bluuebunny/crossref_metadata_2025 huggingface dataset:
TRACE A trajectory intercomparison: 2. Isentropic and kinematic methods
Authors: Fuelberg Henry E. , Loring Robert O. , Watson Mark V. , Sinha M. C. , Pickering Kenneth E. , Thompson Anne M. , Sachse Glen W. , Blake Donald R. , Schoeberl Mark R.
Published: February 2004

Kinematic and isentropic trajectories are compared quantitatively during a single 5‐day period (October 13–18, 1992) when several flights for the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) experiment were conducted off the west coast of Africa. European Centre for Medium‐Range Weather Forecasts (ECMWF) data are used to compute the 5‐day backward trajectories arriving at locations over the South Atlantic Ocean and nearby parts of South America and southern Africa. Two versions of kinematic trajectories are examined. One version employs vertical motions supplied with the ECMWF data. These trajectories often differ greatly from those based on the isentropic assumption. The kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts; however, most diabatic rates are consistent with those of synoptic‐scale systems. Ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a TRACE A flight. A second version of kinematic trajectories employs vertical motions diagnosed from ECMWF horizontal wind components using the continuity equation. These vertical motions are stronger than those supplied with the ECMWF data, causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions. Many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale. This occurs, in part, because the diagnosed vertical motions are inconsistent with the ECMWF data. The research indicates that the kinematic procedure yields realistic 5‐day backward trajectories when the three‐dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ECMWF.
Global vegetation cover changes from coarse resolution satellite data
Authors: Nemani Ramakrishna R. , Running Steven W. , Pielke Roger A. , Chase Thomas N.
Published: February 2004

Land cover plays a key role in various biophysical processes related to global climate and terrestrial biogeochemistry. Although global land cover has dramatically changed over the last few centuries, until now there has been no consistent way of quantifying the changes globally. In this study we used long‐term climate and soils data along with coarse resolution satellite observations to quantify the magnitude and spatial extent of large‐scale land cover changes attributable to anthropogenic processes. Differences between potential leaf area index (LAI), derived from climate‐soil‐leaf area equilibrium, and actual leaf area index obtained from satellite data are used to estimate changes in land cover. Further, changes in LAI between potential and actual conditions are linked to climate by expressing them as possible changes in radiometric surface temperatures (Tr) resulting from changes in surface energy partitioning. As expected, areas with high population densities, such as India, China, and western Europe showed large reductions in LAI. Changes in global land cover expressed as summer, midafternoon Tr, ranged from −8° to +16°C. Deforestation resulted in an increase in Tr, while irrigated agriculture reduced the Tr. Many of the current general circulation models (GCMs) use potential vegetation maps to represent global vegetation. Our results indicate that there are widespread changes in global land cover due to deforestation and agriculture below the resolution of many GCMs, and these changes could have a significant impact on climate. Potential and actual LAI data sets are available for climate modelers at 0.5° × 0.5° resolution to study the possible impacts of land cover changes on global temperatures and circulation patterns.
Sensitivity of the CCM1 hydrologic cycle to CO2
Authors: Roads J. O. , Marshall S. , Oglesby R. , Chen S.‐C.
Published: February 2004

To better understand the global hydrologic cycle, climatological simulations with the National Center for Atmospheric Research global atmospheric general circulation model (GCM) or community climate model (CCM1), coupled to a mixed layer model, are compared to available global hydrologic observations. We find that CCM1 simulates, reasonably well, the large‐scale precipitable water, moisture flux convergence, precipitation, and evaporation potentials. Regional discrepancies are noticeable, though, especially in the eastern tropical Pacific. Smaller‐scale moisture flux convergence, precipitation, and evaporation also compare less well since effects of resolution can be discerned between low‐resolution simulations and higher‐resolution global observations. Sensitivity experiments to changed CO2 show that the CCM1 hydrologic response is similar to other GCMs. Precipitable water, evaporation, and precipitation increase while snow decreases with increasing CO2. Soil moisture changes are seasonally and regionally dependent. In middle latitudes, soil moisture increases during the winter and decreases during the summer with increasing CO2. Changes in moisture transport between land and ocean are also seasonally dependent. Increased CO2 induces increased moisture divergence over the central equatorial Pacific during December, January, February (DJF). This water is transported to the rest of the northern hemisphere land and ocean where precipitation is much greater than evaporation over the climatologically cold land surface. During June, July, August (JJA), water is preferentially converged over the western Pacific Ocean.
Diurnal asymmetry of climatic response to increased CO2 and aerosols: Forcings and feedbacks
Authors: Stenchikov Georgiy L. , Robock Alan
Published: February 2004

To examine the causes of the observed diurnally asymmetrical climate change over land, the roles of different physical mechanisms are evaluated using a radiative‐convective model of the diurnal cycle. This model explicitly calculates a complete set of physical processes, including the water vapor distribution, clouds, transports in the turbulent boundary layer, and convection. Calculations were carried out for midlatitude summer and winter and for tropical spring conditions taking into account the most important climate forcings: CO2 increase, tropospheric aerosol pollution, and the combined case with simultaneous CO2 and aerosol effects. We find that feedbacks in the climate system are more important than forcings in producing diurnal asymmetry. The water vapor shortwave feedback dominates the diurnal distribution of the response. For all cases with warming, the diurnal temperature range (DTR) decreases, not due to the greenhouse effect of water vapor, but as a result of more intensive absorption of the solar radiation in the near infrared by water vapor and cloud water in a warmer, wetter climate independent of the type of forcing. Aerosol reflection and absorption of solar radiation cool the surface and decrease DTR directly, but the negative daytime water vapor feedback virtually cancels out the diurnal asymmetry. In the combined case, with a 50% CO2 content increase combined with tropospheric aerosol pollution, which is not far from the current observed conditions over land, the greenhouse warming raises the temperature enough that the direct aerosol effect decreases the DTR. In all cases the time and spatial redistribution of clouds have a significant impact on the climate sensitivity and diurnal cycle. As in the observations, increasing of cloudiness and water vapor content occurs with decreasing of the DTR. In our model the cloudiness and water vapor changes are produced by the same forcings that lower the DTR; they are not independent causes of changes of the DTR, but rather are important internal feedback mechanisms.
Sensitivity of shallow convective precipitation induced by land surface heterogeneities to dynamical and cloud microphysical parameters
Authors: Liu Yongqiang , Avissar Roni
Published: February 2004

To parameterize shallow convective clouds and precipitation induced by land surface processes in large‐scale atmospheric models (e.g., global climate models and weather forecast models), it is primordial to identify the atmospheric variables and cloud microphysical parameters which have a predominant impact on the development and formation of this type of clouds. For this purpose a sensitivity analysis of the various parameters and processes involved in the development and formation of this type of clouds and precipitation was performed with the Fourier amplitude sensitivity test (FAST). This test determines the relative contribution of the distribution of individual input parameters, assuming that their exact value is unknown, to the variance of the model output. By simultaneously varying all parameters according to their individual probability density function (PDF), the number of computations needed is very much reduced. Assuming various PDFs of cloud microphysical characteristics under a broad range of atmospheric conditions, this analysis demonstrated that given an appropriate atmospheric water content, vertical velocity and air temperature are the dominant atmospheric factor in shallow convective precipitation. This emphasizes the need to correctly calculate the spatial distribution of land surface heat fluxes, which affect the development of microscale and mesoscale turbulence in the atmospheric planetary boundary layer. The uncertainty in estimating cloud droplet concentration, pristine ice concentration, mass coefficient, collision efficiency, terminal velocity, snow crystals diameter, and aggregates diameter can affect quite significantly, one way or the other, the mixing ratio of the various water particles simulated with the cloud microphysics scheme. The relative importance of some of these parameters is very much dependent upon temperature and vertical velocity.
FIFE 1987 water budget analysis
Authors: Duan Q. Y. , Schaake J. C. , Koren V. I.
Published: February 2004

The First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) represents one of the largest data collection campaigns to date in our endeavor to observe the hydrodynamic and thermodynamic processes occurring on the land surface of the Earth. Data for FIFE have been widely used to improve our understanding of land surface processes and to improve the representation of the land surface and boundary layer in atmospheric models. Because FIFE data are being used to test models of land surface processes, it is important to examine how well the FIFE data preserve the water budget. Therefore this study examined the data consistency issue from a hydrologic perspective. More specifically, we investigated whether there is a consistent land surface water balance for the FIFE area over the 1987 experiment period. All components of water balance, i.e., rainfall, evaporation, runoff, and soil moisture, were examined individually as well as collectively. Gridded fields were made of each component. Both the gridded fields and areal averages were analyzed. The processed data were also compared with the data sets processed by other researchers. Inconsistencies in the data were pointed out and the sources were investigated. The results indicate that spatially averaged rainfall, fluxes, and soil moisture storage time series derived from the FIFE data close the water budget reasonably well. It is recommended that these data be used for future development and testing of models.
Pinatubo volcanic aerosol layer decay observed at Ahmedabad (23°N), India, using neodymium:yttrium/aluminium/garnet backscatter lidar
Authors: Jayaraman A. , Ramachandran S. , Acharya Y. B. , Subbaraya B. H.
Published: February 2004

Pinatubo volcanic aerosol layer is studied with a neodymium:yttrium/aluminium/garnet (Nd:YAG) (532 nm) backscatter lidar system at the Physical Research Laboratory, Ahmedabad (23°N, 72.5°E), India, from April 1992 to May 1994. The results obtained on the integrated mass densities and aerosol backscatter from 17 to 30 km show a 1/e‐folding time of 9 months, for the Pinatubo aerosol layer to decay. Calculations show that if the layer decays at the same rate, then it may take about 4.5 years for the stratosphere to attain its background aerosol level over the tropics. However, the peak scattering ratio value shows a longer decay time of 12.5 months as has been reported earlier in the case of Fuego and El Chichon eruptions which could be due to faster removal of particles below the peak altitude. The aerosol size distribution has not undergone any considerable change throughout the decay phase of the layer from 1 year to 3 years after the eruption. Also, about 2 years after the eruption the estimated layer mass and the integrated backscattering coefficient are found similar to the values reported in the case of El Chichon eruption. The results obtained on the aerosol extinction coefficients are found to compare well with Stratospheric Aerosol and Gas Experiment (SAGE) II results.
Emissions of CO2, CO, and hydrocarbons from fires in diverse African savanna ecosystems
Authors: Hao Wei Min , Ward Darold E. , Olbu Gerald , Baker Stephen P.
Published: February 2004

Emissions of CO2, CO, and hydrocarbons from 13 savanna fires (∼7 ha) were investigated in Zambia and South Africa in August and September 1992. The experiments were conducted at two moist woodland savanna sites, a moist grassland savanna site, and a semiarid woodland savanna site in Zambia, and nine semiarid woodland savanna sites in South Africa. The hydrocarbons measured were CH4, C2–C6alkanes, alkenes, and alkynes, and aromatic compounds. The linear relationship between the emission factor of CH4and the combustion efficiency is similar regardless of the phase of combustion (flaming or smoldering), the climatic zone, the herbaceous species, or the amount of aboveground biomass. Concentrations of emitted nonmethane hydrocarbons are linearly correlated with those of CH4. The emission ratio of a trace gas to CH4is constant for either phase of combustion in these ecosystems. Biomass burning in African savannas is a significant source of CO, ethyne, propene, and benzene in the atmosphere. The amount of CO, ethene, ethane, ethyne, propene, propane, and benzene emitted per year from these fires is about 20–95% of the amount released from global industrial activities.
NOy Blue Ribbon panel
Authors: Crosley David R.
Published: February 2004

Total NOy was determined on the Pacific Exploratory Mission‐West A using two separate instruments, one operated by Georgia Institute of Technology and one by Nagoya University. The two data sets exhibited significant disagreement, with no systematic correlation, and differences often a factor of 2 or more. Additionally, regardless of data set chosen, the total NOy was much greater than the sum of its components measured separately. A panel was convened by NASA in July 1993 to examine these conflicting datasets and the question of “missing NOy” on this mision. This paper reports the conclusions and recommendations from the panel.
Mechanisms controlling water vapor in the lower stratosphere: “A tale of two stratospheres”
Authors: Dessler A. E. , Hintsa E. J. , Weinstock E. M. , Anderson J. G. , Chan K. R.
Published: February 2004

We present an analysis of the mechanisms controlling stratospheric water vapor based on in situ profiles made at 37.4°N and at altitudes up to 20 km. The stratosphere can be conveniently divided into two air masses: the overworld (potential temperature θ>380 K) and the lowermost stratosphere (θ<380). Our data support the canonical theory that air primarily enters the overworld by passing through the tropical tropopause. The low water vapor mixing ratios in the overworld, a few parts per million by volume (ppmv), are determined by the low temperatures encountered at the tropical tropopause, as well as oxidation of methane and molecular hydrogen. Air enters the lowermost stratosphere both by diabatically descending from the overworld across the 380‐K potential temperature surface and by passing through the extratropical tropopause. Air parcels crossing the extratropical tropopause experience higher temperatures than air crossing the tropical tropopause, allowing higher water vapor in the lowermost stratosphere (tens of ppmv) than in the overworld. Our data are consistent with the pathway for air crossing the extratropical tropopause being isentropic advection from lower latitudes, although we cannot exclude contributions from other paths.
Atmospheric methane at Mauna Loa and Barrow observatories: Presentation and analysis of in situ measurements
Authors: Dlugokencky Edward J. , Steele L. Paul , Lang Patricia M. , Masarie Kenneth A.
Published: February 2004

In situ methane (CH4) measurement techniques and data from the NOAA Climate Monitoring and Diagnostics Laboratory observatories at Mauna Loa, Hawaii, and Barrow, Alaska, are presented. For Mauna Loa, the data span the time period April 1987 to April 1994. At Barrow the measurements cover the period January 1986 to January 1994. Sixty air samples per day were measured with a fully automated gas chromatograph using flame ionization detection. Details of the experimental methods and procedures are given. Data are presented and assessed over various timescales. The average peak to peak seasonal cycle amplitudes obtained from four harmonics fitted to the detrended data were 25.1 ppb at Mauna Loa and 47.2 ppb at Barrow. When the seasonal cycle amplitude during each calendar year was determined as the difference between the maximum and minimum value from a smooth curve fitted to the data, the average amplitudes were (30.6±4.2) ppb at Mauna Loa and (57.5±11.4) ppb at Barrow. A discrepancy exists between these two methods due to the temporal variability in the positions of the seasonal maxima. The average trend at Mauna Loa was 9.7 ppb yr−1, but this trend was observed to decrease at a rate of 1.5 ppb yr−2. For Barrow the average trend was 8.5 ppb yr−1, and the rate of decrease in the trend was 2.1 ppb yr−2. At Mauna Loa, a diurnal cycle was sometimes observed with an amplitude of up to 10 ppb when averaged over 1 month.
Validation of aerosol measurements from the Halogen Occultation Experiment
Authors: Hervig Mark E. , Russell James M. , Gordley Larry L. , Park J. H. , Drayson S. Roland , Deshler Terry
Published: February 2004

Measurements from the Halogen Occultation Experiment (HALOE) are used to infer profiles of aerosol extinction at five infrared wavelengths. This paper provides a validation of the aerosol measurements based on uncertainty analysis, internal validations, comparisons with theory, and comparisons with independent measurements. Monte Carlo calculations using accepted values of random and systematic errors determine typical measurement uncertainties of less than 15% for pressures from 100 to 10 mbar. Comparisons of coincident HALOE sunrise and sunset observations indicate systematic differences (sunrise > sunset) for pressures less than 10 mbar. Random sunrise‐sunset differences, taken as an upper limit of the measurement precision, are generally from 10 to ∼30% for pressures from 100 to 10 mbar. Measured extinction ratios are compared with ratios determined from theory. These comparisons show that the measurements are consistent with theory at pressures from 100 to 10 mbar, depending on channels, latitude, and season. HALOE extinctions are compared with extinctions calculated from balloon‐borne particle counter measurements. The results show random differences from 30 to 50% for pressures from 100 to 10 mbar and systematic differences (HALOE > particle counters) for pressures less than 40 mbar. The results indicate that the HALOE 2.80 μm aerosol measurements are much less reliable than the other four measurements.
Dinitrogen pentoxide measurements from the improved stratospheric and mesospheric sounder: Validation of preliminary results
Authors: Smith S. E. , Dudhia A. , Morris P. E. , Remedios J. J. , Rodgers C. D. , Taylor F. W. , Kerridge B. J. , Chipperfield M. P. , Kumer J. B. , Roche A. E. , Gunson M. R.
Published: February 2004

The improved stratospheric and mesospheric sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) made some of the first global measurements of dinitrogen pentoxide (N2O5) in the 1991/1992 period. N2O5 is a crucial part of the ozone photochemical cycle in the stratosphere, but measurements of its variability and distribution are difficult and hitherto have been rare, inhibiting adequate testing of dynamical‐chemical models of the stratosphere. This paper describes the production and validation of the first set of ISAMS global N2O5 data to be made publically available (version 10). It is concluded that the results represent a considerable improvement over those previously available and are ready for use in certain kinds of scientific work. There still exist problems regarding the treatment of stratospheric sulfate aerosol which further processing will hopefully resolve.
Lagrangian analysis of the total ammonia budget during Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange
Authors: Zhuang Liangzhong , Huebert Barry J.
Published: February 2004

During the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) program, we made repeated measurements of ammonium aerosol in a European air mass as it passed over the North Atlantic Ocean near the Azores. After tracking balloons had been launched from the R/V Oceanus, the National Center for Atmospheric Research (NCAR) Electra followed a tagged parcel of this air mass for about 42 hours in four successive flights. A different part of this air mass passed over Santa Maria Island, where we measured its aerosol size distribution with a micro‐orifice uniform deposit impactor (MOUDI) impactor and used diffusion denuders to determine that virtually all available ammonia vapor had reacted with sulfuric acid to form ammonium aerosol. We have used a continuity equation to evaluate the budget of total ammonia in this air mass, and conclude that during this experiment the North Atlantic was emitting ammonia vapor. The aircraft observations show that ammonium concentrations stayed relatively constant, in spite of dilution by low‐ammonia free tropospheric air. Balancing that budget requires a surface ammonia source of 26 ± 20 μmol m−2 d−1. By contrast, non‐sea‐salt sulfate (nss SO4=) concentrations decreased with time, causing the neutralization ratio (NH4+/nss SO4=) to increase from about 0.8 to 1.3. Ships at the beginning and end of the track recorded near‐surface ratios of 0.73 and 1.65, respectively. This increasing ratio is further evidence of a substantial sea‐to‐air ammonia flux. Previous estimates of marine ammonia emissions have been in the range of 1.8 to 15 μmol m−2 d−1. Since our flux estimate was made at the end of the spring productivity cycle when the demand for fixed nitrogen may have been at a minimum, it may not be representative of global average ammonia fluxes. It does suggest, however, that the atmosphere may redistribute marine ammonia over hundreds or thousands of kilometers by vapor emission, conversion to aerosols, and deposition in rainfall.
Vertical evolution of gravity wave spectra and the parameterization of associated wave drag
Authors: Medvedev A. S. , Klaassen G. P.
Published: February 2004

Extensions of Weinstock's theory of nonlinear gravity waves and a parameterization of the related momentum deposition are developed. Our approach, which combines aspects of Hines' Doppler spreading theory with Weinstock's theory of nonlinear wave diffusion, treats the low‐frequency part of the gravity wave spectrum as an additional background flow for higher‐frequency waves. This technique allows one to calculate frequency shifting and wave amplitude damping produced by the interaction with this additional background wind. For a nearly monochromatic spectrum the parameterization formulae for wave drag coincide with those of Lindzen. It is shown that two processes should be distinguished: wave breaking due to instabilities and saturation due to nonlinear diffusionlike processes. The criteria for wave breaking and wave saturation in terms of wave spectra are derived. For a saturated spectrum the power spectral density's (PSD) dependence S(m) = AN2/m3 is obtained, where m is the vertical wavenumber and N is the Brunt‐Väisäla frequency. Unlike Weinstock's original formulation, our coefficient of proportionality A is a slowly varying function of m and mean wind. For vertical wavelengths ranging from 10 km to 100 m and for typical wind shears, A varies from one half to one ninth. Calculations of spectral evolution with height as well as related profiles of wave drag are shown. These results reproduce vertical wavenumber spectral tail slopes which vary near the −3 value reported by observations. An explanation of these variations is given.
Atmospheric carbonyl compounds at a rural southeastern United States site
Authors: Lee Yin‐Nan , Zhou Xianliang , Hallock Kristen
Published: February 2004

Atmospheric concentrations of a series of carbonyl compounds known as formaldehyde (FA), acetaldehyde (AC), acetone (AN), glycolaldehyde (GA), glyoxal (GL), methylglyoxal (MG), glyoxylic acid (GD), and pyruvic acid (PD) were measured at a rural site in Georgia in summers of 1991 and 1992. The midafternoon median concentrations, in parts per billion, determined for 1991–1992 were FA, 3.6/3.1; AC, 0.58/0.74; AN, 1.7/1.8; GA, 0.21/0.26; GL, 0.02/0.09; MG, 0.03/0.08; GD, 0.46; and PD, 0.11, the latter two for 1992 only. All of the carbonyls except AC and AN exhibited a strong diurnal dependence, with maxima in the midafternoon and minima during the night, consistent with a rapid in situ photochemical production in the daytime and a loss by dry deposition in a shallow inversion during the night. FA correlated well with O3, GA and MG, consistent with their photochemical production near the surface at the measurement site. GL and MG showed the strongest correlation among all species, suggesting common origins as well as similar atmospheric lifetimes. The presence of GA, MG, and GL along with FA at the observed relative concentrations are consistent with laboratory developed isoprene oxidation mechanism and the expectation that isoprene represents a major reactive hydrocarbon in this rural region. At the concentrations observed, these carbonyls serve as important radical sources. The contribution of FA accounts for half of that by O3 and the higher carbonyls approximates half of that by FA. With respect to production of peroxyacetyl nitrate, isoprene contributes as much as acetaldehyde. These results lend further credence to the notion that isoprene plays a pivotal role in photochemical processes, especially in rural environments.
Cumulus parameterizations in chemical transport models
Authors: Mahowald Natalie M. , Rasch Philip J. , Prinn Ronald G.
Published: February 2004

Global three‐dimensional chemical transport models (CTMs) are valuable tools for studying processes controlling the distribution of trace constituents in the atmosphere. A major uncertainty in these models is the subgrid‐scale parametrization of transport by cumulus convection. This study seeks to define the range of behavior of moist convective schemes and point toward more reliable formulations for inclusion in chemical transport models. The emphasis is on deriving convective transport from meteorological data sets (such as those from the forecast centers) which do not routinely include convective mass fluxes. Seven moist convective parameterizations are compared in a column model to examine the sensitivity of the vertical profile of trace gases to the parameterization used in a global chemical transport model. The moist convective schemes examined are the Emanuel scheme [Emanuel, 1991], the Feichter‐Crutzen scheme [Feichter and Crutzen, 1990], the inverse thermodynamic scheme (described in this paper), two versions of a scheme suggested by Hack [Hack, 1994], and two versions of a scheme suggested by Tiedtke (one following the formulation used in the ECMWF (European Centre for Medium‐Range Weather Forecasting) and ECHAM3 (European Centre and Hamburg Max‐Planck‐Institut) models [Tiedtke, 1989], and one formulated as in the TM2 (Transport Model‐2) model (M. Heimann, personal communication, 1992). These convective schemes vary in the closure used to derive the mass fluxes, as well as the cloud model formulation, giving a broad range of results. In addition, two boundary layer schemes are compared: a state‐of‐the‐art nonlocal boundary layer scheme [Holtslag and Boville, 1993] and a simple adiabatic mixing scheme described in this paper. Three tests are used to compare the moist convective schemes against observations. Although the tests conducted here cannot conclusively show that one parameterization is better than the others, the tests are a good measure of the ability of the schemes to transport trace gases in a realistic manner under important meteorological conditions. From these tests two moist convection schemes and one boundary layer scheme are considered as the most promising for use in CTMs such as the National Center for Atmospheric Research's (NCAR) off‐line model. For moist convection the ECHAM3 form of the Tiedtke scheme and the inverse thermodynamic scheme performed well in the tests against observations. For the boundary layer the results of the nonlocal boundary layer scheme were more similar to observations than the simple adiabatic mixing scheme. Our results suggest that the middle and upper troposphere trace constituent profiles may not be sensitive to the boundary layer scheme employed in the model. The results of this one‐dimensional study imply that the conclusions of chemical transport modeling studies can be highly sensitive to the convective parameterization used in the transport model.
Reactive nitrogen over the Pacific Ocean during PEM‐West A
Authors: Kondo Y. , Ziereis H. , Koike M. , Kawakami S. , Gregory G. L. , Sachse G. W. , Singh H. B. , Davis D. D. , Merrill J. T.
Published: February 2004

Measurements of NO and NOy were carried out during NASA's Pacific Exploratory Mission‐West A. In total, 18 aircraft flights were made over the Pacific Ocean, predominantly over the western Pacific Ocean in September and October 1991. NO and NOy were measured using a chemiluminescence instrument, and NOx was calculated from NO using a chemical box model. The measurements were carried out from 0.3 to 12 km in altitude. The NO, calculated NOx ((NOx)mc), and NOy mixing ratios in continental air were significantly higher than in maritime air. In maritime air, NO increased with altitude. The median values of NO in the boundary layer and the lower, middle, and upper troposphere were 3.7, 5.1, 11.5, and 26.6 parts per trillion by volume (pptv), respectively. In continental air, NO and (NOx)mc mixing ratios revealed a C‐shaped profile. The median NOy values observed in the four altitude regions were 37.8, 17.5, 18.2, and 53.2 pptv, respectively. NOy did not show any apparent altitude dependence either in maritime or in continental air. In maritime air, median NOy, values in the lower, middle, and upper troposphere ranged between 211 and 226 pptv and in continental air between 382 and 401 pptv. The lowest values of NOy, PAN, and O3 were observed in tropical air masses throughout the entire altitude region. In the middle and upper troposphere of the high‐latitude air masses, NO and (NOx)mc values were the lowest, although NOy mixing ratios were similar to those in continental air masses. PAN, O3, CO, CH4, and C2H6 data were used to study the budget of reactive nitrogen over the Pacific Ocean. O3 mixing ratios were found to be correlated with those of (NOx)mc, NOy, PAN, and CH4, although the degree of correlation varied with air mass and altitude. These correlations, together with the profiles of these species, suggest that photochemical production of O3 from precursor species over the continent is important for the O3 budget in the troposphere over the western Pacific Ocean.
Transport of ozone precursors from the Arctic troposphere to the North Atlantic region
Authors: Honrath Richard E. , Hamlin Amy J. , Merrill John T.
Published: February 2004

The importance of Arctic outflow events to the budgets of nitrogen oxides and hydrocarbons in the North Atlantic region is estimated using a climatology of isentropic airflow trajectories, in combination with current understanding of the levels of these compounds in the Arctic troposphere. We first review available measurements of nonmethane hydrocarbons (NMHCs), total reactive oxidized nitrogen (NOy), and major NOy species in the Arctic troposphere to develop best estimate average vertical profiles during January‐May outflow events. Measurements of these compounds in the winter‐spring Arctic are generally consistent. Average levels during March are ≥500 parts per 1012 by volume (NOy) and ∼20 parts per billion carbon (NMHC). Current evidence for a significant vertical gradient above the boundary layer is weak, although additional measurements are needed. Secondly, the flow patterns and frequency of Arctic outflow events which reach the North Atlantic region south of 50°–55°N are investigated using an 11‐year climatology of isentropic forward trajectories originating at 70°N in the months of January‐May. The dominant route of trajectories reaching the temperate North Atlantic originates north of Canada at 2–6 km altitude and continues southward along a semipermanent trough located near the East Coast of North America. Trajectories reaching the temperate North Atlantic originated in this region on ∼70% of the days analyzed. Significant subsidence occurs during the southward flow, resulting in warming conducive to photochemical processing of the Arctic pollutants. Based on these analyses, the southward fluxes of NOy and NMHCs out of the Arctic in events which reach the North Atlantic south of 50°N total 7.3 GgN/month NOy and 250 GgC/month NMHC during March. These values are biased low as they include only those trajectories originating below 6 km and exclude trajectories which pass over the United States or southeastern Canada. The calculated NOy flux during May is lower but may be underestimated due to uncertainty in conditions in the Arctic free troposphere in that month. The May flux of NMHCs is larger than that in March as a result of a more frequent occurrence of outflow events. These fluxes impact air parcels which are not affected by direct transport from source regions and appear to be seasonally significant relative to other sources of ozone precursors to the North Atlantic troposphere. If a significant fraction of the peroxyacetyl nitrate and alkyl nitrates which comprise most of the advected NOy decomposes over the North Atlantic, the transport of anthropogenic pollutants through the Arctic may play a significant role in the ozone budget of the North Atlantic troposphere.
The determination of cloud pressures from rotational Raman scattering in satellite backscatter ultraviolet measurements
Authors: Joiner J. , Bhartia P. K.
Published: February 2004

We have retrieved cloud pressures with the Nimbus 7 solar backscatter ultraviolet spectrometer and total ozone mapping spectrometer by utilizing properties of rotational Raman scattering. The retrieved cloud pressures are compared with coincident cloud pressures derived from the temperature humidity infrared sounder, as well as climatological cloud pressures from the International Satellite Cloud Climatology Project. Results show good agreement between cloud pressures measured using ultraviolet and infrared techniques, although a small bias is present. The bias in cloud pressures is likely due in part to different radiative properties of clouds at ultraviolet and infrared wavelengths. The ultraviolet measurements described here are sensitive to cloud optical thickness, while infrared measurements are sensitive to cloud top temperature. Ultraviolet cloud pressure measurements combined with measurements from other spectral regions may therefore provide information about cloud type. Cloud pressures measured by means of ultraviolet scattering properties will be more appropriate for use in satellite backscatter ultraviolet ozone retrieval algorithms. We suggest ways in which future ultraviolet remote sounding instruments may be designed to more optimally measure cloud pressure.
Eastward propagating ∼2‐ to 15‐day equatorial convection and its relation to the tropical intraseasonal oscillation
Authors: Dunkerton Timothy J. , Crum Francis X.
Published: February 2004

Anomalies of outgoing longwave radiation (OLR) in 1980–1989 were examined in a narrow latitude band about the equator to elucidate the propagation and interaction of tropical intraseasonal oscillations (TIOs) and synoptic‐scale convective activity. Hovmöller diagrams of OLR data reconstructed from two frequency bands (corresponding to periods of ∼30–60 days and ∼2–15 days, respectively) revealed a clear distinction between the phase speed of eastward moving TIOs (3–7 m s−1) and that of eastward synoptic‐scale convection (10–13 m s−1). Coherent propagation of TIOs from the Indian to the western Pacific Oceans was often observed with temporary diminution of amplitude over the maritime continent. Propagation of high‐frequency anomalies was generally confined to an individual basin. Dominance of eastward propagating synoptic‐scale convection in the equatorial zone contrasts sharply with the westward propagation of off‐equatorial convergence zones. Interaction between the TIO and high‐frequency activity resolved by daily OLR was visible as a modest enhancement of eastward synoptic‐scale events (and of high‐frequency activity in general) during the convectively active phase of the TIO.
Long‐term climate variability in a simple, nonlinear atmospheric model
Authors: Kurgansky M. V. , Dethloff K. , Pisnichenko I. A. , Gernandt H. , Chmielewski F.‐M. , Jansen W.
Published: February 2004

A nonlinear, baroclinic, hemispheric, low‐order model of the atmosphere with nonzonal orographic and zonal thermal forcings has been constructed. The model is used to investigate the long‐term climate variability by running it over 1100 years. The model runs show a chaotic behavior in a realistic parameter range. With and without a seasonal cycle in the thermal forcing, the model generates decadal climate variations which are of the same order as interannual variations. The maximum variability is found in a broad range of periods between 3 and 44 years. Empirical orthogonal function analysis reveals that these fluctuations are predominantly caused by the interaction between the orographically excited standing wave and the mean zonal flow. The computed power spectra of the principal component time series stress the importance of the high‐frequency transients in long‐term climate variability.
Intercomparison of UV spectrometer and polarimeter on SMM and Stratospheric Aerosol and Gas Experiment II ozone profiles and trends in the lower mesosphere
Authors: Aikin A. C. , McPeters R. D. , Miles T. , Flynn L. E.
Published: February 2004

Ozone concentrations obtained with the technique of solar occultation from the Solar Maximum Mission (SMM)/Ultraviolet Spectrometer and Polarimeter (UVSP) and Earth Radiation Budget Satellite (ERBS)/Stratospheric Aerosol and Gas Experiment II (SAGE II) satellite‐borne instruments are compared in the latitude regions of 5° to 15° north and south for the lower mesosphere (53–68 km) for 1985–1989, the period when both instruments were operational. The estimated trends are all positive signifying increasing ozone. At 55 km in the northern region they are 0.60(±0.47)%/year for SAGE II and 2.56(±0.61)%/year for SMM/UVSP during the 1985–1989 period. At 60 km the trends are 0.38(±1.06)%/year for SAGE II and 1.63(±0.56)%/year for SMM/UVSP. Corresponding numbers at 55 km in the southern region are 1.23(±0.82)%/year for SAGE II and 2.38(±0.62)%/year for SMM/UVSP. At 60 km the trends are 1.34(±1.01)%/year for SAGE II and 2.14(±0.56)%/year for SMM/UVSP. At 65 km, where only SMM/UVSP data are used, estimated trends are 0.92(±0.74)%/year in the northern region and 2.59(±0.92)%/year in the southern region. Theory predicts that the increase in solar radiation between 1985 and 1989 should enhance ozone by 1.5%. If temperature feedback is included in the model, then ozone is predicted to decrease. These figures are smaller than the observed 5 to 10% increase. A long‐term temperature decrease will also contribute to an ozone increase.
Hydrocarbon ratios during PEM‐WEST A: A model perspective
Authors: McKeen S. A. , Liu S. C. , Hsie E.‐Y. , Lin X. , Bradshaw J. D. , Smyth S. , Gregory G. L. , Blake D. R.
Published: February 2004

A useful application of the hydrocarbon measurements collected during the Pacific Exploratory Mission (PEM‐West A) is as markers or indices of atmospheric processing. Traditionally, ratios of particular hydrocarbons have been interpreted as photochemical indices, since much of the effect due to atmospheric transport is assumed to cancel by using ratios. However, an ever increasing body of observatonial and theoretical evidence suggests that turbulent mixing associated with atmospheric transport influences certain hydrocarbon ratios significantly. In this study a three‐dimensional mesoscale photochemical model is used to study the interaction of photochemistry and atmospheric mixing on select hydrocarbons. In terms of correlations and functional relationships between various alkanes, the model results and PEM‐West A hydrocarbon observations share many similar characteristics as well as explainable differences. When the three‐dimensional model is applied to inert tracers, hydrocarbon ratios andother relationships exactly follow those expected by simple dilution with model‐imposed “background air,” and the three‐dimensional results for reactive hydrocarbons are quite consistent with a combined influence of photochemistry and simple dilution. Analogous to these model results, relationships between various hydrocarbons collected during the PEM‐West A experiment appear to be consistent with this simplified picture of photochemistry and dilution affecting individual air masses. When hydrocarbons are chosen that have negligible contributions to clean background air, unambiguous determinations of the relative contributions to photochemistry and dilution can be estimated from the hydrocarbon samples. Both the three‐dimensional model results and the observations imply an average characteristic lifetime for dilution with background air roughly equivalent to the photochemical lifetime of butane for the western Pacific lower troposphere. Moreover, the dominance of OH as the primary photochemical oxidant downwind of anthropogenic source regions can be inferred from correlations between the highly reactive alkane ratios. By incorporating back‐trajectory information within the three‐dimensional model analysis, a correspondence between time and a particular hydrocarbon or hydrocarbon ratio can be determined, and the influence of atmospheric mixing or photochemistry can be quantified. Results of the three‐dimensional model study are compared and applied to the PEM‐West A hydrocarbon dataset, yielding a practical methodology for determining average OH concentrations and atmospheric mixing rates from the hydrocarbon measurements. Aircraft data taken below 2 km during wall flights east of Japan imply a diurnal average OH concentration of ∼3 × 106 cm−3. The characteristic time for dilution with background air is estimated to be ∼2.5 days for the two study areas examined in this work.
Satellite observations of shallow cumulus coverage over the central United States: An exploration of land use impact on cloud cover
Authors: Rabin Robert M. , Martin David W.
Published: February 2004

A simple algorithm is presented which identifies cumulus clouds in visible and infrared satellite image pairs. The algorithm is applied to hourly pairs of the Geostationary Operational Environmental Satellite (GOES) to determine the relative frequency of daytime cumulus clouds over the central United States for two consecutive Julys: one drought (1988) and one control (1987). In both Julys, cumulus frequency decreased from southeast to northwest, against the gradient of elevation, but with the gradient of midday average relative humidity. On the scale of uplands and lowlands and even isolated ridges it tended to increase with elevation. During the drought in July, contrasts in vegetative cover were especially large. These contrasts tended to oppose contrasts in surface temperature inferred from satellite radiometers. They also tended to oppose contrasts in the frequency of shallow cumulus. Over central and southern Illinois, a flat to gently undulating, mostly rural plain, during July 1988, shallow cumulus clouds occurred more often over lightly vegetated than heavily vegetated landscapes. These clouds also tended to be relatively abundant near the larger urban centers. During the control July of 1987, fewer cumulus clouds were recorded.
Absorption coefficients of ClONO2 at 780 cm−1
Authors: McPheat Robert , Duxbury Geoffrey
Published: February 2004

The absorption coefficients of the Q branch of the ν4 band of ClONO2 at 780 cm−1 have been measured over a sample pressure range of 0.1 to 0.4 torr using a tuneable diode laser spectrometer. The peak absorption coefficients derived from these measurements are 1.98(42) × 10−18 cm2 mol−1 at 296K, and 2.98(47)× 10−18 cm2 mol−1 at 210K. These are in good agreement with those determined previously by Fourier transform spectroscopy once corrections for the resolution of the instruments are made. Band contour analysis of the ν4 + ν6 − ν6 and ν4 + 2ν9 − 2ν9 bands of 35ClONO2 has been carried out and the results incorporated in the fitting of the observed spectrum. At 213K the integrated intensity of the theoretical spectrum calculated for the range of identified bands is 6.4 × 10−18 cm−1 mol−1. The derived integrated intensity of this whole band system is 8.6 × 10−18 cm−1 mol−1, assuming all transition moments of the contributing bands are identical. For the 296K spectrum of the ν4 system a value of 3.9 × 10−18 cm−1 mol−1 is obtained, with a value of 8.4 × 10−18 cm−1 mol−1 if all populated states are included. The differences between the integrated intensities of the theoretical spectrum and of the band system are associated with the “continuum” contributed by the large number of weak bands associated with thermally populated states. The values obtained for the band systems may be compared with those derived by Ballard et al. [1988] over the range 750 to 830 cm−1 for the entire ν3/ν4 system, and by Davidson et al. [1987] over the range 750 to 791 cm−1. These were 2.09 × 10−17 cm−1 mol−1 at 213K and 3.04 × 10−17 cm−1 mol−1 at 296K for the entire ν3/ν4 system, and 8.1 × 10−18 cm−1 mol−1 at 223K and 12.9 × 10−18 cm−1 mol−1 at 296K.