bluuebunny/crossref_metadata_2025 huggingface dataset:
On the theories of type 1 polar stratospheric cloud formation
Authors: MacKenzie A. Robert , Kulmala Markku , Laaksonen Ari , Vesala Timo
Published: February 2004

Several mechanisms for the production of polar stratospheric cloud (PSC) particles are investigated using the classical theories of nucleation and freezing and the multicomponent condensation theory. These mechanisms invoke particle compositions ranging from binary (H2SO4/H2O) solution, solid sulfuric acid tetrahydrate (SAT) and ternary (HNO3/H2O/H2SO4) solution to binary (HNO3/H2O) solution and solid nitric acid trihydrate (NAT). Empirical relations, derived from classical nucleation studies, are used to calculate the surface energies required in calculations of nucleation and freezing. Using these data, we calculate that the nucleation of nitric acid solutions or solid phases onto SAT particles is not efficient. Homogeneous freezing of SAT or NAT from ternary solutions does not occur under stratospheric conditions. Homogeneous freezing of water ice can occur at temperatures near the frost point of pure water. Heterogeneous freezing is a strong function of the contact parameter between the emergent crystal and the initiating seed particle. Heterogeneous freezing of the stratospheric aerosol to SAT and NAT at temperatures above the frost point is not ruled out by our calculations. If formed, NAT can deplete the gas phase nitric acid concentration, by condensational growth, more efficiently than ternary droplets. We conclude that the most likely route to type 1 PSC particles is via condensational growth of ternary solution droplets followed by rapid freezing to NAT, SAT, and water ice at temperatures near the ice frost point. The particles formed are then stable and can reduce nitric acid vapor pressures to the saturation vapor pressure over NAT at all temperatures below the NAT point. Such a mechanism is consistent with observations.
Dispersion properties of the flow in the southern stratosphere during winter and spring
Authors: Trounday Bruno , Perthuis Laurent , Strebelle Sebastian , Farrara John D. , Mechoso Carlos R.
Published: February 2004

The STRATEOLE project, organized by France's Centre National de la Recherche Scientifique (CNRS), will release a large number of isopycnal balloons to drift in the lower stratosphere of the southern hemisphere. In preparation for STRATEOLE this paper studies the structure and dispersion properties of the flow in the lower stratosphere at high southern latitudes during winter and spring. The approach for investigation is based on computing trajectories of fluid parcels and isopycnal balloons using the velocity field obtained on‐line during simulations with a three‐dimensional primitive‐equation model of the stratosphere and mesosphere. A scheme for computation of isopycnal balloon trajectories is devised, and a method for estimating the location of the polar night vortex edge is developed. It is found that trajectories of fluid parcels initiated well inside the vortex remain within the vortex for a period of months. A small number of fluid parcels released near the vortex edge cross this edge with about an equal number of crossings from inside to outside the vortex as from outside to inside. The isopycnal balloons show a stronger tendency to cross the vortex edge than do fluid parcels. The relative dispersion properties of the flow in the lower stratosphere are analyzed in the light of theories on two‐dimensional turbulence. It is determined that the flow inside the polar vortex can be considered as quasi two‐dimensional, isotropic, homogeneous, and stationary for a period of about 6 days. Outside the vortex the differential advection by the strong westerly flow primarily determines the balloon dispersion. The mean square separation between balloons released 2 hours apart within the vortex (70°S, 50 mbar) increases in time, following approximately (1) the Kraichnan‐Lin exponential law for small timescales and space scales (1.5–4 days, 90–150 km), (2) the Richardson‐Obukhov t3 law for intermediate timescales and space scales (7–18 days, 180–640 km), and (3) the asymptotic linear behavior found by Babiano et al. (1990), for large timescales and space scales (20–40 days, 700–1200 km).
Water vapor feedback over the Arctic Ocean
Authors: Curry J. A. , Schramm J. L. , Serreze M. C. , Ebert E. E.
Published: February 2004

Previous studies of the clear sky greenhouse effect and water vapor feedback have focused on subpolar regions. In view of modeled amplification of greenhouse warming in the Arctic we investigate the humidity characteristics, clear sky greenhouse effect and water vapor feedback in the Arctic by using 10 years of radiosonde data obtained from the Russian drifting ice island stations along with a radiative transfer model. By taking advantage of the natural variability associated with seasonal and interannual variations, we can infer the water vapor feedback from the data. Results of this study indicate that water vapor feedback over the Arctic Ocean is substantially more complex than in other regions because of the relative lack of convective coupling between the surface and the atmosphere and the different thermodynamic and radiative environment in the Arctic. In particular, the effect of water vapor on the net flux of radiation is complicated by low temperatures, low amounts of water vapor, and the presence of temperature and humidity inversions. During winter a “hyper” water vapor feedback arises from the control of ice saturation on the lower tropospheric humidity and a water vapor “window” in the rotation band at low atmospheric humidities. Implications for global warming are discussed.
Heterogeneous conversion of HCl and ClONO2 during the Arctic winter 1992/1993 initiating ozone depletion
Authors: Notholt J. , von der Gathen P. , Peil S.
Published: February 2004

Ground‐based Fourier transform infrared (FTIR) measurements, performed in the Arctic polar night using the Moon as an infrared light source, reveal already during the first half of December 1992 a considerable reduction in the amount of stratospheric HCl and ClONO2. Balloon sondes yield that in the altitude range 16–22 km an ozone reduction occurred as soon as the circulating air masses were irradiated by sunlight. Within the same altitude range several polar stratospheric cloud (PSC) events are being reported throughout the winter. Assuming that the reduction of HCl and ClONO2 had occurred in the same altitude range, where the ozone depletion and PSCs were observed, our measurements imply that almost all HCl and ClONO2 in that altitude range had disappeared. This means that the stratosphere was primed for ozone depletion very early in winter. The results confirm model studies that in the Arctic, already weak PSC events can lead to a strong conversion of chlorine reservoir compounds into active forms, initiating the ozone depletion, as soon as sunlight is available.
Moisture flux and mixing processes in the daytime continental convective boundary layer
Authors: Grossman Robert L. , Gamage Nimal
Published: February 2004

This study is used to introduce a conditional sampling technique associated with a heuristic model of the convective boundary layer (CBL) based upon top‐down, bottom‐up physical processes. A new concept of a distribution of neutral buoyancy levels associated with those two classes of physical processes is included in the CBL model. Analysis of surface, aircraft, and sounding data from June 6, 1987, during FIFE showed two periods of drying in an otherwise moistening fair weather CBL with 7 to 9 ms−1 southerly winds. One period was during the so‐called morning boundary layer transition, when the mixed layer was growing rapidly and the other during quasi‐steady state afternoon conditions. Similar drying periods were observed on June 1 and 4. On June 6, however, morning and afternoon National Center for Atmospheric Research King Air missions were specifically designed to investigate time variations in the daytime CBL. The conditional sampling technique and the CBL model are used to investigate the composition of the moisture flux and flux divergence. We conclude that the drying effect of strong surface thermals carrying upward moving moist air was substantially decreased by overturning thermals and that compensating downdrafts were the dominant process associated with the net positive flux divergence responsible for part of the observed drying during the morning transition. The remainder was inferred to be due to a combination of vertical and horizontal advection. By afternoon drying due to compensating downdrafts had ceased and was due entirely to advection mitigated by turbulent processes which were moistening the mixed layer. The drying and inversion rise were coupled phenomena that were due to moist surface thermals which penetrated a weak lower inversion into an elevated mixed layer (EML). The EML was left from the previous day, and was well below a much stronger capping inversion. This penetrative convection into the EML suddenly removed moisture from the lower part of the mixed layer, moistened the region of the EML, and dried a growing mixed layer.
Ozone and temperature changes in the stratosphere following the eruption of Mount Pinatubo
Authors: Randel William J. , Wu Fei , Russell J. M. , Waters J. W. , Froidevaux L.
Published: February 2004

Global variations in stratospheric ozone and lower stratospheric temperature are documented for the period 1991–1994, following the eruption of Mount Pinatubo in June 1991. Column ozone measurements are from the total ozone mapping spectrometer instruments on the Nimbus 7 and Meteor 3 satellites, together with solar backscattered ultraviolet data from NOAA 11; these satellite ozone data are validated by comparisons with ground‐based Dobson spectrophotometer measurements. Ozone profile data from the halogen occultation experiment and microwave limb sounder instruments on the upper atmosphere research satellite are also analyzed. Satellite temperature data are from the microwave sounding unit channel 4, representing a mean of the 150‐ to 50‐mbar layer. The ozone observations show substantial decreases in column ozone (of order 5–10%) over large regions of the globe; largest losses are observed in northern hemisphere middle‐high latitudes during winter‐spring of each year (largest in 1992–1993), over southern hemisphere high latitudes in spring 1993, and episodically over the tropics during 1991–1993. Temperatures are anomalously warm (by order 1 K) over 30°N‐S for 1 to 2 years following the eruption. Significant cold anomalies are also observed over the northern hemisphere polar cap during summer 1993, a result probably related to the decreased ozone levels throughout 1993.
Climatological mean wind observations from the UARS high‐resolution Doppler imager and wind imaging interferometer: Comparison with current reference models
Authors: Fleming Eric L. , Chandra Sushil , Burrage Mark D. , Skinner Wilbert R. , Hays Paul B. , Solheim Brian H. , Shepherd Gordon G.
Published: February 2004

Direct wind measurements from the high‐resolution Doppler imager (HRDI) and wind imaging interferometer (WINDII) instruments onboard the Upper Atmosphere Research Satellite (UARS) represent a substantial increase in the number of available wind observations in the mesosphere‐to lower‐thermosphere region. These unique data sets provide an opportunity to evaluate current climatological reference models in the 80‐ to 120‐km region which are based on limited empirical data coverage available during the pre‐UARS time period. Below 80 km the general climatological features have been fairly well established by previous observational databases. The reference models therefore provide a means for validating the climatological mean UARS observations in the lower mesosphere, especially at midlatitudes. We have used 2–3 years of UARS HRDI and WINDII observations to construct a monthly and diurnal mean zonally averaged climatology of zonal and meridional wind for the 50‐ to 120‐km region. We use this to compare with the current CIRA‐86 and HWM‐93 reference models. Comparisons are limited to regions where the tidal oscillations can be adequately removed from the UARS observations using simple binning and averaging methods. At 50–80 km the reference models, which are based on gradient winds derived from temperatures, compare well with the HRDI data in reproducing the overall seasonal variations, including the magnitudes and positions of the winter westerly and summer easterly jets at midlatitudes. At 95 km, HRDI and WINDII show year‐round easterlies at low latitudes and indicate a strong westerly jet during summer and weaker, more variable flow during winter at midlatitudes. The CIRA‐86 gradient winds at 95 km show some qualitative agreement with the UARS data at midlatitudes, especially in simulating the summertime jet. However, the comparison is poor at low latitudes. We attribute this to the lack of available temperature measurements in this region from which the gradient winds are derived. The HWM‐93 model, which is based mainly on medium frequency and meteor radar winds at 95 km, shows qualitatively similar seasonal variations in both zonal and meridional wind compared with the UARS data in this region. However, the HWM model is consistently smaller by a factor of 2–3 in wind magnitude relative to the UARS measurements at 95 km.
Chemical characteristics of continental outflow from Asia to the troposphere over the western Pacific Ocean during September–October 1991: Results from PEM‐West A
Authors: Talbot R. W. , Dibb J. E. , Klemm K. I. , Bradshaw J. D. , Sandholm S. T. , Blake D. R. , Sachse G. W. , Collins J. , Heikes B. G. , Gregory G. L. , Anderson B. E. , Singh H. B. , Thornton D. C. , Merrill J. T.
Published: February 2004

An important objective of the Pacific Exploratory Mission‐West A (PEM‐West A) was the chemical characterization of the outflow of tropospheric trace gases and aerosol particles from the Asian continent over the western Pacific Ocean. This paper summarizes the chemistry of this outflow during the period September – October 1991. The vertical distributions of CO, C2H6, and NOx showed regions of outflow at altitudes below 2 km and from 8 to 12 km. Mixing ratios of CO were ≈130 parts per billion by volume (ppbv), ≈1000 parts per trillion by volume (pptv) for C2H6, and ≈100 pptv for NOx in both of these regions. Direct outflow of Asian industrial materials was clearly evident at altitudes below 2 km, where halocarbon tracer compounds such as CH3CCl3 and C2Cl4 were enhanced about threefold compared to aged Pacific air. The source attribution of species outflowing from Asia to the Pacific at 8–12 km altitude was not straightforward. Above 10 km altitude there were substantial enhancements of NOy, O3, CO, CH4 SO2, C2H6, C3H8, C2H2, and aerosol 210Pb but not halocarbon industrial tracers. These air masses were rich in nitrogen relative to sulfur and contained ratios of C2H2/CO and C3H8/C2H6 (≈1.5 and 0.1 respectively) indicative of several‐day‐old combustion emissions. It is unclear if these emissions were of Asian origin, or if they were rapidly transported to this region from Europe by the high wind speeds in this tropospheric region (60 – 70 m s−1). The significant cyclonic activity over Asia at this time could have transported to the upper troposphere emissions from biomass burning in Southeast Asia or emissions from the extensive use of various biomass materials for cooking and space heating. Apparently, the emissions in the upper troposphere were brought there by wet convective systems since water‐soluble gases and aerosols were depleted in these air masses. Near 9 km altitude there was a distinct regional outflow that appeared to be heavily influenced by biogenic processes on the Asian continent, especially from the southeastern area. These air masses contained CH4 in excess of 1800 ppbv, while CO2 and OCS were significantly depleted (349 – 352 ppmv and 450 – 500 pptv, respectively). This signature seemingly reflected CH4 emissions from wetlands and rice paddies with coincident biospheric uptake of tropospheric CO2 and OCS.
Trajectory results and interpretation for PEM‐West A
Authors: Merrill John T.
Published: February 2004

The results and interpretation of trajectory analyses for the Pacific Exploratory Mission‐West A (PEM‐West A) experiment are described. The calculations are based on gridded meteorological fields; the first step is the preparation of an analysis of winds and other variables on selected isentropic surfaces. The sources of uncertainty and error in this and the subsequent step of trajectory analysis are described. The most important of these are limitations in the adequacy of the adiabatic approximation and flaws in the parent meteorological fields, particularly caused by data voids over open ocean areas. Examples are presented of the trajectory results for points along the flight track of the DC‐8 during the September–October 1991 expedition. The corroboration of air mass classifications based on trajectories by chemical characterization based on the in situ and remotely sensed observations from the aircraft discussed elsewhere in this issue is noted. An analysis of multiyear patterns of airflow in the western Pacific area, based on trajectory calculations for the September–October period for 1988–1990, is also presented.
Influence of topography and biogenic volatile organic compounds emission in the state of Baden‐Württemberg on ozone concentrations during episodes of high air temperatures
Authors: Vogel B. , Fiedler F. , Vogel H.
Published: February 2004

A nonhydrostatic mesoscale model which is coupled with a transport and diffusion model and the gas phase mechanism RADM2 is used to study the influence of biogenic volatile organic compounds (VOC) emission on the ozone concentration during episodes of high air temperatures in the state of Baden‐Württemberg, Germany. All model parts, including the determination of the biogenic VOC emissions, are run in a coupled mode. The results of the model simulations are compared with observations for a summer smog episode which occurred in August 1990. Simulations which are carried out without biogenic VOC emissions show a maximum difference in the ozone concentration of 18 ppb, while the maximum ozone values are of the order of 100 ppb. This shows that the biogenic VOC emissions play an important role when high temperatures are present in Baden‐Württemberg. Simulations which are carried out with homogeneous terrain height show differences in the biogenic emissions caused by changes in the temperature distribution. Large differences are also found for the concentration distributions. The differences in the results which are obtained with and without biogenic VOC emissions are decreasing; the maximum difference is about 10 ppb. This demonstrates the necessity of a sufficient treatment of topographic effects in the regional scale.
Impact of a total solar eclipse on surface atmospheric electricity
Authors: Manohar G. K. , Kandalgaonkar S. S. , Kulkarni M. K.
Published: February 2004

A study of the impact of a total solar eclipse (TSE) on surface atmospheric electricity was made using observations of surface electrical potential gradient, conductivity, and boundary layer parameters recorded during the TSE of February 16, 1980, and on a control day at Raichur. The study showed that with the progressing of the eclipse, as a consequence of inhibited convection, the responses of turbulent mixing in the boundary layer near the ground exhibited diminution and subsequent restoration, respectively. During the next 45 min after the totality, when the surface layer remained stably stratified, the diminution in the potential gradient and the increase in the conductivity was maximum; this was about 60% and 200%, respectively, of their corresponding control day values. This result is in very good agreement with most earlier studies of solar eclipses. The study of the impact of the TSE during 3–4 hours of posteclipse showed significant cooling (∼3°C) of the entire surface air layer and a considerable drop in wind speed over the stretch (1130 km×120 km) of the totality‐occupied land region. This significant and systematic phenomenon was responsible for setting up a land‐sea breezelike circulation, that is, subsidence/downward air motion over the totality‐occupied land region and upward over the noneclipsed land across the totality stretch. This resulted in a considerable aerosol‐induced reduction in conductivity and about 5 to 8 times increase in potential gradient during the 3–4 hours of posteclipse. This response of the atmospheric electricity parameters was unlike that observed on the normal days.
Effects of moisture and burning on soil‐atmosphere exchange of trace carbon gases in a southern African savanna
Authors: Zepp Richard G. , Miller William L. , Burke Roger A. , Parsons Dirk A. B. , Scholes Mary C.
Published: February 2004

Soil fluxes of carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) were measured during a period of extreme drought at semi‐arid savanna sites located in the Kruger National Park (KNP), South Africa, as part of the SAFARI‐92 experiments (Sept., 1992). Soil respiration in this savanna was little affected by burning, but was strongly stimulated by addition of moisture. Mean soil respiration from the dry soil was 0.4 g C m−2d−1in open savanna plots that had been burned biennially and 0.5 g C m−2d−1in woody savanna plots. A light natural rain (about 0.6 mm) increased the CO2flux in the open savanna sites by 5‐fold but the effect was short‐lived. A simulated heavy rain (25 mm of added distilled water) increased CO2fluxes by over an order of magnitude in both burned and control sites and the emissions remained over 5 times pre‐wetting values during a week of drying. Over 65% of our measurements indicated no significant soil‐atmosphere methane exchange; most of the few non‐zero measurements indicated a small (<1 mg CH4‐C m−2d−1) flux of methane to the atmosphere. Soil‐atmosphere CH4exchange was not significantly affected by either burning the grass layer or by the addition of distilled water to the soil. The net soil CO fluxes, which generally increased with increasing soil temperature, were positive up to 356 × 109molecules cm−2s−1with an average of 8.8 × 1010molecules cm−2s−1for the untreated open savanna plots. After burning, the fluxes rose by over an order of magnitude but dropped back to preburn levels within a few days. Observed CO fluxes were higher than those previously reported for southern Africa savannas during non‐drought conditions. Added moisture had little effect on CO fluxes during the 3‐week period of SAFARI‐92.
Atmospheric sampling of Supertyphoon Mireille with NASA DC‐8 aircraft on September 27,1991, during PEM‐West A
Authors: Newell R. E. , Hu W. , Wu Z‐X. , Zhu Y. , Akimoto H. , Anderson B. E. , Browell E. V. , Gregory G. L. , Sachse G. W. , Shipham M. C. , Bachmeier A. S. , Bandy A. R. , Thornton D. C. , Blake D. R. , Rowland F. S. , Bradshaw J. D. , Crawford J. H. , Davis D. D. , Sandholm S. T. , Brockett W. , DeGreef L. , Lewis D. , McCormick D. , Monitz E. , Collins J. E. , Heikes B. G. , Merrill J. T. , Kelly K. K. , Liu S. C. , Kondo Y. , Koike M. , Liu C.‐M. , Sakamaki F. , Singh H. B. , Dibb J. E. , Talbot R. W.
Published: February 2004

The DC‐8 mission of September 27, 1991, was designed to sample air flowing into Typhoon Mireille in the boundary layer, air in the upper tropospheric eye region, and air emerging from the typhoon and ahead of the system, also in the upper troposphere. The objective was to find how a typhoon redistributes trace constituents in the West Pacific region and whether any such redistribution is important on the global scale. The boundary layer air (300 m), in a region to the SE of the eye, contained low mixing ratios of the tracer species O3, CO, C2H6, C2H2, C3H8, C6H6 and CS2 but high values of dimethylsulfide (DMS). The eye region relative to the boundary layer, showed somewhat elevated levels of CO, substantially increased levels of O3, CS2 and all nonmethane hydrocarbons (NMHCs), and somewhat reduced levels of DMS. Ahead of the eye, CO and the NMHCs remained unchanged, O3 and CS2 showed a modest decrease, and DMS showed a substantial decrease. There was no evidence from lidar cross sections of ozone for the downward entrainment of stratospheric air into the eye region; these sections show that low ozone values were measured in the troposphere. The DMS data suggest substantial entrainment of boundary layer air into the system, particularly into the eye wall region. Estimates of the DMS sulphur flux between the boundary layer and the free troposphere, based on computations of velocity potential and divergent winds, gave values of about 69 μg S m−2 d−1 averaged over a 17.5° grid square encompassing the typhoon. A few hours after sampling with the DC‐8, Mireille passed over Oki Island, just to the north of Japan, producing surface values of ozone of 5.5 ppbv. These O3 levels are consistent with the low tropospheric values found by lidar and are more typical of equatorial regions. We suggest that the central eye region may act like a Taylor column which has moved poleward from low latitudes. The high‐altitude photochemical environment within Typhoon Mireille was found to be quite active as evidenced by significant levels of measured gas phase H2O2 and CH3OOH and model‐computed levels of OH.
Retrieval of tropospheric ozone from simulations of nadir spectral radiances as observed from space
Authors: Clough S. A. , Rinsland C. P. , Brown P. D.
Published: February 2004

The global remote sensing of tropospheric ozone profiles is a critical environmental measurement to be performed by future satellite experiments. We have applied the method of nonlinear least squares in conjunction with an efficient and accurate line‐by‐line radiative transfer model to directly retrieve vertical profiles of tropospheric ozone from simulated clear sky, nadir‐viewing radiances covering the entire 9.6‐μm ozone band. The simulations have been generated for the specifications of the tropospheric emission spectrometer (TES), a Fourier transform spectrometer with 0.032 cm−1 resolution (half width at half maximum (HWHM), unapodized) being developed for NASA's Earth Observing System. Profile retrieval errors for background tropospheric ozone levels are characterized as a function of measurement noise, spectral resolution, and vertical resolution based on a linear error analysis and an initial guess profile with minimal constraint, hence negligible potential profile bias at all altitudes. The main conclusions of the study are that (1) for the TES experiment design, ozone profiles are retrievable to approximately ±5% (1σ) for a vertical resolution of 5 km in the middle and upper troposphere, (2) the stratospheric portion of the profile must be retrieved directly from the measured nadir spectrum, (3) for equal measurement times and considering the effects of both systematic error and source radiance noise, an optimal spectral interferometer resolution exists that is close to the TES resolution (0.032 cm−1; HWHM unapodized), and (4) ozone boundary layer retrievals are highly dependent on the contrast between that layer and the surface. The results from an ozone retrieval utilizing simulated radiances from an atmosphere defined by a radiosonde observation at Ascension Island are considered in the context of the solution of the nonlinear problem and the linear error analysis. The ozone retrieval analyses presented in this paper are principally concerned with the effects of measurement error and thus represent the optimal retrieval capability for the assumed design. However, the availability of the full high‐resolution spectrum will enable the detection and mitigation of the systematic errors.
Cloud scattering optical depth and local surface albedo in the Antarctic: Simultaneous retrieval using ground‐based radiometry
Authors: Ricchiazzi Paul , Gautier Catherine , Lubin Dan
Published: February 2004

We have used solar irradiance measurements from a ground‐based multichannel radiometer system deployed at Palmer Station, Antarctica (64°46′S, 64°04′W), during spring 1991 to simultaneously estimate cloud scattering optical depth and surface albedo. Irradiance measurements at 410 and 630 nm, in conjunction with a discrete ordinate radiative transfer (RT) model, enable this simultaneous retrieval by exploiting the wavelength dependence in Rayleigh scattering strength. The RT model is used in an inverse mode to find the values of surface albedo and cloud optical depth that match calculated and measured irradiances at both wavelengths. Under the homogeneous stratiform cloud cover for which the technique applies, surface albedo at 630 nm was consistently retrieved at above 0.9. For most homogeneous, overcast conditions, cloud optical depth (at 630 nm) is found to be in the range 20–50, with a most probable value of 25. This measurement and retrieval technique should be useful for compiling high‐latitude cloud opacity and surface albedo climatologies of interest for global change and photobiology research.
The ASTEX/MAGE Experiment
Authors: Huebert Barry J. , Pszenny Alex , Blomquist Byron
Published: February 2004

The Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) was a multinational experiment designed to study the relationship between marine chemistry, aerosols, clouds, and air/sea exchange. Several aircraft, ships, and island sites supported measurements of marine boundary layer chemistry in both pristine and polluted North Atlantic air masses in the vicinity of the Azores in June of 1992. The International Global Atmospheric Chemistry (IGAC) Program's MAGE activity organized the chemical experiments in ASTEX because such experiments are beyond the capabilities of any one platform, discipline, or nation working alone. One highlight of ASTEX/MAGE was the development of a Lagrangian experimental strategy. It offered a unique way of constraining fluxes and reaction rates by observing the effect those processes have on a tagged parcel of air.
An international intercomparison of marine atmospheric radon 222 measurements in Bermuda
Authors: Collé R. , Unterweger M. P. , Hodge P. A. , Hutchinson J. M. R. , Whittlestone S. , Polian Georges , Ardouin Bénédicte , Kay Jack G. , Friend James P. , Blomquist Byron W. , Nadler Wolfgang , Dang Thomas T. , Larsen R. J. , Hutter A. R.
Published: February 2004

As part of an international measurement intercomparison of instruments used to measure atmospheric 222Rn, four participating laboratories made nearly simultaneous measurements of 222Rn activity concentration in commonly sampled, ambient air over approximately a 2‐week period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed (“blind”) 222Rn activity concentrations that could be related to U.S. national standards. The standardized sample additions were obtained with a calibrated 226Ra source and a specially designed manifold used to obtain well‐known dilution factors from simultaneous flow rate measurements. The exercise was conducted in Bermuda in October 1991. The 222Rn activity concentrations in ambient Bermudian air over the course of the intercomparison ranged from a few hundredths to about 2 Bq m−3, while the standardized sample additions covered a range from approximately 2.5 to 35 Bq m−3. The overall uncertainty in the latter concentrations was in the general range of 10% at a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an averaged offset of roughly 0.3 Bq m−3. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65–70%, which was also confirmed in their ambient air concentration measurements. The fourth laboratory, participating in only the ambient measurement part of the intercomparison, was also systematically low by at least 40% with respect to the first two aforementioned laboratories.
Comprehensive model for the atmospheric sodium layer
Authors: McNeil William J. , Murad Edmond , Lai Shu T.
Published: February 2004

We present a steady state model of the midlatitude nighttime sodium layer which is comprehensive in the sense that it includes deposition of the metal, diffusion, and kinetics as well as the seasonal variations in the atmosphere. The model is used to compute seasonal variations in the layer parameters and the sodium nightglow. The behavior of the model reproduces well the observed behavior of the layer. We find that the main contributor to the seasonal variation is the temperature dependence of the reaction recycling atomic sodium from NaHCO3. Seasonal variations in the atmospheric minor species including ozone are secondary effects at best. The relative contributions of all factors are compared.
ATMOS/ATLAS 1 measurements of thermospheric and mesospheric nitric oxide
Authors: Kumar C. Krishna , Swaminathan P. K. , Anderson D. E. , Yee J.‐H. , Gunson M. R. , Abrams M. C.
Published: February 2004

The atmospheric trace molecule spectroscopy (ATMOS) instrument obtained solar occultation spectra of the terrestrial atmosphere during the Atmospheric Laboratory for Applications and Science (ATLAS 1) mission of March 26–April 4, 1992. During this time, Ap varied between 11 and 18 while the F10.7 index was near 192. The analyses of the 5.3‐μm spectral data to derive nitric oxide densities in the lower thermosphere and mesosphere are described here. The results show that a peak NO density of 1.0×108 cm−3 occurs at 105±2.5 km for the latitude range 38°N–58°S. The density values are higher than previously reported using UV measurements. These measurements worsen the discrepancy with photochemical models at low latitudes where models already underpredict nitric oxide.
Validation of mesosphere and lower thermosphere winds from the high resolution Doppler imager on UARS
Authors: Burrage M. D. , Skinner W. R. , Gell D. A. , Hays P. B. , Marshall A. R. , Ortland D. A. , Manson A. H. , Franke S. J. , Fritts D. C. , Hoffman P. , McLandress C. , Niciejewski R. , Schmidlin F. J. , Shepherd G. G. , Singer W. , Tsuda T. , Vincent R. A.
Published: February 2004

Horizontal wind fields in the mesosphere and lower thermosphere are obtained with the high resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) by observing the Doppler shifts of emission lines in the O2 atmospheric band. The validity of the derived winds depends on an accurate knowledge of the positions on the detector of the observed lines in the absence of a wind‐induced Doppler shift. Relative changes in these positions are readily identified in the routine measurements of onboard calibration lines. The determination of the absolute values relies on the comparison of HRDI observations with those obtained by MF radars and rockets. In addition, the degrees of horizontal and vertical smoothing of the recovered wind profiles have been optimized by examining the effects of these parameters both on the amplitude of the HRDI‐derived diurnal tidal amplitude and on the variance of the wind differences with correlative measurements. This paper describes these validation procedures and presents comparisons with correlative data. The main discrepancy appears to be in the relative magnitudes measured by HRDI and by the MF radar technique. Specifically, HRDI generally observes larger winds than the MF radars, but the size of the discrepancy varies significantly between different stations. HRDI wind magnitudes are found to be somewhat more consistent with measurements obtained by the rocket launched falling sphere technique and are in very good agreement with the wind imaging interferometer (WINDII), also flown on UARS.
Combined mesosphere/thermosphere winds using WINDII and HRDI data from the Upper Atmosphere Research Satellite
Authors: McLandress Charles , Shepherd Gordon G. , Solheim Brian H. , Burrage Mark D. , Hays Paul B. , Skinner Wilbert R.
Published: February 2004

This paper examines the combined mesospheric and thermospheric (50 to 200 km) longitudinally averaged winds measured by the wind imaging interferometer (WINDII) and the high‐resolution Doppler imager (HRDI) onboard the Upper Atmosphere Research Satellite. The data analyzed cover 2 years from February 1992 to February 1994 and consist of both day and nighttime WINDII winds obtained from the O(1S) green line emission and mesosphere/lower thermosphere daytime HRDI winds from the O2 atmospheric band. The combination of the WINDII and HRDI data sets is first justified by comparing all the data in the lower‐thermosphere overlap region for days and orbits when both instruments were observing the same volume of atmosphere. This comparison shows good agreement between the two instruments. An analysis of the combined WINDII and HRDI winds during equinox and solstice periods is then performed. The amplification with height of the diurnal tide at equinox and its subsequent decay in the lower thermosphere is clearly demonstrated by the observations. The corresponding background (i.e., diurnal mean) zonal wind component exhibits a broad region of easterlies at lower latitudes in the upper mesosphere and lower thermosphere and westerlies at midlatitudes. Above 120 km the mean winds revert to easterlies in the zonal component and a two‐celled equator to pole meridional circulation. The solstice circulation is highly asymmetric about the equator in accordance with the interhemispheric difference in solar heating. The reversal of the mesospheric jets as well as the summer to winter hemisphere meridional flow in the middle thermosphere are clearly shown. At solstice a significantly weaker and more hemispherically asymmetric propagating diurnal tide is also evident.
Comparisons between Stratospheric Aerosol and Gas Experiment II and microwave limb sounder ozone measurements and aliasing of SAGE II ozone trends in the lower stratosphere
Authors: Cunnold D. M. , Wang H. , Chu W. P. , Froidevaux L.
Published: February 2004

SAGE II ozone measurements are compared with coincident microwave limb sounder (MLS) measurements over the period September 1991 to December 1993. Between 1.5 and 10 mbar the MLS ozone values are approximately 5% larger than the Stratospheric Aerosol and Gas Experiment (SAGE) II values. These differences are remarkably systematic in space and time. At 1 mbar the mean differences are zero and the mean differences oscillate with level at lower pressures. A month of comparisons against Halogen Occultation Experiment ozone measurements suggests that the differences at pressures less than 1.5 mbar are a feature of the MLS measurements. There are also differences between SAGE II sunrise and sunset measurements at 1 mbar which may be associated with the diurnal tide. At pressures greater than 10 mbar the comparisons indicate that the SAGE II ozone retrievals are being biased by the large aerosol concentrations resulting from the Mount Pinatubo eruption. For a fixed aerosol extinction the SAGE II/MLS difference (ppm) is larger at higher altitudes. It also depends nonlinearly on the aerosol extinction at pressures greater than 20 mbar. These effects are probably caused by the interpolation of the SAGE II aerosol extinction to 0.6 μm and by the evolution of the aerosol size distribution. For UARS layer aerosol optical depths less than 2 × 10−3 at 1.02 μm, the aerosol effect on the SAGE II ozone retrievals is inferred to be 3 × 1010 cm−3/10−3 aerosol layer optical depth at pressures greater than 20 mbar. This is equivalent to approximately 3% of the aerosol extinction at 0.6 μm being interpreted as ozone. At low aerosol concentrations and between 10 and 31 mbar, MLS ozone values are found to be approximately 5% larger than SAGE II ozone values (in agreement with the higher‐altitude differences). Atmospheric aerosol concentrations prior to the Mount Pinatubo eruption were large enough, particularly in the tropics after Ruiz in 1985, that long‐term trends in SAGE II ozone in the lower stratosphere are inferred to be biased downward. As a result, the SAGE II column ozone trends in the tropics over the period 1984–1991 need to be increased by approximately 0.2%/yr. This effect can account for a large fraction of SAGE II total ozone mapping spectrometer (TOMS) column ozone trend differences over this period. Good agreement is found between the TOMS and the SAGE II column ozone trends if the period of comparison is restricted to times of low aerosol concentrations.
Carbon monoxide gradients in the marine boundary layer of the North Atlantic Ocean
Authors: Springer‐Young Margie , Erickson David J. , Carsey Thomas P.
Published: February 2004

We present an observational data set that suggests that the ocean source of carbon monoxide (CO) may influence the atmospheric CO concentration in the marine boundary layer (MBL). Atmospheric CO concentration gradient data obtained during the 1992 Atlantic Stratocumulus Transition Experiment Marine Aerosol and Gas Exchange (ASTEX/MAGE) show significantly (range of 2–47 ppbv, average of 15 ppbv) more CO at altitudes of 0.05 to 0.5 m above sea level as compared to 10 m above sea level. The seawater CO concentrations needed to support the fluxes obtained from an atmospheric gradient calculation are much higher than generally reported in the literature. However, studies of CO production by Jones and Amador (1993) and data from Seiler (1978) suggest the possibility that CO production and the resultant flux to the MBL could be 1–2 orders of magnitude higher than currently estimated using seawater pumped from depths of 4–10 m below the sea‐air interface. We infer that the surface ocean production and sea‐air exchange of photochemically produced trace gases such as CO may participate in physical, chemical and biological processes on vastly different spatial and temporal scales than those inherent to more stable species such as CO2.
Sulfur gas fluxes and horizontal inhomogeneities in the marine boundary layer
Authors: Jodwalis Clara M. , Benner Richard L.
Published: February 2004

Real‐time total gaseous sulfur concentrations were measured (sampling frequency 1 Hz) from the R/V Oceanus as part of the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) field campaign in the Azores during June of 1992. The measurements were used to estimate sulfur gas sea‐to‐air flux, determine the size scale of sulfur gas inhomogeneities in the marine boundary layer, and the timescale of sampling necessary to characterize a meaningful air mass. Using the time scale of sampling and wind speed measurements, the size scale of sampling can also be determined. Sea‐to‐air sulfur gas flux estimates were obtained using a variance method and the inertial‐dissipation method. Values from five 1‐hour measurement periods on two different days ranged from 21 to 28 μmol/m2 d and 11 to 17 μmol/m2 d, respectively. These values are above the range of 1 to 13 μmol/m2 d reported by Blomquist et al. (this issue) during ASTEX/MAGE, based on the dimethyl sulfide (DMS) concentration in surface seawater, using the stagnant boundary layer model of air‐sea exchange. A power spectrum of the sulfur gas time series shows the contribution of each turbulent eddy size to the total signal variance. In a representation of the power spectrum, the area under any portion of the curve is proportional to variance. From these power spectra we have obtained the fraction of the total variance in ground level sulfur concentration fluctuations as a function of time. The data indicate that air samples should be integrated for 1000 s for ground‐based measurements.
Fuels and fire behavior dynamics on large‐scale savanna fires in Kruger National Park, South Africa
Authors: Stocks B. J. , van Wilgen B. W. , Trollope W. S. W. , McRae D. J. , Mason J. A. , Weirich F. , Potgieter A. L. F.
Published: February 2004

Biomass characterization and fire behavior documentation were carried out on two large (>2000 ha) experimental fires conducted in arid savanna fuels in Kruger National Park in September 1992. Prefire fuel loads, fuel consumption, spread rates, flame zone characteristics, and in‐fire and perimeter wind field dynamics were measured in order to determine overall energy release rates for each fire. Convection column dynamics were also measured in support of airborne trace gas and particulate measurements. Energy release rates varied significantly between the two fires, and this was strongly reflected in convection column development. The lower‐intensity fire produced a weak, poorly defined smoke plume, while a well‐developed column with a capping cumulus top developed during the higher intensity fire. Further experimental burning studies, in savannas with higher fuel loads, are recommended to further explore the fire behavior‐convection column dynamics relationship investigated in this study.
Evaluation of ozone precursor source types using principal component analysis of ambient air measurements in rural Alabama
Authors: Buhr Martin , Parrish David , Elliot Jaimi , Holloway John , Carpenter Jim , Goldan Paul , Kuster William , Trainer Michael , Montzka Stephen , McKeen Stuart , Fehsenfeld Fred
Published: February 2004

The sources of photochemical precursors for ozone, primarily NOX(NO + NO2) and reduced carbon (CO and hydrocarbons), were evaluated using principal component analysis (PCA) of concurrent measurements of [NOX], [NOY] (total reactive oxidized nitrogen species), [CO], [SO2], [C3H8], [C6H6], and [O3] collected at a rural Alabama field site during the summers of 1990 and 1992. Two separate data matrices were analyzed, including a low measurement frequency matrix that included all of the variables and a high measurement frequency matrix that included all of the variables except for the hydrocarbons. The results of the PCA indicated that the major sources of NOYin the region are (1) coal‐fired power plants and (2) biomass burning and/or paper mills. The identifications are based on the [CO]/[NOY] and [SO2]/[NOY] emission ratios derived from the measurements in comparison with the expected emission ratios that are based upon the National Acid Precipitation Assessment Program (NAPAP) emission inventory and upon laboratory experiments. The results indicated that the NAPAP inventory, integrated over the southeastern region of the United States, may overestimate the current [SO2]/[NOY] emission ratio from coal‐fired power plants and may underestimate the [CO]/[NOY] emission ratio from paper mills. The results also suggest that biomass burning in the southeastern United States may be an important component in the NOYinventory, both as a point source associated with paper mills and as a seasonally dependent area source. The variation of [O3] observed at the site was primarily related to the variation of [NOY].