Hydration or dehydration: competing effects of upper tropospheric cloud radiation on the TTL water vapor

Abstract. A tropical channel version of the Weather Research and Forecasting (WRF) model is used to investigate the radiative impacts of upper tropospheric clouds on water vapor in the tropical tropopause layer (TTL). The WRF simulations of cloud radiative effects and water vapor in the upper troposphere and lower stratosphere show reasonable agreement with observations, including approximate reproduction of the water vapor "tape recorder" signal. By turning on and off the upper tropospheric cloud radiative effect (UTCRE) above 200 hPa, we find that the UTCRE induces a warming of 0.76 K and a moistening of 9% in the upper troposphere at 215 hPa. However, the UTCRE cools and dehydrates the TTL, with a cooling of 0.82 K and a dehydration of 16% at 100 hPa. The enhanced vertical ascent due to the UTCRE contributes substantially to mass transport and the dehydration in the TTL. The hydration due to the enhanced vertical transport is counteracted by the dehydration from adiabatic cooling associated with the enhanced vertical motion. The UTCRE also substantially changes the horizontal winds in the TTL, resulting in shifts of the strongest dehydration away from the lowest temperature anomalies in the TTL. The UTCRE increases in-situ cloud formation in the TTL. A seasonal variation is shown in the simulated UTCRE, with stronger impact in the moist phase from June to November than in the dry phase from December to May.

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Hydration or dehydration: competing effects of upper tropospheric cloud radiation on the TTL water vapor

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-7727-2012 ◽

2012 ◽

Vol 12 (16) ◽

pp. 7727-7735 ◽

Cited By ~ 11

Author(s):

L. Wu ◽

H. Su ◽

J. H. Jiang ◽

W. G. Read

Keyword(s):

Water Vapor ◽

Wrf Model ◽

Vertical Motion ◽

Cloud Formation ◽

Upper Troposphere ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Cloud Radiative Effect ◽

Adiabatic Cooling ◽

Cloud Radiative Effects

Abstract. A tropical channel version of the Weather Research and Forecasting (WRF) model is used to investigate the radiative impacts of upper tropospheric clouds on water vapor in the tropical tropopause layer (TTL). The WRF simulations of cloud radiative effects and water vapor in the upper troposphere and lower stratosphere show reasonable agreement with observations, including approximate reproduction of the water vapor "tape recorder" signal. By turning on and off the upper tropospheric cloud radiative effect (UTCRE) above 200 hPa, we find that UTCRE induces a warming of 0.76 K and a moistening of 9% in the upper troposphere at 215 hPa. However, UTCRE cools and dehydrates the TTL, with a cooling of 0.82 K and a dehydration of 16% at 100 hPa. The enhanced vertical ascent due to UTCRE contributes substantially to mass transport and the dehydration in the TTL. The hydration due to the enhanced vertical transport is counteracted by the dehydration from adiabatic cooling associated with the enhanced vertical motion. UTCRE also substantially changes the horizontal winds in the TTL, resulting in shifts of the strongest dehydration away from the lowest temperature anomalies in the TTL. UTCRE increases in-situ cloud formation in the TTL. A seasonal variation is shown in the simulated UTCRE, with stronger impact in the moist phase from June to November than in the dry phase from December to May.

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Signals of El Niño Modoki in the tropical tropopause layer and stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-3619-2012 ◽

2012 ◽

Vol 12 (2) ◽

pp. 3619-3653 ◽

Cited By ~ 1

Author(s):

F. Xie ◽

J. Li ◽

W. Tian ◽

J. Feng

Keyword(s):

Water Vapor ◽

High Latitude ◽

El Niño ◽

El Nino ◽

Polar Vortex ◽

Upper Troposphere ◽

Tropical Tropopause Layer ◽

El Niño Modoki ◽

Tropical Tropopause ◽

Northern Pacific

Abstract. The effects of El Niño Modoki events on the tropical tropopause layer (TTL) and on the stratosphere were investigated using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis data, satellite observations from the Aura satellite Microwave Limb Sounder (MLS), oceanic El Niño indices, and general climate model outputs. El Niño Modoki events tend to depress convective activities in the western and eastern Pacific but enhance convective activities in the central and northern Pacific. Consequently, during Modoki events, negative water vapor anomalies occur in the western and eastern Pacific upper troposphere, whereas there are positive anomalies in the central and northern Pacific upper troposphere. The spatial patterns of the outgoing longwave radiation (OLR) and upper tropospheric water vapor anomalies exhibit a tripolar form. The empirical orthogonal function (EOF) analysis of the OLR and upper tropospheric water vapor anomalies reveals that canonical El Niño events are associated with the leading mode of the EOF, while El Niño Modoki events correspond to the second mode. El Niño Modoki activities tend to moisten the lower and middle stratosphere, but dry the upper stratosphere. It was also found that the canonical El Niño signal can overlay linearly on the QBO signal in the stratosphere, whereas the interaction between the El Niño Modoki and QBO signals is non-linear. Because of these non-linear interactions, El Niño Modoki events have a reverse effect on high latitudes stratosphere, as compared with the effects of typical Modoki events, i.e. the northern polar vortex is stronger and colder but the southern polar vortex is weaker and warmer during El Niño Modoki events. However, simulations suggest that canonical El Niño and El Niño Modoki activities actually have the same influence on high latitudes stratosphere, in the absence of interactions between QBO and ENSO signals. The present results also reveal that canonical El Niño events have a greater impact on the high-latitude Northern Hemisphere stratosphere than on the high-latitude Southern Hemisphere stratosphere. However, El Niño Modoki events can more profoundly influence the high-latitude Southern Hemisphere stratosphere than the high-latitude Northern Hemisphere stratosphere.

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Coordinated Upper-Troposphere-to-Stratosphere Balloon Experiment in Biak

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-16-0289.1 ◽

2018 ◽

Vol 99 (6) ◽

pp. 1213-1230 ◽

Cited By ~ 5

Author(s):

F. Hasebe ◽

S. Aoki ◽

S. Morimoto ◽

Y. Inai ◽

T. Nakazawa ◽

...

Keyword(s):

Water Vapor ◽

Climate Models ◽

Turnover Time ◽

Tape Recorder ◽

Climate Forcing ◽

Upper Troposphere ◽

Tropical Tropopause Layer ◽

Stratospheric Water Vapor ◽

Tropical Tropopause ◽

Balloon Experiment

AbstractThe stratospheric response to climate forcing, such as an increase in greenhouse gases, is often unpredictable because of interactions between radiation, dynamics, and chemistry. Climate models are unsuccessful in simulating the realistic distribution of stratospheric water vapor. The long-term trend of the stratospheric age of air (AoA), a measure that characterizes the stratospheric turnover time, remains inconsistent between diagnoses in climate models and estimates from tracer observations. For these reasons, observations designed specifically to distinguish the effects of individual contributing processes are required. Here, we report on the Coordinated Upper-Troposphere-to-Stratosphere Balloon Experiment in Biak (CUBE/Biak), an observation campaign organized in Indonesia. Being inside the “tropical pipe” makes it possible to study the dehydration in the tropical tropopause layer and the gradual ascent in the stratosphere while minimizing the effects of multiple circulation pathways and wave mixing. Cryogenic sampling of minor constituents and major isotopes was conducted simultaneously with radiosonde observations of water vapor, ozone, aerosols, and cloud particles. The water vapor “tape recorder,” gravitational separation, and isotopocules are being studied in conjunction with tracers that are accumulated in the atmosphere as dynamical and chemical measures of elapsed time since stratospheric air entry. The observational estimates concerning the AoA and water vapor tape recorder are compared with those derived from trajectory calculations.

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The Impact of Cloud Radiative Effects on the Tropical Tropopause Layer Temperatures

Atmosphere ◽

10.3390/atmos9100377 ◽

2018 ◽

Vol 9 (10) ◽

pp. 377 ◽

Cited By ~ 4

Author(s):

Qiang Fu ◽

Maxwell Smith ◽

Qiong Yang

Keyword(s):

Maximum Temperature ◽

Radiative Effects ◽

Heating Rates ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Cloud Radiative Effect ◽

Single Column ◽

Cloud Radiative Effects ◽

Cold Point ◽

The Impact

A single-column radiative-convective model (RCM) is a useful tool to investigate the physical processes that determine the tropical tropopause layer (TTL) temperature structures. Previous studies on the TTL using the RCMs, however, omitted the cloud radiative effects. In this study, we examine the impact of cloud radiative effects on the simulated TTL temperatures using an RCM. We derive the cloud radiative effects based on satellite observations, which show heating rates in the troposphere but cooling rates in the stratosphere. We find that the cloud radiative effect warms the TTL by as much as 2 K but cools the lower stratosphere by as much as −1.5 K, resulting in a thicker TTL. With (without) considering cloud radiative effects, we obtain a convection top of ≈167 hPa (≈150 hPa) with a temperature of ≈213 K (≈209 K), and a cold point at ≈87 hPa (≈94 hPa) with a temperature of ≈204 K (≈204 K). Therefore, the cloud radiative effects widen the TTL by both lowering the convection-top height and enhancing the cold-point height. We also examine the impact of TTL cirrus radiative effects on the RCM-simulated temperatures. We find that the TTL cirrus warms the TTL with a maximum temperature increase of ≈1.3 K near 110 hPa.

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Modeling upper tropospheric and lower stratospheric water vapor anomalies

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-9653-2013 ◽

2013 ◽

Vol 13 (4) ◽

pp. 9653-9679 ◽

Cited By ~ 1

Author(s):

M. R. Schoeberl ◽

A. E. Dessler ◽

T. Wang

Keyword(s):

Water Vapor ◽

Lower Stratosphere ◽

Calculation Model ◽

Vapor Concentration ◽

Cold Temperatures ◽

Tropical Tropopause Layer ◽

Stratospheric Water Vapor ◽

Tropical Tropopause ◽

Minimum Displacement ◽

Asian Monsoons

Abstract. The domain-filling, forward trajectory calculation model developed by Schoeberl and Dessler (2011) is used to further investigate processes that produce upper tropospheric and lower stratospheric water vapor anomalies. We examine the pathways parcels take from the base of the tropical tropopause layer (TTL) to the lower stratosphere. Most parcels found in the lower stratosphere arise from East Asia, the Tropical West Pacific (TWP) and the Central/South America. The belt of TTL parcel origins is very wide compared to the final dehydration zones near the top of the TTL. This is due to the convergence of rising air as a result of the stronger diabatic heating near the tropopause relative to levels above and below. The observed water vapor anomalies – both wet and dry – correspond to regions where parcels have minimal displacement from their initialization. These minimum displacement regions include the winter TWP and the Asian and American monsoons. To better understand the stratospheric water vapor concentration we introduce the water vapor spectrum and investigate the source of the wettest and driest components of the spectrum. We find that the driest air parcels that originate below the TWP, moving upward to dehydrate in the TWP cold upper troposphere. The wettest air parcels originate at the edges of the TWP as well as the summer American and Asian monsoons. The wet air parcels are important since they skew the mean stratospheric water vapor distribution toward higher values. Both TWP cold temperatures that produce dry parcels as well as extra-TWP processes that control the wet parcels determine stratospheric water vapor.

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Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-10565-2020 ◽

2020 ◽

Vol 20 (17) ◽

pp. 10565-10586

Author(s):

Stephanie Evan ◽

Jerome Brioude ◽

Karen Rosenlof ◽

Sean M. Davis ◽

Holger Vömel ◽

...

Keyword(s):

Water Vapor ◽

Indian Ocean ◽

Tropical Cyclones ◽

Austral Summer ◽

Lagrangian Model ◽

Southwest Indian Ocean ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Tropopause Region ◽

The Impact

Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.

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The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-6467-2015 ◽

2015 ◽

Vol 15 (11) ◽

pp. 6467-6486 ◽

Cited By ~ 21

Author(s):

W. Frey ◽

R. Schofield ◽

P. Hoor ◽

D. Kunkel ◽

F. Ravegnani ◽

...

Keyword(s):

Lower Stratosphere ◽

Deep Convection ◽

Horizontal Resolution ◽

Transport Processes ◽

Convective System ◽

Upper Troposphere ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Transport And Mixing ◽

The Impact

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of 50 ppbv. However, the passive carbon monoxide tracer exhibits an increase, while the observations show a decrease of about 10 ppbv, indicative of an erroneous model representation of the transport processes in the tropical tropopause layer. Furthermore, it could point to insufficient entrainment and detrainment in the model. The simulation shows a general moistening of air in the lower stratosphere, but it also exhibits local dehydration features. Here we use the model to explain the processes causing the transport and also expose areas of inconsistencies between the model and observations.

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A model of HDO in the tropical tropopause layer

Atmospheric Chemistry and Physics ◽

10.5194/acp-3-2173-2003 ◽

2003 ◽

Vol 3 (6) ◽

pp. 2173-2181 ◽

Cited By ~ 47

Author(s):

A. E. Dessler ◽

S. C. Sherwood

Keyword(s):

Water Vapor ◽

Isotopic Composition ◽

Vertical Profile ◽

Tropical Tropopause Layer ◽

Physical Constraints ◽

Dry Air ◽

Tropical Tropopause

Abstract. Any theory of water vapor in the tropical tropopause layer (TTL) must explain both the abundance and isotopic composition of water there. In previous papers, we presented a model of the TTL that simulated the abundance of water vapor as well as the details of the vertical profile. That model included the effects of "overshooting" convection, which injects dry air directly into the TTL. Here, we present results for the model after modifying it to include water's stable isotopologue HDO (where D represents deuterium, 2H). We find that the model predicts a nearly uniform HDO depletion throughout the TTL, in agreement with recent measurements. This occurs because the model dehydrates by dilution, which does not fractionate, instead of by condensation. Our model shows that this dehydration by dilution is consistent with other physical constraints on the system. We also show the key role that lofted ice plays in determining the abundance of HDO in the TTL. Such lofted ice requires a complementary source of dry air in the TTL; without that, the TTL will rapidly saturate and the lofted ice will not evaporate.

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A 1D RCE Study of Factors Affecting the Tropical Tropopause Layer and Surface Climate

Journal of Climate ◽

10.1175/jcli-d-18-0778.1 ◽

2019 ◽

Vol 32 (20) ◽

pp. 6769-6782 ◽

Cited By ~ 7

Author(s):

Sally Dacie ◽

Lukas Kluft ◽

Hauke Schmidt ◽

Bjorn Stevens ◽

Stefan A. Buehler ◽

...

Keyword(s):

Water Vapor ◽

Climate Models ◽

Temperature Response ◽

Global Climate Models ◽

Lapse Rate ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Surface Climate ◽

Ozone Profile ◽

Convective Adjustment

Abstract There are discrepancies between global climate models regarding the evolution of the tropical tropopause layer (TTL) and also whether changes in ozone impact the surface under climate change. We use a 1D clear-sky radiative–convective equilibrium model to determine how a variety of factors can affect the TTL and how they influence surface climate. We develop a new method of convective adjustment, which relaxes the temperature profile toward the moist adiabat and allows for cooling above the level of neutral buoyancy. The TTL temperatures in our model are sensitive to CO2 concentration, ozone profile, the method of convective adjustment, and the upwelling velocity, which is used to calculate a dynamical cooling rate in the stratosphere. Moreover, the temperature response of the TTL to changes in each of the above factors sometimes depends on the others. The surface temperature response to changes in ozone and upwelling at and above the TTL is also strongly amplified by both stratospheric and tropospheric water vapor changes. With all these influencing factors, it is not surprising that global models disagree with regard to TTL structure and evolution and the influence of ozone changes on surface temperatures. On the other hand, the effect of doubling CO2 on the surface, including just radiative, water vapor, and lapse-rate feedbacks, is relatively robust to changes in convection, upwelling, or the applied ozone profile.

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