Title: Anthropogenic Aerosol indirect effects in cirrus clouds
Authors: Joyce E. Penner, Cheng Zhou, Anne Garnier and David Mitchell
Contact: Joyce E. Penner, Penner@umich.edu

Key Points:
- A new version of the CAM/IMPACT atmospheric model that includes gravity 13 waves and the effect of aerosols on cirrus clouds is presented.
- The best representation of the particles that act as ice nuclei results in a climate 15 forcing of -0.2 Wm-2 for aircraft soot
- The use of all dust particles as ice nuclei lowers this forcing to near zeroto in-snow light-absorbing aerosols than atmospheric aerosols. 

Research Overview:
We have implemented a parameterization for forming ice in large-scale cirrus clouds that accounts for the changes in updrafts associated with a spectrum of waves acting within each time step in the model. This allows us to account for the frequency of homogeneous and heterogeneous freezing events that occur within each time step of the model and helps to determine more realistic ice number concentrations as well as changes to ice number concentrations. The model is able to fit observations of ice number at the lowest temperatures in the tropical tropopause, but is still somewhat high in tropical latitudes with temperatures above 195K.  The climate forcings associated with different representations of heterogeneous ice nuclei are primarily negative unless large additions of IN are made, such as when we assumed that all aircraft soot acts as an IN. However, they can be close to zero if it is assumed that all the background dust can act as an INP irrespective of how much sulfate is deposited on these particles. Our best estimate for the forcing of aircraft soot in this model is -0.2 ± 0.06 Wm-2 while that from fossil fuel soot is -0.093± 0.033 Wm-2. Open biomass burning leads to a forcing of -0.057 ± 0.05 Wm-2.  

Methodology:
The data are model output form climate simulations conducted with the Community Earth System Model (CESM) version 1.2.2 with the IMPACT aerosol module.

Files contained here:
We include one source code tar file and six major output netcdf files from simulations conducted in the paper. 

The files are described below:

src.cam.tar
This tar file contains the source code of the IMPACT aerosol module that we implemented as additional aerosol module embedded in the CESM version1.2.2 which is publicly available from NCAR repository. These default set-up in the code is for the case dbfc listed in Table 1 of the related publichation. 
•	To change the ice nuclei sources, modify src.cam/um_aero/um_aerosol_number.F90.
•	To change the different updraft velocity for the ice nucleation process, modify src.cam/microp_aero.F90 and src.cam/um_aero/um_KL_ni.F90. 

dbfc_mg15.cam.h0.mean.nc
Netcdf output file of 6-year mean (2006-2011) meteorological and aerosol fields from the simulation dbfc defined in Table 1 in the related paper. Ice nuclei include: Dust<3 monolayers sulfate; 0.1% of biomass aerosols; standard fossil fuel+biofuel aerosols; aircraft soot incorporated in contrails (with < 3 monolayers of sulfate). 

dbf_mg15.cam.h0.mean.nc
Same as dbfc_mg15.cam.h0.mean.nc except aircraft soot incorporated in contrails is not included in ice nuclei. 

d100bfc_mg15.cam.h0.mean.nc
Netcdf output file of 6-year mean (2006-2011) meteorological and aerosol fields from the simulation d100bfc defined in Table 1 in the related paper. Ice nuclei include: All dust; 0.1% of biomass aerosols; standard fossil fuel+biofuel aerosols; aircraft soot incorporated in contrails (with < 3 monolayers of sulfate). 

d100bf_mg15.cam.h0.mean.nc
Same as d100bfc_mg15.cam.h0.mean.nc except aircraft soot incorporated in contrails is not included in ice nuclei. 

dbfc_w_mg15.cam.h0.mean.nc
Same as dbfc_mg15.cam.h0.mean.nc except we used constant updraft velocity in the ice nucleation process. 

dbf_w_mg15.cam.h0.mean.nc
Same as dbfc_w_mg15.cam.h0.mean.nc except aircraft soot incorporated in contrails is not included in ice nuclei. 

Related publication(s):
Penner, J.E, Zhou, C., Garnier, A. and Mitchell, D.: Anthropogenic Aerosol indirect effects in cirrus clouds, (2018), submitted to JGR. 

Use and Access: 
This data set is made available under a Creative Commons Attribution-NonCommercial 4.0 International license(CC BY-NC 4.0).

To Cite Data: 
Penner, J.E, Zhou, C., Garnier, A. and Mitchell, D.: Anthropogenic Aerosol indirect effects in cirrus clouds, (2018)[Data set]. University of Michigan Deep Blue Data Repository. https://doi.org/