Mission and Goals

The mission of the Surface and Sounding Systems Facility (SSSF) is to provide surface-based in situ and sounding measurements, and associated data-processing and analysis software, in support of atmospheric research. The Facility also engages in related scientific research to maintain a leadership role in the development and operation of state-of-the-art measurement systems. SSSF engages in the following major activities:

• Operation of advanced surface and upsonde/dropsonde direct-sensing systems and ground-based microwave and acoustic profiling systems to support field research of atmospheric scientists.

• Development of new in situ and remote surface, profiling, and sounding systems in cooperation with other ATD groups, NCAR divisions, universities, and NOAA and other government agencies.

• Development of new data-telemetry systems to support ATD's field-data communications needs.

• Development of operational and analytical techniques for optimum use of field facilities, including techniques for sensor calibration, instrument deployment, data collection, and data analysis, and transfer of these techniques to the atmospheric sciences community.

• Scientific research and engineering development to support, demonstrate, and advance these capabilities.

• Support of university educational programs by providing state-of-the-art observing systems for student training, and by providing lectures upon request pertaining to meteorological instrumentation and observational research.

The traditional emphasis of the Facility has been to support mesoscale and boundary-layer experiments in keeping with national scientific priorities for research in atmospheric chemistry, mesoscale precipitation systems, cumulus convection, boundary-layer processes, and air-surface interaction. Recent emphasis has also included process study experiments relevant to climate change studies. SSSF has focused significant resources over the past year on numerous requests for field measurements. SSSF attempts first to satisfy all approved community requests for field support. Next in priority is to optimize the use of remaining facility resources to develop new observing systems and improve existing systems to meet the field-support requirements of major experimental programs of national interest, such as the

Aerosol Characterization Experiment (ACE-1). ACE-1 was conducted from 15 November to 14 December 1995 over the southwest Pacific Ocean, south of Australia. Two Integrated Sounding Systems (ISS) and one Omega Cross-Chain LORAN Sounding system (CLASS) were deployed in support of this project. ACE-1 was the first in a series of experiments that will attempt to characterize the chemical and physical processes controlling the evolution and properties of atmospheric aerosols and their role in radiative climate forcing. The data from the two ISS stations provided height estimates of the marine boundary layer and the extent of mixing with the free troposphere. One of the ISS units was deployed on the NOAA ship RV Discoverer (58Kb) and the other was located at the Cape Grim Baseline Monitoring Station (68Kb) on the northwest tip of Tasmania. The data from the ship-borne and the land-based ISS stations will be combined with on-site chemistry and aerosol measurements to complete closure calculations throughout the operational season. The CLASS system was deployed on an Australia fisheries ship, the FRV Southern Surveyor, to enhance the spatial and temporal continuity of the measurements being made during the Lagrangian experiments. The addition of soundings made south of Tasmania by the Southern Surveyor enhanced the regional measurement coverage, improved the air trajectory calculations, and assisted in forecasting and operations planning.

Boundary Layer Experiment - 96 (BLX-96). SSSF deployed the Multiple Antenna Wind Profiler (MAPR) version of the ISS, augmented with a ceilometer (provided by NOAA/ETL), to Dexter, Kansas for remote sensing of atmospheric winds and turbulence in the boundary layer. Data collection was coordinated with overflights of the U. Wyoming King Air, which measured mean flux profiles and the joint frequency distribution of the lifting condensation level and buoyancy for investigators at the U. British Columbia. The MAPR experiment was designed to test spaced-antenna techniques for measuring turbulence profiles. It also had a secondary objective of collecting high-time-resolution observations of the nocturnal low-level jet. Approximately 25 CLASS soundings were launched from Dexter during the three-week experiment. Additional measurements were obtained from other instruments located at the Atmospheric Radiation Measurement (ARM) program's Cloud and Atmospheric Radiation Testbed (CART) site (16Kb).

Coastally-Trapped Waves Experiment. The objectives of this experiment were to study the dynamics of coastally-trapped waves, the ageostrophy of the wind constrained by a coastal mountain range, the interaction of orographically-forced flow with the sea-breeze circulation, the offshore variability and turbulent structure of the boundary layer, and the influence of the orographic barrier on the development of boundary-layer clouds. The NCAR C-130 aircraft (30Kb) provided the primary in situ measurements of boundary-layer structure for this experiment by means of along-shore and across-shore flight segments. Down-looking lidar measurements of the deformation of the marine boundary layer inversion and in situ cloud microphysical measurements were also obtained from the aircraft. SSSF supported the experiment by providing a airborne Lightweight Digital Dropsonde (LD2, 79Kb) system with the capability of using either LORAN or Omega sondes (depending on the quality of the LORAN signals). The LD2 system was used to measure atmospheric profiles, including the detailed structure of the boundary layer below the aircraft. Fifteen sondes were dropped during some of the higher altitude legs of the flight pattern.

Flatland Observatory Project II. This was the second year for this boundary-layer structure and dynamics experiment. The basic intensive observation period ran from 15 June through 15 August 1996, but was extended to the middle of September to support the Lidars in Flat Terrain (LIFT) experiment (see LIFT below for details). The primary focus for this year's experiment was to study boundary-layer height, divergence, entrainment velocity, and entrainment processes, as well as measurements of the atmospheric heat-budget terms. Two ISS stations were deployed in a triangular array with the NOAA 915-MHZ wind profiler that is permanently located at the Flatland Atmospheric Observatory (FAO). This year, three flux-measuring (Flux-PAM) versions of the SSSF Portable Automated Mesonet (PAM-III) stations were added to the experiment as "anchors" for the boundary-layer measurements from the ISS and the FAO instruments. The Flux-PAMs provided flux measurements over typical crops (corn and soybeans) found in the experimental area. In addition to the standard meteorological measurements of wind, pressure, temperature, humidity, and rainfall, the Flux-PAM stations made measurements of soil temperature and moisture, as well as flux measurements of latent heat, momentum, and radiation. Flux measurements of ozone surface deposition were also made for the last thirty days of the experiment. At one site the Flux-PAM was enhanced with components of the ASTER system (64 Kb) in order to better acquire and process the fast data for the ozone surface deposition fluxes.

ARM GPS/Water Vapor Experiment. During 10-30 September 1996, SSSF operated six ground-based GPS receivers capable of obtaining a vertically integrated estimate of atmospheric water vapor. The effort was a joint project with NOAA/ETL, which also operates a GPS receiver network over this region, and UCAR/UNAVCO, which is processing the data. During the experimental period, members of the ARM science team operated a variety of remote and in situ water vapor sensors, co-located with one of the receivers. This experiment was the first deployment of these GPS receivers by ATD, and, to our knowledge, the first dense mesoscale deployment of such receivers primarily for meteorological purposes. The goals of this experiment were (1) to gain experience with this instrumentation for future deployments, (2) to assess the accuracy of these instruments for water-vapor measurements at high temporal resolution (i.e., of order 5 minutes), (3) to test the ability of these instruments to provide spatial variations, through comparisons with the U. Maryland's scanning Raman lidar, and (4) in collaboration with NCAR/MMM, to determine whether these measurements improve the accuracy of the predicted water-vapor profile through use of a variational data-assimilation model.

Lidars in Flat Terrain (LIFT). SSSF also participated in the LIFT experiment, which was closely linked with the Flatland Observatory Project II in central Illinois. In addition to the two ISS (57Kb) and three Flux-PAM stations deployed for Flatland, SSSF installed ATD's Staring Aerosol Backscatter Lidar (SABL, 106KB) and one enhanced Flux-PAM for ozone flux measurements at one of the ISS sites. Other LIFT instrumentation included NOAA/ETL's 2-micron High-Resolution Doppler Lidar (HRDL) and the Ozone Differential Absorption Lidar (DIAL). LIFT's objective was to study the high-resolution structure of winds, aerosol, and ozone as the daytime boundary layer grows and decays. The data gathered during the four-week experiment will also be used to evaluate lidar and profiler techniques for quantifying fluxes, turbulence, and boundary-layer height.

NEXRAD Precipitation Study. SSSF deployed an ISS at a NWS site near Stapleton Airport during June and July 1996. This ISS was operated in a "profiler only" mode in support of a study of remote quantitative precipitation measurement conducted by CIRES-CU and the NOAA Aeronomy Lab. The ISS was operated in conjunction with the NWS NEXRAD radar and the ATD S-Band Polarimetric Radar (S-Pol, 87Kb) in an attempt to quantitatively characterize precipitation using radar measurements. The profiler was operated with every other beam in the vertical mode. Oblique beams were included to obtain the horizontal wind. The vertical velocity Doppler spectra obtained from the profiler will be used to derive precipitation rates and size distributions.

Stratosphere-Troposphere Experiments: Radiation, Aerosols, and Ozone (STERAO-A). SSSF's Mobile CLASS van (74 Kb) was used to support this field program with vertical balloon soundings. The soundings were a component of a detailed investigation of the physical and chemical nature of thunderstorm inflows and outflows. The program attempted to gauge the effects of thunderstorm circulation on the composition and structure of the lower stratosphere and upper troposphere. A total of 45 soundings were made between 17 June and 17 July 1996 from the Fort Morgan Airport near Fort Morgan, Colorado. (Soundings data and data reports are available from SSSF's Home Page.)

Dual-Wavelength Net Radiometer. Tony Delany and Steve Semmer have developed this advanced net radiometer to increase the accuracy of single-instrument measurements of surface radiation flux. Conventional net radiometers make separate determinations of short-wave and long-wave incoming and outgoing radiation which are subsequently differenced, resulting in loss of accuracy. The new system increases accuracy by making differential net shortwave and long-wave radiation determinations. The system was designed to utilize numerically controlled machining techniques to substantially reduce manufacturing costs. Other advanced features include data acquisition and manipulation capabilities and integrated ventilation and leveling.

Infrared Water-Vapor Sensor. Steven Oncley, Steven Semmer, Chuck Frush (ATD/RSF), and Wim Kohsiek (KNMI, The Netherlands) have designed an infrared humidity sensor to be used with Flux-PAM systems. The design is similar to other systems utilizing the 1.4-micron absorption band, but has been optimized to require less power and less maintenance. A prototype is now being constructed and will be tested this winter.

Integrated Surface Radiation Measurement System. Tony Delany and Steve Semmer have developed this integrated system to measure surface radiation flux. The system employs commercially available Eppley pyranometers and pyrgeometers, modified to ensure proper ventilation and mounted on a leveling platform. A special computer algorithm provides appropriate corrections for dome heating and sensitivity of the pyrgeometer to shortwave radiation. The new system will be used with the Atmosphere-Surface Turbulent Exchange Research (ASTER, 64Kb) facility for accurate determination of the surface energy balance. It will also be used for research into the errors introduced by non-leveled radiation sensor arrays deployed over various types of vegetated surfaces.

Multiple-Antenna Profiling Radar (MAPR). MAPR uses newly developed spaced-antenna techniques to measure vertical profiles of wind velocity through the lower troposphere. The goal of MAPR is to obtain better accuracy and much higher time resolution than conventional wind profilers, which measure winds through estimating Doppler shift in multiple beam directions. A refined theoretical treatment of spaced-antenna signals is being tested with MAPR. Hardware upgrades during the past year include modifications to deploy the antenna lower to the ground for clutter reduction, and complete re-tuning and calibration of the four receiver channels. Software upgrades currently being developed will allow winds to be computed in real time, and will allow use of a UNIX operating system. MAPR's deployment during the BLX-96 program provided an opportunity for intercomparison with in situ aircraft data. This data base includes observations of the growing daytime boundary layer and the nocturnal low-level jet. BLX-96 data will also be used to test new ideas for spaced-antenna turbulence measurement techniques.

Ozone Sensor Development. A collaborative project was initiated in FY 96 between SSSF and the German DLR to develop a small, low-powered, lightweight and inexpensive fast ozone sensor suitable for dropsonde use. In its current state of development, the prototype sensor is housed in a small cylinder 7 cm in diameter and 18 cm long. In this form, the sensor meets the size, weight, power, and cost requirements for dropsonde applications. However, an undesirable sensitivity to humidity needs to be corrected before the ozone sensor will be fully satisfactory. Research into modification of the chemiluminescent target material for this purpose is currently being pursued in Germany. The prototype sensor has already been used for tower-based fast-ozone measurements during LIFT. Ozone fluxes were determined and compared to similar measurements from a more sophisticated instrument using gas-phase chemiluminescense. The fluxes determined using the two systems are comparable, although the data from the inexpensive sensor require more processing. The further development of a compact, inexpensive, ozone flux instrument is being pursued in cooperation with the Chemistry Department of U. Colorado.

Portable Automated Mesonet-III (PAM-III, 55Kb). Three Flux-PAM surface stations were constructed in early 1995, field tested, and successfully deployed in support of field programs during the summers of 1995 (SCMS) and 1996 (Flatland). The measurement of turbulent ozone fluxes by a Flux-PAM surface station turned out to be a highlight of the Flatland field project. Over the past year, testing and development has continued to refine and quantify the performance of both standard meteorological and flux-measuring sensors. Particular effort has been devoted to the measurement of water-vapor fluxes. This has involved continued evaluation and development of a bandpass hygrometer, as well as a recently initiated effort to develop a low-power, low-cost, fast-response, infrared-absorption hygrometer. The Flux-PAM network will be expanded in early 1997 with the construction of two additional stations, making a total of five stations available to the scientific community. At the same time, another Flux-PAM station will also be constructed for use by the Japanese National Committee for the GEWEX Asian Monsoon Experiment (GAME).

Real-time Data Communications System for Field Projects. During FY 96 SSSF continued to expand its capabilities for real-time data dissemination during field projects. Data communication and processing systems were implemented to support data delivery to SSSF and the field project control centers. The former allow SSSF scientists and engineers to closely monitor operation of the remote field systems, while the latter make the observations available for project operational planning. In some cases data can also be delivered to the Global Telecommunications System, so that the observations can be incorporated into operational models at the numerical weather centers. Most of the SSSF observing systems deployed over the past year provided real-time data in this manner, including the ISS based on a research vessel during ACE-1. Although this remote communication capability cannot always replace technical staff in the field, it allows real-time ingest of field data into our home computers, with resultant advantages for both experimental control and data quality control.

Relaxed Eddy Accumulator (REA). A version of this original SSSF instrument, specifically designed to investigate fluxes of biogenic hydrocarbons, has been developed through a joint effort with the Environmental Population and Organismic Biology Department of U. Colorado. This Colorado University Flux Facility (CUFF) REA was designed and constructed by Dave Bowling (U. Colorado) and Tony Delany (SSSF), using the latest version of the PAM-III sensor board, plus PC-based software prepared by Bowling in cooperation with SSSF engineers.

Scientific Data Management System. Efforts have continued over the past year in exploring data management systems that will support post-processing of field data, engineering needs for instrument development, and scientific data analysis. The goal is to create a data infrastructure that is versatile and robust enough to cope with the large variety of SSSF data architectures and analysis activities. The primary focus over the last year has been the application to SSSF datasets of the new ATD Information Retrieval System (AIRS), developed by Julie Haggerty and Gary Horton of RAF. A large cross-section of SSSF datasets has been ingested into the AIRS prototype, and testing of AIRS performance and suitability is currently underway.

Sensor Calibration and Evaluation Lab. During FY 96 this lab provided calibration services for a variety of surface instruments used with the SSSF facilities. In addition to routine calibrations, the lab was also used in sensor performance tests. The lab's wind tunnel provided help in understanding the flow-distortion characteristics of a Solvent 3-D sonic anemometer. The Thunder Scientific humidity/temperature chamber in the lab was used to evaluate the time response, over a wide temperature range, of a variety of solid-state humidity devices. This chamber also was used to check the performance of an aircraft air-intake duct housing for a humidity probe.

Wind Profiler Antenna Test Range. The Marshall field station of NCAR has been selected as the site for a basic antenna test range being constructed cooperatively by researchers from SSSF, several NOAA labs, and Radian Corp. The site will initially be used for testing of clutter screens. Signal contamination by moving clutter often limits the ability of lower atmospheric wind profilers to make accurate measurements, especially at low altitudes. A variety of new clutter screen designs and edge treatments for existing clutter screens have been proposed. The new test range will be used to measure the relative radiation pattern at elevation angles near the horizontal of various combinations of screens and edge treatments.

Wind Profiler Real-Time Software Development. SSSF is developing new control and display software for the Doppler Beam Swinging Wind Profiler (56 Kb) and the MAPR (see above). The goal of this project is to develop an operational system that will provide the necessary software environment to support research and improvement in basic wind-profiling techniques. Design features of the new software include operation under a multi-tasking operating system, facility for rapid testing of digital signal-processing algorithms, and adherence to standardized data formats and programming interfaces. The system will allow for development and incorporation of real-time data-processing algorithms, with little modification to the basic data-acquisition system. The system is now approximately 80% complete. Testing will begin in the first half of FY 97.

Cloud and Aerosol Chemistry Experiment (CACHE-94) Data Analysis. This experiment was focused on the turbulent deposition of cloud droplets to forested irregular terrain. This mechanism is an important yet little understood pathway for the deposition of atmospheric pollutants. During the field program in 1994, the ASTER facility was deployed at the Cheek Peak cloud observatory on a ridge line above the ocean, at the northwest extremity of the Olympic peninsula of Washington. Gordon Maclean and Tony Delany completed the data analysis completed early in the year and their paper has been accepted for publication by a scientific journal. The data also formed the basis for a Ph.D. thesis by A. Kowalski and an M.S. thesis by P. Anthoni, both at Oregon State U.

Flux Measurements from Displaced Scalars. Leif Kristensen and Jakob Mann (RISO National Laboratory, Denmark), John Wyngaard (Pennsylvania State U.), and Steven Oncley (SSSF) completed their interpretation of heat-flux measurements using temperature sensors that are physically separated from the velocity sensor. Measurements were taken during SST-93 (an ASTER (64Kb) deployment at the NCAR Marshall field site in 1993), and later at a site near RISO. The somewhat surprising result of this work is that the fluxes are virtually unchanged when the measurement of the scalar is physically located below that of the velocity. These results will be used to configure sensors in future ASTER and Flux-PAM deployments.

Footprint for Measurement of Atmosphere-Surface Exchange Fluxes. The flux footprint relates the vertical flux measured at some height above the surface to the upwind spatial distribution of atmosphere-surface exchange fluxes. A quantitative description of the flux footprint is required both for the design of field experiments and to interpret micrometeorological flux measurements. In 1992-1994, Tom Horst published theoretical estimates of the eddy-correlation flux footprint that are based on an analytic model for vertical dispersion within the atmospheric surface layer. More recently, he has extended the model to calculate the footprint associated with flux estimation by concentration-profile techniques. The upwind extent of the profile footprint was found to be similar to that for eddy-correlation flux measurements, if the latter are made at a height equal to the arithmetic mean of the profile measurement heights for stable stratification or the geometric mean for unstable stratification. However, the concentration-profile flux footprint extends closer to the measurement location than does the eddy-correlation footprint, because the flux estimated from the profile is strongly influenced by the concentration measurements made at heights lower than that of the eddy-correlation flux measurement.

Integrated Data Assimilation/Sounding System (IDASS). Supported by the DOE ARM program, the IDASS program seeks to develop improved measurement and data assimilation strategies. The program includes the MAPR project (headed by Stephen Cohn), as well as joint data assimilation studies between ATD (David Parsons) and MMM (Bill Kuo, Jimy Dudhia, and Yong-Run Guo). The data assimilation effort focuses on using variational techniques and Newtonian nudging in the NCAR/Pennsylvania State U. mesoscale model (MM5) for field experiments conducted in the vicinity of the ARM/CART site in the central U.S. An example of such an effort is the recent GPS water-vapor measurements taken over northern Oklahoma and southern Kansas last fall. The MAPR work includes an examination of the mesoscale organization of a spring frontal system that produced upslope precipitation along the Rocky Mountain Front Range. This analysis demonstrated the usefulness of the MAPR-derived wind measurements.

Natural Emissions of Oxidants Precursors: Validation of Techniques and Assessment (NOVA-96). NOVA-96 represented a continuation of NOVA-95. The field program was conducted in the Tidewater region of North Carolina. It was intended to characterize the measurement of emission fluxes of oxides of nitrogen, using both enclosure techniques and eddy-correlation measurements. Preliminary findings by Tony Delany (SSSF) and project scientists at North Carolina State U. and other universities indicate that, for cropland with a well established vegetation canopy, the bare-soil emission measured by enclosure methods overestimated the net emission to the free atmosphere, compared with surface-layer measurements by eddy correlation. The investigators believe this could be due to redeposition of the oxides of nitrogen onto the plant surfaces. Analysis of the data will continue into the upcoming year.

Orographically Influenced Winds. High-time-resolution data taken by MAPR and the instrumented Boulder Atmospheric Observatory (BAO, 95Kb) 300-m tower during the Erie-95 field program have provided an excellent opportunity to study mesoscale dynamics in rain near the Rocky Mountain Front Range. Unique observations include highly resolved measurements of wave-like fluctuations in the wind speed, a persistent horizontal wind maximum during stratiform rain and associated with the melting-level height, and large pressure fluctuations and surges in wind speed at the surface. Stephen Cohn has been investigating these observations with supporting data from the Colorado mesonet, the Denver WSR88-D (NEXRAD) radar, and the regional rawinsonde network.

Spaced-Antenna Theoretical Development. Theoretical developments associated with the MAPR profiler continued during FY 96. These include estimation of the precision of spaced-antenna and Doppler-beam-swinging wind-measurement techniques, estimation of turbulence, and generalized theory treating measurements in the presence of horizontally anisotropic refractive-index irregularities. MAPR is being used to test these new ideas, using in situ data from the BAO tower for verification. Stephen Cohn and Stephen Oncley are participating in this research, in collaboration with Chris Holloway (NTIA/ITS), Richard Doviak (NOAA/NSSL), and Richard Lataitis (NOAA/ETL).

TOGA COARE Studies. Data obtained from several ISS stations (86 Kb) deployed during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) have provided an excellent opportunity to examine atmospheric circulations over the tropical western Pacific on a variety of scales. Kunio Yoneyama (a visitor from the Japanese Marine Science and Technology Center) and Dave Parsons have collaborated on a study of the appearance of very dry air in the middle troposphere over the equatorial oceans. Their results indicate that the dry air intrusions are due to the horizontal advection of air from subtropical and even middle latitudes rather than simply the subsidence of tropical air. This work has led them to study the impact of these events on convective organization and the surface energy budget over this region. In addition, Parsons is collaborating with George Young (Pennsylvania State U.) and his graduate student in obtaining a more complete climatology of convective outflows over this region.