Atmospheric Radiation Measurement Climate Research Facility US Department of Energy

Eastern North Atlantic


The Eastern North Atlantic (ENA) atmospheric observatory is the newest measurement site established by the Atmospheric Radiation Measurement (ARM) user facility. This observatory is located on Graciosa Island in the Azores archipelago. The Azores are located in the northeastern Atlantic Ocean west of Portugal.


This region of the world is characterized by marine stratocumulus clouds. The ENA is providing a rare, long-term data set about the response of these low clouds to changes in atmospheric greenhouse gases and aerosols—a major source of uncertainty in global and regional climate models.

ARM’s previous research (2009) on Graciosa Island revealed that it has the ideal mix of conditions to study how clouds, aerosols, and precipitation interact. Research in this area is important because:

  • Data from ENA’s 2009 deployment resulted in the first climatology of detailed vertical structure of cloud and precipitation properties of low clouds at a remote subtropical marine site.
  • These data provided new information about the structure and variability of the remote marine boundary-layer system and the factors that influence it.

Instruments and Data

Key instrument systems at the ENA include:

  • Aerosol instrumentation, including hygroscopic tandem differential mobility analyzer, aerosol chemical speciation mass spectrometer, cavity attenuated phase shift particle extinction monitor, carbon monoxide/nitrous oxide/water gas-phase monitor, carbon dioxide/methane/water gas-phase monitor, and ultrah-high-sensitivity aerosol spectrometer
  • Atmospheric and boundary state systems, including surface meteorological instrumentation, boundary-layer cloud system, total sky imager, weighing bucket rain gauge, total precipitation sensor, eddy correlation flux measurement system, and disdrometer
  • Lidars–both the micropulse lidar and Doppler lidar
  • Radars, including the zenith cloud radar, scanning cloud radar, scanning precipitation radar, and radar wind profiler
  • Radiometers, including the atmospheric emitted radiance interferometer, microwave radiometer, 3-channel microwave radiometer, multifilter rotating shadowband radiometer, pyranometer, pyroheliometer, pyrgeometer, and blackbody calibration system.

Researchers supplement the continuous observations with guest instruments during field research campaigns or by requesting increases in the frequency of measurements, such as sonde launches. All data gathered at the ENA are transmitted to the ARM Data Center and made available via Data Discovery.