Tropospheric Emission Spectrometer observations of the tropospheric HDO/H2O ratio: Estimation approach and characterization
TL;DR: In this article, a global, vertical profile estimate of the HDO/H2O ratio from the Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS) Aura satellite is presented.
Abstract: [1] We present global, vertical profile estimates of the HDO/H2O ratio from the Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS) Aura satellite. We emphasize in this paper the estimation approach and error characterization, which are critical to determining the very small absolute concentration of HDO relative to H2O and its uncertainty. These estimates were made from TES nadir-viewing (downlooking) thermal infrared spectral radiances observed on 20 September 2004. Profiles of HDO and H2O are simultaneously estimated from the observed radiances and a profile of the ratio is then calculated. This simultaneous, or “joint,” estimate is regularized with an a priori covariance matrix that includes expected correlations between HDO and H2O. This approach minimizes errors in the profile of the HDO/H2O ratio that are due to overlapping HDO and H2O spectroscopic lines. Under clear-sky conditions in the tropics, TES estimates of the HDO/H2O ratio are sensitive to the distribution of the actual ratio between the surface and about 300 hPa with peak sensitivity at 700 hPa. The sensitivity decreases with latitude through its dependence on temperature and water amount. We estimate a precision of approximately 1% to 2% for the ratio of the HDO/H2O tropospheric densities; however, there is possibly a bias of approximately 5% in the ratio due to the HDO spectroscopic line strengths. These global observations clearly show increased isotopic depletion of water vapor at higher latitudes as well as increased depletion in the upper troposphere versus the lower troposphere.
Citations
More filters
TL;DR: The most important sources of atmospheric moisture at the global scale are identified, both oceanic and terrestrial, and a characterization is made of how continental regions are influenced by water from different moisture source regions as discussed by the authors.
Abstract: [1] The most important sources of atmospheric moisture at the global scale are herein identified, both oceanic and terrestrial, and a characterization is made of how continental regions are influenced by water from different moisture source regions. The methods used to establish source-sink relationships of atmospheric water vapor are reviewed, and the advantages and caveats associated with each technique are discussed. The methods described include analytical and box models, numerical water vapor tracers, and physical water vapor tracers (isotopes). In particular, consideration is given to the wide range of recently developed Lagrangian techniques suitable both for evaluating the origin of water that falls during extreme precipitation events and for establishing climatologies of moisture source-sink relationships. As far as oceanic sources are concerned, the important role of the subtropical northern Atlantic Ocean provides moisture for precipitation to the largest continental area, extending from Mexico to parts of Eurasia, and even to the South American continent during the Northern Hemisphere winter. In contrast, the influence of the southern Indian Ocean and North Pacific Ocean sources extends only over smaller continental areas. The South Pacific and the Indian Ocean represent the principal source of moisture for both Australia and Indonesia. Some landmasses only receive moisture from the evaporation that occurs in the same hemisphere (e.g., northern Europe and eastern North America), while others receive moisture from both hemispheres with large seasonal variations (e.g., northern South America). The monsoonal regimes in India, tropical Africa, and North America are provided with moisture from a large number of regions, highlighting the complexities of the global patterns of precipitation. Some very important contributions are also seen from relatively small areas of ocean, such as the Mediterranean Basin (important for Europe and North Africa) and the Red Sea, which provides water for a large area between the Gulf of Guinea and Indochina (summer) and between the African Great Lakes and Asia (winter). The geographical regions of Eurasia, North and South America, and Africa, and also the internationally important basins of the Mississippi, Amazon, Congo, and Yangtze Rivers, are also considered, as is the importance of terrestrial sources in monsoonal regimes. The role of atmospheric rivers, and particularly their relationship with extreme events, is discussed. Droughts can be caused by the reduced supply of water vapor from oceanic moisture source regions. Some of the implications of climate change for the hydrological cycle are also reviewed, including changes in water vapor concentrations, precipitation, soil moisture, and aridity. It is important to achieve a combined diagnosis of moisture sources using all available information, including stable water isotope measurements. A summary is given of the major research questions that remain unanswered, including (1) the lack of a full understanding of how moisture sources influence precipitation isotopes; (2) the stationarity of moisture sources over long periods; (3) the way in which possible changes in intensity (where evaporation exceeds precipitation to a greater of lesser degree), and the locations of the sources, (could) affect the distribution of continental precipitation in a changing climate; and (4) the role played by the main modes of climate variability, such as the North Atlantic Oscillation or the El Nino–Southern Oscillation, in the variability of the moisture source regions, as well as a full evaluation of the moisture transported by low-level jets and atmospheric rivers.
415 citations
TL;DR: Measurements of the isotopic composition of water vapour near tropical clouds and over the tropical continents suggest that rainfall evaporation contributes significantly to lower troposphere humidity, and convection of vapour from both oceanic sources and evapotranspiration are the dominant moisture sources.
Abstract: Atmospheric moisture cycling is an important aspect of the Earth's climate system, yet the processes determining atmospheric humidity are poorly understood. For example, direct evaporation of rain contributes significantly to the heat and moisture budgets of clouds, but few observations of these processes are available. Similarly, the relative contributions to atmospheric moisture over land from local evaporation and humidity from oceanic sources are uncertain. Lighter isotopes of water vapour preferentially evaporate whereas heavier isotopes preferentially condense and the isotopic composition of ocean water is known. Here we use this information combined with global measurements of the isotopic composition of tropospheric water vapour from the Tropospheric Emission Spectrometer (TES) aboard the Aura spacecraft, to investigate aspects of the atmospheric hydrological cycle that are not well constrained by observations of precipitation or atmospheric vapour content. Our measurements of the isotopic composition of water vapour near tropical clouds suggest that rainfall evaporation contributes significantly to lower troposphere humidity, with typically 20% and up to 50% of rainfall evaporating near convective clouds. Over the tropical continents the isotopic signature of tropospheric water vapour differs significantly from that of precipitation, suggesting that convection of vapour from both oceanic sources and evapotranspiration are the dominant moisture sources. Our measurements allow an assessment of the intensity of the present hydrological cycle and will help identify any future changes as they occur.
402 citations
Centre national de la recherche scientifique1, Cooperative Institute for Research in Environmental Sciences2, California Institute of Technology3, Karlsruhe Institute of Technology4, Spanish National Research Council5, University of Toronto6, University of York7, Agencia Estatal de Meteorología8, National Institute of Water and Atmospheric Research9, University of Bremen10, University of Wollongong11, University of Liège12, Harvard University13, University of the Ryukyus14, Stockholm University15
TL;DR: In this paper, a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) are analyzed to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs).
Abstract: The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity. Copyright © 2012 by the American Geophysical Union.
292 citations
TL;DR: Improved measurement and modeling of water vapor isotopic composition opens the door to new advances in the understanding of the atmospheric water cycle, in processes ranging from the marine boundary layer, through deep convection and tropospheric mixing, and into the water cycle of the stratosphere.
Abstract: The measurement and simulation of water vapor isotopic composition has matured rapidly over the last decade, with long-term datasets and comprehensive modeling capabilities now available. Theories for water vapor isotopic composition have been developed by extending the theories that have been used for the isotopic composition of precipitation to include a more nuanced understanding of evaporation, large-scale mixing, deep convection, and kinetic fractionation. The technologies for in-situ and remote sensing measurements of water vapor isotopic composition have developed especially rapidly over the last decade, with discrete water vapor sampling methods, based on mass spectroscopy, giving way to laser spectroscopic methods and satellite- and ground-based infrared absorption techniques. The simulation of water vapor isotopic composition has evolved from General Circulation Model (GCM) methods for simulating precipitation isotopic composition to sophisticated isotope-enabled microphysics schemes using higher-order moments for water- and ice-size distributions. The incorporation of isotopes into GCMs has enabled more detailed diagnostics of the water cycle and has led to improvements in its simulation. The combination of improved measurement and modeling of water vapor isotopic composition opens the door to new advances in our understanding of the atmospheric water cycle, in processes ranging from the marine boundary layer, through deep convection and tropospheric mixing, and into the water cycle of the stratosphere. Finally, studies of the processes governing modern water vapor isotopic composition provide an improved framework for the interpretation of paleoclimate proxy records of the hydrological cycle.
247 citations
Cites methods from "Tropospheric Emission Spectrometer ..."
..., 2012], which is similar to the TES version 4 retrieval [Worden et al., 2006], uses small microwindows, and is less computationally intensive....
[...]
TL;DR: In this paper, a set of four present-day global experiments with the ECHAM5 atmospheric general circulation model enhanced by stable water isotope diagnostics (ECHAM5-wiso) is presented.
Abstract: [1] In this study, a first set of four present-day global experiments with the ECHAM5 atmospheric general circulation model enhanced by stable water isotope diagnostics (ECHAM5-wiso) is presented. Model resolution varies from a typical coarse horizontal grid of 3.8° × 3.8° (T31) to a fine grid of 0.75° × 0.75° (T159). Vertical resolution varies from 19 to 31 model levels. On a global scale, the ECHAM5-wiso simulation results are in good agreement with available observations of the isotopic composition of precipitation from the Global Network of Isotopes in Precipitation (GNIP), on an annual as well as a seasonal time scale. In many instances, the isotope simulation results clearly benefit from an increased horizontal and vertical model resolution. The exemplary relevance of this model resolution dependence is demonstrated for the simulation of the isotopic composition of Antarctic precipitation. Here, the simulation with the fine T159L31 model resolution not only yields a better agreement with observational data sets but also allows for a more realistic retuning of the supersaturation function leading to improved deuterium excess performance over the Antarctic continent, which is important for the interpretation of polar ice cores. Finally, the ECHAM5-wiso simulation results are compared to newly available measurements of the isotopic composition of atmospheric water vapor. Model and data agree well, with differences in the range of ±10‰ for near-surface atmospheric values at several GNIP stations. A comparison of the ECHAM5-wiso simulations with total column averaged HDO data from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument on board the environmental satellite Envisat shows the same latitudinal gradients but an offset between 20‰ and 50‰ of unknown origin.
230 citations
References
More filters
TL;DR: In this paper, the isotopic fractionation of water in simple condensation-evaporation processes is considered quantitatively on the basis of the fractionation factors given in section 1.2.
Abstract: In chapter 2 the isotopic fractionation of water in some simple condensation-evaporation processes are considered quantitatively on the basis of the fractionation factors given in section 1.2. The condensation temperature is an important parameter, which has got some glaciological applications. The temperature effect (the δ's decreasing with temperature) together with varying evaporation and exchange appear in the “amount effect” as high δ's in sparse rain. The relative deuterium-oxygen-18 fractionation is not quite simple. If the relative deviations from the standard water (S.M.O.W.) are called δ D and δ 18 , the best linear approximation is δ D = 8 δ 18 . Chapter 3 gives some qualitative considerations on non-equilibrium (fast) processes. Kinetic effects have heavy bearings upon the effective fractionation factors. Such effects have only been demonstrated clearly in evaporation processes, but may also influence condensation processes. The quantity d = δ D −8 δ 18 is used as an index for non-equilibrium conditions. The stable isotope data from the world wide I.A.E.A.-W.M.O. precipitation survey are discussed in chapter 4. The unweighted mean annual composition of rain at tropical island stations fits the line δ D = 4.6 δ 18 indicating a first stage equilibrium condensation from vapour evaporated in a non-equilibrium process. Regional characteristics appear in the weighted means. The Northern hemisphere continental stations, except African and Near East, fit the line δ D = 8.0 δ 18 + 10 as far as the weighted means are concerned (δ D = 8.1 δ 18 + 11 for the unweighted) corresponding to an equilibrium Rayleigh condensation from vapour, evaporated in a non-equilibrium process from S.M.O.W. The departure from equilibrium vapour seems even higher in the rest of the investigated part of the world. At most stations the δ D and varies linearily with δ 18 with a slope close to 8, only at two stations higher than 8, at several lower than 8 (mainly connected with relatively dry climates). Considerable variations in the isotopic composition of monthly precipitation occur at most stations. At low latitudes the amount effect accounts for the variations, whereas seasonal variation at high latitudes is ascribed to the temperature effect. Tokyo is an example of a mid latitude station influenced by both effects. Some possible hydrological applications are outlined in chapter 5. DOI: 10.1111/j.2153-3490.1964.tb00181.x
7,081 citations
"Tropospheric Emission Spectrometer ..." refers background in this paper
...A result that is apparent from this single global survey is the ‘‘latitude effect’’ in which the isotopic depletion of water vapor is larger at the higher latitudes than at the equator due to the continual rain-out of the heavier nuclides during poleward transit into an environment with lower temperature [e.g., Dansgaard, 1964 ]....
[...]
...[39] Despite the challenges with estimating the tropospheric HDO/H2O ratio, TES observations are able to capture expected spatial distributions such as the latitude effect (more depletion of heavier water vapor isotopes at higher latitudes) and more depletion of heavier water vapor isotopes at higher altitudes [ Dansgaard, 1964 ]....
[...]
...…whereas the boundary layer vapor inside or downwind of weather systems were most depleted; this excess depletion is suggestive of an ‘‘amount effect’’ [Dansgaard, 1964] in which water recycled in the cloud system becomes successively depleted as the heavier isotopes are removed through…...
[...]
...…estimating the tropospheric HDO/H2O ratio, TES observations are able to capture expected spatial distributions such as the latitude effect (more depletion of heavier water vapor isotopes at higher latitudes) and more depletion of heavier water vapor isotopes at higher altitudes [Dansgaard, 1964]....
[...]
...They found that regions with disorganized or no convection had the least isotopically depleted vapor, whereas the boundary layer vapor inside or downwind of weather systems were most depleted; this excess depletion is suggestive of an ‘‘amount effect’’ [ Dansgaard, 1964 ] in which water recycled in the cloud system becomes successively depleted as the heavier isotopes are removed through precipitation....
[...]
Book•
17 Jul 2000
TL;DR: This book treats the inverse problem of remote sounding comprehensively, and discusses a wide range of retrieval methods for extracting atmospheric parameters of interest from the quantities such as thermal emission that can be measured remotely.
Abstract: Remote sounding of the atmosphere has proved to be a fruitful method of obtaining global information about the atmospheres of the earth and planets. This book treats the inverse problem of remote sounding comprehensively, and discusses a wide range of retrieval methods for extracting atmospheric parameters of interest from the quantities such as thermal emission that can be measured remotely. Inverse theory is treated in depth from an estimation-theory point of view, but practical questions are also emphasized, for example designing observing systems to obtain the maximum quantity of information, efficient numerical implementation of algorithms for processing of large quantities of data, error analysis and approaches to the validation of the resulting retrievals, The book is targeted at both graduate students and working scientists.
4,052 citations
"Tropospheric Emission Spectrometer ..." refers background or methods in this paper
...An a priori covariance is developed which includes the expected variability of both HDO and H2O and the correlations between the two molecules; the inverse of this a priori covariance is used to constrain the joint estimate [Rodgers, 2000]....
[...]
...[8] The estimation method and error characterization for the distribution of the HDO/H2O ratio uses the general methodology and error characterization from Rodgers [2000] and the error characterization used for simultaneous estimates of atmospheric trace gasses and temperature described by Rodgers and Connor [2003] and Worden et al. [2004b]....
[...]
...This equation is equivalent to the information content [ Rodgers, 2000 ] if the smoothing error is replaced by the total error of the estimate given by equation (26)....
[...]
...: TES OBSERVATIONS OF TROPOSPHERIC HDO/H2O 3 of 10 D16309 matrix, and true state can be described by the linear estimate [Rodgers, 2000] x̂ ¼ xa þ Axx x xað Þ þMGznþMGz X i Ki bi bai ; ð8Þ where M is the mapping matrix, Axx is the averaging kernel matrix, n is the noise vector, x is the ‘‘true’’…...
[...]
...Because the mapping used here is linear, the mapping matrix may also be interpreted as M ¼ @x @z : ð5Þ The mapping matrix represents a ‘‘hard constraint’’ because the estimate cannot take on values outside the range space of M [Rodgers, 2000]....
[...]
Harvard University1, University of Reims Champagne-Ardenne2, College of William & Mary3, California Institute of Technology4, Pierre-and-Marie-Curie University5, Université libre de Bruxelles6, Université catholique de Louvain7, University of Paris-Sud8, University of Denver9, National Institute of Standards and Technology10, National Center for Atmospheric Research11, Stony Brook University12, Rutherford Appleton Laboratory13, Langley Research Center14
TL;DR: The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorptionCross-sections, and associated database management software.
Abstract: This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments. (C) 2003 Elsevier Ltd. All rights reserved.
1,231 citations
"Tropospheric Emission Spectrometer ..." refers background in this paper
...There are also many HDO lines that can be used for estimating atmospheric distributions of HDO and H2O [Toth, 1999; Rothman et al., 2003]....
[...]
TL;DR: The Model of Ozone and Related Chemical Tracers (MOZART) as discussed by the authors is based on the NCAR Model of Atmospheric Transport and Chemistry (MATCH) and can easily be driven with various meteorological inputs and model resolutions.
Abstract: [1] We have developed a global three-dimensional chemical transport model called Model of Ozone and Related Chemical Tracers (MOZART), version 2. This model, which will be made available to the community, is built on the framework of the National Center for Atmospheric Research (NCAR) Model of Atmospheric Transport and Chemistry (MATCH) and can easily be driven with various meteorological inputs and model resolutions. In this work, we describe the standard configuration of the model, in which the model is driven by meteorological inputs every 3 hours from the middle atmosphere version of the NCAR Community Climate Model (MACCM3) and uses a 20-min time step and a horizontal resolution of 2.8° latitude × 2.8° longitude with 34 vertical levels extending up to approximately 40 km. The model includes a detailed chemistry scheme for tropospheric ozone, nitrogen oxides, and hydrocarbon chemistry, with 63 chemical species. Tracer advection is performed using a flux-form semi-Lagrangian scheme with a pressure fixer. Subgrid-scale convective and boundary layer parameterizations are included in the model. Surface emissions include sources from fossil fuel combustion, biofuel and biomass burning, biogenic and soil emissions, and oceanic emissions. Parameterizations of dry and wet deposition are included. Stratospheric concentrations of several long-lived species (including ozone) are constrained by relaxation toward climatological values. The distribution of tropospheric ozone is well simulated in the model, including seasonality and horizontal and vertical gradients. However, the model tends to overestimate ozone near the tropopause at high northern latitudes. Concentrations of nitrogen oxides (NOx) and nitric acid (HNO3) agree well with observed values, but peroxyacetylnitrate (PAN) is overestimated by the model in the upper troposphere at several locations. Carbon monoxide (CO) is simulated well at most locations, but the seasonal cycle is underestimated at some sites in the Northern Hemisphere. We find that in situ photochemical production and loss dominate the tropospheric ozone budget, over input from the stratosphere and dry deposition. Approximately 75% of the tropospheric production and loss of ozone occurs within the tropics, with large net production in the tropical upper troposphere. Tropospheric production and loss of ozone are three to four times greater in the northern extratropics than the southern extratropics. The global sources of CO consist of photochemical production (55%) and direct emissions (45%). The tropics dominate the chemistry of CO, accounting for about 75% of the tropospheric production and loss. The global budgets of tropospheric ozone and CO are generally consistent with the range found in recent studies. The lifetime of methane (9.5 years) and methylchloroform (5.7 years) versus oxidation by tropospheric hydroxyl radical (OH), two useful measures of the global abundance of OH, agree well with recent estimates. Concentrations of nonmethane hydrocarbons and oxygenated intermediates (carbonyls and peroxides) generally agree well with observations.
928 citations
"Tropospheric Emission Spectrometer ..." refers methods in this paper
...For TES estimates of the HDO and H2O distributions, the a priori covariance for water, SH, is constructed using the MOZART [Brasseur et al., 1998; Horowitz et al., 2003] model but scaled to the expected uncertainty of NCEP water content predictions [Worden et al., 2004b]....
[...]