bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical structure of the extratropical quasi‐biennial oscillation in ozone, temperature, and wind derived from ozonesonde data
Authors: Sitnov Sergei A.
Published: February 2004

An analysis of the extratropical ozone sounding data shows that ozone, temperature, and wind as well as tropopause height reveal interannual variability with timescales in the range 24–30 months. This quasi‐biennial variability is noticed, as a rule, in a whole range of ozone sounding heights (0–35 km) and connected with the equatorial quasi‐biennial oscillation (QBO). The QBOs in ozone and temperature are revealed differently in the middle and lower stratosphere as well as in the troposphere. In the middle stratosphere a downward phase progression of the ozone QBO is noticed similar to that of the equatorial dynamical QBOs. The rate of the phase descent of the QBO depends on the geographical region and varies from 0.5 km/month to 1 km/month. In the northern hemisphere the rate is greatest in the polar region but lowest in the subtropics. Local maxima are noticed in the vertical structures of the ozone QBOs. In the northern midlatitudes these maxima are centered at heights of about 12, 20, and 30 km. In the lower stratosphere the QBO in ozone is in phase with that in temperature. Mean amplitudes of the temperature QBO in the troposphere are close to those in the stratosphere. The downward phase progression of the temperature QBO is noticed in the northern midlatitude stratosphere. There is an abrupt phase shift between the QBOs in ozone and temperature in the lower stratosphere and those in the middle troposphere. Over the North American stations the phase shift is that the temperature QBOs in the troposphere are in opposite phase with those in the stratosphere. In zonal and meridional winds the QBO are revealed in the northern midlatitudes. In contrast with the QBOs in ozone and temperature, the wind QBOs reveal the small rate of the phase changing with height. There are no significant phase shifts between the wind QBO in the lower stratosphere and that in the troposphere. The maximum amplitudes of the wind QBO are noticed in the vicinity of the tropopause position and at heights of 25–30 km. Amplitudes of the QBO in zonal wind are close to those in meridional wind. The QBO of tropopause height exposed in the northern hemisphere has the greatest amplitude over Japan. The tropopause height QBO is in opposite phase (in phase) with the QBOs in ozone and temperature in the lower stratosphere (troposphere). Vertical structures of the QBOs obtained for ozone, temperature, and wind in the stratosphere as well as the corresponding QBO of tropopause height support a hypothesis that the extratropical QBO is caused by quasi‐biennial forcing of the mean diabatic meridional circulation by planetary‐scale waves with the resulting modulation of vertical advection.
Chemical and optical properties of marine boundary layer aerosol particles of the mid‐Pacific in relation to sources and meteorological transport
Authors: Quinn P. K. , Kapustin V. N. , Bates T. S. , Covert D. S.
Published: February 2004

Incorporating the direct effect of tropospheric aerosol on climate into global climate models involves coupling the optical properties of the aerosol with its physical and chemical properties. This coupling is strengthened if the optical, physical, and chemical properties of the individual aerosol components are known as well as how these properties depend on the air mass source and synoptic scale meteorology. To relate properties of the aerosol components to air mass sources over a wide range of meteorological conditions, two long latitudinal cruises were conducted in the central Pacific Ocean from 55°N to 70°S. Submicron non‐sea‐salt (nss) SO4= aerosol averaged about 35 to 40% of the submicron ionic mass as analyzed by ion chromatography and 6% of the total ionic mass, while supermicron nss SO4= aerosol contributed about 1% to the total ionic mass. About 1% of the remaining total ionic mass was composed of methanesulfonate and 90% was sea salt. Ionic mass fractions of nss SO4= aerosol were highest in regions having the longest marine boundary layer residence times or the largest source of marine or continental gas phase precursors. The calculated scattering by nss SO4= aerosol was highest in these same regions due to the dependence of scattering on particle size and the concentration of nss SO4= in the submicron size range. The calculated scattering by submicron sea salt was similar to that of the nss SO4= aerosol, indicating that its contribution to scattering in the marine boundary layer can be significant or even dominant depending on its mass concentration. Mass scattering efficiencies for nss SO4= at 30% RH ranged from 4.3 to 7.5 m2 g−1 and for submicron sea salt from 3.5 to 7.7 m2 g−1. Mass backscattering efficiencies for nss SO4= ranged from 0.41 to 0.58 m2 g−1 and for submicron sea salt from 0.33 to 0.63 m2 g−1. These values fall within the same range as others reported previously for the marine atmosphere.
Influence of a middle‐latitude cyclone on tropospheric ozone distributions during a period of TRACE A
Authors: Loring Robert O. , Fuelberg Henry E. , Fishman Jack , Watson Mark V. , Browell Edward V.
Published: February 2004

A middle‐latitude cyclone occurring during the Transport and Atmospheric Chemistry near the Equator‐Atlantic (TRACE A) experiment is examined to determine its influence on distributions of tropospheric ozone over the South Atlantic Ocean. A maximum of tropospheric ozone is located in the vicinity of this cyclone on October 3, 1992. Flight level data and meteorological analyses indicate a downward protrusion of dry, ozone‐rich stratospheric air near the cyclone, i.e., a tropopause fold. Backward trajectories show that air parcels arriving in the upper troposphere of the cyclone originate in the stratosphere. Forward trajectories are calculated from these locations having stratospheric histories. They indicate that some air is transported as far north as 22°S, subsiding into the middle troposphere along the southern fringes of a region of enhanced tropospheric ozone that is located west of Africa on October 6. Backward trajectories then are computed along the Greenwich meridian over much of the South Atlantic Ocean. This axis passes through the tropospheric ozone maximum west of Africa and the region of strong horizontal ozone gradients along its southern border. Results indicate that most air parcels arriving north of 20°S (in the ozone‐rich region) originate over Africa. Conversely, most parcels arriving south of 20°S (where there is less ozone) originate from the west, passing over the southern half of South America. Thus the tropospheric ozone maximum west of Africa on October 6 appears to be attributable to outflow from Africa, with stratospheric transport being much less important. Formerly stratospheric air near the cyclone on October 3 also is transported forward into the middle troposphere near Madagascar where there is a second maximum of tropospheric ozone on October 6. Backward trajectories from this region indicate that middle‐latitude systems exert a much greater influence here than over the South Atlantic. This area experiences relatively little outflow from Africa during our period of study.
Millimeter wave spectroscopic measurements over the South Pole: 2. An 11‐month cycle of stratospheric ozone observations during 1993–1994
Authors: Cheng Dongjie , de Zafra Robert L. , Trimble Curtis
Published: February 2004

A quasi‐continuous record of ozone profiles throughout the stratosphere over the South Pole has been obtained over an 11‐month cycle, from February 1993 to January 1994. This record includes the first winter measurements of ozone profiles in the altitude region above ∼30 km. Observations were made approximately every 3 days, using a high‐sensitivity millimeter wave spectrometer to quantitatively measure the pressure‐broadened ozone rotational emission line at 276.923 GHz. Vertical mixing ratio profiles have been derived from pressure‐broadened lineshapes by a deconvolution technique. A number of interesting features are present. We find a persistent double‐peaked structure in the mixing ratio profiles, lasting through most of the winter period until the remains of the lower peak are destroyed by spring “ozone hole” chemistry. A new low‐altitude peak is reformed in December as the vortex breaks up. With the aid of circumpolar UARS/MLS ozone maps, we interpret the lower peak as due to transport from ozone‐rich regions near the edge of the continent, while the profile from ∼30 km upward, composing the “trough” region and upper peak, appears to be the result of normal polar summer photochemistry. This double‐peaked structure then becomes “fossilized” within the strong, isolated, fall‐winter vortex. The mixing ratio of the upper peak increases after polar sunset, which we interpret as due to poleward mixing causing an erasure of the negative poleward gradient maintained by photochemistry before sunset. Mixing ratio isopleths show a relatively steady downward trend for a 3‐month period after the winter vortex pattern is established, preceded by rapid variations in ozone mixing ratios over the 20‐ to 40‐km range. Downward transport rates derived from isopleth slopes in the upper stratosphere are significantly smaller than vertical transport derived from theoretical studies, and we propose an explanation for this discrepancy based on ozone flow from the mesosphere. Descent rates determined from ozone isopleths in the midstratosphere (25 to 35 km) are shown to be in good agreement with recent model estimates of downward transport in the winter vortex, and with the mid to lower stratospheric descent rate inferred from our own South Pole measurements of N2O. Total column measurements are in generally good agreement with those derived from a Dobson photospectrometer at the pole and from local ozonesonde measurements. All three indicate there was no significant increase in total ozone over the pole during the winter of 1993. The onset of the spring ozone hole over the pole was evident by mid‐ to late‐August, well before local stratospheric sunrise on September 11, indicating relatively rapid poleward transport of ozone‐depleted air from sunlit regions of the vortex during this period.
Space‐time variations in water vapor as observed by the UARS Microwave Limb Sounder
Authors: Elson Lee S. , Read William G. , Waters Joe W. , Mote Philip W. , Kinnersley Jonathan S. , Harwood Robert S.
Published: February 2004

Water vapor in the upper troposphere has a significant impact on the climate system. Difficulties in making accurate global measurements have led to uncertainty in understanding water vapor's coupling to the hydrologic cycle in the lower troposphere and its role in radiative energy balance. The Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite is able to retrieve water vapor concentration in the upper troposphere with good sensitivity and nearly global coverage. An analysis of these preliminary retrievals based on 3 years of observations shows the water vapor distribution to be similar to that measured by other techniques and to model results. The primary MLS water vapor measurements were made in the stratosphere, where this species acts as a conserved tracer under certain conditions. As is the case for the upper troposphere, most of the stratospheric discussion focuses on the time evolution of the zonal mean and zonally varying water vapor. Stratospheric results span a 19‐month period and tropospheric results a 36‐month period, both beginning in October of 1991. Comparisons with stratospheric model calculations show general agreement, with some differences in the amplitude and phase of long‐term variations. At certain times and places, the evolution of water vapor distributions in the lower stratosphere suggests the presence of meridional transport.
The seasonality of the CO2 exchange between the atmosphere and the land biosphere: A study with a global mechanistic vegetation model
Authors: Nemry B. , François L. , Warnant P. , Robinet F. , Gérard J.‐C.
Published: February 2004

Two simulations of the seasonal variation of the global atmospheric CO2 distribution are obtained by combining an atmospheric transport model, two parameterizations of soil heterotrophic respiration (SHR), and a mechanistic model of carbon assimilation in the biosphere (CARAIB) that estimates the net primary production (NPP) of continental vegetation. The steady state hypothesis of the biosphere allows the spatial distribution and the global content of the soil carbon to be expressed as a function of the root fractions of soil respiration under forested and herbaceous vegetation covers. The sensitivity of the modeled CO2 signal to the wind field does not exceed the observed interannual variability. The influence of the various vegetation zones is quantified by the Fourier analysis of the modeled atmospheric signal. In the northern hemisphere, the temperate ecosystems dominate the seasonal atmospheric signal of the extratropical latitudes. The ecosystems of the tropical northern zone determine the local signal, while the southern tropical ecosystems influence largely the signal in the whole southern hemisphere. The results give credence to the mechanistic modeling of NPP since the simulated atmospheric signal is comparable with that obtained with normalized difference vegetation index (NDVI) based diagnostic models coupled with a parameterization of SHR fitted to optimize the atmospheric signal.
The seasonal cycle of atmospheric CO2: A study based on the NCAR Community Climate Model (CCM2)
Authors: Erickson D. J. , Rasch P. J. , Tans P. P. , Friedlingstein P. , Ciais P. , Maier‐Reimer E. , Six K. , Fischer C. A. , Walters S.
Published: February 2004

A global three‐dimensional atmospheric model, the NCAR CCM2 general circulation model, has been adapted to study the hourly to yearly variability of CO2 in the atmosphere. Features of this CCM2‐based model include high spatial resolution (2.8° × 2.8° latitude/longitude), 18 vertical levels, a 15‐min time step, and an explicit, nonlocal atmospheric boundary layer parameterization. The surface source/sink relationships used include exchange with the ocean, the terrestrial biosphere, biomass burning, and fossil fuel release of CO2. The timing and magnitude of the model seasonal cycle are compared to observational data for 28 sites. The seasonal cycle of atmospheric CO2 is generally well predicted by the model for most of the northern hemisphere, but estimates of the amplitude of the seasonal cycle in the southern hemisphere are overpredicted. To address this aspect more rigorously, we have used the monthly surface ocean pCO2 maps created by the Max‐Planck‐Hamburg ocean general circulation model to asses the ocean seasonality on the atmospheric surface CO2 seasonality. The globally averaged interhemispheric gradient in atmospheric CO2 concentrations, as computed with the chosen source/sink distributions, is a factor of two too high compared to data, and selected longitudinal bands may be up to 50% higher than the zonal mean. The high temporal resolution of this model allows the infrequent yet real extrema in atmospheric CO2 concentrations to be captured. The vertical attenuation of the seasonal cycle of atmospheric CO2 is well simulated by the boundary layer/free troposphere interaction in the model in the northern hemisphere. Conversely, an increasing amplitude of the seasonal cycle aloft is found in the midlatitude southern hemisphere indicating interhemispheric transport effects from north to south. We use two different models of the terrestrial biosphere to examine the influence on the computed seasonal cycle and find appreciable differences, especially in continental sites. A global three‐dimensional chemical transport model is used to assess the production of CO2 from the oxidation of CO throughout the volume of the atmosphere. We discuss these CO + OH → CO2 + H results within the context of inverse model approaches to ascertaining the global and regional source/sink patterns of CO2. Deficiencies in the model output as compared to observational data are discussed within the context of guiding future research.
Simulated tropical cyclones using the National Center for Atmospheric Research community climate model
Authors: Tsutsui Jun‐ichi , Kasahara Akira
Published: February 2004

The possibility of simulating tropical cyclones (TCs) using the National Center for Atmospheric Research community climate model (CCM2) is explored. Daily outputs from two long‐term simulation runs using the standard T42 resolution CCM2 are examined to identify simulated tropical cyclones (STCs) using a search scheme that selects qualified STCs resembling observed TCs. The two simulation cases are a 20‐year run driven by climatological sea surface temperatures (SSTs) and a 10‐year run, corresponding to the decade from 1979 to 1988, with the same model configuration except for the use of observed SSTs. A composite technique is adopted to reveal the horizontal and vertical structures of well‐developed STCs, and a comparison with those of observed TCs is presented. Then, the climatologies of STCs from the two simulation cases are discussed in terms of their genesis, movements, and seasonal and interannual variations through the comparisons with observed TC statistics. Despite obvious shortcomings of the standard CCM2, such as a coarse horizontal resolution, the structure and climatology of STCs identified in both climate runs are in reasonably good agreement with those of observed TCs. The annual STC frequency shows a better agreement with the observed SST run than the climatological SST run, while many other aspects of STCs in the two climate runs are comparable.
Measurement of O3 and related compounds over southern Nova Scotia: 2. Photochemical age and vertical transport
Authors: Kleinman Lawrence I. , Daum Peter H. , Springston Stephen R. , Leaitch W. Richard , Banic Catharine M. , Isaac George A. , Jobson B. Thomas , Niki Hiromi
Published: February 2004

Chemical measurements of O3 and other trace substances in the atmosphere over southern Nova Scotia, obtained during 48 flights of the National Research Council of Canada Twin Otter aircraft, provide evidence for a variable degree of processing associated with transport times ranging from less than 1 day to 5 days or more. Effects of chemical aging and dilution are determined using photochemical age estimates derived from the ratios, In (n‐butane/propane) and ln (i‐butane/propane). Age estimates are used in a qualitative sense to divide the data set into four age groups. Vertical profiles and relations between O3 and other trace substances are examined as a function of age group. We find that high‐O3 events occurring in dry air are in the oldest age category. Moist high‐O3 events have photochemical ages that span all four age categories, but the most polluted episodes are only observed in relatively “new air.” A geographically wide range of emission regions is suggested by the hydrocarbon measurements, which is consistent with back trajectory results. The relative depletion of soluble substance (i.e., aerosol particles and NOy) in dry, relative to moist, high‐O3 air masses is discussed with respect to the dilution or precipitation scavenging that must accompany the transport of pollutants from the boundary layer to the dryer middle or upper troposphere. Four case studies are presented that span a wide range of conditions associated with high O3 concentrations. In a pair of these cases, samples were obtained in air masses having about the same photochemical age, altitude, and C2H2 and O3 concentration. One of the pair was from dry air and the other from moist air. The dry air mass had much lower concentrations of NOy and aerosol particles, which was interpreted as evidence for the selective removal of soluble constituents during vertical lifting. The other case studies illustrate a biomass burning plume and the effects of a stable layer over the ocean on transport.
Validation of UARS Microwave Limb Sounder temperature and pressure measurements
Authors: Fishbein E. F. , Cofield R. E. , Froidevaux L. , Jarnot R. F. , Lungu T. , Read W. G. , Shippony Z. , Waters J. W. , McDermid I. S. , McGee T. J. , Singh U. , Gross M. , Hauchecorne A. , Keckhut P. , Gelman M. E. , Nagatani R. M.
Published: February 2004

The accuracy and precision of the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) atmospheric temperature and tangent‐point pressure measurements are described. Temperatures and tangent‐point pressure (atmospheric pressure at the tangent height of the field of view boresight) are retrieved from a 15‐channel 63‐GHz radiometer measuring O2 microwave emissions from the stratosphere and mesosphere. The Version 3 data (first public release) contains scientifically useful temperatures from 22 to 0.46 hPa. Accuracy estimates are based on instrument performance, spectroscopic uncertainty and retrieval numerics, and range from 2.1 K at 22 hPa to 4.8 K at 0.46 hPa for temperature and from 200 m (equivalent log pressure) at 10 hPa to 300 m at 0.1 hPa. Temperature accuracy is limited mainly by uncertainty in instrument characterization, and tangent‐point pressure accuracy is limited mainly by the accuracy of spectroscopic parameters. Precisions are around 1 K and 100 m. Comparisons are presented among temperatures from MLS, the National Meteorological Center (NMC) stratospheric analysis and lidar stations at Table Mountain, California, Observatory of Haute Provence (OHP), France, and Goddard Spaceflight Center, Maryland. MLS temperatures tend to be 1–2 K lower than NMC and lidar, but MLS is often 5 – 10 K lower than NMC in the winter at high latitudes, especially within the northern hemisphere vortex. Winter MLS and OHP (44°N) lidar temperatures generally agree and tend to be lower than NMC. Problems with Version 3 MLS temperatures and tangent‐point pressures are identified, but the high precision of MLS radiances will allow improvements with better algorithms planned for the future.
Calibration of the Microwave Limb Sounder on the Upper Atmosphere Research Satellite
Authors: Jarnot R. F. , Cofield R. E. , Waters J. W. , Flower D. A. , Peckham G. E.
Published: February 2004

The Microwave Limb Sounder (MLS) is a three‐radiometer, passive, limb emission instrument onboard the Upper Atmosphere Research Satellite (UARS). Radiometric, spectral and field‐of‐view calibrations of the MLS instrument are described in this paper. In‐orbit noise performance, gain stability, spectral baseline and dynamic range are described, as well as use of in‐flight data for validation and refinement of prelaunch calibrations. Estimated systematic scaling uncertainties (3σ) on calibrated limb radiances from prelaunch calibrations are 2.6% in bands 1 through 3, 3.4% in band 4, and 6% in band 5. The observed systematic errors in band 6 are ∼15%, consistent with prelaunch calibration uncertainties. Random uncertainties on individual limb radiance measurements are very close to the levels predicted from measured radiometer noise temperature, with negligible contribution from noise and drifts on the regular in‐flight gain calibration measurements.
Influence of a priori profiles on trend calculations from Umkehr data
Authors: Mateer C. L. , Dütsch H. U. , Staehelin J. , DeLuisi J. J.
Published: February 2004

Although the new (1992) ozone profile retrieval algorithm for Umkehr measurements provides much better agreement with ozone sounding results than the old (1964) algorithm, considerable discrepancies remain with respect to ozone trends at different levels in the atmosphere. These discrepancies have been found by the comparison of long‐term trends obtained from the Umkehr measurements at Arosa and the ozone balloon soundings at Payerne (Switzerland). It is investigated here whether these obvious discrepancies can be removed by using time‐dependent a priori profiles. This procedure is successful only in the lowest part of the atmosphere, below about 19 km. To further explore this problem, synthetic Umkehr observations are calculated from the ozonesonde profiles. Trends are calculated for both the synthetic and actual Umkehr observations. The difference pattern between these Umkehr observation trends is compared with the difference in ozone profile retrieval trends from the synthetic and actual observations. The distinctive difference patterns strongly indicate an inherent disagreement between the Umkehr observations and the ozonesonde profiles. The application of corrections for stratospheric aerosol effects to the Umkehr profiles reduces, but does not eliminate, a discrepancy above 32 km. It is concluded that the discrepancies are due to the constant mixing ratio assumption used in computing the residual ozone above balloon burst level and to the fair‐weather bias of Umkehr observations (there are Umkehr observations at Arosa on fewer than 20% of the sonde observation days at Payerne). This sampling difference influences the results for the lower stratosphere. The study furthermore indicates that the ozone trends derived from Umkehr measurements for altitudes above about 32 km are robust for time‐dependent changes in the a priori profiles at lower altitudes. Based on the results of this study, we conclude with revised recommendations as to which atmospheric layers should be used for Umkehr trend studies.
Sensitivity of the CH4 growth rate to changes in CH4 emissions from natural gas and coal
Authors: Law K. S. , Nisbet E. G.
Published: February 2004

The observed rate of increase in atmospheric CH4 declined gradually during the late 1980s [Steele et al., 1992] and then fell dramatically by ∼4 to 7 parts per billion by volume (ppbv) yr−1 from 1991 to 1992 [Dlugokencky et al., 1994a]. Post‐1993 the CH4 growth rate has recovered to pre‐1991 levels. In this study, we assess the sensitivity of the CH4 growth rate to changes in CH4 emissions from the coal and gas industries over the last 15 years using a global two‐dimensional (2‐D) model of the atmosphere. Emissions are estimated from available production data, and in the case of natural gas, a spectrum of leakage rates is assumed. Changes in the former Soviet Union (FSU) have been assessed separately from the rest of the world (ROW). Prior to 1989, increased coal and natural gas production led to an increase in the CH4 growth rate (i.e., opposite to that which was observed). During the period 1989 to 1993 the modelled CH4 growth rate decreased by ∼1–2 ppbv yr−2 at northern mid‐latitudes (assuming constant gas leakage rates), showing that declining emissions, primarily in the form of natural gas from the FSU, may have contributed to the general reduction in the CH4 growth rate from 1989 to 1991. However, this does not explain the large reduction which was observed between 1991 and 1992. A model run with FSU gas leakage rates decreasing by 1% yr−1 from 5% in 1990 to 2% in 1993 shows a decrease in the CH4 growth rate of ∼9–12 ppbv yr−1 (or ∼3–5 ppbv yr−2) over this period. This is similar in magnitude to the observed decline over the same period. This sensitivity study illustrates the large potential for significantly lowering the growth rate of atmospheric CH4 by reducing fossil fuel emissions from coal and, in particular, by reducing the leakage rates from natural gas installations.
Accuracy of measurements of total ozone by a SAOZ ground‐based zenith sky visible spectrometer
Authors: Sarkissian A. , Vaughan G. , Roscoe H. K. , Bartlett L. M. , O'Connor F. M. , Drew D. G. , Hughes P. A. , Moore D. M.
Published: February 2004

During a 2‐week intercomparison of ground‐based zenith sky visible spectrometers in September 1994 at Camborne, United Kingdom (50°N, 5°W), ozone profiles were measured by electrochemical cell (ECC) sondes during 11 twilight periods. We use these profiles and a radiative transfer model to calculate separate air mass factors (AMFs) for each twilight period. We examine ozone data from one of the spectrometers of the Système d'Analyse par Observation Zénithale (SAOZ) design and we show that these separate AMFs give very straight Langley plots, except at solar zenith angles exceeding 90°. Total ozone calculated using these AMFs, by a variety of commonly used procedures, agrees with the total ozone calculated by vertically integrating the sonde profiles, with mean differences of 0 to 7 Dobson units (DU), depending on the method, and standard deviations of 9 to 11 DU (1 σ). Total ozone calculated using the best procedure (i.e., averaging twilight values), which is not sensitive to errors in the gradients of AMFs, gave excellent agreement whether using separate AMFs or fixed climatological AMFs. We analyse the variance of the data set and several sources of systematic error in the measurements. We also illustrate from an example during the campaign that such analyses are pointless in the presence of a strong jet stream, which can give rise to changes in ozone during the course of the day that are large enough to invalidate the Langley plot.
Estimates of the water vapor budget of the stratosphere from UARS HALOE data
Authors: Remsberg Ellis E. , Bhatt Praful P. , Russell James M.
Published: February 2004

The water vapor budget of the stratosphere is diagnosed from correlation studies of the UARS Halogen Occultation Experiment sunset measurements of CH4 and H2O in the middle and upper stratosphere, where the correlations are most significant and highly negative. Analyses were conducted for the years 1992–1994 using the methods of (1) linear regression and (2) deterministic differences (or variances of the data). It is assumed that there is conservation of total hydrogen according to a methane oxidation chemical mechanism. Results consist of the zonal mean seasonal distributions of the chemical yield of H2O molecules from each molecule of CH4 (or the β profile) and an estimate of the annual average value of H2O that enters the stratosphere from below (or [H2O]e ), presumably at the tropical tropopause. Average seasonal β values range from 1.6 to 2.4, and their zonal mean patterns are in good agreement with the theoretical model distribution of LeTexier et al., especially for the upper stratosphere. The range for annual average [H2O]e is 2.9 to 3.4 parts per million by volume (ppmv). When adjusted upward by 10% due to known negative biases of about 5% in both the midstratospheric CH4 and the H2O data, [H2O]e becomes 3.2 to 3.7 ppmv and is more consistent with averages of in situ measurements of water vapor at low latitudes of the lower stratosphere. We also find coherent patterns in the seasonal estimates of zonal average water vapor yield that are related to (1) the downward descent of air at winter polar latitudes, (2) the presence of dehydrated air at high latitudes of the southern hemisphere lower stratosphere, and (3) the ascent and relative isolation of the annual (January) minimum in tropical water vapor.
Large‐scale volcanic activity at Maat Mons: Can this explain fluctuations in atmospheric chemistry observed by Pioneer Venus?
Authors: Robinson Cordula A. , Thornhill Gill D. , Parfitt Elisabeth A.
Published: February 2004

Magellan (and Pioneer Venus Orbiter (PVO)) found high mountain terrains on Venus (∼2.5 km above 6051 km planetary radius) exhibit anomalously low radiothermal emissivity. This is thought to result from weathering of primary Venus rock, which at high altitudes produces a distinctive high‐dielectric‐constant mineral assemblage. Deviations from the nominal altitude‐emissivity pattern have been used as a crude chronometric tool with which to date Venusian landforms. This technique indicates Maat Mons (an unusually large shield volcano, standing 9.17 km above 6051 km planetary radius, at 2.1°N, 194.3°E) has undergone a “recent” episode of large‐scale volcanic activity; a deduction also implied morphologically. The present paper investigates whether a plinian eruption at Maat Mons could explain the enhanced concentrations of SO2 gas in the upper atmosphere of Venus that were detected by the Pioneer Venus UV spectrometer. The results show for a minimum vent radius of 156 m, a minimum eruption temperature of 1200 K, and a magmatic volatile content of ∼5 wt%, a plinian eruption at the summit of Maat Mons can explain the anomalous concentration of SO2 gas. This would mean Maat Mons is an active volcano.
The classification and complex thermal history of the enstatite chondrites
Authors: Zhang Yanhong , Benoit Paul H. , Sears Derek W. G.
Published: February 2004

We have carried out instrumental neutron activation analyses of 11 enstatite chondrites and electron microprobe analyses of 17 enstatite chondrites, most of which were previously little described. We report here the third known EH5 chondrite (LEW 88180) and an unusual EL6 chondrite (LEW 87119), new data on four EL3 chondrites (ALH 85119, EET 90299, PCA 91020, and MAC 88136, which is paired with MAC 88180 and MAC 88184), the second EL5 chondrite (TIL 91714), and an unusual metal‐rich and sulfide‐poor EL3 chondrite (LEW 87223). The often discussed differences in mineral composition displayed by the EH and EL chondrites are not as marked after the inclusion of the new samples in the database, and the two classes apparently experienced a similar range of equilibration temperatures. However, texturally the EL chondrites appear to have experienced much higher levels of metamorphic alteration than EH chondrites of similar equilibration temperatures. Most of the petrologic type criteria are not applicable to enstatite chondrites and, unlike the ordinary chondrites, texture and mineralogy reflect different aspects of the meteorite history. We therefore propose that the existing petrologic type scheme not be used for enstatite chondrites. We suggest that while “textural type” reflects peak metamorphic temperatures, the “mineralogical type” reflects equilibration during postmetamorphic (probably regolith) processes. Unlike the ordinary chondrites and EH chondrites, EL chondrites experienced an extensive low‐temperature metamorphic episode. There are now a large number of enstatite meteorite breccias and impact melts, and apparently surface processes were important in determining the present nature of the enstatite chondrites.
Absorption coefficient of propynenitrile in the mid‐UV range for the study of Titan's atmosphere: Solution to sample contaminations
Authors: Andrieux Dominique , Bénilan Yves , de Vanssay Etienne , Paillous Pierre , Khlifi Mohamed , Raulin François , Bruston Paul , Guillemin Jean‐Claude
Published: February 2004

UV spectroscopy is a powerful diagnostic tool in the study of organic composition and chemical processes in planetary atmospheres such as that of Titan. The Spectroscopie UV d'Intérêt Prébiologique dans l'Atmosphère de Titan (SIPAT) laboratory experiment has been developed in order to systematically determine at high resolution the absorption coefficients of expected molecular absorbers in Titan's atmosphere, with the goal of interpreting mid‐UV albedo spectra. We have studied the mid‐UV absorption coefficient of propynenitrile (cyanoacetylene), which is a key compound in prebiotic chemistry. In spite of all the precautions taken during the synthesis of this compound, the samples studied contain impurities. Using complementary techniques, we have been able to characterize the impurities (mainly acetone and acetonitrile) in the propynenitrile gas sample. Thus, we present new absorption coefficients of propynenitrile determined at 298 K and at 0.02 nm resolution between 185 and 200 nm (the wavelength range where acetone presents strong absorption features). A precise determination of impurity mixing ratios affecting previously published spectra leads to a reevaluation and the establishment of associated uncertainty values for HC3N absorption coefficients in the 185‐ to 230‐nm range. Finally, these data have been corrected for an erroneous wavelength calibration implying a 3 Å shift.
Observing the icy Jovian satellites with the Galileo photopolarimeter radiometer instrument
Authors: Tamppari L. K. , Spencer J. R. , Martin T. Z.
Published: February 2004

The photopolarimeter/radiometer (PPR) instrument aboard the Galileo spacecraft will go into orbit around Jupiter in December 1995. The 23‐month tour offers PPR four Ganymede encounters, three Callisto encounters, and three Europa encounters with maximum PPR resolution varying from 0.5 km to 8 km and typical resolution of 200 km. In addition, there will be one Ganymede, one Callisto, and two Europa “nontargeted” encounters, giving maximum PPR resolution from 58 km to 200 km, with a typical resolution of 300 km. There is a single Io encounter before Jupiter orbit insertion that will provide resolutions ranging from 400 km to 2.5 km, and numerous subsequent opportunities to observe Io with resolution as good as 600 km. The PPR will be used to study the polarization of reflected sunlight from each satellite over a wide range of phase angles. It will also map daytime and nighttime surface temperatures to look for spatial variations in thermophysical properties, study volcanic activity on Io, and look for possible endogenic thermal activity on Europa. These observation plans are presented.
The Galileo Imaging Team plan for observing the satellites of Jupiter
Authors: Carr M. H. , Belton M. J. S. , Bender K. , Breneman H. , Greeley R. , Head J. W. , Klaasen K. P. , McEwen A. S. , Moore J. M. , Murchie S. , Pappalardo R. T. , Plutchak J. , Sullivan R. , Thornhill G. , Veverka J.
Published: February 2004

The Galileo spacecraft carries a 1500‐nm focal length camera with a 800 × 800 CCD detector that will provide images with a spatial resolution of 10 μrad/pixel. The spacecraft will fly by Io at the time of Jupiter Orbit Insertion (JOI) and, subsequently, while in Jupiter's orbit, will have a total of 10 close passes by Europa, Ganymede, and Callisto. These close passes, together with more distant encounters, will be used by the imaging experiment primarily to obtain high‐resolution coverage of selected targets, to fill gaps left in the Voyager coverage, to extend global color coverage of each satellite, and to follow changes in the volcanic activity of Io. The roughly 390 Mbit allocated for imaging during the tour will be distributed among several hundred frames compressed by factors that range from 1 to possibly as high as 50. After obtaining high‐resolution samples during the initial Io encounter at JOI, roughly 10% of imaging resources are devoted to near‐terminator mapping of Io's topography at 2‐ to 10‐km resolution, monitoring color and albedo changes of the Ionian surface, and monitoring plume activity. Observations of Europa range in resolution from several kilometers per pixel to 10 m/pixel. The objectives of Europa are (1) to determine the nature, origin, and age of the tectonic features, (2) to determine the nature, rates, and sequence of resurfacing events, (3) to assess the satellite's cratering history, and (4) to map variations in spectral and photometric properties. Europa was poorly imaged by Voyager, so the plan includes a mix of high‐ and low‐resolution sequences to provide context. The imaging objectives at Ganymede are (1) to characterize any volcanism, (2) to determine the nature and timing of any tectonic activity, (3) to determine the history of formation and degradation of impact craters, and (4) to determine the nature of the surface materials. Because Ganymede was well imaged by Voyager, most of the resources at Ganymede are devoted to high‐resolution observations. The Callisto observations will be directed mostly toward (1) filling Voyager gaps, (2) acquiring high‐resolution samples of typical cratered terrain and components of the Valhalla and Asgaard basins, (3) acquiring global color, and (4) determining the photometric properties of the surface. A small number of frames will be used to better characterize the small inner satellites of Jupiter, Thebe, Amalthea, Metis, and Adrastea.
A simple model for the light curve generated by a Shoemaker‐Levy 9 impact
Authors: Zahnle Kevin , Mac Low Mordecai‐Mark
Published: February 2004

The impact of a typical Shoemaker‐Levy 9 fragment produced three light peaks as seen from Earth. The first peak is related to the entry of the fragment into the Jovian atmosphere. The second peak occurs when the exploding fireball rises above Jupiter's limb into direct view from Earth. The third peak, much the brightest, occurs when the ejecta plume falls back on the atmosphere. By contrast, Galileo, which had a direct view of the impacts, saw two peaks, one at entry, and one at plumefall. Here we present a simple, highly idealized model of a ballistic plume, which we then use to fit the observed light curve of the R impact as recorded at Mauna Kea and Mount Palomar. From the light curve we find that the nominal R fragment had diameter 450–500 m and mass ∼2 ‐ 3 × 1013 g. The uncertainty in the mass is probably about a factor of 3, with a smaller event more likely than a larger one.
Detection of very high altitude fallout from the comet Shoemaker‐Levy 9 explosions in Jupiter's atmosphere
Authors: Mallama Anthony , Nelson Peter , Park James
Published: February 2004

A comparison between visible light charge‐coupled device (CCD) photometry and model light curves for several Jovian satellite eclipses reveals that significant attenuating material was present in Jupiter's atmosphere up to about 300 km (relative to the 1‐bar pressure level) over the comet Shoemaker‐Levy 9 impact sites a month after the explosions occurred.
Electromagnetic induction heating of meteorite parent bodies by the primordial solar wind
Authors: Shimazu H. , Terasawa T.
Published: February 2004

We consider the electromagnetic induction heating of meteorite parent bodies in the strong solar wind in the T Tauri phase of the Sun including the effect of the Alfvén wing generated by the interaction between a steady uniformly flowing magnetized plasma and a conductor. The characteristics of the electric current induced in the conductor are determined by the shortest of the three characteristic times: time for the Alfvén wave to propagate from one boundary of the conductor to the other (Alfvén travel time), time for the flow to cross the conductor, and time for the conductor to diffuse the magnetic field. The limit for which the Alfvén travel time is the shortest is applied to the interaction between a meteorite parent body and the solar wind in the T Tauri phase. In this limit the increase of the temperature of meteorite parent bodies is independent of the magnetic field, and inversely proportional to the electrical conductivity of meteorite parent bodies. Numerical calculations are carried out in the case where the electrical conductivity depends on the temperature. The result shows that the region of the high heating rate is confined to the surface. Since the conductivity has a strong positive dependence on the temperature, negative feedback on the heating process tends to suppress the temperature increase. The result also indicates that the lower the surface temperature, the higher the heating rate, since the conductivity is kept low.
Lava flow surface roughness and depolarized radar scattering
Authors: Campbell Bruce A. , Shepard Michael K.
Published: February 2004

Surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations. We compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5.7, 24, and 68 cm (C, L, and P band) wavelengths. The roughness is found to vary with scale in a self‐affine (fractal) manner for scale lengths between 25 cm (the smallest horizontal step size) and 3–5 m. This result is used to demonstrate that a two‐component surface description, consisting of the fractal dimension and rms height or slope at some reference scale, can resolve some of the ambiguities in previous efforts to quantify roughness. At all three radar wavelengths, the HV backscatter cross section is found to vary in an approximately exponential fashion with the rms height or Allan deviation at some reference scale, up to a saturation point, where the surface appears entirely diffusely scattering to the radar. Based on these observations, we use a parameter, γ, defined as the ratio of rms height to the particular scale of measurement. Backscatter values at 24‐cm wavelength and the topographic profile data were used to derive expressions which link the HV radar cross section to γ or to the analogous wavelength‐scale rms slope. These equations provide a reasonable fit to 24‐ and 68‐cm echoes and for rough surfaces at 5.7 cm, but yield poor results for 5.7‐cm echoes on smooth terrain. We conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height, but that texture at very small scales is characterized by different statistics. This inference is supported by analysis of 5‐cm horizontal spacing topographic profiles. The relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength. Given radar data at additional wavelengths, a more complete view of the statistical properties of the surface can be developed. Such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas, Magellan data for Venus, and other planetary radar observations.
Photochemistry of Triton's atmosphere and ionosphere
Authors: Krasnopolsky Vladimir A. , Cruikshank Dale P.
Published: February 2004

The photochemistry of 32 neutral and 21 ion species in Triton's atmosphere is considered. Parent species N2, CH4, and CO (with a mixing ratio of 3×10−4 in our basic model) sublime from the ice with rates of 40, 208, and 0.3 g/cm2/b.y., respectively. Chemistry below 50 km is driven mostly by photolysis of methane by the solar and interstellar medium Lyman‐alpha photons, producing hydrocarbons C2H4, C2H6, and C2H2 which form haze particles with precipitation rates of 135, 28, and 1.3 g/cm2/b.y., respectively. Some processes are discussed which increase the production of HCN (by an order of magnitude to a value of 29 g/cm2/b.y.) and involve indirect photolysis of N2 by neutrals. Reanalysis of the measured methane profiles gives an eddy diffusion coefficient K = 4 × 103 cm2/s above the tropopause and a more accurate methane number density near the surface, (3.1±0.8)×1011 cm−3. Chemistry above 200 km is driven by the solar EUV radiation (λ < 1000 Å) and by precipitation of magnetospheric electrons with a total energy input of 108 W (based on thermal balance calculations). The most abundant photochemical species are N, H2, H, O, and C. They escape with the total rates of 7.7×1024 s−1, 4.5×1025 s−1, 2.4×1025 s−1, 4.4×1022 s−1, and 1.1×1024 s−1, respectively. Atomic species are transported to a region of 50–200 km and drive the chemistry there. Ionospheric chemistry explains the formation of an E region at 150–240 km with HCO+ as a major ion, and of an F region above 240 km with a peak at 320 km and C+ as a major ion. The ionosphere above 500 km consists of almost equal densities of C+ and N+ ions. The model profiles agree with the measured atomic nitrogen and electron density profiles. A number of other models with varying rate coefficients of some reactions, differing properties of the haze particles (chemically passive or active), etc., were developed. These models show that there are four basic unknown values which have strong impacts on the composition and structure of the atmosphere and ionosphere. These values and their plausible ranges are the CO mixing ratio ƒco = 10−4–10−3, the magnetospheric electron energy input (1±0.5)×108 W, the rate coefficient of charge‐exchange reaction N2+ + C k = 10−11–10−10 cm3/s, and the ion escape velocity vi, ≈ 150 cm/s.