Lightning NOx emissions

On this page we list various updates to GEOS-Chem's lightning NOx emissions algorithm.

Generating OTD/LIS factors

When running a GEOS-Chem simulation for a time period that doesn't have OTS/LIS factors, your simulation will stop with the following error:

    Your model framework has not had its
    lightnox code reprocessed for the correction
    to how CLDTOPS are calculated, probably due to
    the lack of your met fields at Harvard.
    
    Please contact Lee Murray
    (ltmurray@post.harvard.edu), who can help you
    prepare the necessary modifications and files
    to get lightnox working for you.
    
    You may remove this trap in lightnox_nox_mod.f
    at your own peril, but be aware that the
    magnitude and distribution of lightnox may be
    unrealistic.
    
    You can explicitly set the beta value in your
    HEMCO configuration file by adding it to the
    'Lightning NOx settings:
    # ExtNr ExtName            on/off Species
    103     LightNOx         : on     NO
        --> OTD-LIS scaling  :        1.00e-3
        
      CALL HCO_ERROR( 'Wrong beta - see information in standard output', RC )

To guarantee that lightning remains reasonable during your simulation period, you'll need to provide Lee Murray with the unconstrained flash rates so he can generate the OTD/LIS factor.

To generate unconstrained flash rates, run GEOS-Chem for your full period and turn off all emissions except lightning in HEMCO_Config.rc:

103     LightNOx          : on    NO
    --> OTD-LIS factors   :       false
    --> OTD-LIS scaling   :       1.000001
    --> CDF table         :       $ROOT/LIGHTNOX/v2014-07/light_dist.ott2010.dat

To speed up the simulation, we also recommend disabling all processes (transport, chemistry, convection, wet deposition, dry deposition) in input.geos. To avoid hitting the above error in this simulation, you can either use OTD-LIS scaling : 1.000001 in HEMCO_Config.rc or manually comment out the IF ( BETA == 1d0 ) trap in HEMCO/Extensions/hcox_lightnox_mod.F90 (you will need to inform Lee of which method you used). Archive monthly mean lightning flash rates using the ND56 diagnostic and send those to Lee Murray.

--Melissa Sulprizio (talk) 16:15, 18 November 2016 (UTC)

Previous issues that are now resolved

Limit flash rate density in hcox_lightnox_mod.F90

This update was included in GEOS-Chem 12.0.0.

Chris Holmes suggested:

When operating outside the time range that Lee has calculated scale factors, we could cap the flash/emission rate at the maximum value at the maximum value that occurs during the OTD/LIS record. That way we use Lee’s work when it’s available, but things don’t go crazy outside it.

Lee Murray wrote:

After we apply the OTD/LIS redistribution, you can globally limit the flash rate to its highest observed value of 4.2e-3 flashes / km2 / s from the newish ENTLN global product.

For the grid-independent lightning product, I'm using local upper values from ENTLN to limit unrealistically high values.

      !-----------------------------------------------------------
      ! (6a) Compute flash rate and apply OTD/LIS redistribution
      !-----------------------------------------------------------

      ! Convert [flashes/min] to [flashes/6h]
      RATE     = FLASHRATE * 360.0d0

      ! Apply regional or local OTD-LIS redistribution so that the 
      ! flashes occur in the right place. 
      RATE = RATE * REDIST

      ! Apply scaling factor to make sure annual average flash rate 
      ! equals that of the climatology. (ltm, 09/24/07)
      RATE = RATE * Inst%OTD_LIS_SCALE

      END IF ! LBOTTOM >  1
      END IF ! LTOP    >= LCHARGE 
      END IF ! LTOP    >  0 
      END IF ! LCHARGE >  1 

      ! Do not allow flash density to become unrealistically high
      IF ( ( RATE / 21600. / A_KM2 ) > 0.004177159 ) THEN
           RATE = 0.004177159 * 21600. * A_KM2
      END IF

      !-----------------------------------------------------------
      ! Eventually overwrite with values determined from imported
      ! flash rate 
      !-----------------------------------------------------------

--Melissa Sulprizio (talk) 12:11, 10 August 2018 (UTC)

Update WEST_NS_DIV to fix ozone overestimate in southern US

This update was validated with 1-month benchmark simulation v11-01f and1-year benchmark simulation v11-01k-Run0. This version was approved on 19 Dec 2016.

From Travis et al. (2016, ACP):

We constrain the lightning NOx source with satellite data as described by Murray et al. (2012). Lightning NOx is mainly released at the top of convective updrafts following Ott et al. (2010). The standard GEOS-Chem model uses higher NOx yields for midlatitudes lightning (500 mol flash^-1) than for tropical (260 mol flash^-1) (Huntrieser et al. 2007, 2008; Hudman et al., 2007; Ott et al., 2010) with a fairly arbitrary boundary between the two at 23° N in North America and 35° N in Eurasia. Zhang et al. (2014) previously found that this leads GEOS-Chem to overestimate background ozone in the southwestern US and we find the same here for the eastern US and the Gulf of Mexico. We treat here all lightning in the 35° S-35° N band as tropical and this remove the distinction between North America and Eurasia.

Katie Travis wrote:

All that is needed [for this update] is to change the following line in hcox_lightnox_mod.F90 from

 REAL*8,  PARAMETER            :: WEST_NS_DIV   =  23d0

to

 REAL*8,  PARAMETER            :: WEST_NS_DIV   =  35d0

--Melissa Sulprizio (talk) 20:57, 2 December 2016 (UTC)