bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnostics and simulation of an annual cycle in the middle atmosphere
Authors: Akmaev Rashid A.
Published: February 2004

A global spectral model extending approximately from 15 up to 120 km is used in both diagnostics and simulations of the observed monthly middle atmospheric climatology as represented in the CIRA‐86 empirical model. First, the model in a two‐dimensional mode is initialized with the empirical temperature and wind distributions for each month. An analog of the nudging data assimilation technique is then applied to retrieve zonal mean zonal momentum deposition rates necessary to keep the model's state in the vicinity of the observed climatology. This is combined with a straightforward procedure for estimating the global mean vertical diffusion coefficient from the thermodynamic equation averaged globally for each month. These estimates agree surprisingly well with recent observations in the mesosphere and lower thermosphere. At the second stage the inferred eddy diffusivities and zonal accelerations that are commonly believed to be produced by dissipating and breaking atmospheric waves of different scales are used as input in annual cycle integrations of the model. For the first time quantitative comparisons of the simulated and initial diagnosed climatologies are presented. The simulation results obtained using the diagnosed zonal forcing and vertical diffusion coefficients compare favorably with the empirical model on the one hand and with simulations using a gravity wave parameterization on the other. In particular, the empirical temperature model is reproduced with an annual global rms temperature deviation of 3.2 K or 2% in the 15‐ to 110‐km layer.
Some theoretical estimations of spectral densities of short‐period electric noises generated near the ground
Authors: Łosakiewicz Andrzej C.
Published: February 2004

The paper presents a theoretical analysis of spectral densities of noises generated by charge advection in a vertical electric field and air‐Earth current measured on the ground by point and linear sensors. The analysis is restricted only to short time‐scales so that the turbulence transporting the charge is close to its inertial subrange and can be considered as homogeneous and locally isotropic. Hence the Kolmogorov scaling law is applied. Next the frozen turbulence approximation is used to obtain frequency spectra. In comparison with point sensors for long antennas, electric noises are considerably damped, especially at high frequencies.
Temperature minima in the average thermal structure of the middle mesosphere (70–80 km) from analysis of 40‐ to 92‐km SME global temperature profiles
Authors: Clancy R. Todd , Rusch David W. , Callan Michael T.
Published: February 2004

Global temperatures have been derived for the upper stratosphere and mesosphere from analysis of Solar Mesosphere Explorer (SME) limb radiance profiles. The analysis of additional SME wavelength radiances at 304, 313, and 442 nm provides for extension of the original SME 60‐ to 90‐km temperature climatology (Clancy and Rusch, 1989a) to a much expanded altitude coverage of 40–92 km. The SME temperatures represent fixed local time observations at 1400–1500 LT, with partial zonal coverage of 3–5 longitudes per day over the 1982–1986 period. These new SME temperatures are compared to the CIRA 86 climatology (Fleming et al., 1990) as well as stratospheric and mesospheric sounder (SAMS); (Barnett and Corney, 1984), National Meteorological Center (NMC); (Gelman et al., 1986), and individual lidar and rocket observations. Significant areas of disagreement between the SME and CIRA 86 mesospheric temperatures are 10 K warmer SME temperatures in the 55‐ to 65‐km altitude region and 10–20 K warmer SME temperatures at altitudes above 80 km. The 1981–1982 SAMS temperatures are in much closer agreement with the SME temperatures between 40 and 75 km. Although much of the SME‐CIRA 86 disagreement probably stems from the poor vertical resolution of the observations comprising the CIRA 86 model, some portion of the differences may reflect 5‐ to 10‐year temporal variations in mesospheric temperatures. The CIRA 86 climatology is based on 1973–1978 measurements. Relatively large (1 K/yr) 5‐ to 10‐year trends in temperatures as functions of longitude, latitude, and altitude have been observed for both the upper stratosphere (Clancy and Rusch, 1989a) and mesosphere (Clancy and Rusch, 1989b; Hauchecorne et al. 1991). The SME temperatures also exhibit enhanced amplitudes for the semiannual oscillation (SAO) of upper mesospheric temperatures at low latitudes, which are not evident in the CIRA 86 climatology. The so‐called mesospheric “temperature inversions” at wintertime midlatitudes, which have been observed by ground‐based lidar (Hauchecorne et al., 1987) and rocket in situ measurements (Schmidlin, 1976), are shown to be a climatological aspect of the mesosphere, based on the SME observations. The winter midlatitude “temperature inversion” is evident in both winter hemispheres and appears more distinctly as a low‐altitude (75 km) temperature minimum at southern midlatitudes. Furthermore, the SME temperatures indicate the related presence of low‐latitude temperature minima at 80‐km altitude during the equinoxes. Both the low‐latitude semiannual minima and the midlatitude annual minima in middle mesospheric temperatures appear to result from the strong SAO in mesospheric temperatures.
Atlantic atmospheric aerosol studies: 2. Compendium of airborne backscatter measurements at 10.6μm
Authors: Vaughan J. M. , Brown D. W. , Nash C. , Alejandro S. B. , Koenig G. G.
Published: February 2004

The airborne backscatter measurements at 10.6 μm, from the South Atlantic Backscatter Lidar Experiment (SABLE) and the Global Atmospheric Backscatter Lidar Experiment (GABLE) programs over the Atlantic, are gathered together and presented. Plots of backscatter versus altitude are shown for 80 flight sequences. These data comprising about 4×105 measurements from over 180 flight hours is statistically analyzed. The material is distributed in altitude (1 km) and backscatter (half decade) intervals and presented in tabular and histogram form for six principal regions and seasons: South Atlantic summer, South Atlantic winter, far‐North Atlantic spring, mid‐Atlantic spring/summer, and Northeast Atlantic winter and summer. Several features of the results are discussed, including the incidence of low backscatter and drop‐outs and the remarkably high incidence of thin cirrus in the southern tropical winter season. The compendium should provide a climatology of atmospheric backscatter at 10.6 μm for regions of the Atlantic during the relatively clean atmospheric period 1988–1990.
Effect of the HITRAN 92 spectral data on the retrieval of NO2 mixing ratios from Nimbus 7 LIMS
Authors: Remsberg Ellis E. , Bhatt Praful P. , Eckman Richard S. , Gordley Larry L. , Russell James M. , Siskind David E.
Published: February 2004

To ensure spectral consistency when comparing Nimbus 7 LIMS NO2 distributions with those from ATMOS and UARS, 1 day (May 5, 1979) of LIMS measurements were reprocessed using the NO2 line list on the HITRAN 92 tape compiled by AFGL. The revised NO2 mixing ratios are smaller by up to 20%. The decrease is not constant with height, latitude, or time of day but depends on the absolute amount of NO2 in the profile, as a result of a change in the degree of saturation for the strong NO2 spectral lines. The revised NO2 agrees better with correlative measurements and with NO2 distributions from the SAGE and HALOE satellite experiments but not with those from ATMOS 85. Profiles of the day/night ratio of revised NO2 are now larger near 5 hPa. There is also some improvement between observed and modeled ozone in the upper stratosphere, when the revised nighttime NO2 profile is used as the estimate of NOy for the model calculations.
Aerosol effects and corrections in the Halogen Occultation Experiment
Authors: Hervig Mark E. , Russell James M. , Gordley Larry L. , Daniels John , Drayson S. Roland , Park Jae H.
Published: February 2004

The eruptions of Mt. Pinatubo in June 1991 increased stratospheric aerosol loading by a factor of 30, affecting chemistry, radiative transfer, and remote measurements of the stratosphere. The Halogen Occultation Experiment instrument on board UARS makes measurements globally for inferring profiles of NO2, H2O, O3, HF, HCl, CH4, NO, and temperature in addition to aerosol extinction at five wavelengths. Understanding and removing the aerosol extinction is essential for obtaining accurate retrievals from the radiometer channels of NO2, H2O and O3 in the lower stratosphere since these measurements are severely affected by contaminant aerosol absorption. If ignored, aerosol absorption in the radiometer measurements is interpreted as additional absorption by the target gas, resulting in anomalously large mixing ratios. To correct the radiometer measurements for aerosol effects, a retrieved aerosol extinction profile is extrapolated to the radiometer wavelengths and then included as continuum attenuation. The sensitivity of the extrapolations to size distribution and composition is small for certain wavelength combinations, reducing the correction uncertainty. The aerosol corrections extend the usable range of profiles retrieved from the radiometer channels to the tropopause with results that agree well with correlative measurements. In situations of heavy aerosol loading, errors due to aerosol in the retrieved mixing ratios are reduced to values of about 15, 25, and 60% in H2O, O3, and NO2, respectively, levels that are much less than the correction magnitude.
Results from the Jet Propulsion Laboratory stratospheric ozone lidar during STOIC 1989
Authors: McDermid I. Stuart , Godin Sophie M. , Walsh T. Daniel
Published: February 2004

Stratospheric ozone concentration profiles measured by the Jet Propulsion Laboratory differential absorption lidar system during the Stratospheric Ozone Intercomparison Campaign in July/August 1989 are presented. These profiles are compared with the mean profiles based on all of the measurements made by the different participating instruments. The results from the blind intercomparison showed that the lidar results agreed with the overall Stratospheric Ozone Intercomparison Campaign average profile to better than 5% between 21 and 45 km altitude. At 20 km the difference was ∼10%, as it was also in the region from 47 to 50 km altitude. Some systematic features were observed in the comparison of the blind results and these were subsequently investigated. The results of this investigation allowed the analysis algorithm to be refined and improved. The changes made are discussed and the comparison of the refined results showed agreement with the STOIC average to better than 4% from 18 to 48 km altitude. For both cases the results above 45 km altitude are subject to the greatest uncertainty and error and are of questionable value even though they agree within 10% with the STOIC average. Examples of comparisons of individual lidar profiles with each of the other instruments are also presented.
Surface ozone levels at Table Mountain during STOIC 1989
Authors: McDermid I. Stuart , Walsh T. Daniel
Published: February 2004

As a part of the routine operations of the Jet Propulsion Laboratory atmospheric measurements program at the Table Mountain Facility, the surface ozone concentration is continuously monitored using a Dasibi photometer. The influence of the Los Angeles basin to the southwest of the facility and the height of the inversion layer cause large fluctuations in the ozone concentration. Peaks as high as 200 parts per billion by volume (ppbv) were observed during the Stratospheric Ozone Intercomparison Campaign (STOIC) compared to a normal background level near 50 ppbv. These measurements, made during STOIC, were important in assessing the impact of the surface ozone concentration on the various instruments participating in the campaign.
Meteor 3/total ozone mapping spectrometer observations of the 1993 ozone hole
Authors: Herman J. R. , Newman P. A. , McPeters R. , Krueger A. J. , Bhartia P. K. , Seftor C. J. , Torres O. , Jaross G. , Cebula R. P. , Larko D. , Wellemeyer C.
Published: February 2004

The development of the springtime (September–November) Antarctic ozone hole was observed by the Meteor 3/total ozone mapping spectrometer (TOMS) to result in the lowest ozone value, 85 DU (Dobson units) on October 8, 1993, ever measured by TOMS. During late September and early October the region of extremely low ozone values was centered on the geographical pole between 85°S and 90°S. The geographical extent of the ozone hole region, the area within the 220‐DU contour, reached a maximum during the first week in October at a near‐circular area covering 24×106 km2 reaching to the southern tip of South America. This approximately matched the 1992 area record. After the maximum area was reached in early October, the 1993 ozone hole region was significantly larger than during 1992 throughout the remainder of the month of October. The very low ozone values over the Antarctic continent have been confirmed by independent ground‐based data. Unlike 1992, the formation of the 1993 Antarctic ozone hole does not coincide with unusually low ozone values observed over most of the globe for the past 2 years. The most recent ozone data from Meteor 3/TOMS show that there has been a recovery at all latitudes from the extraordinarily low values observed during 1992 and part of 1993 after the June 1991 eruption of Mount Pinatubo. Meteor 3/TOMS is described and compared with Nimbus 7/TOMS during the 1991 to May 1993 overlap period. Observations of the 1992 ozone hole are presented from both instruments and are shown to agree within 5 DU.
Reconciling Late Ordovician (440 Ma) glaciation with very high (14X) CO2 levels
Authors: Crowley Thomas J. , Baum Steven K.
Published: February 2004

Geochemical data and models suggest a positive correlation between carbon dioxide changes and climate during the last 540 m.y. The most dramatic exception to this correlation involves the Late Ordovician (440 Ma) glaciation, which occurred at a time when CO2 levels may have been much greater than present (14–16X?). Since decreased solar luminosity at that time only partially offset increased radiative forcing from CO2, some other factor needs to be considered to explain the glaciation. Prior work with energy balance models (EBMs) suggested that the unique geographic configuration of Gondwanaland at that time may have resulted in a small area of parameter space permitting permanent snow cover and higher CO2 levels. However, the crude snow and sea ice parameterizations in the EBM left these conclusions open to further scrutiny. Herein we present results from four experiments with the GENESIS general circulation model with CO2 levels 14X greater than present, solar luminosity reduced 4.5%, and an orbital configuration set for minimum summer insolation receipt. We examined the effects of different combinations of ocean heat transport and topography on high‐latitude snow cover on Gondwanaland. For the no‐elevation simulations we failed to simulate permanent summer snow cover. However, for the slightly elevated topography cases (300–500 m), permanent summer snow cover occurs where geological data indicate the Ordovician ice sheet was present. These results support the hypothesis based on EBM studies. Further results indicate that although average runoff per grid point increases substantially for the Ordovician runs, the decreased land area results in global runoff 10–30% less than present, with largest runoff reductions for flat topography. This response has implications for CO2‐runoff/weathering parameterizations in geochemical models. Finally, simulated tropical sea surface temperatures (SSTs) are the same or only marginally warmer than present. This result is consistent with evidence from other warm time intervals indicating small changes in tropical SSTs during time of high CO2.
Accuracy analysis of wind profiles calculated from volume imaging lidar data
Authors: Piironen Antti K. , Eloranta Edwin W.
Published: February 2004

This paper presents a study of the vertical profiles of horizontal mean winds calculated from data obtained with the University of Wisconsin volume imaging lidar (VIL) during the 1989 First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment program. Wind profiles are determined from cross correlation functions between subsequent constant altitude plan position indicator planes calculated from volume scans of the convective boundary layer. An objective technique to identify unreliable measurements is developed. An error analysis based on determining the errors due to random noise in the data is performed. The VIL wind profiles are compared with radiosonde, aircraft‐based, and ground‐based measurements. On the basis of internal consistency tests we estimate that in the convective boundary layer the hourly averaged VIL wind estimates, which have passed the reliability analysis, have root‐mean‐square errors of 0.03–0.1 ms−1 in speed and 0.4–2.0° in direction.
Trace elements in the atmosphere over the North Atlantic
Authors: Arimoto R. , Duce R. A. , Ray B. J. , Ellis W. G. , Cullen J. D. , Merrill J. T.
Published: February 2004

The concentrations of trace elements in aerosol particles from the atmosphere over the North Atlantic Ocean were determined as part of a program designed to characterize the chemical climatology of the region. For these studies, which were part of the Atmosphere‐Ocean Chemistry Experiment (AEROCE), 2 years of samples were collected at Tudor Hill, Bermuda (BTT), and at Ragged Point, Barbados (BAT); and 1 year of samples was collected at Mace Head, Ireland (MHT) and at the Izaña Observatory, Tenerife, Canary Islands (IZT). One major component of the aerosol was atmospheric dust, and the ranking for the median mineral dust concentrations as represented by aluminum was BAT > IZT > BTT > MHT. The Al concentrations at BAT, IZT, and BTT ranged over 4 orders of magnitude, i.e., from 0.001 to 10 μg m−3. At MHT the maximum dust concentrations were about a factor of 10 lower than at the other sites, but the lower end of the range in dust concentrations was similar at all sites. The mineral dust concentrations generally were highest in summer, and the flux of atmospheric dust was dominated by sources in North Africa. The elements showing clear enrichments over the concentrations expected from sea salt or crustal sources were I, Sb, Se, V, and Zn. At Izaña, which is in the free troposphere (elevation ∼2360 m), the concentrations of Se and I were much lower than at the boundary layer sites; this difference between sites most likely results from the marine emissions of these elements. The impact of pollution sources on trace element concentrations was evident at all sites but varied with season and location. The concentrations of elements originating from pollution sources generally were low at Barbados. Analyses of trace element ratios indicate that there are large‐scale differences in the pollution emissions from North America versus those from Europe and Africa. Emissions from pyrometallurgical industries, steel and iron manufacturing, and possibly biomass burning are more evident in the atmospheric samples influenced by transport from Europe and Africa.
Calculation of surface and top of atmosphere radiative fluxes from physical quantities based on ISCCP data sets: 2. Validation and first results
Authors: Rossow W. B. , Zhang Y‐C.
Published: February 2004

We use global, multiyear observations of the properties of clouds, the atmosphere, and the surface to calculate global shortwave (SW) and longwave (LW) fluxes at the top of the atmosphere and at the surface at a resolution of 280 km and 3 hours for every third month from April 1985 to January 1989. Our validation studies suggest that the specification of cloud effects is no longer the dominant uncertainty in reconstructing the radiative fluxes at the top of atmosphere and at the surface. Rather cloud property uncertainties are now roughly equal contributors to the flux uncertainty, along with surface and atmospheric properties. Overall, the estimated uncertainties in regional, monthly mean fluxes, based on comparisons to more direct measurements, are as follows: for S↑t, 11 W/m2 bias with a rms scatter of 7 W/m2 (the bias may be as little as 5 W/m2); for L↑t, −1 W/m2 bias with a rms scatter of 4 W/m2; for S↓s, 10–20 W/m2 bias with a rms scatter of 10–15 W/m2 (the bias may only be ≈ 10 W/m2 caused by aerosols); for S↑s, ≈ 3 W/m2 bias with a rms scatter of 10 W/m2; for L↓s, probably < 15 W/m2 bias (but with variable sign) with a rms scatter of 15 W/m2 (bias and scatter depend most on atmospheric temperature uncertainties); and for L↑s, ≲ 12 W/m2 and ≲ 24 W/m2 for combined bias and scatter over oceans and land, respectively (very sensitive to surface temperature determinations). The resulting SW and LW flux data sets suggest the following conclusions: (1) The net SW heating of Earth appears predominantly at the surface, whereas the net LW cooling arises predominantly from the atmosphere. The net cooling effect of clouds on top of atmospheric radiation appears primarily at the surface rather than in the atmosphere. (2) Clouds have almost no net effect on the global mean radiation balance of the atmosphere, but they enhance the latitudinal gradient in the LW cooling and reinforce the radiative forcing for the mean atmospheric circulation. Clouds act to mute seasonal contrasts however. (3) Clouds enhance the land‐ocean contrasts of the atmospheric cooling, reinforcing the growth of standing eddy motions; but reduce land‐ocean contrasts of the surface heating.
Longwave radiative cooling rates in axially symmetric clouds
Authors: Guan Hong , Davies R. , Yau M. K.
Published: February 2004

The effects of cloud sides and of cloud top perturbations on radiative cooling rates are examined using an approximate model of longwave radiative transfer that ignores the effect of scattering on net flux divergence. Tuned monochromatic calculations are used for isothermal clouds, and spectral integration from 8 to 13.4 μm for nonisothermal clouds. Water vapor and cloud droplet effects within the cloud are included. Atmospheric conditions outside the cloud are fixed appropriate to a midlatitude summer atmosphere. The distribution of cooling rates in isolated cylindrical clouds shows local maxima at the cloud top and sides as well as modest warming of the base. These rates also depend on cloud and surface temperature. For a 286 K cloud above a 302 K ground, the local cooling rates were typically −34 K h−1 at the cloud top and −14 K h−1 at the cloud sides, with a typical local heating rate of 8 K h−1 at the cloud base. The gradient in cooling rate near the cloud boundaries is very sharp and high rates occur mainly within ≈20 m of the boundary. The possibility of sustained cloud side cooling leading to low‐level convergence and enhanced cloud development is noted. Changes in cloud top cooling rates due to positive (lifting) or negative (sinking), axially symmetric perturbations to the top of horizontally extensive stratiform clouds were also considered. Significant effects were found that do not cancel when averaged over both positive and negative perturbations. A lifting of the cloud top does not increase the cooling rate, whereas the peak cooling rate decreases rapidly in depressions. For small perturbations, ≈10 m, this may tend to inhibit the growth of negative perturbations. For larger perturbations, ≈100 m, changes to the radiative cooling rates within the positive perturbations and next to the negative perturbations may act to sustain the perturbation and promote its growth.
Sensitivity of the climate response of an atmospheric general circulation model to changes in convective parameterization and horizontal resolution
Authors: Colman R. A. , McAvaney B. J.
Published: February 2004

Three equilibrium doubled CO2 experiments have been performed using the Bureau of Meteorology Research Centre atmospheric general circulation model. These experiments used identical versions of the model, apart from changes in the convective parameterization and the horizontal resolution. The penetrative convection parameterizations used were variants of the Tiedtke (1989) mass flux and Kuo (1974) schemes. The shallow convection was also varied in strength. In the control climate the mass flux scheme produces a warmer, moister troposphere, with substantially more high cloud than the Kuo scheme. The precipitation distributions agree reasonably with observations overall, although the mass flux scheme gives improvements in some regions. The increase in resolution is generally found to have a smaller impact upon the climate than the change in convection. Under a doubling of atmospheric CO2, the equilibrium responses of all three experiments were extremely similar in surface and tropospheric temperatures and humidity changes. The model response is at the low end of the scale of simulated climate change, consistent with a strong negative feedback found due to clouds. This feedback is similar to that found in earlier fixed season experiments. It appears to be insensitive to differences in cloud cover simulated in the control climates of the present experiments.
Evaluation of the potential impact of methane clathrate destabilization on future global warming
Authors: Harvey L. D. Danny , Huang Zhen
Published: February 2004

Future global warming due to anthropogenic emissions of greenhouse gases has the potential to destabilize methane clathrates, which are found in permafrost regions and in continental slope sediments worldwide, resulting in the release of methane gas. Since methane is a strong greenhouse gas, this could produce a potentially important positive feedback. Here, the coupled heat transfer and methane destabilization process in oceanic sediments is modeled in a series of one‐dimensional, vertical columns on a 1°×1° global grid. Terrestrial permafrost is divided into 11 columns based on mean annual surface air temperature. Our base case clathrate distribution results in about 24,000 Gt C as methane clathrate in marine sediments and about 800 Gt C in terrestrial sediments, only a small fraction of which could be destabilized by future global warming. Scenarios of anthropogenic CO2 and CH4 emission are used to drive a simple model of the carbon cycle, yielding scenarios of CO2 and CH4 concentration increase. These increases drive a one‐dimensional coupled atmosphere‐ocean climate model. Globally averaged temperature changes as a function of time and ocean depth are used as upper boundary conditions to drive the heat transfer/methane clathrate release models. Three versions of the ocean model are used which result in different temperature perturbations at the sediment‐water interface: a purely diffusive ocean model, an upwelling‐diffusion ocean model with fixed temperature of bottom water formation, and an upwelling‐diffusion ocean model with a feedback between surface temperature and the upwelling velocity. Methane release from clathrate destabilization is added to the anthropogenic CH4 emission, leading to stronger increases in both CH4 and CO2 concentration. Based on a wide variety of parameter input assumptions and anthropogenic emission scenarios, it appears that the potential impact on global warming of methane clathrate destabilization is smaller than the difference in warming between low and medium, or medium and high anthropogenic CO2 emission scenarios, or arising from a factor of two variation in climate sensitivity. Global warming increases by 10–25% compared to the case without clathrate destabilization for our scenarios using what, in many respects, are worst case assumptions.
The use of NOy, H2O2, and HNO3 as indicators for ozone‐NOx‐hydrocarbon sensitivity in urban locations
Authors: Sillman Sanford
Published: February 2004

Correlations are presented between model predictions for O3‐NOx‐hydrocarbon sensitivity and afternoon concentrations of four “indicator species”: NOy, O3/(NOy‐NOx), HCHO/NOy, and H2O2/HNO3. The indicator species correlations are based on a series of photochemical simulations with varying rates of anthropogenic and biogenic emissions and meteorology. Hydrocarbon‐sensitive chemistry in models is shown to be linked to afternoon NOy > 20 ppb, O3/(NOy ‐ NOx) < 7, HCHO/NOy < 0.28, and H2O2/HNO3 < 0.4. Lower NOy and higher ratios correspond with NOx‐sensitive ozone. The correlation between NOx‐hydrocarbon sensitivity and indicator species remains, even when model emission rates and hydrocarbon/NOx ratios are changed by a factor of 2. Methods are developed for evaluating the goodness of fit between model NOx‐hydrocarbon sensitivity and indicator values. Ozone chemistry is also analyzed in terms of fundamental properties of odd hydrogen, and theoretical criteria for the transition between NOx‐ and hydrocarbon‐sensitive regimes are derived. A theoretical correlation between O3 and H2O2 + NOy ‐ NOx is developed as a way to extend rural O3‐NOy correlations into urban locations. Measured indicator values during pollution events in Los Angeles, Atlanta, and rural Virginia are used to illustrate the range of observed values under different environmental conditions.
Land‐atmosphere CO2 exchange simulated by a land surface process model coupled to an atmospheric general circulation model
Authors: Bonan Gordon B.
Published: February 2004

CO2 uptake during plant photosynthesis and CO2 loss during plant and microbial respiration were added to a land surface process model to simulate the diurnal and annual cycles of biosphere‐atmosphere CO2 exchange. The model was coupled to a modified version of the National Center for Atmospheric Research Community Climate Model version 2, and the coupled model was run for 5 years. The geographic patterns of annual net primary production are qualitatively similar to other models. When compared by vegetation type, annual production and annual microbial respiration are consistent with other models, except for needleleaf evergreen tree vegetation, where production is too high, and semidesert vegetation, where production and microbial respiration are too low. The seasonally of the net CO2 flux agrees with other models in the southern hemisphere and the tropics. The diurnal range is large for photosynthesis and lower for plant and microbial respiration, which agrees with qualitative expectations. The simulation of the central United States is poor due to temperature and precipitation biases in the coupled model. Despite these deficiencies the current approach is a promising means to include terrestrial CO2 fluxes in a climate system model that simulates atmospheric CO2 concentrations, because it alleviates important parameterization discrepancies between standard biogeochemical models and the land surface models typically used in general circulation models, and because the model resolves the diurnal range of CO2 exchange, which can be large (15–45 μmol CO2 m−2 s−1).
Stratospheric ClO profiles from McMurdo Station, Antarctica, spring 1992
Authors: Emmons L. K. , Shindell D. T. , Reeves J. M. , de Zafra R. L.
Published: February 2004

We describe ground‐based measurements of ClO made at McMurdo Station, Antarctica, during September and October 1992. Vertical profiles were retrieved from molecular rotational emission spectra at 278 GHz. Peak mixing ratios of 1.6±0.3 ppbv were seen in mid‐September at approximately 18 km altitude, suggestive of somewhat larger quantities than were measured at the same site and season in 1987. As the core of the polar vortex moved away from McMurdo by early October, the ClO mixing ratio at this altitude dropped to less than 0.2 ppbv, coincident with increasing temperature, ozone, and NO2. The diurnal variation of ClO was also observed. The lower stratospheric layer from 15 to 27 km was found to reach approximately midday abundance by 2–3 hours after sunrise. The column abundance in this layer began to decrease by the period 4–2 hours before sunset and had declined to approximately one quarter of its midday value by 2–0 hours before sunset. In contrast, the ClO column in the upper stratosphere, from 28 to 50 km, built up slowly until midday and remained large while sunlight persisted.
Low‐frequency variability of total ozone mapping spectrometer and general circulation model total ozone stationary waves associated with the El Niño/Southern Oscillation for the period 1979–1988
Authors: Stephenson D. B. , Royer J.‐F.
Published: February 2004

Low‐frequency stationary wave variability, having periods of greater than 8 months, has been studied in the total ozone column measured by the Nimbus 7 total ozone mapping spectrometer (TOMS) over the period 1979–1988. This has been compared with the total ozone column variability obtained from a general circulation model (GCM) having prescribed observed sea surface temperatures (SSTs) for the same period. The GCM results demonstrate that the total ozone stationary waves are strongly anticorrelated with the 200‐hPa eddy geopotential height, suggesting that total ozone can be used to study upper level geopotential height stationary waves and their low‐frequency variability. The response to El Niño/Southern Oscillation (ENSO) events is clearly seen in both the TOMS and the GCM total ozone stationary waves. In the tropics, there is a tropical dipole pattern response to ENSO similar to the negative of the dipole response seen in the upper level geopotential height, attributable to the east‐west ENSO see‐saw in tropical convecton. The model total ozone response is about a half of that of the TOMS response consistent with the model geopotential height response being too weak in comparison with analyses from the European Centre for Medium‐Range Weather Forecasts (ECMWF). South of 25°S, the TOMS data show a zonal wave 1 ENSO response in antiphase with the response in the tropics and the response is such that during El Niño (La Niña) events the southern hemisphere stationary waves are weaker (stronger) than normal. No such response is evident in the GCM results or ECMWF analyses, which instead have a zonal wave 3 ENSO response in the southern hemisphere. A zonal wave 1 analysis reveals that the model and analyses have quite different time‐mean zonal wave 1 structures in the tropics and in the southern hemisphere compared with those from the TOMS data reflecting possible model errors.
Dust deposition in southern Nevada and California, 1984–1989: Relations to climate, source area, and source lithology
Authors: Reheis Marith C. , Kihl Rolf
Published: February 2004

Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m2/yr, but in southwestern California the average silt and clay flux is as high as 30 g/m2/yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturbance. Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the regional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative drought) rather than temperature. Although playa and alluvial sources produce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addition, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate‐rich alluvium). Gypsum dust may be produced by the interaction of carbonate dust and anthropogenic or marine sulfates. The dust flux in an arid urbanizing area may be as much as twice that before disturbance but decreases when construction stops. The mineralogic and major‐oxide composition of the dust samples indicates that sand and some silt is locally derived and deposited, whereas clay and some silt from different sources can be far‐traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.
Relative influence of lapse rate and water vapor on the greenhouse effect
Authors: Sinha Ashok
Published: February 2004

Observational data are employed in a radiative transfer model to simulate the mean variation in normalized greenhouse effect (NGE) between January and July. This is performed at a variety of locations, and the mean local rate of change in NGE with surface temperature is determined. The result is 1.5 times larger than the variation of NGE with surface temperature obtained by spatially correlating the aggregated data. This disagreement is ascribed to systematic differences between the two approaches and is interpreted as indicating the significant role that large‐scale circulations as well as surface temperatures have on determining local thermal and humidity structures. The separate effects of water vapor and lapse rate variations are estimated, by simulating the January‐July changes in NGE with each process in turn held constant: beyond the tropics the lapse rate feedback is found to dominate over the water vapor feedback, particularly over land; in the inter‐tropics, lapse rate variations account for about a third of the change in greenhouse trapping, contributing substantially to the “super‐greenhouse effect.” Utilizing a radiative‐convective model, the possible effects on climate change of both lapse rate changes and water vapor feedback are compared: a global mean model climate is perturbed by a doubling of atmospheric carbon dioxide and equilibrium surface temperatures obtained for a variety lapse rates. If, under conditions of climate change, the global mean lapse rate varies with surface temperature in the same manner as in the present‐day mean seasonal cycle (increasing the lapse rate magnitude by 6%), then the lapse rate feedback amplifies the modeled water vapor feedback by 40%; conversely, a 12% reduction in the magnitude of the lapse rate completely nullifies the water vapor feedback.
Space and time aliasing structure in monthly mean polar‐orbiting satellite data
Authors: Zeng Lixin , Levy Gad
Published: February 2004

Monthly mean wind fields from the European Remote Sensing Satellite (ERS1) scatterometer are presented. A banded structure which resembles the satellite subtrack is clearly and consistently apparent in the isotachs as well as the u and v components of the routinely produced fields. The structure also appears in the means of data from other polar‐orbiting satellites and instruments. An experiment is designed to trace the cause of the banded structure. The European Centre for Medium‐Range Weather Forecasts gridded surface wind analyses are used as a control set. These analyses are also sampled with the ERS1 temporal‐spatial sampling pattern to form a simulated scatterometer wind set. Both sets are used to create monthly averages. The banded structures appear in the monthly mean simulated data but do not appear in the control set. It is concluded that the source of the banded structure lies in the spatial and temporal sampling of the polar‐orbiting satellite which results in undersampling. The problem involves multiple timescales and space scales, oversampling and undersampling in space, aliasing in the time and space domains, and preferentially sampled variability. It is shown that commonly used spatial smoothers (or filters), while producing visually pleasing results, also significantly bias the true mean. A three‐dimensional spatial‐temporal interpolator is designed and used to determine the mean field. It is found to produce satisfactory monthly means from both simulated and real ERS1 data. The implications to climate studies involving polar‐orbiting satellite data are discussed.
Seasonal evolutions of N2O, O3, and CO2: Three‐dimensional simulations of stratospheric correlations
Authors: Hall Timothy M. , Prather Michael J.
Published: February 2004

Fluctuations in the concentrations of stratospheric trace gases are often correlated over a large range of space and time scales, an observation frequently used to infer the existence of various chemical processes. Three‐dimensional models provide a tool to examine the causes and variations of trace gas relationships, because they can realistically simulate the interplay between stratospheric photochemistry and meteorology. Thus such models can aid the interpretation of observed trace gas relationships. We use the general circulation model of the Goddard Institute for Space Studies to simulate the evolution and distribution of N2O, CO2, and O3 over a year. In the modeled lower stratosphere the constituents N2O and CO2 have well‐correlated spatial variations, but the slope of the regression line depends on both the season and the direction of sampling. This departure from a universal form is due both to the annual cycle in tropospheric CO2 and to transport of air from the upper stratosphere photochemically depleted in N2O. Due to the short photochemical lifetime of tropical O3, its relationship with N2O is still more varied. In particular, the slope of the O3−N2O regression line changes significantly from middle to high latitudes, behavior relevant to the use of N2O for estimating the rate of polar winter O3 depletion. In general, a tight correlation between two trace gases such as N2O and O3 is often observed, but this datum cannot be used to infer a similar universal relationship because a different direction of sampling may change the slope and the scatter about it.
Tracer transport for realistic aircraft emission scenarios calculated using a three‐dimensional model
Authors: Weaver Clark J. , Douglass Anne R. , Rood Richard B.
Published: February 2004

A three‐dimensional transport model, which uses winds from a stratospheric data assimilation system, is used to study the transport of supersonic aircraft exhaust in the lower stratosphere. A passive tracer is continuously injected into the transport model. The tracer source distribution is based on realistic scenarios for the daily emission rate of reactive nitrogen species for all forecasted flight routes. Winds are from northern hemisphere winter/spring months for 1979 and 1989; there are minimal differences between the tracer integrations for the 2 years. During the integration, peak tracer mixing ratios in the flight corridors are compared with the zonal mean and found to be greater by a factor of 2 or less. This implies that the zonal mean assumption used in two dimensional models is reasonable during winter and spring. There is a preference for pollutant buildup in the heavily traveled North Pacific and North Atlantic flight corridors. Pollutant concentration in the corridors depends on the position of the Aleutian anticyclone and the northern hemisphere polar vortex edge.
Direct carbon monoxide photoproduction from plant matter
Authors: Tarr Matthew A. , Miller William L. , Zepp Richard G.
Published: February 2004

Initial studies to quantify direct carbon monoxide photoproduction from several plant species are reported. In addition to measuring CO emissions from live plant leaves, emission rates from dead leaf matter were also determined. Senescent leaf matter photoproduced CO at rates that ranged from 1.3 to 5.4 times higher per unit area than living leaves, and dead leaves photoproduced CO about an order of magnitude more rapidly than living leaves. It may therefore be necessary to incorporate CO photoproduction from dead plant matter into predictions of global CO emissions from plants. Methods are presented for direct measurement of CO photoproduction from live, intact leaves, from excised leaves, and from fallen leaves. Although these techniques were initially used for laboratory studies, they are directly applicable to field studies. Results of mechanistic studies indicate that oxygen affects CO photoproduction but that carbon dioxide exhibits no direct influence. Formation of CO was shown to be the result of direct photochemical transformation on or in the plant matter. Furthermore, for live plant leaves, CO photoproduction was observed to occur internal to the leaf.
A model simulation of Pinatubo volcanic aerosols in the stratosphere
Authors: Zhao Jingxia , Turco Richard P. , Toon Owen B.
Published: February 2004

A one‐dimensional, time‐dependent model is used to study the chemical, microphysical, and radiative properties of volcanic aerosols produced by the Mount Pinatubo eruption on June 15, 1991. Our model treats gas‐phase sulfur photochemistry, gas‐to‐particle conversion of sulfur, and the microphysics of sulfate aerosols and ash particles under stratospheric conditions. The dilution and diffusion of the volcanic eruption clouds are also accounted for in these conditions. Heteromolecular homogeneous and heterogeneous binary H2SO4/H2O nucleation, acid and water condensational growth, coagulation, and gravitational sedimentation are treated in detail in the model. Simulations suggested that after several weeks, the volcanic cloud was composed mainly of sulfuric acid/water droplets produced in situ from the SO2 emissions. The large amounts of SO2 (around 20 Mt) injected into the stratosphere by the Pinatubo eruption initiated homogeneous nucleation which generated a high concentration of small H2SO4/H2O droplets. These newly formed particles grew rapidly by condensation and coagulation in the first few months and then reach their stabilized sizes with effective radii in a range between 0.3 and 0.5 μm approximately one‐half year after the eruption. The predicted volcanic cloud parameters reasonably agree with measurements in term of the vertical distribution and lifetime of the volcanic aerosols, their basic microphysical structures (e.g., size distribution, concentration, mass ratio, and surface area) and radiative properties. The persistent volcanic aerosols can produce significant anomalies in the radiation field, which have important climatic consequences. The large enhancement in aerosol surface area can result in measurable global stratospheric ozone depletion.
Reduction of lunar basalt 70035: Oxygen yield and reaction product analysis
Authors: Gibson Michael A. , Knudsen Christian W. , Brueneman David J. , Allen Carlton C. , Kanamori Hiroshi , McKay David S.
Published: February 2004

Oxygen production from a lunar rock has been experimentally demonstrated for the first time. A 10 g sample of high‐Ti basalt 70035 was reduced with hydrogen in seven experiments at temperatures of 900–1050°C and pressures of 14.7–150 psia. In all experiments, water evolution began almost immediately and was essentially complete in tens of minutes. Oxygen yields ranged from 2.93 to 4.61% of the starting sample weight, and showed weak dependence on temperature and pressure. Analysis of the solid samples demonstrated total reduction of Fe2+ in ilmenite and small degrees of reduction in olivine and pyroxene. TiO2 was also partially reduced to one or more suboxides. Data from these experiments provide a basis for predicting the yield of oxygen from lunar basalt as well as new constraints on natural reduction in the lunar regolith.