bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of observations and model simulations of tropospheric water vapor
Authors: Gaffen Dian J. , Barnett Tim P.
Published: February 2012

Observations of tropospheric specific humidity from radiosondes for the period 1973–1986 are compared with simulated specific humidity fields from a University of Hamburg version of the European Center for Medium‐Range Weather Forecasting General Circulation Model (GCM), forced by observed sea surface temperatures. The mean January and July fields are shown to be in good agreement, despite the much poorer resolution of the radiosonde network used. Temporal and spatial variations of specific humidity are examined through empirical orthogonal function analysis of tropical data. The first mode of variability of the data was similar to that of the model simulations and shows evidence of a coherent, decadal‐scale variation in tropospheric moisture content. The overall agreement between the model and the data, while not complete, suggests that long‐term mean patterns and decadal variations in moisture, as delineated by a sparse data network, are reasonably well simulated. More comprehensive comparisons of tropospheric moisture data with GCM simulations from different models are suggested.
Conceptual aspects of a statistical‐dynamical approach to represent landscape subgrid‐scale heterogeneities in atmospheric models
Authors: Avissar Roni
Published: February 2012

Land‐surface characteristics play a key role in the partition of energy received at the Earth's surface and, as a result, have a major impact on the atmosphere. Yet the representation of land‐surface processes in atmospheric models is not realistic. Actual state‐of‐the‐art parameterizations of land surfaces do not account for the landscape heterogeneity found on the resolvable scale of these models and are based on a large amount of empirical constants that in practice can be difficult to estimate. An alternative parameterization based on a statistical‐dynamical approach is suggested here. With this approach, the most important characteristics of the soil‐plant‐atmosphere system that affect the partition of energy (e.g., plant stomatal conductance, soil humidity, surface roughness) would be represented by a probability density function (pdf) rather than by a single “representative” value. Typically, such pdf's are characterized by two to four parameters. A primary simplified version of this parameterization was used to estimate the land‐surface energy fluxes that are produced at the grid scale by various distributions of stomatal conductance under a broad range of environmental conditions. To demonstrate the potential of the approach, results were compared with the same fluxes calculated with a big leaf model using the mean stomatal conductance that corresponds to the distributions. Large absolute and relative differences are obtained between the two schemes for many combinations of stomatal conductance pdf's and environmental conditions. These differences are due mainly to the nonlinearity of the processes involved in the redistribution of the energy absorbed at the ground surface. These numerical experiments demonstrate the importance of accounting for landscape heterogeneity in the simulation of land‐surface energy fluxes, and demonstrate the potential benefits of adopting a statistical‐dynamical approach for the representation of land‐surface processes in atmospheric models.
Potential repsonse of an Arctic watershed during a period of global warming
Authors: Hinzman Larry D. , Kane Douglas L.
Published: February 2012

Climatic warming presents an imposing problem to scientists everywhere. Its effect in the Arctic is accentuated for several reasons. The temperature increase is expected to be greatest in the higher latitudes and the ramifications of this warming may be more crucial there due to the melting of permafrost. Precipitation changes will likely accompany climatic warming in the Arctic, compounding the effect of a temperature increase. The interaction of changing hydrologic and thermal processes presents a complex problem which would be difficult if not impossible to analyze without the use of detailed computer modeling. To analyze the thermal impact of climatic warming on a permafrost environment, TDHC, a heat conduction model which incorporates phase change, was used. Then the response of the active layer to climatic warming was incorporated into HBV, a hydrologic model, to elucidate the effects on the hydrologic regime. Several scenarios of climatic warming have been examined to determine the impact on the active layer depth, but only results of 4°C warming at a typical arctic site will be presented here. In the case of 4°C warming, three scenarios of precipitation were studied: no change, +15%, and −15%. The most obvious and perhaps significant response to climatic warming was an increase in active layer depth. Other changes worth noting were warming of the entire soil profile, increased soil moisture storage, increased evaporation, and variable response in runoff, depending upon the scenario. Evaporation now vies with runoff as the primary loss of moisture from the watershed. If evaporation increases due to a warmer climate, the entire character of arctic hydrology could change, depending on changes in precipitation.
A land‐surface hydrology parameterization with subgrid variability for general circulation models
Authors: Wood Eric F. , Lettenmaier Dennis P. , Zartarian Valerie G.
Published: February 2012

Most of the existing generation of general circulation models (GCMs) use so‐called bucket algorithms to represent land‐surface hydrology. Biosphere‐atmosphere models that include the transfer of energy, mass, and momentum between the atmosphere and the land surface are a recent alternative to this highly simplified representation of the land surface in GCMs. These models require estimation of a large number of parameters for which parameter estimation methods and supporting data remain to be developed. We describe a more incremental approach to generalizing the bucket representation of land‐surface hydrology based on a model that represents the variation in infiltration capacity within a GCM grid cell. The variable infiltration capacity (VIC) model requires estimation of three parameters: an infiltration parameter, an evaporation parameter, and a base flow recession coefficient. The VIC model was explored through direct comparisons with the Geophysical Fluid Dynamics Laboratory (GFDL) bucket model for the French Broad River, North Carolina, and via sensitivity analysis for the GFDL R30 grid cell which contains the French Broad River. Generally, the bucket model runoff had much greater variability than the historic streamflows for short time scales (e.g., 1 day); the VIC model was much more similar to the observed flows in this respect. The results also showed that the bucket model tended to have unrealistically high short‐term variability. The sensitivity analysis showed that the base flow parameter exerted the greatest influence on both the mean and variability of most of the hydrologic variables, especially winter runoff, summer evaporation, and summer and winter soil moisture.
Beryllium 7 and Lead 210 in the western hemisphere Arctic atmosphere: Observations from three recent aircraft‐based sampling programs
Authors: Dibb Jack E. , Talbot Robert W. , Gregory Gerald L.
Published: February 2012

Concentrations of the natural radionuclides 7Be and 210Pb were determined in aerosol samples collected in the western hemisphere Arctic during the recent NOAA Arctic Gas and Aerosol Sampling Program (AGASP 3) and NASA Global Tropospheric Experiment/Arctic Boundary Layer Expeditions (GTE/ABLE 3A and ABLE 3B) missions. Beryllium 7 showed a free tropospheric concentration maximum between 4 and 5 km in the summer of 1990. Previous 7Be data obtained in the late 1950s and early 1960s also indicated a similar vertical distribution of 7Be near 70°N. Injection of stratospheric air through tropopause folds associated with the Arctic jet near 70°N appears to explain the presence of a layer of air near 4–5 km in the high Arctic free troposphere with elevated 7Be concentrations. The vertical distribution of 210Pb showed a distinct difference between the high‐Arctic and sub‐Arctic in the summer of 1988. At latitudes greater than 65°N, 210Pb concentrations at 3–6 km were elevated compared to those below 1 km. The reverse of this trend was observed near 60°N. These same vertical distributions were also apparent in aerosol SO42−, determined in separate aerosol samples collected on the same flights (Talbot et al., this issue). The results for 210Pb suggest that some of the difference between the summer troposphere in the high‐ and sub‐Arctic is also due to enhanced stratosphere‐troposphere exchange in the vicinity of the Arctic jet. These observations, and other findings from ABLE 3A presented in this issue, suggest that for some species the stratosphere may be a principal source influencing their distribution in the Arctic summer troposphere. For example, intrusions of stratospheric air constitute the dominant source term for tropospheric budgets of 7Be and ozone, and may be important in the 210Pb, SO42−, and NOy budgets. Further investigation, including determination of detailed 7Be and 210Pb distributions, is needed to quantify the stratospheric impact on the chemistry of the Arctic troposphere during the summer.
Characterization of model polar stratospheric cloud films using Fourier transform infrared spectroscopy and temperature programmed desorption
Authors: Koehler Birgit G. , Middlebrook Ann M. , Tolbert Margaret A.
Published: February 2012

This study combines Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD) measurements of nitric‐acid/ice films representative of type I polar stratospheric clouds (PSCs). Using this combination of techniques, we are able to correlate the FTIR spectra with measurements of the film stoichiometry. The results confirm the assignments for amorphous nitric‐acid/ice films and for crystalline nitric acid trihydrate (NAT), dihydrate, and monohydrate proposed by Ritzhaupt and Devlin (1991). In addition to these films, we observe a new high temperature nitric‐acid/ice film which we attribute to a more stable structure of NAT with fewer defects. When low temperature crystalline NAT is heated, such as during TPD or slow annealing, the IR absorption spectrum irreversibly changes around −88° to −75°C. Future IR absorption measurements of PSCs in the atmosphere should be compared with IR spectra of both amorphous and crystalline nitric acid/ice, including both forms of NAT.
Summertime photochemistry of the troposphere at high northern latitudes
Authors: Jacob D. J. , Wofsy S. C. , Bakwin P. S. , Fan S.‐M. , Harriss R. C. , Talbot R. W. , Bradshaw J. D. , Sandholm S. T. , Singh H. B. , Browell E. V. , Gregory G. L. , Sachse G. W. , Shipham M. C. , Blake D. R. , Fitzjarrald D. R.
Published: February 2012

The budgets of O3, NOx(NO+NO2), reactive nitrogen (NOy), and acetic acid in the 0–6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O3in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NOx(10–50 ppt) are sufficiently high to slow down O3photochemical loss appreciably relative to a NOx‐free atmosphere; if no NOxwere present, the lifetime of O3in the 0–6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NOxpresent in the Arctic troposphere have thus a major impact on the regional O3budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOxbelow 4‐km altitude, but for only 20% at 6‐km altitude. Decomposition of other organic nitrates might supply the missing source of NOx. The lifetime of NOy, in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NOxcould be supplied from distant sources including fossil fuel combustion at northern mid‐latitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in O3; this observation is attributed in part to low NOxemissions in the fires, and in part to rapid conversion of NOxto PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional O3budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CH3CO3with HO2and CH3O2. There remains a major unidentified source of acetic acid in the atmosphere.
Radiative effects of polar stratospheric clouds during the Airborne Antarctic Ozone Experiment and the Airborne Arctic Stratospheric Expedition
Authors: Rosenfield Joan E.
Published: February 2012

Daily, three dimensional fields of both Type I nitric acid trihydrate (NAT) and Type II water ice polar stratospheric clouds (PSCs) have been generated in the polar regions during the period of the Airborne Antarctic Ozone Experiment (AAOE) and the Airborne Arctic Stratospheric Expedition (AASE) aircraft missions. Mission data on particulate composition and size, together with National Meteorological Center (NMC) analyzed temperatures, have been used. A comparison of computed l‐μm extinction coefficients with those observed by the Stratospheric Aerosol Measurement (SAM II) satellite served to constrain the water ice particle size and the nitric acid mixing ratio profiles. For AAOE, both Type I and Type II clouds were formed for the time period August 23 to September 17, after which only Type I clouds formed. During AASE, while Type I clouds were formed for each day between January 3 and February 10, Type II clouds formed on only two days, January 24 and 31. Mie theory and a radiative transfer model were used to compute the radiative heating rates during the mission periods, for clear and cloudy lower sky cases. Only the Type II water ice clouds have a significant radiative effect, with the Type I NAT PSCs generating a net heating or cooling of 0.1 K/d or less. The major effect of PSCs during AAOE appears to be one of net heating, with maximum heating rates as large as 0.5 K/d for particular days. Heating rates of 0.3 K/d or greater were computed during the periods September 1–6 and September 11–14. This additional heating was generally found over the western part of Antarctica and near the coastal regions, while a small cooling was computed over the Antarctic Plateau. However, when the heating rates are averaged over the AAOE mission, a net heating on the order of only 0.1 K/d is generated by the PSCs over western Antarctica, with other regions exhibiting a very small additional cooling, less than 0.05 K/d. Tropospheric clouds turn this net heating to a small amount of net cooling, roughly 0.1 K/d. The average effect of PSCs to the radiative budget during AASE is extremely small. Therefore, on the whole, the radiative effects of PSCs appear to be too small to have an appreciable impact on vertical motions except over time scales of a few days during AAOE. This result makes it unlikely that the radiative‐dynamical mechanisms proposed for the Antarctic ozone depletion play any significant role.
Carbon monoxide and methane in the North American Arctic and Subarctic troposphere: July–August 1988
Authors: Harriss Robert C. , Sachse Glen W. , Hill Gerald F. , Wade Larry , Bartlett Karen B. , Collins James E. , Steele L. Paul , Novelli Paul C.
Published: February 2012

Measurements of carbon monoxide (CO) and methane (CH4) were made in the North American Arctic during July–August 1988. The distribution of CH4 was variable in the atmospheric mixed layer (0–2 km), with concentrations determined primarily by interactions of biogenic emissions from wet tundra and turbulent mixing processes. Carbon monoxide exhibited little variation in unpolluted mixed layer environments indicating a minor role for biogenic sources and/or sinks in determining its distribution. In the free troposphere (2–6 km) both CO and CH4 were variable. Concentration gradients were most frequently associated with intrusions of upper tropospheric or stratospheric air into the midtroposphere, emissions from forest and tundra fires, and long‐range transport of enhanced concentrations of these gases from unidentified sources. Summertime haze layers exhibited midtropospheric enhancements of CH4 similar to those measured in winter Arctic haze events. However, these summer pollution episodes did not exhibit positive correlations with particulate sulfate. The summer Arctic and subarctic haze events observed during the Arctic Boundary Layer Expedition (ABLE 3) were primarily a result of forest and tundra fires of natural origin. The tendency for relatively high variability of CO and CH4 at altitudes of 3–6 km indicates that ground‐based monitoring will not provide an adequate assessment of the chemical composition of the Arctic troposphere to support future global change studies.
The cloud flash‐to‐ground flash ratio and other lightning occurrence characteristics in Kathmandu thunderstorms
Authors: Baral K. N. , Mackerras D.
Published: February 2012

Lightning and thunderstorm observations have been made in Kathmandu, Nepal (27.4°N, 85.2°E) over the 21‐month period March 1987 to November 1988 inclusive, using direct observations of thunder and lightning, and the registrations of a CGR3 lightning flash counter that provided records of the approximate numbers of cloud flashes, positive ground flashes, and negative ground flashes with an effective range of about 14 km. The observation period effectively covered two thunderstorm seasons as almost no lightning occurred during the winter months. During 1987 and 1988 the mean thunderdays per year was 42. The principal use of the CGR3 registrations was to estimate the long‐term ratio of cloud flashes to ground flashes, denoted z; it was found that z was 2.1 in 1987 and 3.0 in 1988, with a two‐season mean of 2.7. The uncertainty in ratio values is about 30%. The registrations also enabled lightning flash densities to be estimated with an uncertainty of about 40%. The two‐season mean ground flash, cloud flash, and total flash densities were 2.4, 6.6, and 9.0 km−2 yr−1, respectively. There were well‐marked seasonal variations in occurrence, with about 82% of all lightning occurring between mid‐February and the end of May. During this premonsoon period there were steady rises to maximum values in May of the thunderdays per month (to 10), the monthly total flash density (to 2.9 km−2 month−1), and the monthly value of z (to 3.6). The range of values of z calculated from the records for individual thunderstorm days was 0.17 to infinity, but very little lightning was associated with the extreme values. A distribution of values of the ratio with respect to cumulative lightning occurrence shows that 80% of all lightning was associated with values of z (calculated on a thunderstorm day basis) between 1.3 and 6.7. There is reasonably good agreement between the value of z for Kathmandu and values of z for other places at similar latitudes. However, major differences have been found for low latitudes between recently measured values of z and earlier predictions of the latitudinal variation of z.
The Arctic Boundary Layer Expedition (ABLE 3A): July–August 1988
Authors: Harriss R. C. , Wofsy S. C. , Bartlett D. S. , Shipham M. C. , Jacob D. J. , Hoell J. M. , Bendura R. J. , Drewry J. W. , McNeal R. J. , Navarro R. L. , Gidge R. N. , Rabine V. E.
Published: February 2012

The Arctic Boundary Layer Expedition (ABLE 3A) used measurements from ground, aircraft, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over Arctic and sub‐Arctic regions of North America during July and August 1988. The primary objectives of ABLE 3A were to investigate the magnitude and variability of methane emissions from the tundra ecosystem, and to elucidate factors controlling ozone production and destruction in the Arctic atmosphere. This paper reports the experimental design for ABLE 3A and a summary of results. Methane emissions from the tundra landscape varied widely from −2.1 to 426 mg CH4 m−2 d−1. Soil moisture and temperature were positively correlated with methane emission rates, indicating quantitative linkages between seasonal climate variability and soil metabolism. Enclosure flux measurement techniques, tower‐based eddy correlation, and airborne eddy correlation flux measurements all proved robust for application to methane studies in the tundra ecosystem. Measurements and photochemical modeling of factors involved in ozone production and destruction validated the hypothesized importance of low NOx concentrations as a dominant factor in maintaining the pristine Arctic troposphere as an ozone sink. Stratospheric intrusions, long‐range transport of mid‐latitude pollution, forest fires, lightning, and aircraft are all potential sources of NOx and NOy to Arctic and sub‐Arctic regions. ABLE 3A results indicate that human activities may have already enhanced NOy inputs to the region to the extent that the lifetime of O3 against photochemical loss may have already doubled. A doubling of NOx concentration from present levels would lead to net photochemical production of O3 during summer months in the Arctic (Jacob et al., this issue (a)). The ABLE 3A results indicate that atmospheric chemical changes in the northern high latitudes may serve as unique early warning indicators of the rates and magnitude of global environmental change.
A hierarchical stochastic model of large‐scale atmospheric circulation patterns and multiple station daily precipitation
Authors: Wilson Larry L. , Lettenmaier Dennis P. , Skyllingstad Eric
Published: February 2012

A stochastic model of weather states and concurrent daily precipitation at multiple precipitation stations is described. Four algorithms are investigated for classification of daily weather states: k‐means clustering, fuzzy clustering, principal components, and principal components coupled with k‐means clustering. A semi‐Markov model with a geometric distribution for within‐class lengths of stay is used to describe the evolution of weather classes. A hierarchical modified Pólya urn model is used to simulate precipitation conditioned on the regional weather type. An information measure that considers both the probability of weather class occurrence and conditional precipitation probabilities is developed to quantify the extent to which each of the weather classification schemes discriminates the precipitation states (rain‐no rain) at the precipitation stations. Evaluation of the four algorithms using the information measure shows that all methods performed equally well. The principal components method is chosen due to its ability to incorporate information from larger spatial fields. Precipitation amount distributions are assumed to be drawn from spatially correlated mixed exponential distributions, whose parameters varied by season and weather class. The model is implemented using National Meteorological Center historical atmospheric observations for the period 1964–1988 mapped to 5° × 5° grid cells over the eastern North Pacific, and three precipitation stations west of the Cascade mountain range in the state of Washington. Comparison of simulated weather class‐station precipitation time series with observational data shows that the model preserved weather class statistics and mean daily precipitation quite well, especially for stations highest in the hierarchy. Precipitation amounts for the lowest precipitation station in the hierarchy, and for precipitation extremes, are not as well preserved.
Hydrologic models and climate change
Authors: Dooge J. C. I.
Published: February 2012

The many gaps in the relationship between theory and practice in hydrologic modelling and between hydrologic modeling and climate modeling are discussed. Important in connection with closing these gaps are topics such as the difficulty of estimating actual evaporation in the water balance at catchment and regional scale, the uncertainty about the role of vegetation in relation to changes in runoff following climate change, and the link that nonlinear system theory may provide between theoretical hydrology and climate theory. Present methods of communication between hydrologists and climate modelers will have to be improved if there is to be a fruitful dialogue and a synergistic relationship between the two groups.
Diurnal variability of atmospheric methane, nonmethane hydrocarbons, and carbon monoxide at Mauna Loa
Authors: Greenberg J. P. , Zimmerman P. R. , Pollock W. F. , Lueb R. A. , Heidt L. E.
Published: February 2012

Atmospheric methane, nonmethane hydrocarbons, and carbon monoxide were measured at the Mauna Loa Observatory on the island of Hawaii in May and June 1988. The daily island upslope/downslope circulation resulted in a variable mixture of boundary layer and free tropospheric air at the observatory. Mixing ratios of these gases were higher during upslope flow than during downslope flow. Mixing ratios characteristic of the free troposphere at this altitude were most often measured during nighttime, downslope flow. Local marine emissions of ethylene and propylene and emissions of isoprene from island vegetation were detected during upslope circulation, but ethylene and propylene were also often detected at night during downslope circulation, indicating that air sampled during nighttime downslope flow may have included some air recently transported from the marine boundary layer. Comparison of data for methane, carbon monoxide, ethane, and propane from in situ measurements with measurements made from canister samples collected during the experiment showed very good agreement. Fluxes of isoprene from selected dominant island flora were also measured.
Measurements of nitric oxide and nitrogen dioxide during the Mauna Loa Observatory Photochemistry Experiment
Authors: Carroll Mary Anne , Ridley Brian A. , Montzka Denise D. , Hubler Gerhard , Walega James G. , Norton Richard B. , Huebert Barry. J. , Grahek Frank E.
Published: February 2012

NO and NO2 were simultaneously measured by photolytic conversion / chemiluminescence techniques during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The field site, located at an elevation of 3.4 km on the north side of the Mauna Loa Volcano, was subject to two airflow regimes which typically corresponded to upslope (marine boundary layer plus island sources) conditions during the day and downslope (middle free tropospheric) conditions at night to mid‐morning. Median values of NOx (NOx = NO + NO2) were 37 and 31 pptv during upslope and downslope conditions, respectively, with the downslope measurements consistent with previous measurements made from aircraft in the middle free troposphere over the North Pacific. Although the difference in median NOx mixing ratios in the upslope and downslope regimes is small, the influence of island sources of NOx is apparent. Indeed, the median upslope values were approximately 2.5 times greater than measurements made previously in the remote marine boundary layer. The data have been examined according to downslope / free tropospheric and upslope air flow regimes for relationships between NOx and the various species that were measured simultaneously (e.g., peroxyacetyl nitrate (PAN), HNO3, NO3, NOy, O3, CO, and hydrocarbons). While positive correlations between NOx and O3 and PAN were typically observed in free tropospheric air, these correlations were considerably weaker than those observed during previous campaigns. This is likely primarily due to the lower sampling altitude during the MLOPEX study. NOx and dew point temperature were weakly anticorrelated in free tropospheric air masses. Linear correlations between NOx and the peroxides, formaldehyde, alkyl nitrates, and hydrocarbons were also weak in the free tropospheric air masses at the MLO. NOx/NOy was typically on the order of 0.1–0.2 in free tropospheric flow. Considerably higher values of NOx/NOy, were occasionally observed under upslope conditions. The NOx/NOy and HNO3/NOx values obtained under downslope conditions were similar to those previously obtained during aircraft measurements in the middle free troposphere over the northeast Pacific. On the whole, the downslope air masses sampled appear to be characteristic of well‐aged, marine free tropospheric air, and this conclusion is supported by 10‐day trajectory analyses.
Measurements of gas phase formic and acetic acids at the Mauna Loa Observatory, Hawaii during the Mauna Loa Observatory Photochemistry Experiment 1988
Authors: Norton R. B.
Published: February 2012

The concentrations of gas phase formic acid (HCOOH) and acetic acid (CH3COOH) were measured at the Mauna Loa, Observatory, Hawaii during the first three weeks (May 1–21, 1988) of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Daytime values were determined mostly during upslope conditions and represent marine boundary layer air modified by contact with the island of Hawaii. Mean values were 452 and 374 pptv for HCOOH and CH3COOH, respectively. Nighttime values were determined mostly during downslope conditions and represent air in the free troposphere near 3400 m above sea level. Mean values were 63 and 94 pptv for HCOOH and CH3COOH, respectively. Aerosol formate and acetate concentration were one to two orders of magnitude less than the gas phase concentration and ranged from less than a few pptv to nearly 50 pptv.
A study of the photochemistry and ozone budget during the Mauna Loa Observatory Photochemistry Experiment
Authors: Liu S. C. , Trainer M. , Carroll M. A. , Hübler G. , Montzka D. D. , Norton R. B. , Ridley B. A. , Walega J. G. , Atlas E. L. , Heikes B. G. , Huebert B. J. , Warren W.
Published: February 2012

Extensive measurements of trace species and parameters that are important to the photochemical production and loss of ozone have been made at Mauna Loa during the Mauna Loa Observatory Photochemistry Experiment experiment. These measurements are used as inputs as well as constraints in a model study of the photochemical budgets of ozone and five other trace species (CH2O, CH3OOH, H2O2, NO, and NOx) that are closely coupled to the photochemical production and loss of ozone. The study shows that there are significant discrepancies in the photochemical budgets of these trace species in this region and suggests that some important uncertainties exist in our understanding of the odd hydrogen photochemical processes.
Meteorological influences during MLOPEX
Authors: Hahn Carole J. , Merrill J. T. , Mendonca B. G.
Published: February 2012

Meteorological data are presented and discussed for the period May 1 to June 4,1988, in support of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Isentropic trajectories were computed to determine air mass origins. Meteorological observations at the Mauna Loa Observatory and radiosonde observations from HiIo, Hawaii, are used to analyze local influences on air mass composition.
A case of Type I polar stratospheric cloud formation by heterogeneous nucleation
Authors: Pueschel R. F. , Ferry G. V. , Snetsinger K. G. , Goodman J. , Dye J. E. , Baumgardner D. , Gandrud B. W.
Published: February 2012

The NASA ER‐2 aircraft flew on January 24, 1989, from Stavanger to Spitsbergen, Norway, at the 430–440 K potential temperature surface (19.2–19.8 km pressure altitude). Aerosols were sampled continuously by an optical particle counter (PMS‐FSSP300) for concentration and size analyses, and during five 10‐min intervals by four wire and one replicator impactor for concentration, size, composition, and phase analyses. During sampling, the air saturation of H2O with respect to ice changed from 20% to 100%, and of HNO3 with respect to nitric acid trihydrate (NAT) from subaturation to supersaturation. Data from both instruments indicate a condensation of hydrochloric acid and, later, nitric acid on the background aerosol particles as the ambient temperature decreases along the flight track. This heterogeneous nucleation mechanism generates type I polar stratospheric cloud particles of 10‐fold enhanced optical depth, which could play a role in stratospheric ozone depletion.
Atmospheric water vapor measurements: Comparison of microwave radiometry and lidar
Authors: England Martin N. , Ferrare R. A. , Melfi S. H. , Whiteman D. N. , Clark T. A.
Published: February 2012

The NASA/GSFC Crustal Dynamics Project microwave water vapor radiometer (J03) is evaluated in terms of measurements of the integrated precipitable water vapor content of a particular column of the troposphere. The measurements were taken during the Atmospheric Moisture Intercomparison Study (ATMIS) held at Wallops Island, Virginia, during April 1989. Various water vapor sensing instruments were used during ATMIS, including radiometers, radiosondes, and the NASA/GSFC Raman lidar. Comparisons between water vapor measurements by the radiometer and the lidar yielded a correlation coefficient of 0.998 and rms differences for three nights of −0.2±0.2mm (April 11–12, 1989), −0.8±0.5 mm (April 16–17, 1989), and −0.4±0.3 mm (April 17–18, 1989). The integrated precipitable water vapor measurements for these three nights were approximately 5, 10, and 21 mm, respectively. The first two periods had clear meteorological conditions, while clouds were present during the third period. The lidar results during the third period are augmented with radiosonde measurements above the cloud base. This study shows that the radiometer provides accurate, continuous measurements of the water vapor integrated through the depth of the atmosphere.
Photochemical partitioning of the reactive nitrogen and chlorine reservoirs in the high‐latitude stratosphere
Authors: Kawa S. R. , Fahey D. W. , Heidt L. E. , Pollock W. H. , Solomon S. , Anderson D. E. , Loewenstein M. , Proffitt M. H. , Margitan J. J. , Chan K. R.
Published: February 2012

Partitioning of the major components of the reactive nitrogen and inorganic chlorine reservoirs is derived from aircraft measurements in the lower stratosphere during the winter season in both hemispheres at latitudes of about 60° to 80°. The goal of this work is to exercise the power of the correlated set of measurements from polar missions of the NASA ER‐2 to extend what can be learned from looking at the measurements individually. The results provide a consistent method for comparing distributions, and hence the controlling processes, between different areas of the near‐polar regions. The analysis provides clear evidence of the effects of heterogeneous processes in the atmosphere. Values for NO2, ClONO2, N2O5, and Cl2O2 are derived in a simplified steady state model based on in situ NO, ClO, O3, temperature, and pressure measurements; laboratory‐measured reaction rates; and modeled photodissociation rates. Values for the reservoir totals are independently derived from measurements of N2O, organic chlorine, and total reactive nitrogen. The relative abundances of the measured and derived species within the reservoirs are calculated, and the longer‐lived species HCl and HNO3 are estimated as the residuals of their respective reservoirs. The resulting latitude distributions in the Arctic outside the vortex agree reasonably well with predictions of a two‐dimensional photochemical model, indicating that partitioning in this region is largely controlled by standard homogeneous gas phase chemistry. Inside the Arctic vortex a large fraction of the HCl has been converted to reactive chlorine species ClO and Cl2O2, consistent with the extensive action of known heterogeneous reactions, presumably occurring on the surfaces of polar stratospheric clouds formed in the cold temperatures of the vortex. The partitioning in the Antarctic suggests that nearly the entire range of latitudes sampled by the ER‐2 is affected by heterogeneous processes in situ, including that portion of the “collar” region equatorward of the nominal chemically perturbed region (CPR). Consideration of heterogeneous processing in the region outside the CPR is important in predicting the possible expansion of Antarctic ozone depletion and the transport of chemically perturbed air to lower latitudes.
A parameterization of ice cloud optical properties for climate models
Authors: Ebert Elizabeth E. , Curry Judith A.
Published: February 2012

We present a new parameterization of the optical properties of ice crystal clouds which is suitable for use in climate models. Five spectral intervals in the shortwave and five intervals in the infrared are employed, with the ice cloud optical properties parameterized in terms of ice water path (IWP) and the effective radius (re) of the ice crystal size distribution. The parameterization thus allows the flexibility of varying the ice water path and effective radius independently of each other. The parameterized optical properties are used to calculate the bulk reflectivity, transmissivity, and emissivity for cirrus clouds with realistic ranges of IWP and re. For a given change in cloud optical depth a change in re alone is more effective than a change in IWP alone in altering the shortwave reflectivity and therefore in altering the strength of the cloud albedo feedback.
Atmospheric net transport of water vapor and latent heat across 70°S
Authors: Giovinetto M. B. , Bromwich D. H. , Wendler G.
Published: February 2012

The annual net atmospheric transports of water vapor and latent heat poleward across 70°S are estimated using the latest compilation of surface mass balance for the Antarctic ice sheet and new estimates of precipitation and evaporation in sectors of the southern oceans and of seaward drifting snow transport in particular sectors of the ice sheet. The mass and energy exchange rates at the ice sheet‐atmosphere and ocean‐atmosphere interfaces are integrated strictly for areas within that latitude. The estimates of net southward water vapor transport (6.6 ± 1.3 kg m−1 s−1) and latent heat transport (18.9 ± 3.6 MJ m−1 s−1) are larger than reported in all preceding studies, based on atmospheric advection and moisture data collected at stations located between 66°S and 80°S, and are generally in agreement with those based on surface mass balance data and seaward drifting snow transport across the ice terminus which extends between 65°S and 79°S.
Natural sulphur species from the North Atlantic and their contribution to the United Kingdom sulphur budget
Authors: Davison B. , Hewitt C. Nicholas
Published: February 2012

Measurements of dimethyl sulphide (DMS) and its oxidation products, methane sulphonic acid (MSA), sulphate, dimethyl sulphoxide (DMSO), dimethyl sulphone (DMSO2), and sulphur dioxide (SO2) in the atmosphere have been made during all seasons of 1988/1990 at coastal sites in northwest Scotland and Eire. The annual average air concentration of DMS was estimated from results obtained on 92 days in 1989/1990 to be 58 ng (S) m−3 and that of MSA to be 6 ng (S) m−3. Backward air mass trajectories were used for each sampling period to explain the observed concentrations in terms of the origins of the sampled air. Seasonal and diurnal cycles were observed for DMS with maximum concentrations > 300 ng (S) m−3 occurring at night and during the spring in air of oceanic origin. Maximum MSA concentrations (up to 120 ng (S) m−3) were observed during the spring. Using a steady state approximation, the sea‐to‐air flux of DMS from the Atlantic north of 45° was estimated to be 0.93 μmol m−2 d−1 or 96 Gg (S) yr−1. Three methods were used to correct the observed air concentrations of the various sulphur species for anthropogenic emissions. The resultant flux of biogenic sulphur into the United Kingdom from the North Atlantic, net of any anthropogenic sulphur, was estimated to be 30 – 96 Gg (S) yr−1, or 2 – 5 % of the total anthropogenic emission rate of sulphur from the U.K. A simple 10‐step model was used to describe the equilibria existing between the various sulphur species and CO2 in cloud water at cloudwater concentrations of 0.1, 0.5, and 2.5 g m−3 and the resultantacidity calculated. Values of pH as low as 3.4 were predicted, with MSA having a negligible effect and sulphate dominating. Biogenic sulphur species from the North Atlantic may therefore make a small but quantifiable contribution to the atmospheric sulphur budget of the U.K. and may play an important role in determining rainwater acidity in the west of the country.
Observations of ozone and polar stratospheric clouds at Heiss Island during winter 1988–1989
Authors: Rosen J. M. , Kjome N. T. , Khattatov V. U. , Rudakov V. V. , Yushkov V. A.
Published: February 2012

Simultaneous balloonborne measurements of ozone and polar stratospheric clouds (PSCs) were made over Heiss Island (80.5°N, 57.6°E) during the 1988–1989 winter. These soundings were supplemented with additional ozonesondes and meteorological information obtained from regular radiosondes and rocketsondes. The ozone measurements taken by themselves do not suggest a spring decrease in ozone over Heiss Island. However, a comparison with ozonesonde data from another location near the solar terminator can be interpreted as suggesting ∼20% ozone loss between 17.5 and 24 km in the outer vortex. This would roughly correspond to a loss of ∼10 Dobson units (DU) or 3–4% loss in total ozone column. Observed transport effects make the identification of true ozone loss considerably more difficult and uncertain. No statistically significant direct correlation in the vertical structure of PSCs and ozone near the center of the dark Arctic vortex was observed in the limited number of soundings.
Toward the four dimensional assimilation of stratospheric chemical constituents
Authors: Austin John
Published: February 2012

A model to assimilate stratospheric chemical constituents is proposed. The chemical transport model used is two dimensional on an isentropic surface and solves the photochemical equations using an extended family approach. Thirty‐day integrations are performed at the three isentropic surfaces given by the potential temperature values 600 K, 850 K and 1400 K starting on January 1, 1979. During the integrations, Limb Infrared Monitor of the Stratosphere (LIMS) satellite data are assimilated into the model and the results are compared with independently mapped (map archive tape (MAT)) data. The assimilation results are found to be in good agreement with the independent analyses at all three levels. Preliminary assimilations revealed significant biases in modeled HNO3 at 850 K and in O3 at 1400 K. However, by changing the adjustable parameters of the assimilation model the HNO3 bias was successfully eliminated. The O3 bias was easily eliminated by the addition of an extra source term. The comparisons reveal possible minor weaknesses in the MAT analyses. First, the chemical constituents appear to be occasionally in error in the MAT data during rapidly changing dynamical events such as stratospheric warmings. Second, the temporal continuity is sometimes lacking in the MAT analyses, leading to rapidly changing concentrations which cannot be understood on the basis of conventionally understood photochemistry. On the other hand, the assimilation model used here does not produce very satisfactory analyses when the chemical data are very noisy. The differences between the assimilated and MAT analyses are quite small and are generally less than data errors. Although the assimilation model is here applied to LIMS data, the method is generally applicable to any data source and could be especially useful for analyzing the large volume of data from the Upper Atmosphere Research Satellite.
Antarctic skies 2. Characterization of the intensity and polarization of skylight in a high albedo environment
Authors: Beaglehole D. , Carter G. G.
Published: February 2012

Work in the Antarctic during spring 1990 has been aimed at obtaining a full understanding of the properties of light falling onto the Antarctic continent. The present paper describes details of the intensity and polarization distribution of the indirect skylight in the Sun‐zenith plane, and these are also compared with measurements made at Wellington, New Zealand. The light in Antarctica is shown to have a low maximum polarization of about 40%, essentially independent of wavelength across the visible spectrum. The intensity is strongest for light coming from directions in opposition to the Sun. A simple model shows that these features are due to multiple scattering in the atmosphere induced by the high snow albedo. A comparison is made with functions derived from theory.
Antarctic skies 1. Diurnal variations of the sky irradiance, and UV effects of the ozone hole, spring 1990
Authors: Beaglehole D. , Carter G. G.
Published: February 2012

This is the first of two papers reporting measurements made near Scott Base, Antarctica, during the spring of 1990 (October‐November). The present paper describes the hourly and daily variations of the light falling on a horizontal surface, with the incident light divided into two components, that from the Sun directly and that from the sky. The light has been separated into four wavelength bands covering the blue to the UVB region of the spectrum. The intensities have been compared with values measured in Wellington, New Zealand. A simple air mass dependence has been found which fits the complete data set once a surface albedo parameter is taken into account, which provides an easy estimate for the daily average illumination throughout the year. The paper also correlates the changes in the UV and UVB with changes in upper atmosphere ozone concentration and compares the total daily UV dose in the Antarctic with that at Wellington, a typical mid‐latitude site.
The chlorine budget of the present‐day atmosphere: A modeling study
Authors: Weisenstein Debra K. , Ko Malcolm K. W. , Sze Nien‐Dak
Published: February 2012

We present results from a time‐dependent model simulation of the atmospheric total chlorine and show the distribution of source gases and of inorganic chlorine (ClY) derived from them as functions of latitude and altitude. Source gases modeled include CFC‐11, CFC‐12, CCl4, CFC‐113, HCFC‐22, CH3CCl3, and CH3Cl. Results are presented for the 1985 atmosphere using historical emissions; steady state results are also shown for comparison. The relationship between the upper stratospheric concentration of ClY derived from a specific source gas and the surface concentration of the source gas reflects both the removal rate of the gas and whether the gas is in steady state with the emissions. Observations show that ozone changes in the past decade have been dominated by losses in the mid‐latitude lower stratosphere and the polar regions (WMO, 1988). The ClY concentration in these regions is derived from source gases in the following proportions for the 1985 model‐calculated atmosphere: CFC‐11 24%, CH3Cl 21%, CCl4 19%, CH3CCl3 18%, CFC‐12 15%, CFC‐113 2%, and HCFC‐22 1%. CFC‐11, CCl4, and CH3CCl3 play a larger role in the lower stratosphere than the corresponding steady state estimates using surface concentration would suggest.