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Monitoring Our Climate: The Value of Atmospheric Reference Observations

The Air Resources Laboratory participates in several national and international climate reference observing networks, providing leadership in establishing networks, designing, operating and maintaining observing sites, and analysis of the data.

How do we know that our climate has changed? How will we know how and why climate will have changed in the coming years, decades, and even centuries? These are two of the many climate-related questions scientists in NOAA have dedicated themselves to addressing. Such information is essential, as the United States and the world decide how to address climate change.

A fundamental requirement to answering these questions is the collection of atmospheric data, such as surface and upper air temperature, precipitation, water vapor, solar radiation, evaporation, and energy fluxes, at geographic scales and temporal and spatial resolutions necessary to improve our understanding. Until recently, data for analysis of climate change were essentially compilations of archived weather observations, sometimes with additional quality control applied, but without the long-term quality and continuity essential for unambiguous identification of climate trends. Changes in instruments, observing methods, station locations, and data processing methods all introduce time-varying biases that could be mistaken for, or mask, real climate changes. Now it is recognized that reference observing networks, dedicated to meeting climate needs, are needed both to monitor climate change in situ and to calibrate measurements from other observing systems, such as satellites, to make them more suitable for climate work. Reference observations also prove valuable for evaluating and improving the models that predict future climate.

What is a climate reference observing network?
A climate reference observing network is a group of stations that collect highly accurate data for the purpose of determining climate variability and trends. This requires long periods (decades) of homogeneous records where there are minimal human influences on the environment in the immediate vicinity of the stations.

NOAA’s Air Resources Laboratory (ARL) participates in several climate reference observing networks both nationally and internationally, including the U.S. Climate Reference Network (USCRN), the U.S. Historical Climatology Network-Modernization project (USHCN-M), the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN), and the Surface Energy Budget Network (SEBN). When asked why so many networks and not just one that can do it all, Dr. Tilden Meyers with ARL explains that different networks are needed to address different aspects of climate. For instance, some networks measure climate at the surface while others measure it aloft. Also, a network with sufficient stations to measure national trends may not have sufficient resolution to measure regional trends. Integration of these networks then provides a more complete picture for our understanding how and why climate has changed.

A map of the Continental United States (CONUS) U.S. Climate Reference Network stations. Seven locations each have two observing stations for data comparisons.

Since 2001, NOAA has focused on the USCRN —a network of roughly 114 stations in the 48 contiguous States that will provide long-term, high quality data over the next 50-100 years. Its purpose is to improve understanding of national climate change. Each USCRN station captures real-time measurements of surface temperature, precipitation, wind speed, and solar radiation at a fine scale using highly accurate and frequently calibrated meteorological instrumentation. This temporal resolution provides climate information, such as precipitation intensity and duration of extreme events that other networks collecting daily data can not provide. ARL worked with NOAA’s National Climatic Data Center (NCDC) to establish these stations and now will add to them measurements of soil moisture and soil temperature. These data are important for a number of applications, including monitoring and predictions of drought. Beginning this year, the USCRN will be expanded into the state of Alaska, a region projected to experience the most significant changes in climate over the next 25-50 years.

To detect regional climate change over the next 50-100 years, NOAA is implementing the USHCN-M. There are approximately 1200 stations in the

GRUAN stations will make reference-quality observations of the atmospheric column with a suite of coordinated instruments. The most important measurements for GRUAN stations are upper-air temperature and humidity profiles, as well as total column water vapor from ground-based GNSS receivers. The second priority includes wind profiles, surface radiation parameters, remotely-sensed temperature and water vapor, and cloud, ozone, methane, and aerosols observations.

existing Historical Climatology Network which collect daily and monthly records of basic meteorological variables (precipitation and temperature). NOAA, in a partnership among ARL, NCDC, and NOAA’s National Weather Service, has proposed deploying in the continental United States roughly 1000 modernized stations located roughly on a regular grid (to improve spatial sampling). These stations will use similar technology and calibration standards as the USCRN and will collect observations every five minutes. Locations will be a combination of existing Historical Climatology Network locations, USCRN stations, and new locations. A pilot deployment of 150 stations in the southwest U.S. will begin soon.

Yet, ground–based systems, such as the USCRN and HCN-M, are only part of the picture. Measurements of the atmosphere’s vertical profile of temperature, humidity, winds, chemical composition and radiation are also needed to more confidently identify upper-air climate change signals in observational data than is now possible. Until now, the vertical structure of these variables, particularly humidity, has been very poorly monitored, even though water vapor is a key greenhouse gas. After much discussion and planning, the establishment of the GRUAN, an international effort, is now in progress. The most important measurements for GRUAN stations are upper-air temperature and humidity profiles, as well as total column water vapor from ground-based Global Navigation Satellite System (GNSS) receivers. ARL will assist GRUAN in designing the network and analyzing the data.

While those three networks allow us to better understand how climate has changed over time, the SEBN seeks to explain why climate variables have changed. Since it is the Earth’s surface energy balance that drives weather, climate, and ocean circulation, fundamental climate-relevant data, such as incoming solar radiation, reflected solar radiation, incoming thermal infrared, upward emitted thermal infrared, evaporation, sensible heat flux, soil heat and soil moisture storage, are needed. The SEBN consolidates several independent but closely related observing systems into a single cost-effective and efficient observing system. Observations are used by NOAA scientists to provide detailed examination of the land-surface feedbacks and related radiative processes that can drive regional climate. In a partnership between ARL and NOAA’s Earth System Research Laboratory Global Monitoring Division, seven SEBN stations are in operation. Plans call for an additional thirteen stations to cover representative eco-regions in the U.S.

SEBN station (Midwest corn field) at Bondville, IL (Photo credit: NOAA)

With more than half the world's population now living in urban areas, urban climate footprints and impacts could spread well beyond the immediate vicinity of cities, affecting local-to global- scale atmospheric composition, surface energy budgets, water and carbon cycle processes, and local ecosystems. Although most climate monitoring networks avoid urban areas because of the potential impact on the climate signature, the extent of the urban impact can only be determined if similar atmospheric reference observations are collected in urban areas. As the percentage of people living in urban areas continues to increase, so does the need to have climate quality reference observations in these areas. As part of a pilot study, ARL will acquire some preliminary reference observations of air temperature and precipitation using similar techniques as those in the USCRN and HCN-M programs. These observations will support analysis of requirements for future urban climate observations.

The Air Resources Laboratory (ARL) conducts research and development in the fields of air quality, atmospheric dispersion, and climate. Key activities include the development, evaluation, and application of air quality models; improvement of approaches for predicting atmospheric dispersion of hazardous materials; and the generation of new insights into air-surface exchange and climate variability and trends.

The goal of our work is to improve the Nation's ability to protect human and ecosystem health while also maintaining a vibrant economy.

4/10/09

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