The Impacts of Convection on Upper-tropospheric and Lower-stratospheric Water Vapor PDF Download
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Author: Jing Feng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Upper-tropospheric and lower-stratospheric (UTLS) water vapor plays an essential role in controlling the outgoing longwave radiation. Convection can affect UTLS water vapor through cross-tropopause transport and by modulating the tropopause temperature. However, this mechanism remains poorly quantified due to a lack of observations above convective storms. In this thesis, we aim to understand the role of convection in shaping the UTLS humidity structure by developing a novel retrieval method.Firstly, we develop a cloud-assisted retrieval method to obtain thermodynamic fields above a thick cloud layer using hyperspectral infrared observations. Based on the Optimal Estimation approach, this method iteratively retrieves temperature and water vapor profiles above a thick cloud layer, which is approximated as a slab with uniform ice density. The retrievability of water vapor is examined by using simulations that represent different instrument settings. These experiments demonstrate that observations from operational infrared sounders, such as AIRS and IASI, contain considerable information for retrieving UTLS water vapor above thick clouds. Interestingly, we find that the underlying cloud layer improves the performance of the retrieval method, compared to clear-sky conditions. Using AIRS observations, further validation with collocated aircraft data shows that this method can detect the elevated water vapor concentration due to convective moistening.We further discover that the cloud properties near the top of convective clouds lead to non-negligible spectral uncertainties in infrared radiances. These uncertainties can be alleviated, but not fully eliminated, by assuming a slab-cloud as in the cloud-assisted retrieval. To overcome this issue, we develop a synergistic method, which incorporates observations from active sensors and nearest reanalysis products in synergy with hyperspectral infrared observations. The improved synergistic method retrieves temperature, water vapor, and cloud properties simultaneously. A simulation experiment is designed to investigate whether retrieval methods can capture anomalous atmospheric conditions above deep convective clouds using existing instruments. We find that the synergistic method reduces the root-mean-square-errors in temperature and column-integrated water vapor by more than half and accurately reproduces the spatial distribution of temperature and humidity anomalies above convective storms.Finally, we implement the improved method by combining infrared radiance observations from AIRS L1B product, ice water content (IWC) profile and effective radius from DARDAR-Cloud, and also atmospheric profiles from ERA5 in the nearest grid. Applying this method to satellite overpasses over tropical cyclones (TCs), we construct a dataset that contains retrieved temperature, humidity above TCs. With a focus on the tropical tropopause layer (TTL), the influence of tropical cyclones on the TTL is investigated by creating composites of temperature, humidity, IWC, and radiative heating rates with respect to the distance to the cyclone centers. We find that overshooting convective clouds (DCC-OTs) greatly impact the TTL water budget. DCC-OTs contribute to 80% of the TTL cloud ice above cyclones and increase the column-integrated water vapor above the tropopause by up to 40% compared to the climatology. Other non-overshooting TTL clouds are found to be collocated with TTL temperature minimum and dehydration. Overall, the synergistic retrieval reveals that cyclones increase the stratospheric humidity above them. However, further radiative transfer calculations show that the increased moisture is typically associated with radiative cooling of the TTL, which inhibits the diabatic ascent of the moistened air. Therefore, the radiative balance of the TTL under the impact of the cyclone is not in favor of maintaining the moist anomalies in the TTL or transporting water vertically to the stratosphere"--
Author: Jing Feng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Upper-tropospheric and lower-stratospheric (UTLS) water vapor plays an essential role in controlling the outgoing longwave radiation. Convection can affect UTLS water vapor through cross-tropopause transport and by modulating the tropopause temperature. However, this mechanism remains poorly quantified due to a lack of observations above convective storms. In this thesis, we aim to understand the role of convection in shaping the UTLS humidity structure by developing a novel retrieval method.Firstly, we develop a cloud-assisted retrieval method to obtain thermodynamic fields above a thick cloud layer using hyperspectral infrared observations. Based on the Optimal Estimation approach, this method iteratively retrieves temperature and water vapor profiles above a thick cloud layer, which is approximated as a slab with uniform ice density. The retrievability of water vapor is examined by using simulations that represent different instrument settings. These experiments demonstrate that observations from operational infrared sounders, such as AIRS and IASI, contain considerable information for retrieving UTLS water vapor above thick clouds. Interestingly, we find that the underlying cloud layer improves the performance of the retrieval method, compared to clear-sky conditions. Using AIRS observations, further validation with collocated aircraft data shows that this method can detect the elevated water vapor concentration due to convective moistening.We further discover that the cloud properties near the top of convective clouds lead to non-negligible spectral uncertainties in infrared radiances. These uncertainties can be alleviated, but not fully eliminated, by assuming a slab-cloud as in the cloud-assisted retrieval. To overcome this issue, we develop a synergistic method, which incorporates observations from active sensors and nearest reanalysis products in synergy with hyperspectral infrared observations. The improved synergistic method retrieves temperature, water vapor, and cloud properties simultaneously. A simulation experiment is designed to investigate whether retrieval methods can capture anomalous atmospheric conditions above deep convective clouds using existing instruments. We find that the synergistic method reduces the root-mean-square-errors in temperature and column-integrated water vapor by more than half and accurately reproduces the spatial distribution of temperature and humidity anomalies above convective storms.Finally, we implement the improved method by combining infrared radiance observations from AIRS L1B product, ice water content (IWC) profile and effective radius from DARDAR-Cloud, and also atmospheric profiles from ERA5 in the nearest grid. Applying this method to satellite overpasses over tropical cyclones (TCs), we construct a dataset that contains retrieved temperature, humidity above TCs. With a focus on the tropical tropopause layer (TTL), the influence of tropical cyclones on the TTL is investigated by creating composites of temperature, humidity, IWC, and radiative heating rates with respect to the distance to the cyclone centers. We find that overshooting convective clouds (DCC-OTs) greatly impact the TTL water budget. DCC-OTs contribute to 80% of the TTL cloud ice above cyclones and increase the column-integrated water vapor above the tropopause by up to 40% compared to the climatology. Other non-overshooting TTL clouds are found to be collocated with TTL temperature minimum and dehydration. Overall, the synergistic retrieval reveals that cyclones increase the stratospheric humidity above them. However, further radiative transfer calculations show that the increased moisture is typically associated with radiative cooling of the TTL, which inhibits the diabatic ascent of the moistened air. Therefore, the radiative balance of the TTL under the impact of the cyclone is not in favor of maintaining the moist anomalies in the TTL or transporting water vertically to the stratosphere"--
Author: Jonathon S. Wright
Publisher:
ISBN:
Category : Convection (Meteorology)
Languages : en
Pages :
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Book Description
Factors governing the efficiency of convective moistening in the tropical upper troposphere between 15°Sand 15°N are investigated using observational satellite data together with a trajectory model. In particular, the relative roles of ambient temperature, convective ice water content, ice cloud effective radius, and ambient relative humidity with respect to ice are examined. Results indicate that humidity downstream from convection is dominated by temperature influences. The correlation between water vapor content and coldest previous temperature along the trajectory accounts for about half of water vapor variance. Cloud ice water content and ice cloud effective radius exert much less influence than temperature, but appear to be important secondary controls downstream. Ice is observed to both hydrate and dehydrate the upper troposphere, primarily as a function of ambient relative humidity; increases in water vapor mixing ratio are typically larger in areas with low ambient relative humidity, while convective detrainment tends to dehydrate regions of high ambient relative humidity. The limits of convective influence on water vapor in the upper troposphere are estimated to be about 36 hours and 600 km removed from convection, consistent with the lifetimes and travel distances of detrainment cirrus. Observations of water vapor are compared with the output of a simple model that includes only temperature influences on water vapor. The model and the observations are generally in good qualitative agreement, but the model is found to overpredict the occurrence of high humidities at all levels of detrainment. Potential applications and implications of these results are discussed.
Author: Jason R. Schroeder
Publisher:
ISBN: 9781339124100
Category :
Languages : en
Pages : 167
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Book Description
Measurements of trace gases were taken onboard the NASA DC-8 during the Deep Convective Clouds and Chemistry (DC3) field project with the goal of understanding the role that midlatitude deep convection plays in altering the vertical distribution of atmospherically-relevant species. Measurements of VOCs were obtained via UC Irvine’s whole air sampler (WAS) instrument, while measurements of CH4, O3, NOx [subscript], N2O, water vapor, CO, and meteorological variables were performed by a variety of other instruments operated by collaborators onboard the DC-8. Using known VOC atmospheric lifetimes and measured VOC mixing ratios in the PBL, a tracer for rapid vertical lofting of air from the planetary boundary layer (PBL) to the upper troposphere/lower stratosphere region (UT/LS) by convection was created. In this study, it was found that light hydrocarbons associated with oil and natural gas (O&NG;) and vehicular sources were widespread throughout the PBL of the DC3 study regions. In the UT/LS, enhanced levels of these light hydrocarbons were strongly correlated with water vapor, indicating a convective source. On the other hand, decreases in the measured mixing ratios of CFCs, HCFCs, and other long-lived halocarbons (LLHCs) in the UT were used as tracers for stratosphere-to-troposphere transport (STT). These two sets of tracers were used to divide the DC3 WAS merge into many subsets of data corresponding to: the PBL, convective outflow in the UT, convective outflow in the LS (i.e. overshooting tops), STT-influenced air in the troposphere, background UT air, and background LS air. Using these derived subsets of data, interactions and mixing between stratospheric intrusions and tropospheric air masses was investigated. A large number of stratospherically-influenced samples were found to have reduced levels of O3 and elevated levels of CO (both relative to background stratospheric air); indicative of mixing with anthropogenically-influenced air. Using n-butane and propane as tracers of anthropogenically-influenced air, it is shown that this type of mixing was present both at low altitudes and in the UT. At low altitudes, this mixing resulted in O3 enhancements consistent with those reported at surface sites during deep stratospheric intrusions, while in the UT, two case studies were performed to identify the process by which this mixing occurs. In the first case study, stratospheric air was found to be mixed with aged outflow from a convective storm, while in the second case study, stratospheric air was found to have mixed with outflow from an active storm occurring in the vicinity of a stratospheric intrusion. From these analyses, it was concluded that deep convective events may facilitate the mixing between stratospheric air and polluted boundary layer air in the UT. Throughout the entire DC3 study region, this mixing was found to be prevalent: 72% of all samples that involve stratosphere-troposphere mixing show influence of polluted air. Applying a simple chemical kinetics analysis to these data, it is shown that the instantaneous production of OH in these mixed stratospheric-polluted air masses was 11 ± 8 (± 1?) times higher than that of stratospheric air, and 4.2 ± 1.8 times higher than that of background upper tropospheric air, which could result in a quick, high magnitude pulse of O3 production and reduced lifetimes of OH-controlled species in the UT. These derived subsets of data were used to investigate the effects of deep convection on mixing ratios of organic chlorine and organic bromine in the UT and LS over the DC3 study region. In the LS, it was found that mixing ratios of organic chlorine in overshooting tops were higher than mixing ratios of organic chlorine in the background LS by an average of 217 ± 179 pptv (6.3 ± 5.2% enhancement), while the total organic bromine mixing ratio in overshooting tops was higher than that of the background LS by an average of 2.8 ± 3.2 pptv (17.4 ± 19.9% enhancement). In both cases, short-lived halocarbons made up a large portion of this enhancement. In the UT, convection was found to play a much more complicated role on the organic halogen content of the region. Model back trajectories and analysis of the chemical composition of the background UT revealed that long-range transport of outflow from East Asia and from the central Pacific affected the background UT of the DC3 study region to varying degrees on different days. When the background UT was affected by East Asian outflow, mixing ratios of organic chlorine in convective outflow were lower than those of the local background UT by up to 150 ± 115 pptv (3.7 ± 2.9% enhancement). On the other hand, when the background UT was affected by clean outflow from the central Pacific, mixing ratios of organic chlorine in convective outflow were higher than the local background UT by up to 115 ± 98 pptv (3.2 ± 2.6% enhancement). Mixing ratios of organic bromine in the background UT were unaffected by these long-range transport processes. However, mixing ratios of organic bromine in convective outflow were highly variable and were affected by the transport of brominated very short-lived halocarbons (VSLH) from the Gulf of Mexico to the surface of the DC3 study region. When organic bromine enhancements in convective outflow were calculated on a flight-by-flight basis, organic bromine mixing ratios in convective outflow were higher than those in the background UT by an average of 1.7 ± 1.6 pptv (8.5 ± 8.1%). Based on these results, it is speculated that deep convection may play an indirect role in climate change by introducing pulses of short-lived halocarbons into the UT/LS, which in turn result in relatively quick (on the order of a few months) pulses of O3 loss in the region.
Author: Mekonnen Gebremichael
Publisher: Springer Science & Business Media
ISBN: 904812915X
Category : Science
Languages : en
Pages : 327
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Book Description
With contributions from a panel of researchers from a wide range of fields, the chapters of this book focus on evaluating the potential, utility and application of high resolution satellite precipitation products in relation to surface hydrology.
Author: Helmut K. Weickmann
Publisher:
ISBN:
Category : Convection (Meteorology)
Languages : en
Pages : 44
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Book Description
Author: David G. Andrews
Publisher: Academic Press
ISBN: 0080954677
Category : Science
Languages : en
Pages : 502
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Book Description
For advanced undergraduate and beginning graduate students in atmospheric, oceanic, and climate science, Atmosphere, Ocean and Climate Dynamics is an introductory textbook on the circulations of the atmosphere and ocean and their interaction, with an emphasis on global scales. It will give students a good grasp of what the atmosphere and oceans look like on the large-scale and why they look that way. The role of the oceans in climate and paleoclimate is also discussed. The combination of observations, theory and accompanying illustrative laboratory experiments sets this text apart by making it accessible to students with no prior training in meteorology or oceanography. * Written at a mathematical level that is appealing for undergraduates and beginning graduate students * Provides a useful educational tool through a combination of observations and laboratory demonstrations which can be viewed over the web * Contains instructions on how to reproduce the simple but informative laboratory experiments * Includes copious problems (with sample answers) to help students learn the material.
Author: Kai (M.S. in statistics) Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 350
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Book Description
Convection and its interactions with transport of heat, water and momentum are essential in understanding many aspects of the climate system, for example, tracer transport in both the troposphere and lower stratosphere, the modelling of rainfall and prediction of climate change. The goal of this dissertation is to examine the role of convection variability in the related atmospheric composition transport and rainfall processes using both observations and climate models. The relationships between deep convection and the global diabatic heat budget are studied to understand the coupling between convection, temperature and general circulation. By examining the influence of convection on diabatic heating in the troposphere and stratosphere, we can gain a comprehensive understanding of the tropical convection and its influence on large-scale atmospheric circulation and stratosphere composition, especially on the cross-tropospuase transport of water vapor. We show that transient variability in deep convection is highly correlated with diabatic heating throughout the troposphere and stratosphere. Enhanced deep convection is linked to amplified heating in the tropical troposphere and in the mid-latitude storm tracks, tied to latent heat release. Enhanced convection is also linked to radiative cooling in the lower stratosphere, due to weaker upwelling longwave (LW) from lower altitudes. Transient deep convection modulates LW and shortwave (SW) radiation in the troposphere, with compensating effects that are linked to variations in cloud fraction and liquid and ice water content. Then we explore the variability of lower stratospheric (LS) water vapor in the Northern Hemisphere (NH) monsoon regions based on satellite observations and trajectory model simulations driven by diabatic heating in reanalyses. The links between stratospheric water vapor, fluctuations in deep convection and large-scale circulation and temperature are quantified. Results suggest that temperature plays a dominant role on water vapor variations with stronger convection leads to cold dehydration temperatures and a relatively dry stratosphere. Besides, the seasonal increase of stratospheric water vapor can be attributed to the geographic variations of convection and resultant variations of the dehydration center, of which the influence is comparable to the influence of the local dehydration temperature increase. Specifically, the seasonal geographic shift of the dehydration center from the east to the west Asian monsoon region with warmer tropopause temperatures could increase water vapor significantly. Dry biases over Southern Amazonia are observed in Community Atmosphere Model version 5 (CAM5). We use hindcast simulations to track the root causes for the biases. Results suggest that the dry bias is present by day 2 (24 to 48 hours) of model integrations and is very robust for all the seasons with largest bias magnitude during the southern summer (Dec-Feb, wet season). The near-surface-warm biases and low biases of humidity in the lower troposphere that exist since day 2 may be significant factors influencing the dry biases. The low biases of humidity are contributed by both physical components (shallow convective scheme and Zhang-McFarlane convective scheme, and maybe weak turbulence term), and dynamics (weak moisture convergence). We further evaluate the CAM5 with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework, referred as the "super-parameterization" (SP) with two different microphysics configurations to investigate their influences on rainfall simulations over Southern Amazonia. The two different microphysics configurations in SP are the one-moment cloud microphysics without aerosol treatment (SP1) and two-moment cloud microphysics coupled with aerosol treatment (SP2). Results show that both SP2 and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season, and reduce low biases of humidity in the lower troposphere with further reduced shallow clouds and increased surface solar flux. These changes increase moist static energy, contribute to stronger convection and more rainfall. SP2 appears to realistically capture the observed increase of relative humidity prior to deep convection and it significantly increases rainfall in the afternoon; CLUBB significantly delays the afternoon peak time and produces more precipitation in the early morning, due to more gradual transition between shallow and deep convection. In CAM5 and CAM5 with CLUBB, occurrence of deep convection appears to be a result of stronger heating rather than higher relative humidity.
Author: Daniel J. Jacob
Publisher: Princeton University Press
ISBN: 0691001855
Category : Nature
Languages : en
Pages : 280
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Book Description
Atmospheric chemistry is one of the fastest growing fields in the earth sciences. Until now, however, there has been no book designed to help students capture the essence of the subject in a brief course of study. Daniel Jacob, a leading researcher and teacher in the field, addresses that problem by presenting the first textbook on atmospheric chemistry for a one-semester course. Based on the approach he developed in his class at Harvard, Jacob introduces students in clear and concise chapters to the fundamentals as well as the latest ideas and findings in the field. Jacob's aim is to show students how to use basic principles of physics and chemistry to describe a complex system such as the atmosphere. He also seeks to give students an overview of the current state of research and the work that led to this point. Jacob begins with atmospheric structure, design of simple models, atmospheric transport, and the continuity equation, and continues with geochemical cycles, the greenhouse effect, aerosols, stratospheric ozone, the oxidizing power of the atmosphere, smog, and acid rain. Each chapter concludes with a problem set based on recent scientific literature. This is a novel approach to problem-set writing, and one that successfully introduces students to the prevailing issues. This is a major contribution to a growing area of study and will be welcomed enthusiastically by students and teachers alike.
Author: PLUMB
Publisher: Birkhäuser
ISBN: 3034858256
Category : Science
Languages : en
Pages : 465
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Book Description
PAGEOPH, stratosphere, these differences provide us with new evidence, interpretation of which can materially help to advance our understanding of stratospheric dynamics in general. It is now weil established that smaller-scale motions-in particular gravity waves and turbulence-are of fundamental importance in the general circulation of the mesosphere; they seem to be similarly, if less spectacularly, significant in the troposphere, and probably also in the stratosphere. Our understanding of these motions, their effects on the mean circulation and their mutual interactions is progressing rapidly, as is weil illustrated by the papers in this issue; there are reports of observational studies, especially with new instruments such as the Japanese MV radar, reviews of the state of theory, a laboratory study and an analysis of gravity waves and their effects in the high resolution "SKYHI" general circulation model. There are good reasons to suspect that gravity waves may be of crucial significance in making the stratospheric circulation the way it is (modeling experience being one suggestive piece of evidence for this). Direct observational proof has thus far been prevented by the difficulty of making observations of such scales of motion in this region; in one study reported here, falling sphere observations are used to obtain information on the structure and intensity of waves in the upper stratosphere.
Author: K. Mohanakumar
Publisher: Springer Science & Business Media
ISBN: 1402082177
Category : Science
Languages : en
Pages : 424
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Book Description
Stratospheric processes play a signi?cant role in regulating the weather and c- mate of the Earth system. Solar radiation, which is the primary source of energy for the tropospheric weather systems, is absorbed by ozone when it passes through the stratosphere, thereby modulating the solar-forcing energy reaching into the t- posphere. The concentrations of the radiatively sensitive greenhouse gases present in the lower atmosphere, such as water vapor, carbon dioxide, and ozone, control the radiation balance of the atmosphere by the two-way interaction between the stratosphere and troposphere. The stratosphere is the transition region which interacts with the weather s- tems in the lower atmosphere and the richly ionized upper atmosphere. Therefore, this part of the atmosphere provides a long list of challenging scienti?c problems of basic nature involving its thermal structure, energetics, composition, dynamics, chemistry, and modeling. The lower stratosphere is very much linked dynamically, radiatively,and chemically with the upper troposphere,even though the temperature characteristics of these regions are different. The stratosphere is a region of high stability, rich in ozone and poor in water - por and temperature increases with altitude. The lower stratospheric ozone absorbs the harmful ultraviolet (UV) radiation from the sun and protects life on the Earth. On the other hand, the troposphere has high concentrations of water vapor, is low in ozone, and temperature decreases with altitude. The convective activity is more in the troposphere than in the stratosphere.
