Overview of the Arctic Middle Atmospheric Chemistry Theme Kimberly Strong Department of Physics, University of Toronto Co-Investigators: J. Drummond, H. Fast, A. Manson, T. McElroy, G. Shepherd, R. Sica, J. Sloan, K. Strawbridge, K. Walker, W. Ward, J. Whiteway Collaborators: J. McConnell, P. Bernath, T. Shepherd Students: C. Adams, A. Fraser, D. Fu, F. Kolonjari, R. Lindenmaier, H. Popova Post-docs: R. Batchelor, T. Kerzenmacher, K. Sung, M. Wolff Env. Canada: M. Harwood, R. Mittermeier CANDAC: P. Fogal, A. Harrett, A. Khmel, C. Midwinter, P. Loewen, O. Mikhailov, M. Okraszewski (Thanks to all!) CANDAC Workshop #5 Toronto, 24-26 October 2007
Overview • Polar Stratospheric Ozone Trends • The Need for Arctic Measurements • The Arctic Middle Atmosphere Chemistry Theme • The First Year of AMAC Activities • Outlook
Introduction Arctic middle atmosphere chemistry • Focus here is on the stratosphere and the ozone budget • Coupled to troposphere & mesosphere, dynamics & radiation Stratospheric ozone • Highly effective absorber of harmful UV-B solar radiation • Dominant source of radiative heating in the stratosphere • This heating determines the stratospheric temperature distribution, which, in turn, influences stratospheric winds Consequences of a decrease in Arctic stratospheric ozone • Enhancement of UV-dependent photochemical reactions in the troposphere • Decrease in radiative forcing • Reduction in stratospheric temperatures • Change in stratospheric dynamics
Polar Total Ozone Trends WMO Ozone Assessment 2006
Seasonal Total Ozone Trends Total ozone column trends as a function of equivalent latitude and season using TOMS and GOME data for 1978-2000 x - mean position of vortex edge Eq. Latitude - a potential vorticity coordinate with vortex centre at 90° Largest Arctic trend is 1.04 ± 0.39 % per year in March WMO Ozone Assessment 2002
Arctic Ozone: March Averages • March monthly averaged total ozone from satellites • Nimbus-4 BUV • Nimbus-7 TOMS • NOAA-9 SBUV/2 • Earth Probe TOMS • Aura OMI WMO Ozone Assessment 2006
Latitudinal Total Ozone Trends Measured and modelled latitudinal total ozone trends WMO Ozone Assessment 2006
Polar Ozone Depletion - Processes (1) Formation of the winter polar vortex (band of westerly winds) • isolates cold dark air over the polar regions (2) Low temperatures in the vortex, T<195 K • PSCs form in the lower stratosphere (liquid & solid HNO3,H2O,H2SO4) (3) Dehydration and denitrification • remove H2O & nitrogen oxides which could neutralize chlorine (4) Release of CFCs, mixing, and transport to the polar regions • enhanced levels of chlorine and other halogen species (5) Heterogeneous reactions on the PSCs • convert inactive chlorine (HCl and ClONO2) into reactive Cl2 (6) Sunlight returns in the spring • UV radiation breaks Cl2 apart to form Cl (7) Catalytic chlorine and bromine cycles • destroy ozone, while recycling Cl This continues until the Sun causes a dynamical breakdown of the winter vortex and PSCs evaporate.
= BrO + BrCl The Role of Bromine • Significant source of uncertainty • May be more important (by 10-15%) in polar ozone depletion than previously thought • BrO + ClO cycle estimated to contribute up to 50% of chemical loss of polar ozone • Bry may be 3-8 ppt larger than expected from CH3Br + halons source • due short-lived bromocarbons and tropospheric BrO ? Frieler at al., 2006; WMO Ozone Assessment 2006
Arctic Vortex and Ozone Loss Large variation from year to year in • area of the Arctic vortex (dominates circulation from Nov. to March) • strength of the sudden warmings associated with planetary-scale waves originating in the troposphere • timing of the final vortex breakdown Large variability in Arctic ozone (short & long term) is due to: • variability in transport of air in the stratosphere • variability in tropospheric forcing • variations in chemical ozone loss Chemical consequences of variability in vortex meteorology: • area over which T is below threshold for PSC formation • amount of sunlight available to drive chemical ozone loss and the volume of air processed through cold regions • timing of the cold periods • the location of the cold areas within the vortex • position of the vortex when cold areas develop
Stratospheric circulation Chemical reaction rates Stratospheric temperature Stratospheric ozone UV Processes Affecting Stratospheric Ozone and Temperature Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002
Stratospheric circulation Chemical reaction rates Stratospheric temperature Stratospheric ozone UV Vertical propagation of planetary and gravity waves Processes Affecting Stratospheric Ozone and Temperature Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002
Stratospheric circulation Chemical reaction rates Stratospheric temperature Stratospheric ozone UV Greenhouse gases Anthropogenic emissions of CO2, CFCs, CH4, N2O Vertical propagation of planetary and gravity waves Processes Affecting Stratospheric Ozone and Temperature Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002
Stratospheric circulation Chemical reaction rates Stratospheric temperature Stratospheric ozone UV Greenhouse gases Stratospheric chlorine, bromine, and nitrogen oxides Troposphere-stratosphere exchange Anthropogenic emissions of CO2, CFCs, CH4, N2O Vertical propagation of planetary and gravity waves Processes Affecting Stratospheric Ozone and Temperature Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002
Stratospheric circulation Chemical reaction rates Stratospheric temperature Stratospheric ozone UV PSC formation Greenhouse gases Stratospheric chlorine, bromine, and nitrogen oxides Stratospheric water vapour CH4 oxidation Troposphere-stratosphere exchange Anthropogenic emissions of CO2, CFCs, CH4, N2O Vertical propagation of planetary and gravity waves Processes Affecting Stratospheric Ozone and Temperature Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002
Future Impact of Climate Change Will climate change enhance or reduce polar ozone loss? Two possibilities: • The stratospheric vortex becomes stronger and colder, and there is a positive Arctic Oscillation trend (e.g., Shindell et al., 1999). • increasing CO2 cools the stratosphere, strengthens the polar vortex • such cooling could increase formation of PSCs • results in more Arctic ozone loss • observations suggest 15 DU Arctic ozone loss per Kelvin cooling • “Dynamical heating” causes a more disturbed and warmer NH stratospheric vortex (e.g., Schnadt et al., Clim. Dyn. 2002; Schnadt & Dameris, GRL 2003). • enhancement of planetary wave activity • causes a weaker and warmer polar vortex • results in less Arctic ozone loss - faster recovery
Two Possibilities (1) Cooling of stratosphere: T (K) (July) in response to CO2 doubling from the Hammonia Model (Brasseur, SPARC Lecture 2004) (2) Warming of stratosphere: T (K) (DJF) from 1990 to 2015 from the ECHAM model (Schnadt et al., Clim. Dyn. 2002)
Sensitivity of Arctic Ozone Loss to T squares, red line - ozonesondes circles, green line - HALOE B&W circles, black lines - SLIMCAT Overall cooling trend in the global-mean lower stratosphere is ~0.5 K/decade (1979-2005) Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Ozone column loss [ DU ] (~14-25 km, mid-Jan to late March) ~80 DUozone loss ~5-6 K temperature change ~ 15 DU additional chemical ozone lossper Kelvin cooling of the Arctic stratosphere Rex et al., GRL 2004, 2006; WMO Ozone Assessment 2006
An Example - Winter 2005 The Arctic vortex was unusually cold and stable in early winter 2005... Courtesy of C.T. McElroy and J. Davies, EC
Montreal Protocol • 1985 - Vienna Convention for the Protection of the Ozone Layer • 1987 - Montreal Protocol on Substances that Deplete the Ozone Layer • Entered into force in 1989 • Established controls on halogen source gases • Later strengthened by a series of Amendments WMO Ozone Assessment 2006
Recovery of Stratospheric Ozone Changes in total ozone from 60°S to 60°N IPCC/TEAP SROC 2005
Polar Ozone - Predictions Gradual recovery of ozone is anticipated as stratospheric chlorine decreases • ozone turnaround in the Arctic likely before 2020 • vunerable to perturbations, such as aerosols from volcanoes • coupled to stratospheric cooling • extreme Arctic ozone loss is not predicted Spring Polar Ozone Anomalies WMO Ozone Assessment 2006
The Need for Arctic Measurements “… the frequency of measurements deep in the Arctic vortex remains low. The situation is unsatisfactory given the highly non-linear sensitivity of Arctic stratospheric ozone to cold winters. … Chemical and dynamical perturbations caused by strong volcanic eruptions make it impossible to derive a linear trend [in total ozone], whichhighlights the importance of continuous measurements throughout the expected recovery of the ozone layer during the coming decades.” IGOS 2004 Atmospheric Chemistry Report
The Need for Arctic Measurements “With regard to the Arctic, the future evolution of ozone is potentially sensitive to climate change and to natural variability, and will not necessarily follow strictly the chlorine loading. There is uncertainty in even the sign of the dynamical feedback to WMGHG changes. … Progress will result from further development of CCMs [chemistry-climate models] and from comparisons of results between models and with observations.” IPCC/TEAP 2005, Special Report on Safeguarding the Ozone Layer and the Global Climate System
Arctic Middle Atmosphere Chemistry Overall goal of this theme • To improve our understanding of the processes controlling the Arctic stratospheric ozone budget and its future evolution, using measurements of the concentrations of stratospheric constituents. This theme addresses two of the four “grand challenges in atmospheric chemistry” identified in the 2004 IGOS Atmospheric Chemistry Theme Report, namely • stratospheric chemistry and ozone depletion • chemistry-climate interactions.
Arctic Middle Atmosphere Chemistry Theme Science Questions • What is the chemical composition of the Arctic stratosphere above PEARL? • How and why is it changing with time? • How is the chemistry coupled to dynamics, microphysics, and radiation? • What is the polar stratospheric bromine budget? • Significant source of uncertainty • BrO + ClO cycle estimated to contribute up to half chemical loss • How will the polar stratosphere respond to climate perturbations? • Particularly while Cl and Br loading is high • How will changes in atmospheric circulation affect polar ozone? • Cooling (more ozone depletion) or warming (less)?
Arctic Middle Atmosphere Chemistry Theme Scientific Objectives (1)To obtain an extended data set of the concentrations of ozone and of other key trace gases in the Canadian Arctic stratosphere above PEARL under both chemically perturbed and unperturbed conditions. (2)To analyse these measurements, in conjunction with dynamical, radiative, aerosol/PSC, and meteorological observations also made at PEARL, in order to unravel the coupled processes controlling Arctic stratospheric composition and to quantify the contributions from dynamics and chemistry to ozone depletion. (3)To investigate the seasonal and interannual variability of the Arctic ozone budget, as well as its longer-term evolution, with a focus on determining the impact of climate change. (4)To combine the measurements with atmospheric models (including chemical box models, chemical transport models and global circulation models) to facilitate both improved modelling of the atmosphere and the interpretation of the measurements, and hence to better understand climate system processes and climate change.
Arctic Middle Atmosphere Chemistry Theme Short-Term Outputs • Better understanding of diurnal, day-to-day, seasonal, and interannual variations in a suite of Arctic stratospheric constituents, including ozone and related trace gases, particularly nitrogen and halogen compounds. • Identification and quantification of chemical ozone loss at Eureka during each Arctic winter-spring. • Process studies of the relative importance of chemical, radiative, microphysical, and transport processes, including comparisons with atmospheric models.
Arctic Middle Atmosphere Chemistry Theme Long-Term Outputs • A significant new long-term dataset of Arctic chemical composition measurements. • Determination of trends in ozone and related stratospheric constituents. • Improved understanding of processes that result in feedbacks between stratospheric ozone depletion, rising greenhouse gas concentrations, and climate change. • Better predictive capabilities regarding the future evolution of the Arctic stratospheric ozone budget.
Arctic Middle Atmosphere Chemistry Theme Primary Composition Instruments • Bruker 125HR Fourier transform infrared spectrometer (FTS) • Direct solar (and lunar) absorption, 700-4500 cm-1 at high resolution • UV-visible grating spectrometer • Zenith-scattered (and direct) solar absorption, 300-600 nm • Stratospheric ozone lidar Differential Absorption Lidar (DIAL) • Brewer spectrophotometer Ozone total columns • Polar Atmospheric Emitted Radiance Interferometer (P-AERI) • Emission, 400-3300 cm-1 (3-25 µm) at low spectral resolution Measurements • Reactive species, source gases, reservoirs, dynamical tracers • O3, NO, NO2, HNO3, N2O5, NO3, N2O, ClONO2, HCl, OClO, BrO, HF, CFCs, CH4, H2O, CO, OCS, ... • Total columns and some information on vertical distribution
Arctic Middle Atmosphere Chemistry Theme Modelling • Interpretation will include comparisons with atmospheric models in order to better understand the underlying processes and to facilitate improved modelling of the atmosphere. • Comparisons with chemical transport models to quantify chemical ozone loss, and the role of nitrogen, chlorine, and bromine families • Back trajectories and box models will be used to investigate the history and chemical evolution of stratospheric air above Eureka • CMAM can provide a detailed global chemical climate model, e.g., for estimating the spatio-temporal variability of the measured trace gases • CMAM-DA will enable combination of the Arctic data with other observations and with a priori information
DA8 FTS Measurements: HNO3 Farahani et al., JGR 2007
DA8 FTS Measurements: HNO3 Comparison of solar and lunar DA8 FTS measurements during winter 2001-2002 with SLIMCAT chemical transport model and CMAM Farahani et al., JGR 2007
2006-2007 AMAC Highlights • February-March 2006 - ACE Arctic validation campaign • March 2006 - installation of SEARCH / U of Idaho AERI • July 2006 - installation of new Bruker IFS 125HR FTS • August 2006 - installation of new UV-visible grating spectrometer (PEARL-GBS) • August-October 2006 - first data from both instruments • February-March 2007 - ACE Arctic validation campaign • May 2007 - P-AERI ordered • July 2007 - Bruker / Bomem intercomparison campaign • August-September 2007 - NDACC Aura validation campaign • Ongoing - daily measurements, implementation and optimization of retrieval algorithms, data analysis
AMAC Students and PDFs • Bruker FTS measurements and data analysis • PDF Rebecca Batchelor, UofT • MSc/PhD student Rodica Lindenmaier, UofT • UV-visible measurements and data analysis • PhD student Annemarie Fraser, UofT • PhD student Cristen Adams, UofT • Analysis of PARIS-IR & Bomem DA8 data using SFIT2 • PDF Keeyoon Sung, UofT (Sept. 2006 - April 2007) • PhD student Dejian Fu, U of Waterloo (just graduated) • Stratospheric ozone lidar measurements and data analysis • MSc student Andrea Moss, UWO • 2006 and 2007 ACE Arctic validation campaigns • PDF Tobias Kerzenmacher, UofT • P-AERI measurements and data analysis • PDF Mareile Wolff, UofT (IPY: Dec. 2007 - )
External Linkages • Canadian Space Agency • Continues to support ACE Arctic validation campaigns, currently “Canadian Arctic Validation of ACE for IPY 2007 & 2008” • Network for the Detection of Atmospheric Composition Change (NDACC) • Contacted Co-Chairs of the NDACC UV-Visible Working Group about the requirements for certifying the UV-visible spectrometer • Invited to upcoming November meeting • Comparing Bruker FTS with Bomem DA8 for NDACC certification • Six weeks of alternating measurements from February-March 2007, linked by continuous measurements with PARIS-IR • Additional intercomparison campaign held in July 2007 • Actively collaborating with Gloria Manney, JPL • Working on linkages with SEARCH, IASOA, SPARC, modelling groups
AMAC-Related Publications *T.E. Kerzenmacher et al., Measurements of O3, NO2 and Temperature During the 2004 Canadian Arctic ACE Validation Campaign. GRL 2005. A. Wiacek et al.,First Detection of Meso-Thermospheric Nitric Oxide by Ground-Based FTIR Solar Absorption Spectroscopy. GRL 2006. E.E. Farahani et al.,Nitric acid measurements at Eureka obtained in winter 2001-2002 Using solar and lunar Fourier transform infrared absorption spectroscopy: Comparisons with observations at Thule and Kiruna and with results from three-dimensional models. JGR 2007. * G. L. Manney et al., The high Arctic in extreme winters: vortex, temperature, and MLS and ACE-FTS trace gas evolution. ACPD 2007. * R. J. Sica et al., Validation of the Atmospheric Chemistry Experiment (ACE) version 2.2 temperature using ground-based and space-borne measurements. ACPD 2007. R. Lindenmaier, First Measurements of ozone with the new Bruker IFS 125HR at Eureka, M.Sc. Thesis, U of Toronto, Toronto, 2007. * D. Fu et al., PARIS-IR and ACE Measurements, Ph.D. Thesis, U of Waterloo, 2007. * A. Fraser et al., Intercomparison of UV-visible measurements of ozone and NO2 during the Canadian Arctic ACE Validation Campaigns: 2004–2006. In preparation. Submission to ACP is imminent. * E. Dupuy et al., Validation of ozone measurements from the Atmospheric Chemistry Experiment (ACE). Submission to ACP is imminent. * K. Sung et al., Partial and total column measurements at Eureka, Nunavut in spring 2004 and 2005 using solar infrared absorption spectroscopy, including comparisons with ACE satellite measurements. Submission to ACP soon. * D. Fu et al., Simultaneous atmospheric measurements using two Fourier transform infrared spectrometers at the Polar Environment Atmospheric Research Laboratory (PEARL) during spring 2006. Submission to ACP soon. * Also ACE validation
TCCON Opportunity • Invited to join proposal to NASA for expansion of the Total Carbon Column Observing Network (TCCON) • Network of Bruker 125HRs for CO2, CH4, H2O, O2, N2O, CO • One goal - validation of NASA's Orbiting Carbon Observatory (OCO) • Travel and loan of hardware (beamsplitters, detectors, data storage) • Attended TCCON meeting at May NDACC IRWG meeting • Provided a report to CANDAC Scientific Steering Committee • Recommended that we accept the invitation to join the network • Issues • TCCON measurements use different beamsplitter and detector from standard mid-IR configuration, with manual intervention needed • Some reduction in "middle atmosphere" observations • General thoughts • An interesting and positive extension of our capabilities, benefits outweigh challenges, links us to this growing network, very topical
Outlook: Tasks and Issues • Installation of new sun-trackers for FTS and UV-visible • Maximization and automation of Bruker FTS measurements • Upgrade and operation of stratospheric ozone lidar • Installation of CANDAC P-AERI • NDACC certification for Bruker FTS and UV-visible spectrometer • Implementation of TCCON capability if proposal successful • Completion of the analysis of Bomem DA8 data archive • Analysis of CANDAC/PEARL measurements • Integration with complementary measurements at PEARL • Contributions to IPY atmospheric science