Volcanically induced stratospheric water vapor changes

2020 ◽  
Author(s):  
Clarissa Kroll ◽  
Alon Azulay ◽  
Hauke Schmidt ◽  
Claudia Timmreck
Keyword(s):  
Water Vapor ◽  
Stratospheric Ozone ◽  
Statistical Significance ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Radiation Budget ◽  
Volcanic Plume ◽  
Indirect Pathway ◽  
Maximum Increase ◽  
Stratospheric Water Vapor

<p><span>Stratospheric water vapor (SWV) is important not only for stratospheric ozone chemistry but also due to its influence on the atmospheric radiation budget.</span></p><p><span>After volcanic eruptions, SWV is known to increase due to two different mechanisms: First, water within the volcanic plume is directly injected into the stratosphere during the eruption itself. Second, the volcanic aerosols lead to a warming of the lower stratosphere including the tropopause layer. The increased temperature of the cold point allows an increased water vapor transit from the troposphere to the stratosphere. Not much is known about this process as it is obscured by internal variability and observations are scare.</span></p><p><span>To better understand the increased SWV entry via the indirect pathway after volcanic eruptions we employ a suite of large volcanically perturbed ensemble simulations of the MPI-ESM1.2-LR for five different eruptions strengths (2.5 Mt, 5 Mt, 10 Mt, 20 Mt and 40 Mt sulfur). Each ensemble consists of 100 realizations for a time period of 3 years.</span></p><p><span>Our work mainly focuses on the tropical tropopause layer (TTL) quantifying changes in relevant parameters such as the atmospheric temperature profile and the consequent increase in SWV. A maximum increase of up to 4 ppmm in the first two years after the eruption is found in the case of the 40 Mt eruption. Furthermore the large ensemble size additionally allows for an analysis of the statistical significance and influence of variability, showing that SWV increases can already be detected for the 2.5 Mt eruption in the ensemble mean, for single ensemble members the internal variability dominates the SWV entry up to an eruption strength of 10 Mt to 20 Mt depending on the season and time after the eruption. The study is complemented by investigations using the 1D radiative convective equilibrium model konrad to understand the radiative effects of the SWV increase.</span></p>

scholarly journals Simulation of stratospheric water vapor trends: impact on stratospheric ozone chemistry

2004 ◽  
Vol 4 (5) ◽  
pp. 6559-6602 ◽  
Author(s):  
A. Stenke ◽  
V. Grewe
Keyword(s):  
Water Vapor ◽  
Model Simulation ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Short Term ◽  
Transient Model ◽  
Stratospheric Water Vapor ◽  
Additional Water ◽  
Phase Chemistry

Abstract. A transient model simulation from 1960 to 2000 with the coupled climate-chemistry model (CCM) shows a stratospheric water vapor trend during the last two decades of +0.7 ppmv and additionally a short-term increase during volcanic eruptions. At the same time this model simulation shows a long-term decrease in total ozone and a short-term tropical ozone decline after a volcanic eruption. In order to understand the resulting effects of the water vapor changes on stratospheric ozone chemistry, different perturbation simulations have been performed with the CCM with the water vapor perturbations fed only to the chemistry part. Two different long-term perturbations of stratospheric water vapor, +1 ppmv and +5 ppmv, and a short-term perturbation of +2 ppmv with an e-folding time of two months have been simulated. Since water vapor acts as an in-situ source of odd hydrogen in the stratosphere, the water vapor perturbations affect the gas-phase chemistry of hydrogen oxides. An additional water vapor amount of +1 ppmv results in a 5–10%  increase. Coupling processes between and / also affect the ozone destruction by other catalytic reaction cycles. The  cycle becomes 6.4% more effective, whereas the cycle is 1.6% less effective. A long-term water vapor increase does not only affect the gas-phase chemistry, but also the heterogeneous ozone chemistry in polar regions. The additional water vapor intensifies the strong denitrification of the Antarctic winter stratosphere caused by an enhanced formation of polar stratospheric clouds. Thus it further facilitates the catalytic ozone removal by the cycle. The reduction of total column ozone during Antarctic spring peaks at −3%. In contrast, heterogeneous chemistry during Arctic winter is not affected by the water vapor increase. The short-term perturbation studies show similar patterns, but because of the short perturbation time, the chemical effect on ozone is almost negligible. Finally, this study shows that 10% of the simulated long-term ozone decline in the transient model simulation can be explained by the water vapor increase, but the simulated tropical ozone decrease after volcanic eruptions is caused dynamically rather than chemically.

scholarly journals Simulation of stratospheric water vapor trends: impact on stratospheric ozone chemistry

2005 ◽  
Vol 5 (5) ◽  
pp. 1257-1272 ◽  
Author(s):  
A. Stenke ◽  
V. Grewe
Keyword(s):  
Water Vapor ◽  
Ozone Depletion ◽  
Total Ozone ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Short Term ◽  
Transient Model ◽  
Stratospheric Water Vapor ◽  
Ozone Destruction

Abstract. A transient model simulation of the 40-year time period 1960 to 1999 with the coupled climate-chemistry model (CCM) ECHAM4.L39(DLR)/CHEM shows a stratospheric water vapor increase over the last two decades of 0.7 ppmv and, additionally, a short-term increase after major volcanic eruptions. Furthermore, a long-term decrease in global total ozone as well as a short-term ozone decline in the tropics after volcanic eruptions are modeled. In order to understand the resulting effects of the water vapor changes on lower stratospheric ozone chemistry, different perturbation simulations were performed with the CCM ECHAM4.L39(DLR)/CHEM feeding the water vapor perturbations only to the chemistry part. Two different long-term perturbations of lower stratospheric water vapor, +1 ppmv and +5 ppmv, and a short-term perturbation of +2 ppmv with an e-folding time of two months were applied. An additional stratospheric water vapor amount of 1 ppmv results in a 5–10% OH increase in the tropical lower stratosphere between 100 and 30 hPa. As a direct consequence of the OH increase the ozone destruction by the HOx cycle becomes 6.4% more effective. Coupling processes between the HOx-family and the NOx/ClOx-family also affect the ozone destruction by other catalytic reaction cycles. The NOx cycle becomes 1.6% less effective, whereas the effectiveness of the ClOx cycle is again slightly enhanced. A long-term water vapor increase does not only affect gas-phase chemistry, but also heterogeneous ozone chemistry in polar regions. The model results indicate an enhanced heterogeneous ozone depletion during antarctic spring due to a longer PSC existence period. In contrast, PSC formation in the northern hemisphere polar vortex and therefore heterogeneous ozone depletion during arctic spring are not affected by the water vapor increase, because of the less PSC activity. Finally, this study shows that 10% of the global total ozone decline in the transient model run can be explained by the modeled water vapor increase, but the simulated tropical ozone decrease after volcanic eruptions is caused dynamically rather than chemically.

Evaluating stratospheric ozone and water vapor changes in CMIP6 models from 1850-2100 

2021 ◽  
Author(s):  
James Keeble ◽  
Birgit Hassler ◽  
Antara Banerjee ◽  
Ramiro Checa-Garcia ◽  
Gabriel Chiodo ◽  
...  
Keyword(s):  
Water Vapor ◽  
Water Vapour ◽  
Tropospheric Ozone ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Global Pattern ◽  
Regional Patterns ◽  
Total Column Ozone ◽  
Stratospheric Water Vapor ◽  
Mixing Ratios

<p>Stratospheric ozone and water vapor are key components of the Earth system, and past and future changes to both have important impacts on global and regional climate. Here we evaluate long-term changes in these species from the pre-industrial (1850) to the end of the 21<sup>st</sup> century in CMIP6 models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has increased from ~300 DU in 1850 to ~305 DU in 1960, before rapidly declining in the 1970s and 1980s following the use and emission of halogenated ozone depleting substances (ODSs). TCO is projected to return to 1960’s values by the middle of the 21<sup>st</sup> century under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0 and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to be ~10 DU higher than the 1960’s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to return to the 1960’s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960’s values, either through reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of the Brewer-Dobson Circulation under other SSPs. In contrast to TCO, there is poorer agreement between the CMIP6 multi-model mean and observed lower stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by ~0.5 ppmv at 70hPa. CMIP6 multi-model mean stratospheric water vapor mixing ratios in the tropical lower stratosphere have increased by ~0.5 ppmv from the pre-industrial to the present day and are projected to increase further by the end of the 21<sup>st</sup> century. The largest increases (~2 ppmv) are simulated under the future scenarios with the highest assumed forcing pathway (e.g. SSP5-8.5). Tropical lower stratospheric water vapor, and to a lesser extent TCO, show large variations following explosive volcanic eruptions.</p>

scholarly journals The impact of volcanic eruptions of different magnitude on stratospheric water vapor in the tropics

2021 ◽  
Vol 21 (8) ◽  
pp. 6565-6591
Author(s):  
Clarissa Alicia Kroll ◽  
Sally Dacie ◽  
Alon Azoulay ◽  
Hauke Schmidt ◽  
Claudia Timmreck
Keyword(s):  
Water Vapor ◽  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Aerosol Layer ◽  
Power Functions ◽  
Max Planck ◽  
Point Temperature ◽  
Stratospheric Water Vapor ◽  
Cold Point ◽  
The Impact

Abstract. Increasing the temperature of the tropical cold-point region through heating by volcanic aerosols results in increases in the entry value of stratospheric water vapor (SWV) and subsequent changes in the atmospheric energy budget. We analyze tropical volcanic eruptions of different strengths with sulfur (S) injections ranging from 2.5 Tg S up to 40 Tg S using EVAens, the 100-member ensemble of the Max Planck Institute – Earth System Model in its low-resolution configuration (MPI-ESM-LR) with artificial volcanic forcing generated by the Easy Volcanic Aerosol (EVA) tool. Significant increases in SWV are found for the mean over all ensemble members from 2.5 Tg S onward ranging between [5, 160] %. However, for single ensemble members, the standard deviation between the control run members (0 Tg S) is larger than SWV increase of single ensemble members for eruption strengths up to 20 Tg S. A historical simulation using observation-based forcing files of the Mt. Pinatubo eruption, which was estimated to have emitted (7.5±2.5) Tg S, returns SWV increases slightly higher than the 10 Tg S EVAens simulations due to differences in the aerosol profile shape. An additional amplification of the tape recorder signal is also apparent, which is not present in the 10 Tg S run. These differences underline that it is not only the eruption volume but also the aerosol layer shape and location with respect to the cold point that have to be considered for post-eruption SWV increases. The additional tropical clear-sky SWV forcing for the different eruption strengths amounts to [0.02, 0.65] W m−2, ranging between [2.5, 4] % of the aerosol radiative forcing in the 10 Tg S scenario. The monthly cold-point temperature increases leading to the SWV increase are not linear with respect to aerosol optical depth (AOD) nor is the corresponding SWV forcing, among others, due to hysteresis effects, seasonal dependencies, aerosol profile heights and feedbacks. However, knowledge of the cold-point temperature increase allows for an estimation of SWV increases of 12 % per Kelvin increase in mean cold-point temperature. For yearly averages, power functions are fitted to the cold-point warming and SWV forcing with increasing AOD.

scholarly journals Multi-timescale variations of modelled stratospheric water vapor derived from three modern reanalysis products

2019 ◽  
Author(s):  
Mengchu Tao ◽  
Paul Konopka ◽  
Felix Ploeger ◽  
Xiaolu Yan ◽  
Jonathon S. Wright ◽  
...  
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Southern Oscillation ◽  
Radiation Budget ◽  
Lagrangian Model ◽  
Linear Regression Method ◽  
Positive Trend ◽  
Volcanic Aerosol ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Water Vapor

Abstract. Stratospheric water vapor (SWV) plays important roles in the radiation budget and ozone chemistry and is a valuable tracer for understanding stratospheric transport. Meteorological reanalyses provide variables necessary for simulating this transport; however, even recent reanalyses are subject to substantial uncertainties, especially in the stratosphere. It is therefore necessary to evaluate the consistency among SWV distributions simulated using different input reanalysis products. In this study, we evaluate the representation of SWV and its variations on multiple timescales using simulations over the period 1980–2013. Our simulations are based on the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by horizontal winds and diabatic heating rates from three recent reanalyses: ERA-Interim, JRA-55 and MERRA-2. We present an inter-comparison among these model results and observationally-based estimates, using a multiple linear regression method to study the annual cycle (AC), the quasi-biennial oscillation (QBO), and longer-term variability in monthly zonal-mean H2O mixing ratios forced by variations in the El-Nino–Southern Oscillation and the volcanic aerosol burden. We find reasonable consistency among simulations of the distribution and variability of SWV with respect to the AC and QBO. However, the amplitudes of both signals are systematically weaker in the lower and middle stratosphere when CLaMS is driven by MERRA-2 than when it is driven by ERA-Interim or JRA-55. This difference is primarily attributable to relatively slow tropical upwelling in the lower stratosphere in simulations based on MERRA-2. Two possible contributors of the slow tropical upwelling in the lower stratosphere are found to be the large long-wave radiative effect and the unique assimilation process in MERRA-2. The impacts of ENSO and volcanic aerosol on H2O entry variability are qualitatively consistent among the three simulations despite differences of 50–100 % in the magnitudes. Trends show larger discrepancies among the three simulations. CLaMS driven by ERA-Interim produces a neutral to slightly positive trend in H2O entry values over 1980–2013 (+0.01 ppmv decade-1), while both CLaMS driven by JRA-55 and CLaMS driven by MERRA-2 produce negative trends but with significantly different magnitudes (−0.22 ppmv decade-1 and −0.08 ppmv decade-1, respectively).

scholarly journals Middle atmospheric water vapor and ozone anomalies during the 2010 major sudden stratospheric warming

2011 ◽  
Vol 11 (12) ◽  
pp. 32391-32422 ◽  
Author(s):  
D. Scheiben ◽  
C. Straub ◽  
K. Hocke ◽  
P. Forkman ◽  
N. Kämpfer
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Atmospheric Water Vapor ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Atmospheric Water ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Water Vapor

Abstract. A major sudden stratospheric warming (SSW) occurred in the Northern Hemisphere in January 2010. The warming started on 26 January 2010, was most pronounced by the end of January and was accompanied by a polar vortex shift towards Europe. After the warming, the polar vortex split into two weaker vortices. The zonal mean temperature in the polar upper stratosphere (35–45 km) increased by approximately 25 K in a few days, while there was a decrease in temperature in the lower stratosphere and mesosphere. Local temperature maxima were around 325 K in the upper stratosphere and minima around 175 and 155 K in the lower stratosphere and mesosphere, respectively. In this study, we present middle atmospheric water vapor and ozone measurements obtained by a meridional chain of European ground-based microwave radiometers in Bern (47° N), Onsala (57° N) and Sodankylä (67° N). The instruments in Bern and Onsala are part of the Network for the Detection of Atmospheric Composition Change (NDACC). Effects of the SSW were observed at all three locations and we perform a combined analysis in order to reveal transport processes in the middle atmosphere above Europe during the SSW event. Further we investigate the chemical and dynamical influences of the SSW event. We find that the anomalies during the warming in water vapor and ozone were different for each location. A few days before the beginning of the major SSW, we observed a decrease in mesospheric water vapor above Bern, which we attribute to movement of the mesospheric polar vortex towards Central Europe. The most prominent H2O anomaly observed in Bern was an increase in stratospheric water vapor during the warming. In Onsala and Sodankylä, mesospheric water vapor increased within a few days during the warming and slowly decreased afterwards. Upper stratospheric ozone decreased during the warming over Bern by approximately 30% and by approximately 20% over Onsala. Over Sodankylä, a decrease in ozone below 30 km altitude was observed. This decrease is assumed to be caused by heterogeneous chemistry on polar stratospheric clouds. After the SSW, stratospheric ozone increased to higher levels than before at all three locations. The observed anomalies are explained by a trajectory analysis with reanalysis data from the European Center for Medium-Range Weather Forecasts (ECMWF). Most of the observed anomalies in water vapor and ozone during the warming are attributed to the location of the polar vortex, depending on whether a measurement site was inside or outside the polar vortex. The observed increase in mesospheric water vapor at high latitudes is explained by advection of relatively moist air from lower latitudes, whereas the observed increase in stratospheric water vapor at midlatitudes is explained by advection from high latitudes, i.e. from the moist stratospheric polar vortex.

Toba volcano super eruption destroyed the ozone layer and caused a human population bottleneck

2020 ◽  
Author(s):  
Sergey Osipov ◽  
Georgiy Stenchikov ◽  
Kostas Tsigaridis ◽  
Allegra LeGrande ◽  
Susanne Bauer ◽  
...  
Keyword(s):  
Rayleigh Scattering ◽  
Stratospheric Ozone ◽  
Population Decline ◽  
Volcanic Eruptions ◽  
Volcanic Plume ◽  
Sulfate Aerosols ◽  
Ozone Loss ◽  
Temperature And Precipitation ◽  
Climatic Responses ◽  
Earth’S Climate

<p>Volcanic eruptions trigger a broad spectrum of climatic responses. For example, the Mount Pinatubo eruption in 1991 forced an El Niño and global cooling, and the Tambora eruption in 1815 caused the "Year Without a Summer." Especially grand eruptions such as Toba around 74,000 years ago can push the Earth's climate into a volcanic winter state, significantly lowering the surface temperature and precipitation globally. Here we present a new, previously overlooked element of the volcanic effects spectrum: the radiative mechanism of stratospheric ozone depletion. We found that the volcanic plume of Toba enhanced the UV optical depth and suppressed the primary formation of stratospheric ozone from O<sub>2</sub> photolysis. Sulfate aerosols additionally reflect the photons needed to break the O<sub>2</sub> bond (λ < 242 nm), otherwise controlled by ozone absorption and Rayleigh scattering alone during volcanically quiescent conditions. Our NASA GISS ModelE simulations of the Toba eruption reveal up to 50% global ozone loss due to the overall photochemistry perturbations of the sulfate aerosols. We also consider and quantify the radiative effects of SO<sub>2</sub>, which partially compensated for the ozone loss by inhibiting the photolytic O<sub>3</sub> sink.</p><p>Our analysis shows that the magnitude of the ozone loss and UV-induced health-hazardous effects after the Toba eruption are similar to those in the aftermath of a potential nuclear conflict. These findings suggest a “Toba ozone catastrophe" as a likely contributor to the historic population decline in this period, consistent with a genetic bottleneck in human evolution.</p>

Impact of Lagrangian transport on lower-stratospheric water vapor and radiative balance in a climate model

2021 ◽  
Author(s):  
Edward Charlesworth ◽  
Felix Plöger ◽  
Patrick Jöckel
Keyword(s):  
Water Vapor ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Chem Phys ◽  
Climate Feedback ◽  
Lagrangian Transport ◽  
Radiative Balance ◽  
Model Simulations ◽  
Stratospheric Water Vapor ◽  
Climate Model Simulations

<p>A robust result of climate model simulations is the moistening of the stratosphere.<br>Many models show their strongest changes in stratospheric water vapor in the extratropical lowermost stratosphere, a change which could have substantial climate feedbacks (e.g. Banerjee et al. 2019). However, models are also heavily wet-biased in this region when compared to observations (Keeble et al. 2020), presenting some uncertainty on the robustness of these model results.</p><p>In this study, we investigate the contribution of the choice of model transport scheme to this wet bias using a climate model (EMAC) coupled with two transport schemes: the standard EMAC flux-form semi-Lagrangian (FFSL) scheme and the fully-Lagrangian scheme of CLaMS. This experiment has the advantage of analytical clarity in that the dynamical fields driving both transport schemes are identical. Prior work using this tool has shown large differences in transport timecales within the extratropical lowermost stratosphere depending on the transport scheme used (Charlesworth et al. 2020). </p><p>These results also suggested that EMAC-CLaMS should reduce the transport of water vapor into this region, but calculations of water vapor fields using this tool were not performed until now. We present the results of that work, comparing the water vapor fields calculated using EMAC-CLaMS and EMAC-FFSL online. Two model simulations were performed, wherein each water vapor field was used to drive radiation calculations, such that the radiative consequences of applying one transport scheme or the other could be assessed.</p><p>References:</p><p>Banerjee, A., Chiodo, G., Previdi, M. <em>et al.</em> Stratospheric water vapor: an important climate feedback. <em>Clim Dyn</em> <strong>53, </strong>1697–1710 (2019). https://doi.org/10.1007/s00382-019-04721-4</p><p>Keeble, J., Hassler, B., Banerjee, A., Checa-Garcia, R., Chiodo, G., Davis, S., Eyring, V., Griffiths, P. T., Morgenstern, O., Nowack, P., Zeng, G., Zhang, J., Bodeker, G., Cugnet, D., Danabasoglu, G., Deushi, M., Horowitz, L. W., Li, L., Michou, M., Mills, M. J., Nabat, P., Park, S., and Wu, T.: Evaluating stratospheric ozone and water vapor changes in CMIP6 models from 1850–2100, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2019-1202, in review, 2020. </p><p>Charlesworth, E. J., Dugstad, A.-K., Fritsch, F., Jöckel, P., and Plöger, F.: Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model, Atmos. Chem. Phys., 20, 15227–15245, https://doi.org/10.5194/acp-20-15227-2020, 2020. </p>

scholarly journals Multitimescale variations in modeled stratospheric water vapor derived from three modern reanalysis products

2019 ◽  
Vol 19 (9) ◽  
pp. 6509-6534 ◽  
Author(s):  
Mengchu Tao ◽  
Paul Konopka ◽  
Felix Ploeger ◽  
Xiaolu Yan ◽  
Jonathon S. Wright ◽  
...  
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Southern Oscillation ◽  
Radiation Budget ◽  
Lagrangian Model ◽  
Linear Regression Method ◽  
Positive Trend ◽  
Volcanic Aerosol ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Water Vapor

Abstract. Stratospheric water vapor (SWV) plays important roles in the radiation budget and ozone chemistry and is a valuable tracer for understanding stratospheric transport. Meteorological reanalyses provide variables necessary for simulating this transport; however, even recent reanalyses are subject to substantial uncertainties, especially in the stratosphere. It is therefore necessary to evaluate the consistency among SWV distributions simulated using different input reanalysis products. In this study, we evaluate the representation of SWV and its variations on multiple timescales using simulations over the period 1980–2013. Our simulations are based on the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by horizontal winds and diabatic heating rates from three recent reanalyses: ERA-Interim, JRA-55 and MERRA-2. We present an intercomparison among these model results and observationally based estimates using a multiple linear regression method to study the annual cycle (AC), the quasi-biennial oscillation (QBO), and longer-term variability in monthly zonal-mean H2O mixing ratios forced by variations in the El Niño–Southern Oscillation (ENSO) and the volcanic aerosol burden. We find reasonable consistency among simulations of the distribution and variability in SWV with respect to the AC and QBO. However, the amplitudes of both signals are systematically weaker in the lower and middle stratosphere when CLaMS is driven by MERRA-2 than when it is driven by ERA-Interim or JRA-55. This difference is primarily attributable to relatively slow tropical upwelling in the lower stratosphere in simulations based on MERRA-2. Two possible contributors to the slow tropical upwelling in the lower stratosphere are suggested to be the large long-wave cloud radiative effect and the unique assimilation process in MERRA-2. The impacts of ENSO and volcanic aerosol on H2O entry variability are qualitatively consistent among the three simulations despite differences of 50 %–100 % in the magnitudes. Trends show larger discrepancies among the three simulations. CLaMS driven by ERA-Interim produces a neutral to slightly positive trend in H2O entry values over 1980–2013 (+0.01 ppmv decade−1), while both CLaMS driven by JRA-55 and CLaMS driven by MERRA-2 produce negative trends but with significantly different magnitudes (−0.22 and −0.08 ppmv decade−1, respectively).

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