1
Trends and Anomalies in Southern Hemisphere OH Inferred from
12 Years of 14CO Data
Martin Manning, Dave Lowe, Rowena Moss, Gordon BrailsfordNational Institute of Water & Atmospheric Research (NIWA)New Zealand
with acknowledgements to: Bill Allan (NIWA)Rodger Sparks, Institute of Geological and Nuclear Sciences, New ZealandCarl Brenninkmeijer, Max Planck Institute fuer Chemie, Mainz, Germany
Research supported by the New Zealand Foundation for Research Science and Technology under contract C01X0204.
2
CH4 oxidn
Isoprene oxidn
Terpene oxidn
Biomass Burng
Industrial NMHCs
Fossil Fuel Comb
0
5
10
15
20
25
3010
12 M
ole
yr-1
CO sources CO vs 14CO sources
Total source ~ 1014 Mole yr-1
Lifetime ~ 8 to 10 weeks
Inventory ~ 1.7 x 1013 Mole
CH4 oxidn
Isoprene oxidn
Terpene oxidn
Biomass Burng
Industrial NMHCs
Fossil Fuel Comb
Cosmic Ray Prodn
0
100
200
300
400
500
Mole
yr-1
14CO sources
1412C
~ 10C
Total source ~ 570 Mole yr-1
Lifetime ~ 10 to 12 weeks
Inventory ~ 120 Mole
3
14CO cycling in the atmosphere
14CO (52%)
14CO (35%)
direct production
direct production
transport
cosmic rayneutrons
14CO2
14CO2
OH
OHStratosphere
Troposphere
In the extra-tropical southern hemisphere, recycled 14CO accounts for 15 to 20% of the total in the troposphere.
14CO (13%)
recycled
Carbon uptake by biosphere and oceans
4
Model derived 14CO distributions
Tropospheric distributions of 14CO are not very sensitive to details of production distribution pattern….
… but are sensitive to the location and strength of cross-tropopause transport, and…
…show large latitudinal gradients in the winter hemisphere
But observed gradients in the high latitudes are less than simulated in models!
Source: Joeckel, P.; “Cosmogenic 14CO as tracer for atmospheric chemistry and transport”. PhD Thesis, Mainz, 2000.
5
The role of the variable Sun
Electrically charged material ejected from the Sun interacts with the magnetic field around the solar system.
During periods of high solar activity a larger proportion of cosmic rays are deflected away from the solar system.
Changes in sunspot numbers track the variation in solar activity - but observed neutron fluxes are a more direct indicator of 14C production.
6
Cycles in 14C production
0
50
100
150
200
1975 1980 1985 1990 1995 2000
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Year
Monthly sun spot numbers.NOAA NGDC web site.
14C production rates (molec cm-2 s-1) derived from neutron count rate data. Lowe and Allan (in press).
7
14CO data analysis - INew Zealand
14CO measurementsAntarctic
14CO measurements
Storage correction for 14CO production in sample cylinders
Lowe et al (in press)
Inverse model CO sources(Bergamaschi et al)
Expected 14C/C ratios for recycled CO
Observed CO concentration Subtract recycled 14CO
compare sites
Direct 14CO
8
Direct 14CO data - New Zealand and Antarctica
Note:
Large annual cycle relative to mean concentration.
No strong gradient between New Zealand and Antarctica.
1990 1995 20000
5
10
15
20
New Zealand Antarctica
mole
c/ c
m3 (S
TP
)
Year
9
Note:
Secular trend following solar cycle of estimated 14C production rates.
1990 1995 20000
5
10
15
20
14C production New Zealand Antarctica
mole
c/ c
m3 (S
TP
)
Year
Direct 14CO data - New Zealand and Antarctica
10
14CO data analysis – I (continued)New Zealand
14CO measurementsAntarctic
14CO measurements
Storage correction for 14CO production in sample cylinders
Lowe et al (in press)
Inverse model CO sources(Bergamaschi et al)
Expected 14C/C ratios for recycled CO
Observed CO concentration Subtract recycled 14CO
merge
14C production rate Scale by production rate(2, 3 or 4 month lag)
Normalized direct 14CO data series
11
Normalized 14CO data
1990 1995 20000
5
10
15
20
mole
c/ c
m3 (
ST
P)
Year
Normalized direct 14CO concentrations have a fairly regular cycle over 12 years (using 3-month lag from production).
However, there is some residual inter-annual variability.
12
Calculate apparent net removal rate R
(for constant source)
0
dCS
dtRC
Analysis of 14CO dynamics(with minimal reliance on models)
Normalized direct 14CO data series
Extratropical southern hemisphere uniformity suggests behavior as a
well mixed box
Tropospheric production +
transport from stratosphere
dC
S Cdt
Removal ratek [OH]
Smooth and calculate derivatives with error analysis
estimate S0 so that mean value for
R = 6 yr-1
Determine average annual cycle in R. NB this includes seasonality in OH
and cross tropopause transport
Hypothesis: Variations in R about climatological average values are most likely due to [OH] variations
Where is this
13
1990 1995 20000
5
10
yr-1
Year
Derived apparent net removal rates
Apparent net removal rate R: monthly values (red band) and average seasonal cycle (blue line)
Net removal rate determined with a mean value of 6 yr-1.
Varies by a factor of ~3 from winter to summer.
14
Apparent removal rate vs calculated [OH] values
2 4 6 8 10 120
5
10
Spivakovsky et al[OH] values for
25oS to 65oS
derived from14CO data
Ap
pare
nt re
mova
l rate
yr-1
Month of year
Phasing and seasonal amplitude agree closely with [OH] values derived by Spivakovsky et al for southern hemisphere mid latitudes.
Lower apparent removal rates in September to December period may reflect higher stratosphere troposphere exchange at this time.
15
1990 1995 20000.4
0.6
0.8
1.0
1.2
1.4
1.6
Anom
aly
rati
o
Year
Variations in Effective Removal Rates
Monthly ratios of apparent net removal rate to climatological average value.
Upper and lower estimates based on data errors (purple lines) plus smoothed values (12 month window).
No significant trend in removal rate from 1990, but two “events” with variations of > 20% over time scales of 3 to 6 months.
Pinatubo eruption?
Kalimantan fires?
16
-0.4
-0.2
0.0
0.2
0.4
1990 1995 2000
1990 1995 2000
-50
0
50
Variations in cross-tropopause transport may be related to QBO in the stratosphere or other dynamical effects.
Schauffler and Daniel proposed that Pinatubo eruption caused an increase in stratosphere troposphere exchange.
However, various indicators suggest that such effects are small.
Anomalies in cross-tropopause transport ?
Daily anomalies in potential vorticity at 350 K isentropic surface over 30 to 70oS
Daily anomalies in total column ozone at 45oS
17
Summary Tropospheric 14CO concentrations appear to scale linearly with our
estimates of 14C production rate
The lag between production and concentration appears consistent with model estimates of 3 months
The apparent net removal rate derived from the data is very similar in phase and seasonality to that expected for mid latitude OH
There appears to be no significant trend in southern hemisphere OH over the 1989 – 2001 period (agrees with the AGAGE analysis of methyl chloroform data)
However, two “events” show major anomalies in apparent removal rates of > 20% over 3 to 6 month time scales
We propose that the main cause of these variations is change in OH concentrations
