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Denitrification in polar stratosphere

D

duderstadtk@gmail_com

New Member
I am trying to match WACCM history variables with the description of "Stratospheric Aerosols" in "cam5_desc.pdf."    Specifically, which WACCM history fields involve the gravitational settling of aerosols that could contribute to denitrification?   
  • 1) Is HNO3_NAT the only[/i] condensed HNO3 involved in PSC aerosol settling in WACCM?  
  • 2) What does HNO3_NAT include? [i.e., Is this variable meant to include both Type I NAT PSCs as well as the "NAT coating" and nitrate from N2O5 heterogeneous reactions associated with Type II PSCs.]
  • 3) Does HNO3_NAT settle at the rate specified by VEL_NAT2?   [i.e., What is the difference between  "small nat" and "large nat" in VEL_NAT1 versus VEL_NAT2?]  
  • 4) What does "NAT large mode" refer to (e.g., RAD_LNAT)?  Is there a "NAT small mode?"   Is there a threshold radius specified for "NAT large mode" or does it depend on model state (e.g., temperature)?   [The description in "cam5_desc.pdf" suggests that only NAT with median radii between 2-5 micrometers settle.
My assumptions after reading "cam5_desc.pdf" are:  A) HNO3_STS  (with STS represented as SAD_SULFC/RAD_SULFC?) occurs on particles too small to be included in aerosol settling.   B) The water ice part of Type II PSCs (e.g., SAD_ICE/RAD_ICE) is treated separately from the condensed nitrate on Type II PSCs that could result in denitrification (e.g, "NAT coating" or adsorbed nitrate from N2O5 heterogeneous reactions).   
Our Goal: We are searching for a method to estimate the potential for deposition of nitrate to Greenland snow from wintertime denitrification in the polar stratosphere.   We are not expecting to see much denitrification in these particular simulations but want to make sure we are interpreting WACCM correctly.   
We are currently using cesm1_0_5 and F_SD_WACCM for the winter of 2000-2001.   

Thanks for any clarification! 
 
mmills

mmills

CSEG and Liaisons
Staff member
Via Doug Kinnison: 1) Is HNO3_NAT the only condensed HNO3 involved in PSC aerosol settling in WACCM?  
  • For stratospheric aerosols, the HNO3_LNAT variable is the only condensed phase variable.
2) What does HNO3_NAT include? [i.e., Is this variable meant to include both Type I NAT PSCs as well as the "NAT coating" and nitrate from N2O5 heterogeneous reactions associated with Type II PSCs.
  • This is a (simple) equilibrium approach, every timestep the model decides how much of the total HNO3 (gas + condensed) is is partitioned into the condensed phase. This partitioning is done in mo_sad.F90 which is called from mo_gas_phase_chemdr.F90. The condensed phase is then settled using the VEL_NAT2 rate (mo_aero_settling.F90). This equilibrium approach is discussed in:Considine, D. B., A. R. Douglass, P. S. Connell, D. E. Kinnison, and D. A., Rotman, A polar stratospheric cloud parameterization for the three dimensional model of the global modeling initiative and its response to stratospheric aircraft, /J. Geophys. Res./, 105, 3955-3975, 2000.Kinnison, D. E., G. P. Brasseur, S. Walters, R. R. Garcia, F. Sassi, B. A. Boville, D. Marsh, L. Harvey, C. Randall, W. Randel, J. F. Lamarque, L. K. Emmons, P. Hess, J. Orlando, J. Tyndall, and L. Pan, Sensitivity of chemical tracers to meteorological parameters in the MOZART-3 chemical transport model, /J. Geophys. Res./, 112, D20302, doi:10.1029/2006JD007879, 2007.
3) Does HNO3_NAT settle at the rate specified by VEL_NAT2?   [i.e., What is the difference between  "small nat" and "large nat" in VEL_NAT1 versus VEL_NAT2?]  
  • The current version only has one type of NAT. The HNO3 contained in this NAT is call HNO3_LNAT. There is not a "small" mode.
4) What does "NAT large mode" refer to (e.g., RAD_LNAT)?  Is there a "NAT small mode?"   Is there a threshold radius specified for "NAT large mode" or does it depend on model state (e.g., temperature)?   [The description in "cam5_desc.pdf" suggests that only NAT with median radii between 2-5 micrometers settle.
  • The radius varies, depending on how much condensed phase is available.
[/list] My assumptions after reading "cam5_desc.pdf" are:  A) HNO3_STS  (with STS represented as SAD_SULFC/RAD_SULFC?) occurs on particles too small to be included in aerosol settling.   
  • Correct.
B) The water ice part of Type II PSCs (e.g., SAD_ICE/RAD_ICE) is treated separately from the condensed nitrate on Type II PSCs that could result in denitrification (e.g, "NAT coating" or adsorbed nitrate from N2O5 heterogeneous reactions).  
  • We do not settle HNO3 on water-ice.
  Our Goal: We are searching for a method to estimate the potential for deposition of nitrate to Greenland snow from wintertime denitrification in the polar stratosphere.   We are not expecting to see much denitrification in these particular simulations but want to make sure we are interpreting WACCM correctly.   
  • The stratospheric HNO3 will eventually be advected of settled into the troposphere. Here wet/dry deposition will remove the HNO3. I've never tried what you are doing - but you will need to examine the wet deposition tendencies to figure out how much HNO3 is deposited on snow. I'll ask a colleague how best to do this.
 
 
mmills

mmills

CSEG and Liaisons
Staff member
Via Doug Kinnison: 1) Is HNO3_NAT the only condensed HNO3 involved in PSC aerosol settling in WACCM?  
  • For stratospheric aerosols, the HNO3_LNAT variable is the only condensed phase variable.
2) What does HNO3_NAT include? [i.e., Is this variable meant to include both Type I NAT PSCs as well as the "NAT coating" and nitrate from N2O5 heterogeneous reactions associated with Type II PSCs.
  • This is a (simple) equilibrium approach, every timestep the model decides how much of the total HNO3 (gas + condensed) is is partitioned into the condensed phase. This partitioning is done in mo_sad.F90 which is called from mo_gas_phase_chemdr.F90. The condensed phase is then settled using the VEL_NAT2 rate (mo_aero_settling.F90). This equilibrium approach is discussed in:Considine, D. B., A. R. Douglass, P. S. Connell, D. E. Kinnison, and D. A., Rotman, A polar stratospheric cloud parameterization for the three dimensional model of the global modeling initiative and its response to stratospheric aircraft, /J. Geophys. Res./, 105, 3955-3975, 2000.Kinnison, D. E., G. P. Brasseur, S. Walters, R. R. Garcia, F. Sassi, B. A. Boville, D. Marsh, L. Harvey, C. Randall, W. Randel, J. F. Lamarque, L. K. Emmons, P. Hess, J. Orlando, J. Tyndall, and L. Pan, Sensitivity of chemical tracers to meteorological parameters in the MOZART-3 chemical transport model, /J. Geophys. Res./, 112, D20302, doi:10.1029/2006JD007879, 2007.
3) Does HNO3_NAT settle at the rate specified by VEL_NAT2?   [i.e., What is the difference between  "small nat" and "large nat" in VEL_NAT1 versus VEL_NAT2?]  
  • The current version only has one type of NAT. The HNO3 contained in this NAT is call HNO3_LNAT. There is not a "small" mode.
4) What does "NAT large mode" refer to (e.g., RAD_LNAT)?  Is there a "NAT small mode?"   Is there a threshold radius specified for "NAT large mode" or does it depend on model state (e.g., temperature)?   [The description in "cam5_desc.pdf" suggests that only NAT with median radii between 2-5 micrometers settle.
  • The radius varies, depending on how much condensed phase is available.
[/list] My assumptions after reading "cam5_desc.pdf" are:  A) HNO3_STS  (with STS represented as SAD_SULFC/RAD_SULFC?) occurs on particles too small to be included in aerosol settling.   
  • Correct.
B) The water ice part of Type II PSCs (e.g., SAD_ICE/RAD_ICE) is treated separately from the condensed nitrate on Type II PSCs that could result in denitrification (e.g, "NAT coating" or adsorbed nitrate from N2O5 heterogeneous reactions).  
  • We do not settle HNO3 on water-ice.
  Our Goal: We are searching for a method to estimate the potential for deposition of nitrate to Greenland snow from wintertime denitrification in the polar stratosphere.   We are not expecting to see much denitrification in these particular simulations but want to make sure we are interpreting WACCM correctly.   
  • The stratospheric HNO3 will eventually be advected of settled into the troposphere. Here wet/dry deposition will remove the HNO3. I've never tried what you are doing - but you will need to examine the wet deposition tendencies to figure out how much HNO3 is deposited on snow. I'll ask a colleague how best to do this.
 
 
mmills

mmills

CSEG and Liaisons
Staff member
Via Doug Kinnison: 1) Is HNO3_NAT the only condensed HNO3 involved in PSC aerosol settling in WACCM?  
  • For stratospheric aerosols, the HNO3_LNAT variable is the only condensed phase variable.
2) What does HNO3_NAT include? [i.e., Is this variable meant to include both Type I NAT PSCs as well as the "NAT coating" and nitrate from N2O5 heterogeneous reactions associated with Type II PSCs.
  • This is a (simple) equilibrium approach, every timestep the model decides how much of the total HNO3 (gas + condensed) is is partitioned into the condensed phase. This partitioning is done in mo_sad.F90 which is called from mo_gas_phase_chemdr.F90. The condensed phase is then settled using the VEL_NAT2 rate (mo_aero_settling.F90). This equilibrium approach is discussed in:Considine, D. B., A. R. Douglass, P. S. Connell, D. E. Kinnison, and D. A., Rotman, A polar stratospheric cloud parameterization for the three dimensional model of the global modeling initiative and its response to stratospheric aircraft, /J. Geophys. Res./, 105, 3955-3975, 2000.Kinnison, D. E., G. P. Brasseur, S. Walters, R. R. Garcia, F. Sassi, B. A. Boville, D. Marsh, L. Harvey, C. Randall, W. Randel, J. F. Lamarque, L. K. Emmons, P. Hess, J. Orlando, J. Tyndall, and L. Pan, Sensitivity of chemical tracers to meteorological parameters in the MOZART-3 chemical transport model, /J. Geophys. Res./, 112, D20302, doi:10.1029/2006JD007879, 2007.
3) Does HNO3_NAT settle at the rate specified by VEL_NAT2?   [i.e., What is the difference between  "small nat" and "large nat" in VEL_NAT1 versus VEL_NAT2?]  
  • The current version only has one type of NAT. The HNO3 contained in this NAT is call HNO3_LNAT. There is not a "small" mode.
4) What does "NAT large mode" refer to (e.g., RAD_LNAT)?  Is there a "NAT small mode?"   Is there a threshold radius specified for "NAT large mode" or does it depend on model state (e.g., temperature)?   [The description in "cam5_desc.pdf" suggests that only NAT with median radii between 2-5 micrometers settle.
  • The radius varies, depending on how much condensed phase is available.
[/list] My assumptions after reading "cam5_desc.pdf" are:  A) HNO3_STS  (with STS represented as SAD_SULFC/RAD_SULFC?) occurs on particles too small to be included in aerosol settling.   
  • Correct.
B) The water ice part of Type II PSCs (e.g., SAD_ICE/RAD_ICE) is treated separately from the condensed nitrate on Type II PSCs that could result in denitrification (e.g, "NAT coating" or adsorbed nitrate from N2O5 heterogeneous reactions).  
  • We do not settle HNO3 on water-ice.
  Our Goal: We are searching for a method to estimate the potential for deposition of nitrate to Greenland snow from wintertime denitrification in the polar stratosphere.   We are not expecting to see much denitrification in these particular simulations but want to make sure we are interpreting WACCM correctly.   
  • The stratospheric HNO3 will eventually be advected of settled into the troposphere. Here wet/dry deposition will remove the HNO3. I've never tried what you are doing - but you will need to examine the wet deposition tendencies to figure out how much HNO3 is deposited on snow. I'll ask a colleague how best to do this.
 
 
D

duderstadtk@gmail_com

New Member
Thanks!  This clarification helps!(The supplementary information in Kinneson et al., 2007 is particularly useful...as it contains information on NAT formation that the version of "cam5_desc.pdf" I have does not address.)   Regarding wet deposition, at this point we are assuming that all HNO3 lost from the gas phase as a result of wet deposition ends up in precipitation at the end of each half-hour time step.  [WD_HNO3/AREA/PRECT].   Although this method overestimates nitrate concentrations in snow by a factor of 2-3, it nonetheless captures the variability observed in surface snow at Summit, Greenland quite well.    Please let us know if there is a better way to do this.   Thanks again,
 
D

duderstadtk@gmail_com

New Member
Thanks!  This clarification helps!(The supplementary information in Kinneson et al., 2007 is particularly useful...as it contains information on NAT formation that the version of "cam5_desc.pdf" I have does not address.)   Regarding wet deposition, at this point we are assuming that all HNO3 lost from the gas phase as a result of wet deposition ends up in precipitation at the end of each half-hour time step.  [WD_HNO3/AREA/PRECT].   Although this method overestimates nitrate concentrations in snow by a factor of 2-3, it nonetheless captures the variability observed in surface snow at Summit, Greenland quite well.    Please let us know if there is a better way to do this.   Thanks again,
 
D

duderstadtk@gmail_com

New Member
Thanks!  This clarification helps!(The supplementary information in Kinneson et al., 2007 is particularly useful...as it contains information on NAT formation that the version of "cam5_desc.pdf" I have does not address.)   Regarding wet deposition, at this point we are assuming that all HNO3 lost from the gas phase as a result of wet deposition ends up in precipitation at the end of each half-hour time step.  [WD_HNO3/AREA/PRECT].   Although this method overestimates nitrate concentrations in snow by a factor of 2-3, it nonetheless captures the variability observed in surface snow at Summit, Greenland quite well.    Please let us know if there is a better way to do this.   Thanks again,
 
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