Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

Stevens, Björn; Brogniez, Hélène; Kiemle, Christoph; Lacour, Jean‐Lionel; Crévoisier, Cyril; Kiliani, Johannes

doi:10.1007/978-3-319-77273-8_10

Cited by 17 publications

(27 citation statements)

References 44 publications

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“…MODIS‐Terra provides estimates of the TCWV, which are concurrent with ASTER observations and are therefore used in the present study. Changes in TCWV are largely determined by water vapor located between the top of the well‐mixed subcloud layer and the height of the triple‐point isotherm (Stevens et al., ). An increase especially in water vapor above cloud tops can increase the absorption of outgoing longwave radiation and thus change the temperature profile, cloud top subsidence, and cloud top entrainment rates, all leading to a change in cloud field properties (Myers & Norris, ).…”

Section: Relations Of Cloud Field Properties To Large‐scale Meteorolomentioning

confidence: 99%

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The Dependence of Shallow Cumulus Macrophysical Properties on Large‐Scale Meteorology as Observed in ASTER Imagery

et al. 2019

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This study identifies meteorological variables that control the macrophysical properties of shallow cumulus cloud fields over the tropical ocean. We use 1,158 high‐resolution Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) images to derive properties of shallow cumuli, such as their size distribution, cloud top heights, fractal dimensions, and spatial organization, as well as cloud amount. The large‐scale meteorology is characterized by the lower‐tropospheric stability, subsidence rate, sea surface temperature, total column water vapor, wind speed, wind shear, and Bowen ratio. The surface wind speed emerges as the most powerful control factor. With increasing wind speed the cloud amount and cloud top heights show a robust increase accompanied by a marked shift in the cloud size distribution toward larger clouds with smoother shapes. These results lend observational support to the deepening response of a wind‐driven marine boundary layer as simulated by large‐eddy models. The other control factors cause smaller changes in the cloud field properties. We find a robust increase in cloud amount with increasing stability and decreasing sea surface temperature, respectively, which confirms a well‐known behavior of marine stratocumulus also for shallow cumulus clouds. Due to the high resolution of cloud images, we are able to study the lower end of the cloud size distribution and find a robust double power law behavior with a scale break at 590 m. We find a variation in the shape of the cloud size distribution with Bowen ratio, qualitatively consistent with modeling results and suggesting the Bowen ratio as a new potential control factor on shallow cumulus clouds.

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Section: Relations Of Cloud Field Properties To Large‐scale Meteorolomentioning

confidence: 99%

“…Concerning the influence of humidity, Stevens et al. () point to the regulating role of water vapor and its distribution in the tropical lower troposphere on cloud patterns. Furthermore, prevailing surface easterly winds are a prominent feature of subtropical regions over ocean, which are often called the trades or trade wind region.…”

Section: Introductionmentioning

confidence: 99%

The Dependence of Shallow Cumulus Macrophysical Properties on Large‐Scale Meteorology as Observed in ASTER Imagery

et al. 2019

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“…The revision has little effect on the ∆ CT F SW and ∆ CB F LW but considerably influences the dominant term, ∆ CT F LW . The original reanalysis sounding gives a ∆ CT F LW = 149 W/m 2 , which is severely biased due to too dry overlying air (Mapes & Zuidema, ; Siems et al, ; Stevens et al, ; Wood, ). The revised ∆ CT F LW of 102 W/m 2 is closer to the radiosonde‐based value of 107 W/m 2 .…”

Section: Estimation Of Ctrc Using Satellite and Reanalysis Datamentioning

confidence: 99%

Satellite‐Based Estimation of Cloud Top Radiative Cooling Rate for Marine Stratocumulus

Zheng

Zhu

2019

Geophysical Research Letters

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Cloud top radiative cooling rate (CTRC) is the leading term in the energy budget of a marine boundary layer capped by stratocumulus. It plays a significant role in the formation, evolution, and maintenance of the stratocumulus cloud system. This study demonstrates the feasibility of estimating the CTRC, with high accuracy, from passive satellite data only. The estimation relies on a radiative transfer model with inputs from satellite‐retrieved cloud parameters in combination with reanalysis sounding that is revised, in a physically coherent way, by satellite data. The satellite‐based estimates CTRC agree with ground‐based ones to within ~10%. The high accuracy largely benefits from the good capability of satellite data in constraining parameters of most influence to the CTRC such as free‐tropospheric sounding, cloud top temperature, and cloud optical depth. Applying this technique, we generate a climatology of CTRC during summer over the Southern Hemisphere tropical and subtropical oceans.

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“…However, global climate models (GCMs) have difficulties in properly capturing continental humidity conditions (Sherwood et al, 2010;Risi et al, 2012;Fischer and Knutti, 2013). Although tropospheric RH results from a subtle balance between different processes (including air mass origins and trajectories, large-scale radiative subsidence, evaporation of falling precipitation, detrainment of convective system, evapotranspiration), it is usually depicted as rather constant in GCMs, in agreement with thermodynamic coupling between atmospheric water vapor and sea surface temperature (Bony et al, 2006;Stevens et al, 2017). A model-data comparison approach is thus essential to progress on this issue.…”

Section: Introductionmentioning

confidence: 99%

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

et al. 2018

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Abstract. Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model-data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17 O-excess ( 17 O-excess = ln (δ 17 O + 1) -0.528 × ln (δ 18 O + 1)), in water, water vapor and minerals. The 17 O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17 O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17 O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40 % decreases the 17 Oexcess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17 O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17 O-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17 O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.

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Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

Cited by 17 publications

References 44 publications

The Dependence of Shallow Cumulus Macrophysical Properties on Large‐Scale Meteorology as Observed in ASTER Imagery

The Dependence of Shallow Cumulus Macrophysical Properties on Large‐Scale Meteorology as Observed in ASTER Imagery

Satellite‐Based Estimation of Cloud Top Radiative Cooling Rate for Marine Stratocumulus

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

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