Seasonal variability of UTLS hydrocarbons observed from ACE and comparisons with WACCM

Mijeong Park, William J. Randel, Louisa K. Emmons, and Douglas E. Kinnison

National Center for Atmospheric Research

UTLS Workshop, Boulder, Oct. 19-22, 2009

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• Useful as tracers in the UTLS• Global satellite measurements (ACE-

FTS)• Chemistry transport model (WACCM3)

Hydrocarbons – UTLS?

CO

C2H

6HCN

sources

Biomass Burning

lifetime

2 months

1.5 months

~4 years (free atmosphere)3 months (ocean contact)

sinks

OH

OH

OH, O(1D)ocean

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ACE-FTS• Atmospheric

Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is a high spectral resolution infrared Fourier Transform Spectrometer on SCISAT-1

• ACE-FTS measures atmospheric absorption spectra (750-4400cm-1) using solar occultation technique

• CO, HCN, C2H6, C2H2, OCS, CH3Cl, O3, HNO3, HCl,…

Tropical sampling ~ 4 times/year

FEB APR AUG OCT

ACE-FTS Observations

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Model Description1) Whole Atmosphere Community

Climate Model, version 3 (WACCM3)2) Driven with GEOS5.1 analyzed

meteorological fields3) Period: 2004 – 2007 (4 years)4) Resolution: 1.9°x2.5° (lat x lon); 88

levels (surface - 150 km)5) Includes detailed tropospheric

chemistry mechanism (125 species)6) Emissions specific to each year

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Carbon Monoxide (CO)ACE CO

ACE CO

WACCM3 CO

WACCM3 CO

DJF

JJA

Zonal mean climatology (4 years of data)

Good agreement

between ACE and WACCM3

min

max

max

min

tropopause

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Ethane (C2H6)

WACCM3 C2H6

WACCM3 C2H6

ACE C2H6

ACE C2H6

DJF

JJA

Overall agreement, but WACCM3 is higher in the lower stratosphere(convection?)

Zonal mean climatology

CO – Horizontal Map

WACCM3 CO 147 hPa WACCM3 CO 147 hPa

ACE CO 13.5 km ACE CO 13.5 km

DJF JJA

max (Africa, America, Maritime continent)

max (Asian Monsoon)

max

max

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C2H6 – Horizontal Map

ACE C2H6 13.5 km ACE C2H6 13.5 km

WACCM3 C2H6 147 hPa WACCM3 C2H6 147 hPa

DJF JJA

Reasonable agreement except higher noise in ACE

max

max

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HCN – Horizontal Map

WACCM3 HCN 147 hPa WACCM3 HCN 147 hPa

ACE HCN 13.5 km ACE HCN 13.5 km

DJF JJA

max (Africa – DJF, Asian Monsoon – JJA)min (ocean)

max min

tropical minimum:air with recentocean contact

Asian monsoon anticyclone as

a pathway to the stratosphere

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monsoonmaximum

minimum for air with recent ocean contact

tropical min

transport tostratosphere via monsoon

ACE HCN Climatology

(JJA, 16.5 km)

ACE HCN (JJA)

Hydrogen Cyanide (HCN)

WACCM3 HCN (JJA)

(Summer, JJA)

Similar structure, but higher values in

WACCM3

ACE HCN (JJA)

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MLS HCN - Time vs. Lat

WACCM3 HCN (16-24 km) 2004-2007

MLS HCN (100 hPa) + ACE HCN (16-24 km)

Maxima in NH summer subtropics, linked to Asian summer monsoon

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Time Series (15°S-15°N)

CO 17.5 km

C2H6 19.5 km

HCN 17.5 km

annual cycle – right above the tropopauseWACCM3 has very good agreement with ACEannual cycle

interannual variability(2 year cycle?)

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Annual Cycle - UTLS

MLS CO

mean d(lnCO)/dz

CO Annual Cycle AmpRandel et al. (2007)

CO annual cycle - driven by the seasonal variation in upwelling acting on the strong background vertical gradient in CO

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CO & HCN – annual cycle? dCO/dz

strong vertical gradient

CO Annual Cycle

strong annual cycle

HCN Annual Cycle

dHCN/dz

CO

HCN

WACCM3climatolo

gy

vertical gradient

normalized annual cycle amplitude

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Tracer-tracer CorrelationsDJF JJA

HCN

C2H

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high altitude (15.5-21.5

km)low altitude

(8.5-14.5 km)

high correlation

(annual cycle)

no correlation

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Summary1.Seasonal variability of hydrocarbons in the

tropical UTLS is analyzed using the ACE-FTS observations and WACCM3.

2.WACCM3 simulates seasonal cycles in the UTLS reasonably well.

3.Strong annual cycle is observed for the chemical tracers with strong vertical gradient (CO and C2H6) right above the tropical tropopause.

4.HCN is a unique tracer with minimum in tropical upper troposphere. Transport to stratosphere through Asian summer monsoon circulation.

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HCN Chemistry

Production Processes (i.e., Emissions)…

•HCN emissions were estimated by scaling CO emissions from biomass burning and biofuel combustion using HCN/CO = 0.012 mol/mol.•Biofuel combustion emissions are constant year-round (primarily domestic heating and cooking).•Biomass burning emissions are monthly averages over 1997-2006 from the GFED-v2 inventory [Van der Werf et al., ACP, 2006].Loss Processes…

• HCN + OH => products. [Strekowski et al, 2001]• HCN + O(1D) => products [Strekowski et al, 2001]• Wet deposition in the troposphere.• Dry deposition over ocean surface.

Seasonal cycleof HCN

from ACE-FTS

HCN source: biomass burning

HCN lifetime: ~4 years in free atmosphere, but sink from contact with ocean