3.2 Site Description
3.4 Implementation
3.5 Data Management
To address the scientific challenges outlined in the previous section, the following experimental strategy will be followed.
The design of CASES has evolved from a collaborative effort among university scientists, federal agencies, and national programs with similar scientific interests. The CASES design positions boundary layer instrumentation such that it coincides with the natural boundaries of a watershed. Such positioning simplifies efforts to close the surface water balance since the net runoff can be measured at one point. This, in turn, also helps verify other atmosphere/surface linkages. Thus, the boundary layer instrumentation, in conjunction with satellites, WSR-88D radars, stream gages, soil moisture data, topographical and land use data, surface meteorological data, biophysical data and coupled atmosphere-biogeochemical models, will allow for a detailed observation and description of event-driven, interseasonal, and interannual surface-atmosphere exchange processes.
The CASES site is located in the upper Walnut River watershed, north of Winfield, Kansas (see Figure 3 [10 kB]). This watershed was chosen for the following reasons:
CASES is envisioned to provide the infrastructure required to carry out long term and episodic field campaigns associated with surface-atmosphere exchange processes. Among the facilities and services provided would be a minimum "critical mass" complement of instruments, operated continuously during the lifetime of CASES, with supporting power, phone, and data management services. Instrument maintenance and site management will be available to ensure that the services provided will be used in an efficient manner. The facility will be available to individual investigators or groups of investigators who would either use the instruments in place or deploy an additional suite of instruments to complement the existing array. These investigators will be responsible for obtaining funding to deploy any additionally desired instrumentation. Mechanisms for data collection and archiving from the supplemental instrumentation will be in place but would also require funding from the PI(s).
As part of the implementation process (see section 3.4), modeling studies will provide guidance as to the preferred number and location of long term instrumentation. At this time, the following instruments are envisioned to eventually be part of the CASES site:
Six boundary layer (915 MHz) wind profilers, with virtual-temperature profiling (RASS) capability at half-hour intervals are envisioned to encompass the watershed. These will be used to observe the vertical structure of the atmospheric boundary layer (ABL) over the site. In conjunction with surface measurements and other methods to measure water vapor, they will also allow description of the horizontal advection of heat, moisture, and momentum. Characterization of the changing ABL is a critical component in understanding air-surface exchange processes.
Six mini-sodars, co-located with the profilers will be used to provide air flow data between 10 and 200m, a region the 915 MHz profilers have trouble resolving.
Six ceilometers, deployed in conjunction with the wind profilers, will be used to measure cloud base and better define the top of the boundary layer.
Ten flux stations, to provide eddy-correlation fluxes of heat, moisture, momentum, CO, and CO2. Measurements of the water and energy budgets will include precipitation, evaporation, soil heat/water content (2-3 m depth), ground water level, solar radiation, net longwave radiation, sensible heat flux, and latent heat flux. Ten soil heat/water content measurement sites within the footprint of each flux tower down to a depth of approximately 1.5 m, depth increment 15 to 30 cm, will be distributed to evaluate the spatial variability of this parameter. Three replicate precipitation measurements at distances of 100m and separated by 120 degrees will also be made.
The flux stations will be situated according to land use as defined by a GIS (Geographical Information Systems) analysis of surface properties. Both ecologists and meteorologists recommend that half be placed in the grassland that generally characterizes the eastern half of the CASES area, and the remaining half placed according to farming practice in the cropland that generally characterizes the western half. Prior experience suggests that ten is about the minimum number needed to represent the different surface types and provide sufficient areal coverage. Evaluation of this number will be part of the implementation process. These stations will characterize the near surface atmospheric environment, the earth boundary layer, and fluxes between the two.
Twenty surface meteorological stations, to get representative surface fields of temperature, insolation, humidity, wind, precipitation, and soil water/heat content. For hydrological/ecological purposes, each site will be surrounded by 3 replicate measurements of precip, and soil water/heat at a distance of 100 meters, separated by 120 degrees.
Surface data aid in the determination of horizontal advection for the long-term budgets and investigations of nonhomogeneous boundary layers, and enhance investigations of the role of the surface and planetary boundary layer in the dynamics of fronts, storm initiation, etc. They also provide mesoscale and microscale data needed for WSR-88D algorithm testing and hydrologic modeling.
Three additional stream gages are proposed between Augusta and Winfield: one each on the two major creeks to the east which feed the main stem of the Walnut, and one on the main stem between the two creeks. This will create four additional sub-basins in the southern half of the Walnut, facilitating hydrologic scaling and modeling studies.
Long-term, continuous humidity profiles need to be collected in conjunction with the profiler sites. However, affordable, accurate humidity profiling techniques remain elusive. The use of serial radiosondes, a tethered balloon, or an instrumented kite (or a combination) at these sites will be weighed against the cost of continuous profiling of humidity through remote sensing. More detailed humidity budgets will probably be the focus of episodic experiments. The CASES site could serve as an ideal testbed for developing and testing new humidity profiling techniques such as combining ground based GPS receivers with independent data and/or models.
Figure 4 (218 kB) and Figure 5 (14 kB) show the schematic locations of most of the proposed instrumentation for the CASES site. In Figure 4, the upper Walnut watershed, north of Winfield and east of Wichita, is heavily outlined. Type and location of various instrumentation is indicated by the colored circles as defined in the Legend. Black letters within the colored circles indicate existing or soon to exist instrumentation. White letters indicate instruments which will hopefully be obtained in the future.
Figure 5 shows 10 surface flux stations distributed throughout the basin in a manner which would reflect appropriate representation of component ecosystems. The 20 meteorological stations would be deployed more uniformly. Decisions on final site locations and numbers will be coordinated with numerical modeling simulations of the watershed and evaluations of site density contributions.
CASES is being initiated in FY 96 with the establishment of the Argonne National Laboratory (ANL) Atmospheric Boundary Layer Experiments (ABLE) in the southern half of the CASES site. The ABLE will be equipped to provide surface-based observations of the vertical profiles of temperature, humidity, and wind and the air-surface exchange rates of heat, moisture, and momentum. A continuous view of atmospheric processes will be provided with sufficient detail to enable significant advances in the description, understanding, and modeling of the atmospheric boundary layer.
The equipment (and variables observed) at the Argonne Boundary Layer Experiments as currently planned includes the following: (1) three 915-MHz radar wind profilers (RWPs) and radio acoustic sounding systems (RASS) (wind speed, direction, virtual temperature profiles); (2) three minisodars (wind and turbulence profiles); (3) one lidar ceilometer (cloud base height); (4) one balloon-borne sounding system (wind, temperature, moisture profiles); (5) five surface flux stations (surface sensible and latent heat, momentum flux, ground heat storage); (6) five soil sampling stations (soil moisture, soil temperature); (7) one satellite data receiver-processor; (8) one data hub at a central location on site for data collection; and (9) one (extra) instrument pad at the central site to facilitate deployment of supplemental instrumentation during episodic experiments.
During FY 1995, efforts at Argonne were focused on planning, coordination with CASES, acquisition of a workstation to serve as part of the data hub, and acquisition of one 915-MHz RWP-RASS. One existing 915-MHz RWP-RASS existing at Argonne was evaluated and modified for installation at the Walnut River Watershed. These two systems and a 915-MHz system independently supplied by the ARM program will be installed during 1996 at the vertices of a triangle drawn over the southern half of the CASES site, and the three systems are expected to begin producing data by summer or early fall of 1996. Efforts are also underway to install and begin operation of an eddy correlation system available at Argonne for measuring fluxes of heat, moisture, momentum, and possibly carbon dioxide within the array during 1996. Satellite data receiving-processing capabilities already exist at Argonne for polar orbiting satellites, and routine data collection for evaluation of non-dimensional vegetative indices will begin as surface data collection begins. In FY 1996, work will include adaptation of minisodars (item 2) existing at Argonne and installation in the ABLE; acquisition of surface flux stations (item 5); and site preparation involving leases, equipment installation, data communications, and related tasks. Methods of exchanging data with the ARM program will be developed. Overall, Argonne plans to complete the ABLE during FY 1998.
Using the ABLE as a nucleus, implementation of the entire CASES facility will be approached via coordinated proposals designed to:
The first effort is embodied in an experiment planned for 15 April-15 June, 1997 called CASES-97, which will address the first three objectives listed above. CASES-97 consists of an original core experiment that has been joined by a number of complementary experiments focusing on one or more of the objectives. Though each is self-contained, all can benefit from coordination with the others. Principal investigators and instrumentation come from several agencies and universities (see Table).
Scientists planning to participate in the CASES 97 core experiment (CASES-97-1a) include:
Margaret A. LeMone, NCAR, who will work with Robert Grossman, CU, on budgets and PBL diurnal variation, and with Richard Coulter, Marv Wesely, and others at Argonne to evaluate profiler data.
Robert L. Grossman, University of Colorado, who will (a) work with LeMone on budgets and PBL diurnal variation, and with Coulter on the effects of regional surface characteristics on surface exchange. (b) use conditional sampling to estimate the effect of entrainment events on the near-surface (3-m) fluxes
Richard Coulter and Marv Wesely, Argonne National Laboratory, who will work with LeMone and Grossman on evaluation of the profiler data.
Roger Pielke, Colorado State University, who will (a) run a version of RAMS to aid in the design of the field campaign, (b) run an operational version as an aid to forecasting during the field program; (c) produce surface-property data sets and analysis products with complete data for post-analysis (both budgets and diurnal variation), with Zeng; (d) produce surface-property datasets to be used along with meteorological datasets for parameterization testing, with Grossman, LeMone, and Zeng; (e) run a version of RAMS to identify the minimal long-term deployment needed to optimize instrumentation of the CASES site.
Xubin Zeng, University of Arizona, who will (a) evaluate a land surface scheme (BATS) coupled with the boundary layer scheme in NCAR climate model (CCM3) with an emphasis on soil moisture, surface temperature, equivalent potential temperature in the boundary layer, and boundary layer top entrainment interactions (with Grossman, LeMone, Pielke, Coulter), and (b) investigate the feasibility of using aircraft to document the effects of mesoscale eddies on boundary layer fluxes.
As part of CASES 97, related studies in hydrology, surface-layer processes, boundary-layer physics, and precipitation measurement, are planned by the following scientists:
Bruce Hicks (NOAA/ARL), Marvin Wesely (Argonne) and Robert Grossman (CU) who plan to use tower and NOAA twin aircraft data to study air-surface exchanges in conditions of patchy surface wetness.
Larry Mahrt (Oregon State Univ.), Jielun Sun (CU) and Robert Grossman (CU), who plan to (a) study the differences between the windy, weakly stratified and very stable, weak wind nocturnal boundary layers, (b) investigate proper use of surface temperature in bulk flux formulas, and (c) study effects of entrainment events on surface fluxes.
Richard Cuenca (Oregon State Univ.), who plans to determine the relationship between the predominant length scales of soil moisture content, soil hydraulic properties and precipitation and whether or not one or more of these length scales is affected by seasonality. Instrumentation includes a combination of automated and manual time domain reflectometry sites for soil moisture content, distributed tension infiltrometer measurements for soil hydraulic properties, and a rain gage network for precipitation.
James Wilson, Edward Brandes and Jothiram Vivekanandan (NCAR), Dusan Zrnic (NSSL), and V. Chandrasekar (Colorado State Univ.) who plan to deploy NCAR's S-Pol radar and evaluate dual-polarimetric data in conjunction with WSR-88D data to determine potential improvements in precipitation estimation and hail detection algorithms. Will cooperate with Duchon, Stewart, and Cuenca.
Claude Duchon (Univ. of Oklahoma) and Michael Stewart (Scientific Operations Officer at the WSFO in Wichita), who plan to evaluate WSR-88D precipitation estimation algorithms, addressing such issues as range biases and modifications to the Z-R relationship.
Ray Arritt and Moti Segal (Iowa State), who plan to use the data from this experiment, along with data they will collect on larger scales, to study the interaction of boundary-layer processes with regional scale dynamics in the evolution of the low-level jet.
Tom Parish and Al Rodi (Univ. of Wyoming), who tentatively plan to use Wyoming King Air measurements to study evolution of the low level jet.
Dennis Ojima (Colorado State Univ.), who plans to use the CENTURY model to assess ecosystem controls on water, carbon, and other trace gas fluxes into the atmosphere. The impacts of changes in climate on land use at the CASES site will be evaluated relative to changes in H2O, and N exchange with the atmosphere. An eddy accumulation system is planned for the CASES site to measure C and H2O exchange and determine the biospheric controls on C and H2O fluxes from different land cover types. Linkages between the atmosphere, hydrosphere, and biosphere will be evaluated using an integrated model of the coupled systems.
Cross-cutting scientifically, the objectives of CASES-97 can be divided generally into fair-weather (CASES-97-1) and rainy-weather (CASES-97-2) goals. The fair-weather goals are to: (a) document effects of surface wetness on atmospheric planetary boundary layer (PBL) diurnal evolution incorporating PBL and surface data into observational analysis and numerical simulations using the Regional Mesoscale Atmospheric Modeling System (RAMS); (b) document the relevant length scales for soil moisture content and hydraulic processes; (c) test the representation of PBL, surface-process, and subsurface evolution parameterization schemes (e.g., the Biosphere-Atmosphere Transfer Scheme, BATS); and (d) use the analyses to evaluate the ABLE profiler data. The rainy- weather goals are to test existing and alternative WSR-88D precipitation-estimation algorithms and to explore use of dual-polarization information as a means for further improvements in precipitation estimation techniques.
The three wind profilers (minisodars plus 915 MHz wind profilers) with RASS that represent the first-stage deployment of the ABLE will serve as the instrumentation nucleus for CASES-97. If all the proposals of the PIs in the table are successful, additional instrumentation will include 11 surface flux stations (8 PAM IIIs requested from the NSF Deployment Pool, one flux tower operated by ARM/CART, one flux tower from Argonne National Laboratory, and one flux tower from NOAA. Each of the flux towers will sample heat, moisture, and momentum fluxes using the eddy-correlation technique, net radiation, incoming solar radiation, and the standard meteorological variables (wind, temperature, humidity, precipitation). At least two flux towers (Argonne, NOAA) will provide estimates of ozone and CO2 fluxes, and at least two (Towanda, one PAM III) will have soil moisture profiles. CLASS radiosondes will be collocated with the profilers (for soundings at 1.5-h intervals for five 24-hour IOPs), and two aircraft (the NOAA Twin Otter and the Wyoming King Air) have been requested for daytime PBL observations (the King Air may also be requested for nighttime observations of the low-level jet, see Table). The NSF S-band POLarimetric (S-POL) radar will be deployed near the Wichita WSR-88D Doppler radar. 35 rain gages will be deployed in the Towanda sub-basin and another 25 will be distributed throughout the remainder of the Walnut watershed. During a 3-4 week period, soil moisture measurements will be taken at 25-30 locations within the Towanda sub-basin every 1-2 days for comparison to the soil-moisture profiles taken at the Towanda flux station. On the larger sale, JETEX-97 has requested collocation of Integrated Sounding Systems (ISSs) with the NOAA 404-MHz wind profilers at Jayton, Texas, Vici, Oklahoma, and Haviland, Kansas.
Numerical models will be used extensively by several of the PIs in the course of their data analysis. Pielke's runs of RAMS (CASES 97-1a) will be used to aid in siting the surface flux stations as well as to aid in deciding on whether or not to have an IOP. After the experiment, RAMS data will be used to evaluate PBL budgets of heat, moisture, and momentum through the diurnal cycle, for comparison with those derived from observations alone. Zeng will be using CASES-97 data to test the Biosphere-Atmosphere Transfer Scheme (BATS), the PBL scheme used in the NCAR Community Climate Model CCM3, and to link the two schemes. Hicks et al. will use a version of RAMS developed at NOAA/ARL as an aid in interpretation of their results. In JETEX-97, the PIs seek to improve the ability of the NCAR/Pennsylvania State University MM5 mesoscale model to replicate the low level jet. Dennis Ojima of Colorado State University will be conducting runs using the CENTURY model to assess ecosystem controls on water, carbon, and other trace gases into the atmosphere, using historical data from the CASES area, and CASES-97 data, in preparation for more ambitious measurements later on. Cuenca will work with Dennis Lettenmaier of the University of Washington to incorporate length-scale information into hydrologic models, and with Larry Mahrt and Michael Ek of Oregon State to incorporate results into the OSU Coupled Ocean Plant Soil (CAPS) model.
Additional scientists may become involved as planned CASES 97 activities are confirmed.
A more ambitious and extended field phase (CASES 98) is envisioned for Fall of 1998 through Spring of 1999 . Preliminary thoughts are that this experiment would include an expansion of the profiler array, flux, and meteorological stations to encompass the entire CASES site. A continuation and expansion of the CASES 97 foci to include an interseasonal component is planned. A national planning meeting in the late Fall of 1997 would be an appropriate forum for the presentation of preliminary results from CASES 97, obtaining guidance for CASES 98, and entraining additional scientists interested in pursuing research as part of CASES.
The development and maintenance of a comprehensive and accurate data archive is critical to meeting the scientific objectives of CASES. The project has been designed as a multi-agency sponsored, multi-disciplinary program with potentially many different investigators and varied instrumentation over several years. An integrated data management activity is central to providing a consistent high quality database that is easily accessible throughout the lifetime of the program and beyond. The CASES data management philosophy is to make the completed dataset available to the research community as soon as possible. This will permit resolution of the interdisciplinary research objectives in a timely fashion and permit access by a broader community.
CASES has proposed that the following data protocols be followed by all participants.
Field observation programs can provide exciting opportunities for students to learn about science. These can range from merely stimulating the scientific curiosity of middle and secondary school students, to providing hands-on experience for undergraduate and graduate students to learn about instrumentation, sampling problems, measurement errors, data collection, analysis and interpretation. The long-term and episodic components of CASES offer some unique possibilities in this regard.
First, CASES is multi-disciplinary, involving meteorology, climate, hydrology, ecology and chemistry. The fact that our environment acts as a system in which each component influences every other component is an important lesson for both students and teachers to learn at all levels of education. CASES will present an opportunity to observe these interactions occurring in a dramatic way when, for example, a thunderstorm passes through the Walnut River watershed in the midst of a dry period during the growing season. The influence of this event on stream flow, water quality, air quality, vegetation, and practically every land and atmospheric variable would be easily seen in data gathered using the proposed instrumentation. With data collected throughout the year, there will be opportunities to observe a spectrum of interesting events.
Second, physical measurements will be made using both standard and state-of-the-art instrumentation. Thus, university students will have the opportunity for hands-on experience collecting data themselves and/or observing how data are collected. Understanding the idiosyncrasies of instrumentation and the limitations of the data acquired are important to balance perceptions gained from the use of computers which generate seemingly "perfect" data. There has been a growing realization in the past few years that too few college science students either appreciate the important role that observational data play in the geophysical sciences or graduate with even a minimal appreciation of the limitations of environmental measurements (Takle, 1989; Atlas et al. 1989, Serafin et al. 1991). CASES can help remedy this situation by providing an incentive for faculty and students to engage in field studies either as part of a course of study or as thesis research. Various levels of student involvement will be possible ranging from short-term non-funded research projects, to summer employment, to discipline specific and multi-disciplinary research assistantships.
A third attribute of CASES is that it is a longer-term field effort. This allows time for developing a substantial educational component which can improve science education in middle and high schools. To enhance science literacy among secondary students and teachers, a long-term field facility with episodic experiments can serve as a classroom-in-the-field for observing scientific activities and a field-in-the-classroom for examining data from those activities and determining their physical meaning. Programs are envisioned in which students and teachers visit field observational sites, scientists and graduate students visit schools, and data sets collected in field projects are made available for classroom study by students and teachers.
What makes all this possible is the ease with which field data can now be brought into classrooms at all education levels using current data communications. Unidata, a branch of UCAR, whose mission is to empower U.S. schools and universities with the ability to access and utilize data streams, has the capability to effect such a distribution. With color display monitors and well-trained teachers to provide guidance, students can quickly grasp salient environmental interactions occurring in the Walnut River watershed. Educational materials (i.e., study guides, problems to be solved) will have to be designed to take advantage of the dynamic physical data that will be available.
Finally, it is critical to the success of any field program that there be a clear understanding of its objectives by the affected land owners, business people, and the general public, and that there be sustained good will between these groups, scientists, and other individuals connected to field projects. Thus, CASES will develop an outreach program where project personnel with sound communication skills can talk to both organizations and the general public through service club meetings, town council meetings, and the media.
A joint Argonne/NCAR/NOAA CASES project office, consisting of a project director and a computer programmer, has been established within the Mesoscale and Microscale Meteorology division of NCAR. The primary roles of the office at this time are to: continue developing funding resources for CASES; identify, coordinate, and facilitate research opportunities for the scientific community; establish an operational data management scheme addressing all aspects involved in providing access to continuously collected observations relating to the CASES site; and to develop three-dimensional graphics to depict the data streams.
Experiment planning and logistics have been and will continue to be coordinated by the CASES project office in conjunction with the national scientific community through participation in planning meetings, workshops, and working groups. Additional coordination with Argonne National Laboratory, UCAR's Office of Field Project Support, federal agencies, and other research programs is ongoing.
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