NDACC News and Highlights

January 2009:

This new section has been instituted to highlight significant items of interest within NDACC. We expect to provide updates at least annually following the NDACC Steering Committee meeting. However, important newsworthy items will be added throughout the year.

Termination of NDACC Primary and Complementary Station Designations

Establishment of an NDACC Cooperating Network Affiliation

Two New Measurement Capabilities Designated as NDACC-Approved

New Species to Be Archived from FTIR Measurements

Establishment of an Ad Hoc Working Group to Assess Future NDACC Measurement Strategies and Emphases

Termination of NDACC Primary and Complementary Station Designations

At the 2008 NDACC Steering Committee meeting, a decision was made to remove the "Primary" and "Complementary" designations of NDACC measurement sites / stations. These original terminologies were instituted at the inception of the Network for designating a minimum of five stations with long-term measurement commitments, representing the major geographical regions of the globe (i.e., Arctic, Northern Hemisphere (NH) Midlatitudes, Tropics, Southern Hemisphere (SH) Midlatitudes, and Antarctic). At that time, some of these stations were instituted as a combination of several sites, each with various types of instrumentation, such that the sum of all sites comprising a Primary Station included a fairly complete suite of NDACC (then NDSC) instrument types. It was anticipated that numerous Complementary Stations / Sites, at which a smaller number of Network-approved instruments were in operation, or at which the measurement commitment was for a shorter period of time, would augment these Primary Stations.

After nearly two decades of successful Network operations, the need for these designations no longer exists. In fact, their use now leads to some confusion and occasional misunderstanding. For example, some Complementary Sites have built up suites of instruments that are more comprehensive than those at some of the Primary Station sites. And many Complementary Stations / Sites have measurement commitments that are just as long-term as those at Primary Stations.

Further, these designations have occasionally been misinterpreted to imply that the measurements at and data from Complementary Stations are of lesser quality that those at Primary Stations, whereas the requirements to become affiliated with NDACC are identical for the two categories. There is no reduction in the expectations of instrument performance or data quality.

Lastly, some NDACC Principal Investigators felt that a Complementary designation was less advantageous than a Primary designation in justifying a long-term measurement need to their institution or funding agency.

From now on, all sites and stations will be designated simply as NDACC-approved measurement sites / stations. The NDACC Measurements and Analyses Directory is being revised to reflect this change, and measurement locations will be listed under one of the following groupings: NH High Latitudes, NH Midlatitudes, NH Subtropics and Tropics, SH Subtropics and Tropics, SH Midlatitudes, and SH High Latitudes.

Establishment of an NDACC Cooperating Network Affiliation

NDACC recognizes the importance of new measurement capabilities and of existing capabilities whose heritage was developed external to NDACC, and has encouraged Network affiliation with such measurements. In some cases, there are regional, hemispheric, or even global networks of instruments that operate independently of NDACC, but where strong measurement and scientific collaboration would be mutually beneficial. Such networks often have set up their own quality-assurance guidelines, operational requirements, and data archiving policies, and they have national or international recognition in their own right. In such cases, bringing the complete network under the NDACC umbrella is neither practical nor desirable. Rather, designation of an interested external network as a "Cooperating Network" may be more appropriate, and can foster collaborative measurement and analysis activities. For such designation to occur, the relevant NDACC Working Group must assess the benefits of mutual data access. The Working Group should further ascertain that the various protocols of the external network are compatible with those of NDACC, and are followed consistently and effectively. A protocol detailing the specific process whereby such affiliation can occur is posted on the NDACC web site.

Two New Measurement Capabilities Designated as NDACC-Approved

Since the onset of formal operations, NDACC (formerly NDSC) has designated several specific instrument types as official measurement capabilities. These are: Dobson / Brewer Spectrometers, Fourier Transform IR Spectrometers (FTIRs), Lidars (temperature, ozone, and aerosol), Microwave Radiometers, and UV/Visible Spectrometers. Balloon Sondes (ozone and aerosol) and UV Spectroradiometers were added shortly after the Network became operational. The Network strives to maintain the operation of as many of these instrument types within the various latitude regions as possible. As NDACC has matured, its measurement and analysis emphases have broadened to encompass issues such as the detection of trends in overall atmospheric composition and understanding their impacts on the stratosphere and troposphere, and establishing links between climate change and atmospheric composition. These challenges require an expansion of measurement capabilities, particularly in the area of some key climate parameters. Thus, after careful consideration and evaluation by the various NDACC Instrument Working Groups, the Steering Committee approved two new instrument types for NDACC designation: Raman Lidars for profile measurements of water vapor in the troposphere and across the tropopause, and Water Vapor Sondes (cryogenic frostpoint hygrometers and Lyman-a hygrometers) for profile measurements in the troposphere and stratosphere. Data from both instrument types soon will be available in the NDACC data archives.

New Species to Be Archived from FTIR Measurements

In the early days of NDACC (then NDSC), the Infrared Working Group (IRWG) targeted the retrieval of total columns of several gases considered of primary importance to the original goals of the Network. These goals focused on increasing our understanding of ozone chemistry and, in the post-Montreal Protocol period, observing the accumulation (and hopefully the eventual decline) of Cl_y  and F_y in the stratosphere. Consequently, the initial gases targeted were ozone, nitric acid (HNO₃), nitrous oxide (N₂O ), chlorine nitrate (ClONO₂), hydrogen chloride (HCl), and hydrogen fluoride (HF). As the Network matured and science questions evolved to encompass the broader issues of climate change, attributing causal relationships for observed changes in atmospheric composition, and air quality, the IRWG reevaluated the ability of high-resolution mid-IR Fourier Transform Spectrometers to contribute and address the new scientific issues. At the 2008 IRWG meeting, the group agreed to add methane (CH₄), carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C₂H₆) to the existing suite of gases. All Principal Investigators in the IRWG maintain an archive of the recorded spectra since their observational program began, thereby allowing a re-analysis of these spectra. Consequently, the data record for the new gases will begin from the earliest observations for each site. Some of these data already are available to the public from the NDACC Data Host Facility. Many more will be archived during 2009.

Establishment of an Ad Hoc Working Group to Assess Future NDACC Measurement Strategies and Emphases

At the 2008 NDACC Steering Committee meeting, an ad hoc working group was established to review existing and assess future Network measurement strategies and emphases in light of the broadening of Network goals over those established at its inception. While NDACC remains committed to monitoring changes in the stratosphere with an emphasis on the long-term evolution of the ozone layer, its priorities now encompass issues such as the detection of trends in overall atmospheric composition, understanding their impacts on the stratosphere and troposphere, and establishing links between climate change and atmospheric composition. The members of this ad hoc working group (G. Braathen, M. Chipperfield, T. Deshler, S. Godin-Beekmann, J. Hannigan, K. Kreher, J.-C. Lambert, T. McElroy, R. McKenzie, G. Nedoluha, and W. Randel) solicit your input for their consideration. Email this group.