Overview of UT/LS Science Issues and New Information from SEAC4RS Steve Wofsy and Jasna Pittman – Harvard University Qing Liang – NASA Goddard Space Flight Center, Universities Space Research Association Paul Newman – NASA Goddard Space Flight Center Presented at the SEAC4RS Science Team meeting Pasadena, CA, 29 April 2015

Science Questions for this introductory talk: What are the transport rates into, within, and out of the stratosphere? How can we measure the overall rates of transport? Is the stratospheric circulation changing in response to warming climate and increasing greenhouse gases? How well to we know the global removal rates/lifetimes of ODSs? The discussion will consider tracer transport phenomena and key observational constraints on the emergent properties of the stratosphere.

52 CFC yr (monthly lifetimes between 49.4 – 63.4) 102 CFC yr (93.6 – 105.9) 93 CFC yr (84.8 – 97.4) 114 N 2 O yr (111.4 – 126.8) 26 CCl yr (42.4 – 54.5) [35 with tropospheric loss] τ WMO Species τ GEOSCCM variability, range

Brewer-Dobson Circulation is Projected to Increase with Climate Warming Implications: Changes in O 3, feedback on climate, shorter lifetimes for ODSs

JGR, 1994 Mean age of air (average time since an air volume entered the stratosphere) directly measures stratospheric circulation

Definition of age of air, age spectrum, width of age spectrum age spectrum mean age Andrews et al, 2001

N 2 O Isopleth Mean Age = Δ CO 2 / b CO2 = Δ SF 6 / b SF6

Vertically integrated global loss b x time rate of change of X b x time rate of change of x=CO 2 (corrected for CH 4 ) or change of SF 6 (corrected for mesospheric loss ) Mean Age  Tracer-tracer and flux ratios Rate of change for tracer (e.g. N 2 O) affects slope and mean lifetime In a 1-d atmosphere, with gases emitted at the surface, the slope of a tracer-tracer plot at Z is proportional to the vertically integrated loss rate above Z + the rate-of-change of the concentration at the surface.

We have (almost) inert tracers that increase linearly with time  direct measure of mean age

De-seasonalized Tracer Trends

The stratosphere approximates the 1-dimensional atmosphere: quasi-horizontal transport rate >> chemistry, vertical transport rate How good is this approximation? CO 2 vs Age of Air:Age of Air vs height Data from GEOSCCM compact simple relationship above about 20 km

Models and Data: Changes over time of mean age and lifetimes for gases in the stratosphere

Vertical Profiles of Mean Age from CO 2 Engel et al., CO 2 -derived mean age

GRL, 2006 Models: Large changes, noisy signal.

  Austin and Li, 2006

Age of Air  Global lifetime of ODSs and tracers

N 2 O (ppb) CO 2 (ppm) CFCl 3 Observations of the Middle Stratosphere (OMS) Ft. Sumner (34 N)  GEOSCCM  Obs (corr CH 4 )  GEOSCCM  Obs

Z* (km)

Eric Ray Andreas Engel Mean Age of Air Observed mean ages in the middle stratosphere are older by 15-25% than for the GEOSCCM model – what is implied about ODS lifetimes? No trend can be discerned due to severe under-sampling, ~ 0 today 32 +/-2 km Mean Age Year

Tropical average local photolytic lifetimes, 20N—20S. Colored dashed lines represent the cutoff levels for each of the trace gases in the tropics. Source: Moore et al., BAMS Photolysis rates increase exponentially vs. altitude  large change in loss rate w/ small change in vertical extent (Local Loss τ ) Z* (km)

Small shifts in tracer distributions in response to 10% increase in overturning circulation Fractional change in tracer vs. alt Change in mean age Fractional change in tracer vs. N 2 O

CFC CO 2 SEAC4RS: Seasonal signal, attenuated  full age spectrum Model Age Spectrum is generally excellent!

Age of Air (days; GEOSSCM) Ethane Ethyne Ethane vs. GEOSCCM mean age Ethyne

Ethyne CH 3 Cl CFC-12CO 2 SEAC4RS (all): Tracers of different character vs Potential T

Source: Anderson, Margitan, Stedman, Science, 1977

Summary and conclusions CO 2 and SF 6 observations provide accurate mean ages for the middle stratosphere and lifetimes for species removed in the stratosphere. CO 2 is better at high altitudes and latitudes (no mesospheric losses; need to measure CH4 also); SF 6 in lower stratosphere (small seasonal variation). CO 2 provides age spectra for the UT/LS. GEOSCCM tracer fields appear to agree well with many tracers, but too young in middle stratosphere We need a strategy for observing the ongoing evolution of stratospheric climate and composition.

SF 6 CCl 4 CFCl 3 HIPPO cross sections, mid-Pacific, Nov 2009 Also Jan 2009, Mar-April 2010, Jun-Jul-Aug-Sep 2011

slope=.601 Annual Emission Fluxes derived from HIPPO lower tropospheric gradients SF 6 10 Gg/yr 2010 (adopted from Rigby, based on interannual trend) CCl 4 62 Gg/yr (ratio 6.0 mole/mole vs. SF 6 ; no sink asymmetry adj) CFCl 3 86 Gg/yr (ratio 9.2 mole/mole vs. SF 6 : the elusive residual source) Note: SF 6 latent heat 12 kJ/mole > CFC-11; greater ΔP vap in summer? Similar approach to get emissions of species emitted in the NH & inert in the troposphere

TTL transport rates, Atmospheric Lifetimes, and Global Stratospheric Removal Rates for Greenhouse Gases and Ozone Destroying Substances from CO 2 -tracer relationships Steven C. Wofsy, Jasna V. Pittman, Bruce C. Daube Harvard University Paul A. Newman and Qing Liang Goddard Space Flight Center Elliot Atlas University of Miami Arlyn E. Andrews NOAA ESRL, Global Monitoring Division

Michael Volk et al. SH high lat

N2O CFC11 CFC12 H1211 lvl co2..ch #age.of.air.lvl0 # N2O CFC11 CFC12 H1211 # ## --- below, not corrected for CH4 (big error !) #N2O CFC11 CFC12 H1211 #

Z* 7*ln( 1000/P) Z* 7*ln( 1000/P)