Ziemke, J. R., S. Chandra, and P. K. Bhartia, A 25-year data record of stratospheric and tropospheric ozone from TOMS Cloud Slicing: Implications for stratospheric ozone recovery, J. Geophys. Res. , submitted, 2004.

Abstract. The newly reprocessed Solar Backscatter Ultraviolet (SBUV) and Total Ozone Mapping Spectrometer (TOMS) data from 1978 to 2003 are used to estimate the seasonal cycle, latitude dependence and long-term trends in ozone in three broad layers of the atmosphere: upper stratosphere (32 hPa and above), lower stratosphere (32 hPa to tropopause), and the troposphere. The ozone amount in these layers is derived by first determining stratospheric column ozone (SCO) from TOMS using deep convective clouds in the Pacific. The validity of this "Cloud Slicing" technique is extensively tested using SCO derived from Stratospheric Aerosols and Gas Experiment (SAGE) data. Tropospheric column ozone (TCO) is then derived by taking the difference between total column ozone and SCO. The validity of the Cloud Slicing technique for obtaining TCO is also tested using extensive data from the Southern Hemisphere Additional Ozonesondes (SHADOZ) ozonesonde network. SBUV ozone data are used to estimate upper stratospheric column ozone (USCO). Finally, lower stratospheric column ozone (LSCO) is derived from the difference between SCO and USCO. This process yields a unique 25-year long record of ozone in three atmospheric layers covering all latitudes and seasons. By contrast, SAGE provides limited spatial and temporal coverage of the stratosphere, albeit at much higher vertical resolution. Our analysis shows that the seasonal cycle, latitude dependence, and trends of USCO, LSCO, and TCO are quite different. In particular, the decreasing trends in USCO have moderated in recent years, while LSCO trends are continuing. In the troposphere, the TCO shows a statistically significant upward trend in mid-latitudes of both hemispheres, but not in the tropics.

Chandra, S., J. R. Ziemke, X. Tie, and G. Brasseur, Elevated ozone in the troposphere over the Atlantic and Pacific oceans in the Northern Hemisphere, Geophys. Res. Lett. , Vol. 31, L23102, doi:10.1029/2004GL020821, 2004.

Abstract. Tropospheric column ozone (TCO) is derived from differential measurements of total column ozone from Total Ozone Mapping Spectrometer (TOMS), and stratospheric column ozone (SCO) from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS). It is shown that TCO during late spring and summer months over the Atlantic and Pacific Oceans at northern mid-latitudes is about 50-60 Dobson Units (DU) which is about the same as over the continents of North America, Europe and Asia (except high altitude mountain regions), where surface emissions of NOx from industrial sources, biomass and biofuel burning, and biogenic emissions are significantly larger. The zonal characteristics of TCO derived from satellite measurements are generally simulated by a global chemical transport model called MOZART-2, but some discrepancies are also shown. The model results are analyzed to delineate the relative importance of surface NOx emission, lightning NOx and stratospheric flux.

Ziemke, J. R., and S. Chandra, A Madden-Julian Oscillation in Tropospheric Ozone, Geophys. Res. Lett. , Vol. 30, No. 23, 2182, 10.1029/2003GL018523, 2003.

Abstract. This study shows evidence of a Madden-Julian Oscillation (MJO) in tropospheric ozone. Tropospheric ozone is derived using differential measurements of total column ozone and stratospheric column ozone measured from total ozone mapping spectrometer (TOMS) and microwave limb sounder (MLS) instruments. Two broad regions of significant MJO signal are identified in the tropics, one in the western Pacific and the other in the eastern Pacific. Over both regions, MJO variations in tropospheric ozone represent 5-10 Dobson Unit (DU) peak-to-peak anomalies. These variations are significant compared to mean background amounts of 20 DU or less over most of the tropical Pacific. MJO signals of this magnitude would need to be considered when investigating and interpreting particular pollution events since ozone is a precursor of the hydroxyl (OH) radical, the main oxidizing agent of pollutants in the lower atmosphere.

Ahn, C., J. R. Ziemke, S. Chandra, and P. K. Bhartia, Derivation of tropospheric column ozone from the Earth Probe TOMS/GOES co-located data sets using the Cloud Slicing technique, J. Atmos. Sol. Terr. Phys. , 65 (10), 1127-1137, 2003.

Abstract. A recently developed technique called cloud slicing used for deriving upper tropospheric ozone from the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) instrument combined with temperature-humidity and infrared radiometer (THIR) is not applicable to the Earth Probe TOMS (EP TOMS) because this satellite platform does not have an instrument to measure cloud-top temperatures. For continuing monitoring of tropospheric ozone between 200-500hPa and testing the feasibility of this technique across spacecrafts, EP TOMS data are co-located in time and space with the Geostationary Operational Environmental Satellite (GOES)-8 infrared data for year 2001 and early 2002, covering most of North and South America (45S-45N and 120W-30W). Results show that the maximum column amounts for the mid-latitudinal sites of the northern hemisphere are found in the March-May season. For the mid-latitudinal sites in the southern hemisphere, the highest column amounts are found in the September-November season with overall seasonal variability smaller than that in the northern hemisphere. The tropical sites show weaker seasonal variability compared to higher latitudes. The derived results for selected sites are cross-validated qualitatively with the seasonality of ozonesonde observations and the results from THIR analyses over the 1979-1984 time period. These comparisons show a reasonably good agreement among THIR, ozonesonde observations, and cloud slicing-derived column ozone. Cloud slicing measurements from TOMS coincide with large-scale convection events, especially in regions of the tropospheric wind jets (around +/-30 degrees latitude). In these cases they may not be representative of typical conditions in the atmosphere. Two new variant approaches, High-Low (HL) cloud slicing and ozone profile derivation from cloud slicing are introduced to estimate column ozone amounts using the entire cloud information in the troposphere. A future satellite platform such as the Earth Observing System (EOS) Aura with the ozone monitoring instrument (OMI) can provide better statistics of derived ozone because of improved spatial resolution and improved measurements of cloud-top pressures.

Ziemke, J. R., S. Chandra, and P. K. Bhartia, Upper tropospheric ozone derived from Cloud Slicing technique: Implications for large-scale convection, J. Geophys. Res. , Vol. 108, No. D13, 4390, 10.1029/2002JD002919, 2003.

Abstract. This study evaluates the spatial distributions and seasonal cycles in upper tropospheric ozone (pressure range 200-500 hPa) from low to high latitudes (60S to 60N) derived from the satellite retrieval method called "Cloud Slicing". The Cloud Slicing method determines ozone profile information in the troposphere by combining co-located measurements of cloud-top pressure and above-cloud column ozone. Measurements of Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) above-cloud column ozone and N imbus 7 Temperature Humidity Infrared Radiometer (THIR) cloud-top pressure during 1979-1984 were merged to derive upper tropospheric ozone. Because of large footprint measurements from TOMS (~100 km diameter on average), upper tropospheric ozone derived from Cloud Slicing coincides with large-scale convection events. These events are not necessarily representative of average atmospheric conditions in regions near and poleward of the tropospheric wind jets (around +/-30 degrees latitude), especially in winter and spring seasons when dynamical wave activity in the troposphere and lower stratosphere is most intense. The Cloud Slicing method with Nimbus 7 geometry in any case provides a unique opportunity to investigate the behavior of upper tropospheric ozone under condition of intense broad-scale convection. In the tropics the measured upper tropospheric ozone shows year-round enhancement in the Atlantic region and evidence of a possible semiannual variability. Outside the tropics upper tropospheric ozone from Cloud Slicing shows greatest abundance in winter and spring seasons in both hemispheres with largest variance and largest amounts in the northern hemisphere. This seasonal cycle behavior under conditions of intense convection is different from general ozonesonde climatology which shows instead upper tropospheric ozone maximizing around early-to-mid summer months. The seasonal cycles and spatial characteristics in upper tropospheric ozone from Cloud Slicing are similar to lower stratospheric ozone. It is suggested that the large-scale convection events with Cloud Slicing coincide with an occurrence of stratosphere-troposphere exchange (STE).

Chandra, S., J. R. Ziemke, and R. V. Martin, Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model, J. Geophys. Res. , Vol. 108, No. D9, 4291, 10.1029/2002JD002912, 2003.

Abstract. The tropospheric ozone residual method is used to derive zonal maps of tropospheric column ozone using concurrent measurements of total column ozone from Nimbus 7 and Earth Probe (EP) Total Ozone Mapping Spectrometer (TOMS) and stratospheric column ozone from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS). Our study shows that the zonal variability in TOMS total column ozone at tropical and sub-tropical latitudes is mostly of tropospheric origin. The seasonal and zonal variability in tropospheric column ozone (TCO), derived from the TOMS/MLS residual, are consistent with that derived from the convective cloud differential (CCD) method and ozonesonde measurements in regions where these data overlap. A comparison of TCO derived from the TOMS/MLS residual and a global 3D model of tropospheric chemistry (GEOS-CHEM) for 1996-1997 shows good agreement in the tropics south of the equator. Both the model and observations show similar zonal and seasonal characteristics including an enhancement of TCO in the Indonesian region associated with the 1997 El Nino. Both show the decline of the wave-1 pattern from the tropics to the extratropics as lightning activity and the Walker circulation decline. Both show enhanced ozone in the downwelling branches of the Hadley Circulation near +/-30 degrees latitude. Model and observational differences increase with latitude during winter and spring.

Ziemke, J. R., and S. Chandra, La Nina and El Nino-induced variabilities of ozone in the tropical lower atmosphere during 1970-2001, Geophys. Res. Lett. , Vol 30, No. 3, 1142, 10.1029/2002GL016387, 2003.

Abstract. This study provides the first evidence from several decades of satellite measurements that both La Nina and El Nino events have a comparable and dramatic impact in altering the interannual variability and distribution of tropospheric ozone in the tropics. Measurements of tropospheric ozone were combined from several total ozone mapping spectrometer (TOMS) and backscatter ultraviolet (BUV) satellite instruments to establish long time series in the tropics extending from April 1970 through December 2001. The changes in tropospheric column ozone (TCO) for both La Nina and El Nino are sizeable when compared to local values which average from less than 15 Dobson Units (DU) up to 25 DU over the year. It is suggested that interannual changes in TCO from combined La Nina and El Nino are the dominant source of decadal variability in the tropics.

Chandra, S., J. R. Ziemke, P. K. Bhartia, and R. V. Martin, Tropical tropospheric ozone: Implications for dynamics and biomass burning, J. Geophys. Res. , Vol. 107, D14, 10.1029/2001JD000447, 2002.

Abstract. This paper studies the significance of large scale transport and pyrogenic (e.g., biomass burning) emissions in the production of tropospheric ozone in the tropics. Using aerosol index (AI) and tropospheric column ozone (TCO) time series from 1979 to 2000 derived from the Nimbus 7 and Earth Probe TOMS measurements, our study shows significant differences in the seasonal and spatial characteristics of pyrogenic emissions north and south of the equator in the African region and Brazil in South America. Notwithstanding these differences, most of the observed seasonal characteristics are well simulated by the GEOS-CHEM global model of tropospheric chemistry. The only exception is the northern African region where modeled and observed TCO differ signficantly. In the Indonesian region, the most significant increase in TCO occurred during September-December 1997, folllowing large-scale forest and savanna fires associated with the El Nino-induced dry condition. The increase in TCO extended over most of the western Pacific well outside the burning region and was accompanied by a decrease in the eastern Pacific resembling a west-to-east dipole about the dateline. These features are well simulated in the GEOS-CHEM model which suggests that both the biomass burning and changes in meteorological conditions during El Nino period contributed almost equally to the observed increase in TCO in the Indonesian region. During 1997, the net increase in TCO integrated over the tropical region between 15N and 15S was about 6-8 Tg (1 Tg = 10^12 gm) over the mean climatological value of about 77 Tg. The GEOS-CHEM model suggests that most of this increase may have been caused by biomass burning in the Indonesian region. However the interannual variability in the area-averaged column ozone in the tropics is influenced by a number of factors including the quasi-biennial oscillation and solar cycle.

Ziemke, J. R., S. Chandra, and P. K. Bhartia, "Cloud Slicing": A new technique to derive upper tropospheric ozone from satellite measurements, J. Geophys. Res., 106, 9853-9867, 2001.

Abstract. A new technique denoted cloud slicing has been developed for measuring upper tropospheric ozone. Cloud slicing takes advantage of the opaque property of water vapor clouds to ultraviolet wavelength radiation. Measurements of above-cloud column ozone from the Nimbus 7 total ozone mapping spectrometer (TOMS) instrument are combined together with Nimbus 7 temperature humidity and infrared radiometer (THIR) cloud-top pressure data to derive ozone column amounts in the upper troposphere. In this study tropical TOMS and THIR data for the period 1979-1984 are analyzed. By combining total tropospheric column ozone (denoted TCO) measurements from the convective cloud differential (CCD) method with 100-400 hPa upper tropospheric column ozone amounts from cloud slicing, it is possible to estimate 400-1000 hPa lower tropospheric column ozone and evaluate its spatial and temporal variability. Results for both the upper and lower tropical troposphere show a year-round zonal wavenumber 1 pattern in column ozone with largest amounts in the Atlantic region (up to around 15 DU in the 100-400 hPa pressure band and around 25-30 DU in the 400-1000 hPa pressure band). Upper tropospheric ozone derived from cloud slicing shows maximum column amounts in the Atlantic region in the June-August and September-November seasons which is similar to the seasonal variability of CCD derived TCO in the region. For the lower troposphere, largest column amounts occur in the September-November season over Brazil in South America and also southern Africa. Localized increases in the tropics in lower tropospheric ozone are found over the northern region of South America around August and off the west coast of equatorial Africa in the March-May season. Time series analysis for several regions in South America and Africa show an anomalous increase in ozone in the lower troposphere around the month of March which is not observed in the upper troposphere. The eastern Pacific indicates weak seasonal variability of upper, lower, and total tropospheric ozone compared to the western Pacific which shows largest TCO amounts in both hemispheres around spring months. ozone variability in the western Pacific is expected to have greater variability caused by strong convection, pollution and biomass burning, land/sea contrast and monsoon developments.

Martin, R. V., D. J. Jacob, J. A. Logan, J. R. Ziemke, and R. Washington, Detection of lightning influence on tropical tropospheric ozone, Geophys. Res. Lett., 11, 1639-1642, 2000.

Abstract. Empirical orthogonal functions (EOFs) are used to analyze a 14-year record of tropical tropospheric ozone columns (TTOCs) determined from satellite measurements. The first EOF explains 54% of TTOC variance and represents biomass burning in Africa and South America. The second EOF explains 20% of the variance and has a distinct lightning signature.

Ziemke, J. R., S. Chandra, and P. K. Bhartia, A new NASA data product: Tropospheric and stratospheric column ozone in the tropics derived from TOMS measurements, Bull. Amer. Meteorol. Soc., 81, 580-583, March, 2000.

Abstract. Tropospheric and stratospheric column ozone data in the tropics for 1979-present are now available for the general scientific community for the first time. These data are derived at NASA Goddard Space Flight Center and may be obtained via either direct ftp, world-wide-web, or electronic mail. The objective of this note is to provide information about the data including an overview of the method, validation efforts, and adjustments. Tropospheric column ozone time series are shown to compare well with recent 1998-1999 ozonesonde measurements from the Southern Hemisphere ADditional OZonesondes (SHADOZ) project. An important adjustment made to this new data set is a correction for absorbing aerosols (e.g., smoke, dust) in the troposphere. The presence of absorbing aerosols produces an underdetermination of tropospheric column ozone amounts. The new data products of tropospheric and stratospheric column ozone provide useful information on variabilities from monthly to decadal timescales. Previous analyses of the data indicate the first detected solar-cycle signal (2-3 DU peak-to-peak) and also a robust El Nino-induced signal (5-10 Dobson units) in tropospheric column ozone. It is anticipated that these new data products from NASA will prove beneficial for the study and modeling of ozone in the tropics.

Ziemke, J. R., and S. Chandra, Seasonal and interannual variabilities in tropical tropospheric ozone, J. Geophys. Res., 104, 21,425-21,442, 1999.

Abstract. This paper presents the first detailed characterization of seasonal and interannual variability in tropical tropospheric column ozone (TCO) to delineate the relative importance of biomass burning and large-scale transport. TCO time series are derived from 20 years (1979-1998) of total ozone mapping spectrometer (TOMS) data using the convective cloud differential (CCD) method. Our study identifies three regions in the tropics with distinctly different characteristics related to seasonal and interannual variability. These three regions are the eastern Pacific, Atlantic, and western Pacific. TCO in the Atlantic region peaks at about the same time (September-October) both north and south of the Equator, while the annual-cycle amplitude in TCO varies from about 3 to 6 Dobson units (DU) from north to south of the Equator. In comparison, annual cycles in TCO in both the eastern and western Pacific are generally weak with largest TCO amount occurring around March-April in the northern hemisphere and September-November in the southern hemisphere. Interannual variabilities in these three regions are also very different. The Atlantic region indicates a quasi-biennial oscillation (QBO) in TCO which is out of phase with the QBO in stratospheric ozone. This is consistent with the photochemical control of this region by ozone-producing precursors. The observed pattern however does not seem to be related to interannual variability in ozone precursors related to biomass burning. Instead it appears to be a manifestation of the UV modulation of upper tropospheric chemistry on a QBO time scale caused by stratospheric ozone. During El Nino events there is anomalously low TCO in the eastern Pacific and high values in the western Pacific, indicating the effects of convectively-driven transport. The observed increase of 10-20 DU in TCO in the Indonesian region in the western Pacific during the recent 1997-1998 El Nino was associated with large-scale fires which may have contributed 5-10 DU of the total increase. Finally, a simplified tropospheric ozone residual (STOR) method is proposed in this study to derive high-resolution maps of TCO in the tropics even in the absence of tropopause-level clouds.

Chandra, S., J. R. Ziemke, and R. W. Stewart, An 11-year solar cycle in tropospheric ozone from TOMS measurements, Geophys. Res. Lett., 26, 185-188, 1999.

Abstract. Tropospheric column ozone derived from Nimbus 7 total ozone mapping spectrometer (TOMS) footprint measurements from 1979 to 1992 provide the first observational evidence of changes in tropospheric ozone in the marine atmosphere of the tropics which are out of phase with stratospheric ozone changes on a time scale of a solar cycle. The estimated changes in tropospheric and stratospheric column ozone over a solar cycle are respectively -2.98 +/-1.31 and +8.63 +/-1.99 Dobson units (DU), or equivalently -12.6 +/-5.6 and +3.69 +/-0.86 % from solar minimum to solar maximum. These values are statistically significant at the 2-sigma level. In comparison, linear trends in tropical tropospheric ozone are not statistically significant. These observations are qualitatively consistent with a modulation effect on tropospheric ozone photochemistry by UV-induced changes in stratospheric ozone. However, in the low NOx regime of the marine atmosphere the observed changes are signficantly larger than estimated from a photochemical model.

Chandra, S., J. R. Ziemke, W. Min, and W. G. Read, Effects of 1997-1998 El Nino on tropospheric ozone and water vapor, Geophys. Res. Lett., 3867-3870, 1998.

Abstract. This paper analyzes the impact of the 1997-1998 El Nino on tropospheric column ozone (TCO) and tropospheric H2O derived from the earth probe (EP) total ozone mapping spectrometer (TOMS) and Upper Atmosphere Research Satellite (UARS) microwave limb sounder (MLS) instruments, respectively. The 1997-1998 El Nino, characterized by an anomalous increase in sea-surface temperature (SST) across the eastern and central tropical Pacific Ocean, is one of the strongest El Nino Southern Oscillation (ENSO) events of the century, comparable in magnitude to the 1982-83 episode. The major impact of the SST change has been a shift in the convection pattern from the western to the eastern Pacific affecting the response of the rain-producing cumulonimbus. As a result, there has been a significant increase in rainfall over the eastern Pacific and decrease over the western Pacific and Indonesia. The dryness in the Indonesian region has contributed to large scale burning by uncontrolled wildfires in the tropical rainforests of Sumatra and Borneo. Our study shows that TCO decreased by 4-8 Dobson units (DU) in the eastern Pacific and increased by about 10-20 DU in the western Pacific as a result of the eastward whift of the tropical convective activity. The effect of this shift is also evident in upper tropospheric H2O which varies inversely as ozone. Our study suggests that a significant increase in TCO and decrease in tropospheric H2O in this region is related to El Nino-induced changes in the Walker circulation as inferred from the National Oceanic and Atmospheric Administration (NOAA) outgoing longwave radiation (OLR) and Geostationary Earth Orbiting Satellite-1 (GEOS-1) zonal and vertical wind data. This does not exclude the possibility that some increase in TCO may have been caused by biomass burning in the Indonesian region.

Ziemke, J. R., S. Chandra, and P. K. Bhartia, Two new methods for deriving tropospheric column ozone from TOMS measurements: The assimilated UARS MLS/HALOE and convective-cloud differential techniques, J. Geophys. Res., 103, 22,115-22,127, 1998.

Abstract. This study introduces two new approaches for determining tropospheric column ozone from satellite data. In the first method, stratospheric column ozone is derived by combining Upper Atmospheric Research Satellite (UARS) halogen occultation experiment (HALOE) and microwave limb sounder (MLS) ozone measurements. Tropospheric column ozone is then obtained by subtracting these stratospheric amounts from the total column. Total column ozone in this study include retrievals from Nimbus-7 (November 1978-May 1993) and earth probe (July 1996-present) total ozone mapping spectrometer (TOMS). Data from HALOE are used in this first method to extend the vertical span of MLS (highest pressure level 46 hPa) using simple regression. This assimilation enables high-resolution daily maps of stratospheric ozone which is not possible from solar occultation measurements alone, such as from HALOE or Stratospheric Aerosols and Gas Experiment (SAGE). We also examine another new and promising technique that yields tropospheric column ozone directly from TOMS high-density footprint measurements in regions of high convective clouds. We define this method as the convective-cloud differential (CCD) technique. The CCD method is shown to provide long time series (essentially late 1978 to the present) of tropospheric ozone in regions dominated by persistent high tropopause-level clouds, such as the maritime tropical Pacific and within or near midlatitude continental landmasses. This method also indicates a dominant coupling of tropospheric ozone in the tropical Pacific region with the El Nino and La Nina events. For validation purposes, both the CCD and assimilated UARS MLS/HALOE results are compared with ozonesonde data from several southern tropical stations. Despite all three measurements being distinctly different in sampling and technique, all three show good qualitative aggreement.

Ziemke, J. R., and S. Chandra, Comment on "Tropospoheric ozone derived from TOMS/SBUV measurements during TRACE A", by J. Fishman et al., J. Geophys. Res., 103, 13,903-13,906, 1998.

Abstract. Recently, Fishman et al. [1996] combined Nimbus 7 total ozone mapping spectrometer (TOMS) total ozone with vertical ozone profiles from the NOAA 11 solar backscatter ultraviolet 2 (SBUV2) instrument in an effort to estimate tropospheric ozone residuals (TOR). They included tropopause height fields from the National Meteorological Center (NMC) to calculate stratospheric column ozone from the SBUV2 profiles. TOR was then calculated by subtracting stratospheric column ozone from TOMS total ozone. We note that this same method for deriving TOR was used earlier by Vukovich et al. [1996]. A more recent study by Vukovich et al. [1997] describes the potentially large errors using this method by comparing one-to-one with ground-based ozonesonde data. In our short comment we focus on tropical latitudes and illustrate that significant errors arise in stratospheric column ozone derived from SBUV because of the combination of vertical weighting functions and the inversion algorithm.

Ziemke, J. R., and S. Chandra, On tropospheric ozone and the tropical wave 1 in total ozone, Atmospheric Ozone, Vol. 1 , Ed. R. D. Bojkov and G. Visconti, pp. 447-450, 1998.

Abstract. Studies have shown that total ozone in the southern tropics exhibits a year-round stationary wave 1 pattern with maximum peak-to-peak amplitudes ~20-30 Dobson units (DU) during southern spring (September-October). The crest of this wave occurs in the south Atlantic region with largest amplitudes occurring within the months of intense biomass burning in South America and Africa from July-October. However, because the wave exists in all months of the year (weakest in May-June with peak-to-peak amplitudes ~10-12 DU), this indicates the presence of a persistent dynamical forcing mechanism. The present study investigates the persistence of the wave, combining ozonesonde data from several tropical stations with 14 years (1979-1992) of both Nimbus 7 total ozone mapping spectrometer (TOMS) ozone and National Centers for Environmental Prediction (NCEP) geopotential height analyses. The limited number of ozonesonde profiles in the tropics indicates that the primary contribution to both tropospheric column ozone and the TOMS ozone wave 1 lies in the low to middle troposphere, maximizing around altitudes 4-5 km. Near this maxima, 500 hPa (~5 km altitude) geopotential heights show a persistent (year-round) wave 1 pattern in the south Atlantic similar to TOMS ozone, indicating both equatorward transport of subtropical ozone into the region and a potential for planetary scale subsidence effects. This is the first study providing evidence that lower tropospheric ozone and dynamical transport have major roles in establishing persistence of the wave 1 anomaly in total ozone.

Ziemke, J. R., S. Chandra, A. M. Thompson, and D. P. McNamara, Zonal asymmetries in southern hemisphere column ozone: Implications of biomass burning, J. Geophys. Res., 101, 14,421-14,427, 1996.

Abstract. Studies have shown that total ozone in the southern tropics exhibits a year-round stationary wave 1 pattern with maximum peak-to-peak amplitudes ~20-30 Dobson units (DU) during southern spring (September-October). The crest of this wave occurs in the south Atlantic region with largest amplitudes occurring within the months of intense biomass burning in South America and Africa from July-October. However, because the wave exists in all months of the year (weakest in May-June with peak-to-peak amplitudes ~10-12 DU), this indicates the presence of a persistent dynamical forcing mechanism. The present study investigates the persistence of the wave, combining ozonesonde data from several tropical stations with 14 years (1979-1992) of both Nimbus 7 total ozone mapping spectrometer (TOMS) ozone and National Centers for Environmental Prediction (NCEP) geopotential height analyses. The limited number of ozonesonde profiles in the tropics indicates that the primary contribution to both tropospheric column ozone and the TOMS ozone wave 1 lies in the low to middle troposphere, maximizing around altitudes 4-5 km. Near this maxima, 500 hPa (~5 km altitude) geopotential heights show a persistent (year-round) wave 1 pattern in the south Atlantic similar to TOMS ozone, indicating both equatorward transport of subtropical ozone into the region and a potential for planetary scale subsidence effects. This is the first study providing evidence that lower tropospheric ozone and dynamical transport have major roles in establishing persistence of the wave 1 anomaly in total ozone.

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