A12B-01 INVITED
Ozone and Temperature Trends in the Upper Stratosphere at Five Stations of the Network for the Detection of Atmospheric Composition Change
We use comprehensive records of upper stratospheric (35 to 45~km) ozone and temperature from several space- and ground-based data sets at five stations of the Network for the Detection of Atmospheric Composition Change (NDACC), from 45°S to 48°N, and starting in 1979. The space based ozone records come from the Solar Backscatter Ultra-Violet (SBUV), Stratospheric Aerosol and Gas Experiments (SAGE I and II), Halogen Occultation Experiment (HALOE), Global Ozone Monitoring by Occultation of Stars (GOMOS), and Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY). The ground-based records come from lidars and microwave radiometers at the NDACC stations. For temperature, European Centre for Medium Range Weather Forecast reanalyses (ERA-40), National Centers for Environmental Prediction (NCEP) operational analyses, and HALOE and lidar measurements are used. All data sets show essentially the same long-term variations, attributable to QBO, 11-year solar-cycle, anthropogenic chlorine and other trends. Monthly mean anomalies from the different data-sets typically agree within 5% for ozone, and within 3~K for temperature. From 1979 until the late 1990s, due to increasing anthropogenic chlorine, all available data-sets show a clear decline of ozone near 40~km, by 10% to 15%. This decline has not continued in the last 10~years. At some sites, ozone at 40~km even appears to have increased since 2000, consistent with the beginning decline of stratospheric chlorine. Temperatures near 40~km altitude have been fluctuating around a constant level at all five NDACC stations since about 1985. This non-decline of upper stratospheric temperatures would be a new and significant change from the more or less linear cooling of the upper stratosphere seen before the 1990s, and reported in previous trend assessments. Chemistry-climate model (CCM) simulations track the historical ozone anomalies and reproduce the change in ozone tendency in the late 1990s. The phaseout of chlorofluorocarbons after the 1987 International Montreal Protocol now shows positive effects on ozone in the upper stratosphere. However, due to increasing CO2, the CCMs simulate a continuous linear cooling by 1~K per decade over the entire 1979 to 2010 period. This is not consistent with the near-constant temperatures observed since the late 1980s.
A12B-02 INVITED
Long-term Changes of Water Vapor in the Stratosphere
Water vapor in the stratosphere plays an important role in the radiative and chemical balance of this region of the atmosphere. Although the basic processes controlling the water vapor distribution are known, details of the processes and the degree to which they are subject to change are less well understood. Longer term measurements of water vapor in the stratosphere are very limited. The only continuing measurement of water vapor in the stratosphere with a multi-decadal record is the balloon profile measurements from Boulder, Colorado that began in 1980. These soundings done on an approximately monthly basis until recently when the frequency has been increased to twice a month are made with a cryogenically cooled frost point hygrometer. Although the instrument has undergone a number of changes since its adaptation from an earlier design by John Mastenbrook, the basic principle and calibration scale have remained consistent. An important feature of the Boulder time series is its overlap with a number of satellite, balloon, and airborne measurements that have been made over the past two decades. These include satellite instruments such as SAGE II, HALOE and MLS on UARS, MLS and HRDLS on Aura, ACE-FTS, and MIPAS. Airborne and balloon sensors have included the Lyman á, TDL, and other chilled mirror instruments. A number of these observations have been compared in intercomparison exercises. Here several recent satellite observations from MLS and MIPAS over Boulder are compared with the balloon profiles. The time series of balloon water vapor observations at Boulder has shown a significant increase over the 25+ years of soundings. These increases moderated significantly beginning with the dramatic drop in lower stratospheric water vapor beginning in 2000 that has been noted in the satellite as well as the balloon data. More recently the balloon soundings suggest that these dryer conditions have begun to turnaround. Recent satellite observations over Boulder are investigated to determine if this recent change is confirmed in these data.
A12B-03 INVITED
Current and Future Emissions and Concentrations of Trace Gases Impacting the Stratosphere
A large number of long-lived trace gases, predominantly or exclusively of anthropogenic origin, are
contributing to destruction of stratospheric ozone through release of halogens, or to cooling of the
stratosphere through the greenhouse effect. The tropospheric mole fractions of these gases are being
measured in the Advanced Global Atmospheric Gases Experiment (AGAGE) and other networks and these
measurements are then used to estimate their current emissions using inverse methods. We briefly review
the current trends in these gases and their inferred emissions. To predict future emissions and tropospheric
mole fractions of long-lived trace gases that impact the stratosphere, we utilize the MIT Integrated Global
System Model (IGSM). It comprises coupled sub-models of economic development, atmospheric chemistry,
climate dynamics, terrestrial hydrology, and oceanic and terrestrial ecosystems. We present results through
the year 2100 for the case where there is no explicit climate policy, and for cases where greenhouse gas
mole fractions in the troposphere are stabilized at about 450, 550, 650 and 750 ppm carbon dioxide
equivalents. Projected stratospheric impacts depend sensitively on: the ODPs and GWPs of these gases
(and hence on their lifetimes and molecular compositions); future adherence and amendments to the
Montreal Protocol; and the nature and stringency of future climate policies. Significant uncertainties
accompany these predictions that will be discussed and quantified.
http://web.mit.edu/globalchange/
A12B-04
Updated observations of stratospheric water vapor and temperature trends
We present updated observations of stratospheric water vapor variability and trends, by combining global satellite observations from HALOE (1992-2005) and Aura MLS (2004-2008). Time series show a continuation of the low water vapor values that began in 2001 to present. There is strong correlation between water vapor in the lower stratosphere and temperature anomalies at the tropical cold point tropopause, and these temperatures have been anomalously low since 2001. Lower stratospheric tropical ozone also mirrors this behavior. These observations are consistent with an increase in the strength of the tropical upwelling circulation in the lower stratosphere since the early 1990's, and we compare corresponding diagnostics of upwelling derived from meteorological data sets.
A12B-05 INVITED
Linkages Between Stratospheric Ozone and Climate Change
Stratospheric ozone has been the subject of intense research since the mid-1970s, when the prospect of ozone depletion by human activities was first raised. Recent research has shown that ozone changes can play a far more important role in modifying surface climate than envisaged. The massive Antarctic ozone hole has been shown to lead to changes in temperatures and hence the climate not only in the Antarctic stratosphere, but also in its troposphere. The unique characteristics of the Antarctic ozone hole and its links to surface climate trends in Antarctica will be described. Evidence for linkages between stratospheric processes and climate changes in other regions will also be discussed, including the tropics, subtropics, and Arctic.
A12B-06
Anthropogenic and Natural Influences on Stratospheric Halogen Abundance as Inferred From Tropospheric Measurements of Long- and Short-Lived Gases.
The chemical composition of the stratosphere is changing as a result of international limits on the industrial use of ozone-depleting substances (ODSs). Natural processes also influence the abundance of halogen- and sulfur-containing gases and affect stratospheric composition through changes in emissions or loss rates. Through a global network of flask sampling and in situ sampling, both at Earth's surface and from aircraft, we regularly measure a wide range of anthropogenic and natural ODSs, substitutes for ODSs, and other chemicals. The results suggest large changes in emission rates of chlorine and bromine from anthropogenic activities as a result of Montreal Protocol restrictions and smaller changes in the natural system. They imply a significant decline in ozone-depleting halogen abundance in the stratosphere, though the magnitude of this decline is location dependent. Here we will discuss recent changes observed for anthropogenic chemicals, explore their implications, and touch upon the magnitudes of changes in the natural system influencing the chemical composition of the stratosphere.
A12B-07
Decadal Trends in the Background Stratospheric Aerosol
Stratospheric aerosol measurements are made with Nd(YAG) lidars at Boulder, Colorado and at Mauna Loa Observatory, Hawaii. Since the eruption of the volcano Pinatubo in June 1991, minor eruptions having brief, local stratospheric effects have been observed, but there have been no major eruptions capable of perturbing the global stratosphere above 20 km. This has provided an unusual opportunity to study the background aerosol, free of volcanic effects. The period following the decay of the Pinatubo aerosol, from about 1996 to the present, is the longest period without a major volcanic stratospheric aerosol perturbation since the sulfate layer was discovered by Junge in 1959. Both Boulder and Mauna Loa show a well-defined annual variation in the background aerosol with a maximum in winter associated with transport from the tropical reservoir. There appears to be a clear Quasi-Biennial (QBO) variation with the aerosol backscatter altitude profiles showing distinct characteristics during the east to west and west to east tropical wind transition periods. At Boulder, where aerosol lidar measurements began about 2000, an increasing trend of about 10 percent per year in the integrated stratospheric lidar backscatter has been observed in the 20-25 km layer. At Mauna Loa, where the lidar record extends back to the 1970's, an identical increase in background aerosol backscatter, beginning in about 2000, has been observed in the 20-25 km layer. Under non-volcanic conditions, the background sulfate aerosol is sustained mainly by sulfur dioxide (predominantly from the burning of coal) and carbonyl sulfide emissions at the surface which enter the stratosphere in the tropics. Increased emissions and/or enhanced tropical upwelling circulation in the lower stratosphere, possibly related to climate change, could thus affect the decadal trend of the background stratospheric aerosol.