overview of ut/ls science issues and new information from seac4rs steve wofsy and jasna pittman –...
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Overview of UT/LS Science Issues and New Information from SEAC4RS Steve Wofsy and Jasna Pittman – Harvard UniversityQing Liang – NASA Goddard Space Flight Center, Universities Space Research AssociationPaul Newman – NASA Goddard Space Flight Center
Presented at the SEAC4RS Science Team meetingPasadena, 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-11 56.2 yr (monthly lifetimes between 49.4 – 63.4)102 CFC-12 100.4 yr (93.6 – 105.9) 93 CFC-113 91.3 yr (84.8 – 97.4)114 N2O 118.5 yr (111.4 – 126.8) 26 CCl4 50.4 yr (42.4 – 54.5) [35 with tropospheric loss]
τWMO Species τGEOSCCM variability, range
Brewer-Dobson Circulation is Projected to Increase with Climate Warming
Implications: Changes in O3, 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
N2O Isopleth
Mean Age = Δ CO2 / bCO2
= Δ SF6 / bSF6
Vertically integrated global loss bx time rate of change of X
bx time rate of change of x=CO2 (corrected for CH4 ) or change of SF6 (corrected for mesospheric loss )
Mean Age Tracer-tracer and flux ratios
Rate of change for tracer (e.g. N2O) 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?CO2 vs Age of Air: Age of Air vs height
Data from GEOSCCMcompact 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 CO2
Engel et al., 2009
-2 0 2 4 6 8 CO2-derived mean age
GRL, 2006 Models:Large changes, noisy signal.
3.35 2.85
Austin and Li, 2006
Age of Air Global lifetime of ODSs and tracers
100 150 200 250 300 356 358 360 362 364 366 368 370 N2O (ppb) CO2 (ppm)
0
5
0
100
150
20
0
250
0
5
0
100
150
20
0
250
CFCl
3
CFCl
3
Observations of the Middle Stratosphere (OMS)1998 05 18 Ft. Sumner (34 N)
GEOSCCM Obs (corr CH4)
GEOSCCM Obs
Z* (k
m)
Eric Ray Andreas Engel
Mea
n Ag
e of
Air
0
2
4
6
8
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 Ag
e 4.5 5.0 5.5 6.0
1985 1995 2005Year
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 2014.
Photolysis rates increase exponentially vs. altitude large change in loss rate w/ small change in vertical extent
(Local Loss τ )
16.1 24.5 32.2 40.7 48
.3
Z* (k
m)
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. N2O
CFC-
1235
0
4
00
4
50
500
390 392 394 396CO2
SEAC4RS: Seasonal signal, attenuated full age spectrum
Model Age Spectrum is generally excellent!
Age
of A
ir (d
ays;
GEO
SSCM
)0
2
00
400
60
0 8
00 1
000
120
0
0 500 1000 1500 2000 2500 3000 0 20 40 60 80 100 120 Ethane Ethyne
Ethane vs. GEOSCCM mean age Ethyne
EthyneCH3Cl
CH3Cl
CFC-12 CO2
SEAC4RS (all): Tracers of different character vs Potential T
Source: Anderson, Margitan, Stedman, Science, 1977
Summary and conclusions
• CO2 and SF6 observations provide accurate mean ages for the middle stratosphere and lifetimes for species removed in the stratosphere.
• CO2 is better at high altitudes and latitudes (no mesospheric losses; need to measure CH4 also);
• SF6 in lower stratosphere (small seasonal variation).
• CO2 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.
SF6
CCl4 CFCl3
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 gradientsSF6 10 Gg/yr 2010 (adopted from Rigby, based on interannual trend)CCl4 62 Gg/yr (ratio 6.0 mole/mole vs. SF6 ; no sink asymmetry adj)CFCl3 86 Gg/yr (ratio 9.2 mole/mole vs. SF6 : the elusive residual source)
Note: SF6 latent heat 12 kJ/mole > CFC-11; greater ΔPvap 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 CO2-tracer relationships
Steven C. Wofsy, Jasna V. Pittman, Bruce C. DaubeHarvard University
Paul A. Newman and Qing LiangGoddard Space Flight Center
Elliot AtlasUniversity of Miami
Arlyn E. AndrewsNOAA ESRL, Global Monitoring Division
Michael Volk et al.
SH high lat
N2O CFC11 CFC12 H1211 lvl0 356.9 358.5 357.2 359.0 co2..ch4 1.5 0.7 1.3 0.6
#age.of.air.lvl0# N2O CFC11 CFC12 H1211 #6.277696 4.698718 5.960831 4.310113 ## --- below, not corrected for CH4 (big error !) #N2O CFC11 CFC12 H1211 #5.290422 4.248600 5.095080 3.923031
Z* 7*ln( 100
0/P)
0 10
20
30
Z* 7*ln( 100
0/P)
0 10
20
30