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Junhua Liu and Jennifer Logan

Transport analysis and source attribution of the tropical CO seasonal and interannual variability in the UT/LS. Junhua Liu and Jennifer Logan School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA Dec 17 th 2010, AGU

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Junhua Liu and Jennifer Logan

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  1. Transport analysis and source attribution of the tropical CO seasonal and interannual variability in the UT/LS JunhuaLiu and Jennifer Logan School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA Dec 17th 2010, AGU Acknowledgements: Thanks to the MLS Science team

  2. Gases exchanged between the UT/LS Modified from Holton et al. (1995) H2O tape recorder Jiang et al. (2010)

  3. CO Tape Recorder First identified by Schoeberl et al. (2006) using MLS data, GCM model analysis by Duncan et al. (2007). Two mechanisms hypothesed: • Advection of the CO seasonal signal near the tropopause. (Schoeberl et al., 2006) • Seasonal cycle in upwelling acting on the background vertical gradient in CO (Randel et al., 2007). • Objective: • To understand the processes that determine observed temporal and spatial variability in CO signal in the UT/LS.

  4. MLS (Microwave Limb Sounder) MLS Mozaic Courtesy of Inna Megretskaia • MLS V3.3 level 2 data • Prelim. validation with MOZAIC aircraft transects at 215 hPa • the 100% positive bias in MLS v2.2 has been eliminated

  5. GEOS-Chem Model • Standard chemistry run: • 4o × 5o horizontal resolution • Two runs driven by archived GEOS-4 (2005-06) or GEOS-5 (2005-08) assimilated met. fields • diff. convection parameterization • Model profiles sampled along the MLS orbit track at the obs. time, and vertically smoothed with the MLS AK. • Tagged CO run: • 2o × 2.5o horizontal resolution • OH fields from chemistry run • CO (P-L) rate in stratosphere from GMI model

  6. CO tape recorder (12ºN- 12ºS) MLS The GEOS-Chem models capture the main features. Inter-annual variation (IAV) driven by CO fire emissions, especially from Indonesia. GEOS-4 CO from Indonesian fires in late 2006 IAV in emissions in NH fire season apparent (Jan.-Apr.). GEOS-5 4-yr mean is subtracted from time series ppb

  7. Initial conditions of CO and transport at 226 hPa Tagged CO (12N-12S) source contributions Biomass Burning S. America S. Africa N. Africa max. in Apr-May, min. in Aug-Sep. GEOS-4 stronger than GEOS-5 Indonesia Left: temporal overlapping of surface BB from different continents generates the semi-annual cycle ~200 hPa. Isoprene

  8. Tropical CO - Seasonality and interannual variation CO peak at 70 hPa from NH fires lags peak at 147 hPa by ~0-2 mon.; lag in peak ~3-4 mon. for CO from SH fires. MLS GEOS-4 GEOS-5 70 hPa: CO maximum from SH and NH fires add - shift to annual cycle. 70 hPa 100 hPa • 100 hPa: • MLS : semi-annual cycle • Models: • Fall peak damped in 07, 08. • Matches phase of MLS but amplitude too small. Vert. transport too weak? CO anomaly (ppb) 147 hPa 215 &147 hPa:: Semi-annual cycle 215 hPa N.Af, Indo. S.Af, S.Am Indo. 4-yr mean is subtracted from time series Jan 06 Jan 05 Jan 08 Jan 09 Jan 07

  9. Seasonality and vertical profile of upward transportin assimilated met. fields Max. in winter-spring Min. in summer-fall Velocity (cm/s) Transport minimum at ~80 hPa, causing the maximum lag of CO peak from 100 hPa to 70 hPa. Much slower transport of SH burning signal. Winter-spring(Dec-May) Summer-fall (Jun-Nov) Pressure(hPa) Velocity (cm/s)

  10. CO mixing ratio (ppb) CO mixing ratio and anomaly at 215 & 70 hPa CO anomaly (ppb) CO mixing ratio (ppb) CO anomaly (ppb) MLS GEOS-4 GEOS-5 • Much less CO has been lofted in GEOS-5. • CO anomalies show comparable results in GEOS-4 and GEOS-5; Models match the seasonal cycles of MLS - CO tape recorder pattern depends more on phase of vertical transport. • The model amplitudes are ~10-16 ppb smaller than the obs. at 70 hPa.

  11. GEOS-5: vertical transport too weak GEOS vertical velocities computed from mass divergence (zonal mean of 15°S-10°N) GEOS-4 GEOS-5: 100-75 hPa - Transport too low in all seasons. GEOS-4: Comparable vertical transport in fall below 90 hPa. Weaker vertical transport in winter and spring below 90 hPa – possibly causing the damped seasonal cycle in the model Pressure (hPa) GEOS-5 NH spring (MAM) NH summer (JJA) NH fall (SON) NH winter (DJF) Vertical velocity deduced from heating rates (obs. H2O and O3 Radiative transfer model) Pressure (hPa) Yang et al., 2008

  12. Conclusion • Semi-annual cycles of CO below 80 hPa in the TTL - determined by the temporal overlapping of surface BB emissions from different continents. • Transition from semi-annual to annual cycles around 80 hPa – induced by a combination of the signal at the tropopause and the annual cycle of BDC in the LS • Strong interannual variation with a CO maximum in boreal fall 2006, mainly caused by fires in the Indonesian region. • GEOS-5: too weak vertical transport, but matches the phase shift in transport, so similar tape recorder pattern. • GEOS-4: possibly too weak vertical transport in winter and spring - decreasing the amplitude of the seasonal cycle.

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