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Surface and Sounding Systems Facility (SSSF)

• 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, NOAA, and other government agencies.
• Development of new data-telemetry systems to support ATD’s field-data communication 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.

Field Support Activities

The Lake-Induced Convection Experiment (Lake-ICE). This project sought to determine how the atmosphere is modified by underlying heat and moisture sources by focusing on two important scientific goals: (1) to determine mechanisms which control the structure and evolution of mesoscale convective circulations (such as rolls and shore-parallel bands) in boundary layers strongly heated from below, and (2) to determine interrelationships between these mesoscale circulations, fluxes throughout the depth of the boundary layer, and cloud and precipitation development.  Additionally, Lake-ICE sought to identify the processes by which heat and moisture fluxes from each of the Great Lakes augment large-scale atmospheric processes.  The SSSF GPS/Loran Atmospheric Sounding System (GLASS) and Integrated Sounding System (ISS) systems were deployed around Lake Michigan to give detailed information on the atmospheric conditions immediately before and after the passage of air over the lake.  There were three primary goals for the Lake-ICE sounding facilities:  (1) obtain atmospheric profiles around the boundary of Lake Michigan, (2) observe and quantify the Great Lakes Mesoscale Aggregate Vortices (MAVs), and (3) observe conditions in and near intense snowbands over the lake.

Snowband Dynamics Project (Snowband).  The Snowband experiment was run concurrently with the Lake-ICE experiment and utilized the same aircraft and ground facilities.  The two experiments were synergistic and complementary.  The Snowband project sought to understand the dynamic and thermodynamic structures of heavy precipitation bands in the northwest quadrant of cyclones and in the “reverse lake-effect” regions west of Lake Michigan.  One goal of the project was to determine the relative goals of isentropic ascent, conditional symmetric instability, and transverse ageostrophic circulations associated with frontogenesis in the production and maintenance of the heavy snowbands associated with cyclones.  A second goal was to determine how boundary-layer fluxes of heat and moisture from the lake modify frontal structure, stability, and precipitation band dynamics in the vicinity of the lake during the approach of cyclones from the west.  The GLASS and ISS systems provided atmospheric profiles during the snowband events.  The GPS Dropsonde System was installed on the NCAR Electra and provided measurements of the cross-band frontal structure.  Dropsondes were deployed at about 20-km intervals across the storm front.

South China Sea Monsoon Experiment (SCSMEX).  SCSMEX was directed toward an improved understanding of air-sea coupling and convective processes over the  South China Sea during the onset of the summer monsoon.  Current skill in predicting the monsoon onset is limited and the nature of air-sea exchange and convective processes, which may have an important influence on the timing of the onset, are relatively unknown.  To investigate the details of the air-sea exchanges associated with the onset of the monsoon, SSSF provided two enhanced surface stations (one for each of the PRC ships, Kexue No.1 and Shiyan No. 3) to measure surface fluxes utilizing the bulk method.  The automatic surface stations measured pressure, temperature, relative humidity, incoming solar radiation, incoming infrared radiation, wind speed, wind direction, and sea-surface skin temperature.  The latter measurement was made using a modified version of C. Fairall’s (NOAA/ETL) “sea snake”.  The data were logged by ISS data loggers and laptop computers and transmitted to the operations center at the Hong Kong Institute of Science and Technology via the INMARSAT satellite.

Oklahoma Atmospheric Surface-Layer Instrumentation System - Phase I (OASIS).  The University of Oklahoma Climatological Survey (OCS) is developing the capacity for Oklahoma Mesonet meteorological stations to make additional measurements suitable for estimation of the components of the surface energy budget, in particular the surface sensible and latent heat fluxes.  OCS proposes to use indirect aerodynamic and surface energy budget measurement techniques at the majority (90) of their Mesonet sites.  Additional, direct eddy-covariance instrumentation will be installed at nine “Super-Sites”, one located within each of the nine climatic divisions in the state of Oklahoma.  In order to evaluate and quantify the measurement uncertainties of the Oklahoma Mesonet flux estimates, SSSF deployed the Integrated Surface Flux Facility (ISFF) from mid-June to mid-August 1998, adjacent to a prototype OCS flux station in Norman, Oklahoma.  The project was designed to provide a direct comparison between fluxes measured by ISFF using eddy-covariance techniques and fluxes measured by OCS using indirect techniques.  This detailed evaluation utilized the ISFF configured in an intensive micrometeorological array to measure multi-covariance fluxes of momentum, heat, and moisture at two levels, as well as incoming and outgoing fluxes of long-wave and short-wave radiation.

Regional Forest-Atmospheric Boundary Layer Coupling (Forest - ABL).  Terrestrial ecosystems are strongly coupled to the atmospheric boundary layer (ABL).  Long-term, tower-based, eddy-covariance flux measurements have been used to study ecosystem-atmosphere exchange of CO2.  These tower-based measurements reveal a great deal about exchanges at the surface, but they do not capture the coupled dynamics of the ecosystem-ABL system.  For the Forest-ABL experiment, SSSF deployed an ISS next to an instrumented television tower in Park Falls, Wisconsin.  The ISS was deployed on 1 March 1998 and has been operating for the entire growing season.  This year’s experiment will end on 31 October 1998. The instrumented tower obtains flux measurements up to 400 m above ground level, while the 915-MHz wind-profiler portion of the ISS continuously measures the boundary-layer height.  Radiosondes are periodically launched to obtain boundary-layer heights and water-vapor profiles.  The PIs will use the observations with a one-dimensional coupled ecosystem-ABL model to try to determine the significance of ecosystem/ABL coupling in (1) estimates of the Northern Hemisphere “missing sink” of CO2, (2) the net ecosystem exchange of CO2 and (3) modification of the local climate.

Surface Heat Budget of the Arctic Ocean (SHEBA).  Four portable Integrated Surface Flux Facility (ISFF) surface flux stations were deployed in September 1997 in support of a 13-month field program to study the surface heat budget of the Arctic ice pack. The field site is a camp placed on the drifting ice in the Beaufort Sea north of Alaska, and the ISFF stations have been placed at sites chosen to sample the diversity of local ice and snow conditions.  In addition to the standard meteorological measurements of wind, pressure, temperature, and humidity, the ISFF stations are measuring turbulent fluxes of momentum and heat, incoming and outgoing fluxes of long-wave and short-wave radiation, and the surface heat flux at the snow/ice boundary.  The data are telemetered in real-time to the project field base located on a Canadian ice-breaker research ship frozen into the ice pack for the duration of the project. The ISFF stations were heavily modified prior to their deployment to produce electrical power with propane thermoelectric generators and to warm the electronics by housing them with the generators. Other modifications include the use of GPS receivers and electronic compasses to continuously monitor station location and orientation, as well as to provide accurate time-keeping.

Development Activities

During the year, system software development continued to provide better display capabilities and to improve the overall reliability of the main data-collection program.  A new program, AVAPS Editor (see Radiosonde Sounding Analysis), was developed by SSSF for efficient post-processing of the dropsonde data.  The first prototype version of AVAPS Editor was installed on the AVAPS systems on all the USAF WC-130H aircraft.  The new software has been used by the Air Force to provide in-flight data quality control and operational capability to send a coded WMO message in real time via a satcom link to the National Hurricane Center during missions.  Over 1,000 soundings have been successfully processed this past year with AVAPS Editor.

Colorado University Flux Facility (CUFF).  During FY 1998, the Colorado University Flux Facility (CUFF) has been successfully deployed on Niwot Ridge west of Boulder, Colorado.  In addition, The CUFF Relaxed Eddy Accumulator (an SSSF development) has been used in determining CO2 isotope exchange fluxes.

Dual-Wavelength Net Radiometer.  Tony Delany and Steven Semmer have developed an advanced net radiometer to increase the accuracy of single-instrument measurements of surface radiation flux. Conventional net radiometers make separate measurements 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 direct measurements of differential net short-wave and long-wave radiation. The system was designed so that numerically controlled machining techniques could be used in its manufacture, thus substantially reducing construction costs. Other advanced features include data acquisition and manipulation capabilities, and integrated ventilation and leveling. The further development, fabrication, and testing of this system depends upon approval of outside funding.

Infrared (IR) Water Vapor Sensor.  Steven Oncley and Steven Semmer redesigned the electronics for a prototype low-power IR water vapor sensor to be used for flux measurements.  The new electronics are expected to reduce the excessive noise level in an earlier prototype.  Testing of the improved design of the sensor will continue in 1999.

Integrated Surface Radiation Measurement System.  During the past year, four of these new systems have been operated with the ISFF Flux stations used in the SHEBA field program; an additional system was used during the OASIS-98 project.  The SHEBA project provided useful insight into how to prevent riming on the dome surfaces of the sensors.  A paper was published in Journal of Atmospheric Technology during the year on this new system.

Ozone Sensor Development.  This past year has seen continued development of a small, low-powered, lightweight, inexpensive, fast ozone sensor using a Surface Effect Chemiluminescence (SECL) technique.  The initial motivation for the development of this small sensor was for use in a dropsonde that could be deployed from a high-altitude aircraft.  Even though this is still a potential use for the sensor, other applications have arisen.  One of those applications is for making fast, accurate, surface ozone flux measurements using eddy correlation.  To develop a sensor for this purpose, two different ozone measurement methodologies have been integrated.  The SECL sensor provides the fast response, while an ultraviolet absorption (UVAB) technique is used for accuracy.  An onboard microprocessor enables the output of the two different sensors to be integrated and promising.  The initial test results look very promising.  Further field testing will be conducted in the coming year, with the sensor to be deployed alongside an ISFF station in an upcoming field program.

Integrated Surface Flux Facility (ISFF).  Over the past 18 months, the Portable Automated Mesonet (Flux-PAM) and the Atmosphere-Surface Turbulent Exchange Research Facility (ASTER) have been combined into a single Integrated Surface Flux Facility (ISFF).  Since the sensors used by the two formerly separate facilities are quite similar, this has primarily entailed integration of the data transmission, archival, and display software used in the ISFF field base.  The ISFF retains the capability to be deployed either as a mesonet of surface flux stations, as an intensive micrometeorological array at a single site, or as some combination of these two configurations. 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 the bandpass covariance technique, as well as the prototype development of a low-power, low-cost, fast-response, infrared-absorption hygrometer.  Efforts have also continued to refine sonic anemometer design to minimize the effects of flow distortion by the sonic array.  Finally, in order to solve sensor icing problems arising during the SHEBA field project, low-power-consumption hardware and self-diagnosing control software were developed to provide heating for both sonic anemometers and radiometers.

Radiosonde Sounding Analysis.  Initiated by the AVAPS program, new software is under development for the quality control and analysis of radiosonde data.  Based on procedures refined by the National Hurricane Center, the software applies a suite of well-tested and robust techniques to detect and compensate for errors in the sounding observation.  The software can process both AVAPS dropsonde and GLASS upsonde data sets.  The initial development is approximately 80% finished.  A fully generic WMO TEMP message encoder is being developed as part of the package.  The final product will be capable of performing the first-order processing of data from most radiosonde types.  This software will become the core radiosonde data processing package employed within SSSF.

ISFF Software Infrastructure.  Support software was developed during the year to provide daily transfer of real-time project data sets and online field logbooks from the remote ISFF base station over low-bandwidth Internet links.  This new capability was first used during the year-long SHEBA project, where the communications link was provided by an INMARSAT satellite.  Daily summary plots, weekly drift plots of the ISFF stations, and completed data sets for PIs are now made available on the Web.  Software for integration of the PAM and ASTER systems into ISFF was enhanced to support assimilation of general flux time series from other systems, allowing real-time intercomparison of NCAR and non-NCAR sensors during the OASIS-98 field project.

Wind-Profiler Antenna Test Range.  A basic antenna test range to measure the relative radiation pattern at low elevation angles was built cooperatively at the Marshall field site by researchers from SSSF, the NOAA Aeronomy Laboratory (NOAA/AL), the NOAA Environmental Technology Laboratory (NOAA/ETL), and Radian Corporation.  The range is currently being used to test the near-horizon sidelobe energy of a boundary-layer profiler antenna newly designed by ETL to minimize sensitivity near the horizon.  (Signal contamination by moving clutter can limit the ability of  profilers to make accurate measurements in severe environments, especially at very low altitudes.)  The range will also be used to test a variety of clutter-screen designs and edge treatments for existing clutter screens that have been proposed to address the clutter problem.

Multiple Antenna Profiling Radar (MAPR).  MAPR uses 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.  The latter measure winds through the Doppler technique, using multiple beam directions.  Measurements from MAPR are being compared directly with those from Doppler systems, and from in-situ sensors on a 300-m tower.  Recent emphasis has been on improving the sensitivity of this profiler to get reliable measurement in clear-air conditions when the signal-to-noise ratio is weak.  Pulse coding capability and a more powerful transmitter have recently been added.  Software upgrades have also been incorporated to allow operation under a UNIX (multi-tasking) operating system.  Planned software upgrades will allow wind computation in real-time, eliminating a post-processing step formerly required.

Wind-Profiler Real-Time Software Development.  The MAPR real-time control software was significantly enhanced by the addition of analysis and display functions.  These allow for the real-time calculation and archival of the full suite of correlation functions, and real-time display of time series, power spectra, and correlation functions for all receivers.  In particular, the online calculation of correlation functions results in significant reductions in MAPR data handling and post-processing calculations, allowing for increased production of the primary data products.  The addition of pulse-coding capability in the real-time control and signal processing software has allowed for a quadrupling of the radar power output and associated improvements in the signal-to-noise ratio and measurement quality.

UW Sonic Anemometer.  SSSF staff built a new sonic anemometer array to house commercially available transducers and electronics.  This array is based on a University of Washington design that has been demonstrated to produce wind velocities with minimal array-induced distortion.  Furthermore, this array should operate well in precipitation, since the transducer faces are inclined.  Two such probes were operated during OASIS-98.  Analysis of these data will be completed in FY 1999.

Research Activities

Atmospheric Radiation Measurement Program (ARM).   A long-term research effort, termed the Integrated Data Assimilation and Sounding System (IDASS) Program, has been funded by DOE ARM. This effort, led by Dave Parsons, includes staff funding for the MAPR program, a broad collaboration on data assimilation between MMM and ATD, and field measurements in the tropical western Pacific. The measurements in the tropical western Pacific were taken during the Tropical Ocean Climate Study (TOCS) cruise aboard the Japanese research vessel R/V Kaiyo. This deployment included an ISS with the SABL lidar to examine the diurnal variations of precipitation systems and to measure the impact of tongues of dry mid-latitude air on tropical cloud systems. These measurements will test hypothesis put forth on these topics in a recent manuscript. High-resolution modeling tests of the cloud fields during these dry intrusions are also being conducted. A unique aspect of this cruise was that the observation time corresponded to a strong westerly wind burst associated with the early stages of the intense 1997-1998 El Nino. Further research on this data set is underway by Parsons, in collaboration with M. Reynolds (BNL) and K. Yoneyama (JAMSTEC).

Lidars in Flat Terrain (LIFT).  Three lidars were deployed at the LIFT experiment in 1996, a backscatter lidar (SABL), a Doppler lidar (HRDL), and an ozone DIAL.  In addition, two ISS and three Flux-PAM stations were deployed for a companion field study, Flatland Observatory Project II.  Stephen Cohn (SSSF), along with Wayne Angevine (NOAA Aeronomy Laboratory) are examining the ability of different instruments used in this study to measure convective boundary-layer height and entrainment-zone thickness.  Other boundary-layer properties, including vertical velocity statistics, boundary-layer turbulence, and shallow nocturnal low-level jets, are being studied using the LIFT dataset in collaboration with Robert Banta  and Christoff Senff (NOAA/NCAR Joint Optical Remote Sensing Group).

Spaced-Antenna Analysis.  Under the ARM/IDASS program Stephen Cohn and William Brown are examining theoretical limits to the performance of spaced-antenna (SA) wind profilers (MAPR in particular) under low wind speed or strongly turbulent conditions.  In these situations the cross-correlation functions used in SA wind measurement quickly become decorrelated. It was found that “zero-lag” techniques have an advantage over those  techniques relying on features of the correlation functions at longer lags.  Cohn and Brown are collaborating in this work with Chris Holloway (NTIA/ITS), Richard Doviak (NOAA/NSSL), and Richard Lataitis (NOAA/ETL).

Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE).  During the past year Dave Parsons continued his work on the TOGA COARE (TC) data set. His primary focus is to understand the large-scale flow that leads to the lateral transport of extremely dry, mid-latitude air into the middle and lower troposphere over the equatorial western Pacific. Previous researchers hypothesized that this dry air had subtropical origins. However, in a paper to be published in Journal of Atmospheric Science (in press), Yoneyama and Parsons show that this air had middle latitude origins and was transported equatorward in association with the breaking of middle latitude Rossby waves. Recent work by Parsons in collaboration with C. Thorncroft and A. Dethof (University of Reading) suggests that these dry air masses may actually originate in the stratosphere and be initially transported downward and equatorward by baroclinic waves. This research also suggests that this lateral mixing of dry air is a major term in the moisture budget in the tropics, and could even exceed the drying resulting from large-scale, convectively induced subsidence over tropical areas.

U.S. Weather Research Program (USWRP).  According to the goals of the USWRP, one of the main stumbling blocks to improving quantitative forecasts of precipitation, especially during the warm seasons, is the need for more accurate estimates of the vertical profile of water vapor. Michael Hardesty and Dave Parsons received support from the USWRP to explore methods to improve estimates of the vertical profile of water vapor and to determine the impact of this improvement on precipitation forecasts. Hardesty and colleagues are concentrating on developing a low-cost water-vapor DIAL system to provide a direct measurement of water vapor. Parsons is collaborating with Yong-run Guo, Bill Kuo, and James Dudhia (MMM) on using the indirect approach of variational data assimilation (4D-VAR) to estimate this profile. The results thus far  are promising and are being submitted to Monthly Weather Review. for publication later this fall.  Improvement in the vertical profile of water vapor was noted through assimilating GPS measurement of the vertically integrated water-vapor content, the surface dew-point temperature, surface rainfall, and data from the wind-profiler demonstration network. Significant improvements in the predicted temperature fields were also noted. William Brown is also working with Parsons on using the GPS data systems to nowcast convective systems.

TOGA COARE Radiosonde Humidity Data Problem. ATD scientists and engineers have continued to work this past year on trying to resolve the TC dry-bias errors in the radiosonde humidity data.  Good progress has been made by ATD working closely with the radiosonde manufacturer (Vaisala) in understanding the cause of the dry-bias and in developing algorithms to resolve the problem.  Contamination of the humidity sensor polymer (used as the dielectric in the capacitive sensor) during packaging and storage was determined to cause the dry bias.  Occupation of sites in the polymer by contaminant molecules reduces the response of the polymer to water-vapor molecules and thus induces an apparent dry bias relative to the original calibration condition.  This coming year all of the TC data will be reprocessed using the correction algorithms developed by ATD and Vaisala.  These general correction algorithms, tested by application to the TC data set, will have a wide application to global re-analyses and to weather and climate research.  This work will also lead to improved manufacturing and calibration processes that will largely eliminate future biases, resulting in significantly improved humidity measurements.

South China Sea Monsoon Experiment (SCSMEX).  Through funding from the NOAA Office of Global Programs, Dave Parsons is collaborating with Richard Johnson (CSU) to develop improved understanding of the Asian monsoon in the vicinity of southeastern China. The Asian monsoon has a pronounced impact on the social and economic condition of over 60% of the earth’s population. The variation in the monsoon also impacts the climate and weather in other locations in the middle latitude and tropics. During the SCSMEX project, ATD surface stations were deployed on two Chinese research vessels located in the South China Sea. For the first time in an ATD deployment, the surface stations included two in-situ devices to measure the sea surface temperature. Research is underway to use these measurements to derive surface fluxes from bulk formulas. These data will be combined with data from the sounding and radar networks, together with numerical modeling efforts, to study the factors that control the variation in monsoon rainfall over this region.

Improved Forecasts of Hurricane Re-Intensification.  Some of the most damaging large-scale flooding events in middle latitudes result from the remnants of tropical cyclones. Unfortunately, these events are often poorly predicted in forecast models. While a visitor at the University of Reading during summer 1998, Dave Parsons collaborated with K. Browning, A. Thorpe, and others at that university on the problem of improving the forecast of a selected event of this type that struck Ireland and the British Islands. Through using the concepts of potential vorticity and singular vector analysis, these investigators were able to improve the forecasts of the ECMWF and British Meteorological Office prediction models. A publication on this subject will be submitted soon to the Quarterly Journal of the Royal Meteorological Society.

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