ARM Southern Great Plains Observatory

A programme to fix the models

Climate models disagreed about how clouds affect radiation, and the largest uncertainty was cloud and aerosol effects. In 1989 the US Department of Energy created the Atmospheric Radiation Measurement (ARM) programme to collect long-term, continuous, comprehensive measurements to test and improve those models. The Southern Great Plains site in north-central Oklahoma, near Lamont, was the first, and data collection began in 1992.

The central facility is surrounded by extended facilities spread over about 140,000 square kilometres of Oklahoma and Kansas, which sample the surrounding variation in land use and weather.

A family of sites

ARM added a site on the North Slope of Alaska in 1997, one in the tropical western Pacific, and in 2013 the Eastern North Atlantic site in the Azores. Mobile facilities can be sent to field campaigns anywhere in the world, and an aerial facility flies instrumented aircraft and drones.

The instruments are chosen to measure everything that matters to radiation at the surface and in the column: cloud radars, lidars, microwave radiometers, radiosondes, flux towers and sun photometers.

Data as a standard product

The raw data are processed to a uniform standard by the ARM Data Center, with quality flags, and combined into value-added products such as retrieved cloud properties and estimates of the energy balance. Data are free and open to all users, and the programme is a user facility, meaning researchers can propose measurements and campaigns. The result is a consistent, three-decade record of the atmosphere over a farm in the Great Plains, now used to test the next generation of climate models.

Thirty years of the same measurement

The value of the Southern Great Plains record is that it has been collected for three decades with a consistent set of instruments and a rigorous quality-control system. A scientist can ask how the cloud base height or the aerosol optical depth over Oklahoma has changed over thirty years, and get a defensible answer. That is a property of an observatory that a field campaign cannot provide. The cost of the programme is the recurring one of replacement of ageing instruments by newer models without breaking the record, handled by running old and new in parallel and publishing the comparison.

Instruments and technologies

• Cloud radars Millimetre-wavelength Doppler radars measure the height, thickness and motion of cloud layers.
• Raman lidar A laser sends light up through the atmosphere and measures the returned scattering to profile water vapour, aerosol and temperature.
• Radiometer sets Pyranometers, pyrgeometers and spectral radiometers measure the solar and thermal radiation reaching the ground.

Timeline

• 1989 DOE creates the ARM programme.
• 1992 Data collection begins at the Southern Great Plains site.
• 1997 ARM's North Slope of Alaska site begins operating.
• 2013 ARM's Eastern North Atlantic site begins operating in the Azores.

Key lessons for observation today

• Measure the whole column Clouds, aerosols and radiation are measured together. Single measurements rarely explain a process; coordinated sets do.
• Standard processing is a service A uniform pipeline and quality flags make data from different instruments and years comparable. Processing standards are part of the observatory.
• Be a user facility Researchers propose campaigns on a permanent platform. Shared infrastructure with open access stimulates science.

Sources

• ARM User Facility, Southern Great Plains (SGP) Atmospheric Observatory
• Wikipedia, Atmospheric Radiation Measurement Climate Research Facility
• ARM User Facility