bluuebunny/crossref_metadata_2025 huggingface dataset:
A thermal front within the marine atmospheric boundary layer over the Agulhas Current south of Africa: Composite aircraft observations
Authors: Jury Mark R.
Published: February 2004

Aircraft cross‐section observations across the northern edge of the warm Agulhas Current to the south of Africa are used to form composite results of mean and turbulent meteorological parameters over a 4‐day period characterized by winter zonal westerlies. Across a sea surface temperature (SST) front of 8°C (40 km)−1 near 35°S, 23°E, surface heat fluxes and wind stress increase fivefold. The moist unstable marine atmospheric boundary layer is 400 m deeper on the warm side of the SST front, and turbulent variances increase with SST in a logarithmic correlation (r = +0.76). A jetlike core of accelerated winds (17 m s−1) over the axis of warmest water is found. Its existence is thought to be due to secondary circulations set up by enhanced pressure gradients and baroclinic effects. The sharp thermal front is quasi‐stationary and semipermanent during synoptic prefrontal conditions and zonal flows and lies approximately over the 200‐m isobath in association with the Agulhas Current.
Concentrations of chlorophyll, suspended matter, and gelbstoff in case II waters derived from satellite coastal zone color scanner data with inverse modeling methods
Authors: Doerffer Roland , Fischer Jürgen
Published: February 2004

Color ratio techniques used to derive chlorophyll concentrations from radiance data of the coastal zone color scanner (CZCS) fail in areas with high concentrations of suspended matter and gelbstoff (optically defined as case II water). In order to take into account all water constituents which modify the backscattered radiation field as well as the aerosol path radiance, an inverse modeling technique based on a two‐flow radiative transfer approximation and a simplex optimization procedure has been developed. It uses simultaneously the radiances of the first four CZCS spectral channels and minimizes the χ2 difference between the modeled and CZCS‐derived “Rayleigh‐corrected radiances.” The two‐flow model is calibrated with a set of radiance data which was simulated with a matrix‐operator radiative transfer model. In a first test, the inverse modeling procedure has been used to produce maps of the quantitative distributions of phytoplankton chlorophyll, suspended matter (dry weight), and gelbstoff; aerosol path radiance; and signal depth of the North Sea. By including the aerosol path radiance as a variable, the procedure implies the atmospheric correction. A map of the residual χ2 values indicates the success of the retrieval for each of the pixels.
Arctic sea ice variability: Model sensitivities and a multidecadal simulation
Authors: Chapman William L. , Welch William J. , Bowman Kenneth P. , Sacks Jerome , Walsh John E.
Published: February 2004

A dynamic‐thermodynamic sea ice model is used to illustrate a sensitivity evaluation strategy in which a statistical model is fit to the output of the ice model. The statistical model response, evaluated in terms of certain metrics or integrated features of the ice model output, is a function of a selected set of d (= 13) prescribed parameters of the ice model and is therefore equivalent to a d‐dimensional surface. The d parameters of the ice model are varied simultaneously in the sensitivity tests. The strongest sensitivities arise from the minimum lead fraction, the sensible heat exchange coefficient, and the atmospheric and oceanic drag coefficients. The statistical model shows that the interdependencies among these sensitivities are strong and physically plausible. A multidecadal simulation of Arctic sea ice is made using atmospheric forcing fields from 1960 to 1988 and parametric values from the approximate midpoints of the ranges sampled in the sensitivity tests. This simulation produces interannual variations consistent with submarine‐derived data on ice thickness from 1976 and 1987 and with ice extent variations obtained from satellite passive microwave data. The ice model results indicate that (1) interannual variability is a major contributor to the differences of ice thickness and extent over timescales of a decade or less, and (2) the timescales of ice thickness anomalies are much longer than those of ice‐covered areas. However, the simulated variations of ice coverage have less than 50% of their variance in common with observational data, and the temporal correlations between simulated and observed anomalies of ice coverage vary strongly with longitude.
The response of ice floes to ocean waves
Authors: Meylan Michael , Squire Vernon A.
Published: February 2004

A precise linear mathematical theory is reported to model the response of a solitary ice floe in ocean waves, allowing the floe to bend with the passing wave. Both infinite and finite water depths are considered, and the model is also extended to include a pair of separated floes of different length, the case of n‐floes then being a natural and straightforward development. For a single ice floe, perfect transmission is achieved whenever the wavelength beneath the ice couples perfectly to the length of the ice floe. Then the strains induced in the bending ice floe reach a maximum, and because multiple‐cycle tuning can occur in floes which are long compared to the wavelength, strain response amplitude operators (RAOs) are complicated. By considering the case of infinite stiffness, heave and roll RAOs are also found for typical ocean wave periods, and these agree well with two‐dimensional rigid‐body models. Finally, ice floes of different diameters but constant 1‐m thickness are subjected to spectral forcing, and the strain spectral density for each is found. Spectral density envelopes increase gradually with floe diameter, achieving a maximum value for a floe of about 102m. Thereafter strains never decrease below those for the 80‐m curve owing to multiple‐cycle tuning. This may explain the presence of zones within an ice field where floe size never exceeds some prescribed value. Results obtained from the complete theory for two adjacent floes do not differ significantly from those found by applying the single‐floe model serially except when the separation is very small.
Ripple geometry in wave‐dominated environments
Authors: Wiberg Patricia L. , Harris Courtney K.
Published: February 2004

The wavelength, height, and steepness of ripples formed under oscillatory flows in flume and field studies are reexamined to construct a simple and accurate method of predicting these ripple properties. Ripples with wavelengths proportional to near‐bed wave orbital diameter (orbital ripples), predominant in laboratory experiments, are found to have heights in excess of the thickness of the wave boundary layer. Ripples with wavelengths that are roughly proportional to grain size and nearly independent of orbital diameter (anorbital ripples), which predominate in the field, have heights at least several times smaller than wave boundary layer thickness. Relating wave boundary layer height to the generally more easily estimated wave orbital diameter, a set of expressions are developed for predicting ripple type and geometry based on mean grain size, wave orbital diameter, and estimated anorbital ripple height. This method provides a good characterization of ripple wavelength and steepness for a large set of combined field and flume data.
Sun glitter radiance and radar cross‐section modulations of the sea bed
Authors: Hennings Ingo , Matthews John , Metzner Margitta
Published: February 2004

Aircraft and satellite‐borne multispectral sensors such as ocean color scanners, spectrometers, and scanning Lidar's have proved to be effective in detecting submarine shallow‐water bottom topography in clear coastal waters. For such studies the blue‐green band of the visible electromagnetic spectrum (wavelength between 400 and 580 nm) is used, because natural light in this range has the deepest penetration into the water column. However, if the water becomes turbid, the reflection from the submarine sea bed disappears. In this case the only possible mechanism available in the optical range of the electromagnetic spectrum for detecting surface signatures of shallow water bottom topography is through the observation of direct sunlight specularly reflected from a roughened sea surface, known as sun glitter radiance. As the tidal flow over irregularities on the submarine sea bed creates surface roughness variations, sun glitter imagery can be used to detect such features. In this paper a first‐order theory of the sun glitter imaging mechanism of submerged sand waves is presented. The results of sun glitter radiance modulations are compared with simulations of P band radar cross‐section modulations and with experimental data. Calculations of both the constant background sun glitter radiance and the sun glitter radiance modulation show that these parameters are very sensitive to wind speed, to view angle with respect to acquisition time, and to observation geometry as a whole.
Heat flux parameterizations for the Mediterranean Sea: The role of atmospheric aerosols and constraints from the water budget
Authors: Gilman Craig , Garrett Chris
Published: February 2004

The semi‐enclosed nature of the Mediterranean Sea makes it an excellent place to test data sets and standard formulae used to estimate the heat flux into the world's oceans. Oceanographic observations at the Strait of Gibraltar imply a mean annual net loss of 5.2±1.3 W m−2 from from the sea surface (Macdonald et al., 1994). Investigations using bulk heat‐flux formulae, however, generally give a large heat gain (≈ 20 to 30 W m−2) through the Mediterranean Sea surface. This discrepancy has been attributed by different authors to an underestimation of the latent heat flux, an underestimation of the longwave radiation, or an overestimation of the incoming shortwave radiation. Examination of the heat flux formulae themselves, and of the transport of anthropogenic and mineral aerosols, suggests that the shortwave radiation has been previously overestimated by approximately 20 W m−2. This overestimation results from an incorrect use of a commonly used bulk formula at very low cloud levels, and direct radiative attenuation due to aerosols. Allowing for the seasonal variability of aerosols over the Mediterranean basin, rather than employing a constant aerosol attenuation factor, improves the agreement of the annual Qs cycle with ground measurements at one location. Current data support a maximum increase in the net longwave radiation of 10 W m−2 from previous estimates. Recent estimates of the Mediterranean water budget do not indicate that the latent heat flux estimate is incorrect.
The effects of temporal variability of mixed layer depth on primary productivity around Bermuda
Authors: Bissett W. Paul , Meyers Mark B. , Walsh John J. , Müller‐Karger Frank E.
Published: February 2004

Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size‐fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high‐ and low‐frequency changes of the mixed layer depth within 32°‐34°N, 62°‐64°W between 1979 and 1984. Results from the model derived from high‐frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low‐frequency (case 2) mixed layer depth changes. Incorporation of size‐fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low‐frequency temporal resolution and oversimplified biological simulations.
The effect of temporal undersampling on primary production estimates
Authors: Wiggert Jerry , Dickey Tom , Granata Tim
Published: February 2004

Annual primary production estimates for specific oceanic regions have typically been made using a variety of measures of productivity spaced, at best, several weeks apart Primary productivity in the oceans is known to be extremely episodic. It is hypothesized here that primary production data with a temporal resolution of several weeks have a high potential for error due to undersampling. In the present analysis, time series of gross primary productivity were calculated using time series of photosynthetically available radiation and chlorophyll a concentration as input to an optical production model. The input data are of minute scale resolution and were gathered during a number of moored experiments. These took place over the past 5 years at several oceanic sites. The minute scale productivity time series were integrated to form time series of daily estimates of gross production. These range in duration from 40 to 260 days. The time series exhibit several regimes characteristic of oceanic primary productivity, such as phytoplankton blooms, productivity pulses associated with advected water masses, steady state growth, and development of a subsurface productivity maximum. The presence of these features makes our time series ideal for investigating (1) the sensitivity of annual production estimates to the timing of the sample set and (2) the error introduced by undersampling inherent in coarser sampling methods. It was found that distinct pulses of productivity generate the greatest error and that high variability leads to large errors, even for well‐resolved sampling intervals. The maximum percent error due to undersampling was found to be 85%. Additionally, up to a fourfold range between the maximum and minimum estimates of average daily production was found over all sampling intervals. Finally, the maximum expected range (300 g C m−2 yr1) and the expected standard deviation (±42 g C m−2 yr1) for annual water column production were determined at a Sargasso Sea site for which long‐term productivity time series were available at four depths within the euphotic zone.
Modeling phytoplankton dynamics in the northeast Atlantic during the initiation of the spring bloom
Authors: Stramska Malgorzata , Dickey Tommy D.
Published: February 2004

Primary productivity in the North Atlantic (59°29′N, 20°50′W) was estimated by applying a “light‐pigment” productivity model (Kiefer and Mitchell, 1983) to mooring data collected during the spring of 1989. We show that the choice of the parametrization of the light captured by phytoplankton cells in a turbulent mixed layer has a significant effect on the calculated productivity estimates. It appears that the quality of such estimations benefits largely from using high‐resolution time series data (minutes). We also examined phytoplankton dynamics by incorporating the Kiefer‐Mitchell model into a one‐dimensional model of the turbulent mixed layer (Mellor and Yamada, 1982). The calculated time‐depth distribution of phytoplankton biomass compares relatively well with that measured in situ. The model results indicate that small changes in the water column stability can be sufficient to initiate phytoplankton bloom even before the apparent formation of the seasonal thermocline. The model also describes the diel cycle of biomass concentration, suggesting that near the sea surface the daytime losses of biomass by vertical diffusion can be much larger than nighttime losses. Thus, if not accounted for, such losses may bias estimates of primary production from diel variations in biomass concentration, for example, when using a method based on beam attenuation measurements. These losses should also be considered for the proper interpretation of in situ primary production measurements by incubation methods.
An empirical relation between ocean‐surface wind direction and the Bragg line ratio of HF radar sea echo spectra
Authors: Harlan J. A. , Georges T. M.
Published: February 2004

Twelve days of tests with six U.S. Air Force OTH‐B over‐the‐horizon radars produced a large surface wind direction data set covering much of the North Atlantic and Pacific oceans. We compare wind directions derived from the sea echo Bragg line ratio with concurrent in situ measurements made by ships and buoys and with the National Meteorological Center (NMC) Global Data Assimilation System model. Using 1900 such comparisons, we derive an empirical model for the dependence of surface wind direction on the Bragg line ratio of HF radar sea echoes. The rms difference between the empirical model and the combined NMC and in situ data is about 33°. When only very high quality radar data are used, the rms difference between the radar and buoy measurements alone is 24°. The pattern of surface streamlines derived from 1 day's radar measurements over the northeastern Pacific Ocean closely matches that derived from the NMC model.
Circulation driven by observed surface thermohaline fields in a coarse resolution ocean general circulation model
Authors: Cai Wenju
Published: February 2004

This paper reports the results from a series of mechanistic studies on the global ocean circulation by assimilating a set of observed surface thermohaline data into a low‐resolution Geophysical Fluid Dynamics Laboratory (GFDL) global ocean general circulation model (OGCM). In most of the experiments the surface wind stress is set to zero. The surface thermohaline forcing features a strong relaxation of surface temperature and salinity towards observed values. The ocean circulation resulting from the assimilation of surface thermohaline fields depends heavily upon the various parameterizations of vertical mixing processes. Consistent with previous studies, a greater vertical diffusivity results in a greater meridional overturning stream function and a greater meridional heat transport. The vertical structure of stratification is particularly well reproduced if the vertical diffusivity is set to be buoyancy dependent. Even in the absence of explicit wind forcing, the major circulation features are reproduced. In particular, water mass properties are realistic, and the Antarctic Circumpolar Current (ACC) and the Gulf Stream have significant barotropic components (especially the ACC). The feature of realistic water masses can be attributed to the reproduction of convection‐dominated heat and freshwater fluxes in the polar and subpolar regions, where these water masses are formed. In the absence of explicit wind, the barotropic transports are driven by bottom pressure torque, which is associated with variable bottom topography and upslope/downslope bottom flows. Convective processes play an important role in redistributing the water mass, generating the barotropic transport, and maintaining the thermohaline structure. In the absence of convective adjustment, the global circulation is characterized by a thermocline reversal in polar and subpolar regions. Deep convection also leads to larger bottom flows, and hence indirectly play a role in generating the barotropic transports. In the low‐resolution model, the barotropic ACC is broad; this seals the Indian Ocean from the Atlantic Ocean, and prevents both the barotropic and baroclinic interbasin exchange between the Indian and the Atlantic oceans. In this situation, the North Atlantic Deep Water (NADW) outflow is compensated by the cool and fresh South Pacific water from the east of Drake Passage (cool water route). When convection is used as a device to suppress ACC, and to ensure that the NADW is the only deep water source, the NADW formation is seen to cause a large Indonesian throughflow. The teleconnection between the throughflow and the NADW is via the Agulhas leakage water. In the absence of ACC, the NADW outflow is compensated by the warm and salty Indian water through the leakage (warm water route). The results show that the realization of warm water route depends on the structure of the modeled ACC.
Summertime tropospheric ozone distributions over central and eastern Canada
Authors: Anderson B. E. , Gregory G. L. , Barrick J. D. W. , Collins J. E. , Sachse G. W. , Shipham M. C. , Hudgins C. H.
Published: February 2004

Ozone measurements were obtained between the surface and the 6‐km altitude on aircraft flights over central and eastern Canada during the summer 1990 NASA Global Tropospheric Experiment Arctic Boundary Layer Expedition (GTE/ABLE 3B). Tropospheric O3 budgets for these regions were observed to be highly variable and significantly impacted by long‐range transport and regional scale air mass modification processes. For example, integrated O3 abundance below 5‐km altitude averaged 40% and 30% greater in air masses influenced by anthropogenic sources and biomass burning, respectively, than in background (polar) air. Conversely, aged air transported from subtropical areas of the Pacific at times reduced O3 abundance in this height interval by up to 20%. Though intrusion of anthropogenic air was infrequent during the experiment period, the influence of biomass‐burning emissions was particularly notable as two thirds of the flights sampled air influenced by plumes from fires burning in Alaska and western Canada. The impinging pollution, both natural and anthropogenic, not only elevated O3 levels directly but also was a source of reactive nitrogen (and nonmethane hydrocarbons) which generally increases the tropospheric lifetime of O3 via moderation of photochemical destruction rates.
Growing season boundary layer climate and surface exchanges in a subarctic lichen woodland
Authors: Fitzjarrald David R. , Moore Kathleen E.
Published: February 2004

Between June and August 1990, observations were made at two surface micrometeorological towers near Schefferville Quebec (54° 52′N, 66° 40.5′W), one in a fen and one in the subarctic lichen woodland, and at four surface climatological stations. Data from these surface stations were supplemented by regular radiosonde launches. Supporting measurements of radiative components and soil temperatures allowed heat and moisture balances to be obtained at two sites. The overall surface meteorological experiment design and results of micrometeorological observations made on a 30‐m tower in the lichen woodland are presented here. Seasonal variation in the heat and water vapor transport characteristics illustrate the marked effect of the late summer climatological shift in air mass type. During the first half of the summer, average valley sidewalls only 100 m high are sufficient to channel winds along the valley in the entire convective boundary layer. Channeling effects at the surface, known for some time at the long‐term climate station in Schefferville, are observed both at ridge top and in the valley, possibly the response of the flow to the NW‐SE orientation of valleys in the region. Diurnal surface temperature amplitude at ridge top (≈ 10° C) was found to be half that observed in the valley. Relatively large differences in precipitation among these stations and the climatological station at Schefferville airport were observed and attributed to the local topography. Eddy correlation observations of the heat, moisture and momentum transports were obtained from a 30‐m tower above a sparse (≈ 616 stems/ha) black spruce lichen woodland. Properties of the turbulent surface boundary layer agree well with previous wind tunnel studies over idealized rough surfaces. Daytime Bowen ratios of 2.5–3 are larger than those reported in previous studies. Surface layer flux data quality was assessed by looking at the surface layer heat balance. Diurnal and seasonal scale heat budget imbalances were found. We suggest that unmeasured surface heat storage may be responsible for some of the observed imbalance. The presence of the unexplained residual in this and other studies of energy balance over forests casts a note of caution on the interpretation of energy balance components obtained using heat residual methods.
Effect of vibrationally excited oxygen on ozone production in the stratosphere
Authors: Patten K. O. , Connell P. S. , Kinnison D. E. , Wuebbles D. J. , Slanger T. G. , Froidevaux L.
Published: February 2004

Photolysis of vibrationally excited oxygen produced by ultraviolet photolysis of ozone in the upper stratosphere is incorporated into the Lawrence Livermore National Laboratory two‐dimensional zonally averaged chemical‐radiative‐transport model of the troposphere and stratosphere. The importance of this potential contributor of odd oxygen to the concentration of ozone is evaluated based on recent information on vibrational distributions of excited oxygen and on preliminary studies of energy transfer from the excited oxygen. When energy transfer rate constants similar to those of Toumi et al.(1991) are assumed, increases in model ozone concentrations of up to 4.0% in the upper stratosphere are found, and the model ozone concentrations are found to agree slightly better with measurements, including recent data from the Upper Atmosphere Research Satellite. However, the ozone increase is only 0.3% when the larger energy transfer rate constants indicated by recent experimental work are applied to the model. An ozone increase of 1% at 50 km requires energy transfer rate constants one‐twentieth those of the preliminary observations. As a result, vibrationally excited oxygen processes probably do not contribute enough ozone to be significant in models of the upper stratosphere.
Impact of a cutoff low development on downward transport of ozone in the troposphere
Authors: Ancellet Gerard , Beekmann Matthias , Papayannis Alexandros
Published: February 2004

A study of ozone transfer from the stratosphere to the troposphere has been performed during two phases of the evolution of a cutoff low using both ozone vertical profiles and objective analysis of the European Center for Medium range Weather Forecasting to compute potential vorticity distributions and air mass trajectories. Ozone profiles were measured by a ground‐based lidar system at the Observatoire de Haute Provence (OHP)(43°55N, 5°42E) on November 1990. A stratospheric ozone transport into the troposphere has been observed during a tropopause fold which occurred at the beginning of the cutoff low formation. On a timescale of a few days the correlation is rather good between the potential vorticity and the ozone time evolution in the upper part of the tropopause fold, and the ozone to potential vorticity ratio is of the order of 30–40 ppb/PVu (1 PVu = 10−6 K m2 s−1 kg−1) in the tropopause fold. The amount of stratospheric ozone transferred by the folding process is estimated to be 6.5±3.5 1032 molecules d−1, using a trajectory analysis, the potential vorticity distribution along the trajectory path, and temperature radio sounding profiles, in order to estimate the likelihood of the downward transport of ozone. During the erosion phase of the cutoff low, the tropopause definition has been changing, and the stratospheric ozone decrease associated with the cutoff low evolution corresponds to an ozone transport of 4.0±2.0 1032 molecules d−1, which is of the same order of magnitude as the impact of the folding process. The mechanism resulting in the downward flux of ozone can be twofold: a tropopause lifting associated with convective clouds and small‐scale turbulent mixing near the jet stream. None of them can be discarded, due to the large uncertainties for their respective influences, when using the data set available for this study.
Low ozone amounts during 1992–1993 from Nimbus 7 and Meteor 3 total ozone mapping spectrometers
Authors: Herman J. R. , Larko D.
Published: February 2004

The global distribution of ozone during the October 31, 1978, to May 6, 1993, observing lifetime of the Nimbus 7 total ozone mapping spectrometer (TOMS) is described, with emphasis on the low ozone amounts observed during 1992 and 1993. Ozone amount time series are extended beyond May 6, 1993, to the end of July 1993 using preliminary Meteor 3 TOMS data. Time series for zonally averaged ozone amounts show that there has not been a significant shift in the seasonal patterns of ozone maxima and minima caused by the Mount Pinatubo eruption or by the onset of very low ozone values during 1992 and 1993. There has been a relatively slow, nearly linear decrease in the amount of ozone over the entire globe from 1979 to the end of 1991, with rates ranging from no change at the equator to a 4–6% decrease per decade at midlatitudes and a 10–12% decrease per decade at higher latitudes. After the eruption of Mount Pinatubo during June 1991, the ozone amount decreased in the equatorial latitudes (10°S to 10°N) for about 6 months (−10 Dobson units (DU) between 0° and 10°S and −3 DU between 0° and 10°N). During 1992 and continuing into 1993, the rate of ozone decrease deviated from the previously linear trend with the onset of changes that were large in comparison with the historical range of ozone values from 1979 to 1991. The first of the large decreases in ozone amount occurred earlier, in February 1990 to May 1990, at 50°–70°N. At high northern latitudes, the 1993 decreased ozone amounts were about 12.5% below the envelope of historical values; at midlatitudes they were about 7% lower; and at low latitudes they were about 4% lower. Area‐weighted averages in the northern and southern hemispheres show that most of the 1992–1993 ozone losses have occurred in the northern hemisphere. The 1993 global average (70°S to 70°N) ozone amount is 3% below the 1979 to 1991 minimum, 5% below the historical envelope in the northern hemisphere, and near the lower boundary of the historical envelope in the southern hemisphere. In the 70°–60°S latitude band, the ozone losses between 1979 and 1993 have reduced the annual minimum amount to values below those seen in the equatorial regions.
Influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter
Authors: Kodera Kunihiko
Published: February 2004

It has been suggested that the zonal‐mean stratospheric zonal‐wind anomalies can propagate downward into the troposphere, producing considerable changes. On the other hand, volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere. If these suggestions are correct, the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process. In the present study, this idea is examined by analyzing changes in the January circulation after three recent volcanic eruptions. Regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole‐type anomalies in the zonal‐mean zonal winds, which are similar to those observed in a previous work on the influence of polar night jet.
Lead isotope ratios of airborne particulate matter as tracers of long‐range transport of air pollutants around Japan
Authors: Mukai Hitoshi , Tanaka Atsushi , Fujii Toshihiro , Nakao Makoto
Published: February 2004

The use of airborne lead isotope ratios as tracers of long‐range transport of air pollutants in the Asian region was evaluated using air trajectory analysis. Airborne particulate matter was collected in various seasons from 1988 to 1991 at the Oki Islands located between the Asian continent and Japan. Air masses coming from Japan had lead isotope ratios nearly equal to those measured on mainland Japan. Air masses from the Asian continent had less radiogenic isotope ratios than those from Japan. Trajectory analysis showed that these less radiogenic values could be used to further subdivide Asian air masses as having come from one of three regions: the southern part of the Korean Peninsula, north China, and Russia. The isotope ratios of the samples classified into three regions were close to previously reported values measured in each region, except for those assigned to Korea, where it is believed that the ratios are currently changing. It was concluded that lead isotope ratios were reliable tracers of the long‐range transport of air pollutants, especially when used in conjunction with air trajectory analysis.
Observations of horizontal and vertical wave number spectra of gravity wave motions in the stratosphere and mesosphere over the mid‐Pacific
Authors: Hostetler Chris A. , Gardner Chester S.
Published: February 2004

We present vertical and horizontal wave number spectra of density perturbations in the upper stratosphere (25–40 km) and the upper mesosphere (∼80–105 km) inferred from ∼45 hours of airborne Na/Rayleigh lidar observations in the vicinity of Hawaii. The mean density variance is (0.92%)2 for the upper stratosphere and (6.1%)2 and for the upper mesosphere. The mean vertical shear variance and Richardson's number for the upper mesosphere are (6.1%/km)2 and 0.69, respectively. The observed vertical wave number m and horizontal wave number k spectra exhibit power law dependencies. The mean slopes of the vertical wave number spectra are −2.5 for the upper stratosphere and −3.1 for the upper mesosphere. The mean slope of the horizontal wave number spectra is −1.9 for the upper mesosphere. The mean characteristic vertical and horizontal wavelengths inferred from the spectra are 13.4 and 5810 km, respectively. In all cases the magnitudes of the upper stratosphere m spectra are more than an order of magnitude smaller than those of the upper mesosphere at all observable scales. In the stratosphere the m spectra exhibit significant energy at low wave numbers that are less than the values expected for the characteristic wave numbers. This suggests the presence of gravity wave sources capable of generating significant energy at long vertical scales. The source is believed to be geostrophic adjustment of the jet stream. A large‐amplitude, highly coherent, quasi‐monochromatic, short horizontal scale (λh ∼ 16 km) oscillation in the Na layer was observed on the March 22 flight. The oscillation resembled short horizontal scale structures often observed in OH airglow images and was found to be consistent with a gravity wave interpretation.
Potential for meteorological bias in lidar ozone data sets resulting from the restricted frequency of measurement due to cloud cover
Authors: De Backer Hugo , Visser Eric P. , De Muer Dirk , Swart Daan P. J.
Published: February 2004

Lidar‐based ozone data sets may be meteorologically biased since the measurements are performed in the absence of precipitation and fog and the vertical profiles are truncated at the cloud base. This problem was studied for the routine ozone lidar facility at Bilthoven, Netherlands (52°07′N, 5°12′E). We used the long‐term data record of balloon soundings at Uccle, Belgium (50°48′N, 4°21′E) between 1969 and 1992 to examine the average ozone concentrations as a function of altitude and season at different amounts of cloud cover. Since Uccle and Bilthoven are only 160 km apart and to a large extent have the same climatology, the Uccle data are assumed to be representative of the atmospheric conditions at Bilthoven. The data set of ozone profiles was arranged into several subsets according to increasing amounts of cloud cover. When compared to the total set, the subset for clear sky conditions showed significantly lower ozone partial pressures (absolute differences down to −2.37 mPa and percentage differences down to −43.6%) around the tropopause in spring and early summer and higher values (up to +1.10 mPa and +39.2%) in the lower troposphere in summer. These phenomena are explained by differences in the average origin of air masses and photochemical ozone production. The results have led to the definition of the monitoring strategy for the tropospheric ozone lidar facility at Bilthoven such that a meteorological bias in the set of ozone profiles is avoided.
The importance of atmospheric chemistry in the calculation of radiative forcing on the climate system
Authors: Hauglustaine D. A. , Granier C. , Brasseur G. P. , Mégie G.
Published: February 2004

An interactive two‐dimensional model of the troposphere, stratosphere, and mesosphere, in which dynamics, radiation, and chemistry are treated interactively, is used to investigate the anthropogenic changes in the steady state chemical composition of the atmosphere since preindustrial times and to assess the associated changes in radiative forcing on climate. The perturbations in the atmospheric oxidation capacity due to anthropogenic emissions of source gases are found to be significant. In the troposphere, an ozone increase of 80–120% at northern midlatitudes and a global decrease of 10–20% in the OH concentration since the preindustrial period are calculated. In the polar lower stratosphere of the southern hemisphere, an ozone depletion since preindustrial times reaching more than 60% during spring is calculated as a result of rapid catalytical destruction of ozone by chlorine radicals in the presence of polar stratospheric clouds. Particular attention is given to the induced changes in radiative forcing. These results stress the potentially important role of chemical feedbacks on climate and indicate that the direct forcing associated with increasing concentrations of greenhouse gases is enhanced by about 30% when these feedbacks are taken into account. On a global average basis, the greenhouse effect of tropospheric ozone represents approximately 17% of the total radiative perturbation. This forcing is characterized by a strong latitudinal dependence, peaking at midlatitudes in the northern hemisphere. The importance of indirect climate forcings by stratospheric ozone (including local cooling of the stratosphere) is confirmed. It is found that the net (solar + infrared) indirect effect of stratospheric ozone changes is to increase the chlorofluorocarbon direct radiative forcing. On the other hand, the change in the longwave forcing associated with water vapor increase in the stratosphere appears to play a minor role.
Methodology for the estimation of terrestrial net primary production from remotely sensed data
Authors: Ruimy A. , Saugier B. , Dedieu G.
Published: February 2004

Kumar and Monteith's (1981) model for the remote sensing of crop growth has been used to estimate continental net primary productivity (NPP) as well as its seasonal and spatial variations. The model assumes a decomposition of NPP into independent parameters such as incident solar radiation (S0), radiation absorption efficiency by canopies (ƒ), and conversion efficiency of absorbed radiation into organic dry matter (e). The precision on some of the input parameters has been improved, compared to previous uses of this model at a global scale: remote sensing data used to derive ƒ have been calibrated, corrected of some atmospheric effects, and filtered;ehas been considered as biome‐dependent and derived from literature data. The resulting global NPP (approximatively 60 GtCper year) is within the range of values given in the literature. However, mean NPP estimates per biome do not agree with the literature (in particular, the estimation for tropical rain forests NPP is much lower and for cultivations much higher than field estimates), which results in zonal and seasonal variations of continental NPP giving more weight to the temperate northern hemisphere than to the equatorial zone.
Distribution of organic hydroperoxides during aircraft measurements over the northeastern United States
Authors: Tremmel H. G. , Junkermann W. , Slemr F.
Published: February 2004

Distributions of organic hydroperoxides (ROOH), hydrogen peroxide (H2O2), other trace gases, and meteorological parameters were measured from an aircraft over the northeastern United States in August and September 1988. The data set consists of 13 flight missions on 14 days with 177 vertical profiles at altitudes between 100 and 3500 m. The mixing ratio of ROOH varied from below the detection limit of 0.1 parts per billion by volume (ppbv) up to 3.14 ppbv, with generally higher average values in the free troposphere (FT) than in the planetary boundary layer (PBL). The average ratio of ROOH to the H2O2 mixing ratios was about 50%. The ROOH mixing ratio was strongly correlated with H2O2, indicating similar production and loss mechanisms for ROOH and H2O2. The observed lower variability of the ROOH mixing ratios in comparison with that of H2O2 is probably due to a longer atmospheric residence time of ROOH. Combined with the lower ROOH mixing ratios, this longer residence time indicates that the production and loss processes of ROOH are slower than those of H2O2. An ROOH formation rate of 56±8 parts per trillion by volume ROOH/h% H2O was determined from the difference of ROOH mixing ratios between afternoon and morning flights on September 16. This formation rate is about twice as large as the rate predicted by a simple photochemical box model with methane chemistry, indicating that organic hydroperoxides other than CH3OOH may also be formed. The estimations of HO2 and RO2 concentrations in the free troposphere from H2O2, ROOH, and O3 formation rates were consistent.
Seasonal trend analysis of published ground‐based and TOMS total ozone data through 1991
Authors: Reinsel Gregory C. , Tiao George C. , Wuebbles Donald J. , Kerr James B. , Miller Alvin J. , Nagatani Ronald M. , Bishop Lane , Ying Lisa H.
Published: February 2004

A seasonal trend analysis of published Dobson (including stations' newly revised and Brewer‐simulated Dobson) total ozone data through 1991 from a network of 56 stations has been performed, using three different data periods. The trend results for the longest data period 1964–1991 indicate substantial negative trends in ozone in the higher northern latitudes during the winter and spring seasons, some evidence of negative trend in the higher southern latitudes (30°S–55°S) during all seasons, and trends close to zero for all seasons over the 30°S–30°N latitude range. For the shortest data period, November 1978 through 1991, there is a clear indication that trends have become more negative in the higher northern latitudes, especially during the winter and spring seasons, and also in the higher southern latitudes in all seasons. A seasonal trend analysis of zonal averages of total ozone mapping spectrometer (TOMS) satellite total ozone data for the comparable period November 1978 through 1991 has also been performed, and moderately good agreement is found between trends in Dobson and TOMS data over this period.
Tracer evolution in winds generated by a global spectral mechanistic model
Authors: Nielsen J. Eric , Rood Richard B. , Douglass Anne R. , Cerniglia Mark C. , Allen Dale J. , Rosenfield Joan E.
Published: February 2004

The lower boundary of a spectral mechanistic model is prescribed with 100 hPa geopotentials, and its performance during a November 1989 through March 1990 integration is compared with National Meteorological Center observations. Although the stratopause temperatures quickly become biased near the pole in both hemispheres, the model develops a residual mean circulation which shows significant descent over the winter pole and ascent in the tropics and over the summer pole at pressures less than 10 hPa. The daily correspondence of observed to modeled features in the upper stratosphere and mesosphere degrades after one month. However, the long‐term variability qualitatively follows the observations. The results of off‐line transport experiments are also described. A passive tracer is instantaneously injected into the flow over the poles and evolves in a manner which is consistent with the residual mean circulation. It demonstrates a significant cross‐equatorial flux in the mesosphere near solstice, and air which originates in the southern hemisphere polar mesosphere can be found descending deep into the northern polar stratosphere at the end of the integration. Nitrous oxide is also transported, and its ability to act as a dynamical tracer is evaluated by comparison to the evolution of the passive tracer.
Hubble Space Telescope UV spectral observations of Io passing into eclipse
Authors: Clarke John T. , Ajello Joe , Luhmann Janet , Schneider Nick , Kanik Isik
Published: February 2004

Time‐resolved spectra of Io have been obtained with the Faint Object Spectrograph on the Hubble Space Telescope in January 1992 at times centered on the passage of Io into Jupiter's shadow. Two different eclipse observations covered 1100–1600 Å and 2250–3300 Å. In the far‐UV range, emission lines of atomic sulfur and oxygen from Io's atmosphere (similar to those previously detected with IUE) have been observed from Io in sunlight, and the spatial extent of the emitting region has been resolved for the first time: this is 0.5–1 Io radii (RIo) above the surface. The emission lines are typically 1 kR in brightness while Io is in sunlight, and decrease to a few hundred Rayleighs within 20 min or less of Io's passing into shadow. If the emissions are produced in Io's ionosphere, the decrease in shadow appears consistent with the collisional slowing and recombination of photoelectrons in 100–1000 s, with recombination an important quenching process if the dominant ion is molecular (i.e., SO2+). By contrast, the impact of corotating torus electrons is expected to continue when Io is in shadow. If impact by torus plasma dominates the emission, the decrease in shadow may be due to surface SO2 condensation, with the residual emission in shadow due either to plasma impact of gas above the hot volcanic calderas or electron impact on S and O. In the near‐UV range, we have not detected any airglow emissions from Io's atmosphere in shadow, with the main limitation being a high level of scattered light from Jupiter. We derive a 3σ upper limit to the 2560 Å SO emission feature of 1 kR, which is close to what is expected from electron impact on SO2 based on the observed brightness of the FUV S and O lines in shadow. A high signal‐to‐noise spectrum of Io's albedo in sunlight reveals a spectral shape similar to laboratory spectra of SO2 frost reflectivity, and the relative albedo spectrum changed as Io passed into eclipse and part of the disk was in shadow. No specific SO2 gas absorption features appear in the albedo spectrum, although there could be substantial gas absorption near 2800 Å if the individual lines are narrow and saturated. Finally, we present preliminary models for the near‐UV spectrum of Io as functions of SO2 frost areal coverage and SO2 gas density.