Project 2002 (IHOP 2002) domain (32N to 42N latitude and 90W to 105W longitude) and time period (13 May 2002 through 25 June 2002) are contained within this dataset. This IHOP 2002 Five Minute Surface Composite dataset contains data from 261 stations.

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.

2.0 Detailed Data Description

2.0.1 Oklahoma Mesonet Algorithms

The Oklahoma Mesonet is a permanent mesoscale observing network. The Mesonet consists of 115 stations, including at least one station in each of Oklahoma's 77 counties. The average station spacing is 32 km.

Instrumentation

     Sensor:            R.M. Young 5103 Propeller Vane Anemometer
     Measures:          WSPD, WVEC, WDIR, WDSD, WSSD, WMAX
     Height:            10 m AGL
     Interval:          3-second sampling, averaged over 5 minutes
                        (WMAX is highest of the 3-second samples in
                         the 5-minute interval)
     Characteristics:   Speed: 1-60 ms; Direction: 0-355 -1    E
     Inaccuracy:        Speed: 2% reading; Direction: 3        E
     Resolution:        Speed: 0.03 ms; Direction: 0.05 -1     E
     
    
     Sensor:            Vaisala HMP35C temperature thermistor and sorption 
                        humidity sensor
     Measures:          TAIR, RELH
     Height:            1.5 m AGL
     Interval:          3-second sampling, averaged over 5 minutes
     Characteristics:   Temperature: -30- 50 E  C; Humidity 0 - 100% E
                        Coastal Climate unaspirated 12-plate type radiation shield
     Inaccuracy:        Temperature: 0.35C; Humidity 3% E
     Resolution:        Temperature: 0.01C; Humidity 0.03%
     
    
     Sensor:            Vaisala PTB202 Barometer
     Measures:          PRES
     Height:            0.75 m AGL
     Interval:          12-second sampling, averaged over 5 minutes
     Characteristics:   700-1100 mb
     Inaccuracy:        0.4 mb
     Resolution:        0.01 mb
    
     Sensor:            Metone 099M Tipping Bucket Rain Gauge
     Measures:          RAIN
     Height:            0.6 m AGL
     Interval:          Accumulated tips over 5 minutes
     Characteristics:   30-cm Gauge, 0.25-mm bucket; Alter style wind screen
     Inaccuracy:        1% reading
     Resolution:        0.25 mm
     

Algorithms

The following parameters are included in this IHOP 2002 Five Minute Surface Composite. These parameters were measured at every site within the Oklahoma Mesonet.

     at 0.6 m
         Rainfall (RAIN) 

     at 0.75 m
         Barometric Pressure (PRES) 

     at 1.5 m 
         Air Temperature (TAIR) 
         Relative Humidity  (RELH)

     at 10 m
         Wind Speed (WSPD) 
         Direction (WDIR)
         Maximum Wind Gust (WMAX)

All reports are averages of three to thirty-second samples over the preceding five minutes, except rainfall, which is an accumulation over the previous five minutes.

Site Characteristics

Mesonet sites are predominantly located in rural areas, as free from anthropogenic influences as possible (Shafer et al, 1993). A Site Standards Committee developed a set of recommendations for site characteristics and measurements. These recommendations were followed as closely as possible to assure a consistency in the data reported from the field sites. Instrumentation on the Mesonet was selected to conform as closely to WMO standards as possible. Wind speed and direction are measured at a height of 10 m and air temperature and relative humidity are measured at 1.5 m for consistency with existing NOAA cooperative observations and airport stations. The measurements are taken over natural vegetation. The tower stands near the center of a 10 m by 10 m plot of land, surrounded by a cattle-panel fence, 1.3 m high, to secure the area from animals and nearby human activity. Each site can be viewed on the worldwide web at the following URL: http://okmesonet.ocs.ou.edu. Two of the sites (Hobart and McAlester) are co-located with ASOS instrumented towers so that data can be compared between the two networks. Eleven additional sites are located within two km of an NWS Cooperative Observer site. Two towers are installed at the Norman site. One is operational while the other provides an opportunity to compare instrumentation and test network upgrades without affecting the operational sites.

Information on the mesonet, site information and photographs, and a list of mesonet-related publications can be found on the Oklahoma Mesonet web site (Oklahoma Mesonet, 2003).

For information on, and to access, data and parameters not included in this IHOP 5-minute surface composite, see the complete IHOP_2002 Oklahoma Mesonet Meteorological Data (5-min) dataset in Oklahoma Climate Survey (OCS) Format.

For information on the calculation of parameters derived by UCAR/JOSS from the raw parameters available, see Section 2.2.

2.0.2 National Center for Atmospheric Research (NCAR) Atmospheric Technology Division (ATD) Integrated Surface Flux Facility (ISFF) Algorithms

The Integrated Surface Flux Facility (ISFF) is designed to study exchange processes between the atmosphere and Earth's surface. This includes the direct measurement of fluxes of momentum, sensible and latent heat, trace gases, and radiation as well as standard atmospheric and surface variables. Only surface variables are included in this IHOP 5-minute surface composite. There are 9 ISFF stations included in this IHOP 2002 Five Minute Surface Composite.

Instrumentation

Measurements from the following instrumentation are included in this IHOP 5-minute surface composite.

    * Vaisala 50Y Humitter to measure air temperature and RH; in NCAR aspirated
      radiation shield at 2 m agl
    * Barometer, Vaisala PTB220B, with a Ser single-disk static pressure port
    * MRI model 302/303/304 tipping bucket rain gauge, with Alter wind screen at
      sites 1-3
    * Sonic anemometer, initially either Campbell CSAT3 or ATI-NUW

Wind speed and direction were calculated from U and V wind components.

Algorithms and Sensor Notes

Following are notes on the deployment, operation, and post-project processing of data from each of the sensors. All deployment, operation, and post-project processing described in this section were performed by NCAR/ATD/ISFF. For information on the calculation of parameters derived by UCAR/JOSS from the raw parameters available, see Section 2.2. See Section 3.0 for the quality control processing performed by UCAR/JOSS on the composite dataset which contains this data.

Hygrothermometers

The Vaisala 50Y Humitters were calibrated in the NCAR Sensor Calibration Laboratory prior to the IHOP field program. The 50Y temperature sensors were calibrated over the range 0-45 C, and the relative humidity sensors were calibrated over the range 10-90 %RH at 15, 25, and 35 C. The calibration coefficients for temperature and relative humidity were entered into the EPROMs of the individual NCAR hygrothermometers, and the hygrothermometer microprocessors applied the coefficients to the 50Y output to produce the calibrated temperature and humidity data that was archived during the field project.

Following the field program, a second calibration data set was collected with each 50Y, and the hygrothermometer outputs using the pre-project calibration coefficients were compared to the laboratory standards. In general the 50Y temperatures agreed with the laboratory standard within 0.05 degrees, the exception being s/n 001 deployed at site 4 and having an apparent offset on the order of -0.1 degrees. The 50Y relative humidities agreed with the laboratory standards within 2 %RH, with the exception of s/n 003-005 deployed at sites 7, 3, and 2 and having maximum differences of 2.5-4 %RH.

Barometers

Barometer data are missing at station 8 for two extended periods, May 10 15:00 - May 15 17:15 CDT and May 25 02:00-10:35 CDT. In order to calculate air density during those two periods, the atmospheric pressure at station 8 have been estimated with one of the following three formulas, depending on the availability of pressure data from sites 7 and 9:

P8 = (P7 + P9)/2 - 1.72 mb

P8 = P7 - 5.26 mb

P8 = P9 + 1.82 mb

The pressure offsets in each of the preceding formulas was calculated from IHOP data when it was available from all of the required barometers. A comparison of the measured and estimated values of P8 finds that the errors in the estimated values are generally considerably less than 1 mb. The mean absolute error of the first formula is 0.1 mb, while those of the second and third formulas are 0.2 mb.

Data edited when PAM mast in lowered position It was occasionally necessary to lower the mast on the ISFF remote stations, in order to service sensors mounted on the mast. During periods when the mast was in a lowered position, data from the hygrothermometer, barometer, and sonic anemometer have been eliminated from the QC data set provided.

Rain gauge

False tips have been removed (replaced with 0) from the rain gauge data to the extent possible. These include both false tips generated during station service visits, as well as isolated tips that occur during apparently clear sky situations.

The intent was to err on the side of possibly including a false tip rather than deleting valid data. One apparent cause of the `clear sky' false tips is mice living in the rain gauge. Mouse nests and/or mice were found in the gauges at sites 1, 4, 5, 6, 8, and 9. No evidence of mice was found at sites 3 and 7. No `clear sky' tips were detected at sites 2 and 3.

Sonic anemometers

The sonic anemometers were mounted with their booms extending to the east of the PAM mast. It was planned to install the sonic anemometers at a height z determined by the geometry and path length of the sonic array and by the height of the vegetation, z = zs + D , where

    * zs =  2.7 m for the CSAT3 sonic
    * zs =  4.0 m for the ATI-K sonic
    * zs =  4.6 m for the ATI-NUW sonic
    * D  =  canopy zero-plane displacement, estimated as 2/3 the height of the 
            vegetation 

However, in some cases it was not possible to mount the sonic boom at exactly the planned height because it occurred at the same height as a joint in the PAM mast. The actual heights, above ground level, were

Sonic Heights
Site		1 	2 	3 	4 	5 	6 	7 	8 	9
Height, m agl 	2.5 	3.43 	2.7 	2.6 	5.0 	4.9 	2.7 	4.6 	4.7

These heights did not change during IHOP. The original deployment included only CSAT and ATI-NUW sonics, and when maintenance required replacing an ATI-NUW sonic by an ATI-K sonic, the sonic height was not changed. The CSAT sonics did not require maintenance during IHOP.

The sonic anemometer at site 6, ATI-K serial number 980202, output increasingly high wind speeds beginning around 16:15 CDT, June 17. The sonic was replaced around 19:00 CDT, June 20. Based on the data, the problem appears to have been a wind speed offset in the u and/or v paths of the sonic. Since the turbulent fluxes appear to be unaffected, only the mean horizontal wind components have been eliminated from the QC sonic data.

The sonic anemometer originally deployed at site 9, ATI-NUW serial number 7, had an intermittent failure of its "a" path. This sonic was replaced around 19:00 CDT, May 15. The erroneous sonic data have been eliminated from the QC data set.

The sonic anemometer data have also been edited to remove data that both look anomolous and also have concurrent diagnostic warning flags set by the sonic firmware. For the CSAT3 sonics this required that both bits 14 and 15 in the fourth word of the data message were set high during at least one sample within a 5-minute period. These bits indicate poor signal lock (bit 14) and a difference in the speed of sound between the three measurement axes greater than 2.36 m/s, equivalent to about a 4 C difference in inferred temperature (bit 15). For the NUW and ATIK sonics this required that the number of pulses per data sample per axis dropped below the set value, generally 11 pulses per data sample.

The coordinates of the three-dimensional sonic wind data have been rotated during data post-processing to align the vertical axis of the sonic anemometers normal to the mean wind field and to align the horizontal axes with geographic coordinates (u is a wind from the west, v is a wind from the south). The tilt angles for each sonic have been estimated from its wind data using the planar fit technique. The tilt angles, as well as the calculated vertical velocity offset, are tabulated in the logbook for each sonic. This table also includes the azimuths of the sonic booms.

Site characteristics

Nine ISFF Flux-PAM stations were deployed in 3 groups of 3 stations. Each group of three stations corresponded to an IHOP flight track. Stations 1-3, comprising the West leg, were aligned south to north in the Oklahoma panhandle. Stations 4-6, comprising the Central leg, were aligned roughly west to east, southwest of Wichita, Kansas. Stations 7-9, comprising the East leg, were aligned roughly west to east, southeast of Wichita.

For detailed information on siting, instrumentation, and algorithms used during the IHOP project, and for information on, and to access, data and parameters not included in this IHOP 5-minute surface composite see the NCAR ATD ISFF web page (NCAR/ATD/ISFF, cited 2003).

2.0.3 Texas Tech West Texas Mesonet (WTXMESO)

This data set contains 5-minute resolution surface meteorological data from the West Texas Mesonet operated by Texas Tech. The West Texas Mesonet includes 31 stations in the region around Lubbock, Texas.

Instrumentation

Each mesonet station consists of a fenced 10x10 meter plot of land, 10 meter tower, solar panel, RF modem and antenna.

Instrumentation for a basic mesonet station follows:

For more information see the West Texas Mesonet home page (Texas Tech University, cited 2003).

For information on, and to access, data and parameters not included in this IHOP 5-minute surface composite, see the IHOP_2002 Mesonet: Texas West Texas Mesonet Data [Texas Tech] dataset

For information on the calculation of parameters derived by UCAR/JOSS from the raw parameters available, see Section 2.2 .

2.0.4 United States Department of Agriculture (USDA) Agricultural Research Service (ARS) Micronet

The USDA Agricultural Research Service (ARS) has measured hydrologic conditions in the Little Washita Watershed in southwestern Oklahoma since 1961. In 1994, the ARS began monitoring the meteorological conditions in this watershed with an automated network called the ARS Micronet.

The ARS Micronet is operated and maintained by the USDA Agricultural Research Service's Grazinglands Research Laboratory in cooperation with Oklahoma State University and the Oklahoma Climatological Survey. The ARS Micronet is located within the larger Oklahoma Mesonet, which is operated by the Oklahoma Climatological Survey.

The support and cooperation of area landowners, without which the ARS Micronet and related research would not be possible, is acknowledged and greatly appreciated. As a result of the cooperation between landowners and the ARS, progress in agricultural and hydrological research has been made possible.

There are 41 ARS stations included within this IHOP 2002 Five Minute Surface Composite. These stations are all located in the Little Washita Watershed in southwestern Oklahoma.

Instrumentation and Algorithms

Temperature

The average air temperature is measured at a height of 1.5 meters above the ground using a thermistor sensor. This sensor is quite rugged and accurate. However, power and cost limitations dictated using an unaspirated radiation shield. Unfortunately, such shields can create temperature errors of several degrees Celsius when the wind is calm (less than 1 m/sec) and radiation is strong (more than 800 Watts per square meter). Radiation at high sun angles near 70 degrees seem to induce the worst errors. The temperature reported is an average of the five minutes previous to the report time.

Dewpoint

The average relative humidity is measured at a height of 1.5 meters above the ground during the last 5-minute interval before the time designated on the record. Relative humidity changes when either the moisture content of the air or the air temperature changes.

Relative humidity is measured using a Sorption Sensor. The sensor can detect relative humidity (RH) between 0 and 100%. The error for readings of 0 - 90% RH is 2%, while readings of 90 - 100% RH have a 3% error.

Dewpoint temperature was computed by UCAR/JOSS from station pressure, temperature, and relative humidity using the formula from Bolton (1980).

Precipitation

The total amount of rainfall is measured just above the ground in discrete tips of the bucket (approximately 0.01 inch per tip, or 0.254 mm) using a Tipping-Bucket Rain Gauge.

The Mesonet uses an unheated tipping-bucket rain gauge with a 30 cm diameter opening 0.6 m above the ground. The gauge works by funneling rainfall into one of two small buckets mounted on either side of a balance pivot. As each bucket fills, tips, and brings the other bucket beneath the funneled rain, the tip is counted (one tip is 0.254 mm or 0.01" of rain). Precipitation reported by UCAR/JOSS is the precipitation collected during the five minutes previous to the record time.

If the rainfall is very light, the bucket may only tip once every half hour or so. Thus, even if the rain is continuous, rainfall might be recorded during every sixth 5-minute interval. If the rainfall is very heavy, there is a strong likelihood that rain has splashed out of the bucket. Thus, measurements during heavy rainfall periods generally underestimate the total amount of rainfall.

Unheated gauges were chosen because of constraints on cost and power; the drawback is that unheated gauges underestimate snow or freezing rain totals. In addition, wet snow can clog the bucket while dry snow often blows away. Therefore, do not rely on the gauge observations during frozen precipitation events. Moreover, once air temperatures rise above freezing, the water equivalent of the melting precipitation is finally measured. The result is a delayed measurement of winter precipitation.

For more information on ARS data, instrumentation, and siting, see the ARS Micronetwork web site (USDA/GRL, 2003).

Disclaimer

The ARS Micronet data of the Little Washita River Watershed are accepted and used by the recipient upon the express understanding that the ARS and it's employees make no warranties, expressed or implied, concerning the accuracy, completeness, reliability or suitability for any one purpose, and that ARS and it's employees shall be under no liability to any person by reason of any use made thereof.

The ARS requests that the recipient of the ARS Micronet data does not distribute, publish or disseminate the data under the recipient's name without full and up-front acknowledgement of the ARS as the source of the data, and that the recipient acknowledges the support and role of the ARS in publications that use and are based on the ARS data. The data can be requested from the ARS Micronet Data manager at USDS-ARS, 7207 W. Cheyenne St., El Reno, OK 73036.

For information on, and to access, data and parameters not included in this IHOP 5-minute surface composite, see the OKMESO Little Washita Micronet and Soil Data [USDA/ARS] dataset

For information on the calculation of parameters derived by UCAR/JOSS from the raw parameters available, see Section 2.2 .

2.0.5 IHOP_2002 Mesonet 5-Minute Surface Extract from IHOP_2002 Mesonet 1-Minute Surface Meteorological Composite

This dataset is formed by extracting 5-Minute Surface Meteorological Data from the IHOP_2002 Mesonet 1-Minute Surface Meteorological Composite. Refer to the IHOP_2002 Mesonet 1-Minute Surface Meteorological Composite description document for more information.

The following networks were extracted from the 1-Minute Surface Meteorological Composite: Automated Surface Observing System (ASOS), Department Of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Surface Meteorological Observation System (SMOS) [ARMSFC], DOE Atmospheric Boundary Layer Experiments (ABLE) Automatic Weather Station (AWS), National Center for Atmospheric Research Atmospheric Technology Division (NCAR/ATD) Supplemental Surface Meteorological data (NCAR_supp), and the NCAR/ATD Homestead Integrated Sounding System (ISS) observation stations. A 5-Minute file is created from a 1-minute file by summarizing the 5 1-minute observations as follows:

Parameter        Summarization technique
-------------------------------------------------------------------------
Cloud Height     Use amount reported at each 5-minute interval
Visibility       Use amount reported at each 5-minute interval
Precip           Total over the 5 1-minute periods
Temperature      Average over the 5 1-minute periods
Dew Point        Average over the 5 1-minute periods
Wind Dir/Speed   Break into components, average components
                 over last two 1-minute periods, compute new vector
Wind Gust        Greatest value in last two 1-minute periods
Station Pressure Convert altimeter setting to station pressure;
                 average over 5 1-minute periods
Sea Level Pressure  Average over the 5 1-minute periods

A 5-minute average is calculated from the 1-minute averages provided that at least 4 valid 1-minute averages are available. No record will be written to the output file if more than one observation is missing in the 5-minute interval.

Wind Direction, Speed, and Gusts:

A 5-minute average is calculated from the last two 1-minute averages for the 5-minute time period. If either of these two 1-minute averages are missing, then wind direction, speed, and wind gusts will be set to missing.

2.1 Detailed Format Description

The IHOP 2002 Five 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 five munite 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.

     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

This dataset contains all five 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: Oklahoma Mesonet, NCAR/ATD/ISFF, and ARS.

This IHOP 2002 Five Minute Surface Composite does not contain any Sea Level Pressures.

The occurance for station ARS 151 should have been set to one in this composite.

3.0 Quality Control Processing

The IHOP 2002 Five Minute Surface Composite was formed from several datasets. These IHOP 2002 Five 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 Five Minute Surface Composite.

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 1.1 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.

Table 3-1 Normalizing factors used for IHOP 2002 Five 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 Five Minute Surface Composite

    
     Parameter                      Good      Questionable   Unlikely
     ---------                      ----      ------------   --------

     Station Pressure (mb)         < 1.1       [0.5-2.7]      > 1.3
     Calculated SLP (mb)           < 3.0       [1.1-7.4]      > 2.8
     Dry Bulb Temperature (deg.C)  < 3.0       [1.2-6.0]      > 2.5
     Dew Point Temperature (deg.C) < 2.7       [1.0-5.4]      > 2.0
     Wind Speed (m/s)              < 7.6       [1.6-13.6]     > 2.8
     Wind Direction(degrees)       < 120.5     [54.6-180.0]   >98.4

The squall/gust wind speed data were not quality controlled.

There are no Sea Level Pressure values within this IHOP 2002 Five 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.

Table 3-3 - Precipitation Gross Limit Values

     Parameter              Good      Questionable     Unlikely
     ---------              ----      ------------     --------
     1 Minute Precip       < 6.0 mm   >= 6.0 mm       >= 11.0 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

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.

NCAR/ATD ISFF, cited 2003: NCAR Integrated Surface Flux Facility at IHOP2002 [Available online from http://www.atd.ucar.edu/rtf/projects/ihop_2002/isff/]

Oklahoma Mesonet, cited 2003: [Available online from http://okmesonet.ocs.ou.edu]

Shafer, M.A., T. Hughes, and J.D. Carlson, 1993: The Oklahoma Mesonet: Site Selection and Layout. Eighth Symposium on Meteorological Observations and Instrumentation, Anaheim, CA, Amer. Meteor. Soc., 231-236.

Texas Tech University, cited 2003: West Texas Mesonet home page [Available online from http://www.mesonet.ttu.edu/]

UCAR/JOSS, cited 2003: IHOP Master Table of Datasets [ Available online f rom http://www.joss.ucar.edu/ihop/dm/archive/index.html]

USDA/GRL, cited 2003: United States Department of Agriculture, GrazingLands Research Laboratory ARS Micronetwork [Available online from http://grl1.grl.ars.usda.gov/micronet/]

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.