Long-Term Measurement Records Related to Global Stratospheric Constituent Change II
Presiding: C H Jackman, NASA Goddard Space Flight Center; R D McPeters, NASA Goddard Space Flight Center
A52A-01 INVITED 10:40h
The contribution of NOAA/CMDL ground-based measurements to understanding long-term stratospheric changes
Atmospheric histories of halocarbons and other gases provide a basis for understanding long-term changes in stratospheric ozone. Furthermore, long-term measurement records enable more accurate projections of future halocarbon mixing ratios and stratospheric ozone recovery. At NOAA's Climate Monitoring and Diagnostics Laboratory, we have measured halocarbons in ambient air during the past 25 years and have inferred changes for earlier years through studies of air trapped in firn (consolidated snow). Firn air measurements reveal that most long-lived, ozone-depleting halocarbons are entirely anthropogenic, though methyl halides clearly have substantial natural sources. The results over the past two decades have provided a picture of the atmospheric response to efforts by humans to eliminate ozone-depleting gases from the atmosphere. They show the abundance of both chlorine and bromine declining in the lower atmosphere in recent years, after decades of continued increases. The observed declines to date stem primarily from rapid decreases in short-lived gases; atmospheric levels of chlorine and bromine in long-lived gases remain near their peak. While the declines are good news for stratospheric ozone, the direct radiative influence of long-lived halocarbons continues to increase
A52A-02 INVITED 11:00h
The Network for the Detection of Stratospheric Change: Tracking Changes in the Earth's Atmosphere
The international Network for the Detection of Stratospheric Change (NDSC) was formed to provide a consistent standardized set of long-term measurements of atmospheric trace gases, particles, and physical parameters via a suite of globally distributed research stations. Officially operational since 1991, the NDSC was incepted and formalized during the late1980s in response to the need to document and understand worldwide stratospheric perturbations resulting from increased anthropogenic emissions into the atmosphere of long-lived halogenated source gases with strong ozone depletion and global warming potentials. The initial objective of the NDSC was to monitor, from pole to pole, the temporal evolution of the stratosphere, including its protective ozone layer, and to understand the causes (i.e., natural versus anthropogenic, chemical versus dynamical) of the observed changes and their impacts on the troposphere and at the ground. This dual goal of long-term global measurement and understanding has led to the implementation of a ground-based network of "primary" NDSC stations equipped with a suite of remote instruments (such as UV/Visible spectrometers, various types of lidars, Fourier transform infrared spectrometers, microwave radiometers, in situ radiosondes, etc.), allowing the quasi-simultaneous study of a large number of chemical compounds and physical parameters identified as priority targets for the Network. Over forty "complementary" sites, equipped with a subset of such instruments and/or operating less regularly than the primary stations, contribute to the global coverage of the Network and provide substantial support during coordinated campaigns targeted at special process studies, at calibration/validation phases of space-based sensors, and at more regional subtle atmospheric characteristics. During the past decade, the NDSC has contributed to the understanding of stratospheric ozone depletion in the polar regions and at mid-latitudes, and documented the increase and leveling-off of ozone-depleting chemicals in the atmosphere and the continued growth of greenhouse gases. Because of its worldwide dimension, the NDSC has been recognized as a major component of the international atmospheric research effort. As such, it has been endorsed by national and international scientific agencies, including the United Nations Environmental Programme (UNEP) and the International Ozone Commission (IOC) of the International Association of Meteorology and Atmospheric Physics (IAMAP). It has also been recognized by the World Meteorological Organization (WMO) as a major contributor to WMO's Global Ozone Observing System (GO3OS) within the frame of its Global Atmosphere Watch (GAW) Programme. While the NDSC remains committed to monitoring changes in the stratosphere, with an emphasis on the long-term evolution of the ozone layer (its decay, likely stabilization and expected recovery), it's priorities have broadened considerably to encompass - detecting trends in overall atmospheric composition and understanding their impacts on the stratosphere and troposphere, - establishing links between climate change and atmospheric composition, - calibrating and validating space-based measurements of the atmosphere, - supporting process-focused scientific field campaigns, and - testing and improving theoretical models of the atmosphere.
http://www.ndsc.ws
A52A-03 INVITED 11:20h
Long-term atmospheric constituent and temperature change from 13-plus years of HALOE observations
The Halogen Occultation Experiment (HALOE) has been operating on the Upper Atmosphere Research Satellite without flaw since it was first turned on October 11, 1991. The experiment uses the broadband and gas filter radiometry instrument techniques and the solar occultation experiment approach to measure vertical profiles of temperature, HCl, HF, O3, NO, NO2, CH4, H2O and aerosols from the upper troposphere in some cases (i.e. H2O and O3) to the lower thermosphere for other parameters (e.g. NO). The experiment has operated for over thirteen years at this point and has provided an extensive long-term data set for studies of trends. The basic measurement for a solar occultation experiment is a ratio of endoatmospheric to exoatmospheric signals making HALOE virtually self calibrating. Also, its low noise gives high measurement precision providing an attractive data set for studies of long-term atmospheric changes and variability. Many scientific studies have been done using HALOE data including polar vertical descent, polar vortex phenomena, dynamics, NOx, Clx and HOx chemistry, effects of solar storms on stratospheric NO and O3, the relation between Lyman-Alpha and high altitude water vapor, polar mesospheric cloud characteristics and trends in H2O, HCl, HF, O3, NO2, CH4 and temperature. The data were also used extensively in the SPARC ozone and water vapor trend study reports. This paper will focus on long-term atmospheric change including the state of the instrument and observed trends in atmospheric parameters.
A52A-04 INVITED 11:40h
Trends From the Long-Term Data Record and Models: What do They Tell us About our Ability to Predict Ozone Recovery?
Our industrial society has performed an experiment on the stratospheric ozone layer over the last several decades. Initially there was the rapidly increasing release of halogen-containing compounds that carry chlorine and bromine to the stratosphere where they can cause a loss of ozone. The present part of this experiment is the implementation of the Montreal Protocol, which has led to a leveling off of halogen compounds and the beginning of their slow removal from the atmosphere. The observation and attribution of ozone response to the halogens has been a particularly difficult task because of the impact of solar cycle UV variation, two major volcanic eruptions, and interannual dynamic variability of the stratosphere. We have run 3 different 50-year simulations of the chemistry and transport of ozone and other constituents to help evaluate our understanding of the causes of ozone change and to assess our ability to predict ozone recovery with the removal of halogens. One simulation, using the Goddard chemical transport model (CTM), had interannual variability in the dynamics for the entire 50 years of simulation (1974-2022). The other two simulations used the Global Modeling Initiative (GMI) CTM with no dynamical variability: one used meteorology from a repeating warm Arctic winter and the other from a repeating cold Arctic winter. All simulations included the effects of aerosol surfaces from volcanic eruptions on chemical reactions as well as the variation in UV over the 11-year solar cycle. Differences between these simulations, and their comparisons to the long-term data record of the last several decades, allow us to ask questions about our understanding of the physical basis of the stratosphere's response to chemical change. We will show comparisons of the CTM calculations to the long-term data records from several sources. These include the SBUV/TOMS and ground-based total ozone column records, the SAGE and sonde ozone profile records, and the NDSC column records of key chemical constituents. The understanding that we gain from the combination of our model results and the long-term data record should lead to a better capability to predict how ozone will change in the future as chlorine and bromine are slowly removed from the stratosphere.