The Effects of Deep Convection on Regional Temperature Structure in the Tropical Upper Troposphere and Lower Stratosphere

Johnston, Benjamin R.; Xie, Feiqin; Liu, Chuntao

doi:10.1002/2017jd027120

Cited by 27 publications

(32 citation statements)

References 47 publications

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“…There are many processes that are likely to contribute to TTL temperature variability on sub-monthly timescales. The shortest timescales are likely to be associated with gravity waves generated by convection, with a strong diurnal component (particularly over land) and deep convection (Maritime Continent and West Pacific Ocean) at daily timescales (Johnston et al, 2018); the spatial pattern of regions with higher sub-monthly temperature variability in Fig. 8b appears to be consistent with this.…”

Section: Role Of Sub-seasonal Time Variability In Tropopause Temperaturesupporting

confidence: 55%

Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport

Smith¹,

Haynes²,

Maycock³

et al. 2020

Preprint

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Abstract. Concentrations of water vapour entering the tropical lower stratosphere are primarily determined by conditions that air parcels encounter as they are transported through the tropical tropopause layer (TTL). Here we quantify the relative roles of variations in TTL temperatures and transport in determining seasonal and interannual variations of stratospheric water vapour. Following previous studies, we use trajectory calculations with the water vapour concentration set by the Lagrangian Dry Point along trajectories. To isolate the roles of transport and temperatures, the Lagrangian Dry Point calculations are modified by time-shifting temperatures relative to transport, and vice versa, with the shift made by years to investigate interannual variations and by months to investigate seasonal variations. Both ERA-Interim reanalysis data for the 1999–2009 period and data generated by a chemistry-climate model (UM-UKCA) are investigated. Variations in temperatures, rather than transport, dominate interannual variability, typically explaining more than 70 % of variability, including individual events such as the 2000 stratospheric water vapour drop. Similarly seasonal variation of temperatures, rather than transport, is shown to be the dominant driver of the annual cycle in lower stratospheric water vapour concentrations in both model and reanalysis, but it is also shown that seasonal variation of transport plays an important role in reducing the seasonal cycle maximum (reducing the annual range by about 30 %). The quantitative role in dehydration of sub-seasonal and sub-monthly Eulerian temperature variability is also examined by using time-filtered temperature fields in the trajectory calculations. Sub-monthly temperature variability reduces annual mean water vapour concentrations by 40 % in the reanalysis calculation and 30 % in the model calculation. These results indicate that, whilst capturing seasonal and interannual variation of temperature is a major factor in modelling realistic stratospheric water vapour concentrations, simulation of seasonal variation of transport and of sub-seasonal and sub-monthly temperature variability are also important and cannot be ignored.

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Section: Role Of Sub-seasonal Time Variability In Tropopause Temperaturesupporting

confidence: 55%

Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport

Smith¹,

Haynes²,

Maycock³

et al. 2020

Preprint

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“…Furthermore, this cooling must take place without abundant effective ice nuclei. Africa and South America are also the locus of strong winter convection associated with the diurnal cycle of surface heating (Carminati et al, ; Johnston et al, ; Khaykin et al, ). These regions will be the subject of future analyses.…”

Section: Introductionmentioning

confidence: 99%

Water Vapor, Clouds, and Saturation in the Tropical Tropopause Layer

et al. 2019

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The goal of this investigation is to understand the mechanism behind the observed high relative humidity with respect to ice (RHi) in the tropical region between ~14 km (150 hPa) and the tropopause, often referred to as the tropical tropopause layer (TTL). As shown by satellite, aircraft, and balloon observations, high (>80%) RHi regions are widespread within the TTL. Regions with the highest RHi are colocated with extensive cirrus. During boreal winter, the TTL RHi is highest over the Tropical Western Pacific (TWP) with a weaker maximum over South America and Africa. In the winter, TTL temperatures are coldest and upward motion is the greatest in the TWP. It is this upward motion, driving humid air into the colder upper troposphere that produces the persistent high RHi and cirrus formation. Back trajectory calculations show that comparable adiabatic and diabatic processes contribute to this upward motion. We construct a bulk model of TWP TTL water vapor transport that includes cloud nucleation and ice microphysics that quantifies how upward motion drives the persistent high RHi in the TTL region. We find that atmospheric waves triggering cloud formation regulate the RHi and that convection dehydrates the TTL. Our forward domain‐filling trajectory model is used to more precisely simulate the TTL spatial and vertical distribution of RHi. The observed RHi distribution is reproduced by the model, and we show that convection increases RHi below the base of the TTL with little impact on the RHi in the TTL region.

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“…essentially by the inertia of upwelling air) and gravity waves generated by deep convection (Yu et al 2019) may therefore be important for a part of the annual mean indirect flow in the lower stratosphere. This view is supported by observations that link cold anomalies at the tropical tropopause to deep convection (Gettelman et al 2002;Schoeberl et al 2019;Johnston et al 2018). On the other hand, even models that have no convection up to the cold point manage to describe the thermal structure of this region well (Gettelman and Birner 2007).…”

Section: Discussionmentioning

confidence: 62%

Thermodynamic cycles in the stratosphere

Nycander¹,

Ruggieri²,

Ambaum³

2021

Preprint

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<p>Large-scale overturning mass transport in the stratosphere is commonly explained through the action of potential vorticity (PV) rearrangement in the flank of the stratospheric jet. Large-scale Rossby waves, with their wave activity source primarily in the troposphere, stir and mix PV and an overturning circulation arises to compensate for the zonal torque imposed by the breaking waves. In this view, any radiative heating is relaxational and the circulation is mechanically driven. Here we present a fully thermodynamic analysis of these phenomena, based on ERA-Interim data. Streamfunctions in a thermodynamic, log(pressure) &#8211; temperature space are computed. The sign of a circulation cell in these coordinates directly shows whether it is mechanically driven, converting kinetic energy to potential and thermal energy, or thermally driven, with the opposite conversion. The circulation in the lower stratosphere is found to be thermodynamically indirect (i.e., mechanically driven). In the middle and upper stratosphere thermodynamically indirect and direct circulations coexist, with a prominent semiannual cycle. A part of the overturning in this region is thermally driven, while a more variable indirect circulation is mechanically driven by waves. The wave driving does not modulate the strength of the thermally direct part of the circulation. This suggests that the basic overturning circulation in the stratosphere is largely thermally driven, while tropospheric waves add a distinct indirect component to the overturning. This indirect overturning is associated with poleward transport of anomalously warm air parcels.</p>

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The Effects of Deep Convection on Regional Temperature Structure in the Tropical Upper Troposphere and Lower Stratosphere

Cited by 27 publications

References 47 publications

Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport

Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport

Water Vapor, Clouds, and Saturation in the Tropical Tropopause Layer

Thermodynamic cycles in the stratosphere

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