This comment can be found in the attached pdf.

Please see attached pdf for comments.

Comments on Okamoto et al. focusing on the models used in data assimilation systems and treatment of lightning NO_x production:

Major comments:   

I do not think that the authors should have included MERRA-2 in this analysis.  There is no detailed tropospheric ozone photochemistry included in the model -- only a simple month-dependent  O₃ parameterization (Stanjer et al., 2008, JGR) derived from a 2-D chemistry model that was originally developed for the stratosphere.  Monthly mean O₃ production and loss terms from the 2-D model are utilized in the GEOS-5 model, and these terms are not really useful below the upper troposphere.  As a result, O₃ in the lower and middle troposphere is not well represented in the assimilation, especially with regard to longitudinal variations in O₃.  The MERRA-2 developers do not recommend use of the O₃ values below 500 hPa.

 Section 2.2 on the Atmospheric Chemistry Reanalyses:  The descriptions of the three reanalyses do not say how lightning flashes are predicted in the models or say how lightning NO_x (LNO_x) emissions are treated (NO_x production per flash and how those emissions are distributed vertically in the model).  Therefore, the reader does not know how realistic the distribution of LNO_x emissions is represented in the model.  This horizontal and vertical distribution will have a large impact on the source attribution results for O₃.  LNO_x is not included at all in MERRA-2, significantly affecting the longitudinal distribution of O₃ especially in the upper troposphere.  Assimilation of OMI and MLS O₃ will partially correct for this deficiency, but not totally.  Lack of LNO_x leads to a small low bias in UT O₃ in MERRA-2.

Specific comments:

Abstract line 22-23:   most of the lift occurs over the continents, not the ocean

 Figure 1:   shows 2017 maps of the World-Wide Lightning Detection Network (WWLLN) Global Lightning Climatology (WGLC) from Kaplan and Lau (2021, Earth Sys. Sci. Data).  Much greater maximum amounts of lightning are shown over Central and South America than over Africa.  The satellite (OTD/LIS) climatology (Cecil et al., 2014, Atmos. Res.) is much different, showing the strongest maximum over Central Africa.   WWLLN detection efficiency over Africa is very low.  I'm wondering if enough attention has been given to this when the WGLC was created.  Uncertainty in use of this climatology should be mentioned in the paper.

 Figures 4, 6, and others:  MERRA-2 O₃ plots for 0-3 km should not be shown here – O₃ is obviously wrong in the lower troposphere

Figures 5 and 7:  MERRA-2 O₃ plots for a specific day should not be trusted and therefore not shown.  The chemistry in the model is based on monthly mean O₃ production and loss rates. 

6 Feb. 2025, Comments on Okamoto et al Paper

The paper as a whole follows a reasonable outline and is well-organized but it begins with serious omissions that must be remedied. It is easy to forget the pioneering satellite work or major experiments that paved the way for ATom or HIPPO (Wofsy: https://royalsocietypublishing.org/doi/10.1098/rsta.2010.0313 ), a similar experiment that preceded the ATom Atlantic and Pacific transects. The SAFARI-92/TRACE-A sampling over the Atlantic and similar DC-8 campaigns over the Pacific provided baseline data and the insights into tropical chemistry and dynamics that remain relevant.

Lines 40 ff.  Context with prior published work.  The south and tropical Atlantic is NOT one of the regions “with the sparest coverage of in-situ observations!” On the contrary, south Atlantic ozone structure is well-characterized and has been studied in detail since the early 1990s. Before that a classic paper by Jack Fishman on satellite data from TOMS (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JD092iD06p06627) called attention to the high tropospheric ozone over the south Atlantic. That was the beginning of “Tropical Atlantic” studies on ozone. A number of satellite-based products have focused on the tropical south Atlantic, e.g., Fishman et al., JGR, 1996; Thompson et al., GRL, 2000; Hudson et al., JGR, 1995; Leventidou et al., ACP, 2017.

              Just as important, pioneering international aircraft campaigns led by the US, France and Germany probed causes of the “tropical south Atlantic ozone maximum” with flights from Brazil, western and southern Africa and from Brazil. The early aircraft campaigns were:

• TROPOZ II – led by A. Marenco from Toulouse!!  For example: https://www.sciencedirect.com/science/article/abs/pii/S1352231099005087 by Gouget. Also - https://www.semanticscholar.org/paper/Study-of-ozone-formation-and-transatlantic-from-the-Jonqui%C3%A8res-Marenco/fcdb685886daa73cd211fb1e3e740d5138d2c02a

• Early IGAC “Projects” on biomass burning and south tropical Atlantic (BIBEX, STARE). In September-October 1992 a massive umbrella experiment “STARE” was conducted during the southern African burning season: IGAC/STARE/SAFARI-92/TRACE A (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Southern African Fire Atmospheric Research Initiative/Transport and Atmospheric Chemistry near the Equator-Atlantic) with multiple aircraft, including NASA’s DC-8 with comprehensive lidar ozone measurements, in-situ profiling of ozone precursors like NO/NO2, CO, hydrocarbons; SAFARI-92 operated a DC-3 over southern Africa. The aircraft measurements were augmented by balloon ozonesonde profiles from Brazil, Ascension Island, Brazzaville, Congo; Irene, South Africa. There are ~65 papers from the 1992 campaigns in Journal of Geophysical Research, published 1 Oct. 1996!  

An outgrowth of the SAFARI-92/TRACE-A balloon data was the initiation of the SHADOZ (Southern Hemisphere ADditional Ozonesondes) network of ozone sounding stations that has operated from 1998 to the present day (Thompson et al., 2003; Thompson et al., 2017). SHADOZ provides ozone profiles 2-4 times/month from Ascension Island (central south tropical Atlantic, 8S, 15W), Natal, Brazil (6S, 35W) and Paramaribo (5N, 55W). The ozone profiles from these 3 stations since 1998 number more than 2000!  Comment on Figs 9 and 10.  Comparisons of satellite and model ozone with April 2017 SHADOZ sondes should be carried out for comparison to the ATOM comparisons.

The earlier work must be cited. One way to revise the paragraph starting on Line 40 …

The South and Tropical Atlantic has been a region of intense interest in the ozone community since a regional maximum in tropospheric ozone derived from satellite measurements was identified by Fishman and Larson (1987). This discovery was the motivation for a large-scale ground and aircraft study in the southern biomass burning season in September and October 1992: IGAC/STARE/SAFARI-92/TRACE A (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Southern African Fire Atmospheric Research Initiative/ Transport and Atmospheric Chemistry near the Equator-Atlantic). SAFARI-92/TRACE A confirmed the regional ozone feature with aircraft profiling and lidar plus ozonesondes deployed over Brazil, Ascension Island and 3 sites in subSaharan Africa. In addition, analyses of the comprehensive SAFARI-92/TRACE-A data confirmed links of the Atlantic maximum to fire activity over Africa (Fishman et al., 1996; Thompson et al., 1996) and to ozone formed from a combination of fires, deep convection and lightning activity over South America (Pickering et al., 1996). Based on the ozonesonde profiles, it was estimated that the relative contributions to the Atlantic ozone were approximately 2/3 from African sources and 1/3 from South America (Thompson et al., 1996). However, dynamical influences were required for the ozone feature to form. Krishnamurti et al. (1996) demonstrated that recirculation within the south Atlantic gyre allowed the ozone to accumulate so that the highest ozone amounts were over the ocean rather than the continents.

Shipboard ozone sampling over the tropical Atlantic provided additional insights into south tropical Atlantic ozone (Weller et al., 1996; Thompson et al., 2000). The ozone maximum occurred at all seasons, not only during the peak of southern hemisphere burning but also when African fire activity was at its greatest north of the ITCZ. This so-called “Atlantic ozone paradox” was associated with upper tropospheric-stratospheric subsidence and lightning in addition to fires (Thompson et al., 2000). These contributions were evaluated in an early model study (Moxim and Levy, 2000). The SAFARI-92/TRACE-A experiments were instrumental in assembling the SHADOZ (Southern Hemisphere Additional Ozonesondes; https://tropogsfc.nasa.gov/shadoz) network of stations that has operated from 1998 to the present day (Thompson et al. 2017). With coordinated launches of ozonesondes from more than 10 stations across the tropics, the Atlantic maximum is a strong feature with the south tropical Atlantic always exhibiting more tropospheric column ozone (5-15 Dobson Units,1 DU = 2.69x10¹⁶ cm-²). When looking at tropospheric ozone structure across the entire tropical band, the Atlantic ozone feature leads to a zonal wave-one pattern (Thompson et al., 2003).

More recently, the role of biomass burning (van der Werf et al., 2017), biogenic (Sindelarova et al., 2022) and lightning (Schumann and Huntreiser, 2007) contributions to Atlantic, African and South America ozone has been investigated. In-Service Aircraft….

REFERENCES TO ADD:

Fishman, J. and Larsen, J. (1987) Distribution of total ozone and stratospheric ozone in the tropics: Implications for the distribution of tropospheric ozone, J. Geophys. Res., 92 (D6), 6627-6634

Fishman, J., Watson, C. E., Larsen, J. C., Logan, J. A. (1990) Distribution of tropospheric ozone determined from satellite data, J. Geophys. Res, 95 (D4), 3599-3617

Fishman, J., Hoell, J. M., Jr., Bendura, R. D., McNeal, R. J., Kirchhoff, V. W. J. H. (1996) NASA GTE TRACE A experiment (September–October 1992): Overview, J. Geophys. Res.,   https://doi.org/10.1029/96JD00123

Hudson, R. D., Kim, J., Thompson, A. M. (1995) On the derivation of tropospheric column ozone from radiances measured by the total ozone mapping spectrometer, J. Geophys. Res. 100, 11137-11145;

https://doi.org/10.1029/94JD02435

Krishnamurthi, T. N., Sinha, M. C., Kanamitsu, M., Oosterhof, D., Fuelberg, H., Chatfield, R., Jacob, D. J., & Logan, J. (1996). Passive tracer transport relevant to the TRACE-A experiment. Journal of Geophysical Research-Atmospheres, 101(D19), 23889-23907

Leventidou, E. Weber, M., Eichmann, K-U., Burrows, J. P., Heue, K-P., Thompson, A. M.,  Johnson, B. (2017) Harmonisation and trends of 20-years tropical tropospheric ozone data, Atmos. Chem. Phys., https://doic.org/10.5194/acp-2017-815.

Moxim, W. J., and Levy II, H. (2000) A model analysis of the tropical South Atlantic Ocean tropospheric ozone maximum: The interaction of transport and chemistry J. Geophys. Res., https://doi.org/10.1029/2000JD900175

Pickering, K. E., Thompson, A. M., Pickering, K. E., Wang, Y., Tao, W-K., McNamara, D. P., Kirchhoff, V. W. J. H., Heikes, B. G., Sachse, G. W., Bradshaw, J. W. D., Gregory, G. L, Blake, D. R. (1996) Convective transport of biomass burning emissions over Brazil during TRACE-A, J. Geophys. Res., https://doi.org/10.1029/96JD00346

Thompson, A. M., Pickering, K. E., McNamara, D. P., Schoeberl, M. R., Hudson, R. D., Kim J. W., Browell, E. V., Kirchhoff, V. W. J. H., Nganga, D. (1996) Where did tropospheric ozone over southern Africa and the tropical Atlantic come from in October 1992?  Insights from TOMS, GTE/TRACE-A and SAFARI-92, J. Geophys. Res., 101, 24,251-24,278; https://doi.org/10.1029/96JD01463

Thompson, A. M., Doddridge, B. G., Witte, J. C., Hudson, R. D., Luke, W. T., Johnson, J. E., Johnson, B. J., Oltmans, S. J., R. Weller, R. (2000), A tropical Atlantic paradox: Shipboard and satellite views of a tropospheric ozone maximum and wave-one in January-February 1999, Geophys. Res. Lett., https://doi.org/10.1029/1999GL011273

Thompson, A. M., J. C. Witte, S. J. Oltmans, F. J. Schmidlin, J. A. Logan, M. Fujiwara, V. W. J. H. Kirchhoff, F. Posny, G. J. R. Coetzee, B. Hoegger, S. Kawakami, T. Ogawa, J. P. F. Fortuin, H. M. Kelder (2003) Southern Hemisphere ADditional Ozonesondes (SHADOZ) 1998-2000 tropical ozone climatology. 2.  Tropospheric Variability and the Zonal Wave-One, J. Geophys. Res., 108, 8241, doi: 10.1029/2002JD002241

Thompson, A. M., Witte, J. C., Sterling, C., Jordan, A. Johnson, B. J., Oltmans, S. J., Fujiwara, M.,  Vömel, M., Allaart, M., Piters, A., Coetzee, J. G. R., Posny, F., Corrales, E., Andres Diaz, J., Félix, C.,  Komala, N., Lai, Maata, M., Mani, F., Zainal, Z., Ogino, S-Y., Paredes, F., Luiz Bezerra Penha, T., . Raimundo da Silva, F., Sallons-Mitro, S., Selkirk, H. B., Schmidlin, F. J., Stuebi, R., Thiongo, K. (2017) First reprocessing of Southern Hemisphere Additional Ozonesondes (SHADOZ) Ozone Profiles (1998-2016). 2. Comparisons with satellites and ground-based instruments, J. Geophys. Res., 122, 13000-13025, doi: 10.1002/2017JD027406

Weller, R., Lilischkis, R., Schrems, O., Neuber, R., Wessel, S. (1996) Vertical ozone distribution in the marine atmosphere over the central Atlantic Ocean (56°S-50°N), J. Geophys. Res., 101, 1387–1399; https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/95JD02838