bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of resolution and physics on precipitation in the NCAR Community Climate Model
Authors: Marshall S. , Roads J. O. , Oglesby R. J.
Published: February 2004

Simulations of precipitation at different horizontal resolutions from the National Center for Atmospheric Research Community Climate Model (NCAR CCM2) version 2, are compared to four observed global climatologies. Simulations were available at the following resolutions: R15, T21, T31, T42, T63, T106, and T170 and range from 2 years in length (for the highest resolution T170) to 10 years in length. These runs all had prescribed, climatological sea surface temperatures and soil moisture which varied by month. An additional simulation of CCM2 at T42 coupled to a soil‐vegetation atmospheric transfer (SVAT) package was also used. We also show the climatology of the latest version of the NCAR CCM (CCM3) and compare this to the T42 simulations of CCM2 as well as to the observations. The main results include the following: (1) The models fall within the uncertainty of the observations. (2) Little systematic difference is seen in the simulation of precipitation as one goes from T42 to T170 resolution. (3) The SVAT interactive land surface package simulation does as well as a specified surface hydrology. (4) The simulation by CCM3 shows a marked improvement over all CCM2 simulations at the global scale and particularly within the tropics.
Reduction of air ion mobility to standard conditions
Authors: Tammet H.
Published: February 2004

The Langevin rule of the reduction of air ion mobility is adequate in case of zero‐size ions. An alternative is the Stokes‐Millikan equation that is adequate in the limit of macroscopic charged particles. The temperature variation of air ion mobility predicted by the Stokes‐Millikan equation radically contradicts the Langevin rule. The temperature and pressure variation of air ion mobility is examined by using a new semiempirical model that describes the transition from the kinetic theory to the Stokes‐Millikan equation. The model is valid in full mobility range. It allows to calculate at first the size of an ion according to the measured mobility and then the standard mobility according to the size. The ascent of the temperature‐mobility curve on a logarithmic chart approaches the Langevin value of 1 only at very high mobilities not found in the atmosphere. The value of the ascent is 0.6 in the case of small ions of the mobility of 1.5 cm2 V−1 s−1 which brings about a considerable error when using the Langevin rule. It is recommended to store the natural values of the mobility in databases together with the values of temperature and pressure and to definitely indicate the method when the reduced mobilities are presented in publications.
Information content of Umkehr and solar backscattered ultraviolet (SBUV) 2 satellite data for ozone trends and solar responses in the stratosphere
Authors: Miller A. J. , Flynn L. E. , Hollandsworth S. M. , DeLuisi J. J. , Petropavlovskikh I. V. , Tiao G. C. , Reinsel G. C. , Wuebbles D. J. , Kerr J. , Nagatani R. M. , Bishop L. , Jackman C. H.
Published: February 2004

Within the past few years, several papers have been published which present updated profile ozone trends from the recently revised ground‐based Umkehr record [Miller et al., 1995] and the combined Nimbus 7 solar backscattered ultraviolet (SBUV) and NOAA 11 SBUV 2 satellite data record [Hollandsworth et al., 1995; Miller et al., 1996]. Within these papers, however, there has remained an overriding question as to the actual information content of the measurement systems and their ability to detect atmospheric responses. In this paper, we compare the ozone trends and responses to the 11‐year solar cycle (derived from model and/or data specifications of these effects) to results of forward model/retrieval algorithm computations through the algorithms. We consider data at northern midlatitudes (30°–50°N) so that we may compare the satellite results with those of the ground‐based systems. Our results indicate that the Umkehr data contain only four independent pieces of information in the vertical and that the SBUV system contains five. In particular, we find that consideration should be restricted to the following regions; Umkehr: the sum of Umkehr layers 1–5, and layers 6, 7, and 8+ (the sum of layers 8 and above), SBUV: the sum of layers 1–5, and layers 6, 7, 8, and 9+ (the sum of layers 9 and above). Additionally, we compare the actual trends and solar coefficients derived in these layers for the periods 1968–1991 and 1979–1991 for the Umkehr and SBUV data. Finally, we include within the latter comparisons the stratospheric aerosol and gas experiment (SAGE) I and II results from Wang et al. [1996] and the computations from the ozonesondes.
Aerosol particle evolution in an aircraft wake: Implications for the high‐speed civil transport fleet impact on ozone
Authors: Danilin M. Y. , Rodriguez J. M. , Ko M. K. W. , Weisenstein D. K. , Brown R. C. , Miake‐Lye R. C. , Anderson M. R.
Published: February 2004

Previous calculations of the ozone impact from a fleet of high‐speed civil transports (HSCTs) have been carried out by global two‐dimensional (2‐D) models [Bekki and PyIe, 1993; Pitari et al., 1993] which have not included explicit wake processing of sulfur species. This processing could be important for the global sulfate aerosol and ozone perturbations [Weisenstein et al., 1996]. For an HSCT scenario with emission indices of NOx and sulfur equal to 5 and 0.4, respectively, and a cruise speed of Mach 2.4 [Stolarski and Wesoky, 1993b], the Atmospheric and Environmental Research (AER) 2‐D model gives 0.50–1.1% as the range of the annually averaged O3 column depletion at 40°–50°N. This range is determined by the extreme assumption that emitted SO2 is diluted into the global model grid box either as gas or as 10 nm sulfate particles. A hierarchy of models is used here to investigate the impact of processes in the wake on the calculated global ozone response to sulfur emissions by a proposed HSCT fleet. We follow the evolution of aircraft emissions from the nozzle plane using three numerical models: the Standard Plume Flowfield‐II/Plume Nucleation and Condensation model (SPF‐II/PNC), an AER far wake model incorporating microphysics of aerosol particles, and the AER global 2‐D chemistry‐transport model. Particle measurements in the wake of the Concorde [Fahey et al., 1995a] are used to place constraints on sulfur oxidation processes in the engine and the near field. To explain the Concorde measurements, we consider cases with different fractions of SO3 (2%, 20%, and 40%) in the sulfur emissions at the nozzle plane and also the possibility of other unknown heterogeneous or homogeneous oxidation processes for SO2 in the wake. Assuming similar characteristics for the proposed HSCT fleet, the global ozone response is then calculated by the 2‐D model. Using the model‐calculated wake processing of sulfur emissions under the above assumptions and constrained by the Concorde particle measurements, the range of annually averaged O3 column depletion at 40°–50°N is reduced from 0.5–1.1% to 0.75–1.0%. Our analysis shows that the global ozone response is more sensitive to the assumed partitioning of sulfur emissions between SO2 and SO3 at the nozzle plane than to the wake dilution rate. Outstanding uncertainties and recommendations for further wake‐sampling experiments are also discussed.
Passive remote sensing of tropospheric aerosol and atmospheric correction for the aerosol effect
Authors: Kaufman Y. J. , Tanré D. , Gordon H. R. , Nakajima T. , Lenoble J. , Frouin R. , Grassl H. , Herman B. M. , King M. D. , Teillet P. M.
Published: February 2004

The launch of ADEOS in August 1996 with POLDER, TOMS, and OCTS instruments on board and the future launch of EOS‐AM 1 in mid‐1998 with MODIS and MISR instruments on board start a new era in remote sensing of aerosol as part of a new remote sensing of the whole Earth system (see a list of the acronyms in the Notation section of the paper). These platforms will be followed by other international platforms with unique aerosol sensing capability, some still in this century (e.g., ENVISAT in 1999). These international spaceborne multispectral, multiangular, and polarization measurements, combined for the first time with international automatic, routine monitoring of aerosol from the ground, are expected to form a quantum leap in our ability to observe the highly variable global aerosol. This new capability is contrasted with present single‐channel techniques for AVHRR, Meteosat, and GOES that although poorly calibrated and poorly characterized already generated important aerosol global maps and regional transport assessments. The new data will improve significantly atmospheric corrections for the aerosol effect on remote sensing of the oceans and be used to generate first real‐time atmospheric corrections over the land. This special issue summarizes the science behind this change in remote sensing, and the sensitivity studies and applications of the new algorithms to data from present satellite and aircraft instruments. Background information and a summary of a critical discussion that took place in a workshop devoted to this topic is given in this introductory paper. In the discussion it was concluded that the anticipated remote sensing of aerosol simultaneously from several space platforms with different observation strategies, together with continuous validations around the world, is expected to be of significant importance to test remote sensing approaches to characterize the complex and highly variable aerosol field. So far, we have only partial understanding of the information content and accuracy of the radiative transfer inversion of aerosol information from the satellite data, due to lack of sufficient theoretical analysis and applications to proper field data. This limitation will make the anticipated new data even more interesting and challenging. A main concern is the present inadequate ability to sense aerosol absorption, from space or from the ground. Absorption is a critical parameter for climate studies and atmospheric corrections. Over oceans, main concerns are the effects of white caps and dust on the correction scheme. Future improvement in aerosol retrieval and atmospheric corrections will require better climatology of the aerosol properties and understanding of the effects of mixed composition and shape of the particles. The main ingredient missing in the planned remote sensing of aerosol are spaceborne and ground‐based lidar observations of the aerosol profiles.
NO emissions from soils in the southeastern United States
Authors: Thornton Frank C. , Pier Paul A. , Valente Ralph J.
Published: February 2004

Biogenic soil emissions of nitric oxide (NO) are important in the formation of tropospheric ozone (O3) in the rural environment. This paper summarizes our recent estimates of soil NO emissions from a wide variety of sites in nine southeastern United States. A total of over 12,000 individual flux measurements was made from crop, pasture, and forests representing major physiographic regions within the southeast. These measurements were used to determine flux algorithms relating NO emissions from land types. Strong relationships were found between NO flux and temperature that explained over 80% of the variation in emissions. Using these relationships and Geographic Information Systems land base information for the states, calculated seasonal emissions for NO are reported. Crop land regulated regional soil NO emissions, accounting for 83% of the emissions in summer, 61% in spring, and 55% in fall. The summertime contribution of soil NO to the overall NO inventory, including anthropogenic sources, averaged 4.1% for the states, ranging from a high of 9.5% for Mississippi to a low of 2.2% for Florida. The importance of high summertime temperatures in controlling soil NO was evident in that emissions on a prototypical summer day were only one fifth the emissions of a hot (36°C, maximum daily high) summer day. Comparisons of the algorithms we developed to those of the current model used by the Environmental Protection Agency, BEIS 2.2, showed reasonable agreement, that is, agreement within a factor of 2, given the inherent temporal and spatial variability of soil NO emissions.
Sensitivity of northern hemisphere air temperatures and snow expansion to North Pacific sea surface temperatures in the Goddard Institute for Space Studies general circulation model
Authors: Peteet Dorothy , Del Genio Anthony , Lo Kenneth K.‐W.
Published: February 2004

Circum‐Pacific marine and terrestrial records indicate a series of temperature‐inferred oscillations during the late glacial. While many previous studies have probed the role of the North Atlantic in these oscillations, we test the sensitivity of the northern hemisphere air temperatures to North Pacific sea surface temperature (SST) oscillation in the Goddard Institute for Space Studies general circulation model. The effect of a colder North Pacific is to cool air temperatures over North America, as well as parts of Europe and Asia. The colder SSTs result in a large hemispheric response due to the loss of water vapor as a greenhouse gas. The large sensitivity of the northern hemisphere to a North Pacific SST change has implications for the ice age climate as well as the late glacial interval. The results of this experiment provide a rapid mechanism for widespread cooling which has not been previously addressed.
The influence of radiation on tropopause behavior and stratosphere‐troposphere exchange in an upper tropospheric anticyclone
Authors: Zierl Bärbel , Wirth Volkmar
Published: February 2004

In this paper we investigate the influence of radiation on the evolution of an idealized, upper tropospheric anticyclone, focusing on the tropopause behavior and stratosphere‐troposphere mass exchange. A realistic radiation scheme is implemented in an axisymmetric balanced vortex model. A number of numerical integrations are performed, starting from an upper tropospheric anticyclone as the initial state. For average midlatitude conditions the secondary cross‐vortex circulation induced by the radiative heating and cooling is such that the vertical wind is almost zero near the tropopause. Nevertheless, the tropopause in the center of the anticyclone is displaced downward by about 1.5 km within 10 days of integration, resulting in a substantial transfer of mass from the troposphere to the stratosphere. One part of the diabatic heating, which is responsible for the cross‐tropopause mass transfer, is due to the temperature anomalies in the center of the anticycone, while another part should be attributed to the suppression of convection there. The amount of mass transferred across the tropopause is sensitive to the structure and the strength of the upper tropospheric temperature anomalies and, especially, to the humidity close to the tropopause, with upper tropospheric and lower stratospheric humidity playing rather different roles. The cross‐tropopause mass transfer does not sensitively depend on the definition of the tropopause.
Toward monitoring the tropospheric temperature by means of a general circulation model
Authors: Stendel Martin , Bengtsson Lennart
Published: February 2004

The recent global tropospheric temperature trend can be reproduced by climate models that are forced only by observed sea surface temperature (SST) anomalies. In this study, simulations with the Hamburg climate model (ECHAM) are compared to temperatures from microwave sounding units (MSU) and to reanalyses from the European Centre for Medium‐Range Weather Forecasts. There is overall agreement of observed and simulated tropospheric temperature anomalies in many regions, in particular in the tropics and over the oceans, which lack conventional observing systems. This provides the opportunity to link physically different quantities, such as surface observations or analyses (SST) and satellite soundings (MSU) by means of a general circulation model. The proposed method can indicate inconsistencies between MSU temperatures and SSTs and has apparently done so. Differences between observed and simulated tropospheric temperature anomalies can partly be attributed to stratospheric aerosol variations due to major volcanic eruptions.
Satellite investigations of fire, smoke, and carbon monoxide during April 1994 MAPS mission: Case studies over tropical Asia
Authors: Christopher Sundar A. , Chou Joyce , Welch Ronald M. , Kliche Donna V. , Connors Vickie S.
Published: February 2004

During April 9–19, 1994, the Measurement of Air Pollution from Satellites (MAPS) measured free tropospheric carbon monoxide (CO) concentrations on a near‐global basis. For these eleven days the global 1 km advanced very high resolution radiometer (AVHRR) Pathfinder data are used to detect fires and smoke over the Indo‐Burma region (85°E‐110°E; 10°N‐30°N). The fire activities are categorized for four major ecosystems that include (1) cropland/natural vegetation mosaic (CNVM), (2) evergreen broadleaf forest (EBF), (3) mixed forest (MFD), and (4) grassland (GL). Using published emission rates between particulate matter and carbon monoxide concentrations from temperate areas, the fire counts along with other information are used to obtain estimates of CO concentrations from the AVHRR data. More than 7000 fires are detected during the study period with 23%, 43%, 24%, and 10% fires in the CNVM, EBF, MFD, and GL ecosystems, respectively. The enhanced CO concentrations over the area of study are either over or downwind of the fires detected by the AVHRR. The preliminary AVHRR estimates of CO concentrations are smaller than the MAPS‐measured values by a factor of 4 to 5 for fire counts greater than 200. The differences are attributed to the lack of transport mechanisms and other assumptions in the current model. However, these results show a good potential for using the AVHRR measurements to detect fires and smoke and also to estimate CO concentrations.
Vertical profiling using a complementary kite and tethered balloon platform at Ferryland Downs, Newfoundland, Canada: Observation of a dry, ozone‐rich plume in the free troposphere
Authors: Knapp K. G. , Jensen M. L. , Balsley B. B. , Bognar J. A. , Oltmans S. J. , Smith T. W. , Birks J. W.
Published: February 2004

Vertical profiles of ozone mixing ratio, water vapor mixing ratio, and temperature obtained during August 3–13, 1995, at Ferryland Downs, Newfoundland, Canada, as part of the North Atlantic Regional Experiment (NARE) demonstrate the use of high‐altitude tethered balloons and kites as measurement platforms. In combination with a novel, fast winching system, previously developed for use with kites, tethered balloons were used for profiling chemical species and meteorological parameters to altitudes as high as 7.6 km. Tethered balloon profiling complements profiling with kite systems by expanding the range of wind conditions over which data can be obtained. A total of 65 profiles were collected using these platforms. Elevated ozone mixing ratios highly anticorrelated with water vapor mixing ratios observed during August 4–7 suggest an upper atmospheric source for ozone‐rich air during summertime in the Maritime Provinces of Canada. Ozone mixing ratios reaching 100 parts per billion by volume (ppbv) in this air mass were associated with water vapor mixing ratios as low as 0.1 g kg−1. Profiles collected during August 11–13 demonstrate the use of kite and balloon systems to obtain vertical profiles over a wide range of wind conditions. Ozone mixing ratios of 65 ppbv were observed at 1 km altitude on August 12, while profiles collected on August 13 exhibit no evidence of elevated ozone. These results document the rapid transport of an air mass containing elevated ozone levels over the sampling site that would not have been possible with either system alone.
Uncertainties in modeled and measured clear‐sky surface shortwave irradiances
Authors: Kato Seiji , Ackerman Thomas P. , Clothiaux Eugene E. , Mather James H. , Mace Gerald G. , Wesely Marvin L. , Murcray Frank , Michalsky Joseph
Published: February 2004

A comparison of five independent measurements of the clear‐sky downward shortwave irradiance at the surface shows that they scatter within a 5% range depending on their calibration constants. When the measurements are corrected using data from two cavity radiometers, three of the five independent measurements agree within 3 W m−2 over three clear‐sky days, which is well within the estimated error limit of ±1.5%. A comparison of these three sets of irradiance measurements with the computed irradiance by a δ2‐stream model reveals that the model overestimates the irradiance by 5%. Detailed investigation of the approximations and uncertainties associated with the computations (including the measurement error in the water vapor and ozone amounts, neglecting the state of polarization and trace gas absorption, the 2‐stream approximation, the neglect of the spectral dependence of the surface albedo, and the uncertainties associated with aerosols) demonstrates that the discrepancy is not due to these approximations. Further analysis of the modeled and measured irradiance shows that the discrepancy is almost entirely due to the difference between modeled and measured diffuse field irradiances. An analysis of narrow‐band diffuse to total irradiance ratios shows that this discrepancy is the largest near 400 nm and decreases with wavelength. These results rely on the absolute calibrations of two cavity radiometers, two shaded pyranometers, and one unshaded pyranometer, as well as ratios of irradiances measured by a multifilter rotating shadow‐band radiometer. Therefore, in order for instrumental error to account for the diffuse field discrepancy, three independent measurements of the diffuse field irradiance must be biased low by at least 40%. For an aerosol to account for this discrepancy, it must be highly absorbing with a single‐scattering albedo as low as 0.3. The unlikelihood of instrumental errors of 40% and aerosol single‐scattering albedos of 0.3 suggests a third possibility: the neglect of some gaseous absorption process at visible wavelengths.
Water balance of the Amazon Basin: Dependence on vegetation cover and canopy conductance
Authors: Costa Marcos Heil , Foley Jonathan A.
Published: February 2004

The availability and geographic distribution of fresh water resources may undergo significant changes in response to global environmental change. In this study, we examine the water balance of the Amazon Basin using a modified version of the LSX land surface model [Pollard and Thompson, 1995; Thompson and Pollard, 1995a, b] which includes a representation of land surface processes, canopy physiology (stomatal conductance, transpiration, and photosynthesis), and continental‐scale hydrological routing. The model operates on a 0.5° by 0.5° grid and is forced with observed long‐term climatological data. As an initial application of the model, we examine the seasonal variability of water balance within the Amazon Basin. The simulation is evaluated by comparing (1) simulated evapotranspiration with observations for different vegetation cover types and (2) simulated river discharge against the long‐term records of 56 fluviometric stations spread throughout the basin. The model results show that evapotranspiration is strongly dependent on the vegetation cover, especially during the rainy season. Overall, we find good agreement between the simulated and the observed water balance: for most of the fluviometric stations the error is less than 25%. In addition, we perform a model sensitivity study to determine the role of changes in vegetation cover on the water balance, without considering feedbacks on climate. When forests, woodlands, and savannas are replaced with grasslands, annual average evapotranspiration decreases by ∼0.5 mm d−1 (∼12%), which is comparable to observations. Finally, we perform a model sensitivity study in order to assess the potential physiological effects of increased CO2 on stomatal (canopy) conductance and, as a consequence, on the water balance of the Amazon Basin, again without considering feedbacks on the atmosphere. The model results suggest that doubling atmospheric CO2 concentrations (from 325 to 650 ppmv) would decrease the canopy conductance by 20 to 35% (depending on the vegetation type) arid would decrease evapotranspiration by ∼4% throughout the region. As a consequence, annual river discharge increases by between 3% and 16.5%, depending on the position within the basin. At the mouth of the Amazon arid Tocantins Rivers, annual discharge increases by 5 and 9%, respectively.
Evolution of tropospheric ions observed by an ion mobility spectrometer with a drift tube
Authors: Nagato Kenkichi , Ogawa Toshio
Published: February 2004

The evolution of tropospheric ions has been studied by investigating the change in the mobility spectrum of ions generated in laboratory air as a function of aging time. An ion mobility spectrometer with a drift tube was constructed to get high‐resolution measurements of mobility spectra of ions aged for about 0.03–5 s. Mobility spectra and their changes with ion age obtained in the present study showed the following features of tropospheric ion evolution near the ground: The positive ion mobility spectrum changes significantly with aging time, in which the peak mobility value shifts from 1.8 to about 1.0 cm2 V−1 s−1. Six peaks are usually distinguished in the mobility range between 2.0 and 1.0 cm2 V−1 s−1 in the positive spectrum, and a tendency of positive ions to evolve to have lower mobilities with increasing ion age is observed. Four additional peaks are sometimes resolved at around 0.9 cm2 V−1 s−1, indicating formation of heavy positive ions (probably over 400 amu). The negative ion mobility spectrum obtained is characterized by two prominent peaks at 1.9 and 1.7 cm2 V−1 s−1. The relative intensity of the two peaks varies with ion age, and the ions with a mobility of 1.9 cm2 V−1 s−1 dominate after about 1 s. Further conversions of the negative ions to those with lower mobilities can be expected from a comparison with the natural ion spectra obtained so far by the Gerdien type aspiration condenser.
Ammonium in coastal Antarctic aerosol and snow: Role of polar ocean and penguin emissions
Authors: Legrand Michel , Ducroz François , Wagenbach Dietmar , Mulvaney Robert , Hall Julie
Published: February 2004

Year‐round aerosol samples collected in the boundary layer at coastal Antarctic sites (Dumont D'Urville, Neumayer, and Halley) indicate a seasonal cycle of ammonium concentrations with a minimum in winter (April–September). A large intersite difference appears in the summer (November–February) maxima values, from ∼12.5 ng m−3 at Neumayer to 140–230 ng m−3 at Dumont D'Urville. At Dumont D'Urville, ammonium concentrations are the largest ever reported from Antarctic sites, and the large summer maxima are associated with large enrichments with respect to sea salt for potassium and calcium. In addition, seasonal ammonium variations at Dumont D'Urville are in phase with a well‐marked seasonal cycle of oxalate concentrations which exhibit maxima of 5–10 ng m−3 in spring and summer and minima of less than 0.5 ng m−3 in winter. Such a composition of aerosols present in the boundary layer at Dumont D'Urville in summer is linked to the presence of a large Adélie penguin population from the end of October to March at the site. Ornithogenic soils (defined as guano‐enriched soils), together with the bacterial decomposition of uric acid, are a source of ammonium, oxalate, and cation (such as potassium and calcium) aerosol, in addition to a subsequent large ammonia loss from ornithogenic soils to the atmosphere. The total breeding population of 5 million Adélie penguins widely distributed around the Antarctic continent may emit, at most, some 2.5 × 10−4 Mt of NH3‐N during the summer months. In contrast, Halley and Neumayer Stations are far less exposed to penguin colony emissions. At Neumayer, ammonium concentrations peak from January to March and are in phase with the increase of biogenic sulfur species. Here the NH4+/(MSA + nss SO4−) molar ratio is close to 13% in summer aerosol and to 40% in winter aerosol. Using this summer ratio, which may be related to ammonia and sulfur oceanic emissions occurring south of 50°S in summer and estimated DMS emissions in these regions at this time, we derive an upper limit of 0.064 Mt NH3‐N emitted per year by the high‐latitude Southern Ocean in summer. This study indicates a very limited ammonia neutralization of acidic sulfate aerosols at high southern latitudes, except in the vicinity of ornithogenic soils occupied by large penguin colonies.
Sensitivity of climate simulations to radiative effects of tropical anvil structure
Authors: Zender Charles S. , Kiehl J. T.
Published: February 2004

Climate sensitivity to the representation of tropical anvil is investigated in a version of the National Center for Atmospheric Research Community Climate Model. Common features of tropical anvil generation and structure, consistent with observations and cloud resolving models, are incorporated into a simple prognostic anvil parameterization. These features include anvil convective origin, vertical profile, phase, areal extent, and life span. Two numerical climate integrations are forced by 1985–1989 sea surface temperature (SST): the control, with simple diagnostic anvil, and the experiment, which simulates tropical anvil structure prognostically. The prognostic anvil formulation enhances ice and reduces liquid in the tropics. Increase in hydrometeor size associated with anvil weakens cloud radiative extinction per unit mass by factors of 1–3. The weaker mass extinction efficiency approximately balances enhanced ice amount so that anvil ice mass quadruples without biasing the mean radiative energy balance but significantly alters the vertical distribution of radiative effects. Enhanced anvil perturbs the tropical upper troposphere temperature structure more strongly in winter, when the column is clearer and anvil radiatively heats the troposphere above 200 mbar. In the summer tropics, enhanced anvil reduces radiative cooling up to 200 mbar and enhances cooling above that. The prognostic anvil formulation improves longwave cloud radiative response to SST cooling but worsens response to warming >2°C. The net response of convection is a shift toward the winter hemisphere in solstice months. These changes lead to a significant response in the extratropical height field in January. These results emphasize the importance of representing tropical anvil structure in climate simulations.
The isotopic composition of tropospheric ozone in three environments
Authors: Johnston Jeffrey C. , Thiemens Mark H.
Published: February 2004

Ground‐level ozone (O3) has been sampled from three environments: La Jolla and Pasadena, California, and White Sands Missile Range, New Mexico, using recently developed techniques for cryogenically collecting and isotopically analyzing samples of atmospheric O3. Significant isotopic variability is observed at each location, in addition to potentially important differences between the sampling locations. The isotopic composition of O3 is a sensitive indicator for the formation and decomposition processes which have influenced the O3 reservoir Thus the isotopic characterization of ground‐level O3 could provide a new source of information regarding atmospheric transformation mechanisms. To date, the measured isotopic variability in ground‐level O3 shows no correlation with O3 or NOx mixing ratios, meteorological parameters, or time of day. However, preliminary results show a correlation between the pattern of isotopic fractionation and degree of photochemical control over the local O3 budget at each sampling location. It should be noted that the conclusions presented are preliminary because of the relatively small data sets, particularly at the Pasadena and New Mexico locations. However, we believe that the results of this research indicate that the isotopic composition of tropospheric O3 is variable and contains information which could be useful in the effort to understand the tropospheric O3 budget.
Concerning the interpretation of enhanced cloud shortwave absorption using monthly‐mean Earth Radiation Budget Experiment/Global Energy Balance Archive measurements
Authors: Zhang Minghua , Cess Robert D. , Jing Xiaodu
Published: February 2004

To study the signature of enhanced shortwave absorption in clouds, several recent studies have used monthly‐mean shortwave radiation measurements from the Earth Radiation Budget Experiment (ERBE) together with monthly‐mean surface insolation as obtained from the Global Energy Balance Archive (GEBA). In this paper we discuss probable causes of inconsistent results, among themselves, from these studies and with other studies that have reported enhanced shortwave cloud absorption relative to theoretical model calculations. Two factors are identified as potential contributing sources of inconsistencies. One is the inseparability of the seasonal variations of water vapor and clouds in the continental area of the northern hemisphere when using collocated monthly ERBE/GEBA data. The second is the impact of data collocation errors on the signature of cloud absorption. Both factors are quantitatively examined using observational data and radiative transfer models.
Role of entrainment in surface‐atmosphere interactions over the boreal forest
Authors: Davis Kenneth J. , Lenschow Donald H. , Oncley Steven P. , Kiemle Christoph , Ehret Gerhard , Giez Andreas , Mann Jakob
Published: February 2004

We present a description of the evolution of the convective boundary layer (CBL) over the boreal forests of Saskatchewan and Manitoba, as observed by the National Center for Atmospheric Research (NCAR) Electra research aircraft during the 1994 Boreal Ecosystem‐Atmosphere Study (BOREAS). All observations were made between 1530 and 2230 UT (0930–1630 local solar time (LST)). We show that the CBL flux divergence often led to drying of the CBL over the course of the day, with the greatest drying (approaching 0.5 g kg−1 h−1) observed in the morning, 1000–1200 LST, and decreasing over time to nearly no drying (0–0.1 g kg−1 h−1) by midafternoon (1500–1600 LST). The maximum warming (0.45 K h−1 ) also occurred in the morning and decreased slightly to about 0.4 Kh−1 by midafternoon. The CBL vapor pressure deficit (VPD) increased over the course of the day. A significant portion of this increase can be explained by the vertical flux divergence, though horizontal advection also appears to be important. We suggest a linkage among boundary layer growth, the vertical flux divergences, and boundary layer cloud formation, with cloud activity peaking at midday in response to rapid CBL growth, then decreasing somewhat later in the day in response to CBL warming and decreased growth. We also see evidence of feedback between increasing VPD and stomatal control. We use eddy‐covariance flux measurements from the Electra to compute the virtual temperature entrainment ratio Ar. The computed mean value of 0.08±0.12 is somewhat lower than the commonly assumed value of 0.2, as well as with other estimates from BOREAS. This value is very sensitive to the determination of CBL depth. We find that Ar increases with an increasing jump in mean wind across the CBL top. The entrainment flux of water vapor is found to be most dependent on time of day (negative correlation). The ratio of entrainment to surface flux of water vapor is 1.57±0.25. Airborne lidar observations of the CBL top reveal a CBL top “thickness” that is smaller than would be expected from simple theory but consistent with past lidar observations. The normalized thickness is found to have a very consistent value
, where 12 cases were examined. A new method of computing the variability of the CBL top is illustrated, and we show that this variance in the CBL depth also scales with the depth but that the value of this normalized variance differs substantially from the “thickness” defined in past literature.
Ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at Vostok Station (East Antarctica)
Authors: Salamatin Andrey N. , Lipenkov Vladimir Y. , Barkov Nartsiss I. , Jouzel Jean , Petit Jean Robert , Raynaud Dominique
Published: February 2004

An interpretation of the deuterium profile measured along the Vostok (East Antarctica) ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis. An inverse problem is solved to infer a local “geophysical metronome,” the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of Milankovich periods. By correlating the smoothed isotopic temperature record to the metronome, a chronostratigraphy of the Vostok ice core is derived with an accuracy of ±3.0–4.5 kyr. The developed timescale predicts an age of 241 kyr at a depth of 2760 m. The ratio δD/δTi between deuterium content and cloud temperature fluctuations (at the top of the inversion layer) is examined by fitting simulated and measured borehole temperature profiles. The conventional estimate of the deuterium‐temperature slope corresponding to the present‐day spatial ratio (9 per mil/°C) is confirmed in general. However, the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature, responsible for the thermal state of the ice sheet, to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record. With this assumption, we obtain the long‐term temporal deuterium‐temperature slope to be 5.8–6.5 per mil/°C which implies that the glacial‐interglacial temperature increase over central Antarctica was about 15°C in the surface temperature and 10°C in the inversion temperature. Past variations of the accumulation rate and the corresponding changes in the ice‐sheet surface elevation are simultaneously simulated.
Wind erosion prediction over the Australian continent
Authors: Shao Yaping , Leslie Lance M.
Published: February 2004

Wind erosion is a complicated process influenced by weather patterns, soil conditions, and vegetation cover. In this work we present an integrated wind erosion assessment and prediction system which couples a wind erosion scheme with an atmospheric prediction model and a Geographic Information System database. The system is applied to the February 1996 dust storms over the Australian continent, and the predictions are in good agreement with meteorological records and satellite images. It is found that over the 1 week period from February 6 to 12, 1996, the total dust emission from the Australian continent was around 6 million tons. As demonstrated in this study, the system can be used to identify areas and periods under wind erosion threat and to identify the responsible environmental factors. For atmospheric studies the integrated system provides a possibility of quantifying the sources of dust particles which in turn play an important role in atmospheric radiative processes.
A detailed assessment of snow accumulation in katabatic wind areas on the Ross Ice Shelf, Antarctica
Authors: Braaten David A.
Published: February 2004

An investigation of time dependent snow accumulation and erosion dynamics in a wind‐swept environment was undertaken at two automatic weather stations sites on the Ross Ice Shelf between January 1994 and November 1995 using newly developed instrumentation employing a technique which automatically disperses inert, colored (high albedo) glass microspheres onto the snow surface at fixed intervals throughout the year. The microspheres act as a time marker and tracer to allow the accumulation rate and wind erosion processes to be quantified with a high temporal resolution. Snow core and snow pit sampling was conducted twice during the study period to identify microsphere horizons in the annual snow accumulation profile, allowing the snow accumulation/erosion events to be reconstructed. The two sites chosen for this investigation have characteristically different mean wind speeds and therefore allow a comparative examination on the role of wind on ice sheet growth. Mass accumulation rate at the two sites for the 14‐day integration periods available ranged from 0.0 to >2.0 kg m−2 d−1. The mean mass accumulation rate during the study period was greater at the site with stronger winds (0.69 kg m−2 d−1) than the site with lower mean wind speeds (0.61 kg m−2 d−1); however, the difference between the two means is not statistically significant. Accumulation rates derived from an ultrasonic snow depth gauge operated at one of the sites are compared to the actual tracer‐derived accumulation rates and show the limitations of only having a measure of snow surface height with no instantaneous measurements of the snow density profile. Snow depth gauge derived accumulation rates were found to be greatly overestimated during high‐accumulation periods and were greatly underestimated during low‐accumulation periods.
Principal modes of the total ozone on the Southern Oscillation timescale and related temperature variations
Authors: Kayano Mary T.
Published: February 2004

Total ozone and associated temperature variations on the Southern Oscillation timescale have been investigated using monthly total ozone mapping spectrometer and temperature data for the latitudinal domain between 70°N and 70°S and from 1979 to 1991. The first two modes for total ozone describe the anomalous total ozone patterns associated with the extremes in the Southern Oscillation. The first mode has the largest loadings in the southern hemisphere (SH) subtropics and midlatitudes with an east‐west dipole in antiphase with a tropical east‐west dipole. The second mode has its largest loadings in the tropics with an east‐west dipolar pattern. These modes are intimately related to variations in the mean temperature in the lower stratosphere, and this relation is such that the total ozone and mean temperature anomalies are positively correlated. The tropospheric temperature patterns are confined in the tropics, where temperature and total ozone anomalies are negatively correlated. The tropical temperature and total ozone variations are driven by modulations in the tropical convection associated with the Southern Oscillation. The Southern Oscillation signals in the stratospheric temperature and in the total ozone are strongest in the SH midlatitudes during the winter‐spring period and precede the extremes in the Southern Oscillation Index (SOI) by a few months. Thus the total ozone index, defined similarly to the SOI, seems to be more appropriate than the SOI to monitor the stratospheric temperature in the extratropics, in particular in the SH middle to high latitudes.
UV‐visible absorption cross sections of bromine nitrate determined by photolysis of BrONO2/Br2 mixtures
Authors: Deters Bernd , Burrows John P. , Orphal Johannes
Published: February 2004

Experiments on the determination of absorption cross sections of bromine nitrate by photolysis of BrONO2/Br2 mixtures were carried out using a UV‐visible absorption spectrometer. The relatively stable end products of photolysis were identified as Br2 and N2O5. NO3 was observed as intermediate product in the photolysis of BrONO2/Br2. Absorption cross sections for BrONO2 at 298 K and 230 K were determined between 208 and 500 nm. The results are in good agreement with a recent independent study. Calculations of atmospheric photolysis rates of BrONO2 as a function of solar zenith angle and surface albedo were undertaken using the PHOTOGT program. The latter are in the range between 0.5×10−3 s−1 and 4.0×10−3 s−1, indicating that during daylight BrONO2 is rapidly photolyzed.
The diffuse aurora: A significant source of ionization in the middle atmosphere
Authors: Frahm R. A. , Winningham J. D. , Sharber J. R. , Link R. , Crowley G. , Gaines E. E. , Chenette D. L. , Anderson B. J. , Potemra T. A.
Published: February 2004

Energetic electrons can penetrate into the middle atmosphere causing excitation, dissociation, and ionization of neutral constituents, resulting in chemical changes. In this paper, representative electron spectra measured by the Upper Atmosphere Research Satellite particle environment monitor are used to determine the relative contributions of bremsstrahlung X rays and direct electron impact on the energy deposition and ionization production rates for altitudes between 20 and 150 km. Above 50 km most of the ionization comes from direct electron impact. However, in the stratosphere the energy contributed below 50 km is mostly due to bremsstrahlung X rays. In the diffuse aurora the ionization from the bremsstrahlung component exceeds that due to the galactic cosmic ray background to altitudes as low as 30 km during geomagnetically active periods. This paper demonstrates that a diffuse auroral source can input as much or more energy into the upper portion of the lower and middle atmosphere as previously reported for relativistic electron events. The effects of the diffuse aurora (including both the direct electron and the bremsstrahlung contributions) on atmospheric chemistry may be significant.
Comparisons between the microwave sounding unit temperature record and the surface temperature record from 1979 to 1996: Real differences or potential discontinuities?
Authors: Jones P. D. , Osborn T. J. , Wigley T. M. L. , Kelly P. M. , Santer B. D.
Published: February 2004

This paper reports a detailed comparison at the global, hemispheric, three 60°‐latitude zone, and grid‐box scale between lower tropospheric temperatures from the microwave sounding units (MSU2R) on board NOAA polar orbiting satellites and surface temperatures. The comparisons reveal differences in the course of temperature trends over the 1979–1996 period in the two sets of time series. The surface data warms relative to MSU2R by 0.19°C per decade over this period, with much of the change occurring as a jump in the difference series, particularly during 1991 but also in 1981. The differences either reflect problems in one or both of the surface or MSU2R records or, if both records are correct, a significant change in lapse rates in the lower part of the atmosphere on a global scale particularly since mid‐1991. Although MSU2R data agree well with radiosonde data on global and hemispheric scales over 1979–1996, surface and radiosonde data agree almost exactly when their trends are compared over 1958–1993 and 1965–1996. The differences in the two data sets are discussed in terms of possible natural causes and data homogeneities.
Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE): Experimental and data details
Authors: Valero Francisco P. J. , Bucholtz Anthony , Bush Brett C. , Pope Shelly K. , Collins William D. , Flatau Piotr , Strawa Anthony , Gore Warren J. Y.
Published: February 2004

Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) was conducted to study the magnitude and spectral characteristics of the absorption of solar radiation by the clear and cloudy atmosphere. Three aircraft platforms, a Grob Egrett, a NASA ER‐2, and a Twin Otter, were used during ARESE in conjunction with the Atmospheric Radiation Measurements (ARM) central and extended facilities in north central Oklahoma. The aircraft were coordinated to simultaneously measure solar irradiances in the total spectral broadband (0.224–3.91 μm), near infrared broadband (0.678–3.3 μm), and in seven narrow band‐pass (∼10 nm width) channels centered at 0.500, 0.862, 1.064, 1.249, 1.501, 1.651, and 1.750 μm. Instrumental calibration issues are discussed in some detail, in particular radiometric power, angular, and spectral responses. The data discussed in this paper are available at the ARM ARESE data archive via anonymous FTP to ftp.arm.gov.