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Seasonality of in-mixing diagnosed from CLaMS sensitivity studies. Top: Setup with two artificial meridional transport barriers at ±15 • N. Bottom: Relative contribution of the Northern (NH, cyan) and Southern (SH, orange) Hemisphere (in %, right axis) to the seasonality of CLaMS passive ozone (P-O 3 ) in the tropics (±10 • N) at θ =380 K (black line).
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Multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) were conducted to study the seasonality of O3 within the stratospheric part of the tropical tropopause layer (TTL), i.e. above θ=360 K potential temperature level. In agreement with satellite (HALOE) and in-situ observations (SHADOZ), CLaMS simulations show a pr...
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... transport process in the model (horizontal or vertical advection or the diffusive part of trans- port, i.e. mixing) is responsible for the seasonality of P-O 3 . We employ a model set-up that allows the contribution of stratospheric O 3 to the O 3 in the TTL to be quantified (see middle panel in Fig. 4 and the black lines in the bottom panel of Fig. 6 quantifying P-O 3 at θ=380 K within the ±10 • N band). In particular, we trace back the origin of the air re- sponsible for the strong annual and weak semi-annual cycle of enhanced P-O 3 at θ=380 K. For this purpose, model simu- lations are carried out with two artificial meridional transport barriers which are set in both hemispheres ...
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... weak semi-annual cycle of enhanced P-O 3 at θ=380 K. For this purpose, model simu- lations are carried out with two artificial meridional transport barriers which are set in both hemispheres along the ±15 • N latitude and which extend vertically between the Earth's sur- face and the 420 K isentrope (thick cyan and orange lines in the top panel of Fig. ...
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... a consecutive suc- cession of pure advective (24-h trajectories) and mixing steps applied for all Lagrangian air parcels. In our sensitivity stud- ies, we set the P-O 3 value of each CLaMS air parcel to zero if the trajectory of this air parcel crosses equatorwards one of the two artificial transport barriers (see the idealized red trajectory in Fig. 6, crossing the cyan meridional barrier). In this way we set the advective, equatorward transport to zero, so only the diffusive transport across the barrier or the trans- port from above the upper edge of the barriers can influence P-O 3 in the tropics (note that P-O 3 at the Earth's surface is set to ...
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... the second model study, we quantify the contribution of both hemispheres to the ±10 • N seasonality of P-O 3 at θ=380 K (black line in the bottom panel of Fig. 6). By switching on only one of the artificial transport barriers, the relative contributions (in %) of the northern (only the cyan barrier is active) and Southern Hemisphere (only the orange barrier is active) were determined. The results are shown in the bottom panel of Fig. 6 with the right axis as the refer- ence for the percentage ...
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... • N seasonality of P-O 3 at θ=380 K (black line in the bottom panel of Fig. 6). By switching on only one of the artificial transport barriers, the relative contributions (in %) of the northern (only the cyan barrier is active) and Southern Hemisphere (only the orange barrier is active) were determined. The results are shown in the bottom panel of Fig. 6 with the right axis as the refer- ence for the percentage and with the cyan and orange colors marking the contribution of the northern and Southern Hemi- sphere, respectively. Thus, more than 90% of P-O 3 is trans- ported from the Northern Hemisphere in summer and more than 60% of the weak maximum in February is caused by transport ...
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... the last sensitivity study, we quantify those vertical re- gions of the barriers (without resolving any longitudinal de- pendence) through which the contribution of the advective transport to the seasonality of P-O 3 at θ=380 K is largest. Here, a 30 K "window" is defined in each artificial trans- port barrier (yellow segments in the top panel of Fig. 6) through which the trajectories can pass. By varying the verti- cal position of these windows, which can be shifted between the Earth's and the θ=420 K surface, the θ-range with the strongest contribution to the seasonality of P-O 3 at θ=380 K can be found. Our simulations show that about 80% of the P-O 3 seasonality at 380 K is due to ...
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... although the minimum of P-O 3 in the tropics at θ=380 K (see middle panel in Fig. 4 or bottom panel of Fig. 6) is due to seasonality of up-welling, the maximum of P-O 3 can only be understood as a consequence of in- mixing with the most dominant contribution from the North- ern Hemisphere in summer. On the other hand, the weaker winter maximum diagnosed in the model is hardly present in the HALOE/SHADOZ observations. In CLaMS this signal is ...
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... This can help us better understand both particle-scale transport and the statistical properties of large injections in the stratosphere for SAI. Even though Lagrangian trajectory models have been widely used in simulating the transport of water vapor, ozone, and volcanic particles [27][28][29] , there are limited SAI studies using this Lagrangian method 22,30 . ...
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... The transport behavior indicates that this air largely originated from southeast Asia as recently as 2 d previously and was located within the monsoon circulation for the preceding 10 d. The path of these trajectories largely resembles equatorward wave breaking of midlatitude LMS air along the eastern portion of the monsoon anticyclone shown in previous studies (e.g., Konopka et al., 2010). The transport of this air into the deep tropics would retain some characteristics of its source region for up to 1 week, namely higher PV and potential temperature, which is likely what allows for this air to meet the threshold requirements set here and be identified as LMS though it is encompassed by tropical upper-troposphere air. ...
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... These circulations are the dynamical response to the deep convective heating that usually happens during the summer season over the land masses and the Maritime Continent, which is somewhat displaced from the Equator (e.g., Gill, 1980;Holton and Hakim, 2013) and results in largescale anticyclone circulations in the UTLS. The large-scale monsoon circulations are important for the upward transport of tracers into the stratosphere (e.g., Park et al., 2009;Konopka et al., 2010;Randel et al., 2010;Ungermann et al., 2016;Vogel et al., 2021, and references therein), and the monsoon regions act as sources of upward-propagating small-scale gravity waves that have strong effects on the dynamics of the middle atmosphere (e.g., Sato et al., 2009;Ern et al., 2013;Thurairajah et al., 2017;Chen et al., 2019;Forbes et al., 2022, and references therein). Particularly the westward-directed winds on the southern flank of the Asian summer monsoon contribute to the predominantly westwarddirected winds in the Eastern Hemisphere (see also, for example, Park et al., 2007Park et al., , 2009Konopka et al., 2010) and therefore to the strong zonal wavenumber 1 structure seen in the low-latitude zonal wind in the tropical UTLS. ...
... The large-scale monsoon circulations are important for the upward transport of tracers into the stratosphere (e.g., Park et al., 2009;Konopka et al., 2010;Randel et al., 2010;Ungermann et al., 2016;Vogel et al., 2021, and references therein), and the monsoon regions act as sources of upward-propagating small-scale gravity waves that have strong effects on the dynamics of the middle atmosphere (e.g., Sato et al., 2009;Ern et al., 2013;Thurairajah et al., 2017;Chen et al., 2019;Forbes et al., 2022, and references therein). Particularly the westward-directed winds on the southern flank of the Asian summer monsoon contribute to the predominantly westwarddirected winds in the Eastern Hemisphere (see also, for example, Park et al., 2007Park et al., , 2009Konopka et al., 2010) and therefore to the strong zonal wavenumber 1 structure seen in the low-latitude zonal wind in the tropical UTLS. A more detailed investigation, however, including the effects of the other large-scale monsoon systems, is beyond the scope of the current study. ...
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... As can be seen from Fig. 7a, c, e, and g, the symmetric quasi-stationary wave 1 has a huge maximum in the upper convective heating that happens usually during the summer season over the land masses and the Maritime Continent, somewhat displaced from the equator (e.g., Gill, 1980;Holton and Hakim, 2013), which results in large-scale anticyclonal circulations in the UTLS. The large-scale monsoon circulations are important for the upward transport of tracers into the stratosphere (e.g., Park et al., 2009;Konopka et al., 2010;Randel et al., 2010;Ungermann et al., 2016;Vogel et al., 2021, and references therein), and the monsoon regions act as sources for upward-propagating small-scale gravity waves that have strong effect on 395 the dynamics of the middle atmosphere (e.g., Sato et al., 2009;Ern et al., 2013;Thurairajah et al., 2017;Chen et al., 2019;Forbes et al., 2022, and references therein). Particularly the westward directed winds at the southern flank of the Asian summer monsoon contribute to the predominantly westward directed winds in the Eastern Hemisphere (see also, for example, Park et al., 2007Park et al., , 2009Konopka et al., 2010), and therefore to the strong zonal wavenumber 1 structure seen in the low-latitude zonal wind in the tropical UTLS. ...
... The large-scale monsoon circulations are important for the upward transport of tracers into the stratosphere (e.g., Park et al., 2009;Konopka et al., 2010;Randel et al., 2010;Ungermann et al., 2016;Vogel et al., 2021, and references therein), and the monsoon regions act as sources for upward-propagating small-scale gravity waves that have strong effect on 395 the dynamics of the middle atmosphere (e.g., Sato et al., 2009;Ern et al., 2013;Thurairajah et al., 2017;Chen et al., 2019;Forbes et al., 2022, and references therein). Particularly the westward directed winds at the southern flank of the Asian summer monsoon contribute to the predominantly westward directed winds in the Eastern Hemisphere (see also, for example, Park et al., 2007Park et al., , 2009Konopka et al., 2010), and therefore to the strong zonal wavenumber 1 structure seen in the low-latitude zonal wind in the tropical UTLS. A more detailed investigation, however, including the effect of the other large-scale monsoon 400 systems, is beyond the scope of the current study. ...
The quasi-biennial oscillation (QBO) of the stratospheric tropical winds influences the global circulation over a wide range of latitudes and altitudes. Although it has strong effects on surface weather and climate, climate models have large difficulties in simulating a realistic QBO, especially in the lower stratosphere. Therefore, global wind observations in the tropical upper troposphere and lower stratosphere (UTLS) are of particular interest for investigating the QBO and the tropical waves that contribute significantly to its driving. In our work, we focus on the years 2018–2022 and investigate the QBO and different tropical wave modes in the UTLS region using global wind observations by the Aeolus satellite instrument, and three meteorological reanalyses (ERA-5, JRA-55, and MERRA-2). Further, we compare these data with observations of selected radiosonde stations. By comparison with Aeolus observations, we find that on zonal average the QBO in the lower stratosphere is well represented in all three reanalyses, with ERA-5 performing best. Averaged over the years 2018–2022, agreement between Aeolus and the reanalyses is better than 1 to 2 m s−1, with somewhat larger differences during some periods. Different from zonal averages, radiosonde stations provide only local observations and are therefore biased by global-scale tropical waves, which limits their use as a QBO standard. While reanalyses perform well on zonal average, there can be considerable local biases between reanalyses and radiosondes. We also find that, in the tropical UTLS, zonal wind variances of stationary waves and the most prominent global-scale traveling equatorial wave modes, such as Kelvin waves, Rossby-gravity waves, and equatorial Rossby waves, are in good agreement between Aeolus and all three reanalyses (in most cases better than 20 % of the peak values in the UTLS). On zonal average, this supports the use of reanalyses as a reference for comparison with free-running climate models, while locally certain biases exist, particularly in the QBO wind shear zones, and around the 2019–2020 QBO disruption.
... During the winters, mixing in the lower stratosphere is driven by synoptic-scale wave breaking, while during the summer, this mixing is predominantly driven by the Asian Monsoon anticyclone in the northern hemisphere, and the Australian Monsoon and the Bolivian high in the southern hemisphere. These systems transport midlatitude tracers into the tropics in the lower stratosphere, and also weaken the subtropical transport barriers, by weakening the subtropical jet (Konopka et al., 2010;Shuckburgh et al., 2009). These systems are completely absent in the idealized FV3 model considered in this study, possibly causing it to suggest a more isolated tropics than actually observed. ...
Wave‐induced adiabatic mixing in the winter midlatitudes is one of the key processes impacting stratospheric transport. Understanding its strength and structure is vital to understanding the distribution of trace gases and their modulation under a changing climate. Age‐of‐air is often used to understand stratospheric transport, and this study proposes refinements to the vertical age gradient theory of Linz et al. (2021), https://doi.org/10.1029/2021JD035199. The theory assumes exchange of air between a well‐mixed tropics and a well‐mixed extratropics, separated by a transport barrier, quantifying the adiabatic mixing flux across the interface using age‐based measures. These assumptions are re‐evaluated and a refined framework that includes the effects of meridional tracer gradients is established to quantify the mixing flux. This is achieved, in part, by computing a circulation streamfunction in age‐potential temperature coordinates to generate a complete distribution of parcel ages being mixed in the midlatitudes. The streamfunction quantifies the “true” age of parcels mixed between the tropics and the extratropics. Applying the revised theory to an idealized and a comprehensive climate model reveals that ignoring the meridional gradients in age leads to an underestimation of the wave‐driven mixing flux. Stronger, and qualitatively similar fluxes are obtained in both models, especially in the lower‐to‐middle stratosphere. While the meridional span of adiabatic mixing in the two models exhibits some differences, they show that the deep tropical pipe, that is, latitudes equatorward of 15° barely mix with older midlatitude air. The novel age‐potential temperature circulation can be used to quantify additional aspects of stratospheric transport.
... Tropopause folds, or RWB, are dynamical phenomena that can lead to an exchange of air between the stratosphere and the troposphere (Baray et al., 1998;Folkins & Appenzeller, 1996;Gouget et al., 1996;Postel & Hitchman, 1999). They lead to the intrusions of the lower stratospheric dry, ozone-rich, and high PV air masses into the tropical upper troposphere (Konopka et al., 2010;Ploeger et al., 2012;Waugh, 2005). PV is relatively conserved under an adiabatic flow and hence is considered an ideal diagnostic for understanding the dynamical exchange of atmospheric air parcels (Homeyer & Bowman, 2013). ...
Deep convection associated with tropical cyclones leads to stratosphere‐troposphere exchange (STE), which affects the upper‐tropospheric ozone concentrations in the vicinity of the cyclones. This study estimates the ozone enhancements over India due to the North Indian Ocean (NIO) cyclones‐driven STE. Indicators such as stratospheric fraction and potential vorticity calculated using the reanalysis data sets suggest that roughly 70% of the cyclones show anomalously high stratospheric intrusions. Aircraft observations over different locations across India also show elevated ozone concentrations in the mid‐to‐upper troposphere on cyclone days. Further, ozone and stratospheric ozone tracer concentrations from Goddard Earth Observing System‐Chemistry simulations and the Copernicus Atmosphere Monitoring Service reanalysis data sets show up to 40 ppb of excess upper tropospheric ozone over India, of which stratospheric ozone accounts for roughly 60%. Stratospheric intrusion due to the Bay of Bengal and the Arabian Sea cyclones affected the upper tropospheric ozone amounts over North and South India, respectively. The stratospheric ozone was observed to propagate downwards into the troposphere, often reaching ∼600 hPa and, in some cases, even the surface.
... The modal age maps show that the closed Rossby wave anticyclones isolate air from the in mixing of older air. This produces young air anomalies in both modal and mean ages over the TWP in DJF and over the Asian monsoon in JJA. Figure 5h also shows the advection of slightly older air around the Asian monsoon anticyclone, a process that transports extratropical trace gases deep into the tropics (also see Konopka et al., 2010;Figure 7). The effect of this mixing on the mean minus modal age is to produce the shelf structure at 17 km 20°-40°N in Figure 5b. ...
... The effect of this mixing on the mean minus modal age is to produce the shelf structure at 17 km 20°-40°N in Figure 5b. Overall, our mean and modal age distributions agree with the location of mixing regions described in Konopka et al. (2010 and Ploeger and Birner, 2016. ...
... J. Randel et al., 2010;Wu et al., 2020). Lagrangian or trajectory model investigation of STE is an ideal way to explore the exchange process as was done by Postel and Hitchman (1999), Konopka et al. (2010) and Homeyer and Bowman (2013). In this paper, we use the FDF trajectory model developed by M. R. Schoeberl and Dessler (2011). ...
We use our forward domain filling trajectory model coupled with a new convective parcel injection system to explore stratosphere‐troposphere exchange (STE). We use Modern‐Era Retrospective Analysis for Research and Applications, Version 2 reanalysis and study the December‐February (DJF) and June‐August (JJA) seasons averaged for the years 2006–2015. Maps of age‐of‐air and STE regions show coincidence with stationary forced tropical Rossby waves that straddle the equator. The anticyclonic circulation generated by these waves isolates air over the Asian monsoon, the Tropical West Pacific, and North and South America. We map the preferred locations of troposphere to stratosphere (T2S) and stratosphere to troposphere (S2T) exchange. During DJF, the highest concentration of T2S locations is spread over the tropical west Pacific and in a broad region over Central/South America and Africa. During JJA, the highest concentration T2S locations is in the vicinity of the Asian monsoon. The highest concentration T2S crossing points is nearly always positioned on the eastern side of the Rossby waves where the tropopause is higher. Along the jets that bracket the tropics, the STE locations are consistent with earlier studies of Rossby wave breaking and two‐way exchange. S2T exchange above 12 km occurs at the edges of the tropics along the jet boundaries for both seasons.
... The non-deep learning methods roughly include two major models: deterministic ones and statistical ones (Liu et al., 2021). The most representative deterministic methods are the Community Multiscale Air Quality (CMAQ) model (Mueller and Mallard, 2011;Thongthammachart et al., 2021;Kitagawa et al., 2021), the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) Zhou et al., 2017), Weather Research and Forecasting/Chemistry-Madrid (WRF/Chem-MADRID) (Chuang et al., 2011), the Nested Air Quality Prediction Modeling System (NAQPMS) (Wang et al., 2001(Wang et al., , 2014, Chemical Lagrangian Model of the Stratosphere (CLaMS) (Konopka et al., 2010), Operational Street Pollution Models (OSPM) (Assael et al., 2008) and Comprehensive Air-quality Model with extension (CAMx) (Koo et al., 2015), LOTOS-EUROS (Manders et al., 2009), MOZART (Tie et al., 2006). Due to some reasons, such as the use of ideal theory in the determination of model structure and the estimation of parameters by experience, the predictive performance of these models is limited (Pak et al., 2020;Vautard et al., 2007;Stern et al., 2008). ...
... CLaMS (Konopka et al., 2010) Chemical Lagrangian Model of the Stratosphere CTMs Chemical Transport Models NAQPMS (Wang et al., 2001(Wang et al., , 2014 Nested Air Quality Prediction Modeling System OSPM (Assael et al., 2008) Operational Street Pollution Models WRF (Thongthammachart et al., 2021;Wang et al., 2022a;Zhou et al., 2017;Chuang et al., 2011) Weather Research and Forecasting WRF-Chem Zhou et al., 2017) Weather Research and Forecasting/Chemistry WRF/Chem-MADRID (Chuang et al., 2011) Weather Research and Forecasting/Chemistry-Madrid Table 2 The description of statistical methods. ...
Air pollution has become one of the critical environmental problem in the 21st century and has attracted worldwide attentions. To mitigate it, many researchers have investigated the issue and attempted to accurately predict air pollutant concentrations using various methods. Currently, deep learning methods are the most prevailing ones. In this paper, we extend a comprehensive review on deep learning methods specifically for air pollutant concentration prediction. We start from the analysis on non-deep learning methods applied in air pollutant concentration prediction in terms of expertise, applications and deficiencies. Then, we investigate current deep learning methods for air pollutant concentration prediction from the perspectives of temporal, spatial and spatio-temporal correlations these methods could model. Further, we list some public datasets and auxiliary features used in air pollutant prediction, and compare representative experiments on these datasets. From the comparison, we draw some conclusions. Finally, we identify current limitations and future research directions of deep learning methods for air pollutant concentration prediction. The review may inspire researchers and to a certain extent promote the development of deep learning in air pollutant concentration prediction.
... Here P −L represents chemical ozone production minus loss terms. In contrast to the thermodynamic balance discussed above, the eddy terms for ozone transport in the tropical lower stratosphere are not negligible, and there is a maximum during boreal summer near the tropopause related to transport from the subtropical monsoon circulations (Konopka et al., 2009(Konopka et al., , 2010Abalos et al., 2013). This contribution is relatively large below ∼ 80 hPa (18 km). ...
... Figure 2 shows this behavior for the 19 km level, near the peak of the annual cycle. This correlated ozone-temperature behavior is mainly a response to the annual cycle in tropical upwelling (Randel et al., 2007); horizontal transport from the boreal sum-mer monsoons also contributes to the seasonal maximum in ozone close to the tropopause (Konopka et al., 2009(Konopka et al., , 2010Stolarski et al., 2014;Tweedy et al., 2017), but mean upwelling is the dominant mechanism above 18 km (Abalos et al., 2013). Above 23 km, the annual cycle becomes small and the dominant seasonal variation becomes semiannual in both ozone and temperature. ...
... Observations for the annual cycle (b) are only shown over altitudes 19-23 km where the annual cycle is relatively large and distinct. tion in the tropical lower stratosphere above the tropical tropopause layer (TTL) (Abalos et al., 2013), although eddy transport from monsoon circulations makes important contributions to ozone tendencies during boreal summer at and below ∼ 18 km (Konopka et al., 2009(Konopka et al., , 2010Stolarski et al., 2014). Thermodynamic balance includes linear radiative damping (α) and ozone feedback (β) terms, and the coupled equations (including linear ozone damping δ) can be solved analytically to calculate the (T / O 3 ) ratio as a function of frequency and altitude, dependent on model parameters α, β and δ and the ratio of background gradients expressed as (S/X z ). ...
Observations show strong correlations between large-scale ozone and temperature variations in the tropical lower stratosphere across a wide range of timescales. We quantify this behavior using monthly records of ozone and temperature data from Southern Hemisphere Additional Ozonesonde (SHADOZ) tropical balloon measurements (1998–2016), along with global satellite data from Aura microwave limb sounder and GPS radio occultation over 2004–2018. The observational data demonstrate strong in-phase ozone–temperature coherence spanning sub-seasonal, annual and interannual timescales, and the slope of the temperature–ozone relationship (T / O3) varies as a function of timescale and altitude. We compare the observations to idealized calculations based on the coupled zonal mean thermodynamic and ozone continuity equations, including ozone radiative feedbacks on temperature, where both temperature and ozone respond in a coupled manner to variations in the tropical upwelling Brewer–Dobson circulation. These calculations can approximately explain the observed (T / O3) amplitude and phase relationships, including sensitivity to timescale and altitude, and highlight distinct balances for “fast” variations (periods
