CMAQv5.0 Lightning NO

Lightning NO release notes - 2 February 2012

Rob Pinder and Jeff Young

Lightning is the largest source of oxidized nitrogen in the upper troposphere. During the summer of 2004, nitrogen oxide (NO) produced from lightning over the US was equivalent to 25% of the anthropogenic NOx emissions. CMAQ supports production of NO from lightning with four different options.

Summer of 2004, CMAQ simulated total nitrate wet deposition (kg / ha), National Atmospheric Deposition Program monitoring locations shown as overlay circles.

Options and runtime configuration

no lightning NOx

CMAQ will not generate NO from lightning. Set CTM_LTNG_NO = N or unsetenv CTM_LTNG_NO

lightning NOx from a 4-D file

This option reads in NO defined as a rate of production (moles / sec) for each model layer at each timestep. Set CTM_LTNG_NO = Y and set LTNGNO to the file that contains these data.

lightning NOx derived strictly from the convective precipitation rate

This option calculates the number of lightning flashes using the convective precipitation calculated in the meteorology model and provided in the MCIP files. Each flash produces 500 moles of NO, which are distributed vertically based on the MCIP calculated cloud top. Set CTM_LTNG_NO = Y and set LTNGNO to "inline". Recommended for hemi-spheric scale simulations when no better information is available.

lightning NOx derived from user provided flash counts

Summertime convective precipitation is challenging to simulate accurately in modern meteorological models. This option uses user provided flash counts to ensure that the seasonal lightning totals match observed lightning totals. Set CTM_LTNG_NO = Y and set LTNGNO to "inline" and set LTNGPARAM = Y and set LTNGPARM_FILE to point to the lightning parameters file: a time independent file that includes

1. monthly flash totals per CMAQ grid cell
2. a grid-cell specific scaling factor for calculating flashes using the convective precipitation rate, such that the calculated flash count matches the monthly total
3. ratio of intercloud to cloud to ground flashes
4. moles of NO per cloud to ground flash
5. moles of NO per inter-could flash
6. mask for offshore flashes -- to remove spurious flashes over the ocean

This option is recommended for all simulations of nitrogen deposition at less than 50km horizontal resolution. There are several utility programs that can be used to translate US National Lightning Detection Network Data to construct the parameter file.

diagnostics (not available in this release)

To generate a output file that contains the lightning NOx produced during the CMAQ simulation, set LTNGDIAG to the desired output filename.

Developing a lightning NOx parameters file from user provided flash counts

To develop a lightning NOx parameters file, you will need

1. Lightning strike data projected onto your grid
2. The METCRO2D file for your simulation

You can download a series of utility scripts that are available to project the lightning strike data onto your model grid. These require a fortran compiler, ioapi, netcdf, and The R Project for Statistical Computing. The steps in this process are to first generate gridded mean lightning strike density data and then use that data to develop the CMAQ lightning NO parameters file.

Mean strike density data

For the US, mean strike density data can be generated two ways. First, the NLDN is a lightning flash detection network deployed across the US. Use the script run.NLDN_2D.sh. This program reads in NLDN data and generates the mean strike density on the grid that matches your METCRO2D file averaged over the dates / times that are in the NLDN data file.

Second, monthly mean strike density data has already been calculated at a 12km spatial resolution across the continental US. These monthly files are available for download. These data may need to be reprojected to your model domain and grid specification.

CMAQ lightning NO parameters file

Use the script run.LTNG_2D.sh to generate the parameter file.

The steps in run.LTNG_2D.sh are

1. build ocean mask file: this identifies the areas in your domain that are offshore and have lower lightning strike density.
2. build iccg file: this calculates the ratio of inter-cloud strike v. cloud to ground strikes using climatological data for summer and winter.
3. build 2D file parameter file: using the output from the two steps above and the mean strike density data, this generates the CMAQ lightning NO parameters file.
4. generate plots for QA: generates spatial plots of the CMAQ lightning NO parameters for your review.

To check if your setup is working correctly, the scripts point to sample data. You can compare you results found in the output and R-output directories to the files in the verify directory.

To use these lightning parameters data to generate lightning NO in a CMAQ simulation, in the CMAQ run script, set LTNGPARM_FILE to the output from run.LTNG_2D.sh.

References:

• Description: Allen et al., 2011, Atmos. Chem. Phys. Discussions
• Evaluation: Appel et al., A multi-resolution assessment of the Community Multiscale Air Quality (CMAQ) Model v4.7 wet deposition estimates for 2002–2006