Ground-based in situ measurements—ranging from thermometer measurements to ecosystem surveys—are the oldest and most diverse type of environmental observations, and they remain a fundamental component of an integrated climate observing system. Over the past 60 years, direct ground-based measurements have been supplemented by airborne in situ measurements, from both aircraft and balloons, and by ground-based, remotely sensed data, such as weather radars and vertical profilers of atmospheric composition. Collectively, these observations span a broad range of instruments and types of information, from instruments initially deployed as part of research experiments to operational networks at the local, state, regional, national, and international levels deployed by a range of public and private institutions. In addition to directly supporting research on the Earth system and specific decisionmaking needs, these observations are critical for calibrating and validating satellite measurements and for developing and testing climate and Earth system model parameterizations.
There have been significant advances in in situ and ground-based monitoring networks over the past several decades. Examples include the Arctic observing network, the Tropical-Atmosphere Ocean (TAO) array constructed primarily to monitor temperature profiles in the upper equatorial Pacific ocean and support predictions of the El Nino-Southern Oscillation, "Argo" floats that provide dispersed observations of temperature and salinity of the upper ocean, the FLUXNET network of ecosystem carbon exchange with the atmosphere, the Aerosol Robotic Network (AERONET) that provides observations of atmospheric optical properties, and the Atmosphere Radiation Measurement (ARM) program. In addition, there is a wealth of observations from a broad range of public and private systems designed primarily for other purposes—such as wind monitoring for port safety—that could potentially be tapped to supplement existing climate observations and yield new and valuable insights. These systems will have to be integrated and maintained for decades to realize their full potential as components of a climate observing system.
The recent study Observing Weather and Climate from the Ground Up: A Nationwide Network of Networks (NRC, 2009j) discusses the value and challenges of coordinating the wide range of ground-based weather, climate, and climate-related observing systems to create a more integrated system that could be greater than the sum of its individual parts. The report calls for improved coordination across existing public and private networks of in situ observations. However, the number and diversity of entities involved make this a major organizational and governance challenge. If properly developed, an integrated, nationwide network of weather, climate, and related observations would undoubtedly be a tremendous asset for supporting improved understanding of climate change as well as climate-related decision making.
In addition to maintaining and enhancing observational capacity, research on new methods of observation, such as the miniaturization of instruments for in situ data collection, could both enhance data collection capabilities and lower the often substantial costs associated with data collection systems. To become effective components of an integrated climate observing system, these observational capacities, whether they represent the continuation of existing capabilities or the development of new ones, should be developed with a view toward providing meaningful, accurate, well-calibrated, integrated, and sustained data across a range of climate and climate-related variables.
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