SGP Science

Overall Objectives

The primary goal of the Southern Great Plains (SGP) site is to produce data adequate to support significant research addressing the objectives of the overall ARM Climate Research Facility. These overall objectives, as paraphrased from the ARM Program Plan (DOE 1990), are the following:

  • to describe the radiative energy flux profile of the clear and cloudy atmosphere
  • to understand the processes determining the flux profile
  • to parameterize the processes determining the flux profile for incorporation into general circulation models

To meet these objectives, an empirical data set must be developed that includes observations of the evolving radiative state of the column of air over the central facility, in addition to the processes that control that radiative state. This data set must have sufficient detail and quality to support the investigations proposed by the ARM Science Team.

To address the entire SGP site, ARM scientists rely on models to compute the processes or properties that affect radiative transfer. This set of data includes measurements of radiative fluxes (solar and infrared) and the advective and surface fluxes of moisture, heat, and momentum occurring within the column and across its boundaries. Other entities to be described are cloud types, composition, and distribution (depth, fractional coverage, and layering); thermodynamic properties of the columnar air mass (temperature, pressure, and concentrations of all three phases of water); the state and characteristics of the underlying surface (the lower boundary condition); processes within the column that create or modify all of these characteristics (including precipitation, evaporation, and the generation of condensation nuclei); and radiatively significant particles, aerosols, and gases. Basic continuous observations must be made as often as is feasible within budgetary constraints. For limited periods of time, these observations will be supplemented by directed intensive operational periods (IOPs) providing higher resolution or more difficult-to-obtain in situ data.

Furthermore, it is imperative that scientists determine the data stream character and quality as early as possible in the observational program. This evaluation will provide the basic operational understanding of the data necessary for an ongoing program of such scope. Although both a reason and ample opportunity will exist to develop a further understanding of ARM observations over the course of the program, the task of investigating and ensuring the data quality is extremely important. In this regard, early and definitive quality measurement experiments (QMEs), routine instrument mentors, Site Scientist Team (SST) data quality assessments, definitive QMEs, and value-added products (VAPs) will help establish confidence in the measurements.

The SGP site is the first of three global locations chosen and instrumented for data collection. As summarized in the Science Plan for ARM (U.S. DOE 1996), the scientific issues to be addressed using data from a midlatitude continental observatory site include the following:

  • Radiative transfer in cloudless, partly cloudy, and overcast conditions
  • Cloud formation, maintenance, and dissipation
  • Nonradiative flux parameterizations
  • The role of surface physical and vegetative properties in the column energy balance
  • Other complications in the radiative balance in the atmosphere, particularly those due to aerosols, cloud condensation nuclei (CCN), and cloud-aerosol radiative interaction
  • Feedback processes between different phenomena and different domains

The variety, surface density, and atmoshperic volumetric coverage of the SGP instrumentation will be more coprehensive than that at any other ARM site, and the SGP site will experience a wider variety of atmospheric conditions than will any other ARM site. The resulting data will accordingly support a greater range and depth of scientific investigation than data from any other location, making it imperative for the ARM Program to develop and maintain a high-quality, continuous data stream from the SGP site.

The measurements required by Science Team proposals, the Data and Science Integration Team (DSIT), and the science director are catagorized into scientific applications areas or groups within ARM. The DSIT and other teams coordinated activities to develop integrated and well-focused data sets. Focus areas include shortwave radiation, water vapor, longwave radiation, aerosols, clouds, surface fluxes, and the single-column model (SCM). A goal is to facilitate algorithm development that prescribes geophysical phenomena as products of multiple data streams.

Near-Term Priorities

Within this ranking, the differences in relative importance between adjacent items are not large. The categorization is also somewhat artificial because many site activities have multiple purposes. For example, IOP activities can simultaneously support Science Team, IDP, and campaign requirements. Even so, this ranking reflects our scientific assessment of the activities that should receive the most support during this period. The IOPs will focus on providing critical data sets on an episodic basis to the Science Team, as well as field support for instrument development and testing and for collaborative campaigns.

Funding will now be provided for 2 SCM IOPs, each lasting 3 weeks. Funding can be made available for a third if a strong need can be demonstrated. The SCM working group will provide a recommendation as to when SCM IOPs will take place. So far this year a winter SCM IOP took place January 16-February 8. Another SCM IOP is scheduled for late spring (May time frame).

In 1994, the ARM Program identified a need for the creation of a Site Advisory Committee (SAC) to provide assistance to the ARM Program Science Team, the SGP SST, and the SGP site program manager. The SAC is composed of seven members (ARM and non-ARM scientists) who meet formally at least once a year. Individual committee memberships last for 3 years. The SAC's charter is to:

  • Evaluate the SGP site scientific mission
  • Provide scientific mission guidance for Site operations
  • Evaluate research program of the site scientist
  • Evaluate the potential for collaboration with other research programs, and
  • Provide recommendations for the SGP site educational outreach program

The SST helps to ensure that the scientific productivity of the SGP site is maximized by both the routine and special (IOP) operations at the site. The SST acts as a resource for the site operations manager and his staff on scientific matters by doing the following:

  • Working with site operations personnel and instrument mentors on potential instrument problems
  • Reviewing proposed instrument siting and deployment strategies, including the needs of the instrument mentors and instrument requirements for IOPs and campaigns
  • Reviewing schedules and procedures for instrument calibration and maintenance
  • Providing an early assessment of suspected instrument or data problems through the use of performance metrics, graphic display techniques, and data quality research investigations, and distributing their findings so that corrective actions can be taken
  • Planning and conducting IOPs and campaigns.

In summary, our goals are to provide the Science Team with a suite of measurements that will support a wide range of research, to establish solid procedures for instrument calibration and maintenance (particularly for broadband radiometry), to operate the series of VAPs and QMEs, to provide input for the scientific applications groups, and install required instrumentation and facility support. Quality assessment efforts remain central to the success of the entire program.