Stratospheric water vapor: an important climate feedback

Banerjee, Antara; Chiodo, Gabriel; Previdi, Michael; Ponater, Michael; Conley, Andrew; Polvani, Lorenzo M.

doi:10.1007/s00382-019-04721-4

Cited by 66 publications

(112 citation statements)

References 55 publications

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“…When the additional aerosol layer is closer to the tropopause, this aerosol‐induced warming leads to an increase in tropopause temperature and an associated enhancement in the water vapor transport from the troposphere to the stratosphere (Dessler et al, ). The increase in water vapor in the stratosphere can lead to strong positive water vapor feedback by increased SW absorption (Banerjee et al, ). The amount of additional water vapor in the stratosphere decreases as the aerosol layer is moved away from the tropopause (Figure S5).…”

Section: Resultsmentioning

confidence: 99%

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The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere

et al. 2020

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Solar geoengineering by deliberate injection of sulfate aerosols in the stratosphere is one of the proposed options to counter anthropogenic climate warming. In this study, we focus on the effect of a specific microphysical property of sulfate aerosols in the stratosphere: hygroscopic growth—the tendency of particles to grow by accumulating water. We show that stratospheric sulfate aerosols, for a given mass of sulfates, cause more cooling when prescribed at the lower levels of the stratosphere because of hygroscopic growth. The larger relative humidity in the lower stratosphere causes an increase in the aerosol size through hygroscopic growth that leads to a larger scattering efficiency. In our study, hygroscopic growth provides an additional cooling of 23% (0.7 K) when 20 Mt‐SO4 of sulfate aerosols, an amount that approximately offsets the warming due to a doubling of CO2, are prescribed at 100 hPa. The hygroscopic effect becomes weaker at higher levels as relative humidity decreases with height. Hygroscopic growth also leads to secondary effects such as an increase in near‐infrared shortwave absorption by the aerosols that causes a decrease in high clouds and an increase in stratospheric water vapor. The altitude dependence of the effects of hygroscopic growth is opposite to that of sedimentation effects or the fast adjustment effects due to aerosol‐induced warming identified in a recent study.

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Section: Resultsmentioning

confidence: 99%

“…The increase in water vapor in the stratosphere can lead to strong positive water vapor feedback by increased SW absorption (Banerjee et al, 2019). The amount of additional water vapor in the stratosphere decreases as the aerosol layer is moved away from the tropopause ( Figure S5).…”

Section: Effective Radiative Forcingmentioning

confidence: 99%

The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere

et al. 2020

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“…Unrealistically high ozone concentrations in the tropical upper troposphere lead to a warm bias in the cold point temperature at the tropical tropopause (Hardiman et al, ; Oh et al, ), which in turn leads to increased water vapor entering the stratosphere (Fueglistaler & Haynes, ; Gettelman et al, ; Hardiman et al, ). This excess stratospheric water vapor then alters the downwelling clear‐sky long‐wave (LW) radiation at the tropopause, impacting the global energy budget and surface temperature (Banerjee et al, ; Dessler et al, ; Joshi et al, ; Solomon et al, ; Stuber et al, ), potentially increasing the modeled climate sensitivity (Andrews et al, ; Gregory et al, ). This could in theory create a positive feedback (between high ozone concentrations in the upper troposphere and climate sensitivity).…”

Section: Introductionmentioning

confidence: 99%

The Impact of Prescribed Ozone in Climate Projections Run With HadGEM3‐GC3.1

Hardiman

Andrews

et al. 2019

J Adv Model Earth Syst

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The Coupled Model Intercomparison Project 6 protocol suggests prescribing preindustrial ozone concentrations in abrupt-4xCO2 simulations. This leads to a mismatch between the thermal tropopause, which rises due to climate change, and the ozone tropopause, which remains fixed. The result is unphysically high ozone concentrations in the upper troposphere, leading to a warm bias in cold point temperature and increased stratospheric water vapor. In the U.K. physical climate model HadGEM3-GC3.1 this increases the surface climate sensitivity. In the future, other climate models without interactive ozone schemes may face similar problems. We describe a method to interactively redistribute ozone in climate simulations, which removes the inconsistency between the thermal and ozone tropopause heights while retaining the prescribed ozone distribution as closely as possible. This removes unphysical consequences of the tropopause mismatch, while still allowing a fair comparison against other Coupled Model Intercomparison Project 6 model simulations. After each model year, the monthly mean, zonal mean, thermal tropopause is formed based on the previous two model years. The ozone tropopause is defined at 1 km below the thermal tropopause by setting ozone concentrations there to 80 ppbv, and smoothing appropriately. The mass of ozone removed from the troposphere is added to the stratosphere thus conserving the total mass of ozone. This redistribution is then applied proportionally to the 3-D monthly mean ozone concentrations. The climate model is run for the following year, using this redistributed ozone, and then the whole process is repeated. Results are presented from preindustrial and abrupt-4xCO2 simulations, but this method can be used for any climate simulation.

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“…A ubiquitous feature here is a sudden decrease in the altitude of the thermal tropopause near the subtropical jet, known as the "tropopause break". The layer poleward of the break is defined as the lowermost stratosphere and is strongly influenced by transport via isentropic mixing associ-ated with Rossby wave breaking (e.g., Chen, 1995;Scott and Cammas, 2002). The role of isentropic mixing in the budget of lowermost-stratosphere water vapour has been highlighted by both in situ airborne and balloon observations (e.g., Dessler et al, 1995;Hintsa et al, 1998;Ray et al, 1999) and satellite measurements (e.g., Pan et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Observational evidence of moistening the lowermost stratosphere via isentropic mixing across the subtropical jet

et al. 2020

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Abstract. Isentropic mixing across and above the subtropical jet is a significant mechanism for stratosphere–troposphere exchange. In this work, we show new observational evidence on the role of this process in moistening the lowermost stratosphere. The new measurement, obtained from the Spatial Heterodyne Observations of Water (SHOW) instrument during a demonstration flight on the NASA's ER-2 high-altitude research aircraft, captured an event of poleward water vapour transport, including a fine-scale (vertically <∼1 km) moist filament above the local tropopause in a high-spatial-resolution two-dimensional cross section of the water vapour distribution. Analysis of these measurements combined with ERA5 reanalysis data reveals that this poleward mixing of air with enhanced water vapour occurred in the region of a double tropopause following a large Rossby wave-breaking event. These new observations highlight the importance of high-resolution measurements in resolving processes that are important to the lowermost-stratosphere water vapour budget.

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Stratospheric water vapor: an important climate feedback

Cited by 66 publications

References 55 publications

The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere

The Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere

The Impact of Prescribed Ozone in Climate Projections Run With HadGEM3‐GC3.1

Observational evidence of moistening the lowermost stratosphere via isentropic mixing across the subtropical jet

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