Interannual Variability Of Tropospheric Ozone Research Articles

Stratospheric impact on the Northern Hemisphere winter and spring ozone interannual variability in the troposphere

Abstract. In this study we use ozone and stratospheric ozone tracer simulations from the high-resolution (0.5∘×0.5∘) Goddard Earth Observing System, Version 5 (GEOS-5), in a replay mode to study the impact of stratospheric ozone on tropospheric ozone interannual variability (IAV). We use these simulations in conjunction with ozonesonde measurements from 1990 to 2016 during the winter and spring seasons. The simulations include a stratospheric ozone tracer (StratO3) to aid in the evaluation of the impact of stratospheric ozone IAV on the IAV of tropospheric ozone at different altitudes and locations. The model is in good agreement with the observed interannual variation in tropospheric ozone, except for the post-Pinatubo period (1992–1994) over the region of North America. Ozonesonde data show a negative ozone anomaly in 1992–1994 following the Pinatubo eruption, with recovery thereafter. The simulated anomaly is only half the magnitude of that observed. Our analysis suggests that the simulated stratosphere–troposphere exchange (STE) flux deduced from the analysis might be too strong over the North American (50–70∘ N) region after the Mt. Pinatubo eruption in the early 1990s, masking the impact of lower stratospheric ozone concentration on tropospheric ozone. European ozonesonde measurements show a similar but weaker ozone depletion after the Mt. Pinatubo eruption, which is fully reproduced by the model. Analysis based on the stratospheric ozone tracer identifies differences in strength and vertical extent of stratospheric ozone impact on the tropospheric ozone interannual variation (IAV) between North America and Europe. Over North American stations, the StratO3 IAV has a significant impact on tropospheric ozone from the upper to lower troposphere and explains about 60 % and 66 % of the simulated ozone IAV at 400 hPa and ∼11 % and 34 % at 700 hPa in winter and spring, respectively. Over European stations, the influence is limited to the middle to upper troposphere and becomes much smaller at 700 hPa. The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), assimilated fields exhibit strong longitudinal variations over Northern Hemisphere (NH) mid-high latitudes, with lower tropopause height and lower geopotential height over North America than over Europe. These variations associated with the relevant variations in the location of tropospheric jet flows are responsible for the longitudinal differences in the stratospheric ozone impact, with stronger effects over North America than over Europe.

Seasonal and interannual variability of tropospheric ozone over an urban site in India: A study based on MOZAIC and CCM vertical profiles over Hyderabad

This study is based on the analysis of Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) data measured over Hyderabad, India during the years 2006–2008. Tropospheric profiles of O3 show clear seasonality with high and low values during the premonsoon and monsoon seasons, respectively. Analysis of back trajectory and fire count data indicates major roles for long-range transport and biomass burning in the seasonal variation of O3. Typically, lower levels of O3 in the monsoon season were due to the flow of marine air and negligible regional biomass burning, while higher levels in other seasons were due to transport of continental air. In the upper troposphere, relatively low levels of O3 during the monsoon and postmonsoon seasons were associated with deep convection. In the free troposphere, levels of O3 also show year-to-year variability as the values in the premonsoon of 2006 were higher by about 30 ppbv compared to 2008. The year-to-year variations were mainly due to transition from El Nino (2006) to La Nina (2008). The higher and lower levels of O3 were associated with strong and weak wind shears, respectively. Typically, vertical variations of O3 were anticorrelated with the lapse rate profile. The lower O3 levels were observed in the stable layers, but higher values in the midtroposphere were caused by long-range transport. In the PBL region, the mixing ratio of O3 shows strong dependencies on meteorological parameters. The Chemistry Climate Model (CCM2) reasonably reproduced the observed profiles of O3 except for the premonsoon season.

Impacts of the East Asian monsoon on lower tropospheric ozone over coastal South China

The impact of the East Asian monsoon (EAM) on climatology and interannual variability of tropospheric ozone (O3) over the coastal South China was investigated by analyzing 11 years of ozonesonde data over Hong Kong with the aid of Lagrangian dispersion modeling of carbon monoxide and calculation of an EAM index. It was found that the seasonal cycle of O3 in the lower troposphere is highly related to the EAM over the study region. Ozone enhancements in the free troposphere are associated with the monsoon-induced transport of pollutants of continental anthropogenic and biomass burning origins. Lower tropospheric O3 levels showed high interannual variability, with an annual averaged amplitude up to 61% of averaged concentrations in the boundary layer (0–1 km altitudes) and 49% below 3 km altitude. In spring and autumn, the interannual variability in boundary layer O3 levels was predominately influenced by the EAM intensity, with high O3 mixing ratios associated with northeasterly circulation anomalies.

Optimized regional and interannual variability of lightning in a global chemical transport model constrained by LIS/OTD satellite data

Nitrogen oxides (NOx ≡ NO + NO2) produced by lightning make a major contribution to the global production of tropospheric ozone and OH. Lightning distributions inferred from standard convective parameterizations in global chemical transport models (CTMs) fail to reproduce observations from the Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) satellite instruments. We present an optimal regional scaling algorithm for CTMs to fit the lightning NOxsource to the satellite lightning data in a way that preserves the coupling to deep convective transport. We show that applying monthly scaling factors over ∼37 regions globally significantly improves the tropical ozone simulation in the GEOS‐Chem CTM as compared to a simulation unconstrained by the satellite data and performs equally well to a simulation with local scaling. The coarse regional scaling preserves sufficient statistics in the satellite data to constrain the interannual variability (IAV) of lightning. After processing the LIS data to remove their diurnal sampling bias, we construct a monthly time series of lightning flash rates for 1998–2010 and 35°S–35°N. We find a correlation of IAV in total tropical lightning with El Niño but not with the solar cycle or the quasi‐biennial oscillation. The global lightning NOxsource ± IAV standard deviation in GEOS‐Chem is 6.0 ± 0.5 Tg N yr−1, compared to 5.5 ± 0.8 Tg N yr−1 for the biomass burning source. Lightning NOx could have a large influence on the IAV of tropospheric ozone because it is released in the upper troposphere where ozone production is most efficient.

Increases in global tropospheric ozone following an El Niño event: examining stratospheric ozone variability as a potential driver

AbstractThe stratosphere can strongly influence the interannual variability of tropospheric ozone. It has been discussed previously that tropospheric ozone can increase following an El Niño event, due to enhanced stratosphere/troposphere exchange (STE) of ozone. Here, we run a chemical‐transport model for 5 years, covering a period including a strong El Niño event (1997–1998), and find that variability of ozone in the stratosphere is an almost negligible driver of modelled post‐El Niño increases of ozone STE and tropospheric ozone abundances. Changes in the dynamics, affecting the cross‐tropopause air‐mass flux, may be far more important in driving these anomalies. Copyright © 2011 Royal Meteorological Society

Influence of El Niño–Southern Oscillation on the interannual variability of tropospheric ozone in the northern midlatitudes

We use the Goddard Earth Observing System Chem (GEOS‐Chem) model to interpret long‐term measurements of tropospheric ozone (O3) and carbon monoxide (CO) and to investigate the factors that contribute to their interannual variation (IAV) during the period from 1987 to 2005. The model reproduces relatively well the observed IAV of CO. The simulation of O3 IAV is not as successful. In particular, the negative anomalies in 1991–1993 and the following upward trend in 1993–1996 observed at several sites in the northern midlatitudes are not reproduced by the model, which may result from a poor representation of stratospheric chemistry and dynamics. We examine in detail the period of 1998–1999 when a large anomaly in tropospheric ozone column is observed and simulated over Europe (maximum of +4.9 Dobson units). Three consecutive periods can be distinguished from January 1998 to April 1999, during which different processes affected the O3 burden over Europe. Spring 1998 is largely influenced by the preceding 1997 El Niño that affects (1) stratosphere‐troposphere exchange and (2) Asian pollution export and transport toward Europe by a change in convective activity in East Asia and a strengthening of the subtropical jet stream. An enhanced pollution export from North America is also noticed for this period. The second period (summer‐fall 1998) shows a mixed influence from both boreal wildfires and Asian pollution. The third period is influenced by enhanced wildfires in Southeast Asia. Throughout the period from 1987 to 2005, positive anomalies in tropospheric O3 column and in surface O3 are found over Europe in the spring following an El Niño year.

Contribution of stratospheric ozone to the interannual variability of tropospheric ozone in the northern extratropics

We examined the role of variability in the input of stratospheric ozone on the interannual variability of tropospheric ozone in the northern extratropics using correlations of monthly ozone anomalies for the lower stratosphere and the troposphere. We used output from a multiyear simulation of the NASA Goddard Space Flight Center (GSFC) Chemistry and Transport Model (CTM), and evaluated model results using ozonesonde data. The GSFC CTM explicitly calculates stratospheric ozone and simulates separate tracers of stratospheric and tropospheric ozone (O3‐strat and O3‐trop, respectively). The climatological seasonal cycle of ozone shows that O3‐strat contributes significantly to the spring maximum of ozone at 500 hPa, ∼40% at high latitudes and ∼30% at midlatitudes. We find large regional differences in the correlation of ozone in the lower stratosphere and troposphere in the model that are supported by the ozonesonde data. Highest correlations are found from the eastern Atlantic to Europe, from the eastern Pacific to the western United States, and over the polar regions, in winter‐spring. This spatial pattern is due to the input of O3‐strat into the troposphere. The distribution and time lag of the correlations (highest with no lag for midlatitudes and a 1–2 month lag for polar regions) are consistent with the dynamical indicators of stratosphere‐troposphere exchange (STE), such as storm tracks in the midlatitudes and slow descending motion in the polar region. Our simple approach can be widely applied to diagnose the effect of STE on tropospheric ozone.

Influence of El Niño Southern Oscillation on stratosphere/troposphere exchange and the global tropospheric ozone budget

We use a combined climate/chemistry model to assess the interannual variability of tropospheric ozone associated with the El Niño Southern Oscillation (ENSO). Simulations cover the years 1990 to 2001 with prescribed SSTs. El Niño and La Niña events are reproduced by the model. Previous studies have emphasized the impact of ENSO on tropospheric composition through changing emissions or convection. Here we show that there is a close relationship between ENSO and stratosphere‐troposphere exchange (STE); different patterns of circulation and meteorology in El Niño and La Niña years result in significant differences in transport of ozone‐rich air from the stratosphere to the troposphere. We calculate an anomalously large increase of STE following a typical El Niño year, most evident after the 1997–1998 El Niño event. La Niña events result in a decrease of STE. STE is one factor affecting tropospheric ozone; we find highest ozone after the 1997–1998 El Niño.

Arctic Oscillation modulation of the Northern Hemisphere spring tropospheric ozone

This study identifies the Arctic Oscillation (AO) signature on the interannual variability of tropospheric ozone, with an emphasis on spring ozone over the North American and European continents. The analysis is first performed on ozonesonde data. It is shown that the variability in AO explains up to 50% of the tropospheric ozone variability in the lower troposphere over North America during the spring months. Chemistry‐transport model simulations in which the meteorology varies from year to year, but the emissions and net stratospheric production of ozone remain the same show similar results. The model results indicate the role of the AO in modulating stratosphere‐troposphere exchange and in regulating the transport of ozone and its precursors from North America, Europe and Asia.