bluuebunny/crossref_metadata_2025 huggingface dataset:
A three‐dimensional synthesis study of δ18O in atmospheric CO2: 2. Simulations with the TM2 transport model
Authors: Ciais Philippe , Tans Pieter P. , Denning A. Scott , Francey Roger J. , Trolier Michael , Meijer Harro A. J. , White James W. C. , Berry Joseph A. , Randall David A. , Collatz G. James , Sellers Piers J. , Monfray Patrick , Heimann Martin
Published: February 2004

In this study, using a three‐dimensional (3‐D) tracer modeling approach, we simulate the δ18O of atmospheric CO2. In the atmospheric transport model TM2 we prescribe the surface fluxes of 18O due to vegetation and soils, ocean exchange, fossil emissions, and biomass burning. The model simulations are first discussed for each reservoir separately, then all the reservoirs are combined to allow a comparison with the atmospheric δ18O measurements made by the National Oceanic and Atmospheric Administration‐University of Colorado, Scripps Institution of Oceanography‐Centrum Voor Isotopen Onderzoek (United States‐Netherlands) and Commonwealth Scientific and Industrial Research Organisation (Australia) air sampling programs. Insights into the latitudinal differences and into the seasonal cycle of δ18O in CO2 are gained by looking at the contribution of each source. The isotopic exchange with soils induces a large isotopic depletion over the northern hemisphere continents, which overcomes the concurrent effect of isotopic enrichment due to leaf exchange. Compared to the land biota, the ocean fluxes and the anthropogenic CO2 source have a relatively minor influence. The shape of the latitudinal profile in δ18O appears determined primarily by the respiration of the land biota, which balances photosynthetic uptake over the course of a year. Additional information on the phasing of the terrestrial carbon exchange comes from the seasonal cycle of δ18O at high northern latitudes.
Noctilucent cloud observed in late April at South Pole Station: Temperature anomaly or meteoritic debris?
Authors: Warren Stephen G. , Thomas Gary E. , Hernandez G. , Smith Roger W.
Published: February 2004

A sunlit cloud was observed near the horizon at South Pole Station (90°S), four months after summer solstice in 1992, at a solar depression angle of 14.6°. The angular location of the transition from sunlit to twilit cloud in the photograph establishes the cloud height at about 80 km. The cloud extended horizontally at least from 81° to 85°S and from 40°W to 20°E. The probable origin of this cloud by formation of water‐ice crystals near the mesopause suggests that mesospheric temperatures occasionally deviate by at least 70 K from their climatological means. An alternative explanation that the cloud was a debris cloud formed by disintegration of a reentering man‐made satellite is ruled out. A debris cloud from an entering meteoroid is a possible explanation but would be unprecedented. Hydroxyl airglow emissions at the south pole in May give a frequency of 1% for mesopause temperatures below 155 K, consistent with the rarity of out‐of‐season sightings of noctilucent clouds in Antarctica.
What role do type I polar stratospheric cloud and aerosol parameterizations play in modelled lower stratospheric chlorine activation and ozone loss?
Authors: Sessler J. , Good P. , MacKenzie A. R. , Pyle J. A.
Published: February 2004

The chlorine activation and subsequent ozone loss of the northern winter lower stratosphere have been modelled using different schemes for type I polar stratospheric clouds (PSCs) and sulphate aerosols. Type I PSCs were assumed to consist of either nitric acid trihydrate (NAT) at equilibrium, supercooled ternary solutions (STS) at equilibrium, or to follow a hysteresis cycle between frozen and liquid particles depending on the temperature history. The sulphate aerosol was assumed to be present as either liquid binary H2SO4/H2O aerosol (LBA) or as solid sulphuric acid tetrahydrate (SAT). Our box model integrations show that NAT and STS, representing the upper and lower limits of lower stratospheric chlorine activation, respectively, appear to destroy ozone equally efficiently after a cold PSC event (Tmin ≤ 190K at 50 mbar). For higher minimum temperatures, up to the equilibrium NAT point, there is significantly more ozone loss in the NAT scheme than in the STS scheme. On NAT, chlorine is activated directly by ClONO2 + HCl → 2Cl + HNO3, whereas on STS, indirect activation by ClONO2 + H2O → HOCl + HNO3 followed by HOCl + HCl → 2Cl + H2O, dominates. During the processing period, the indirect activation on STS will produce a temporary peak in HOCl. Box model integrations also show that direct chlorine activation is faster on SAT than on LBA, yielding significantly more ozone loss in air parcels which remain below the SAT melting point (215–220 K). Our single‐layer chemical transport model simulations (θ = 465K) of the lower stratospheric chlorine activation during Arctic winter 1994/1995 show that chlorine is activated more quickly on NAT than on STS. However, in mid December 1994, when temperatures are low enough for substantial STS particle growth, maximum active chlorine becomes similar in both schemes and remains similar until the end of January 1995. A model integration which includes SAT produces up to 200 parts per trillion by volume more ClOx, inside the polar vortex during Arctic winter 1994/1995, than a model integration which includes LBA. The high melting point of SAT means that it may contribute to midlatitude ozone loss when filaments of processed air are shed by the vortex. For example, a model integration shows that air peeling off the Arctic vortex on February 14, 1995, contains 10% more ClOx at middle latitudes in an integration that includes SAT formation in a hysteresis scheme, than in an integration that includes LBA. The major differences in ozone loss predicted by the model PSC schemes occur inside the polar vortex. The largest differences in ozone at 465 K inside the vortex at the end of March 1995, up to 500 parts per billion by volume, are found between the equilibrium NAT and STS schemes. Ozone values in the hysteresis schemes are intermediate between those of the NAT and STS schemes. The inclusion of SAT in a hysteresis scheme des not have a major global effect.
Long‐term daily monitoring of Saharan dust load over ocean using Meteosat ISCCP‐B2 data: 1. Methodology and preliminary results for 1983–1994 in the Mediterranean
Authors: Moulin C. , Guillard F. , Dulac F. , Lambert C. E.
Published: February 2004

In this paper we describe a method to perform an accurate long‐term monitoring of the optical thickness and mass column density of airborne desert dust over the Atlantic and the Mediterranean using Meteosat wideband solar (visible (VIS) plus near infrared) sensor. The dust load is retrieved using aerosol models and an Earth‐atmosphere radiative transfer model. The method focuses on multiyear (from 1983 to 1994) daily retrieval of the atmospheric dust load using Meteosat low‐resolution images prepared for the International Satellite Cloud Climatology Project (B2 format). We account for the variable calibrations, radiometric sensitivities, and spectral bands of the successive sensors (Meteosat 2 to Meteosat 5) as well as for the presence of marine background and stratospheric aerosols. We discuss the sensitivity of the method to different factors, and its accuracy is assessed in a companion paper. The results obtained include the daily geographical distribution of the dust load and the temporal variation of the dust load over marine areas. We illustrate and briefly discuss the results for the western Mediterranean and particularly for the Dynamique des Flux Atmosphériques en Méditerranée (DYFAMED) marine station in the Ligurian Sea. The dust transport mainly takes place during summer in this area. More than half a million metric tons of suspended dusts are occasionally observed over the western Mediterranean, and we observed an average of 16 dust events per year. At DYFAMED station the 11.5‐year mean dust optical thickness is 0.11, with annual means ranging from 0.055 in 1985 to 0.19 in 1992.
Vertical stratification of tropical cloud properties as determined from satellite
Authors: Sheu Rong‐Shyang , Curry Judith A. , Liu Guosheng
Published: February 2004

A new retrieval scheme is developed to infer tropical cloud properties and vertical structure, including liquid and ice water content, cloud top and base, and cloud layering. The retrieval scheme utilizes a cloud classification scheme that uses both International Satellite Cloud Climatology Project (ISCCP) cloud top temperature and a microwave index from the special sensor microwave/imager (SSM/I). Different cloud classes have different allowed numbers of cloud layers. The retrieval scheme also incorporates findings from observational studies. When multiple liquid layers are judged to be possible, a “cloudiness likelihood” parameter is used to determine the priority for the presence of liquid layer at each level, based on the European Centre for Medium‐Range Weather Forecasts analyzed relative humidity field. Cloud liquid water path is determined using a microwave satellite retrieval. In case of multiple liquid layers, the liquid water path is partitioned and assigned to each liquid layer in proportion to the adiabatic liquid water path in each layer. Depending on the cloud class, ice water paths are determined using one of the following methods: (1) ISCCP ice optical depth; (2) a microwave ice retrieval that uses ice scattering signals at high SSM/I frequencies; and (3) a residual method that infers ice from the difference between a “virtual” liquid water path derived from ISCCP total optical depth and the true liquid water path determined from SSM/I. The retrieved cloud layering is indirectly validated using cloud cooccurrence climatology from surface observations. The cloud base retrieval is compared with lidar measurements obtained during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment.
Seasonal variation of middle atmospheric CH4 and H2O with a new chemical‐dynamical model
Authors: Summers Michael E. , Siskind D. E. , Bacmeister J. T. , Conway R. R. , Zasadil S. E. , Strobel D. F.
Published: February 2004

A new zonally averaged, chemical‐dynamical model of the middle atmosphere is used to study the processes which control the distributions and seasonal variability of CH4 and H2O. This model incorporates a nondiffusive, nondispersive advection scheme, a time‐dependent linear model of planetary wave drag and horizontal mixing (Kyy), a new parameterization of gravity wave drag and vertical mixing (Kzz), and an explicit treatment of LTE (local thermodynamic equilibrium) and non‐LTE IR cooling. Model chemistry is calculated using a Newton‐Raphson iterative scheme, which allows consistent simulations of species with highly nonuniform chemical lifetimes. In this study we focus on the sensitivity of model CH4 and H2O to the magnitude of tropospheric latent heat release, planetary wave and gravity wave activity, and the methane oxidation rate. Model results show that in the tropical stratosphere their vertical distributions are strong functions of both the methane oxidation rate and the ascent rate, the latter driven by a combination of tropospheric latent heat release and atmospheric drag. At low latitudes HALOE observations and model results both show conservation of “potential H2” (2×CH4+H2O) below ∼50 km. However, the conservation of potential H2 from HALOE observations breaks down above ∼55 km, while the model shows conservation well into the middle mesosphere (∼70 km). This may suggest serious inadequacies in our understanding of the photochemistry of water vapor and mesospheric HOx, in particular those processes which control the partitioning of H2 and H2O. At high latitudes, H2O model/data comparisons suggest that horizontal mixing is important in determining the observed latitudinal gradient in mesospheric water vapor. We also find that inside the polar winter vortex, while the strength of tropical latent heat forcing and planetary wave drag influence the descent rate, both horizontal mixing and the methane photochemistry play important roles in determining the CH4 mixing ratio. Finally, we suggest that the observed interhemispheric asymmetry in the seasonal cycle of mesospheric H2O may be linked to larger values of Kzz in the southern winter mesosphere. This represents a key difference between mesospheric and stratospheric tracer transport. In the stratosphere, greater net unmixed descent in the southern hemisphere directly translates into lower tracer values relative to the northern hemisphere, while mesospheric tracer transport shows the opposite behavior.
Production and decay of ClNO2 from the reaction of gaseous N2O5 with NaCl solution: Bulk and aerosol experiments
Authors: Behnke Wolfgang , George Christian , Scheer Volker , Zetzsch Cornelius
Published: February 2004

The chemistry of N2O5 on liquid NaCl aerosols or bulk NaCl solutions was studied at 291 K by aerosol smog chamber and wetted‐wall flow tube experiments. The uptake of N2O5 on deliquescent aerosol was obtained to be (3.2±0.2)×10−2 (1σ error) from the aerosol experiments. In the wetted‐wall flow tube we observed that nitryl chloride (ClNO2) is the main product of the reaction at NaCl concentrations larger than approximately 0.5 M and almost the only product at concentrations larger than 1 M. The ClNO2 yield does not depend linearly on the NaCl concentration, especially at small sodium chloride concentrations (i.e., smaller than 1 M). It appeared that a simple mechanism where N2O5 undergoes two reaction channels (hydrolysis and reaction with Cl−) is unable to explain the observed concentration dependence of the product yield. We propose that N2O5 dissociates to NO2+ and NO3− (rate constant kl>104 s−1) mainly. The directly hydrolysis of N2O5 (k3[H2O]) is less than 20% of the total reaction. NO2+ reacts with water to form 2H+ and NO3− (k5) or with Cl− to form ClNO2 (k4). Neglecting the influence of ionic strength we evaluate k4/k5 to be 836±32 (1σ error). Using the wetted‐wall flow tube technique, we studied the uptake of nitryl chloride by aqueous solutions containing NaCl. We observed that the uptake coefficient γ decreased from (4.84±0.13)×10−6 on pure water to (0.27±0.02)×10−6 on a 4.6 M NaCl solution. The sharp decrease of γ with increasing salt concentrations is evidence of reversible hydrolysis. ClNO2 dissociates to Cl− + NO2+(k6). In the absence of Cl− we evaluate H ⋅ k61/2 to be 0.44±0.01 mol L−1 atm−1 s−1/2. Finally, we discuss that atomic Cl from photolysis of ClNO2 may play a role in the marine boundary layer at high northern latitudes.
On the correlation between ozone and potential vorticity for large‐scale Rossby waves
Authors: Riishøjgaard Lars Peter , Källén Erland
Published: February 2004

We study the relationship between ozone and potential vorticity in the region around the tropopause using a linear, quasi‐geostrophic model for large‐scale Rossby waves. The ozone field at the start of the simulations is assumed to be horizontally uniform and to have zones of constant mixing ratios in the troposphere and middle stratosphere separated by a zone with a sharp vertical ozone gradient above the tropopause. We find that the observed correlations between potential vorticity and ozone column values agree well with the characteristics of vertically propagating Rossby waves. We also show that realistic potential vorticity anomalies lead to disturbances of the total ozone field in the model that are equal in magnitude to what is observed during the winter in midlatitudes. For trapped waves there is little correlation between total ozone and potential vorticity. Furthermore, we discuss some implications for the assimilation of total ozone data from satellites in general circulation models.
Effect of Pinatubo aerosols on stratospheric NO
Authors: Kondo Y. , Sugita T. , Salawitch R. J. , Koike M. , Deshler T.
Published: February 2004

Concentrations of nitric oxide (NO), total reactive nitrogen (NOy), O3, and aerosol were measured between 14 and 32 km on balloon platforms launched from Aire sur l'Adour (44°N, 0°W), France, on October 20 and November 6, 1992. Aerosol surface area has been deduced from the observed concentrations of aerosols with radii ranging from 0.18 to 0.7 μm. On these days the surface area was enhanced due to the eruption of Mount Pinatubo, which occurred in June 1991. The data set is used to investigate the effect of heterogeneous reactions on sulfuric acid aerosol reducing NOx. A diurnal photochemical model, which takes into account heterogeneous chemistry, is used to calculate the changes in the partitioning of reactive nitrogen in the altitude region between 18 and 32 km. The observed values of NO and NOx/NOy ratio are significantly lower than those calculated by the model without taking into account heterogeneous chemistry. The degree of reduction of NOx. by heterogeneous reaction was observed to vary sensitively with surface area for values lower than 2 μm2cm−3. The net reduction of NOx by aerosol tended to saturate at surface area larger than 4 μm2cm−3. Observations of NO and NOx/NOy, are shown to be in generally good agreement with theoretical values found using the same model but including heterogeneous chemistry, indicating that NOx was reduced primarily by the hydrolysis of N2O5 on sulfuric acid aerosol.
Air‐sea interactions over Terra Nova Bay during winter: Simulation with a coupled atmosphere‐polynya model
Authors: Gallée Hubert
Published: February 2004

A preliminary simulation of the Terra Nova Bay polynya has been performed with a coupled atmosphere–polynya model. The atmospheric model is a hydrostatic primitive equations model that has been validated previously by a simulation of the strong katabatic winds observed in that area. The polynya model includes a representation of the free drift of frazil ice and simple sea‐ice dynamics and thermodynamics. Two and three‐dimensional experiments have been performed under polar night conditions. Two‐dimensional experiments show that an open (warm) water area influences significantly the atmospheric circulation in the antarctic coastal zone: an additional ice‐breeze effect is simulated and is responsible for the strenghthening of the katabatic winds near the coast. Because of the important temperature difference between the continental air and the ice‐free ocean (up to 40°C), strong surface heat fluxes are simulated over the polynya. Finally, a three‐dimensional experiment has been performed. The integration domain includes Terra Nova Bay. The polynya observed in that region is well simulated. It is found that heat losses from the polynya surface are stronger than previously thought but are probably constrained by the idealized representation of frazil ice, which is assumed to be uniform in each grid box. This stresses the need for having a better knowledge of frazil ice evolution in large polynyas.
A 200‐year 210Pb record from Greenland
Authors: Dibb Jack E. , Clausen Henrik B.
Published: February 2004

A continuous profile of 210Pb activity extending back to 1766 has been developed for a firn/ice core collected at Site D in central Greenland in 1984. Unexpectedly high activities of 210Pb were found at the base of this core (0.032 pCi kg−1 in samples more than 200 years old), calling into question the common assumption that supported 210Pb can be neglected when constructing chronologies in glacial snow and ice. It is problematic to assert that all of the 210Pb measured at depth should be attributed to the supported fraction, given previous estimates of dust loading in Greenland ice cores. However, even if an estimated constant value of 0.032 pCi supported 210Pb kg−1 is subtracted from the measured values to estimate excess 210Pb, the 210Pb chronology for Site D yields ages that are significantly younger (mean accumulation rate too high) than an independent depth‐age scale based on annual layer counting. It is apparent that the flux of excess and/or supported 210Pb to this site must have decreased over the past 2 centuries, with decreasing trends in both fractions most likely. Previously published 210Pb profiles for cores from Summit and Dye 3, Greenland, show similar trends, which had been interpreted as decreasing fluxes of excess 210Pb only. For all three sites, it is not possible to separate variations in the fluxes of the excess and supported fractions of 210Pb, but variations in the total 210Pb flux will impact 210Pb‐based chronologies generally if these variations have not been restricted to the Greenland ice sheet.
Influence of Antarctic denitrification on two‐dimensional model NOy/N2O correlations in the lower stratosphere
Authors: Nevison C. D. , Solomon S. , Garcia R. R. , Fahey D. W. , Keim E. R. , Loewenstein M. , Podolske J. R. , Gao R. S. , Wamsley R. C. , Donnelly S. G. , DelNegro L. A.
Published: February 2004

The mechanisms responsible for latitudinal and seasonal variations in the stratospheric NOy/N2O correlation, represented by the effective NOy yield from N2O loss, or FNOy, are explored using the Garcia‐Solomon two‐dimensional model. The model is run with and without Antarctic denitrification. Model results are compared to in situ NOy/N2O measurements taken onboard the NASA ER‐2 high‐altitude aircraft in the lower stratosphere during the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft campaign, and to global‐scale measurements taken onboard the Upper Atmosphere Research Satellite (UARS) from 1992 to 1993. The southern hemisphere midlatitude seasonal cycle observed by the ER‐2 and the latitudinal gradients observed by UARS are consistent with the results of the denitrified model, although some aspects of the model results are sensitive to prescribed and/or calculated horizontal diffusion coefficients. The consistency with observations supports the model's prediction of a seasonal cycle in which FNOy, increases at southern midlatitudes during winter due to descent of FNOy‐enriched air from above and decreases in spring due to mixing with FNOy‐depleted air from the denitrified polar vortex. Antarctic denitrification appears to affect midlatitudes mainly by a one‐time dilution of the polar vortex following the final warming rather than by flow‐through vortex processing during the winter. Because of the high concentrations of NO3, at polar latitudes before denitrification a large fraction of total stratospheric NOy can be removed by a one‐time dilution of the denitrified polar vortex. The nondenitrified model results generally do not agree well with observations, suggesting that denitrification strongly influences latitudinal and seasonal variations in FNOy in the southern hemisphere.
Evaluation of the pseudo‐spherical approximation for backscattered ultraviolet radiances and ozone retrieval
Authors: Caudill T. R. , Flittner D. E. , Herman B. M. , Torres O. , McPeters R. D.
Published: February 2004

The pseudo‐spherical approximation for solving the radiative transfer equation has been used for many years in an attempt to account for the sphericity of the atmosphere. However, even with this “correction” there has been some uncertainty about the accuracy of the radiances calculated by using this method at large solar zenith angles. With a new model for numerically solving the radiative transfer equation in a spherical atmosphere the accuracy of the pseudo‐spherical approximation can now be evaluated. The comparisons between the pseudo‐spherical and spherical models presented in this paper for backscattered ultraviolet (BUV) radiances show virtually no difference for the nadir direction. The off‐nadir radiances, however, show large differences (±8%) for a solar zenith angle of 85° and depend on the solar zenith angle and azimuth angle as well as the view angle. These differences increase rapidly at larger solar zenith angles to nearly 20% at 88°. This disagreement is primarily caused by the incorrect attenuation of the solar radiation along the observers' line of sight in the pseudo‐spherical method. Differences are also exhibited in the multiple‐scatter component but are generally much smaller than the solar attenuation term. In general, the resultant error in total ozone estimation can be as large as 6% but is less than 1% for the Nimbus 7 total ozone mapping spectrometer.
Validation of operational numerical analyses in Antarctic latitudes
Authors: Cullather Richard I. , Bromwich David H. , Grumbine Robert W.
Published: February 2004

Available rawinsonde, automatic weather station (AWS), ship, and synthesized long‐term observations are used to evaluate the Antarctic numerical analyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the U.S. National Centers for Environmental Prediction (NCEP) from 1985 to 1994. Twice‐daily variations in the ECMWF surface pressure analyses compare closely with AWS units of the U.S. Antarctic Program and ship observations. The NCEP analyses over the same period show substantial improvement, particularly during the period 1985–1990. Surface air temperatures and winds do not agree so closely, which may result from analyses error, the localized nature of the fields, or a combination. Validation of the analyses standard pressure level fields using available rawinsonde data reveal a general long‐term decrease in RMS errors with time for both analyses. RMS errors in NCEP 200 hPa geopotential heights of over 200 geopotential meters (gpm) for central plateau stations are evident only prior to May 1986. However, a significant upward trend from 1989 to 1993 in geopotential height RMS differences is apparent at several levels. The ECMWF analyses are generally found to be superior and offer a reasonable depiction of the broadscale atmospheric circulation; however, deficiencies in midtropospheric temperatures and lower tropospheric winds are evident. Comparisons of ship data from individual cruises of the S.A. Agulhas and the R/V Nathaniel B. Palmer to the numerical analyses reveal substantial agreement for pressure and temperature variables. Observations from the Nathaniel B. Palmer in the Amundsen and Bellingshausen Seas were not available to the weather forecasting centers. Results presented here indicate that a large amount of the available data is being incorporated and that large deficiencies identified in previous studies are being addressed, although areas of concern remain. Deficiencies in comparisons to specific stations are common to both analyses, implying continued communications problems. In particular, grid values corresponding to individual stations including the now‐closed Leningradskaya base and Mirnyy are found to be conspicuously deficient at the 200 hPa level for both analyses.
Variability of precipitation over the coastal western Antarctic Peninsula from synoptic observations
Authors: Turner J. , Colwell S. R. , Harangozo S.
Published: February 2004

Observations of precipitation events at Faraday and Rothera Stations are analyzed to investigate the spatial and temporal variability of precipitation along the western coastal (Pacific) side of the Antarctic Peninsula. The record of observations made at Faraday since 1956 show a statistically significant increase in the number of winter‐season precipitation events. During this season, there are now, on the average, almost 50% more reports of precipitation than during the 1950s. On a year‐to‐year basis the number of precipitation events is not correlated with the mean surface temperature on the western side of the Antarctic Peninsula but is dependent on synoptic weather system activity. The annual total number of precipitation events at Rothera is also increasing, but because the length of the record is relatively short, this is not statistically significant. The semiannual cycle in the latitudinal location and depth and position of the circumpolar trough is reproduced in the record of precipitation events at both Faraday and Rothera. It is argued that the systematic increase in the number of precipitation events at Faraday since the 1950s is associated with changes in the depression tracks across the Bellingshausen Sea, with an increase in the number of depressions approaching from outside the Antarctic rather than from the west.
Surface wind fields of Antarctic mesocyclones derived from ERS 1 scatterometer data
Authors: Marshall Gareth J. , Turner John
Published: February 2004

The effectiveness of ERS 1 scatterometer data as a tool for studying the wind fields of Antarctic mesocyclones is analyzed by using 1 year's observations of these systems derived from satellite imagery encompassing the Antarctic Peninsula and Bellingshausen and Weddell Seas. It is shown that the scatterometer processing scheme utilized can affect the resultant wind fields, particularly the accuracy of the external forecast winds used for “meteorological ambiguity removal.” Very few of the mesocyclones (9%) were “captured” by the scatterometer data because (1) ∼60% of the vortices did not form over the open ocean (25% of those that did were included in the scatterometer data) and (2) the narrow scatterometer swath results in a poor temporal resolution that is less than ideal for observing small‐sized, short‐lived Antarctic mesocyclones over the Southern Ocean. Close agreement between the derived wind fields and those predicted by a simple model suggests that a mesocyclone may be considered as a vorticity anomaly superimposed on a uniform flow. Most systems had a surface circulation, varying from a slight deviation from the geostrophic flow to a closed circulation; however, 25% of mesocyclones did not exhibit a surface circulation. Four case studies are used to illustrate the different types of observed circulation. Derived maximum cyclonic relative vorticity values (those most negative in the southern hemisphere) varied between −100 and −400×10−6 s−1, an order of magnitude lower than that calculated for an Arctic mesocyclone. The scatterometer wind field data represent an important new tool for studying Antarctic mesocyclones but need to be used in conjunction with sensors having a higher frequency of coverage to allow multitemporal analyses of such systems throughout their development.
Aerosol‐induced chemical perturbations of stratospheric ozone: Three‐dimensional simulations and analysis of mechanisms
Authors: Zhao Xuepeng , Turco Richard P. , Kao C.‐Y. Jim , Elliott Scott
Published: February 2004

An atmospheric general circulation model is coupled with a stratospheric photochemical model to simulate the chemical/dynamical perturbations associated with background and volcanically perturbed aerosols in the lower stratosphere. The present work focuses on short‐term anomalies at middle and high latitudes in the northern hemisphere, where large ozone depletions have been observed in late winter and early spring, particularly following the eruption of Mount Pinatubo. Five fully coupled simulations are analyzed, corresponding to a control case with only gas phase chemistry, and cases including heterogeneous chemistry on background aerosols, on El Chichón‐type, and on Pinatubo‐type aerosols. It is found that heterogeneous reactions occurring on sulfate aerosols (background or postvolcanic) can strongly perturb the chemical partitioning in the lower stratosphere, leading to significant ozone depletion through enhanced chlorine, bromine, and odd‐hydrogen catalytic cycles. In the Arctic lower stratosphere, the maximum zonal and March monthly mean local ozone reductions (with respect to the control case) can exceed 15% for the background aerosol case, 40% for the El Chichón case, and 50% for the Pinatubo case. The corresponding zonal mean total column ozone decreases are roughly 5% and 15% for the background and volcanic aerosol cases, respectively. In the most extreme case tested (post‐Pinatubo), a large ozone depletion below 30 mbar is offset to some extent by an ozone increase above that level. The results of a sensitivity study (in which the aerosols are distributed closer to the tropics, as might occur early after an eruption at low latitude) lead to relatively small total ozone depletions at northern high latitudes, and small ozone increases in the tropical lower stratosphere. The reduced impact on total ozone at high latitudes is associated both with local ozone increases above 30 mbar and with poleward transport of enhanced ozone from the tropical lower stratosphere. The ozone increase at low latitudes is the net result of compensating changes in the catalytic destruction cycles involving odd‐nitrogen and chlorine species activated by heterogeneous processes at the low temperatures and abundant sunlight found near the tropical tropopause. Our simulations indicate that ozone variations triggered by volcanic injections of aerosols depend on the global distribution as well as the abundance of the particles and their evolution over time, and on the initial dynamical‐radiative‐chemical state of the atmosphere, which itself exhibits large seasonal and interannual variability.
Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) Earth limb spectral measurements, calibration, and atmospheric O3, HNO3, CFC‐12, and CFC‐11 profile retrieval
Authors: Bingham G. E. , Zhou D. K. , Bartschi B. Y. , Anderson G. P. , Smith D. R. , Chetwynd J. H. , Nadile R. M.
Published: February 2004

During the Space Transportation System 39 (STS 39) flight of April 28 to May 6, 1991, the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) measured spectral and spatial (“Earth limb scan”) distributions of the atmospheric infrared (IR) emissions using a Michelson interferometer. The IR spectral radiant emissions from the greenhouse gases were collected at a shuttle altitude of 260 km in the 9–13 μm atmosphere infrared window. Before and after the flight, the response of CIRRIS 1A to the IR spectral emission sources was calibrated using absolute and spectral source types. The Fast Atmospheric Signature Code 3, which used the HITRAN92 database and predetermined temperature‐pressure profiles from the National Meteorological Center, was used in an onion‐peeling routine to retrieve gas concentrations from absolutely calibrated spectral data (moderate resolution ∼1.0 cm−1). Vertical profiles of O3, HNO3, CFC‐12, and CFC‐11 are presented. An error analysis is presented to show the quality of the measured spectral data and the accuracy of these retrieval results. The concentrations of CFC‐11 (3.0×10−4 ppmv) and CFC‐12 (4.9×10−4 ppmv) in the tropopause region are consistent with a global flux increment rate of about 5% yr−1. The observed concentrations of HNO3 are consistent with previous reports for a relatively clean stratosphere.
Equatorial dynamics observed by rocket, radar, and satellite during the CADRE/MALTED campaign: 1. Programmatics and small‐scale fluctuations
Authors: Goldberg Richard A. , Lehmacher Gerald A. , Schmidlin Frank J. , Fritts David C. , Mitchell J. D. , Croskey C. L. , Friedrich M. , Swartz W. E.
Published: February 2004

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alcântara rocket site in northeastern Brazil as part of the International Guará Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3°S) and magnetic (∼0.5°S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike‐Orion payloads designed to investigate small‐scale turbulence and irregularities were coordinated with 20 meteorological falling‐sphere rockets designed to measure temperature and wind fields during a 10‐day period. These in situ measurements were coordinated with observations of global‐scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground‐based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike‐Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50‐MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike‐Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral‐atmospheric turbulence between 85 and 90 km. Furthermore, falling‐sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.
Radar observations of gravity waves over Jicamarca, Peru, during the CADRE campaign
Authors: Riggin Dennis M. , Fritts David C. , Fawcett Clinton D. , Kudeki Erhan , Hitchman Matthew H.
Published: February 2004

We present results obtained with the mesosphere‐stratosphere‐troposphere (MST) radar at Jicamarca, Peru, from three 10‐day experiments in January 1993, March 1994, and August 1994. Horizontal and vertical velocities were measured over ranges spanning the lower part of the stratosphere and most of the mesosphere. In the stratosphere, the fluctuating part of the wind field was found to be dominated by inertia‐gravity waves. Sinusoids of different period were fit to the velocity time series using a least squares procedure. The dominant periods of the inertia‐gravity wave motions were found to be 1.5 days for the January 1993 experiment and 2.1 days for the August 1994 experiment. For the January 1993 experiment, the amplitudes and phases of the inertia‐gravity wave oscillations were extracted for the vertical as well as the horizontal components. The vertical amplitude of the 1.5‐day period wave was small (<0.1 ms−1), but measurable with the Jicamarca radar. The intrinsic periods of the inertia‐gravity waves were inferred from the fits using two different methods. The first method predicted the intrinsic period using the orbital ellipses traced out in time by fits to the horizontal winds. The second method used information taken from the vertical as well as the horizontal fits. The values of intrinsic period made using the second method were found to have much less scatter than the values inferred solely from the orbital ellipses. The momentum flux estimates in both the stratosphere and mesosphere were found to depend significantly on the exact methodology used. A technique was adopted whereby estimates were formed only when radial velocities were measured simultaneously on both beams of a coplanar beam pair. Most of the total wave stress was usually contributed by waves at periods ≥4 hours in the stratosphere and ≥1 hour in the mesosphere. In the stratosphere, localized layers of enhanced momentum flux were sometimes observed. The obvious anticorrelation between the shear of the mean wind and the momentum flux in these layers suggests that they were caused by in situ generation of waves by the Kelvin‐Helmholtz instability, rather than gravity waves propagating from lower levels. At short periods, momentum flux spectra in the stratosphere and mesosphere showed numerous positive and negative peaks. A correlation analysis revealed that the high‐frequency peaks were associated with discrete wave packets. The short‐scale waves associated with these packets were fairly isotropic in their direction of propagation, and due to cancellation they contributed little net momentum.
Mixing of polar vortex air into middle latitudes as revealed by tracer‐tracer scatterplots
Authors: Waugh D. W. , Plumb R. A. , Elkins J. W. , Fahey D. W. , Boering K. A. , Dutton G. S. , Volk C. M. , Keim E. , Gao R.‐S. , Daube B. C. , Wofsy S. C. , Loewenstein M. , Podolske J. R. , Chan K. R. , Proffitt M. H. , Kelly K. K. , Newman P. A. , Lait L. R.
Published: February 2004

The occurrence of mixing of polar vortex air with midlatitude air is investigated by examining the scatterplots of insitu measurements of long‐lived tracers from the NASA ER‐2 aircraft during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE, April, May 1993; northern hemisphere) and the Airborne Southern Hemisphere Ozone Experiment / Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA, March‐October 1994; southern hemisphere) campaigns. The tracer‐tracer scatterplots from SPADE form correlation curves which differ from those measured during previous aircraft campaigns (Airborne Antarctic Ozone Experiment (AAOE), Airborne Arctic Stratospheric Experiments I (AASE I) and II (AASE II)). It is argued that these anomalous linear correlation curves are “mixing lines” resulting from the recent mixing of polar vortex air into the middle latitude environment. Further support for this mixing scenario is provided by contour advection calculations and calculations with a simple one‐dimensional strain‐diffusion model. The scatterplots from the midwinter deployments of ASHOE/MAESA are consistent with those from previous midwinter measurements (i.e., no mixing lines), but the spring CO2:N2O scatterplots form altitude‐dependent mixing lines which indicate that air from the vortex edge region (but not from the inner vortex) is mixing with midlatitude air during this period. These results suggest that at altitudes above about 16 km the mixing of polar vortex air into middle latitudes varies with season: in northern and southern midwinter this mixing rarely occurs, in southern spring mixing of vortex‐edge air occurs, and after the vortex breakup mixing of inner vortex air occurs.
Season‐long measurement of carbon dioxide exchange in a boreal fen
Authors: Suyker Andrew E. , Verma Shashi B. , Arkebauer Timothy J.
Published: February 2004

Atmospheric CO2 exchange was measured in a boreal minerotrophic patterned fen in central Saskatchewan, Canada, using the eddy correlation technique. The study was conducted from mid‐May to early October 1994, as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). Herbaceous vegetation was dominated by buckbean (Menyanthes trifoliata) and various species of sedges (Carex and Eriphorum spp). Bog birch (Betula pumila) and willow species (Salve spp.) were dominant shrubs. Brown mosses were the predominant nonvascular vegetation. Canopy photosynthesis approached light saturation for PAR (photosynthetically active radiation) above 1000–1200 μmol m−2 s−1. High temperature (>20°C) and vapor pressure deficit (>1.5 kPa) decreased photosynthesis significantly. On cool days with low vapor pressure deficit, canopy photosynthesis tended to follow incident PAR. The diurnal pattern of canopy photosynthesis exhibited a midmorning maximum on days with high temperature and vapor pressure deficit. Canopy photosynthesis reached a peak of 0.59 mg CO2 m−2 s−1 (midday) in early July, corresponding to the period of maximum leaf area index. Another increase in photosynthesis occurred in late August as the canopy recovered from a brief rise in water table that inundated some of the leaf area. The daily net CO2 exchange showed significant day‐to‐day variability resulting from changes in environmental conditions. The integrated value of the net ecosystem‐CO2 exchange during the measurement period (mid‐May to early October) was about 88 g C m−2. Consistent with the high productivity and high water table, this fen exhibited magnitudes of CO2 exchange larger than other northern wetlands reported in the literature.
A correction for total ozone mapping spectrometer profile shape errors at high latitude
Authors: Wellemeyer C. G. , Taylor S. L. , Seftor C. J. , McPeters R. D. , Bhartia P. K.
Published: February 2004

The total ozone mapping spectrometer (TOMS) ozone measurement is derived by comparing measured backscatter ultraviolet radiances with theoretical radiances computed using standard climatological ozone profiles. Profile shape errors occur in this algorithm at high optical path lengths whenever the actual vertical ozone distribution differs significantly from the standard profile used. These errors are estimated using radiative transfer calculations and measurements of the actual ozone profile. These estimated errors include a short‐term component resulting from day‐to‐day variability in profile shape that gives rise to a standard deviation of 10% in total column ozone amount, as well as a systematic error in the long‐term trend at very high solar zenith angles. The trend error resulting from the long‐term changes in the ozone profile shape is estimated using measurements from the solar backscattered ultraviolet instrument. At the maximum retrieval solar zenith angle of 88°, these calculations indicate that TOMS long‐term ozone depletions may be overestimated by 5% per decade. For trend studies that are restricted to latitudes lower than 60° (a maximum of 83° solar zenith angle), this error is reduced to no more than 1–2% per decade. Differential impact of the profile shape error at the various TOMS wavelength pairs indicates that profile shape information is present in the TOMS measurements at high solar zenith angles. An interpolation method internal to TOMS is proposed to extract this information. It improves the retrieval at high solar zenith angle, reducing the short‐term variability to a standard deviation of 5%, and essentially eliminates the long‐term error. The set of standard profiles used in the algorithm are adjusted based on an analysis of empirical orthogonal functions derived from a composite climatology of Stratospheric Aerosol and Gas Experiment II and balloonsonde profile measurements.
Precipitation water path and rainfall rate estimates over oceans using special sensor microwave imager and International Satellite Cloud Climatology Project data
Authors: Lin Bing , Rossow William B.
Published: February 2004

The liquid/ice water paths (LWP/IWP) and the rainfall rate (RR) of precipitation systems over oceans are estimated using a combination of data from the special sensor microwave/imager (SSM/I) and the International Satellite Cloud Climatology Project (ISCCP). The retrieval scheme is based on microwave radiative transfer simulations. Collocated ISCCP cloud top temperatures are used to separate warm from cold precipitating clouds: cold precipitating clouds occur much more frequently than warm precipitating clouds and produce over 80% of the precipitation, but warm precipitating clouds are not negligible in the tropics and summer midlatitudes. SSM/I data are used to identify precipitating clouds: precipitating clouds are very rare (about 5% of all locations). Estimated IWP values, with mean about 7 mg/cm2, are quite variable, ranging from as little as 5 mg/cm2 to as much as 200 mg/cm2. The mean LWP in precipitating clouds is approximately 80 mg/cm2, occasionally reaching 1000 mg/cm2. Average RR (both cold and warm) is about 1.5 mm/hr, generally larger in the tropics than in midlatitudes. RR is larger in the northern hemispheric midlatitudes than in the southern midlatitudes. The global annual cycle of precipitation is dominated by tropical variations and is in phase with boreal seasons. The largest annual total precipitation occurs in the eastern Pacific (about 5000 mm). The subtropical precipitation minima may be underestimated because drizzle does not produce strong microwave signals.