# Presentation: 388218

## The Impact of Convection on CO Distribution in the Tropical Troposphere

**M. Manyin**1**, M. Schoeberl**2**, A. Douglass**2

- _x0016_*Abstract*
- Convective transport plays a important role in the vertical redistribution of atmospheric constituents.  To better characterize this role we use CO as a tracer, evaluating satellite data, numerical model output, and in situ measurements. Observations from MLS and AIRS are analyzed, revealing complementary distributions of CO in the upper and lower troposphere respectively.  Convective regions are identified using TRMM-calibrated rainrates. Model results from GEOS-5 (global) and WRF-Chem (mesoscale) are used to interpret the observed distributions.  In situ data from the TC4 campaign are included in the analysis.  Preliminary results are presented.

- _x0016_*Motivation*
- How important is convection in the transport of trace gases in the troposphere?
- Does convection lead to characteristic patterns of vertical distribution, particularly in the ITCZ region near Central America?
- How well do global models simulate this convective transport?
- Do mesoscale models with parameterized convection permit more accurate characterization?

- _x0016_*Primary Concept*
- CO was selected as a tracer in this study, because of its tropospheric lifetime (1 to 3 months) and this initial observation:  In July 2005, AIRS observed plumes of CO traveling westward from Africa to South America, at a relatively low altitude (500 hPa).  In subsequent days, MLS detected a trail of CO at a higher level (215 hPa) covering Central America and points west.
- A possible explanation lies in the mass flux associated with deep convective systems:  entrainment at low levels, and detrainment at higher levels.  Using high rainrates as a proxy for convection, the TRMM-calibrated 3B43 monthly product shows significant convective activity in the same region where AIRS CO arrives from the east, and MLS CO begins to head west.

- _x0016_*Approach*
- In order to incorporate in situ aircraft data from the Tropical Composition, Cloud and Climate Coupling (TC4) Mission, initial work has focused on the July/August 2007 timeframe.  CO retrievals from MLS and AIRS were studied, along with TRMM-calibrated 3B42 (3-hourly product), for evidence of convective lofting.  Once likely cases were identified, global model data were consulted, to see if they corroborated.  The model provided a more complete spatial picture and  finer temporal resolution.  Then aircraft data were compared against both satellite measurements and model output, primarily to confirm upper level CO patterns.  Lastly, a mesoscale model was brought to bear, allowing higher resolution simulations.

- AURA  MLS:  Microwave Limb Sounder
- near polar/sun synchronous orbit
- resolution: 300 km at limb tangent pt
- 16 days before repeating scan pattern
- processed with Goddard Trajectory Model

- AQUA  AIRS: Atmospheric Infrared Sounder
- polar, sun synchronous orbit
- resolution: 13.5 km at nadir
- coverage: global, twice daily
- retrievals using Joiner’s algorithm

- GEOS-5 (including GOCART)
- GCM / DAS
- resolution: 0.5 x 0.625 deg.
- convective parameterization:  RAS
- vertical levels:   72
- run in support of TC4

- WRF-Chem (run in tracer mode)
- mesoscale, nonhydrostatic atmos. model
- resolution:  outer grid=54km, inner=18km
- conv param’n:  Grell-Devenyi ensemble
- vertical levels:  36
- initialization, boundaries and emissions from GEOS-5

- DC-8 flown during TC4
- diode laser spectrometer
- altitude:  up to 200 hPa
- references: Sachse, Glen

*Satellite Data*

*Numerical Models*

*Aircraft data*

**Using Satellite-based Data**
- Starting with TRMM-calibrated rainfall [A], classify areas of high rainrate as candidate convective regions.  For each region, consult lower tropospheric measurements of CO from AIRS [B].  Where significant, search the same region directly above (MLS 215 hPa) for evidence of increased CO burden [C].  In this example, there are several areas to pursue in the ITCZ.  Where matches are found in MLS we must determine if the CO appeared at that level during the time of heaviest rainfall, or if it already resided at that level, upwind of its current location.  Where CO is _not_ found at 215 hPa, CO may have risen to an intermediate level, or beyond.  AIRS measurements alone do not distinguish between different vertical levels, as they only provide a single independent measurement in the troposphere.

**Including Numerical Simulations**
- We turn to an AGCM to help compensate for the sparse MLS measurements and the lack of vertical definition in the AIRS data.  The Goddard Earth Observing System (GEOS-5) global model was run in support of the TC4 campaign.  The model’s convective precipitation patterns [D] tend to follow those of the TRMM product, particularly in the tropics.  The low level CO [E] is aligned with the AIRS retrievals, although concentrations over water are somewhat lower.  At upper levels [F] pattern in the ITCZ region are similar to MLS but the CO burden in the model tends to be greater.  To effectively use the GEOS-5 output we must systematically characterize its correlation to the satellite data, and then gauge the convective effects on CO.

**A**

**B**

**C**

**D**

**E**

**F**

**3B42 Rainfall**

**AIRS**
**lower tropospheric CO**

**MLS  CO at 215 hPa**
**(Scaled by 0.6)**

**GEOS-5 Convective Precipitation**

**GEOS-5 CO at 800 hPa**

**GROS-5 CO at 200 hPa**

- All images show
- daily values for
- July 29, 2007

**Using Aircraft Data**
- Data measured from a DC8 during TC4 are useful for gauging accuracy of the MLS retrievals as well as providing vertical profiles against which model output can be compared.  CO measurements from one day are shown here both as a time series [G] and as a spatial plot of upper level segments [H].  Using the Goddard Trajectory Model, MLS products with enhanced spatial resolution were generated at 144-minute intervals.  Three timesteps are shown, with the corresponding in situ measurements plotted over them.  These segments show a convincing visual correlation; a statistical evaluation remains to be done, and the aircraft data should also be compared to model output.

- TRMM: 3B42 Rainrate Product
- calibrated with TMI instrument aboard the Tropical Rainfall Measuring Mission (TRMM) satellite
- resolution: 0.25 x 0.25 degree, 50 N-S
- product interval:  every 3 hours
- combination of IR and microwave precipitation estimates

- CO data from DC8  7/29/07

- CO from DC8  and MLS 13:12-15:36 UTC

- CO from DC8  and MLS 15:36-18:00 UTC

- CO from DC8  and MLS 18:00-20:24 UTC

**G**

**H**

**Global vs. Regional Model**
- The GEOS-5 global model is run at 0.5x0.625 degree resolution, while convective storms occur on much smaller scales.  We can turn to mesoscale models such as the Weather Research and Forecasting (WRF) model to achieve higher resolution.  We have begun to use WRF-Chem in tracer mode to run at GEOS-5 resolution on an outer grid, and 18 km on a nested grid.  Convection must still be parameterized, but higher accuracy is possible, as well as flexibility in parameterization settings. The figures to the right show upper level CO concentrations for the nested domain run with and without convective effects.  Convection clearly enhanced the CO levels in three areas.  Again, a thorough analysis is required, as well as comparison with in situ data.

*Acknowledgements*
- CO is in GEOS-5 thanks to those who coupled it with the GOCART aerosol model:  Peter Colarco, Randy Kawa, Huisheng Bian and Arlindo Dasilva  (see http://gmao.gsfc.nasa.gov/highlights/tc4mission/ #g5chem)
- Thanks to Joanna Joiner for the AIRS CO retrievals and her advice on their use.
- Plots of 3B42 were produced using the Giovanni online data system, developed and maintained by the NASA Goddard Earth Sciences (GES) Data and Information Services Center (DISC).

*References*
- Bloom, S. et al, 2005. Documentation and Validation of the Goddard Earth Observing System (GEOS) Data Assimilation System - Version 4. Technical Report Series on Global Modeling and Data Assimilation 104606, 26
- Grell, G. A. et al, 2005: Fully coupled online chemistry within the WRF model, Atmos. Environ., 39, 6957-6975.
- Schoeberl, M., and L. Sparling (1995), Trajectory modelling, in Diagnostic tools in Atmospheric Physics: Varenna on Lake Como, Villa Monastero, 22 June ミ 2 July 1993, Int. School. Phys. Enrico Fermi, vol. 124, edited by G. Fiocco and G. Visconti, pp. 289 ミ 305, IOS Press, Amsterdam.

- _x0016_*Next Steps*
- Proceed from anecdotal to statistical analysis as mentioned above
- Consider Ice Water Content from MLS
- Request that AIRS retrievals be recomputed with a priori profile derived from GEOS-5

- AIRS CO

- MLS CO

- Convective area in TRMM 3B43

- 3B43  Average Rainrate July 2005

- 1 Science Systems and Applications, Inc.
- 2 NASA Goddard Space Flight Center