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Chun Zhao Advisor: Yuhang Wang

Modeling the impacts of convective transport and lightning NOx production over North America: Dependence on cumulus parameterizations. Chun Zhao Advisor: Yuhang Wang. Introduction.

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Chun Zhao Advisor: Yuhang Wang

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  1. Modeling the impacts of convective transport and lightning NOx production over North America: Dependence on cumulus parameterizations Chun Zhao Advisor: Yuhang Wang Earth&Atmospheric Sciences, Georgia Tech

  2. Introduction • Convection and associated lightning are two important meteorological processes affecting the production and distribution of tropospheric chemical tracers. Earth&Atmospheric Sciences, Georgia Tech

  3. http://www.metoffice.gov.uk/research/nwp/numerical/physics/convection_image.htmlhttp://www.metoffice.gov.uk/research/nwp/numerical/physics/convection_image.html • Subgrid cloud convection redistributes chemical tracers vertically and then horizontally. It also deplete the soluble tracers by scavenging process [Wang et al., 2001; Doherty et al., 2005; Choi et al., 2005; Folkins et al., 2006]. Earth&Atmospheric Sciences, Georgia Tech

  4. http://someonewhocares.org/photos/lightning/ • Lightning NOx (NO2+NO) production is the main source of NOx in the upper troposphere. It affects other species (e.g. O3, PAN, and HNO4) by NOx in the free troposphere. [Hudman et al., 2006]. Earth&Atmospheric Sciences, Georgia Tech

  5. Introduction • Convection and associated lightning are two important meteorological processes affecting the production and distribution of tropospheric chemical tracers. • The parameterizations of sub-grid scale convection and lightning NOx production result in large uncertainties in chemical transport models (CTMs) [Doherty et al., 2005; Choi et al., 2005]. Earth&Atmospheric Sciences, Georgia Tech

  6. Introduction • Two parameterizations of cloud convection (KF-eta and Grell) are implemented in a Regional chEmical trAnsport Model (REAM). Lightning NOx production is parameterized differently in each scheme. • MM5 with Grell convective scheme is used to provide meteorological inputs for REAM with Grell scheme (MM5-REAM) [Choi et al., 2005]. • WRF with KF-eta convective scheme is used to provide meteorological inputs for REAM with KF-eta scheme (WRF-REAM) [this work]. Earth&Atmospheric Sciences, Georgia Tech

  7. Data description Data used in the study: • Intercontinental Chemical Transport Experiment – North America (INTEX-NA) in summer 2004. CO,NMHCs, NOx, O3, and HNO3…… • SCIAMACHY satellite retrieved tropospheric columns of NO2. Earth&Atmospheric Sciences, Georgia Tech

  8. Cloud convective parameterization Grell Scheme KF-eta Scheme Cloud top Cloud top Downdraft original layer Downdraft Original layer entrainment detrainment Updraft flux Updraft flux Downdraft flux Downdraft flux entrainment detrainment Cloud bottom Cloud bottom Downdraft End layer Ground surface Ground surface Earth&Atmospheric Sciences, Georgia Tech

  9. Cloud convective parameterization • Cloud information affecting convective transport: • Mass flux • Cloud top height • Cloud bottom height • Downdraft original level • Entrainment and detrainment Earth&Atmospheric Sciences, Georgia Tech

  10. Cloud convective parameterization • Cloud information affecting convective transport: • Mass flux • Cloud top height • Cloud bottom height • Downdraft original level • Entrainment and detrainment Earth&Atmospheric Sciences, Georgia Tech

  11. Mean deep convective updraft mass fluxes from WRF and MM5 simulations during summer (June, July, and August) 2004. Earth&Atmospheric Sciences, Georgia Tech

  12. Vertical profiles of mean deep convective mass fluxes from WRF and MM5 simulations, and entrainment detrainment rate from WRF simulation during summer 2004. Earth&Atmospheric Sciences, Georgia Tech

  13. Cloud convective impact • Tracers sensitive to convective transport: • CO, C4H10, and C3H8 • Tracers scavenged by convective updrafts: • Highly soluble tracer HNO3 Earth&Atmospheric Sciences, Georgia Tech

  14. Cloud convective vertical transport • Convection affects non-soluble tracers through the turnover of their concentrations in the troposphere [Wang et al., 2001]. • Convection lifts the non-soluble tracers with elevated concentrations from the low altitude to the high altitude and subsides them with low concentrations from the high altitude to the low altitude, then increasing the concentrations in the upper troposphere and decreasing the concentrations in the lower and middle troposphere. Entrainment and detrainment provide a pathway for mixing convective updrafts and downdrafts with background atmosphere in the middle troposphere. Earth&Atmospheric Sciences, Georgia Tech

  15. Convective transport enhances CO, C4H10, and C3H8 concentrations by 15, 150, and 100% respectively in the upper troposphere. • Entrainment and detrainment drive the enhancement of the concentrations of tracers in the mid-troposphere (3-7km) in WRF-REAM simulation. Earth&Atmospheric Sciences, Georgia Tech Vertical profiles of CO, C4H10, and C3H8 from aircraft measurements, REAM simulations with and without convection.

  16. Earth&Atmospheric Sciences, Georgia Tech Spatial distributions of the average convection driven relative changes of the concentrations of CO, C4H10, and C3H8 from REAM simulation during summer 2004.

  17. Cloud convective scavenging • Convection affects highly soluble tracers through the scavenging process in convective updrafts [Folkings et al., 2006]. • Entrainment and detrainment provide additional channels to diminish the soluble tracers in the free troposphere (above 3 km) through grabbing the soluble tracers in the background atmosphere into convective updrafts and downdrafts. Earth&Atmospheric Sciences, Georgia Tech

  18. Earth&Atmospheric Sciences, Georgia Tech Vertical profiles of HNO3 from aircraft measurements and REAM standard simulations.

  19. Vertical profiles of the average convection driven relative changes of the concentrations of HNO3 from REAM simulations during summer 2004. Earth&Atmospheric Sciences, Georgia Tech

  20. Cloud convective outflow • Convective transport was found to be an important pathway for inflow and outflow of pollution over high-polluted continents such as North America [Wang et al., 2001; Choi et al., 2005; Li et al., 2005; Liang et al., 2007]. • INTEX-NA aircraft campaign was conducted with a major goal to understand the mechanisms by which pollutants are lofted and transported during the warm season [Singh et al., 2006]. Earth&Atmospheric Sciences, Georgia Tech

  21. Flight tracks in INTEX-NA campaign over the Atlantic Ocean in July 28th and August 6th. Concentration of C3H8 along the aircraft tracks in July 28th and August 6th. Earth&Atmospheric Sciences, Georgia Tech

  22. Flight tracks in INTEX-NA campaign over the Atlantic Ocean in July 28th and August 6th. C3H8 concentrations and winds at 300 hpa at 18:00 GMT on July 28th and August 6th in 2004 from REAM simulation with and without convection. Earth&Atmospheric Sciences, Georgia Tech

  23. Cloud convective outflow The higher concentration of C3H8 at 300 hpa in WRF-REAM simulation totally results from the sub-grid convective transport, on the contrary, that in MM5-REAM simulation just partly result from the sub-grid convective transport. So in these two cases, besides sub-grid convective transport, MM5-REAM simulation should include some other vertical transport mechanisms, possibly large-scale convection or convection related warm conveyor belts (WCBs). So it is likely that the vertical transport in MM5-REAM has roots in large-scale convection, which is too large to be parameterized as a sub-grid convection. Earth&Atmospheric Sciences, Georgia Tech

  24. Cloud convective impact Through the investigation of convective impact: • Vertical transport of non-soluble tracers: • The convective impacts on non-soluble tracers are significantly affected by the cumulus cloud top height. The maximum convective impact on non-soluble tracers appears at different altitudes related with cloud top height. • The entrainment and detrainment effects are shown in the comparison. They are important for the mixing in the middle troposphere. • Convective scavenging of soluble tracers: • The model (WRF-REAM) with entrainment and detrainment in convective parameterization simulates more effective scavenging process for highly soluble pollutants (e.g. HNO3) in the free troposphere. Earth&Atmospheric Sciences, Georgia Tech

  25. Cloud convective impact Through the investigation of convective impact: • Vertical transport of non-soluble tracers: • The convective impacts on non-soluble tracers are significantly affected by the cumulus cloud top height. The maximum convective impact on non-soluble tracers appears at different altitudes related with cloud top height. • The entrainment and detrainment effects are shown in the comparison. They are important for the mixing in the middle troposphere. • Convective scavenging of soluble tracers: • The model (WRF-REAM) with entrainment and detrainment in convective parameterization simulates more effective scavenging process for highly soluble pollutants (e.g. HNO3) in the free troposphere. Earth&Atmospheric Sciences, Georgia Tech

  26. Cloud convective impact Through the investigation of convective impact: • Convective outflow • The two days outflow during INTEX-NA were driven by the vertical transport originating from the convection. However, the convection system was parameterized as a sub-grid convection in WRF with KF-eta scheme simulation but was too large to be parameterized as a sub-grid convection in MM5 with Grell scheme simulation, indicating that MM5 with Grell scheme involves less sub-grid convections. Earth&Atmospheric Sciences, Georgia Tech

  27. Acknowledgments • I would like to thank Dr. Wang for his advisements. I thank Dr. Tao Zeng, Dr. Yunsoo Choi and all my officemates for their helps and suggestions. Earth&Atmospheric Sciences, Georgia Tech

  28. Thank you very much! Earth&Atmospheric Sciences, Georgia Tech

  29. Lightning NOx production parameterization • Lightning NOx production is parameterized as a function of certain meteorological variables: convective updraft mass fluxes (UMF), convective available potential energy (CAPE), cumulus cloud top height, and precipitation [Price et al., 1993; Allen et al., 1999; Choi et al., 2005]. • MM5-REAM • UMF and CAPE from Grell scheme (Choi et al., 2005) • WRF-REAM • UMF and CAPE from KF-eta scheme (this work) • Cloud-to-ground lightning flash rate is scaled to National Lightning Detection Network (NLDN) observation. Intra-cloud (IC) to cloud-to-ground (CG) flash ratio is calculated following Wang et al. [1998]. Earth&Atmospheric Sciences, Georgia Tech

  30. Mean deep convective cloud top pressures from the measurements of GOE-10 and GOE-12 satellites and the simulations of WRF and MM5 during July 2004. Earth&Atmospheric Sciences, Georgia Tech

  31. Lightning NOx production impact • Lightning NOx (NO2+NO) production is a major source of NOx in the upper troposphere and significantly enhances tropospheric NO2 columns over the ocean, where NO2 columns are more sensitive to the lightning NOx [Labrador et al., 2004; Choi et al. 2005; Martin et al., 2006; Hudman et al., 2006]. It provides the best explanation for the highly elevated NOx in the upper troposphere, which is difficult to be explained by deep convective injection of boundary layer pollution and aircraft emissions [Hudmain et al., 2006]. Earth&Atmospheric Sciences, Georgia Tech

  32. Spatial distributions of average NO2 concentrations above 8 km, from measurements and REAM simulation. Earth&Atmospheric Sciences, Georgia Tech

  33. NO2 columns from SCIAMACHY, WRF-REAM and MM5-REAM. • Lightning enhances tropospheric NO2 columns especially over the ocean by more than a factor of 2. Both WRF-REAM and MM5-REAM reproduce tropospheric NO2 columns well and highly correlate with the measurements by a coefficient 0.73 and 0.63 respectively. • MM5-REAM with higher cloud top height (up to 15 km) over-distributes lightning NOx to above 12 km, while WRF-REAM with lower cloud top height (10-12 km) performs better in the vertically distribution of the lightning NOx. Earth&Atmospheric Sciences, Georgia Tech

  34. O3 concentration is increased by up to 20 ppb due to the lightning in the upper troposphere. The upper tropospheric O3 concentration is more sensitive to the lightning over the ocean. Both WRF-REAM and MM5-REAM simulates larger lightning related enhancement of upper troposphere O3 concentration in the regions where lightning NOx production is larger. Spatial distributions of average O3 concentrations above 8 km from measurements and simulations with and without lightning. Earth&Atmospheric Sciences, Georgia Tech

  35. Lightning NOx production parameterization Through the investigation of lightning impacts: • Lightning effects are found to be important in simulations. Lightning enhances the concentrations of NO2 by a factor of 2 in the upper troposphere. It also enhances O3 concentration by up to 20 ppb in the upper troposphere. • The lightning NOx production and distribution are sensitive to cumulus cloud top height in the parameterization following Wang et al. [1998] and Allen et al. [1999]. The WRF-REAM model with lower cloud top height (10-12 km) simulates much better lightning NOx production and distribution than the MM5-REAM model with higher cumulus cloud top height (up to 15 km). Earth&Atmospheric Sciences, Georgia Tech

  36. Lightning NOx production parameterization Through the investigation of lightning impacts: • Lightning effects are found to be important in simulations. Lightning enhances the concentrations of NO2 by a factor of 2 in the upper troposphere. It also enhances O3 concentration by up to 20 ppb in the upper troposphere. • The lightning NOx production and distribution are sensitive to cumulus cloud top height in the parameterization following Wang et al. [1998] and Allen et al. [1999]. The WRF-REAM model with lower cloud top height (10-12 km) simulates much better lightning NOx production and distribution than the MM5-REAM model with higher cumulus cloud top height (up to 15 km). Earth&Atmospheric Sciences, Georgia Tech

  37. Summary • The cumulus cloud top height (CTH) is a critical factor in determining the convective impacts on chemical tracers. • The CTH is also a significant factor controlling lightning NOx production and distribution. WRF-REAM model with lower CTH (10-12 km) simulates better lightning NOx production and distribution than the MM5-REAM model with higher CTH (up to 15 km). • The entrainment and detrainment provide effective scavenging processes for soluble pollutants. WRF-REAM model with convective parameterization including entrainment and detrainment simulates better highly soluble pollutants (e.g. HNO3) in the free troposphere. • KF-eta scheme are found to provide better simulations for tropospheric trace gases than Grell scheme. Earth&Atmospheric Sciences, Georgia Tech

  38. Acknowledgments • I would like to thank Dr. Wang for his advisements. I thank Dr. Tao Zeng, Dr. Yunsoo Choi and all my officemates for their helps and suggestions. Earth&Atmospheric Sciences, Georgia Tech

  39. Thank you very much! Earth&Atmospheric Sciences, Georgia Tech

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