Vertical Atmospheric Soundings and Profiles
II. REVISION DATE
Robert J. Lutz, Donald E. Strebel
Vertical soundings of the atmosphere over the FIFE site were received from investigators in the field (obtained for FIFE research purposes) and from NOAA (obtained for National Weather Service operational purposes). The investigator data sets include data obtained from radiosondes and light and sound ranging devices (LIDAR, SODAR). The NOAA data sets include standard operational radiosonde data, NMC analysis (model-derived) vertical profile data, and satellite retrievals from the TIROS Operational Vertical Sounder (TOVS).
During the FIFE Intensive Field Campaigns (IFCs), balloon-borne radiosondes were launched from the site every 1-3 hours during daylight hours. These flights provide data on pressure, temperature, humidity, and winds over the site with a vertical resolution of 15-20m. Standard operational radiosonde data are also available from two NOAA stations in Kansas. Only vertical profiles of atmospheric temperature are available for 1985 through 1988; a more complete vertical profile data set (temperature, winds, humidity) exists for 1988-1989.
LIDAR systems were used to measure the height of the boundary layer and clouds, and also to provide data on winds as a function of height. Data is available for selected days from two LIDAR systems during IFC2 (June-July, 1987) and one system during IFC5 (July-August, 1989), both located at a site near the center of the FIFE study area.
The SODAR data set reports temperature inversion heights determined using an acoustic ranging device. It was active during IFC's 1-3.
The model-derived NMC analysis data contains vertical profiles of temperature and humidity from the "first-guess" field of the NMC Numerical Weather Model for four locations near the FIFE site. The satellite retrieval data (TOVS) contains temperatures and water equivalent for several standard layers in the atmosphere, along with tropopause temperature, pressure, total ozone, and cloud parameters (coverage and pressure level).
V. ABSTRACTS OF THE DATA SETS
Atmospheric profiles of wind velocity, temperature, and relative humidity were measured during some 450 radiosonde flights conducted at the FIFE site during the Summer and Fall of 1987 and the late Summer of 1989 (i.e. The FIFE IFCs). Balloons were launched every two or three hours during the FIFE IFCs.
FIFE Standard Pressure Level Atmospheric Profiles
This data set provides standard level profiles (5 mb pressure
intervals) from over 450 radiosonde balloon flights, which occurred every one to three hours (daylight hours) during the FIFE IFCs. These derived profiles were computed from the FIFE Radiosonde Data using a simple linear interpolation. In addition to the interpolated temperatures and mixing ratios, the directional components of the wind velocity and the potential temperature have been computed and added to the data set.
FIFE Temperature and Humidity Profile Data
The temperature and humidity profile data are corrected data derived from the FIFE Radiosonde Data. The corrections include adjusting the profiles for the response time lag of the dry-bulb and wet-bulb sensors and recalculating the height from the pressure, temperature, and humidity.
FIFE Radiosonde Wind Profile Data
The radiosonde wind profile data is a corrected data set derived from the FIFE Radiosonde Data. The corrections reduce noise and scatter in the wind speed and direction by using a locally correct (flat earth approximation) algorithm instead of the global algorithm provided by the instrument manufacturer. In order to do this, it was necessary to calculate the ground positions of the sonde (x and y offsets), which data are also recorded in the data set.
These data are field estimates (based on real time displays of the LIDAR returns) of the approximate boundary layer height. During periods that the University of Wisconsin LIDAR was operating in 1987 and 1989, these estimates were made by a human operator at roughly half hour intervals.
UW Boundary Layer Winds and Clouds
[Investigator: Edwin W. Eloranta]
The University of Wisconsin LIDAR recorded daytime boundary
layer measurements between July 26 and August 11, 1989. Boundary layer mean depths, plume tops, cloud bases, cloud tops, and horizontal mean winds were calculated from the measurements. Graphs providing an altitude vs. time depiction of the LIDAR data are also included in image format. These data (found in the "grab bag" section of the CD-ROM) are not stored or documented in standard FIFE Information System formats.
During FIFE a single, vertically pointing, conventional SODAR (Second Detection and Ranging) system was operated at an acoustic frequency near 1500Hz to provide estimates of the height of the mixed layer and the vertical dimensions of inversions within the lower kilometer of the atmosphere.
A pulsed Doppler LIDAR was operated near the center of the FIFE experiment area during IFC-2 to measure atmospheric winds, turbulence, and energy backscatter, using aerosols as tracers. This data set records the wind speed, direction, and altitude determined with the instrument.
The data were extracted from the NOAA Operational Analysis System and transmitted to FIS. They include atmospheric profiles of temperature for two NOAA operational stations (Dodge City and Topeka, Kansas). Data are for the period July 1985 through October 1988, usually recorded at 0000 hrs and 1200 hrs, GMT.
Atmospheric profiles of temperature, wind speed and direction, and relative humidity for two NOAA Operational Stations (Dodge City and Topeka, Kansas). Data are for the period October 1988 through October 1989, usually recorded at 0000 hrs and 1200 hrs, GMT.
Derived estimates of atmospheric profiles of temperature and humidity at standard pressure levels (1000, 850, 700 mb...). This data is the first guess field of the NMC Numerical Weather Prediction Model. Data are for four fixed locations near the FIFE site and are from July 1985 through October 1988. Estimates are provided daily for 0600 hrs and 1800 hrs, GMT.
This data set contains the tropopause pressure and temperature, total ozone, and cloud parameters (coverage and pressure level) obtained from satellite retrieval using the TIROS Operational Vertical Sounder (TOVS instrument). Included also are layer (i.e., 1000-850 mb, 850-700 mb...) temperatures and water equivalent parameters. FIS obtained all available data from January 1987 through December 1987. There is a data gap from March 1987 through August 1987, when no NOAA-9 TOVS data were acquired by NOAA/NESDIS.
VI. SPECIAL PROPERTIES OF THESE DATA
The FIFE Radiosonde Data contains very detailed profiles of the atmosphere over the FIFE site during the Intensive Field Campaigns. The sonde transmits meteorological data every 4 to 8 seconds. Two corrected data sets (FIFE Temperature and Humidity Profile Data; FIFE Radiosonde Wind Profile Data) and a derived data set (FIFE Standard Pressure Level Atmospheric Profiles) provide more readily usable data for specific purposes.
The NOAA Radiosonde Data only contains standard (mandatory) pressure levels (i.e., 1000, 850, 700). The later data set obtained from NCDC contains data at both standard and significant levels, resulting in a very fine (dense) coverage in the vertical.
Wind profiles are only computed above 500 meters in the LIDAR data, due to the positioning and operation of the LIDAR. In addition, the maximum height at which clouds can be detected is 15 km.
The derived NMC analysis data contains the "first-guess" field from a numerical model for four grid points (geographic locations) 381 km apart and 10 defined pressures in the vertical.
Three TOVS instruments are used to derive the sounding products. The High Resolution Infrared Sounder-version 2 (HIRS-2), using 19 infrared and 1 visible channel, provides temperature and water vapor sounding, surface temperature, cloud detection, and total ozone concentration. The Microwave Sounding Unit (MSU) has four microwave channels and provides temperature sounding under all sky conditions, except rain, and determines surface emissivity and cloud attenuation. The Stratospheric Sounding Unit (SSU) provides temperature soundings using carbon dioxide gas cells.
VII. RELATIONS AMONG THESE DATA
In general, these data sets present various vertical characteristics of the atmosphere. The data sets obtained by researchers (investigators) in the field are complemented by the NOAA operational data sets acquired by FIS staff in support of the experiment.
The FIFE Radiosonde Data is the "richest" of the radiosonde data, providing detailed information in both the vertical and temporal dimensions. Three additional data sets have been defined from this original data: corrections to the temperature values for sensor delays, corrections to wind variables using a more consistent algorithm, and an interpolation to standard pressure levels. There are several relations between these additional data and other data sets obtained in FIFE. For example, radiosonde data may be used in studies where the calculation/verification of heat and momentum fluxes is examined at the surface, or in the boundary layer or the lower troposphere. The corrected temperature radiosonde data set would be important in heat flux studies, in which precise energy exchanges are examined between two layers (i.e., the energy being examined, which may be a relatively small number, is a resultant of the difference of two larger numbers). In numerical models, where the stability of the model is of concern, the corrected wind data set would be useful in that it has less noise and scatter. Standardized pressure level data sets of radiosonde data may be utilized to set initial conditions and/or forcing functions for numerical models. They can also be employed in verification and comparison of model results.
The two NOAA radiosonde data sets complement the FIFE Radiosonde Data with vertical profiles of atmospheric data from NWS operational stations east and west of the FIFE study area. While these data cover almost five years, their temporal resolution (12 hrs) is not as fine as the FIFE observations. At times when special meteorological needs warrant it, however, observations may be taken at three-hour or six-hour intervals.
LIDAR measurements provide another method of examining the vertical structure of the atmosphere. Some advantages of this method are that the meteorological parameters may be measured almost instantaneously, and that parameters may be computed about a perpendicular plane directly above the instrument. There are some overlapping time periods with the radiosonde data sets.
The NMC analysis data set is a derived data set. The data are the first guess fields of a numerical model which has been spatially (horizontally and vertically) averaged. In addition, within the one NMC model, the "raw" original radiosonde data which were used as initial conditions within the model were probably "filtered" before use.
The TIROS Operational Vertical Sounder (TOVS) data appears in matched pairs of files on the CD-ROM. The first file contains single point observations such as the tropopause temperature and pressure, total ozone, and cloud measurements. The second file of each pair provides information on layer derived temperatures and humidities on a layer by layer basis.
VIII. CONFIDENCE AND ERROR
The FIFE Radiosonde Data has several known but generally correctable problems. For example, many flights record data inconsistencies during the preparation period before the balloon was actually launched. Also, at times the instruments would continue to record at the end of the flight after the balloon burst. Another general problem that was noted was that several times when the wet-bulb thermometer froze, it would continue to record, providing erroneous values. The derived standardized level data has for the most part detected and corrected these problems, though some may still exist.
The NOAA radiosonde data sets were collected for the National Weather Service for forecasting purposes using well specified procedures, and may be regarded as high quality data sets. The second data set (October 1988 through October 1989) is a QA'd product that also includes data quality flags along with the observed parameters. Limiting factors in the utilization of these data would be the infrequent sonde launches (usually only twice a day) and the location of the sonde releases 70-80 miles from the FIFE site. This latter factor is probably not a major concern if meteorological conditions are somewhat constant within the area (i.e., no fronts, severe weather, etc..).
The NMC derived meteorological parameters have unspecified error estimates. It should be remembered that these data are spatially and temporally averaged and will inherit some properties from the numerical model used to generate them.
Within the data set containing the wind profiles, it was noted that biases may be present in the data. This may be partially corrected by manual inspection of the data and the detection of "outliers".
The uncertainty quoted for the height measurements for the SODAR data set are plus or minus 25 meters. This would be much greater accuracy than a conventional radisonde could provide. However, it is limited to heights less than 1 km.
The estimated error bars in the TOVS-derived meteorological parameters are large; i.e., several degrees on layer temperatures and plus or minus 30% on layer precipitable water. For most purposes, the FIFE or NOAA radiosonde data sets would be preferable.
Analyses of the radiosonde data showed that when the time rates of change throughout the lower boundary layer are slow due to the absence of strong advection, the radiosonde data can provide useful information about surface fluxes. For example, on a given day a small number of instantaneous measurements of evaporation rate, combined with continuous measurements of net radiative flux or incoming radiative flux, could be used to estimate the total daytime evaporation.
A newly developed method of using upper LIDAR measurements to compute vertical wind profiles agreed reasonably well when compared with data gathered by the radiosondes.
The Doppler LIDAR and radiosondes differed considerably in estimates of heat fluxes. Nevertheless, it was shown that LIDAR can provide reasonable estimates of the large-scale sensible heat flux when compared to surface flux estimates, though with a fairly large random error.
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