bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ measurements of enhanced crystal number densities in cirrus clouds caused by aircraft exhaust
Authors: Ström Johan , Ohlsson Sofia
Published: February 2004

Concurrent measurements of crystal number densities and concentrations of absorbing material contained in cirrus crystals reveal statistically higher crystal number densities in areas of the cloud where absorbing material exceeds 0.01 μg m−3. This enhancement in crystal number density ranged between a factor 1.6 and 2.8 depending on the aerosol number density. The absorption signature appeared as banded structures 2 to 8 km wide, which suggests aged aircraft plumes as the source of absorbing material. In the altitudes of the most frequently used flight levels, the concentration of absorbing material in crystals exceeded 0.01 μg m−3 during more than 40% of the time in cirrus clouds.
A global three‐dimensional atmosphere‐ocean model of methyl bromide distributions
Authors: Lee‐Taylor J. M. , Doney S. C. , Brasseur G. P. , Müller J.‐F.
Published: February 2004

A three‐dimensional ocean‐atmosphere model of the global methyl bromide budget is presented including an analysis of the temporally and spatially varying source and sink distributions. No correlation is found between oceanic net biological CH3Br production, implied by surface water saturation anomaly observations, and oceanic variables such as surface chlorophyll and primary production; therefore model ocean fluxes are constrained directly by the saturation anomaly observations. The resulting diagnosed biological production rates imply net production in the tropics and subtropics and net consumption at high latitudes. Results from this semicoupled ocean‐atmosphere model show substantial longitudinal variability in the atmospheric boundary layer CH3Br concentrations with land‐ocean contrasts of 1–6 ppt due to regional industrial and agricultural emissions on land and net fluxes into the ocean. Owing to an imbalance in current understanding of the global budget, our simulated mixing ratios of 3.5 to 6.5 ppt for the southern and northern hemispheres, respectively, are significantly lower than available measurements. Sensitivity studies reducing the ocean and soil surface sinks slightly improve the global mean CH3Br concentration but increase the interhemispheric ratio further beyond that supported by observations. Accordingly, an apparent terrestrial missing source of 89–104 kT yr−l is derived and applied to the model. This is of the same order as the sum of all other sources in the model (85 kT yr−1). The hemispheric distribution of the missing source is explored, indicating that 50–70% of this source occurs in the southern hemisphere and is likely to be biased toward tropical regions. Modeled seasonal variability in the interhemispheric ratio at specific monitoring sites agrees well with observations. The model‐predicted vertical gradient of CH3Br through the troposphere and lower stratosphere is also presented.
First difference method: Maximizing station density for the calculation of long‐term global temperature change
Authors: Peterson Thomas C. , Karl Thomas R. , Jamason Paul F. , Knight Richard , Easterling David R.
Published: February 2004

The calculation of global land surface air temperature trends using the instrumental record has been based primarily upon two methods of maximizing the availability of station records. Hansen and Lebedeff[l981] developed a technique that is still used today, known as the reference station method; Jones et al. [1986a] popularized the climate anomaly method in their calculations of global temperature trends. In this paper we introduce yet another approach designed to maximize station records, referred to as the first difference method. To test the sensitivity of global temperature trend analysis to the method used, we calculate worldwide‐averaged land surface mean temperature using each of these methods with an identical data base, the Global Historical Climatology Network. For further comparisons, a global climate model (GCM) transient model simulation is interpolated to the Global Historical Climatology Network station locations and the three techniques are then applied to data interpolated to the station locations from the model. The Intergovernmental Panel on Climate Change (IPCC); [Nicholls et al. 1996] estimated a global land and ocean temperature change of 0.45°C±0.15°C since the 19th century. Their assessment of the uncertainty associated with this temperature trend did not specifically address the differences that the method of calculating a global temperature time series might produce. Our results indicate that the differences in 1880–1990 trends produced by these three different methods are only a few hundredths of a degree centigrade per 100 years on trends of approximately 0.5°C/100 years. This is quite small compared to the 0.15°C/100 years uncertainty associated with the IPCC global land and ocean assessment which included factors such as data homogeneity which are not addressed here. Indeed, our results indicate that the source of differences in trends is more likely to be the method used to calculate a linear trend from a global temperature time series than the method used to create the global temperature time series. The modeled results confirm this finding but highlight other important characteristics: the reference station method has uncharacteristically low interannual variance, more similar to time series from the entire globe (land and ocean) than the global land area from which the data were observed. This lower variance can impact the statistical significance associated with linear trends.
Laboratory study of closed and dynamic flux chambers: Experimental results and implications for field application
Authors: Gao Fang , Yates S. R.
Published: February 2004

Flux chambers are useful and convenient tools for measuring gas emissions at soil and water surfaces in agricultural, ecological, environmental, and engineering studies. In this experiment, a closed chamber and a dynamic chamber were tested to study their general behavior and to identify factors affecting flux measurement. The experiment was designed and conducted on the basis of a previous study where the behavior of these flux chambers was simulated using mathematical models. Emission of a volatile solvent (CH2Cl2) from a constant source was measured at the surface of a soil layer by both closed and dynamic chambers. Measurements from the closed chamber tests show that the average flux calculated over a placement time (ti to) by a linear model is smaller than the initial flux at t0 = 0 but greater than the temporal flux at ti − ti−1. The results from the dynamic chamber tests indicate that the steady‐state flux may underestimate the actual flux when the chamber is operating at low airflow rates but overestimate the actual flux at high airflow rates. The underestimate at a low airflow rate is probably due to a depression on the diffusive flux at the enclosed soil surface, while the overestimate is due to a pressure deficit present within the chamber headspace that induces an advective flux from the covered soil matrix. The vacuum system operating the dynamic chamber in this experiment was found to be a predominant source of the pressure deficit. The air permeability of soil matrix and its surface condition are demonstrated to be important factors that determine how significant the effect of the pressure deficit is. In general, the experimental results agree with the simulation results reported previously. When using closed chambers, it is recommended that appropriate nonlinear models be used to calculate flux. When using dynamic chambers, which are more desirable, relatively high airflow rates should be employed and the pressure deficit within the chamber headspace should be measured and minimized.
High‐resolution pollen analysis of tundra polygons from the North Slope of Alaska
Authors: Eisner Wendy R. , Peterson Kim M.
Published: February 2004

Modern and fossil pollen analyses have established the local vegetation succession and landscape evolution along the Meade River near Atqasuk, Alaska. Three data sets were analyzed: (1) a 142‐cm‐long peat deposit on the exposed river bluff face, (2) a short, 13‐cm peat monolith from the near‐surface sediment, and (3) a modern data set of surface samples collected along a transect representative of a geomorphic gradient of low‐center, transitional, and high‐center polygons. Pollen‐microfossil assemblages changed significantly along this gradient. Detailed analysis of the short pollen profile shows successional vegetation changes over the last 250 years. The long profile, a 9400‐year record of past vegetation, indicates that initially, the site was covered by shallow lakes. Eolian activity had a substantial effect on sediment deposition, but a period of rapid peat growth from 8500 to 5000 14C year B.P. is coincident with increased vegetation cover of mixed grass‐shrub tundra. Following this period, peat growth slowed, and shrub vegetation was replaced by tussock‐forming sedge vegetation.
Comparisons of cloud microphysics with cloud condensation nuclei spectra over the summertime Southern Ocean
Authors: Yum Seong Soo , Hudson James G. , Xie Yonghong
Published: February 2004

In spite of the many factors that determine cloud droplet concentrations, relationships were found between cloud condensation nuclei (CCN) and cloud droplet concentrations for the First Aerosol Characterization Experiment (ACE 1). Measurements were made in summertime stratocumulus clouds over the Southern Ocean far from anthropogenic sources. The closest relationship of CCN and droplet concentrations was found for CCN measured just below near‐adiabatic cloud parcels. Moreover, an adiabatic droplet growth model successfully predicted these droplet concentrations from the CCN spectra and updraft velocities. Correlations of the averages of CCN and cloud droplet concentrations over the entirety of each of the flights were also good. The model also predicted, with reasonable accuracy, these flight‐wide average droplet concentrations from flight‐wide average CCN spectra and flight‐wide average cloud updraft velocities. Drizzle was a major reason for the larger variations in droplet concentrations than in CCN concentrations. Vertical differences in CCN concentrations may have also affected cloud droplet concentrations. Despite variabilities in droplet concentrations, there was a clear relationship between CCN and droplet concentrations. Many of the inferred supersaturations (0.5 to 1.4%) in the “adiabatic” clouds ranged higher than some previous estimates (e.g., 0.2%) for stratus clouds. This may have been due to the cleaner air of the Southern Ocean but is more likely attributable to the more intensive analysis used in this study. Nonetheless, even where the inferred cloud supersaturations were lower (i.e., 0.2%), due to reductions of the droplet concentrations, there was still a relationship between CCN and droplet concentrations.
Raman lidar measurements of aerosol extinction and backscattering: 2. Derivation of aerosol real refractive index, single‐scattering albedo, and humidification factor using Raman lidar and aircraft size distribution measurements
Authors: Ferrare R. A. , Melfi S. H. , Whiteman D. N. , Evans K. D. , Poellot M. , Kaufman Y. J.
Published: February 2004

Aerosol backscattering and extinction profiles measured by the NASA Goddard Space Flight Center Scanning Raman Lidar (SRL) during the remote cloud sensing (RCS) intensive operations period (IOP) at the Department of Energy Atmospheric Radiation Measurement (ARM) southern Great Plains (SGP) site during two nights in April 1994 are discussed. These profiles are shown to be consistent with the simultaneous aerosol size distribution measurements made by a PCASP (Passive Cavity Aerosol Spectrometer Probe) optical particle counter flown on the University of North Dakota Citation aircraft. We describe a technique which uses both lidar and PCASP measurements to derive the dependence of particle size on relative humidity, the aerosol real refractive index n, and estimate the effective single‐scattering albedo ω0. Values of n ranged between 1.4–1.5 (dry) and 1.37–1.47 (wet); ω0 varied between 0.7 and 1.0. The single‐scattering albedo derived from this technique is sensitive to the manner in which absorbing particles are represented in the aerosol mixture; representing the absorbing particles as an internal mixture rather than the external mixture assumed here results in generally higher values of ω0. The lidar measurements indicate that the change in particle size with relative humidity as measured by the PCASP can be represented in the form discussed by Hanel [1976] with the exponent γ = 0.3 ± 0.05. The variations in aerosol optical and physical characteristics captured in the lidar and aircraft size distribution measurements are discussed in the context of the meteorological conditions observed during the experiment.
Comparison of ozone profiles obtained with Brewer‐Mast and Z‐ECC sensors during simultaneous ascents
Authors: De Backer Hugo , De Muer Dirk , De Sadelaer Geert
Published: February 2004

Uccle is a European station with a long tradition in measuring ozone profiles with Brewer‐Mast (BM) ozone sensors. In 1996 the use of model Z electrochemical concentration cell (Z‐ECC) ozonesondes, manufactured by EN‐SCI Corporation, was considered. To document the changeover from BM to Z‐ECC ozonesondes, a program of double soundings was started in October 1996. With the use of an appropriate correction procedure, accounting for the loss of pump efficiency with decreasing pressure and temperature, it is possible to reduce the mean difference between ozone profiles obtained with both types of sondes below 3%, which is statistically insignificant over nearly the whole operational altitude range (from the ground to 32 km). It is concluded that with this new method the uncertainty, introduced in trend analyses by the changeover, is less than the internal uncertainty within the BM time series. The required corrections are discussed according to measurements of the pump efficiencies at different pressures and temperatures in a vacuum chamber.
Nonmigrating diurnal tides in the troposphere and lower stratosphere over Gadanki (13.5°N, 79.2°E)
Authors: Sasi M. N. , Ramkumar Geetha , Deepa V.
Published: February 2004

A study of diurnal tidal oscillations in horizontal winds using Indian mesosphere‐stratosphere‐troposphere radar located at Gadanki (13.5°N, 79.2°E) shows that during autumnal equinox season diurnal amplitudes of 1–2 m s−1 of horizontal winds prevail in the troposphere. The vertical structure of amplitudes and phases indicate a vertical wavelength of ∼3 km in the lower troposphere and ∼6 km in the upper troposphere. A comparison of these amplitudes and vertical wavelengths with results from theoretical tidal models suggests that these oscillations in the lower troposphere are manifestation of nonmigrating diurnal tidal oscillations excited by eddy heat flux in the planetary boundary layer and those in the upper troposphere excited by latent heat release in deep convective clouds. However, nonmigrating diurnal tidal modes generated by solar radiation absorption by water vapor and clouds in the troposphere cannot be ruled out.
Stratocumulus processing of gases and cloud condensation nuclei: 1. Trajectory ensemble model
Authors: Feingold Graham , Kreidenweis Sonia M. , Zhang Yiping
Published: February 2004

Aqueous‐phase processing of gases and of the cloud condensation nucleus (CCN) spectrum is addressed using a trajectory ensemble model. We first derive a set of boundary layer parcel trajectories from a large‐eddy simulation model (LES) and then use this trajectory set for subsequent cloud microphysical/chemical studies. We explore this approach in the stratocumulus‐capped marine boundary layer and show examples of aqueous‐phase processing of gases and CCN. The microphysical model is a Lagrangian parcel model that is driven by the thermodynamic and kinematic fields produced by the LES and calculates CCN deliquescence and droplet growth by condensation on a moving mass grid. It is coupled with a sulfate chemistry model that treats oxidation of S(IV) to S(VI) via ozone and hydrogen peroxide for a size‐resolved droplet spectrum. The model reproduces the observed (and previously modeled) aqueous processing of particles that leads to growth of CCN and lowering of their critical supersaturations. Results show that important information on parcel in‐cloud residence times and boundary layer mixing timescales can be gleaned from this approach. By averaging the results of 500 parcel trajectories, a more representative picture of CCN and gas processing is obtained compared with that derived from a single parcel simulation representing average conditions. Finally, processed CCN spectra are used as input to a coupled microphysical/dynamical cloud‐resolving model, and it is suggested that cloud processing may either enhance or suppress drizzle formation, depending on the concentration and sizes of the CCN.
Retrieval of tropospheric carbon monoxide for the MOPITT experiment
Authors: Pan Liwen , Gille John C. , Edwards David P. , Bailey Paul L. , Rodgers Clive D.
Published: February 2004

A retrieval method for deriving the tropospheric carbon monoxide (CO) profile and column amount under clear sky conditions has been developed for the Measurements of Pollution In The Troposphere (MOPITT) instrument, scheduled for launch in 1998 onboard the EOS‐AM1 satellite. This paper presents a description of the method along with analyses of retrieval information content. These analyses characterize the forward measurement sensitivity, the contribution of a priori information, and the retrieval vertical resolution. Ensembles of tropospheric CO profiles were compiled both from aircraft in situ measurements and from chemical model results and were used in retrieval experiments to characterize the method and to study the sensitivity to different parameters. Linear error analyses were carried out in parallel with the ensemble experiments. Results of these experiments and analyses indicate that MOPITT CO column measurements will have better than 10% precision, and CO profile measurement will have approximately three pieces of independent information that will resolve 3–5 tropospheric layers to approximately 10% precision. These analyses are important for understanding MOPITT data, both for application of data in tropospheric chemistry studies and for comparison with in situ measurements.
Latitudinal distribution of reactive nitrogen in the free troposphere over the Pacific Ocean in late winter/early spring
Authors: Singh H. B. , Viezee W. , Chen Y. , Thakur A. N. , Kondo Y. , Talbot R. W. , Gregory G. L. , Sachse G. W. , Blake D. R. , Bradshaw J. D. , Wang Y. , Jacob D. J.
Published: February 2004

The late winter/early spring (February/March, 1994) measurements of Pacific Exploratory Mission‐West (PEM‐W) B have been analyzed to show latitudinal distributions (45°N to 10°S) of the mixing ratios of reactive nitrogen species (NO, peroxyacetylnitrate (PAN), HNO3, and NOy), ozone, and chemical tracers (CO, NMHCs, acetone, and C2Cl4) with a focus on the upper troposphere. Mixing ratios of all species are relatively low in the warm tropical and subtropical air south of the polar Jetstream (≈28°N) but increase sharply with latitude in the cold polar air north of the Jetstream. Noteworthy is the continuous increase in reservoir species (PAN and HNO3) and the simultaneous decrease in NOx toward the northern midlatitudes. The Harvard global three‐dimensional model of tropospheric chemistry has been used to compare these observations with predictions. In the upper troposphere the magnitude and distribution of measured NOy and PAN as a function of latitude is well represented by this model, while NOx (measured NO + model calculated NO2) is underpredicted, especially in the tropics. Unlike several previous studies, where model‐predicted HNO3 exceeded observations by as much as a factor of 10, the present data/model comparison is improved to within a factor of 2. The predicted upper tropospheric HNO3 is generally below or near measured values, and there is little need to invoke particle reactions as a means of removing or recycling HNO3. Comparison between measured NOy and the sum of its three main constituents (PAN + NOx + HNO3) on average show a small mean shortfall (<15%). This shortfall could be attributed to the presence of known but unmeasured species (e.g., peroxynitric acid and alkyl nitrates) as well as to instrument errors.
Corection of thin cirrus path radiances in the 0.4–1.0 μm spectral region using the sensitive 1.375 μm cirrus detecting channel
Authors: Gao Bo‐Cai , Kaufman Yoram J. , Han Wei , Wiscombe Warren J.
Published: February 2004

We have developed an empirical algorithm for removing thin cirrus effects from AVIRIS (airborne visible infrared imaging spectrometer) images at any wavelength in the region 0.4–1 μm using narrow channels near 1.38, 1.24, and 0.66 μm. In this algorithm the imaging pair of 1.38 and 1.24 μm channels is used for cirrus removal over water surfaces, while the imaging pair of 1.38 and 0.66 μm channels is used over land surfaces. The AVIRIS data on which the algorithm is based were measured from an ER‐2 aircraft at 20 km altitude during several field programs over both land and ocean. From these data we earlier discovered that narrow channels near the center of the strong 1.38‐μm water vapor bands are very sensitive in detecting thin cirrus clouds. The present paper is a logical continuation of that work. Our new algorithm has considerable generality. As a first application, it can be incorporated as a front end to the first‐generation moderate resolution imaging spectrometer (MODIS) (on EOS AM and PM platforms) atmospheric correction algorithms for ocean color and land applications in order to yield improved atmospheric aerosol, land surface, and ocean color products.
Nitrous oxide, nitric oxide, and methane fluxes from soils following clearing and burning of tropical secondary forest
Authors: Weitz A. M. , Veldkamp E. , Keller M. , Neff J. , Crill P. M.
Published: February 2004

Conversion of humid tropical forest to agriculture significantly alters trace gas emissions from soils. We report nitrous oxide (N2O), nitric oxide (NO), and methane (CH4) fluxes from secondary forest soils prior to and during deforestation, and throughout the first agricultural cropping. Annual average nitrogen oxide emissions from forest soils were 1.5 ng N cm−2h−1for N2O and 0.9 ng N cm−2h−1for NO. Forest clearing increased the level of extractable nitrate in soils and average nitrogen oxides fluxes (2.7 ng N cm−2h−1for N2O, and 8.1 ng N cm−2h−1for NO). Immediately after biomass burning, short‐term peaks of N2O and NO (123 ng N cm−2h−1for N2O, and 41 ng N cm−2h−1for NO) were superimposed on generally increased fluxes. Peak emissions declined within 3 days after burning. Postburn fluxes stayed higher than measured on adjacent forest sites for 3–4 months (averages for postburn fluxes were 17.5 ng N cm−2h−1for N2O, and 19.2 ng N cm−2h−1for NO). Increased N2O and NO emissions after clearing and until cropping were probably due to a combination of increased rates of nitrogen cycling and higher gaseous diffusion in drying soils. Compared to emissions from young pastures in the region, fluxes of nitrogen oxides from unfertilized agricultural areas were low (3.9 ng N cm−2h−1for N2O and 3.4 ng N cm−2h−1for NO), probably due to nitrogen uptake by fast growing corn plants and losses by leaching with draining soil water in the wet season. Variation in CH4fluxes was high for all land use periods. Forest soils consumed an average of 1.0 mg CH4m−2d−1, which slightly increased in drier soils after clearing (1.2 mg CH4m−2d−1). Postburn CH4consumption by soils was slightly reduced (0.8 mg CH4m−2d−1) compared to forest soils. Unfertilized agricultural soils consumed less CH4than forest soils.
Biomass burning signatures in the atmosphere of central Greenland
Authors: Jaffrezo J.‐L. , Davidson C. I. , Kuhns H. D. , Bergin M. H. , Hillamo R. , Maenhaut W. , Kahl J. W. , Harris J. M.
Published: February 2004

Daily atmospheric concentrations of participate oxalate measured at the Summit of the Greenland Ice Sheet are presented for the summers 1992–1995. We believe that four episodes of elevated concentrations are due to biomass burning plumes passing over the site. In at least two cases the source regions of the fires are located in northern Canada. Further characteristics of the aerosol are examined during one of these events. A large increase of particle number concentrations in the accumulation mode can be observed, while the increase is much more limited for total particle number. The suite of chemical species enriched in the aerosol includes typical biomass burning tracers like fine K, large concentrations of ammonium, particulate formate and acetate, as well as other organic species like glycolate. The size distributions of K, oxalate, and glycolate are skewed toward the accumulation mode and exhibit the very same shape as sulfate, suggesting internal mixing of these species in the same particles. Molar ratios S/K indicate incorporation of S during transport, most probably by production of sulfate. Concentrations of these species were measured in fog samples for radiative events that occurred during the plume passage. There is a good agreement in the relative variation of concentrations between the aerosol and fog for oxalate and glycolate, while the gas phase probably dominates incorporation in the fog droplets for acetate, formate, chloride, nitrate, and sulfate (incorporated as SO2, which is further oxidized). The complexity of the transfer of the organic acids from the atmosphere to fog is underlined.
A general circulation model study on the interannual variability of soil dust aerosol
Authors: Tegen Ina , Miller Ron
Published: February 2004

To assess interannual soil dust aerosol variability, we computed dust as a tracer in the Goddard Institute for Space Studies general circulation model. Comparisons of dust model results with results from an off‐line tracer model, satellite retrievals, and ground observations show mostly good agreement, but also reveal problems with the model results and difficulties with such comparisons. Two 15–year runs with prescribed sea surface temperatures were carried out, one with identical dust sources for each year and one with varying dust sources in order to investigate the contribution of dust sources and transport to the variability of dust concentrations in different regions. Specifically for the North Atlantic and the Mediterranean region, 70–90% of the dust variability is attributable to transport variability. Correlation coefficients between dust concentrations with precipitation and surface winds were calculated to find controlling factors for dust concentration for different regions of the world.
Transport of carbon dioxide, water vapor, and ozone by turbulence and local circulations
Authors: Sun Jielun , Desjardins Raymond , Mahrt Larry , MacPherson Ian
Published: February 2004

Nocturnal land breezes and daytime lake breezes are studied using data collected by the Canadian Twin Otter aircraft and a deck boat which traversed Candle Lake during the Boreal Ecosystem‐Atmosphere Study (BOREAS). The nocturnal vertical transport of CO2, water vapor, and ozone over the lake consists of two parts: (1) mesoscale rising motion associated with land breeze convergence and (2) significant turbulence and vertical mixing driven by buoyancy in the lower part of the internal boundary layer and shear generation in the top part of the internal boundary layer. For comparison, the role of the lake in the daytime is examined in terms of formation of a stable internal boundary layer due to advection of warm air from land with small CO2 concentration over the cooler lake surface. Analysis of the aircraft and boat data indicates that the nocturnal land breeze plays an important role in the regional CO2 budget in the lake region. In the present study, CO2 is advected horizontally by a nocturnal land breeze circulation and vented vertically over Candle Lake (“chimney effect”). Such near‐surface horizontal transport implies that part of the respirated CO2 never reaches the tower observational level, particularly under light wind conditions. This study speculates that preferred locations of vertical venting of CO2 may also occur due to convergence of nocturnal drainage circulations or flow meandering, although probably weaker than that associated with the land breeze. These circulations partly explain recent findings that tower‐measured nocturnal turbulent fluxes of CO2 above the canopy and the subcanopy storage of CO2 frequently sum to less than the total respiration of CO2, leading to “missing CO2.” Unfortunately, the present study does not allow evaluation of all of the terms in the carbon dioxide budget.
Retrieval of stratospheric temperatures from spaceborne microwave limb sounding measurements
Authors: Wehr T. , Bühler S. , von Engeln A. , Künzi K. , Langen J.
Published: February 2004

Microwave limb sounding is a well‐suited technique for the observation of the composition and temperature of the middle atmosphere. The Shuttle‐borne millimeter‐wave atmospheric sounder (MAS) measures three oxygen lines in the 61–64 GHz region. Since oxygen is uniformly mixed in the lower and middle atmosphere, the amplitude and shape of the emission lines depend only on temperature and pressure. From these oxygen emission lines, vertical temperature profiles are retrieved with a vertical resolution of 5km in the altitude region of 15–45 km (127–1.5 hPa). The estimated total error is 1.5 K at altitudes of 25–35 km (24.5–5.7 hPa) and up to 5 K above and below this region. Simultaneously with the temperature profile, certain instrument parameters are retrieved. We present the first MAS temperature retrieval results taken at three different locations from measurements of March 31, 1992, during the ATLAS 1 mission. The temperature retrieval results are basically in good agreement with National Center for Environmental Prediction (NCEP) analysis data, but the MAS retrievals have a tendency to low temperatures in the lower stratosphere.
Investigations of error sources of the Global Precipitation Climatology Project emission algorithm
Authors: McCollum Jeffrey R. , Krajewski Witold F.
Published: February 2004

An error analysis of the Global Precipitation Climatology Project emission algorithm is conducted to identify the major error sources of the algorithm and to quantify the estimation biases resulting from these sources. Several error sources are investigated and uncertainties in spatial rainfall rate variability and freezing level height are identified as the most significant. Spatial rainfall rate variability contributes to beam filling error, and beam filling error is investigated in detail by simulation of brightness temperatures resulting from rainfall rate fields with known spatial variabilities. The algorithm is used to estimate rainfall from the simulated brightness temperatures, and the estimation bias is calculated by comparison of the monthly rainfall estimates with the monthly rainfall used to simulate the brightness temperatures. The final result of the study is the mean monthly multiplicative bias error as a function of the freezing level height and the instantaneous rainfall rate variability.
Seasonal course of isoprene emissions from a midlatitude deciduous forest
Authors: Goldstein Allen H. , Goulden Michael L. , Munger J. William , Wofsy Steven C. , Geron Christopher D.
Published: February 2004

Continuous measurements of whole canopy isoprene emissions over an entire growing season are reported from Harvard Forest (42°32′N, 72°11′W). Emissions were calculated from the ratio of observed CO2 flux and gradient multiplied by the observed hydrocarbon gradients. In summer 1995, 24‐hour average emissions of isoprene from June 1 through October 31 were 32.7×1010 molecules cm−2 s−l (mg C m−2 h−l = 2.8 × 1011 molecules cm−2 s−1), and the mean midday mixing ratio was 4.4 ppbv at 24 m. Isoprene emissions were zero at night, increased through the morning with increasing air temperature and light, reached a peak in the afternoon between the peaks in air temperature and light, and then declined with light. Isoprene emissions were observed over a shorter seasonal period than photosynthetic carbon uptake. Isoprene emission was not detected from young leaves and reached a peak rate (normalized for response to measured light and temperature conditions) 4 weeks after leaf out and 2 weeks after emissions began. The normalized emission rate remained constant for approximately 65 days, then decreased steadily through September and into October. Total isoprene emissions over the growing season (42 kg C ha−1 yr−1) were equal to 2% of the annual net uptake of carbon by the forest. Measured isoprene emissions were higher than the Biogenic Emission Inventory System‐II model by at least 40% at midday and showed distinctly different diurnal and seasonal emission patterns. Seasonal adjustment factors (in addition to the light and temperature factors) should be incorporated into future empirical models of isoprene emissions. Comparison of measured isoprene emissions with estimates of anthropogenic volatile organic compound emissions suggests that isoprene is more important for ozone production in much of Massachusetts on hot summer days when the highest ozone events occur.
Composition‐dependent freezing nucleation rates for HNO3/H2O aerosols resembling gravity‐wave‐perturbed stratospheric particles
Authors: Prenni Anthony J. , Onasch Timothy B. , Tisdale Robert T. , Siefert Ronald L. , Tolbert Margaret A.
Published: February 2004

Laboratory measurements are presented for the freezing kinetics of H2O/HNO3 aerosols over the temperature range of 188–204 K. For 2:1 H2O:HNO3 aerosols crystallizing to NAD we observed a maximum nucleation rate of J = 9.3×109 cm−3 s−1 at 194 K. This temperature is between the glass point of 161 K [Ji et al., 1993] and the melting point of 235.5 K [Ji et al., 1996]. This can be compared to a previous measurement of J = 6.7×109 cm−3 s−1 at 193 K [Disselkamp et al., 1996] and lower temperature measurements of J ≈ 1010–1012 cm−3 s−1 at 178.8 ‐ 175.8 K [Bertram and Sloan, 1998a]. Measured nucleation rates decrease as the aerosol becomes dilute, but NAD formation is still observable for 2.5:1 H2O:HNO3 at temperatures near 195 K. In contrast, freezing of 3:1 H2O:HNO3 aerosol was not observed for constant temperature experiments throughout this temperature range, yielding an upper limit of J<1.5×109 cm−3 s−1. This is the lowest experimental value determined for 3:1 H2O:HNO3 freezing rates at these temperatures. From the measured freezing rates and knowledge of the free energy of diffusion the average interfacial free energy for NAD in a 2:1 H2O:HNO3 solution was determined to be σ = 25.2 ergs cm−2. A limit for the interfacial free energy was placed on 3:1 H2O:HNO3 particles, for which freezing was not observed. These data imply that if aerosols reach compositions more concentrated than 3:1 H2O:HNO3 in the atmosphere, NAD may play a role in polar stratospheric cloud formation.
The composition of the Jovian atmosphere as determined by the Galileo probe mass spectrometer
Authors: Niemann H. B. , Atreya S. K. , Carignan G. R. , Donahue T. M. , Haberman J. A. , Harpold D. N. , Hartle R. E. , Hunten D. M. , Kasprzak W. T. , Mahaffy P. R. , Owen T. C. , Way S. H.
Published: February 2004

The Galileo probe mass spectrometer determined the composition of the Jovian atmosphere for species with masses between 2 and 150 amu from 0.5 to 21.1 bars. This paper presents the results of analysis of some of the constituents detected: H2, He, Ne, Ar, Kr, Xe, CH4, NH3, H2O, H2S, C2 and C3 nonmethane hydrocarbons, and possibly PH3 and Cl. 4He/H2 in the Jovian atmosphere was measured to be 0.157±0.030. 13C/12C was found to be 0.0108±0.0005, and D/H and 3He/4He were measured. Ne was depleted, ≤0.13 times solar, Ar ≤1.7 solar, Kr ≤5 solar, and Xe ≤5 solar. CH4 has a constant mixing ratio of (2.1±0.4) × 10−3 (12C, 2.9 solar), where the mixing ratio is relative to H2. Upper limits to the H2O mixing ratio rose from 8 × 10−7 at pressures <3.8 bars to (5.6±2.5) × 10−5 (16O, 0.033±0.015 solar) at 11.7 bars and, provisionally, about an order of magnitude larger at 18.7 bars. The mixing ratio of H2S was <10−6 at pressures less than 3.8 bars but rose from about 0.7 × 10−5 at 8.7 bars to about 7.7 × 10−5 (32S, 2.5 solar) above 15 bars. Only very large upper limits to the NH3 mixing ratio have been set at present. If PH3 and Cl were present, their mixing ratios also increased with pressure. Species were detected at mass peaks appropriate for C2 and C3 hydrocarbons. It is not yet clear which of these were atmospheric constituents and which were instrumentally generated. These measurements imply (1) fractionation of 4He, (2) a local, altitude‐dependent depletion of condensables, probably because the probe entered the descending arm of a circulation cell, (3) that icy planetesimals made significant contributions to the volatile inventory, and (4) a moderate decrease in D/H but no detectable change in (D + 3He)/H in this part of the galaxy during the past 4.6 Gyr.
Complex depositional systems in Hydraotes Chaos, Mars: An example of sedimentary process interactions in the Martian hydrological cycle
Authors: Ori Gian Gabriele , Mosangini Claudia
Published: February 2004

Hydraotes Chaos is a complex basin located between the equatorial areas of chasma, east of Valles Marineris and the Chryse basin. The interactions in time and space of several sedimentary processes dominate the geological history of the chaos. The basin formed after the middle Noachian. The outflow channels related to the chaos probably flowed, during an early stage, to the south (Hydraotes channel) and to the north (Simud and Tiu Valles). After the capture of the southern Hydraotes channel by the chasma areas, the floods reversed direction and flowed northward into Hydraotes Chaos. Deltaic and lacustrine environments formed at this stage. The main consequence of the filling of the basin was the activation of Tiu Vallis. This scenario probably occurred intermittently several times during favorable climatic conditions. During these periods the water was liquid at the surface or, at least, with a frozen top layer. The major pieces of evidence for lacustrine sedimentation are: (1) terraces, (2) multiple strandlines and raised beaches, and (3) sediment drape on the basin floor. Hydraotes Chaos was the transition from the chasma areas next to Valles Marineris and the Chryse Basin. Its geological setting suggests that the water was released to Tiu Vallis episodically (during a large span of time, upper Noachian to middle Amazonian) from lakes.
Modeling the paleocirculation of the Mediterranean: The Last Glacial Maximum and the Holocene with emphasis on the formation of sapropel S1
Authors: Myers Paul G. , Haines Keith , Rohling Eelco J.
Published: February 2004

An ocean general circulation model is used to simulate the thermohaline circulation in the Mediterranean sea during the last glacial maximum and the Holocene, when the sapropel S1 was deposited. The model is forced by prescribed surface temperatures and salinities, where present‐day values lead to very realistic surface buoyancy fluxes. Different paleoreconstructions for the surface salinity and temperature distributions during these periods are tested. In both periods, under all reconstructions, antiestuarine flow is maintained at Gibraltar and Sicily. The Holocene circulation has fresh intermediate water produced in the Adriatic and an upward salt flux from the old waters below help maintain its outflow at Sicily. The depth of ventilation around the basin is broadly consistent with the shallowest sapropel layers observed. Shoaling of the eastern pycnocline occurs in all experiments in both periods, possibly indicating enhanced productivity, although the reasons for this are different in each case.
Interference fringes detected by OEDIPUS C
Authors: James H. G. , Calvert W.
Published: February 2004

An HF transmitter was operated at one end of the tethered sounding rocket payload OEDIPUS C, and a synchronized receiver was operated at the other end. Both the transmitter and the receiver were connected to dipoles. On the flight downleg after the tether had been cut, direct bistatic propagation experiments were carried out with the transmitter‐receiver pair. During the flight, sharp minima which can be attributed to interference fringes were detected in the directly transmitted signal. Fringe frequencies observed on OEDIPUS C ionograms for four different interference schemes have been examined using the cold‐plasma theory. First, fringes were observed which can be attributed to the Faraday rotation of the plane of linear electric field polarization for the combined O‐ and X‐mode or O‐ and Z‐mode waves. The electric field rotation was calculated using independent measurements of the plasma parameters and the attitudes of the transmitting and receiving dipoles. Another kind of fringe occurred for the whistler (W) and Z‐mode waves as a result of their triple‐valued refractive index below half the cyclotron frequency for the W mode and just below the plasma frequency for the Z mode. The hypothesis has been tested that these “single‐mode” fringes are caused by the cancellation of the wave field of two circularly polarized Z‐mode or W‐mode waves excited by the linearly polarized transmitting antenna, at the point where the two waves' electric fields are shifted in phase by 180°. The theory for the single‐mode nulls correctly predicts the frequency range and the spacing of the fringes but fails to explain absolute frequencies in all cases. This failure points to the need for a complete computation of the dipole radiated field which is expected to have considerable structure on account of the inflection points on the W‐ and Z‐mode refractive index surfaces. The OEDIPUS C bistatic propagation experiment has demonstrated Faraday rotation in situ. The agreement between observations and cold‐plasma theory suggests that future bistatic propagation facilities can exploit the Faraday effect to measure density, density gradient, and parameters dependent upon wave polarization.
Wet delay variability calculated from radiometric measurements and its role in space geodetic parameter estimation
Authors: Jarlemark Per O. J. , Emardson T. Ragne , Johansson Jan M.
Published: February 2004

The “wet delay,” the excess radio path length due to atmospheric water vapor, has been derived from 71 days of microwave radiometer measurements at the Onsala Space Observatory, Onsala, Sweden. The temporal and spatial variability in the wet delay was analyzed. When we estimated daily “variance rates,” the parameter characterizing a random walk process, values in the range 3.1×10−9 to 1.1×10−7 m2/s were found for the timescales 10–20 min. We estimated horizontal gradients in the wet delay and found that the temporal variability of the gradient components changed significantly from day to day. The variations in the gradients were also found to be significantly larger if data acquired only at relatively high elevation angles were used in the calculation. The effect of the wet delay variations on Global Positioning System (GPS) geodetic estimates was analyzed by performing Monte Carlo simulations. We used a Kalman filter with parameters for geodetic GPS data processing, first modeling the atmosphere as a horizontally homogeneous random walk process in time. In this case the estimated wet delay was found to be more sensitive to a detuning of the Kalman filter than the vertical component estimates. The RMS errors in the wet delay estimates increased from 2.2 to 3.6 mm when the atmospheric variance rate changed from 1.0×10−8 to 1.0×10−7 m2/s and when the filter parameter was set to 1.0×10−8 m2/s. When simulated wet delay gradients were added to the data, it was seen that if gradients are not estimated by the Kalman filter on days with large gradient variability, the scatter introduced by the gradients can dominate the other modeled error sources.
Comparison of over‐the‐horizon radar surface‐current measurements in the Gulf of Mexico with simultaneous sea truth
Authors: Harlan J. A. , Georges T. M. , Biggs D. C.
Published: February 2004

On June 14, 1995, the U.S. Navy's Relocatable Over‐the‐Horizon Radar (ROTHR) west of Corpus Christi, Texas, mapped the radial component of ocean surface current with 15‐km resolution over a 230,000‐km2area in the Gulf of Mexico. Concurrently, an oceanographic research vessel measured near‐surface currents within part of the area illuminated by the radar, providing an opportunity to compare radarderived surface currents with in situ sea truth. The R/VGyre, operated by Texas A&M University, twice traversed the Gulf of Mexico Loop Current while measuring current vectors with an acoustic Doppler current profiler (ADCP). We compared radar‐derived currents with currents measured in the uppermost ADCP bin (centered at 10‐m depth). If only radar data exceeding a quality threshold are considered, the rms difference in the radial currents measured by the two techniques is 27 cm s−1. This difference most likely reflects the different sampling employed by these instruments, as well as unremoved ionospheric biases in the radar measurements.
Preliminary estimates of the vertical profiles of inner and outer scales from White Sands Missile Range, New Mexico, VHF radar observations
Authors: Eaton Frank D. , Nastrom Gregory D.
Published: February 2004

There are very few reliable results of the inner and outer scales of turbulence in the remote atmosphere. Knowledge of these parameters is of high interest to the propagation and remote sensing communities. Seasonal profiles from 5 to 20 km above mean sea level of the inner scale have been estimated based on the kinematic viscosity and eddy dissipation rates which were determined from 5 years of nearly continuous 49.25‐MHz radar observations at White Sands Missile Range, New Mexico. Inner scale values were found to increase from about 1 cm at 5 km to near 7 cm at 19 km altitude. Outer scale profile determinations were made using a method proposed by Tatarskii [1971] that involves vertical wind shear and the eddy dissipation rate, both derived from the longterm VHF radar measurements. The outer scale decreased from about 60 m at 5 km altitude for all seasons to 12–20 m at 15 km (depending on season) and then increased to 22 m at 19 km. Seasonal differences in the inner and outer scales and background meteorological conditions are also presented and discussed.
An analysis of leaky‐wave dispersion phenomena in the vicinity of cutoff using complex frequency plane singularities
Authors: Hanson George W. , Yakovlev Alexander B.
Published: February 2004

In this paper we analyze characteristics of the dispersion function for leaky‐wave modes in the vicinity of cutoff for several representative waveguiding structures. Our principal purpose is to demonstrate that in the vicinity of leaky‐wave cutoff in open‐boundary waveguides (in the spectral‐gap region), dispersion behavior is controlled by the presence of branch points in the complex frequency plane. A similar situation occurs for the ordinary modes of homogeneously filled, perfefctly conducting cylindrical waveguides. These closed waveguides admit to simple analysis, leading to an explicit dispersion function which indicates frequency domain branch points. For open‐boundary waveguides, the presence of frequency domain branch points is obscured by the necessity of numerically solving an implicit dispersion equation. A set of sufficient conditions is provided here which defines these branch points in a unified manner for both open and closed waveguides. Identification of these points allows for rapid determination of important and interesting regions in both the frequency and wavenumber planes and leads to increased understanding of dispersion behavior, especially in the case of dielectric loss. Examples are shown for several waveguiding geometries to demonstrate the general nature of the presented formulation.