bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in pigment concentration in warm‐core rings as determined by coastal zone color scanner satellite imagery from the Mid‐Atlantic Bight
Authors: García‐Moliner Graciela , Yoder James A.
Published: February 2004

A time series of coastal zone color scanner (CZCS) derived chlorophyll (CZCS‐chl) and sea surface temperature (SST) satellite imagery was developed for the Mid‐Atlantic Bight (MAB). Warm‐core rings (WCR) were identified by both the warmer SST signal as well as the low pigment concentrations of their cores. The variation in pigment concentrations and SST observed in satellite imagery over the geographic range and life span of four WCRs is investigated. The hypotheses are that pigment concentration increase during the lifetime of the WCR is a response to processes such as convective overturn, upwelling, edge enhancement due to increased vertical mixing, active convergence, or lateral exchange. Empirical orthogonal function analysis (EOF) is used to investigate the relationship between SST and pigment patterns observed in the presence of a WCR. The first two EOF modes explain more than 80% of the variability observed in all four WCRs and in both (SST and pigment) data sets. Temperature and pigment data from a sampling quadrat, 100 × 100 pixels in size and centered on each of the four WCRs (81F, 82B, 82J, and 83E), were extracted from 41 matching pairs of images. The sampling quadrat was moved along the MAB, tracking temperature and pigment concentration in and around the WCRs. The two data sets covary, as shown by the eigenmaps, for same day images when advection of water from the productive shelf region is the source of the variability observed in the CZCS. Advection, determined to be the principal cause of the variability observed, is seen in the imagery as occurring through the north, northeast, southeast, and northwest sides of the rings. Eigenmaps show that the spatial distribution and source of the variability (e.g., shelf/slope or Gulf Stream) was not the same for all four rings examined. The results of this study show that, at the synoptic scales of satellite data, the variability observed in the WCRs is greater at the periphery of the rings. These results show that advective entrainment, rather than processes at ring center (e.g., shoaling of the pycnocline/nutricline in response to frictional decay) or at the periphery due to other processes such as vertical mixing, is the mechanism responsible for the observed variability.
Experimental studies of sediment enrichment of arctic ice covers due to wave action and frazil entrainment
Authors: Ackermann Norbert L. , Shen Hung Tao , Sanders Brian
Published: February 2004

Two processes are investigated that are believed to contribute to the sediment enrichment of ice covers in coastal arctic waters. One process results from wave action which pumps sediment rich underlying water into the surface cover. The other enriching mechanism is produced by rising frazil that entrains suspended sediment which subsequently becomes incorporated in the surface ice layer. In both processes the sediment enrichment of the ice cover is found to depend upon the sediment size and concentration in the underlying water column. In the wave dependent process the rate of sediment enrichment is influenced by the period, amplitude, and duration of the wave action as well as the size of the ice particles and motion of the cover. Frazil rising through sediment laden water was found to entrain particles of sand far more effectively than silt. Sand laden frazil floe would often become so loaded with sediment that the floe would eventually settle to the floor of the water column.
Acetone in the atmosphere: Distribution, sources, and sinks
Authors: Singh H. B. , O'Hara D. , Herlth D. , Sachse W. , Blake D. R. , Bradshaw J. D. , Kanakidou M. , Crutzen P. J.
Published: February 2004

Acetone (CH3COCH3) was found to be the dominant nonmethane organic species present in the atmosphere sampled primarily over eastern Canada (0–6 km, 35°–65°N) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (= 10−12v/v) with a mean value of 1140±413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios of 550±100 ppt were present in much of the troposphere studied. Correlations between atmospheric mixing ratios of acetone and select species such as C2H2, CO, C3H8, C2C14and isoprene provided important clues to its possible sources and to the causes of its atmospheric variability. Biomass burning as a source of acetone has been identified for the first time. By using atmospheric data and three‐dimensional photochemical models, a global acetone source of 40–60 Tg (= 1012g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons (principally propane, isobutane, and isobutene) provides the single largest source (51%). The remainder is attributable to biomass burning (26%), direct biogenic emissions (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also suggest that acetone photolysis contributed significantly to PAN formation (100–200 ppt) in the middle and upper troposphere of the sampled region and may be important globally. While the source‐sink equation appears to be roughly balanced, much more atmospheric and source data, especially from the southern hemisphere, are needed to reliably quantify the atmospheric budget of acetone.
A meteorological interpretation of the Arctic Boundary Layer Expedition (ABLE) 3B flight series
Authors: Shipham Mark C. , Bachmeier A. Scott , Cahoon Donald R. , Gregory Gerald L. , Anderson Bruce E. , Browell Edward V.
Published: February 2004

The Arctic Boundary Layer Expedition (ABLE) 3B was conducted to determine the summertime tropospheric distribution, sources, and sinks of important trace gas and aerosol species over the wetlands and boreal forests of central and eastern Canada. Isentropic trajectories and analyzed midtropospheric circulation patterns were used to group flights according to the transport histories of polar, midlatitude, or tropical air masses which were sampled. These data were then divided into bands of potential temperature levels representing the low, middle, and maximum aircraft altitudes to assess the effects of both local and long distance transport and natural and man‐made pollutants to the measured chemical species. Detailed case studies are provided to depict the complex three‐dimensional airflow regimes that transported air with differing chemical signatures to the study area. Mission 6 details the large‐scale movement of smoke in the generally prevailing west to northwesterly airflow that was observed on the majority of flights. Mission 1 analyzes the horizontal and vertical motions of maritime Pacific air in the upper troposphere that was routinely mixed downward to the aircraft altitude. Finally, mission 14 tracks the far northward excursion of tropical air that had been associated with a Pacific typhoon. The following three factors all had important influences on the collected chemical data sets: (1) local and distant stratospheric in puts into the upper and middle troposphere; (2) biomass‐burning plumes from active fires in Alaska and Canada; (3) a band of“low ozone”upper tropospheric air that was observed by airborne differential absorption lidar (DIAL) above the aircraft maximum altitude. Other modification factors observed on some flights included urban pollution from U.S. and Canadian cities, tropical air that had been associated with a Pacific typhoon, and precipitation scavenging by clouds and rain. Many flights were affected by several of the above factors which led to complex chemical signatures that will be discussed in other companion papers.
Airborne flux measurements of CO2, sensible, and latent heat over the Hudson Bay lowland
Authors: Desjardins R. L. , MacPherson J. I. , Schuepp P. H. , Hayhoe H. N.
Published: February 2004

As part of the Northern Wetlands Study (NOWES) in the summer of 1990, 30 flights were conducted with the National Research Council (NRC) Twin Otter research aircraft to quantify the spatial and temporal variations of CO2, H2O, and sensible heat fluxes over the Hudson Bay lowland. These consisted of two regional runs of approximately 100 km in length from James Bay to the Kinosheo Lake and 13‐km runs in the form of “L” and grid patterns near the Atmospheric Environment Service (AES) tower in the Kinosheo Lake area. An examination of the average fluxes shows that day‐to‐day differences were larger than the spatial differences. Significant correlations were found between the fluxes of CO2, sensible heat and latent heat, and selected environmental characteristics, such as air temperature, vapor pressure deficit, surface temperature minus air temperature, and incident solar radiation, for different sections of the NOWES area. The presentation of the spatial variations of aircraft‐based fluxes of CO2, sensible heat, and latent heat over a 13 km × 13 km area near Kinosheo Lake permits an evaluation of the spatial representativeness of the AES tower observations.
Numerical simulations of the effects of gravity waves on noctilucent clouds
Authors: Jensen Eric J. , Thomas Gary E.
Published: February 2004

We have used a two‐dimensional numerical model of mesospheric cloud formation to simulate the effects of internal gravity waves on the formation and appearance of ice clouds at the mesopause. We have used gravity wave parameters (amplitude, wavelength, period, etc.) consistent with measurements of gravity waves in the high‐latitude mesosphere, including observations of band and billow structures in noctilucent clouds (NLCs). We have investigated both the dynamical effects due to wave‐induced winds and the microphysical effects due to wave‐induced temperature perturbations. We find that the structures observed in NLC from the ground are predominantly caused by dynamical processes. Since the time required for ice crystal growth at the mesopause is much longer than the observed wave periods and ice crystal sublimation is much more rapid than deposition growth, the primary effect of wave‐induced temperature perturbations is to decrease the albedo of the clouds. The fact that gravity waves with periods less than a few hours are ubiquitous near the high‐latitude, summertime mesopause imposes an additional constraint on the formation of visible NLC. We find that the mean mesopause temperature must be about 5 K colder for NLC to form when gravity waves are present than when they are not present. Long‐period (>10 hours) waves may temporarily enhance the brightness of existing NLC but will not induce the formation of NLC.
The Arctic Boundary Layer Expedition (ABLE‐3B): July–August 1990
Authors: Harriss R. C. , Wofsy S. C. , Hoell J. M. , Bendura R. J. , Drewry J. W. , McNeal R. J. , Pierce D. , Rabine V. , Snell R. L.
Published: February 2004

The Arctic Boundary Layer Expedition (ABLE) 3B used data from ground‐based, aircraft, and satellite platforms to characterize the chemistry and dynamics of the troposphere in subarctic and Arctic regions of midcontinent and eastern Canada during July–August 1990. This paper reports the experimental design for ABLE 3B and a brief overview of results. The detailed results are presented in a series of papers in this issue. The chemical composition of the atmospheric mixed layer over remote tundra, boreal wetland, and forested environments was influenced by emissions of CH4 and nonmethane hydrocarbons from biogenic sources, emissions of gases and aerosols from local biomass burning, and transport of pollutants into the study areas from urban/industrial sources. Minimum concentrations of both trace gas and aerosol species in boundary layer air were associated with Arctic source areas. In the free troposphere the biospheric influence was undetectable, and major sources of chemical variability were related to long‐range transport of pollutants into the study areas from biomass burning and industrial sources in Alaska and the Great Lakes regions, respectively. Minimum concentrations of both trace gas and aerosol species in the free troposphere were associated with a persistent, widespread air mass which both chemistry and air mass trajectory analyses suggested had originated in the tropical Pacific. Subsidence of air from the upper troposphere and lower stratosphere frequently enhanced ozone and influenced other trace gas and aerosol species at midtropospheric altitudes. The North American Arctic is a complex dynamical and chemical environment with considerable spatial and temporal variability in aerosol and trace gas concentrations. The use of atmospheric chemical indicators for climate change detection will require a much more comprehensive Arctic monitoring program than currently exists.
CO2 exchange in the Hudson Bay lowlands: Community characteristics and multispectral reflectance properties
Authors: Whiting Gary J.
Published: February 2004

Net ecosystem CO2 exchange was measured during the 1990 growing season (June to August) along a transect starting 10 km inland from James Bay and extending 100 km interior to Kinosheo Lake, Ontario. Sites were chosen in three distinct areas: a coastal fen, an interior fen, and a bog. For the most productive sites in the bog, net daily uptake rates reached a maximum of 2.5 g C‐CO2 m−2 d−1 with an area‐weighted exchange of 0.3 g C‐CO2 m−2 d−1 near midsummer. This site was estimated to be a net carbon source of 9 g C‐CO2 m−2 to the atmosphere over a 153‐day growing season. The interior fen was less productive on a daily basis with a net maximum uptake of 0.5 g C‐CO2 m−2 d−1 and with corresponding area‐weighted uptake of 0.1 g C‐CO2 m−2 d−1 during midsummer. Early and late season release of carbon to the atmosphere resulted in a net loss of 21 g C‐CO2 m−2 over the growing season from this site. The coastal fen was the most productive site with uptake rates peaking near 1.7 g C‐CO2 m−2 d−1 which corresponded to an area‐weighted uptake of 0.8 g C‐CO2 m−2 d−1 during midsummer and an estimated net uptake of 6g C‐CO2 m−2 for the growing season. Associated with net CO2 exchange measurements, multispectral reflectance properties of the sites were measured over the growing season using portable radiometers. These properties were related to exchange rates with the goal of examining the potential for satellite remote sensing to monitor biosphere/atmosphere CO2 exchange in this biome. The normalized difference vegetation index (NDVI) computed from surface reflectance was correlated with net CO2 exchange for all sites with the exception of areas with large proportions of Sphagnum moss cover. These mosses have greater near‐infrared reflectance than typical surrounding vegetation and may require special adjustment for regional exchange/remote sensing applications.
Airborne boundary layer flux measurements of trace species over Canadian boreal forest and northern wetland regions
Authors: Ritter John A. , Barrick John D. W. , Watson Catherine E. , Sachse Glen W. , Gregory Gerald L. , Anderson Bruce E. , Woerner Mary A. , Collins James E.
Published: February 2004

Airborne heat, moisture, O3, CO, and CH4 flux measurements were obtained over the Hudson Bay lowlands (HBL) and northern boreal forest regions of Canada during July–August 1990. The airborne flux measurements were an integral part of the NASA/Arctic Boundary Layer Expedition (ABLE) 3B field experiment executed in collaboration with the Canadian Northern Wetlands Study (NOWES). Airborne CH4 flux measurements were taken over a large portion of the HBL. The surface level flux of CH4 was obtained from downward extrapolations of multiple‐level CH4 flux measurements. Methane source strengths ranged from −1 to 31 mg m2− d−1, with the higher values occurring in relatively small, isolated areas. Similar measurements of the CH4 source strength in the boreal forest region of Schefferville, Quebec, ranged from 6 to 27 mg m−2 d−1 and exhibited a diurnal dependence. The CH4 source strengths found during the ABLE 3B expedition were much lower than the seasonally averaged source strength of 51 mg m−2 d−1 found for the Yukon‐Kuskokwim delta region of Alaska during the previous ABLE 3A study. Large positive CO fluxes (0.31 to 0.53 parts per billion by volume (ppbv) m s−1) were observed over the inland, forested regions of the HBL study area, although the mechanism for the generation of these fluxes was not identified. Repetitive measurements along the same ground track at various times of day near the Schefferville site also suggested a diurnal dependence for CO emissions. Measurements of surface resistance to the uptake of O3 (1.91 to 0.80 s cm−1) for the HBL areas investigated were comparable to those observed near the Schefferville site (3.40 to 1.10s cm−1). Surface resistance values for the ABLE 3B study area were somewhat less than those observed over the Yukon‐Kuskokwim delta during the previous ABLE 3A study. The budgets for heat, moisture, O3, CO, and CH4 were evaluated. The residuals from these budget studies indicated, for the cases selected, a moderate net photochemical production of O3 present in the boundary layer over the HBL that coincided with an in situ destruction of CO, although the mechanism responsible for the destruction of CO was not identified. Results from the O3 budget analysis indicate the importance of in situ photochemical production and its possible dominance over surface deposition to the local O3 budget at the Schefferville site. Measurements of the in situ production of O3 indicated a direct relationship between the presence of biomass burning or large‐scale pollution effects. Residuals from budget calculations for conserved quantities (heat, moisture, and CH4) were compared with their respective surface fluxes to provide a measure of the internal selfconsistency of the flux measurements.
Methane emissions from wetlands, southern Hudson Bay lowland
Authors: Moore T. R. , Heyes A. , Roulet N. T.
Published: February 2004

Methane emissions were measured by a static chamber technique at 39 sites along a transect from the James Bay coast at the southeastern tip of Hudson Bay to Kinosheo Lake, northwest of Moosonee, Ontario, Canada. These sites represented five major wetland ecosystems along a successional gradient from the coast inland. Measurements were made at ≈ 10‐day intervals from early June to mid‐August, and once in mid‐September and mid‐October 1990. Seasonal CH4fluxes were small (<2 g m−2) at the recently emerged coastal marsh, coastal fen, tamarack fen, and interior fen ecosystems, except where there were shallow ponds and pools, which emitted 2–5 g CH4m−2. At the more complex bog ecosystem locations, CH4fluxes were small (0.3–2.0 g m−2) from hummock/hollow microtopography in the raised bogs and from the forested margin. The largest CH4fluxes were recorded from the degrading peat sections forming shallow pools and the moss/sedge mats which were always close to saturation (1.8–16.6 g m−2). A deeper (1‐m water depth) pool emitted less CH4(1.4 g m−2). In terms of ecological succession along the transect, covering emergence over ≈ 4000 yr, CH4emission rates increase from marsh to fen and bog, primarily through the development of peat degradation and the formation of moss/sedge lawns and pools. There were very weak statistical relationships at each site between the daily CH4flux and peat temperature and water table. However, there was a significant (r2= 0.44, p < 0.001) correlation between the seasonal CH4flux and the mean position of the water table over the complete range of sites, emphasizing the overall importance of hydrology in determining CH4flux. Laboratory incubation experiments were conducted to determine the capacity of the surface (0–20 cm depth) peat samples to produce CH4anaerobically and consume CH4aerobically. They revealed that many samples exhibited high CH4consumption rates, suggesting that although CH4production in the subsurface peat is high, CH4emissions from these wetlands to the atmosphere are limited to a large extent by CH4oxidation in the surface layers of the peat. Trophic status of the peat appeared to have little influence on emission rates, with the highest fluxes in the most acid (pH < 3.5) samples.
Effects of biomass burning on summertime nonmethane hydrocarbon concentrations in the Canadian wetlands
Authors: Blake D. R. , Smith T. W. , Chen T.‐Y. , Whipple W. J. , Rowland F. S.
Published: February 2004

Approximately 900 whole air samples were collected and assayed for selected C2‐C10hydrocarbons and seven halocarbons during the 5‐week Arctic Boundary Layer Expedition (ABLE) 3B conducted in eastern Canadian wetland areas. In more than half of the 46 vertical profiles flown, enhanced nonmethane hydrocarbon (NMHC) concentrations attributable to plumes from Canadian forest fires were observed. Urban plumes, also enhanced in many NMHCs, were separately identified by their high correlation with elevated levels of perchloroethene. Emission factors relative to ethane were determined for 21 hydrocarbons released from Canadian biomass burning. Using these data for ethane, ethyne, propane,n‐butane, and carbon monoxide enhancements from the literature, global emissions of these four NMHCs were estimated. Because of its very short atmospheric lifetime and its below detection limit background mixing ratio, 1,3‐butadiene is an excellent indicator of recent combustion. No statistically significant emissions of nitrous oxide, isoprene, or CFC 12 were observed in the biomass‐burning plumes encountered during ABLE 3B. The presence of the short‐lived biogenically emitted isoprene at altitudes as high as 3000 m implies that mixing within the planetary boundary layer (PBL) was rapid. Although background levels of the longer‐lived NMHCs in this Canadian region increase during the fire season, isoprene still dominated local hydroxyl radical photochemistry within the PBL except in the immediate vicinity of active fires. The average biomass‐burning emission ratios for hydrocarbons from an active fire sampled within minutes of combustion were, relative to ethane, ethene, 2.45; ethyne 0.57; propane, 0.25; propene, 0.73; propyne, 0.06;n‐butane, 0.09;i;‐butane, 0.01; 1‐butene, 0.14;cis‐2‐butene, 0.02;trans‐2‐butene, 0.03;i‐butylene, 0.07; 1,3‐butadiene, 0.12;n‐pentane, 0.05;i‐pentane, 0.03; 1‐pentene, 0.06;n‐hexane, 0.05; 1‐hexene, 0.07; benzene, 0.37; toluene, 0.16.
Budget analysis of FIFE 1987 sonde data
Authors: Betts Alan K. , Ball J. H.
Published: February 2004

Mean thermodynamic profiles are presented for the daytime convective boundary layer evolution for three groups of sunny days in late June and early July, August, and October using data from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) 1987 Kansas experiment. Budget models for the mixed layer evolution and the boundary layer rise are used to estimate the boundary layer top entrainment parameter. A value of AR = 0.44±0.21 is found for the mean ratio of the inversion level virtual heat flux to the surface virtual heat flux.
A particle grid air quality modeling approach: 2. Coupling with chemistry
Authors: Chock David P. , Winkler Sandra L.
Published: February 2004

The particle grid method is applied to a system of 10 reacting chemical species in a two‐dimensional rotating flow field with and without diffusion. Two types of chemistry grids are used to describe the chemical reactions: a fixed coarse grid and a moving (the advection case) or stationary (the advection plus diffusion case) fine grid. Two particle number densities are also used: 256 and 576 particles per fixed coarse grid cell. The species mass redistributed back to the particle after each reaction step is assumed to be proportional to the species mass in the particle before the reaction. The simulation results are very accurate, especially in the advection chemistry case. Accuracy improves with the use of a fine grid. A higher particle number density also reduces the concentration fluctuation in the cases involving diffusion. We also show by examples that chemistry can lead to significantly different results from numerical methods for the diffusion equation (let alone the advection equation) which otherwise yield almost identical solutions. The absence of this difficulty in the particle grid method further enhances its attractiveness.
Sulfate and MSA in the air and snow on the Greenland Ice Sheet
Authors: Jaffrezo Jean‐Luc , Davidson Cliff I. , Legrand Michel , Dibb Jack E.
Published: February 2004

Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surface snow, and snowpit samples have been measured at two sites on the Greenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the surface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but the ratios of the concentrations are comparable. The seasonal variations for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter and short episodes of elevated concentrations in spring. In contrast, the variations in concentrations of MSA are similar to those measured at sea level, with a first sequence of elevated concentrations in spring and another one during summer, and a winter low resulting from low biogenic production. The ratio MSA/sulfate clearly indicates the influence of high‐latitude sources for the summer maximum of MSA, but the large impact of anthropogenic sulfate precludes any conclusion for the spring maximum. The seasonal pattern observed for these species in a snowpit sampled according to stratigraphy indicates a deficit in the accumulation of winter snow at the summit of the Greenland Ice Sheet, in agreement with some direct observations. A deeper snowpit covering the years 1985–1992 indicates the consistency of the seasonal pattern for MSA over the years, which may be linked to transport and deposition processes.
Spatial and seasonal trends in particle concentration and optical extinction in the United States
Authors: Malm William C. , Sisler James F. , Huffman Dale , Eldred Robert A. , Cahill Thomas A.
Published: February 2004

In the spring of 1988 an interagency consortium of Federal Land Managers and the Environmental Protection Agency initiated a national visibility and aerosol monitoring network to track spatial and temporal trends of visibility and visibility‐reducing particles. The monitoring network consists of 36 stations located mostly in the western United States. The major visibility‐reducing aerosol species, sulfates, nitrates, organics, light‐absorbing carbon, and wind‐blown dust are monitored as well as light scattering and extinction. Sulfates and organics are responsible for most of the extinction at most locations throughout the United States, while at sites in southern California nitrates are dominant. In the eastern United States, sulfates contribute to about two thirds of the extinction. In almost all cases, extinction and the major aerosol types are highest in the summer and lowest during the winter months.
High‐resolution analysis of direct and scattered radiation in the stratosphere between 175 and 210 nm
Authors: Minschwaner K.
Published: February 2004

Direct and scattered components of solar radiation in the stratosphere are examined at wavelengths between 175 and 210 nm. Absorption by oxygen in the Schumann‐Runge system is treated exactly using temperature dependent cross sections at a spectral resolution of 0.5 cm−1 (≈ 0.002 nm). Consistent with previous studies employing spectrally averaged cross sections, the calculated ratio of scattered to direct flux is more than a factor of 2 smaller than observed below 210 nm. The flux ratio is constrained above a minimum value at large opacities due to a twilight effect, occurring when the attenuation of scattered light from overhead paths is not as great as over the slant path of the direct beam; however, this phenomenon alone cannot account for observations. An improved description of scattering by O2 for wavelengths below 200 nm is presented which includes effects of incoherent scattering. Use of the revised parameters for oxygen scattering does not bring the calculated flux ratios into agreement with observations, but does lead to small changes in the scattered field and O2 photodissociation rate below 190 nm.
The Moon as a light source for FTIR measurements of stratospheric trace gases during the polar night: Application for HNO3 in the Arctic
Authors: Notholt J.
Published: February 2004

A Fourier Transform Infrared (FTIR) spectrometer has been used with the Moon as an IR light source to derive column densities of stratospheric trace gases. The measurements were performed during the polar night in the Arctic winter 1992/1993 at the Network for Detection of Stratospheric Change (NDSC) station in Ny‐Ålesund (79°N, 12°E) located at Spitsbergen. Because of the emission of the Moon itself it was possible to use not only the Indium Antimonide (InSb) detector for the wavenumber region 2600–4000 cm−1 but also the less sensitive Mercury Cadmium Telluride (MCT) detector covering the interval 600–1000 cm−1. Solar OH lines, missing in the lunar spectra, demonstrate the contribution of the Moon's emission effect to the overall infrared intensity. The measurements could be performed for about a week around the full Moon. Spectra were recorded at 0.01 cm−1 or 0.02 cm−1 resolution. It was possible to derive zenith column densities of N2O, CH4, C2H6, HF, HCl, O3, NO2, HNO3, and ClONO2. They were retrieved using a version of the FASCOD2 program for personal computers or the retrieval of atmospheric trace gas profiles (RAT) program. Spectral data were taken from the HITRAN92 database. Lunar observations for HNO3, performed in December 1992 and February 1993, are compared with solar observations from March 1992 and March–July 1993 performed at the same location. Our measurements at 79°N agree with literature results for this trace gas. Owing to the occurrence of the polar night and polar summer, the seasonal cycle in the column densities of HNO3 is found to be more pro‐nounced in the Arctic than at midlatitudes. Although polar stratospheric clouds (PSCs) were frequently observed throughout the winter, the data do not indicate a significant removal of HNO3 from the atmosphere by sedimentation via PSCs. A denitrification, the irreversible removal of NOx, as observed during the winter in Antarctica, did not occur.
Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica: 10. Reductions of stratospheric NO2 due to Pinatubo aerosols
Authors: Solomon S. , Sanders R. W. , Jakoubek R. O. , Arpag K. H. , Stephens S. L. , Keys J. G. , Garcia R. R.
Published: February 2004

Visible absorption spectroscopy was employed for stratospheric measurements at McMurdo Station, Antarctica, during the summer and fall seasons in 1990, 1991, 1992, and 1993. Observed column amounts of NO2 were as much as 50% smaller in 1992 and 1993 than in 1990 and 1991. The measured decreases in NO2 are believed to be due to the hydrolysis of N2O5 on the enhanced volcanic aerosols injected by the massive eruption of Mount Pinatubo in mid‐1991. Such decreases in NO2 are broadly consistent with observations at other latitudes and with model calculations. However, substantially reduced NO2 was also observed during the polar day period in summer under conditions of continuous local solar illumination. The formation of the key N2O5 intermediate and reduction of NO2 at this time of year probably occurs via two mechanisms: (1) excursions of air parcels to lower latitudes where nighttime chemistry can produce N2O5 and (2) conversion of a small fraction of the NO3 formed during the day to N2O5. Model calculations show that the latter mechanism can be important in spite of the fast daytime photolysis of NO3.
Temporal inhomogeneities in radiosonde temperature records
Authors: Gaffen Dian J.
Published: February 2004

Historical information on changes in radiosonde instruments and observing methods is combined with time series of upper‐air temperature data to estimate the effects of (1) changes in sensors, (2) changes in solar radiation corrections to the data, and (3) changes in the length of the train between the balloon and the instrument package. These changes can induce discontinuities in the temperature records from several tenths to as high as several degrees Celsius. The discontinuities can be larger than the temperature trends of a few tenths of a degree per decade, computed by previous investigators from radiosonde observations. An assessment of the 63‐station network used by Angell to monitor tropospheric and stratospheric temperature suggests that about 43% of those stations' records have inhomogeneities, most notably in the stratosphere. These findings suggest that some previously computed temperature trends, especially estimates of stratospheric cooling, may be influenced by data inhomogeneities.
Retrieval of sizes and total masses of particles in volcanic clouds using AVHRR bands 4 and 5
Authors: Wen Shiming , Rose William I.
Published: February 2004

The advanced very high resolution radiometer (AVHRR) sensor on polar orbiting NOAA satellites can discriminate between volcanic clouds and meteorological clouds using two‐band data in the thermal infrared. This paper is aimed at developing a retrieval of the particle sizes, optical depth, and total masses of particles from AVHRR two‐band data of volcanic clouds. Radiative transfer calculations are used with a semi‐transparent cloud model that is based on assumptions of spherical particle shape, a homogeneous underlying surface, and a simple thin cloud parallel to the surface. The model is applied to observed AVHRR data from a 13‐hour old drifting cloud from the August 19, 1992, eruption of Crater Peak/Spurr Volcano, Alaska. The AVHRR data fit in the range of results calculated by the model, which supports its credibility. According to the model results, the average of effective particle radius in the test frame of this cloud is in the range of 2 to 2.5 μm, the optical depth at 12 μm is about 0.60–0.65. The total estimated mass of ash in the air amounts to 0.24–0.31×106tons, which is about 0.7–0.9% of the mass measured in the ashfall blanket. Sensitivity tests show that the mass estimate is more sensitive to the assumed ash size distribution than it is to the ash composition.
Microwave observations and modeling of O3, H2O, and HO2 in the mesosphere
Authors: Clancy R. Todd , Sandor Brad J. , Rusch David W. , Muhleman Duane O.
Published: February 2004

Microwave (wave ∼1.2 mm) spectral line observations of HO2, H218O, and O3 were obtained at the Kitt Peak National Radio Astronomy Observatory (NRAO) on April 10–12, 1992. The spectral bandwidth and resolution of the observed collisional line shapes are appropriate to retrieving profile abundances for O3, H2O, and HO2 in the upper stratosphere and mesosphere (45‐ to 70‐km altitude) with 20–30% uncertainties. The derived profile for O3 exhibits 20–30% larger mesospheric ozone abundances than indicated by the April 30°N average profiles from Solar Mesosphere Explorer (SME) and Stratosphere Aerosol Gas Experiment (SAGE) II and 60–80% larger than a photochemical model employing current photochemical rate constants and an H2O profile constrained by the microwave H218O observations. Surprisingly, the microwave measurement of HO2 yields mesospheric HO2 abundances roughly twice those predicted by the standard model photochemistry. As HOx(OH, HO2, H) is the primary agent for catalytic destruction of ozone in the mesosphere, the model underpredictions of both HO2 and O3 suggest a change in the model photochemistry that is distinct from errors in Ox production and HOx loss rates. Increases in Ox production and/or increases in HOx loss rates have been considered as the likely sources for the persistent data‐model disagreement in upper stratospheric/mesospheric ozone abundances. Based on the microwave measurements of O3 and HO2, we propose changes to model rates for partitioning between OH and HO2.Specifically, a large (60–80%) decrease in the rate coefficient for the reaction O + HO2 → OH + O2 is shown to be uniquely capable of increasing model abundances for O3 and HO2, in accordance with the microwave observations as well as the outstanding underprediction of upper stratospheric/mesospheric ozone by photochemical modeling.
On the thermal evolution of Venus
Authors: Arkani‐Hamed Jafar
Published: February 2004

Several models are calculated in order to assess the effects of different physical parameters on the thermal evolution of Venus. The models are based on three‐dimensional thermal convection calculations in an incompressible mantle of infinite Prandtl number using a modified Boussinesq approximation. The mantle is assumed to have a temperature‐ and pressure‐dependent viscosity, temperature‐dependent thermal conductivity, depth‐dependent thermal expansion coefficient, and time‐dependent internal heat generation rate. The physical parameters considered are the initial temperature distribution, a possible D″‐like layer at the base of the mantle, the temperature at the core/mantle boundary, the core solidification, the decrease of thermal expansion coefficient with depth, the rate of internal heat generation, the radially dependent viscosity, and the velocity boundary condition at the surface. A constant temperature at the core/mantle boundary develops a strong thermal boundary layer at the base of the mantle, resulting in highly oscillatory mantle convection. Allowing the core to cool suppresses the boundary layer and reduces the amplitude of the oscillations substantially. The initial temperature distribution, the core solidification, and a D″‐like layer have minor effects on the overall cooling of the mantle, although the enhanced heat of fusion of the core hampers the cooling of the core. The decrease of the thermal expansion coefficient with depth lowers the slope of the adiabatic temperature gradient in the mantle and reduces the temperature in the lower part of the mantle and the core appreciably. The heat generation rate has a significant effect on the present thermal state of the mantle; a higher rate of heat generation enhances the mantle temperature, Similarly, a higher mantle viscosity decreases the convection velocities and hampers the heat loss from the mantle. However, the most important parameter that controls the thermal evolution of the planet is the velocity boundary condition at the surface. A stress‐free (we examined semifree) surface allows mantle material to approach the surface and cool efficiently, whereas a rigid (we examine semirigid) surface hampers heat loss from the planet, resulting in a hot planet even when the internal heat sources are reduced by about an order of magnitude.
Evolution of Early Cenozoic marine temperatures
Authors: Zachos James C. , Stott Lowell D. , Lohmann Kyger C.
Published: February 2004

The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water δ18O related to changes in global ice volume over time and (2) latitudinal gradients in surface water δ18O. These reconstructions indicate that sea‐surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°–12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub‐tropical temperatures remained constant and well within the range of Holocene temperatures (24°ndash;25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near‐surface foraminifera tests which biased sediment assemblages toward deeper‐dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high‐latitude warmth of the early Eocene.
Heat flow from the Earth's interior: Analysis of the global data set
Authors: Pollack Henry N. , Hurter Suzanne J. , Johnson Jeffrey R.
Published: February 2004

We present a new estimate of the Earth's heat loss based on a new global compilation of heat flow measurements comprising 24,774 observations at 20,201 sites. On a 5° × 5° grid, the observations cover 62% of the Earth's surface. Empirical estimators, referenced to geological map units and derived from the observations, enable heat flow to be estimated in areas without measurements. Corrections for the effects of hydrothermal circulation in the oceanic crust compensate for the advected heat undetected in measurements of the conductive heat flux. The mean heat flows of continents and oceans are 65 and 101 mW m−2, respectively, which when areally weighted yield a global mean of 87 mW m−2 and a global heat loss of 44.2 × 1012 W, an increase of some 4–8% over earlier estimates. More than half of the Earth's heat loss comes from Cenozoic oceanic lithosphere. A spherical harmonic analysis of the global heat flow field reveals strong sectoral components and lesser zonal strength. The spectrum principally reflects the geographic distribution of the ocean ridge system. The rate at which the heat flow spectrum loses strength with increasing harmonic degree is similar to the decline in spectral strength exhibited by the Earth's topography. The spectra of the gravitational and magnetic fields fall off much more steeply, consistent with field sources in the lower mantle and core, respectively. Families of continental and oceanic conductive geotherms indicate the range of temperatures existing in the lithosphere under various surface heat flow conditions. The heat flow field is very well correlated with the seismic shear wave velocity distribution near the top of the upper mantle.
Ecology of deep‐sea hydrothermal vent communities: A review
Authors: Lutz Richard A. , Kennish Michael J.
Published: February 2004

Studies of the many active and inactive hydrothermal vents found during the past 15 years have radically altered views of biological and geological processes in the deep sea. The biological communities occupying the vast and relatively stable soft bottom habitats of the deep sea are characterized by low population densities, high species diversity, and low biomass. In contrast, those inhabiting the generally unstable conditions of hydrothermal vent environments exhibit high densities and biomass, low species diversity, rapid growth rates, and high metabolic rates. Biological processes, such as rates of metabolism and growth, in vent organisms are comparable to those observed in organisms from shallow‐water ecosystems. An abundant energy source is provided by chemosynthetic bacteria that constitute the primary producers sustaining the lush communities at the hydrothermal sites. Fluxes in vent flow and fluid chemistry cause changes in growth rates, reproduction, mortality, and/or colonization of vent fauna, leading to temporal and spatial variation of the vent communities. Vent populations that cannot adapt to modified flow rates are adversely affected, as is evidenced by high mortality or lower rates of colonization, growth, or reproduction. Substantial changes in biota have been witnessed at several vents, and successional cycles have been proposed for the Galapagos vent fields. Dramatic temporal and spatial variations in vent community structure may also relate to variations in larval dispersal and chance recruitment, as well as biotic interactions.
Long‐term compositional variation in solar corpuscular radiation: Evidence from nitrogen isotopes in the lunar regolith
Authors: Kerridge John F.
Published: February 2004

Implantation of solar corpuscular radiation into the lunar surface generates a population of solar atoms in the rims of lunar regolith grains. Laboratory analysis of those atoms can yield a measure of solar composition. Nitrogen trapped in the lunar regolith consists of at least two components, putatively originating in the Sun, differing in release temperature and therefore probably in implantation energy. The higher‐energy component is depleted in 15N relative to the lower‐energy component by amounts that range up to at least 20%. These components superficially resemble those identified previously in the solar‐derived light noble gases, though with several marked differences. Thus the higher‐energy noble gas components are depleted in the lighter isotope. Unlike the noble gas case, the 15N/14N ratios of both N components vary with antiquity in a complex fashion; the lower‐energy component echoes the variations in the higher‐energy component which dominate the isotopic evolution of the bulk samples. The magnitude of the bulk sample variation exceeds 30%; the higher‐energy component varies by at least 25%. The bulk long‐term trend in 15N/14N does not result from variations in mixing ratio of the two components. Both the compositional difference between the components and the long‐term variations within them apparently originate in the Sun, though this conclusion is inconsistent with current understanding of solar structure and evolution. The nitrogen isotopic record therefore appears to represent a major challenge to solar physics.