bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of ship and satellite chlorophyll from California and Peru
Authors: Chavez Francisco P.
Published: February 2004

Ship surface chlorophyll measurements from coastal California and Peru have been processed for comparison with surface chlorophyll estimated during the lifetime of the coastal zone color scanner (CZCS). The ship data shows that chlorophyll concentrations are higher off Peru than California, consistent with the Peru Current system's being more productive. Off California the ship and satellite measurements yield similar estimates of chlorophyll concentration (the average ratio of ship to satellite is 1.1), but off Peru the satellite yields substantially lower concentrations (average ratio of 3.8). The lower satellite values off Peru are likely due to sparse satellite coverage and/or problems with atmospheric corrections. For California, the inshore (0–100 km) ship and satellite chlorophyll estimates are similar, but offshore (200–250 km) the satellite yields higher values. Both estimates, however, confirm the presence of a winter chlorophyll maximum in offshore California waters (likely due to increased nutrient concentrations), increases in chlorophyll per cell, and mixing of subsurface chlorophyll maximum to the surface. Conversely, off Peru, offshore ship and satellite values are in closer agreement than inshore values. As a result onshore‐offshore gradients are weaker in the satellite data for both California and Peru. The gradient problem is likely the result of the satellite algorithm. Different algorithms may be needed for coastal waters, dominated by relatively large and colonial phytoplankton, and open ocean waters, dominated by small solitary phytoplankton.
Variability and frontogenesis in the large‐scale oceanic frontal zones
Authors: Kazmin Alexander S. , Rienecker Michele M.
Published: February 2004

Sea surface temperature (SST) from weekly global advanced very high resolution radiometer data for the period of 1982–1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large‐scale oceanic frontal zones (OFZs), the variability of SST gradient in several frontal zones, and the meridional frontogenesis in the North Pacific. Subpolar frontal zones are identifiable in the SST gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere. The magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres, with maximum intensity in November to March. During this period, subtropical fronts in the northern hemisphere become clearly identifiable, separate features, while in the southern hemisphere their southern boundaries tend to merge with the subpolar front. In the northern hemisphere, the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by August. In the southern hemisphere, subtropical fronts separate from the subpolar front during this period and become clearly distinguishable, though less intense. Singular spectrum analysis of the 11‐year time series of SST gradient in several OFZs revealed a seasonal signal as well as interannual variations that, in the equatorial zone, are related to El Niño events. The amplitude of the annual cycle is comparable in the subtropical and subpolar North Pacific, but the subtropics leads the subpolar zone by about 4 months. Combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in North Pacific midlatitudes on seasonal timescales, but not on shorter timescales. In the subtropical zone, the Ekman convergence alone was not sufficient to provide the observed frontogenesis/frontolysis on seasonal time scales. In fact, when the maximum frontogenesis associated with Ekman convergence occurs in late spring/early summer, this is counteracted by the frontolytic effect of Ekman pumping and the dominating frontolytic effect of surface heat forcing. In summer, Ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both Ekman pumping and surface heat forcing. Surface forcing due to wind stress and heat flux considered in this study does not explain the high‐amplitude intraseasonal frontogenesis variations, especially in the subpolar region.
A comparison of surface wind products over the North Pacific Ocean
Authors: Rienecker Michele M. , Atlas Robert , Schubert Siegfried D. , Willett Cynthia S.
Published: February 2004

This study compares four surface wind products which may be used to force ocean circulation models of the North Pacific: wind stress derived from the Atlas special sensor microwave imager (SSM/I) based surface wind analyses (July 1987–June 1990), the Goddard Earth Observing System (GEOS) wind assimilation product at 10 m (March 1985–February 1990), and, at the appropriate overlapping times, the European Centre for Medium‐Range Weather Forecasts (ECMWF) wind analyses and the Comprehensive Ocean‐Atmosphere Data Set (COADS). Overall, there is good agreement in spatial and temporal variations between COADS and the model‐based analyses. The COADS product used in this study, based on monthly averaged winds, underestimates the monthly averaged stresses in the higher latitudes where the submonthly variance is high. In the tropics and subtropics where the variance is lower, the COADS stresses are closer to climatology than the weaker model‐based winds. The largest differences between the model‐based analyses occur during winter in the northernmost region of the North Pacific basin where the spatial and temporal variability is largest. The seasonal mean Atlas SSM/I stresses are stronger overall than the other model‐based analyses, with differences reaching as high as 0.09 N m−2 in the high latitudes during winter. The Atlas product is also consistently stronger in the curl. Of the four curl products, the Atlas SSM/I and GEOS are closest in pattern and intensity in the tropics in both summer and winter. These also have the closest wavenumber spectral distribution in the high latitudes during winter. Integrations of a nonlinear, baroclinic quasi‐geostrophic ocean model using three of the wind stress curl distributions show differences of 30–45% in the mean integrated volume transport in the Kuroshio Extension. The Atlas SSM/I wind stress curl seems to force a more realistic subtropical gyre (in terms of transport and eddy energy levels) and western boundary current structure. The GEOS curl seems to force a more realistic subpolar gyre circulation. Overall, the assimilation of the SSM/I wind speed data improves the comparison between the model‐based analyses and ship‐based observations and produces a more realistic ocean model circulation.
Observations and simulations of physical and biological processes at ocean weather station P, 1951–1980
Authors: McClain Charles R. , Arrigo Kevin , Tai King‐Sheng , Turk Daniella
Published: February 2004

Physical and biological processes in the mixed layer at ocean weather station (OWS) P (50°N, 145°W) over a 30‐year period (1951–1980) were investigated using observations and model simulations. The observations include 30 years of surface meteorological and sea surface temperature data collected at OWS P and Ekman upwelling velocities derived from the Comprehensive Ocean‐Atmosphere Data Set, 14 years (1953–1966) of daily temperature profiles, nearly 150 chlorophyll a profiles spanning all months of the year, monthly climatological solar irradiances, and 0‐ to 50‐m integrated nitrate concentrations. The simulations incorporated models for the estimation of surface solar downwelling irradiance, surface heat fluxes, subsurface diffuse attenuation, mixed layer dynamics, and biological processes. The time‐dependent model inputs were the surface observations of cloud cover, air temperature, dew point temperature, and wind speed. The atmospheric irradiance, marine diffuse attenuation, and mixed layer models were adapted from existing models developed by others. The biological model, developed by the authors, has four components (nitrate, ammonium, phytoplankton nitrogen, and zooplankton nitrogen) and computes a variety of additional quantities, including chlorophyll a concentration and gross and new production. Model comparisons with in situ time series showed that predictions of sea surface temperature and mixed layer depth were reasonably accurate. Climatological monthly profiles of chlorophyll a and temperature were within 1 standard deviation of the observed values at nearly all depths. Also, the climatological annual cycles of solar irradiance and 0‐ to 50‐m integrated nitrate accurately reproduced observed values. Annual primary production was estimated to be ∼190 g C m−2 yr−1 and varied by no more than ±5% in any year. This estimate is consistent with recent observations but is much greater than earlier estimates, indicating that carbon cycling in the North Pacific is much more important to the global carbon budget than previously thought. Significant interannual variability in sea surface temperature, Ekman upwelling, mixed layer depth, and surface nitrate concentration had little impact on productivity. The model also indicates that the nitrate supply to the euphotic zone is very sensitive to Ekman upwelling and that amplification of the wind stress curl can result in complete nitrate depletion when the winds are persistently downwelling favorable.
Topographic Rossby modes in the Strait of Sicily
Authors: Pierini Stefano
Published: February 2004

In this paper, numerical results of a barotropic circulation model are presented, indicating that topographic Rossby modes can be excited in the area of the Strait of Sicily. The results also suggest that such motions are robust features, since they can be resonantly generated by different forcings. A numerical barotropic shallow‐water model is implemented in the central Mediterranean Sea, and, in order to perform a spectroscopic analysis, the initial value problem is solved, both in the presence of a white wind with spatially constant curl and of a white boundary flow representing an equivalent remote pressure forcing. A spectral analysis in selected points in the region of the strait reveals five peaks with periods ranging from 2 to 5 days. The associated circulation patterns are then studied by forcing the system with monochromatic winds or boundary flows at the periods of the energy peaks. Traveling patterns are recognized, whose spatial/temporal structures and periods are found to compare well with those of analytical Rossby modes, thus obtaining a clear evidence of their dynamical nature. In order to investigate the actual excitation of Rossby modes in realistic conditions, the system is then forced by the 1980 National Meteorological Center momentum flux data. The main mode at nearly 3 days obtained from the preceding spectral analysis is indeed found to be excited in the narrowest section of the strait during winter and autumn months. Rossby modes in the numerical time series are identified by means of the analysis of the energy spectra and of the coherence and phase of current signals between two points along the theoretical propagation direction. Finally, the existence of topographic Rossby modes in the Strait of Sicily is discussed in connection with the local properties of horizontal mixing in that area.
Comparison of field observations of the vertical distribution of suspended sand and its prediction by models
Authors: Lee T. H. , Hanes D. M.
Published: February 2004

Models for the vertical distribution of suspended sediment under waves and currents are compared with field observations. The models include a diffusion‐based model, a convection‐based model, and a combined convection‐diffusion model. The field observations were carried out at Vilano Beach, Florida, in a water depth of approximately 3 to 4 m, with a median grain diameter of 0.14 mm. The rms wave height ranged from approximately 0.4 to 1.2 m. Under low waves, the seabed was covered with very small ripples, and, under the higher waves, sheet flow conditions were present. The diffusion‐based model was found to best describe the observed data under high wave conditions, but the convection model was more accurate under low wave conditions. Over all conditions, the combined model was the most accurate. These results are consistent with the different mechanisms for mixing suspended sediment over flat versus rippled beds.
Observation of a nonlinear wave disturbance in the marine atmosphere by the synthetic aperture radar aboard the ERS 1 satellite
Authors: Alpers Werner , Stilke Gerd
Published: February 2004

A nonlinear wave disturbance in the marine atmosphere associated with an atmospheric cold front has been identified on a spaceborne radar image of the North Sea by its imprint on the sea surface. This nonlinear wave disturbance is either a solitary wave disturbance or an undular bore propagating in the lower marine atmosphere. The radar image showing sea surface manifestations of this atmospheric wave disturbance was acquired over the North Sea by the synthetic aperture radar (SAR) aboard the first European Remote Sensing Satellite ERS 1 on March 8, 1992. Atmospheric waves become visible on radar images of the sea surface because they are associated with a varying wind field at the sea surface, which modulates the sea surface roughness, and, thus, the backscattered radar power. The identification of the wave pattern visible on the ERS 1 SAR image as a sea surface manifestation of an atmospheric nonlinear wave disturbance has been possible because this disturbance was also captured by meteorological sensors mounted on an 80‐m high meteorological mast located on the island of Heligoland. Geophysical parameters characterizing the atmospheric wave disturbance are derived from the ERS 1 SAR image and from the in situ meteorological data. The wave period in the reference frame moving with the average wind is 9.5 min, the average wavelength is 2300 m, and the propagation velocity is 4.5–4.9 m s−1. Estimates of the amplitude of the wind speed fluctuations in the wave propagation direction derived from the meteorological measurements at Heligoland and from the gray level variations in the SAR image yield values between 1.3 and 3.0 m s−1. The experimental data are interpreted in terms of theories of atmospheric nonlinear gravity waves.
Assimilation of wave data into the wave model WAM using an impulse response function method
Authors: Bauer E. , Hasselmann K. , Young I. R. , Hasselmann S.
Published: February 2004

A new method for the assimilation of wave data into a third‐generation wave model is presented. Deviations between observed and modeled wave spectra are used to derive corrections of the wind field which drives the wave model. The wave field can then be subsequently corrected by a new integration of the wave model with the improved wind field. A basic difficulty of such dynamically consistent wave data assimilations schemes which correct both wind and wave data is the nonsynchronous and nonlocal nature of the wind field corrections: errors observed in the wave spectrum at a given measurement time and location can be produced by errors in the wind field at much earlier times and far distant locations. Formally, these problems can be rigorously resolved by the adjoint modeling method. However, in practice, the adjoint technique requires an order of magnitude more computer time than the integration of the wave model itself. Here an alternative method is developed. The linearized wave model equation which relates small wind to wave spectrum changes is inverted. The central assumption of the inversion is that the wind impact functions representing the impulse response (Green's) function of the wave evolution can be approximated by a δ‐function. Physically, this implies that the wind field perturbations responsible for observed perturbations in the wave spectrum can be regarded as strongly localized in space and time for any given component of the spectrum. To obtain stable estimates, the corrections for different wave components are averaged over wavenumber clusters representing different wave systems. For cases in which the linear approximation is inadequate, the method can be applied iteratively. Tests of the concept and application of the method for a number of synthetic wind field cases are encouraging.
Insolation over the western Mediterranean Sea: A comparison of direct measurements and Reed's formula
Authors: Schiano Maria Elisabetta
Published: February 2004

Direct measurements of solar radiation at sea were carried out in the Western Mediterranean Sea during several cruises in the years 1989–1994. The data collected were used to perform a test on the empirical formula proposed by Reed [1977]. The agreement between measured and empirical data is noteworthy, taking into account the coarseness of the formula. Nevertheless, Reed's estimates show a bias of about 5 W m−2. In order to investigate the causes of this bias, the data were analyzed according to the time of year and the cloud cover index. The results reveal that the computed insolation is overestimated under clear sky conditions and underestimated for cloudy sky. The disagreement of clear sky predictions can be ascribed to a regional misevaluation of both aerosols and water vapor attenuation. The inadequacy of the cloud cover index is indicated to explain the discrepancy of the estimates under cloudy sky. In any case, the mean difference between observations and formula is very slight, and this supports the use of this type of formula to compute long time average insolation over the sea.
Modeling the dispersal of Levantine Intermediate Water and its role in Mediterranean deep water formation
Authors: Wu Peili , Haines Keith
Published: February 2004

This paper demonstrates the importance of Levantine Intermediate Water (LIW) in the deep water formation process in the Mediterranean using the modular ocean general circulation model at 0.25° resolution, 19 vertical levels, over the entire Mediterranean with an open Gibraltar strait. LIW formation is strongly prescribed in the Rhodes Gyre region by Haney [1971] relaxation, while in other regions, surface salinity relaxation is much reduced by applying the ‘mixed’ thermohaline surface boundary conditions. Isopycnal diagnostics are used to trace water mass movements, and volume fluxes are monitored at straits. Low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal. The overall water budget is measured by an average flux at Gibraltar of 0.8 Sv, of which 0.7 Sv is exchanged with the eastern basin at Sicily. LIW (density around 28.95) spreads rapidly after formation throughout the entire Levantine due to baroclinic eddies. Toward the west, LIW accumulates in the northern and central Ionian, with some entering the Adriatic through Otranto and some mixing southward in eddies and exiting to the western Mediterranean through Sicily. LIW is converted to deep water in the south Adriatic at an average rate of 0.4 Sv. Water exchange through the Otranto strait appears to be buoyancy driven, with a strong bias to the end of winter (March–April), while at Sicily the exchange has a strong symmetric seasonal cycle, with maximum transport of 1.1 Sv in December indicating the effects of wind driving. LIW pathways in the west are complex and variable. In the Tyrrhenian, intermediate water becomes uniform on isopycnal surfaces due to eddy stirring. West of Sardinia, two LIW boundary currents are formed in the Balearic basin; one flows northward up the west coast of Sardinia and Corsica, and one westward along the northern African coast. The northward current is consistent with observations, while the westward current is intermittent for the first 10 years, often breaking up into eddies which enter the basin interior. Some observations of high‐salinity waters near the African coast may support this interpretation. LIW retains a subsurface salinity maximum of 38.4–38.5 practical salinity units (psu) when reaching the northwestern Mediterranean, contrasting with surface waters fresher than 38.0 psu. West Mediterranean deep water is formed below 1500 m depth with climatological characteristics, when it is mixed and cooled during winter convection in Lions Gyre.
Current structure of the south Indian Ocean
Authors: Sparrow Michael D. , Heywood Karen J. , Brown Juan , Stevens David P.
Published: February 2004

Using recently published atlas data [Olbers et al., 1992] and the Fine Resolution Antarctic Model (FRAM) [Webb et al., 1991], an investigation has been conducted into the structure of the frontal jets centered around the region of the islands of Crozet (46°27′S, 52°0′E) and Kerguelen (48°15′S, 69°10′E) in the south Indian Ocean. Geostrophic current velocities and transports were calculated from the temperature and salinity fields available from the atlas and compared with results from FRAM and previous studies. We have identified the Agulhas Return Front (ARF) and the Subtropical Front (STF), as well as the following fronts of the Antarctic Circumpolar Current (ACC): the Subantarctic Front (SAF), the Polar Front (PF), and the Southern ACC Front (SACCF), from temperature and salinity characteristics and from geostrophic currents. This analysis of model and atlas data indicates that the jets associated with the ARF, STF, and SAF are topographically steered into a unique frontal system north of the islands, having some of the largest temperature and salinity gradients anywhere in the world ocean. The frontal jet associated with the ARF is detectable up to 75°E and has associated with it several northward branching jets. The PF bifurcates in the region of the Ob'Lena (Conrad) seamount; subsurface and surface expressions are identified, separated by as much as 8° of latitude immediately west of the Kerguelen Plateau. The surface expression, carrying the bulk of the transport (∼65 Sv), is steered through the col in the Kerguelen Plateau at 56°S, 6° south of the latitude normally associated with the PF at this meridian. On crossing the plateau it rejoins the subsurface expression. In the south, passing eastward along the margin of the Antarctic continent and through the Princess Elizabeth Trough, a frontal jet is identified transporting up to 35 Sv, believed to be the SACCF [Orsi et al., 1995], placing the southern extent of the ACC in the region at 67°S.
Turbulence in the statically unstable oceanic boundary layer under Arctic leads
Authors: McPhee Miles G. , Stanton Timothy P.
Published: February 2004

Measurements of turbulent stress, heat flux, salinity flux, and turbulent kinetic energy (TKE) dissipation were made in the oceanic boundary layer under freezing leads during the 1992 Lead Experiment project in the Arctic Ocean north of Alaska. Results from two instrument systems, one comprising a vertical array of four turbulence‐measuring instrument clusters, the other an automated, loose‐tethered microstructure profiler, show that forcing by modest surface fluxes (surface friction velocity u*0 ∼ 0.7 cm s−1, surface buoyancy flux 〈w′b′〉0 ∼ −0.7 × 10−7 W kg−1) substantially changes the scales and character of boundary layer turbulence relative to forcing by stress alone. Despite continuous freezing at the surface, a diurnal cycle of heating and cooling of the mixed layer was seen, with downward oceanic heat flux as high as 70 W m−2 observed at middepth in the mixed layer near solar noon. Heat flux was determined both by direct eddy covariance of temperature and vertical velocity at fixed levels and from TKE and thermal dissipation estimates from the profiling instrument, with reasonable agreement. Similarly, there was close correspondence between TKE dissipation estimates obtained from inertial subrange spectral levels at the fixed instruments and from microstructure shear profiles. TKE production was dominated by buoyancy flux through most of the boundary layer. Thermal and saline eddy diffusivities were computed from directly measured fluxes and mixed layer temperature and salinity gradients, with mean values of 0.046 and 0.049 m2 s−1 for temperature and salinity, respectively. Kolmogorov constants for relating thermal and saline dissipations to inertial subrange spectral levels were found to be 0.9 and 1.0, respectively, but with large scatter.
Aerosols as dynamical tracers in the lower stratosphere: Ozone versus aerosol correlation after the Mount Pinatubo eruption
Authors: Borrmann S. , Dye J. E. , Baumgardner D. , Proffitt M. H. , Margitan J. J. , Wilson J. C. , Jonsson H. H. , Brock C. A. , Loewenstein M. , Podolske J. R. , Ferry G. V.
Published: February 2004

Stratospheric in situ aerosol and ozone measurements aboard the NASA‐operated ER‐2 high‐altitude research aircraft from August 1991 to May 1993 provide an opportunity to document the temporal evolution of the correlation between the stratospheric aerosol and the ozone from shortly after the Mount Pinatubo eruption until almost two years later. The observations show that at midlatitudes a linear relationship evolves between aerosol surface (or number) mixing ratios and ozone at altitudes ranging from slightly above the tropopause to 14–16 km. This correlation is linear for values of ozone from 200 to 1300 parts per billion by volume and for potential temperatures between 310 K and 467 K. The linear correlation persisted from late December 1991 until early March 1992 but degraded by October 1992.
Long‐range transport of ozone in the East Asian Pacific rim region
Authors: Akimoto Hajime , Mukai Hitoshi , Nishikawa Masataka , Murano Kentaro , Hatakeyama Shiro , Liu Chung‐Ming , Buhr Martin , Hsu K. J. , Jaffe Daniel A. , Zhang Lizhen , Honrath Richard , Merrill John T. , Newell Reginald E.
Published: February 2004

Measurements of surface ozone were conducted at three remote island sites in the East Asian Pacific rim region during the Pacific Exploratory Mission‐West (A) campaign period in September–October, 1991. The ozone concentrations observed at the three measurement stations at Oki and Okinawa, Japan, and Kenting, Taiwan, had similar ranges varying between 6–63, 8–58, and 4–65 ppb, respectively, except for one event of short‐range transport of polluted air at Kenting. Day‐to‐day variations have been analyzed by using backward air parcel trajectories on isentropic surfaces. The results showed that continental air masses which originated from northwestern Asia and passed through the high anthropogenic emission region of East Asia contained the highest concentration of ozone, 30–60 ppb with an average of 43–45 ppb at the three stations. In contrast, the lowest concentrations were observed for air parcels originating from the mid‐Pacific and transported without mixing with the continental outflow. These parcels contained 5–20 ppb of ozone with the average of 11, 15, and 9 ppb at Oki, Okinawa, and Kenting, respectively. The air parcels from the South China Sea contained 22 and 18 ppb of ozone at Okinawa and Kenting, respectively, which were higher than those from mid‐Pacific. Continental air mass from the north‐northeast to Oki containing 35–40 ppb ozone with the average of 37 ppb was recognized as continental “background.” The high ozone concentrations in the northwesterly continental outflow exceeding the background was ascribed to photochemical buildup in the planetary boundary layer.
Peroxy radical concentration and ozone formation rate at a rural site in the southeastern United States
Authors: Kleinman Lawrence , Lee Yin‐Nan , Springston Stephen R. , Lee Jai H. , Nunnermacker Linda , Weinstein‐Lloyd Judith , Zhou Xianliang , Newman Leonard
Published: February 2004

As part of the Southern Oxidants Study, Brookhaven National Laboratory operated an intensive measurement site near Metter, Georgia, during parts of the summers of 1991 and 1992. Measurements were made of photochemically active trace gases and meteorological parameters relevant to determining causes for elevated ambient ozone concentration. The 1992 data set was used to calculate peroxy radical concentration and ozone formation rate based on determining the departure from the photostationary state (PSS) and based on a radical budget equation, such as applied previously to the 1991 data set. Averaged over the 28‐day experimental period, we find maximum radical production occurring near noon at 2.5 ppb h−1, maximum peroxy radical concentration also occurring near noon at 80 ppt, and maximum ozone production of 8 ppb h−1 occurring near 1000 EST. Ozone photolysis accounts for 55% of radical production, HCHO and other carbonyl compounds about 40%. The radical budget and PSS methods depend in different ways on atmospheric photochemistry and a comparison between them affords a test of our understanding of the photochemical production of O3. We find that these methods agree to the extent expected based on uncertainty estimates. For the data set as a whole, the median estimate for fractional error in hourly average peroxy radical concentration determined from the radical budget method is approximately 30% and from the PSS method, 50%. Error estimates for the PSS method are highly variable, becoming infinite as peroxy radical concentration approaches zero. This behavior can be traced back to the difference form of the PSS equations. To conduct a meaningful comparison between the methods, the data set was segregated into subsets based on PSS uncertainty estimates. For the low‐uncertainty subset, consisting of a third of the whole data set, we find that the ratio of peroxy radical concentration predicted from the PSS method to that predicted from the radical budget method to be 1.22±32%.
A reanalysis of carbonyl sulfide as a source of stratospheric background sulfur aerosol
Authors: Chin Mian , Davis D. D.
Published: February 2004

This study investigates the importance of carbonyl sulfide (OCS) in the formation of stratospheric background sulfur aerosol. Specific questions examined include the loss rate in the stratosphere, the net flux into the stratosphere, and the contribution of OCS to the stratospheric background sulfur aerosol. From an analysis of current atmospheric measurements of OCS, the total amount of OCS in the atmosphere is evaluated to be 5.2 Tg. Of this total, 4.63 Tg is in the troposphere and 0.57 Tg in the stratosphere. Based on the estimated global OCS source strength of 1.2 Tg yr−1, the global atmospheric lifetime of OCS is estimated to be 4.3 years. Using a one‐dimensional photochemical model, the stratospheric photochemical lifetime of OCS is estimated to be 10 years, more than 2 times longer than its global atmospheric lifetime. These results suggest that most of the OCS transported into the stratosphere returns to the troposphere where it is mainly taken up by surface vegetation. The production of stratospheric background sulfur aerosol from OCS oxidation is calculated to be 3.0×1010 gS yr−1, 2 to 5 times smaller than the most recent estimates of the amount of sulfur required to maintain the stratospheric background aerosol level. Possible explanations for this difference include (1) an overevaluation of the nonvolcanic background aerosol burden; (2) an underevaluation of the lifetime of stratospheric background aerosol; (3) the presence of other sulfur sources such as high‐altitude aircraft emissions; or (4) that the stratospheric OCS database used in our analysis is flawed with a substantial yet unidentified systematic error.
An intercomparison of model ozone deficits in the upper stratosphere and mesosphere from two data sets
Authors: Siskind David E. , Connor Brian J. , Eckman Richard S. , Remsberg Ellis E. , Tsou J. J. , Parrish Alan
Published: February 2004

We have compared a diurnal photochemical model of ozone with nighttime data from the limb infrared monitor of the stratosphere (LIMS) and ground‐based microwave observations. Consistent with previous studies, the model underpredicts the observations by about 10–30%. This agreement is strong confirmation that the model ozone deficit is not simply an artifact of observational error since it is unlikely to occur for two completely different ozone data sets. We have also examined the seasonal, altitudinal, and diurnal morphology of the ozone deficit. Both comparisons show a deficit that peaks in the upper stratosphere (2–3 mbar) and goes through a minimum in the lower mesosphere from 1.0 to 0.4 mbar. At lower pressures (<0.2 mbar) the deficit appears to increase again. The seasonal variation of the deficit is less consistent. The deficit with respect to the LIMS data is least in winter while with respect to the microwave data, the deficit shows little seasonal variation. Finally, the night‐to‐day ratio in our model is in generally good agreement with that seen in the microwave experiment. Increasing the rate coefficient for the reaction O + O2 + M → O3 + M improves the fit, while a very large (50%) decrease in the HOx catalytic cycle is not consistent with our observations. Increasing the atomic oxygen recombination rate also improves the overall agreement with both data sets; however, a residual discrepancy still remains. There appears to be no single chemical parameter which, when modified, can simultaneously resolve both the stratospheric and mesospheric ozone deficits.
Non‐local thermodynamic equilibrium model for H2O 6.3 and 2.7‐μm bands in the middle atmosphere
Authors: López‐Puertas M. , Zaragoza G. , Kerridge B. J. , Taylor F. W.
Published: February 2004

A non‐local thermodynamic equilibrium radiative transfer model is presented for the populations of H2O and O2(1) vibrational levels in the middle atmosphere. Radiative transfer in the H2O bands is treated using the Curtis matrix method, and an exhaustive review of the collisional processes and their rate constants affecting the populations of these levels has been carried out. The near resonant vibrational‐vibrational coupling between H2O(010) and O2(1) is crucial for establishing their respective populations in the mesosphere. The population of H2O(010) starts departing from LTE significantly above about 65 km at night, this precise altitude being dependent on the temperature structure. At daytime, non‐LTE begins at approximately the same height but is significantly enhanced with respect to nighttime. The principal additional daytime excitation processes are absorption of solar radiation by H2O at 2.7 and 6.3 μm in the upper mesosphere and lower thermosphere and excitation from the photodissociation of O3 through O2(1) in the lower mesosphere. A sensitivity study of the H2O and O2(1) vibrational temperatures to the atmospheric and model parameters has been carried out. A preliminary analysis of ISAMS/UARS measurements in the 6.9‐μm H2O pressure‐modulated (PM) and wideband (WB) channels is presented. The measurements show enhancements in the daytime radiances in both channels, as compared to the nighttime values, above about 55 km. The effect is larger in the WB channel. Comparisons with the model show that non‐LTE excitation of the H2O (010) and (020) levels is responsible.
Validation of downwelling longwave computations with surface measurements during FIFE 89
Authors: Schweizer Diane , Gautier Catherine
Published: February 2004

The amount of longwave radiation reaching the surface is a necessary parameter for climate modeling. As no extensive array of surface‐based stations exists for monitoring the downwelling longwave surface flux (F ↓ (0)), satellites are expected to provide the data necessary for its computation. Before global fields of satellite‐derived values of F ↓ (0) can be used for climate modeling, computations of F ↓ (0) need to be validated with surface measurements. In this study the validation of computations of F ↓ (0) is carried out for both clear and cloudy conditions using data from the 1989 phase of the First ISLSCP Field Experiment (FIFE 89). FIFE 89 data is particularly useful for this study, as it contains lidar measurements of cloud base height and cloud fraction, thereby eliminating the need to estimate these parameters from other available data. Using a combination of the delta‐Eddington approximation for atmospheric scattering and the LOWTRAN 7 transmission functions, the computation of F ↓ (0) was carried out with particular emphasis on the reliability of the available data. Our results show that the two largest sources of discrepancies between the measured and calculated F ↓ (0) values are the lack of knowledge of cloud optical depth and the measurement error inherent in pyrgeometer instruments. The uncertainty due to the lack of optical depth information ranges from 1 to 22 W/m2, while the uncertainty of the pyrgeometer measurements ranges from 15 to 23 W/m2. For both clear and cloudy conditions the radiative transfer model was able to predict surface irradiance values within 4% of the measured values. In each case the standard deviation of the calculated values fell within the accuracy range of the pyrgeometer. As more detailed observations become available, such as those from the Atmospheric Radiation Measurement program, we anticipate a refinement in our ability to compute F ↓ (0).
Airborne observations of spatial and temporal variability of tropospheric carbon dioxide
Authors: Anderson B. E. , Gregory G. L. , Collins J. E. , Sachse G. W. , Conway T. J. , Whiting G. P.
Published: February 2004

Fast response (5‐s resolution) CO2 measurements were recorded on two recent NASA‐sponsored airborne atmospheric chemical survey missions: the summer/fall 1991 Pacific Exploratory Mission‐West A (PEM‐West A) and the winter 1992 Airborne Arctic Stratospheric Expedition II (AASE II). Both missions were conducted aboard the NASA Ames Research Center DC‐8 aircraft and included sampling between the surface and 12‐km altitudes over a wide range of latitudes and longitudes. In the following text, these data, along with simultaneous surface measurements from the NOAA flask sampling network, are examined to establish the vertical distribution and variability of CO2 as a function of location and season. Results indicate that middle to upper tropospheric (>5 km altitude) CO2 concentrations often differ considerably (>5 parts per million by volume in some cases) from values recorded at surface stations within the same geographic region. These differences are particularly notable at middle to high northern latitudes where midtropospheric concentration changes and seasonal cycles are generally delayed in time and highly damped in amplitude relative to surface observations.
Lidar observations of gravity wave activity in the upper stratosphere over Toronto
Authors: Whiteway James A. , Carswell Allan I.
Published: February 2004

The Rayleigh lidar technique has been applied to observe temperature fluctuations induced by gravity waves within the upper stratosphere. Observations were carried out on a routine basis for 1 year (130 clear nights) at the campus of York University near Toronto (44°N, 80°W). The waves were on occasion observed to induce marginal convective instability while exhibiting no substantial vertical amplitude growth. In general, the vertical variation in the amplitude of fractional temperature perturbations and associated available potential energy density implied the waves were strongly dissipated. Dramatic changes in the distribution of spectral energy with respect to vertical wave number were observed over the course of a few hours. The total resolved available potential energy in the gravity wave field varied considerably from day to day and seasonally with a winter maximum and summer minimum.
Aerosol size distribution and aerosol water content measurements during Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange
Authors: Kim Y. , Sievering H. , Boatman J. , Wellman D. , Pszenny A.
Published: February 2004

Aerosol size distribution data measured during the June 1992 Marine Aerosol and Gas Exchange experiment are analyzed to investigate the characteristics of fine marine aerosol particles measured over the North Atlantic near the Azores Islands. Measured aerosol size distribution data were corrected using the corrected size calibration data based on the optical properties of particles being measured. The corrected size distribution data were then approximated with either one or two lognormal size distributions, depending on air mass conditions. Under clean air mass conditions <3 μm diameter aerosol size distributions typically exhibited two modes, consisting of an accumulation mode and the small end of the sea‐salt particle mode. However, under the influence of continental polluted air masses, the aerosol size distribution was dominated by <1 μm diameter particles in a single mode with an increased aerosol concentration. Aerosol water content of accumulation mode marine aerosols was estimated from differences between several series of ambient and dried aerosol size distributions. The average aerosol water fraction was 0.31, which is in good agreement with an empirical aerosol growth model estimate. The average rate of SO4= production in the accumulation mode aerosol water by H2O2 oxidation was estimated to be <7×10−10 mol L−1 s−1, which is an insignificant contributor to the observed non‐sea‐salt SO4= in the accumulation mode.
Balloons as a Lagrangian measurement platform for atmospheric research
Authors: Businger Steven , Chiswell Steven R. , Ulmer Warren C. , Johnson Randy
Published: February 2004

The history of constant‐level balloons as observational platforms for atmospheric research is reviewed. Recent experience in using simple tetroons with Global Positioning System transponders for long‐range tracking during the Atlantic Stratocumulus Transition Experiment (ASTEX) is presented, along with an overview of the results of the ASTEX/Marine Aerosol and Gas Exchange Lagrangian strategy experiments. Progress in balloon materials and tracking capabilities is discussed, and a design is presented for an economical, lightweight “smart balloon” for use in future Lagrangian strategy, atmospheric chemistry experiments.
Parameterization of the solar radiative characteristics of low clouds and studies with a general circulation model
Authors: Chen C.‐T. , Ramaswamy V.
Published: February 2004

A broadband parameterization that improves the quantitative estimates of the solar radiative characteristics of low clouds is developed using reference solutions. The accuracy of the parameterization in determining the shortwave cloud absorption for a wide variety of low‐cloud conditions is better than 20%. Other broadband treatments, which do not adequately account for the influences due to above‐ and in‐cloud water vapor and water drop extinction, are also considered to investigate the sensitivity to these factors. The computed northern hemisphere summertime fluxes reveal that (1) the absorbed solar flux in low clouds (Fabs) is overestimated at high latitudes if the effect of attenuation by the above‐cloud vapor is ignored in the determination of the water drop absorption, (2) Fabs is underestimated in the tropical regions if in‐cloud vapor absorption is not considered, and (3) the conservative scattering assumption for drops yields a substantial underestimate of Fabs at most latitudes. General circulation model simulations with fixed sea surface temperatures and cloud amounts further highlight the significance of the vapor and drop optical properties. Differences in the broadband treatment of the radiative interactions with vapor and drops in low clouds introduce changes in the solar fluxes absorbed by the atmosphere and the surface; for the cases considered here, the solar flux change at the top of the atmosphere differs in sign from that at the surface. The flux differences bring about changes in vertical motion and precipitation; these, in turn, are accompanied by perturbations in the various components of the land surface heat (e.g., latent and sensible heat losses) and moisture (e.g., soil moisture, evaporation) budgets. For approximately similar solar flux differences the changes in the vertical motion, precipitation, and land surface parameters are dissimilar in the tropical and the midlatitude continental regions. Thus because of the adjustments in the atmosphere and the coupling between the atmosphere and the land surface processes, solar flux differences due to biases or deficiencies in the radiative treatment of vapor and drops affect the simulation of the hydrologic fields and the heat balance, including the atmospheric and land surface temperatures.
Intercomparison of UV/visible spectrometers for measurements of stratospheric NO2 for the Network for the Detection of Stratospheric Change
Authors: Hofmann David , Bonasoni Paolo , De Maziere Martine , Evangelisti Franco , Giovanelli Giorgio , Goldman Aaron , Goutail Florence , Harder Jerald , Jakoubek Roger , Johnston Paul , Kerr Jim , Matthews W. Andrew , McElroy Tom , McKenzie Richard , Mount George , Platt Ulrich , Pommereau Jean‐Pierre , Sarkissian Alain , Simon Paul , Solomon Susan , Stutz Jochen , Thomas Alan , Van Roozendael Michel , Wu Edmund
Published: February 2004

During the period May 12–23, 1992, seven groups from seven countries met in Lauder, New Zealand, to intercompare their remote sensing instruments for the measurement of atmospheric column NO2 from the surface. The purpose of the intercomparison was to determine the degree of intercomparability and to qualify instruments for use in the Network for the Detection of Stratospheric Change (NDSC). Three of the instruments which took part in the intercomparison are slated for deployment at primary NDSC sites. All instruments were successful in obtaining slant column NO2 amounts at sunrise and sunset on most of the 12 days of the intercomparison. The group as a whole was able to make measurements of the 90° solar zenith angle slant path NO2 column amount that agreed to about ±10% most of the time; however, the sensitivity of the individual measurements varied considerably. Part of the sensitivity problem for these measurements is the result of instrumentation, and part is related to the data analysis algorithms used. All groups learned a great deal from the intercomparison and improved their results considerably as a result of this exercise.
Modeling land surface fluxes using a sparse canopy model and radiometric surface temperature measurements
Authors: Friedl M. A.
Published: February 2004

Land surfaces with fractional vegetation cover possess distinctive micrometeorological properties that complicate the use of energy balance models to simulate surface fluxes. The use of thermal infrared (TIR) measurements to drive surface energy balance models over such surfaces is further complicated because TIR sensors view both soil and canopy elements. A land surface energy balance model specifically designed for sparse vegetation canopies is presented that addresses both of these issues. The model consists of a one‐dimensional, two‐layer energy balance formulation based on a potential‐resistance representation of the soil‐canopy‐atmosphere system. In this model, land surface TIR radiance is treated as being composed of soil and canopy components with different temperatures and emissivities. Model simulations demonstrated that modeled fluxes agreed well with observed fluxes and that deviations between observed versus modeled values were generally within the measurement error of the observed fluxes. Sensitivity analysis showed that model stability is sensitive to several input parameters, especially soil and canopy emissivity, and canopy stomatal resistance. Examination of modeled within‐canopy temperature and moisture regimes demonstrated that variation in canopy leaf area index exerted strong controls on the sources and sinks of latent and sensible heat within the soil‐canopy system. Finally, model simulations illustrated systematic differences between soil and vegetation temperatures that help to explain the complex relationship between surface radiometric and aerodynamic temperatures, and clearly demonstrated the need to distinguish between canopy and soil background temperatures in surface energy balance models that use TIR data to estimate land surface fluxes.