bluuebunny/crossref_metadata_2025 huggingface dataset:
The California Current system in the Southern California Bight and the Santa Barbara Channel
Authors: Bray N. A. , Keyes A. , Morawitz W. M. L.
Published: September 2002

Recent observations in the Santa Barbara Channel and over the California Cooperative Oceanic Fisheries Investigations (CalCOFI) southern California grid are used to examine seasonal circulation patterns in and near the Southern California Bight, defined as the region east of the Santa Rosa Ridge and including the Santa Barbara Channel. Poleward flow relative to 500 m is found throughout the bight, in all seasons except for spring and all subregions except the western part of the Santa Barbara Channel. In spring there is equatorward flow throughout the bight at all depths to 500 m, though it tends to be surface or midcolumn intensified. Equatorward flow offshore of the bight, present in all seasons, narrows and accelerates into a jet‐like feature and simultaneously moves close to the Santa Rosa Ridge in summer. Current meter data from the eastern entrance to the Santa Barbara Channel are consistent with the seasonal results from the CalCOFI data and further show an upward propagation of phase at annual period, with a phase speed of 1 to 2 m d−1. Comparison with the CalCOFI ship winds suggests that poleward flow in the bight may be the result of positive wind stress curl, through a Sverdrup balance, though the observed transport is only about 75% of that expected from the curl amplitude. Equatorward flow in the bight may be the result of coastal upwelling, though the transport is larger than expected from the relatively weak winds in the bight, and the offshore extent of the equatorward flow is about 10 Rossby radii, farther than might be expected for linearized coastal upwelling. Equatorward flow outside the bight cannot be explained as a Sverdrup flow because the wind stress curl is positive throughout most of the region. Upward propagation of phase and downward propagation of energy may be indicative of forcing by remote wind equatorward of the bight. Given the complexity of possible forcing mechanisms for circulation in and near the bight, a model that includes effects of remote wind forcing, Ekman pumping, and topography is needed to explain the observations in a satisfactory way.
Turbulent properties in a homogeneous tidal bottom boundary layer
Authors: Sanford Thomas B. , Lien Ren‐Chieh
Published: September 2002

Profiles of mean and turbulent velocity and vorticity in a tidal bottom boundary layer are reported. Friction velocities estimated (1) by the profile method using the time mean streamwise velocity, (2) by the eddy‐correlation method using the turbulent Reynolds stress, and (3) by the dissipation method using the turbulent kinetic energy dissipation rate ε are in good agreement. The mean streamwise velocity component exhibits two distinct log layers. In both layers, ε is inversely proportional to the distance from the bottom Z. The lower log layer occupies the bottom 3 m. In this layer, the turbulent Reynolds stress is nearly constant. The dynamics in the lower log layer are directly related to the stress induced by the seabed. The upper log layer spans 5 to 12 m above the bottom. In this layer, the turbulent Reynolds stress decreases toward the surface. The friction velocity estimated by the profile method in the upper log layer is about 1.8 times of that estimated in the lower log layer. Form drag might be important in the upper log layer. A detailed study of upstream topography is required for the bed stress estimate. The mean profile of vertical flux of spanwise vorticity is nearly uniform with Z and is at least a factor of 5 larger than the vertical divergence of turbulent Reynolds stress to which it may be compared. A new method of estimating the friction velocity is proposed that uses the vertical flux of turbulent spanwise vorticity. This is supported by the fact that the vertical eddy diffusivity for the turbulent vorticity is about equal in magnitude and vertical structure to the eddy viscosity for the turbulent momentum. The friction velocity calculated from the vorticity flux is equal to that estimated by the other three methods. Turbulent enstrophy, corrected for the sensor response function, is proportional to Z−1 for the entire water column. The relation between ε and enstrophy for high‐Reynolds‐number flows is confirmed by our observations.
Effect of large eddies on atmospheric surface layer turbulence and the underlying wave field
Authors: Savtchenko Andrey
Published: September 2002

To improve existing models for air‐sea interaction, a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air‐sea interface is needed. Recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples. This was done using synthetic aperture radar (SAR) imagery of ocean surface and almost simultaneous advanced very high resolution radiometer (AVHRR) imagery of cloud streets at a cold‐air outbreak. The intent of our study is to further validate this hypothesis in a general case of coastal circulation. For this purpose we analyze a suite of collocated simultaneous records of airflow, radar return, and surface elevations from a coastal platform. We investigate the influence of large eddies (20–60 min) on the turbulent properties of the airflow in the first 2 m above the ocean surface. The analysis shows very prominent peaks in the magnitude of 12‐ to 16‐min fluctuations which are further modulated in 20‐ to 40‐min intervals. These scales and modulations are characteristic for all variables of interest here. The detected scales and their modulation suggest significant interaction of surface layer within the first 1–2 m with large eddies of scales of O(1) and O(10) km. The intermittent structure of turbulence responds by alternating contributions from bursts and sweeps; the frequency of occurrence of bursts and sweeps also reveals the influence of large structures. The instantaneous cross correlation between the shorter scales of momentum flux and radar return, corresponding to the individual burst events, can be 4 times as strong as the overall cross correlation.
Study of the formation of North Pacific Intermediate Water by a general circulation model and the particle‐tracking method: 1. A pitfall of general circulation model studies
Authors: Kobayashi Taiyo
Published: September 2002

Formation processes of North Pacific Intermediate Water (NPIW) are examined by a numerical model with fine vertical grids. The model produces a salinity minimum in the North Pacific (calculated NPIW (C‐NPIW)), which is very similar to observed NPIW except for its lighter density. Upon examination with the particle‐tracking method and T‐S diagram, it is determined that C‐NPIW is formed around the Kuroshio Separation, most C‐NPIW is transported by the Kuroshio, and some originates from the subarctic by turbulent mixing. However, C‐NPIW cannot be formed by only a mixture of the Kuroshio and the subarctic waters. Cooling and freshening surface fluxes with a thick mixed layer are generated near the Kuroshio Separation, and less saline C‐NPIW is formed by 4.5 m yr−1 freshening surface flux. While the less saline mixed layer is carried eastward, its upper part becomes saline by the surface flux and a salinity minimum is formed. Thus its density is determined by the surface density at the Kuroshio Separation. These processes of C‐NPIW formation are inconsistent with observations, thus C‐NPIW is not the counterpart of NPIW and should be called “false NPIW.” The false NPIW results from the northward extension of the northwestern North Pacific subtropical gyre (NPSTG) beyond the Subarctic Front. In this situation the surface water near the Kuroshio Separation is the densest in NPSTG, and also, it has lowest salinity in the lower part of the ventilated layer in NPSTG. Hence the less saline water formed at the Kuroshio Separation spreads over NPSTG as false NPIW. The boundary of the subtropical/subarctic gyres expected from the annual mean wind is at the north of the Subarctic Front in the western Pacific, thus the problem will be common to most numerical models. Therefore models must be used that can simulate a realistic Kuroshio Separation in order to reproduce NPIW.
Representativity analysis and statistical modeling of snow and ice thickness data sets from the southern polar Pacific Ocean
Authors: Adolphs Ute
Published: September 2002

Data sets of sea ice and snow thickness, acquired as drilling profiles and shipboard observations during three Antarctic expeditions in the Ross, Amundsen and Bellingshausen Seas are studied with respect to their statistical robustness towards “weed‐out”, “sectional”, and “random” subsampling. For individual profiles of the drilling data the resulting subsampling errors, associated with the means and standard deviations of ice and snow thicknesses, and freeboard were generally smallest for the weed‐out method, where the spacing between drilling points was increased, while the profile length was unchanged. On the “cruise” level, floe drilling data and shipboard observations (consisting of individual sets of 25 single observations) were subsampled by picking every nth floe (or observation set). Up to n = 3, subsampling errors were negligible against the inherent errors of the full data sets. The effects of subsampling depend on the measured probability density functions (PDFs) of the full data sets whose statistical properties are studied in the section 2. It was found that lognormal or gamma distributions are better statistical representations for both drilling and shipboard data than normal distributions. A simple statistical ice thickness model is presented, which explains how different ice growth and development processes influence the shape of the ice thickness PDF. Appropriate choices of the parameters, consistent with cruise dates and observational evidence of ice deformation, give good representations of the measured ice thickness PDFs for the three cruises.
Isoprene in the marine boundary layer (southeast Asian Sea, eastern Indian Ocean, and Southern Ocean): Comparison with dimethyl sulfide and bromoform
Authors: Yokouchi Yoko , Li Hong‐Jun , Machida Toshinobu , Aoki Shuji , Akimoto Hajime
Published: September 2002

Sampling for atmospheric isoprene and some other volatile organic compounds was conducted during two cruises in the austral summer, covering the western Pacific, eastern Indian Ocean, Southeast Asian Sea, and Southern Ocean. High isoprene levels were observed in the marine air masses over the southern Indian Ocean (up to 280 parts per trillion by volume (pptv)) and over the Southern Ocean (up to 60 pptv), as well as high levels of dimethyl sulfide and bromoform, both of which are mainly emitted by marine biota. It is highly probable that the high phytoplankton activity in the Southern Ocean during the austral summer was responsible for the high oceanic isoprene levels. The findings suggest a possible significant influence of oceanic isoprene on marine atmospheric chemistry.
Lower tropospheric aerosol loadings over South Africa: The relative contribution of aeolian dust, industrial emissions, and biomass burning
Authors: Piketh S. J. , Annegarn H. J. , Tyson P. D.
Published: September 2002

The southern African haze layer is a ubiquitous subcontinental‐scale feature of the lower atmosphere that extends to a depth of ∼5 km(∼500 hPa level) on non rain days, particularly in winter. Aerosols derived from biomass burning are commonly thought to contribute substantially to the total background aerosol loading within the layer. It is shown that in both summer and winter this supposition is without foundation over South Africa. Summer and winter aerosol loadings are derived from gravimetric analysis of stacked filter units and from proton‐induced X ray emission (PIXE) analysis of one to four hourly resolved streaker samples. From concentrations of eleven inorganic elements, apportionment into four primary sources, biomass burning particulates, aeolian dust, industrial sulphur aerosols, and marine aerosols, has been effected. It is shown that the background biomass burning component of the total aerosol loading over South Africa in general, and within the plume of material being recirculated over South Africa and from there exported from the subcontinent south of 22°S to the Indian Ocean in particular, is minimal in both summer and winter. Except over coastal and adjacent inland areas, marine aerosols likewise make up a small fraction of the total loading. This is particularly so over the inland plateau areas. Crustally‐derived aeolian dust and industrially‐produced sulphur aerosols are demonstrated to be the major summer and winter constituents of the haze layer over South Africa and the particulate material being transported to the Indian Ocean region. Sulphur is transported within the aerosol plume exiting southern Africa to the Indian Ocean as agglomerates on aeolian dust nuclei.
Impact of the Cerro Hudson and Pinatubo volcanic eruptions on the Antarctic air and snow chemistry
Authors: Legrand Michel , Wagenbach Dietmar
Published: September 2002

Atmospheric records of sulfate and MSA in aerosols were obtained by year‐round samplings in the boundary layer at two coastal Antarctic sites, Neumayer (1983–1995) and Dumont d'Urville (1991–1997). At Dumont D'Urville and Neumayer the non‐sea‐salt sulfate (nssSO42−) level observed from October 1991 to October 1993 exceeded by 44 and 48 ng m−3, respectively, the mean level (˜150 ng m−3) observed during nonvolcanic years. The Neumayer and Dumont d'Urville records first exhibit spring (October to December) 1991 nssSO42− concentrations exceeding mean spring concentrations by some 100 to 150 ng m−3 caused by a significant poleward transport of the Cerro Hudson volcanic aerosol in the lower stratosphere beneath the polar vortex and possibly in the middle/upper troposphere. Limited to 10 ng m−3 during winter 1992, the nssSO42− perturbation reached 78 ng m−3 in fall 1993 at Neumayer. The latter enhancement corresponds to the input of the Pinatubo volcanic aerosol advected through stratosphere/troposphere air mass exchanges. An enhancement of nssSO42− concentrations is also recorded in snow layers deposited between 1991 and 1993 at various sites located over the high Antarctic plateau. On the basis of these firn data the relative impact of the three latest volcanic eruptions of global concern, namely, Mount Agung (1963), El Chichon (1982), and Pinatubo (together with Cerro Hudson) (1991), was evaluated in terms of sulfate input at high southern latitudes. The fallout of sulfate in central Antarctic snow following the Cerro Hudson/Pinatubo eruptions was slightly lower than fallout after the Mount Agung eruption. Sulfate fallout after El Chichon was 2 to 3 times lower than that from either Mount Agung or Pinatubo. The enhancement of sulfate levels detected in central Antarctic snow deposits during the 1991–1993 time period allows us to estimate a mean atmospheric sulfate perturbation of around 60 ng m−3 in the boundary layer of these regions (i.e., at least 35% higher than that seen at coastal sites). This observation suggests that coastal Antarctic regions are less sensitive than the high plateau in detecting volcanic sulfate fallouts following eruptions of global concern. Atmospheric near‐surface, year‐round sampling achieved at coastal Antarctic sites reveals no significant enhancement of the nitrate level over 1992 and 1993, suggesting that volcanic aerosols have had a limited effect on the transfer of nitric acid from the lower Antarctic stratosphere to the boundary layer in these regions.
Toward understanding of the nonlinear nature of atmospheric photochemistry: Multiple equilibrium states in the high‐latitude lower stratospheric photochemical system
Authors: Konovalov Igor B. , Feigin Alexander M. , Mukhina Anna Y.
Published: September 2002

We investigate the qualitative nonlinear dynamic properties of the high‐latitude stratospheric (HLS) photochemical system (PCS). For the investigation we use the model of HLS PCS, which includes all the most significant processes of chemical nature, taking place in the high‐latitude (both Arctic and Antarctic) lower stratosphere in winter‐spring period, and adequately simulates the evolution of the Antarctic ozone hole. We analyze the photochemistry in the stratospheric region at 17–18 km altitude and 70–80 degrees latitude and reveal that HLS PCS may possess simultaneously several equilibrium states (multistability) under conditions, which differ from the conditions of the actual present‐day atmosphere only by smaller total mixing ratio of inorganic chlorine species. The required conditions were typical for the atmosphere in recent past and are expected in future. Through a graphical‐analytical consideration we reveal the origin of multistability of HLS PCS and in doing so we insure that multistability is not a consequence of any approximation used in the model but is a property inherent in nature of HLS PCS. We demonstrate that when the multistability of HLS PCS is present, it may considerably influence the spring evolution of the Antarctic photochemistry.
Photochemical production and aging of an urban air mass
Authors: Dommen J. , Prévôt A. S. H. , Hering A. M. , Staffelbach T. , Kok G. L. , Schillawski R. D.
Published: September 2002

Aircraft measurements of O3, NO, NO2, NOy, HCHO, and H2O2 over the Swiss Plateau during 4 days in July 1993 were analyzed. Special emphasis was put on the urban plume of Zurich. An effective photochemical age for an urban plume was introduced, which accounts for a background NOz concentration. Only the effective photochemical age of the urban air mass increased with the time of transport between Zurich and the flight leg, where the aircraft crossed the plume. Ozone and NOz were strongly correlated. Ozone production rates ranged from 2.4 to 6.5 ozone molecules produced per NOx processed. The production of ozone per NOx molecule was lowest when the effective photochemical age was lowest and vice versa. Good correlations between HCHO and NOy have been found in the urban plume of Zurich as well as over the Swiss Plateau. Between H2O2 and NOz, a negative correlation was observed. On the basis of Sillman's [1995] indicator species, the ozone production in the Zurich plume and other air masses over the Swiss Plateau is in the NOx‐sensitive range. However, there remains some uncertainty in this approach regarding the influence of biogenic emissions and the initial concentration of indicator species. Taking the low emissions of biogenic hydrocarbons compared to Sillman's model calculation into consideration, the central portion of the Zurich plume falls in the transition or even reactive organic gases (ROG)‐ limited range of all indicators. Estimates of production rates of HNO3 and peroxides support a ROG‐sensitive ozone production in the most polluted portion of the plume.
Aircraft lidar observations of an enhanced type Ia polar stratospheric clouds during APE‐POLECAT
Authors: Tsias A. , Wirth M. , Carslaw K. S. , Biele J. , Mehrtens H. , Reichardt J. , Wedekind C. , Weiß V. , Renger W. , Neuber R. , von Zahn U. , Stein B. , Santacesaria V. , Stefanutti L. , Fierli F. , Bacmeister J. , Peter T.
Published: September 2002

Polar stratospheric clouds (PSCs) which do not fit into the standard type Ia/Ib scheme were measured by the airborne lidar OLEX (Ozone Lidar Experiment) on board the Deutsches Zentrum für Luft‐ und Raumfhart (DLR) Falcon during the Airborne Polar Experiment and Polar stratospheric clouds, Leewaves, Chemistry Aerosol and Transport (APE‐POLECAT) campaign. In contrast, the standard classification is satisfied by almost all observations for four winters at Ny Ålesund, Spitsbergen, which is one of the most comprehensive data sets of ground station lidar measurements presently available. The cloud observed by the Falcon south of Spitsbergen on December 31, 1996, was a 400‐km long type I cloud with backscatter ratio S = 2.5 and aerosol depolarization δA = 15%, which is clearly distinct from the Ny Ålesund 4 year record. Using a combination of microphysical and optical modeling, we investigate the possible evolution of this cloud assuming either in situ freezing of ternary HNO3/H2SO4/H2O droplets as nitric acid trihydrate, or the formation of the clouds in mountain waves over the east coast of Greenland, as suggested by a mountain wave model. Best agreement with the observations was obtained by assuming mountain‐wave‐induced cloud formation, which yields nitric acid trihydrate particles with much higher total mass than achieved by assuming synoptic‐scale freezing. Our analysis suggests that this rare type of PSC, which we term type Ia‐enh, is characterized by nitric acid hydrate particles rather close to thermodynamic equilibrium, while the more common type Ia PSCs appear to contain much less mass than representative of equilibrium.
Characterization of turbulent transport in the marine boundary layer during flight 7 of PEM‐Tropics A
Authors: Considine Geoffrey D. , Anderson Bruce , Barrick John , Lenschow Donald H.
Published: September 2002

A series of aircraft measurements taken in the marine boundary layer in the vicinity of Christmas Island during the NASA Pacific Exploratory Mission‐Tropics (PEM‐Tropics) A mission allow for a partial characterization of the turbulent transfer through the mixed layer. The measurements were obtained during a series of 12 circular sampling legs (of 30 min each) at five altitudes in the boundary layer, including the entrainment layer. The data include high‐frequency measurements of moisture and the wind field in three dimensions (18.7 Hz) and slower‐response temperature (1 Hz). Computed fluxes and variances are filtered using standard Fourier filters as well as moving‐average filters. The uncertainties associated with the choice of filter are discussed. The vertical structure of the boundary layer and the profiles of the variance of vertical velocity are consistent with the standard conceptual picture of the mixed layer. The humidity flux and variance of vertical velocity vary by 50% between three 30‐min horizontal samples midway through the mixed layer but remain essentially constant at the bottom of the mixed layer. The variability in the humidity flux and the variance of vertical velocity appear to be caused by changes in the dynamical scales associated with the transport, with a high correlation between the peak length scale derived from the cospectrum and the net flux of humidity. The observed changes in the fluxes are consistent with changes in the rate of entrainment into the mixed layer, coinciding with changes in the fraction of vertical transport associated with mesoscale processes. The vertical flux divergence of humidity appears to be significantly affected by mesoscale influences.
Design and initial characterization of an inlet for gas‐phase NOy measurements from aircraft
Authors: Ryerson T. B. , Huey L. G. , Knapp K. , Neuman J. A. , Parrish D. D. , Sueper D. T. , Fehsenfeld F. C.
Published: September 2002

An understanding of gas‐phase HNO3 transmission through an inlet is necessary to evaluate the quality of NOy measurements from an aircraft platform. A simple, inexpensive, low‐volume Teflon inlet is described and its suitability as an aircraft inlet for gas‐phase NOy is assessed. Aerosol transmission is not characterized, but inlet design and orientation probably discriminates against the majority of aerosol by mass. Laboratory data, in‐flight HNO3 standard addition calibrations, and ambient NOy measurements from the 1997 North Atlantic Regional Experiment aircraft mission are used to characterize inlet transmission efficiencies and time constants. Laboratory tests show high transmission efficiencies for HNO3 which are relatively independent of ambient temperature and humidity. In‐flight standard addition calibrations were carried out at ambient temperatures ranging from −20° to +8°C and relative humidities from 3% to 71%. These data suggest that nearly all the sampled air contacts an inlet surface, with 90% of added HNO3 being transmitted in ∼1.5 s. Ambient data are presented to demonstrate negligible hysteresis in 1‐Hz NOy measurements, relative to variability observed in ozone data, from an air mass where HNO3 is expected to be a large fraction of the total NOy. Power spectra of ambient NOy (at temperatures from −35° to +35°C and relative humidities from 3% to 100%) and ozone measurements suggest an effective NOy instrument time constant of ∼2 s.
NOx and NOy over the northwestern North Atlantic: Measurements and measurement accuracy
Authors: Peterson Matthew C. , Honrath Richard E.
Published: September 2002

Measurements of NOx (NO+NO2) and NOy (total reactive nitrogen oxides) during February‐April 1996 at the northern tip of Newfoundland are used to determine levels in the local marine boundary layer (MBL) and assess the adequacy of current understanding of the processes controlling NOx levels over the northern North Atlantic, as expressed through previously reported simulations using the Geophysical Fluid Dynamics Laboratory (GFDL) Global Chemical Transport Model (GCTM). Median mixing ratios of NOx and NOy in the local MBL were 24 parts per trillion by volume (pptv) and 200 pptv, respectively. These levels are 35–64% above background levels measured in the remote MBL in summer and fall during the Chemical Instrumentation Test and Evaluation (CITE 2), North Atlantic Regional Experiment (NARE‐93), and Pacific Exploratory Mission‐West (PEM‐West) A measurement campaigns and are similar to or somewhat higher than anthropogenically influenced levels observed in winter‐spring during the PEM‐West B campaign. The magnitude of median NOx and NOy, levels in the local MBL is not due to events with high reactive nitrogen oxides levels. Instead, these relatively high median levels are likely the result of dispersion of anthropogenic emissions over a large region. A detailed comparison with results from the GFDL GCTM indicates that measured March and April average NOx levels are significantly lower than simulated levels over the north central North Atlantic. The frequency and magnitude of modeled and observed elevated‐NOx events were similar, indicating that the conditions responsible for relatively direct long‐range transport events were similar. This indicates that interannual variability probably did not cause the discrepancy in monthly average NOx values. However, simulated elevated NOx events are much longer than are observed. This difference appears to be at least partially responsible for the higher average NOx values simulated by the model. These results indicate that model‐based estimates of this region's contributions to the global ozone budget may be too high. Accuracy of the NOx measurements is estimated to be 6%, while conservative analysis of conversion efficiencies indicates a negative bias of ≲18% in the determination of gas‐phase NOy compounds.
Smart tetroons for Lagrangian air‐mass tracking during ACE 1
Authors: Businger Steven , Johnson Randy , Katzfey Jack , Siems Steven , Wang Qing
Published: September 2002

A series of “smart” tetroons was released from shipboard during the recent ACE 1 field experiment designed to monitor changes in the sulfur budget in a remote marine boundary layer (MBL) south of Tasmania, Australia. The smart tetroons were designed at NOAA Air Resources Laboratory Field Research Division to provide air parcel tracking information. The adjective smart here refers here to the fact that the buoyancy of the tetroons automatically adjusts through the action of a pump and valves when the tetroon travels vertically outside a range of pressures set prior to tetroon release. The smart tetroon design provides GPS location, barometric pressure, temperature, relative humidity, and tetroon status data via a transponder to the NCAR C‐130 research aircraft flying in the vicinity of the tetroons. In this paper we will describe (1) the design and capability of the smart tetroons and their performance during the two Lagrangian experiments conducted during ACE 1, (2) the synoptic context of the Lagrangians, including the origin of the air parcels being tracked, and (3) the results of trajectory predictions derived from the National Center for Environmental Prediction (NCEP) Global Spectral Model (GSM) and Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) Division of Atmospheric Research (DAR) limited‐area model.
A study on the concentration, distribution, and behavior of metals in atmospheric particulate matter over the North Pacific Ocean by using inductively coupled plasma mass spectrometry equipped with laser ablation
Authors: Narita Yasushi , Tanaka Shigeru , Santosa Sri Juari
Published: September 2002

The concentrations and distribution of 11 metal elements (Al, Ti, V, Mn, Ni, Zn, As, Se, Cd, Sb, and Pb) in marine atmospheric particulate matter collected daily over the North Pacific Ocean during the 14 separate cruises of M/V Skaugran from Japan to the west coast of the American continent and back to Japan from March 1995 to October 1996 have been investigated in order to clarify their behavior. A total of 223 samples were collected and analyzed by laser ablation inductively coupled plasma mass spectrometry (LA/ICP‐MS). For crustal elements such as Al and Mn, their concentrations decreased from the western to central and then only slightly increased in the eastern North Pacific Ocean. The concentrations of anthropogenically derived elements such as Zn and Pb were also significantly higher in the western than in the central and eastern North Pacific Ocean. Both crustal and anthropogenic elements displayed high concentrations in the commonly known dust season (March to May) and low concentrations in the summer (June to August). In winter (November to December), however, only anthropogenic elements showed significantly high concentrations. The high concentrations for crustal elements in the dust season are suggested as resulting from the input of mineral particulate matter transported from the Asian continent by westerly winds. This input does not occur in winter because the land surface is frozen. The westerly winds also distribute anthropogenic elements to the North Pacific Ocean. However, in summer the westerly wind is replaced by the oceanic wind that dilutes both crustal and anthropogenic elements in the marine atmosphere, and therefore their concentrations were significantly lower in summer.
Fate of long‐lived trace species near the Northern Hemispheric tropopause: Carbon dioxide, methane, ozone, and sulfur hexafluoride
Authors: Zahn Andreas , Neubert Rolf , Maiss Manfred , Platt Ulrich
Published: September 2002

The mixing ratios of CO2, CH4, O3, and SF6 were measured in 118 whole air samples collected onboard a Transall C‐160 aircraft around the NH extratropical tropopause in the winters 1993–1994 and 1994–1995. The samples originate mainly from the upper troposphere (∼7 km) and partly from the lowermost stratosphere up to altitudes of 12 km. With help of 7‐day back trajectories the potential temperature θ of an air mass in the free troposphere was established to be a reliable measure of the average latitude the air mass spent the last week before sampling. The potential temperature are thus interpreted in terms of a “representative latitude” allowing −1‐ for the creation of representative meridional trace gas profiles in the troposphere that show a lower scatter than if the data were plotted versus the sampling latitude itself and‐2‐ for the distinction of different types of air masses. For example, by categorizing the sampled air masses by their potential temperatures and by their trace gas composition, the 300 K θ ‐ surface was identified to separate cold polar air from warmer subtropical air. The 300 K θ ‐ surface is thus found to mark the polar front in the wintertime upper troposphere and can be viewed as the lowest isentrope that allows quasi‐isentropic cross‐tropopause transport. The midlatitude upper troposphere was frequently affected by surface air resulting in a positive correlation of CH4, SF6, and O3. In contrast, in the arctic upper troposphere and in the lowermost stratosphere, both CH4 and SF6 were negatively correlated with O3. Surprisingly, variable CO2 levels (spanning ∼14 ppm) found just above the ozonopause point to intensive mixing of tropospheric air into the lowermost stratosphere. From the high SF6 growth rate of nearly 7% per year a clear aging of the observed air masses since their entry into the stratosphere could be inferred. This SF6 age was rather high, for example around 2 years at an altitude of 11.5 km and thus just 3.5 km above the dynamical tropopause.
Simulated time‐dependent climate response to solar radiative forcing since 1600
Authors: Rind D. , Lean J. , Healy R.
Published: September 2002

Estimated solar irradiance variations since 1500 have been used to force the GISS atmospheric GCM coupled to a mixed layer “q‐flux” ocean with heat diffusion through the bottom of the mixed layer. The goal is to assess solar‐induced climate change in preindustrial and postindustrial epochs. Six simulations and control runs were made to test the effects of different initial conditions, estimates of initial solar forcing conditions, and ocean heat uptake. The results show that an estimated solar forcing increase of 0.25% accounts for a 0.45°C temperature increase since 1600 and an increase of about 0.2°C over the past 100 years. Global surface temperatures lag solar fluctuations by up to 10 years; the lag is greater over the oceans and so is the correlation due to reduced noise. With only a mixed layer ocean the phase lag is 5 years less. Solar forcing and water vapor feedback each directly account for 35% of the temperature response, with cloud cover changes contributing 20% and sea ice/snow cover 10%. Uncertainty in the initial radiation imbalance or solar forcing affects the surface temperatures for 60–90 years. Modeled and observed periodicities show dominance of long‐period forcing (>50 years), as provided by the solar input in these experiments. Tropical temperatures correlate best with solar forcing, due to the influence of water vapor feedback, especially at these multidecadal periods. Sea ice and extratropical temperatures have less long‐period power, while high‐frequency fluctuations dominate simulated cloud cover variations, which are relatively independent of solar forcing changes. Global and extratropical precipitation increase as the climate warms, but not low and subtropical precipitation, due to conflicting influences of absolute temperature and temperature gradient changes. Solar forcing by itself was not sufficient to produce the rapid warming during the last several decades. A comparison experiment varying trace gas forcing suggests that if the solar estimate is correct, then negative forcing by tropospheric aerosols (and perhaps volcanoes, ozone, and land use changes) has been about −1.2 W m−2 since 1700, implying approximately equal contribution from direct and indirect tropospheric aerosol effects.
Contribution of the different aerosol species to the aerosol mass load and optical depth over the northeastern tropical Atlantic
Authors: Chiapello Isabelle , Bergametti Gilles , Chatenet Bernadette , Dulac Francois , Jankowiak Isabelle , Liousse Catherine , Soares Emmanuel Santos
Published: September 2002

Simultaneous ground‐based measurements of chemical composition, size distribution, and column optical thickness at 670 nm of atmospheric aerosols have been performed at Sal Island (Cape Verde) during the winter season when African dust is transported in the lower troposphere. Mineral dust and, occasionally, sea salt dominate the aerosol mass load, whereas the excess sulfates plus the carbonaceous aerosol (particulate organic matter and black carbon) contributions to the mass load remain lower than 5% on average. We compute the total aerosol optical depth (AOD) by combining optical properties derived from measured size distributions and vertical concentration profile of each aerosol type estimated from surface elemental concentrations and meteorological observations. Results are very consistent with direct Sun photometer measurements. This allows us to derive the chemical apportionment of AOD in this region: mineral dust from Africa controls the total AOD and generally dominates AOD even in the absence of dust outbreak; on average, sea salt, excess sulfate, and carbonaceous aerosols all together only contribute to an averaged background AOD of 0.04 at 670 nm.
Optimal climate signal detection in four dimensions
Authors: Stevens Mark J.
Published: September 2002

Previous efforts at climate signal detection using the space‐time optimal filter approach have been limited to the time evolution of surface temperature data. This limitation arises from the lack of long‐term data sets of temperature which have sufficient data density in both the horizontal and vertical dimensions of the atmosphere to be useful in such an approach. Future data sets from satellites should provide a wealth of such data. To investigate the potential improvement in climate signal detection when sufficient vertical information becomes available, data from a coupled ocean‐atmosphere climate model is used. For a transient simulation of the doubling of carbon dioxide in the atmosphere, it is found that the signal‐to‐noise ratio is increased by a factor of 2.28 when temperature data from the tropical upper troposphere and stratosphere are used, as compared with using only the tropical surface temperature data. When only tropospheric data are used, the signal‐to‐noise ratio is increased by a factor of 1.12.
Early evolution of a stratospheric volcanic eruption cloud as observed with TOMS and AVHRR
Authors: Schneider David J. , Rose William I. , Coke Larry R. , Bluth Gregg J. S. , Sprod Ian E. , Krueger Arlin J.
Published: September 2002

This paper is a detailed study of remote sensing data from the total ozone mapping spectrometer (TOMS) and the advanced very high resolution radiometer (AVHRR) satellite detectors, of the 1982 eruption of El Chichón, Mexico. The volcanic cloud/atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud [Krueger et al., 1995] with thermal infrared retrievals of the size, optical depth, and mass of fine‐grained (1–10 μm radius) volcanic ash [Wen and Rose, 1994]. Our study provides the first direct evidence of gravitational separation of ash from a stratospheric, gas‐rich, plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds. The eruption column reached as high as 32 km [Carey and Sigurdsson, 1986] and was injected into an atmosphere with a strong wind shear, which allowed for an observation of the separation of sulfur dioxide and volcanic ash. The upper, more sulfur dioxide‐rich part of the cloud was transported to the west in the stratosphere, while the fine‐grained ash traveled to the south in the troposphere. The mass of sulfur dioxide released was estimated at 7.1 × 109kg with the mass decreasing by approximately 4% 1 day after the peak. The mass of fine‐grained volcanic ash detected was estimated at 6.5 × 109kg, amounting to about 0.7% of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano. Over the following days, 98% of this remaining fine ash was removed from the volcanic cloud, and the effective radius of ash in the volcanic cloud decreased from about 8 μm to about 4 μm.
Retrieval of aerosol optical thickness and size distribution over ocean from the MODIS airborne simulator during TARFOX
Authors: Tanré D. , Remer L. A. , Kaufman Y. J. , Mattoo S. , Hobbs P. V. , Livingston J. M. , Russell P. B. , Smirnov A.
Published: September 2002

Radiation and in‐situ measurements collected during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) are used to test the method for remote sensing of aerosol properties and loading from the MODIS instrument. MODIS, a Moderate Resolution Imaging Spectroradiometer, will be launched in 1999 aboard the first EOS (Earth Observing System). Following the MODIS procedure [Tanré et al, 1997], the spectral radiance at the top of the atmosphere (TOA) measured over the ocean in a wide spectral range (0.55–2.13 μm) is used to derive the aerosol optical thickness (proportional to the aerosol total loading) and the aerosol size distribution (integrated over the vertical column) of the ambient (undisturbed) aerosol by comparing measured radiances with values in look‐up table (LUT). The LUT includes the gas‐phase oxidation accumulation mode, cloud‐phase accumulation mode, and a coarse mode that represents maritime particles (salt) and dust. In each inversion, one accumulation and one coarse mode can be retrieved. The inversion retrieves the ratio of the contribution to the optical thicknesses of the two particle modes and the mean particle size that best fits the measurements. This algorithm is successfully applied to the data sets acquired during TARFOX. The MODIS airborne simulator (MAS) aboard the NASA ER‐2 aircraft flew several times during the experiment above the University of Washington C‐131A research aircraft on which the six‐channel Ames Airborne Tracking Sun Photometer (AATS‐6) was mounted. It flew also above surface‐based Sun photometers. Optical thicknesses (at λ = 550 nm) as well as the spectral dependence from the various data sets compare very well.
Tropical aerosol in the Aleutian High
Authors: Harvey V. Lynn , Hitchman Matthew H. , Pierce R. Bradley , Fairlie T. Duncan
Published: September 2002

Stratospheric aerosol profiles at high northern latitudes from the Stratospheric Aerosol Measurement (SAM) II experiment are used to document the aerosol maxima that occur in the major wintertime anticyclones. Fourteen years (1978–1991) of 1 μm extinction are used to calculate median values for each season in bins of 5° latitude by 30° longitude by 1 km altitude. Longitude‐altitude sections of estimated surface area density show that tropical, aerosol rich air tends to accumulate in the Aleutian High from 15 to above 30 km, and in the North Atlantic High in the 15–25 km layer. A trajectory case study with winds from the European Center for Medium‐Range Weather Forecasting is used to investigate the hypothesis that the observed aerosol maxima are maintained by episodic poleward surges of high aerosol air from the tropical stratospheric reservoir. Lagrangian trajectories are initialized and run backward in time, from both a high‐resolution grid and SAM II occultations, for selected days when high aerosol is found in the Aleutian High. Results show that during the case study provided, a deep sheet of aerosol rich air originating over Africa is advected poleward and eastward around the polar vortex and entrained into the Aleutian High.
A detailed evaluation of the stratospheric heat budget: 1. Radiation transfer
Authors: Mertens Christopher J. , Mlynczak Martin G. , Garcia Rolando R. , Portmann Robert W.
Published: September 2002

We present part 1 of a two‐part series on a detailed evaluation of the stratospheric heat budget. In part 2 [Mlynczak et al., this issue] we present radiative heating, radiative cooling, net radiative heating, global radiation balance, radiative relaxation times, and diabatic circulations in the stratosphere using temperature and minor constituent data provided by instruments on the Upper Atmosphere Research Satellite (UARS) between 1991 and 1993 and by the limb infrared monitor of the stratosphere (LIMS) instrument, which operated on the Nimbus‐7 spacecraft in 1978–1979. Here we describe the radiative transfer techniques used to compute the climatology of radiative heating and circulations given in part 2. Included in the radiation transfer calculations are heating due to absorption of solar radiation from the ultraviolet through near‐infrared wavelengths and radiative cooling due to emission by carbon dioxide, water vapor, and ozone from 0 to 3000 cm−1 (∞‐3.3 μm). Infrared radiative effects of stratospheric aerosols are also considered in detail.
Shape dependence of the optical properties in size‐shape distributions of randomly oriented prolate spheroids, including highly elongated shapes
Authors: Schulz F. M. , Stamnes K. , Stamnes J. J.
Published: September 2002

A sensitivity study is conducted to assess the effect of particle shape on the optical properties of size‐shape distributions of randomly oriented prolate spheroidal particles. The emphasis is on covering a large range of the spheroids' aspect ratio in order to include the effects of highly aspherical particles. A modified separation of variables method is used to compute the optical properties of an ensemble of randomly oriented particles of different sizes and shapes. The investigation shows that the elements F11, F22/F11, and F34/F11 of the Stokes scattering matrix are very sensitive to a variation in the effective aspect ratio of the equiprobable shape distribution considered here. This implies that the effective aspect ratio will have significant impact on the radiance, the degree of linear polarization, and the degree of circular polarization of light multiply scattered by such an ensemble of particles. The same elements are only mildly sensitive to a variation in the effective variance of the shape distribution. The remaining elements of the scattering matrix are moderately sensitive to a variation in the effective aspect ratio, and rather insensitive to a variation in the effective variance. The single‐scattering albedo and the asymmetry parameter are found to be near‐linear functions of the effective aspect ratio and rather insensitive to the effective variance. The results indicate that knowledge of the effective aspect ratio might be sufficient to characterize the single‐scattering albedo and the asymmetry parameter of the shape distribution.
The Mars seasonal CO2 cycle and the time variation of the gravity field: A general circulation model simulation
Authors: Smith David E. , Zuber Maria T. , Haberle Robert M. , Rowlands David D. , Murphy James R.
Published: September 2002

We investigate the time variation of the long wavelength gravitational field of Mars due to mass redistribution associated with the annual cycle of CO2 exchange between the atmosphere and polar caps. Our analysis utilizes simulated monthly estimates of atmospheric pressure and CO2 polar frost as calculated by the NASA Ames general circulation model (GCM) for a “typical” year. We show that the deposition and sublimation of CO2 polar frost is expected to be the dominant effect on the gravity field at all low degrees. Variations in the amplitude and phase of time variations of gravity are sensitive to multiple factors, including polar elevation and the eccentricity of the Martian orbit. Phase effects associated with additive and competing influences at the summer and winter poles dictate that odd‐numbered harmonic coefficients produce an annual signal in the gravity field while even‐numbered coefficients show a semiannual signal. The predicted changes in the planetary flattening and pear‐shaped terms of the field are at or above the noise level of expected X band Doppler tracking observations from Mars Global Surveyor and so could conceivably be detected from an orbital spacecraft.