History and Status of the ARM Program

Introduction

More than 20 years after the dedication of the first research site of the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility, ARM’s primary tenet has remained unchanged: to improve the performance of the general circulation models used for climate research and prediction by improving how those models deal with radiative energy transfer and the impact of clouds.

To this end, ARM has made a significant contribution in improving climate prediction models: radiative heat transfer, radiation absorption, and cirrus cloud properties. ARM scientists use data gathered from ARM’s fixed, mobile, and aerial facilities worldwide to address these issues and compare the observations to their models. Users worldwide propose and conduct field campaigns that target specific science questions as well as test and validate new instruments. This worldwide interest bodes well for the ARM Program and for the future of ground-based remote sensing for climate modeling and weather forecasting.

Initial Concept

The initial concept for ARM arose from a series of studies that fell under the auspices of the Intercomparison of Radiation Codes in Climate Models (ICRCCM). ICRCCM pointed to several key issues that are now central to the ARM approach and strategy. First, ICRCCM was based on the assertion that one must understand the quality of the physics inside a climate model if one is to understand the quality of the climate model itself. Second, it is possible, and in fact necessary, to understand the relatively coarse representations of the physical processes in a climate model in terms of higher resolution process models. Finally, the hierarchy of models that leads to needed parameterizations must be built on a sound base of experimental verification.

At the same time as the release of the ICRCCM results, it was becoming clear that the radiative transfer of energy in the atmosphere and the impact of clouds was, and remains, one of the greatest sources of error and uncertainty in the current generation of general circulation models used for climate research and prediction. With this starting point, DOE proposed a major program targeted at improving the understanding of the role and representation of atmospheric radiative processes and clouds in models of the earth's climate. Initially, the DOE program focused on the radiative aspects of the climate problem. As the scientific issue was studied in more detail, however, it was obvious that a study of radiative processes associated with clouds could not be decoupled from the problem of representing the processes by which clouds form, are maintained, and dissipate in climate models. As a result, the ARM Program was proposed to the then Committee on Earth Sciences of the Federal Coordinating Council on Science Engineering and Technology with two basic objectives:

to improve the treatment of radiative transfer in climate models under all relevant conditions
to improve the treatment of clouds in climate models, including the representation of the cloud life cycle and the prognosis of cloud radiative properties.

The Approved Plan

The ARM Program Plan was subjected to peer review in the fall of 1989. The key element of the proposed ARM effort was to be the Cloud and Radiation Testbed (CART). This user facility would consist of four to six semi-permanent observational facilities designed to allow detailed investigations of processes represented in climate research models. These semi-permanent facilities would be supplemented with a mobile facility to allow related measurements at other locations on a campaign-oriented basis. The CART facility would include a data management and communications system capable of acquiring and quality-controlling site data; ability to acquire data from sources outside the program; and to communicate that data to a Science Team. The Science Team would be selected through a peer review process open to all investigators nationally and internationally.

Based on the peer review, the subcommittee on Global Change Research of the Committee on Earth Sciences approved the Plan. The scope was broadened beyond radiative transfer to include clouds and cloud processes represented in general circulation models, a change deemed necessary to adequately address those atmospheric properties important to radiative transfer in the atmosphere and the atmosphere's radiation balance. The Committee also recommended that the DOE implementation of this program involve the talents of other federal agencies to the extent possible and that an interagency steering group be formed to assist in that process. Finally, DOE agreed to coordinate its deployment of facilities with the schedules of other relevant national and international programs.

Early Implementation

The implementation of the ARM Program began in January 1990. First, a multi-laboratory team was formed to plan the detailed implementation of the ARM facilities. Because the science drivers were important to the design of the ARM facilities, a series of scientific workshops were held in the spring and summer of 1990 to clarify the scientific foundations of the program. In parallel, a solicitation process was initiated to establish the Science Team.

As the implementation moved forward, features of the program emerged. One of the most significant was a pattern of collaboration with other programs. This collaboration was characterized by a series of joint field campaigns and by involvement in program planning for other major research efforts. With the field collaborations, ARM attempted to bring a value-added contribution to another agency's or group's planned effort, while at the same time trying to gain operational experience necessary to guide its own field deployment.

From the standpoint of planning, ARM attempted to gain early involvement in the program planning of other programs that would be evolving in parallel with it. One of these joint planning activities culminated in the field deployment of the Pilot Radiation Observation Experiment (PROBE) to Kavieng, Papua New Guinea, as part of the Tropical Ocean Global Atmosphere-Coupled Ocean Atmosphere Response Experiment (TOGA-COARE), in the winter of 1992-1993. Experience gained during TOGA-COARE has been a crucial influence in ARM planning.

The science and facility tracks converged in the selection of a siting strategy for ARM facilities. This process resulted in the identification of five locales in which ARM should locate its semi-permanent facilities and a comparable number of secondary locales in which the program should consider shorter, campaign-like activities. The primary locales were the Southern Great Plains (SGP) of the United States, the Tropical Western Pacific (TWP), the North Slope of Alaska (NSA), the marine stratus zones of either the Atlantic or Pacific Ocean, and the Gulf Stream.

Deployment of the first instrumentation to the SGP site occurred in the spring of 1992, just 24 months after the program was approved. The site was dedicated in November 1992. TWP began phased operations in 1996 at its first facility on Manus Island. The second facility on Nauru Island was implemented in 1998. In 2002, a third facility in Darwin, Australia was established in collaboration with the Australian Bureau of Meteorology to support the other two sites. The NSA site at Barrow was dedicated in July 1997. Barrow is located at the northernmost point in the United States, 330 miles north of the Arctic Circle. ARM chose this location because the Arctic is particularly sensitive to climate changes.

The ARM Climate Research Facility Today

The SGP site is the largest and most extensive climate research field site in the world, consisting of in situ and remote-sensing instrument clusters arrayed across approximately 55,000 square miles (143,000 square kilometers) in north-central Oklahoma. The heart of the SGP site is the heavily instrumented central facility located on 160 acres of cattle pasture and wheat fields southeast of Lamont, Oklahoma. The SGP site is designed to continuously sample all of the components of the radiation budget at the Earth’s surface and all the relevant constituents in the atmosphere above the site. The largest event at the SGP site so far was the 1997 execution of a single field campaign comprised of seven distinct areas of research involving between 70 to 100 scientists and colleagues of the science team and collaborating programs.

Since the SGP site was established in 1992, more than 30 instrument clusters have been placed around the site. The delivery and installation of Vaisala ceilometers and atmospheric emitted radiance interferometers (AERIs) completed the boundary facilities and enabled studies to compare driving single-column model (SCM) research using remote sensors and satellite data instead of driving these models solely with radiosonde data.

Covering the area roughly between 10° N and 10° S of the equator and from 130° E to 167° E, the TWP locale includes a region that plays a large role in the interannual variability observed in the global climate system. For example, a phenomenon called the El Niño/Southern Oscillation, or ENSO, has far-reaching implications for weather patterns over much of the Northern Hemisphere and perhaps the entire planet.

The North Slope of Alaska (NSA) site, which includes facilities at Barrow and Atqasuk, provides data about cloud and radiative processes at high latitudes. These data are being used to refine models and parameterizations as they relate to the Arctic.

In addition to routine data collection, ARM provides opportunities for user-proposed field campaigns targeted at specific science problems. For example, field campaigns have been directed at understanding the accuracy of routine atmospheric measurements, and at specific cloud problems such as anomalous absorption of solar radiation. The ARM Mobile Facilities (AMF) and ARM Aerial Facility (AAF) provide additional methods of gathering measurements during field campaigns.

Collaborations

Collaboration with other agencies and programs is a fundamental philosophy of ARM. In December 1997, DOE committed ARM to support the GEWEX Water Vapor Program (GVap) by coordinating the establishment of the GVap ground-based validation network. This network was comprised of up to 20 sites worldwide that acquired water vapor profile data using advanced radiosondes. More recently, in September 2007 the ARM Climate Research Facility became an official member of the National Science Foundation’s Center for Collaborative Adaptive Sensing of the Atmosphere, or CASA. CASA is a multi-sector partnership among academia, industry, and government dedicated to engineering revolutionary weather-sensing networks for the region of the lower atmosphere currently below conventional radar range. The Mid-latitude Continental Convective Clouds Experiment, planned for 2011, will take place at the ARM Southern Great Plains site. This joint campaign with the NASA Global Precipitation Measurement (GPM) Project will study cloud and precipitation transitions and environmental quantities that are important for convective parameterization in large-scale models and cloud-resolving model simulations. This campaign also takes advantage of Recovery Act investments at the SGP site, providing enhanced radiosonde flights and new precipitation and cloud radars to supplement the already comprehensive ground-based instrument suite at the site.

History of the ARM Science Team

The Science Team’s research efforts were largely focused on the activities of various working groups and fell into the two fundamental strategies through which ARM sought to achieve its programmatic objectives and to focus its scientific efforts. These strategies were also the basic organizing principle behind defining the requirements for field campaigns and determining what additional measurement capabilities were required. The first strategy was the "instantaneous radiative flux" measurement and modeling effort. The second was single-column modeling to evaluate the cloud and radiative process models either used in, or being developed for, general circulation models being used for climate studies. A third focused area of activity, related to establishing the lower boundary condition for both SCM evaluations and instantaneous radiative flux (IRF) calculations, was the effort to characterize surface fluxes, surface radiative properties, and planetary boundary layer behavior on scales appropriate to general circulation models.

On October 1, 2009, the ARM science component was merged with the Atmospheric Sciences Program to become Atmospheric System Research, and is no longer part of the ARM Climate Research Facility.

Accomplishments

ARM was the first climate research program to deploy a suite of cutting-edge instrumentation for obtaining continuous measurements of cloud and aerosol properties. This strategy revolutionized our ability to collect long-term statistics of detailed cloud properties and now serves as a model for programs around the world. ARM has formed some surprising relationships along the way. For one, ARM works in close cooperation with weather forecasting operational centers. The weather centers have found that ARM data is extremely helpful for evaluation and improving their own models. In turn, they have supplied research support and ideas for the ARM community. The ARM Climate Research Facility has become an integral part of international collaborations and of U.S. government research programs sponsored by agencies such as NASA and the NOAA. This worldwide interest speaks well for the future of ground-based remote sensing for climate modeling and weather forecasting.