bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar backscattered ultraviolet (SBUV) observations of polar mesospheric clouds (PMCs) over two solar cycles
Authors: DeLand Matthew T. , Shettle Eric P. , Thomas Gary E. , Olivero John J.
Published: May 2003

Previous satellite measurements have provided nearly complete seasonal and geographic coverage of polar mesospheric clouds (PMCs), but previous data sets have not been able to evaluate changes in PMC behavior on decadal timescales. The Solar Backscattered Ultraviolet (SBUV) series of ozone measuring instruments have been flying continuously since 1978. While the instrument design is not optimized for PMC detection, the radiance data can be analyzed to examine the occurrence frequency and intensity of relatively bright PMCs. In this paper, we present PMC results from five SBUV and SBUV/2 instruments covering more than 23 years (1978–2002), starting just before the maximum of solar cycle 21 and extending through the maximum of solar cycle 23. The overlapping data sets from nearly identical instruments give an accurate picture of long‐term variations. Multiple linear regression fits are used to examine solar and secular correlations. PMC occurrence frequency is anticorrelated with solar Lyman alpha irradiance, with an approximate 0.5‐year phase lag in the Northern Hemisphere (Rsolar = −0.87) and no phase lag in the Southern Hemisphere (Rsolar = −0.65). The distribution of cloud brightness by season appears to be changing over time. When the PMC brightness for each season is characterized using an exponential cumulative distribution function, the exponent decreases in magnitude by a factor of 2 from 1978 to 2002 in the Southern Hemisphere (Rtime = +0.85). This implies an increase in the relative proportion of the brightest PMCs. The secular brightness trend is less significant in the Northern Hemisphere (Rtime = +0.58). We discuss possible origins for these changes.
Influence of sea surface temperature anomalies in the Gulf of California on North American monsoon rainfall
Authors: Mo Kingtse C. , Juang H. M. Henry
Published: May 2003

Linkages between sea surface temperatures (SSTs) in the Gulf of California and the North American monsoon rainfall were examined using observational data and regional model experiments. SSTs in the Gulf start to increase in late June and reach a maximum in August. Monsoon onset dates in the Southwest were determined from the gridded rainfall analysis. Monsoon onsets can occur before SSTs in the Gulf reach a maximum. There is no relationship between monsoon rainfall onset dates or seasonal total rainfall over the Southwest and SSTs in the Gulf. Regional model experiments were then performed to study the impact of local SSTs on monsoon rainfall using the NCEP regional spectral model (RSM). RSM experiments were performed with the observed SSTs for four summers (July–September 1997–2000). The experiments were repeated with the same initial and boundary conditions but with the climatological SSTs in the Gulf of California and its vicinity. The model is able to capture the general features of monsoon rainfall and the diurnal cycle. Warm (cold) SSTs in the Gulf are responsible for more (less) rainfall along the western slopes of the Sierra Madre Occidental. Over the Southwest, the impact of local SSTs is small. Large‐scale flow has more influence on monsoon rainfall than SSTs in the Gulf of California because the SST forcing does not produce significant changes in the low level flow needed to influence rainfall over the Southwest.
Sea surface temperature forcing of the upward trend in U.S. extreme precipitation
Authors: Kunkel Kenneth E.
Published: May 2003

Retrospective climate simulations using the Goddard Institute for Space Studies SI2000 global climate model were used to examine possible causes of the observed upward trend in the frequency of U. S. extreme precipitation events. Three experiments were performed for the period 1951–1997, all with identical external radiative forcing but with different ocean treatments. One experiment used the “Q flux” ocean model. The second experiment imposed observed time‐varying sea surface temperatures (SSTs). The third experiment imposed observed time‐varying SSTs for the tropical Pacific only and imposed climatological SSTs elsewhere. The Q flux ocean experiment did not reproduce the observed upward trend. Both experiments using observed time‐varying SSTs produced an upward trend qualitatively similar to the observed trend for 7‐day duration events, although agreement was not as good for 1‐day duration events. However, the experiment with time‐varying SSTs only in the tropical Pacific was found to be overly sensitive to the increasing frequency of El Niño events. Changes in atmospheric water vapor content for the two imposed‐SST experiments were consistent with what might be expected to accompany increases in extreme precipitation. These results suggest that the spatial and temporal variations of SSTs on a global scale may be one direct and proximate cause of the recent observed upward trend in U. S. extreme multiday‐duration precipitation events.
Inorganic and carbonaceous aerosols during the Southern African Regional Science Initiative (SAFARI 2000) experiment: Chemical characteristics, physical properties, and emission data for smoke from African biomass burning
Authors: Formenti P. , Elbert W. , Maenhaut W. , Haywood J. , Osborne S. , Andreae M. O.
Published: May 2003

We collected filter samples of the atmospheric aerosol during the Southern African Regional Science Initiative (SAFARI 2000) experiment onboard the UK Met Office C‐130 aircraft. The main operational area was the Atlantic Ocean offshore of Namibia and Angola, where biomass‐smoke haze at least 1–2 days old was widespread. The size‐fractionated aerosol samples were analyzed for the major inorganic ions, carbonaceous material (elemental and organic carbon), and elements with atomic numbers between 11 (Na) and 82 (Pb). The regional haze aerosol was composed mostly of carbonaceous aerosols (on the average, 81% of the submicron mass), with secondary inorganic aerosols (sulfate, ammonium, and nitrate) accounting for another 14%. K+ and Cl−, typical pyrogenic species, constituted only 2% of the mass. The aerosol chemical data were used to estimate mass emission fluxes for various aerosol components. For African savanna/grassland burning, the estimated emission flux of carbonaceous particles (particulate organic matter plus elemental carbon) is 14 ± 1 Tg yr−1, and that of the nitrogen species (nitrate and ammonium) is 2 ± 2 Tg yr−1. For the flight segments in regional haze, the mean particle scattering coefficient at 550 nm was σs = 101 ± 56 Mm−1 and the mean particle absorption coefficient σa at 565 nm averaged 8 ± 5 Mm−1 (mean single scattering albedo of 0.93 ± 0.06 at 550 nm). The dry mass scattering efficiency αs, calculated from the linear regression of the mean scattering versus the estimated submicron mass, is estimated to be between 4.2 ± and 4.6 ± 0.6 m2 g−1, depending on the assumptions made in calculating the aerosol mass. The dependence of the scattering enhancement ratios Δσs/ΔCO on the distance from the burning regions suggests that the evolution of particle size with time influences the light scattering efficiency. Fresh smoke was sampled during a dedicated flight in the proximity and within the plume of an active biomass burning fire. Here the enhancement ratio with respect to CO of particles in the Aitken‐size range (5–100 nm diameter) was ΔNAitken/ΔCO ∼25 cm−3 (STP) ppb−1. These particles were removed rapidly after emission, and they were not detectable in the regional haze. The enhancement ratio for accumulation mode particles (0.1–1 μm diameter) ΔNAcc/ΔCO was ∼26–30 cm−3 (STP) ppb−1 in young smoke, and 16 ± 3 cm−3 (STP) ppb−1 in aged haze, suggesting that the number concentration of accumulation mode particles was reduced by about 41% during aging.
Tangent linear analysis of the Mosaic land surface model
Authors: Yang Runhua , Cohn Stephen E. , da Silva Arlindo , Joiner Joanna , Houser Paul R.
Published: May 2003

In this study, a tangent linear eigenanalysis is applied to the Mosaic land surface model (LSM) [Koster and Suarez, 1992] to examine the impacts of the model internal dynamics and physics on the land surface state variability. The tangent linear model (TLM) of the Mosaic LSM is derived numerically for two sets of basic states and two tile types of land condition, grass and bare soil. An additional TLM, for the soil moisture subsystem of this LSM, is derived analytically for the same cases to obtain explicit expressions for the eigenvalues. An eigenvalue of the TLM determines a characteristic timescale, and the corresponding eigenvector, or mode, describes a particular coupling among the perturbed states. The results show that (1) errors in initial conditions tend to decay with e‐folding times given by the characteristic timescales; (2) the LSM exhibits a wide range of internal variability, modes mainly representing surface temperature and surface moisture perturbations exhibit short timescales, whereas modes mainly representing deep soil temperature perturbations and moisture transfer throughout the entire soil column exhibit much longer timescales; (3) the modes of soil moisture tend to be weakly coupled with other perturbed variables, and the mode representing the deep soil temperature perturbation has a consistent e‐folding time across the experiments; (4) the key parameters include soil moisture, soil layer depth, and soil hydraulic parameters. The results agree qualitatively with previous findings. However, tangent linear eigenanalysis provides a new approach to the quantitative substantiation of those findings. Also, it reveals the evolution and the coupling of the perturbed land states that are useful for the development of land surface data assimilation schemes. One must be careful when generalizing the quantitative results since they are obtained with respect to two specific basic states and two simple land conditions. Also, the methodology employed here does not apply directly to an actual time‐varying basic state.
Solar spectral radiative forcing during the Southern African Regional Science Initiative
Authors: Pilewskie P. , Pommier J. , Bergstrom R. , Gore W. , Howard S. , Rabbette M. , Schmid B. , Hobbs P. V. , Tsay S. C.
Published: May 2003

During the dry season component of the Southern African Regional Science Initiative (SAFARI) in late winter 2000, the net solar spectral irradiance was measured at flight levels throughout biomass burning haze layers. From these measurements, the flux divergence, fractional absorption, instantaneous heating rate, and absorption efficiency were derived. Two cases are examined: on 24 August 2000 off the coast of Mozambique in the vicinity of Inhaca Island and on 6 September 2000 in a very thick continental haze layer over Mongu, Zambia. The measured absolute absorption was substantially higher for the case over Mongu where the measured midvisible optical depth exceeded unity. Instantaneous heating from aerosol absorption was 4 K d−1 over Mongu, Zambia and 1.5 K d−1 near Inhaca Island, Mozambique. However, the spectral absorption efficiency was nearly identical for both cases. Although the observations over Inhaca Island preceded the “river of smoke” from the southern African continent by nearly 2 weeks, the evidence here suggests a continental influence in the lower tropospheric aerosol far from source regions of burning.
Influences of ice particles on the ion chemistry of the polar summer mesosphere
Authors: Gumbel J. , Siskind D. E. , Witt G. , Torkar K. M. , Friedrich M.
Published: May 2003

In the polar summer mesosphere, charge is distributed over a wide range of constituents closely connected to phenomena like noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs). In this paper, we study how the presence of ice particles influences mesospheric ion chemistry, and how this may feed back on the particle population. To this end, we present an ion‐chemical model that for the first time features close coupling with cluster growth and ice particle charging. Starting out from molecular ion reactions, the H+(H2O)n proton hydrate chain is described using the Thomson model and Natanson's recombination scheme. Under most mesospheric conditions, electron capture by particles is expected to enhance the lifetimes and concentrations of positive ions and clusters. This has important consequences for the total charge density and mobility in the environment of particle layers. Extending the proton hydrate chain to large cluster sizes, we also quantify the efficiency of ionic nucleation of mesospheric ice particles. While ionic nucleation is not feasible as a major mesospheric nucleation process, it can become efficient given moderate atmospheric variations as induced by gravity waves. This leads to a scenario of rapid generation of populations with many small particles in local temperature minima. We show that electron capture to existing particles can significantly enhance the ionic nucleation of new particles. In summary, there are many potential connections between ion chemistry and layered phenomena in the mesosphere that should be included in comprehensive models of NLC/PMSE. Unfortunately, uncertainties in ionic reaction rates are a persistent problem and in great need of laboratory measurements representative for cold summer mesopause conditions.
Real‐time monitoring of environmental radiation in Tunguska (Siberia)
Authors: Cecchini S. , Galli M. , Giovannini G. , Longo G. , Pagliarin A.
Published: May 2003

The results of the environmental radiation (ER) monitoring obtained during the Tunguska expedition of July 1999 with a NaI(Tl) scintillation detector are reported. Some interesting meteorological effects related to the airborne radioactive components (radon and thoron decay products) have been observed. The main effects observed are (1) the doubling of the ER during two quite different rain‐out episodes and (2) a fairly regular diurnal wave in the intensity of the total radiation. The rain‐out phenomenon allows us to approximate the timescale for the removal by precipitation of radioactivity from the air, while the wave phenomenon gives us the opportunity to develop a simplified model for estimating the time‐averaged, dry weather surface radon concentration.
Noctilucent clouds above ALOMAR between 1997 and 2001: Occurrence and properties
Authors: Fiedler J. , Baumgarten G. , von Cossart G.
Published: May 2003

We report on observations of noctilucent clouds (NLCs) by a ground‐based lidar located in northern Norway at 69°N, 16°E. The ALOMAR Rayleigh/Mie/Raman (RMR) lidar conducted measurements of the Arctic middle atmosphere from 1 June to 15 August during each year from 1997 to 2001. This data set contains 1122 hours of lidar observations whereof 408 hours include NLC signatures. The interannual variation of the NLC occurrence frequency shows a decrease of strong NLCs, while weak NLCs occur more frequent. The seasonal variation of the NLC occurrence shows a well pronounced core period where NLCs appeared during 43% of the time. The basic properties of NLCs are characterized by three parameters: maximum value of the volume backscatter coefficient βmax (≡brightness), centroid altitude zc, and half width δz (≡thickness). A typical NLC above ALOMAR during the 5‐year period reported here owns a brightness of βmax = 9.6 × 10−10 m−1 sr−1, an altitude of zc = 83.3 km, and a thickness of δz = 1.2 km. The interannual variation of the parameters shows a decrease of the brightness, an increase of the altitude, and a nearly constant thickness, while seasonal variability is higher than these interannual changes. During the core period, the NLCs are noticeably brighter than at the beginning as well as the end of the season. Altitude and thickness of NLCs decrease during the season.
Aeolian iron input to the ocean through precipitation scavenging: A modeling perspective and its implication for natural iron fertilization in the ocean
Authors: Gao Yuan , Fan Song‐Miao , Sarmiento Jorge L.
Published: May 2003

Aeolian dust input may be a critical source of dissolved iron for phytoplankton growth in some oceanic regions. We used an atmospheric general circulation model (GCM) to simulate dust transport and removal by dry and wet deposition. Model results show extremely low dust concentrations over the equatorial Pacific and Southern Ocean. We find that wet deposition through precipitation scavenging accounts for ∼40% of the total deposition over the coastal oceans and ∼60% over the open ocean. Our estimates suggest that the annual input of dissolved Fe by precipitation scavenging ranges from 0.5 to 4 × 1012 g yr−1, which is 4–30% of the total aeolian Fe fluxes. Dissolved Fe input through dry deposition is significantly lower than that by wet deposition, accounting for only 0.6–2.4 % of the total Fe deposition. Our upper limit estimate on the fraction of dissolved Fe in the total atmospheric deposition is thus more than three times higher than the value of 10% currently considered as an upper limit for dissolved Fe in Aeolian fluxes. As iron input through precipitation may promote episodic phytoplankton growth in the ocean, measurements of dissolved iron in rainwater over the oceans are needed for the study of oceanic biogeochemical cycles.
Can the variability in tropospheric OH be deduced from measurements of 1,1,1‐trichloroethane (methyl chloroform)?
Authors: Krol Maarten , Lelieveld Jos
Published: May 2003

Global three‐dimensional (3‐D) model calculations have been used to inversely determine OH concentrations from 1,1,1‐trichloroethane (methyl chloroform or CH3CCl3) measurements at the Atmospheric Lifetime Experiment (ALE)/Global Atmospheric Gases Experiment (GAGE)/Advanced GAGE (AGAGE) measurement stations. Annual global and biannual hemispheric estimates of OH show large fluctuations. With the aid of “pseudo data,” it is shown that these estimates are sensitive to simplifying assumptions in the model that is used for the inversion. The use of climatological transport and errors in the emissions cause spurious fluctuations in the retrieved OH levels. If only the slow OH variations are considered, an OH increase of about 12% is calculated in the 1978–1990 period, which is followed by a slightly larger decline in the 1991–2000 period. The N/S interhemispheric ratio is optimized to a value of about 0.98. Model calculations indicate that because of a rapidly decreasing CH3CCl3 burden in the 1990s, the stratospheric sink has become less important. Moreover, owing to the changed CH3CCl3 distribution, interhemispheric transport of CH3CCl3 has ceased in recent years. These effects lead to systematic differences with results obtained with highly parameterized models with very low resolution. The large OH anomaly that is inferred around 1990 vanishes if CH3CCl3 emissions of about 65 Gg were delayed from the early to the late 1990s.
Simultaneous lidar observations of a noctilucent cloud and an internal wave in the polar mesosphere
Authors: Collins R. L. , Kelley M. C. , Nicolls M. J. , Ramos C. , Hou T. , Stern T. E. , Mizutani K. , Itabe T.
Published: May 2003

Lidar and radar observations of the upper mesosphere and lower thermosphere were conducted in interior Alaska (65°N, 147°W) during the summer of 2001. Lidar observations of a noctilucent cloud (NLC) were made on the night of 20–21 August 2001 during a visible noctilucent cloud display when the midnight solar depression angle was 12°. These nighttime lidar observations in late August have yielded measurements of both the NLC at 82.7 km and the mesospheric temperature profile below the cloud (∼40–80 km). Analysis of the temperature profile indicates the presence of a wave with a vertical wavelength of 7.9 km. The altitude of the NLC coincides with the cold phase of the temperature wave. Located approximately 50 km from the lidar, radar observations yielded measurements of polar mesosphere summer echoes (PMSEs) during daytime on 21 August 2001. The PMSE layer occurs just above the NLC layer and also shows structural characteristics associated with the passage of gravity waves through the layer. The presence of NLCs in late August supports recent reports that the late summer Arctic mesosphere is colder and wetter than represented in “standard” models. These NLC observations are discussed in terms of earlier lidar observations over Alaska, observations at other sites, and current models.
Relations between small scale electron number density fluctuations, radar backscatter, and charged aerosol particles
Authors: Blix Tom Arild , Rapp Markus , Lübken Franz‐Josef
Published: May 2003

During several campaigns during the last 10 years, detailed in situ studies of electrons, positive ions, and charged aerosols have been performed by means of rocket borne instruments in the presence of Polar Mesophere Summer Echoes (PMSE) and Noctilucent Clouds (NLC). We have studied the correlation between the amount of charged aerosols present in the mesopause region and the PMSE echo power. We have also correlated the PMSE echo strength with the small‐scale structure of electrons at the radar Bragg scale that are responsible for the echoes. We find that PMSE occur for rather small amounts of charged aerosols, with the number of electrons exceeding the number of charged aerosols. This is in contradiction with previous, mainly theoretical, studies predicting that PMSE only occur when the ratio between the aerosol charge number density and the number density of electrons is larger than about 1. We also find that there is a high degree of correlation between the PMSE echo power and the fluctuation intensity of electrons at scales comparable to half the radar wavelength. This confirms that variations in electron number density are responsible for the echoes, but does not explain the mechanism that creates the fluctuations.
Development of a chlorine mechanism for use in the carbon bond IV chemistry model
Authors: Tanaka Paul L. , Allen David T. , McDonald‐Buller Elena C. , Chang Sunghye , Kimura Yosuke , Mullins C. Buddie , Yarwood Greg , Neece James D.
Published: May 2003

Chlorine chemistry has been incorporated into the carbon bond IV mechanism and employed in a regional photochemical model (the Comprehensive Air Quality Model with Extensions (CAMx)) for preliminary use in assessing the regional impact of chlorine on ozone formation in Houston, Texas. Mechanisms employed in regional photochemical models do not currently account for chlorine chemistry. However, when chlorine chemistry is accounted for, predicted ozone levels are enhanced by up to 16 ppbv in the Houston area, with the greatest enhancement predicted for morning hours after sunrise. Thirteen reactions have been added to the chemical mechanism used by CAMx to describe chlorine chemistry in the urban atmosphere. The reactions include photolysis of chlorine radical (Cl·) precursors, Cl·+ hydrocarbon reactions, and Cl·+ ozone reactions. The hydrocarbon reactions include the reactions of Cl· with isoprene and 1,3‐butadiene that yield unique reaction products, or marker species. The development of this mechanism is presented along with a discussion of the initial set of predictions of chlorine‐based ozone enhancement in the Houston area. Of significant interest is that methane may be activated by chlorine to contribute significantly to the predicted ozone enhancement in the Houston area. Such behavior suggests that the impact of chlorine chemistry would be proportional to the availability of Cl· precursor. In urban areas with anthropogenic sources of chlorine radical precursors, chlorine radical chemistry may be important to more accurately predict ozone formation.
Estimates of the spectral aerosol single scattering albedo and aerosol radiative effects during SAFARI 2000
Authors: Bergstrom Robert W. , Pilewskie Peter , Schmid Beat , Russell Philip B.
Published: May 2003

Using measurements of the spectral solar radiative flux and optical depth for 2 days (24 August and 6 September 2000) during the SAFARI 2000 intensive field experiment and a detailed radiative transfer model, we estimate the spectral single scattering albedo of the aerosol layer. The single scattering albedo is similar on the 2 days even though the optical depth for the aerosol layer was quite different. The aerosol single scattering albedo was between 0.85 and 0.90 at 350 nm, decreasing to 0.6 in the near infrared. The magnitude and decrease with wavelength of the single scattering albedo are consistent with the absorption properties of small black carbon particles. We estimate the uncertainty in the single scattering albedo due to the uncertainty in the measured fractional absorption and optical depths. The uncertainty in the single scattering albedo is significantly less on the high‐optical‐depth day (6 September) than on the low‐optical‐depth day (24 August). On the high‐optical‐depth day, the uncertainty in the single scattering albedo is 0.02 in the midvisible whereas on the low‐optical‐depth day the uncertainty is 0.08 in the midvisible. On both days, the uncertainty becomes larger in the near infrared. We compute the radiative effect of the aerosol by comparing calculations with and without the aerosol. The effect at the top of the atmosphere (TOA) is to cool the atmosphere by 13 W m−2 on 24 August and 17 W m−2 on 6 September. The effect on the downward flux at the surface is a reduction of 57 W m−2 on 24 August and 200 W m−2 on 6 September. The aerosol effect on the downward flux at the surface is in good agreement with the results reported from the Indian Ocean Experiment (INDOEX).
Seasonal variation of water‐soluble ions of the aerosol at the high‐alpine site Jungfraujoch (3580 m asl)
Authors: Henning S. , Weingartner E. , Schwikowski M. , Gäggeler H. W. , Gehrig R. , Hinz K.‐P. , Trimborn A. , Spengler B. , Baltensperger U.
Published: May 2003

Within the Global Atmosphere Watch (GAW) Aerosol Program of the World Meteorological Organization (WMO), the aerosol chemical composition has been continuously measured since July 1999 at the Jungfraujoch (JFJ) of which the first 1.5‐year data set is presented. Sampling is performed in two size classes (total suspended particles (TSP) and particles with aerodynamic diameters smaller than 1 μm). The filters are analyzed for major ions, which constitute 30% of the total dry aerosol mass collected at this site. As annual mean, a total ion mass concentration of 1.04 μg m−3 was observed. Sulfate, ammonium, and nitrate were the major components of the fine aerosol fraction, while calcium and nitrate were two major water‐soluble components in the coarse mode. Single particle analysis confirmed the internal mixture of calcium and nitrate in the coarse mode. The total ion mass concentration showed strong seasonal differences, with 1.25, 1.62, 0.70, and 0.25 μg m−3 for spring, summer, fall, and winter, respectively. The variability was stronger for sulfate, ammonium, and nitrate than for calcium. The reason for this is believed to be local sources of calcium, which do not require vertical transport, along with Sahara dust episodes, which occur occasionally over the whole year, independent from the season.
The quasi 2‐day wave observed in the polar mesosphere
Authors: Nozawa S. , Imaida S. , Brekke A. , Hall C. M. , Manson A. , Meek C. , Oyama S. , Dobashi K. , Fujii R.
Published: May 2003

Using MF radar data obtained at Tromsø (69.6°N, 19.2°E) for ∼37 months between 1 November 1998 and 8 December 2001, we have examined characteristics of the quasi 2‐day wave (Q2DW) in the polar mesosphere in the height range from 70 to 91 km. The activity of the Q2DW is higher in winter months (November–February) than in summer months (May–August) over this height region. The maximum values of the amplitude are ∼25 m s−1 in winter and ∼15 m s−1 in summer. Between 70 and 82 km, the amplitude appears to maximize near winter solstice over the 3 years. The average ratio of meridional to zonal amplitudes is ∼1.1–1.2 over the height region. Thus, there is no significant preference towards either components. The variations of the periods of maximum amplitude are also examined, and periods with 45.2 and 54.9 hours occur more frequently than those with 48.0 and 51.2 hours. However, no clear seasonal trend of the variation of the period is found. In addition, the amplitude is modulated at 4–10 day rate. With simultaneous observational data from the MF radar and the EISCAT UHF radar colocated in Tromsø, we have examined whether or not the Q2DW was able to penetrate to the lower thermosphere for the period of 1–9 July 1999. It is found that the amplitude of the Q2DW with period of 51.2 hours maximized at 95 km height with values of ∼25 m s−1 in both meridional and zonal components. The Q2DW was attenuated above 95 km, but it appears to survive up to 108 km height in the meridional component. Between 85 and 95 km for the meridional component during this 8‐day interval, the Q2DW and semidiurnal tide were the strongest among the periodic components.
A 100‐year record of North Pacific volcanism in an ice core from Eclipse Icefield, Yukon Territory, Canada
Authors: Yalcin Kaplan , Wake Cameron P. , Germani Mark S.
Published: May 2003

A record of regionally significant volcanic eruptions in the North Pacific over the last century has been developed using a glaciochemical record from Eclipse Icefield, Yukon Territory, Canada. Tephrochronology of the Eclipse ice core provides positive identification of the 1907 Ksudach, Kamchatka, the 1912 Katmai, Alaska, the 1947 Hekla, Iceland, and the 1989 Redoubt, Alaska, eruptions. Non‐sea‐salt SO42− residuals above a robust spline and empirical orthogonal function (EOF) analysis were used to identify volcanic SO42− signatures. Volcanic sulfate values are more conservatively identified by the EOF analysis as sulfate deposition from other sources is more robustly accounted for. Some eruptions are also recorded as peaks in non‐sea‐salt chloride. The volcanic signals in the Eclipse ice core are mostly attributable to Alaskan, Aleutian, or Kamchatkan eruptions. Conversely, the Eclipse ice core provides a poor record of globally significant tropical eruptions. These results are promising for the development of longer ice core based records of paleovolcanism in the North Pacific rim.
Retrieval analysis of aerosol integral properties from simulated extinction at SAGE II and HALOE wavelengths
Authors: Lu Cheng‐Hsuan , Yue Glenn K. , Joseph Everette D. , Mohnen Volker A.
Published: May 2003

Aerosol integral properties inferred from simulated multispectral extinction data at Stratospheric Aerosol and Gas Experiment (SAGE) II and the Halogen Occultation Experiment (HALOE) wavelengths using two different retrieval methods are analyzed and compared. The discrepancy in aerosol integral properties that results from using different retrieval techniques is analyzed, and the differences caused by sampling the same aerosol population at different wavelengths with the same retrieval technique are evaluated. We found that a better agreement was achieved when different methods were applied to the same data set as compared to a case where the same method is applied to data recorded by two different sensors. Our results demonstrate that when comparing aerosol properties derived from different instruments, the particle size information contents from optical instruments have to be taken into consideration together with the propagation of measurement errors and the systematic errors arising from the retrieval methods.
Relative performance of three SAGE‐II data versions under high aerosol conditions based on comparisons with microwave and ozonesonde profiles measured at two NDSC sites
Authors: Parrish A. , Boyd I. S. , Zawodny J. M. , Thomason L. W. , Bodeker G. E. , Connor B. J.
Published: May 2003

Intercomparisons between SAGE‐II data versions 5.93, 5.96, and 6.1 with microwave ozone and ozonesonde measurements made at the NDSC primary station at Lauder, New Zealand, and with microwave measurements made at the NDSC complementary station at Table Mountain, California, are reported on here. The focus is on SAGE‐II measurement performance during the period when stratospheric aerosol levels were substantially elevated following the 1991 Mt. Pinatubo eruption. SAGE‐II ozone retrievals are potentially affected by aerosol levels and size distributions because extinction due to aerosol must be estimated and subtracted from the measured total extinction in the 600 nm ozone channel to determine the ozone amount; the microwave and ozonesonde comparison measurements are aerosol insensitive. Around 10–25 hPa, the newer algorithm versions retain a tendency toward extinction‐dependent bias previously reported for version 5.9; this dependence may be larger than previously indicated at moderately high aerosol levels. In the 30–40 hPa range, the extinction dependence of version 6.1 (and, usually, version 5.96) data is a few times less than that of version 5.93. Between about 30 and 80 hPa most points at moderately elevated aerosol extinctions are less affected than in version 5.93, and these are fewer and/or less affected in version 6.1 than in version 5.96. When aerosols are at background levels, the precisions of version 5.93 and 5.96 measurements are at least somewhat better, around 30 hPa, than the errors provided with the data. The errors provided with version 6.1 data are substantially smaller than in previous versions, and small enough that the experimental sensitivity was insufficient to draw conclusions regarding the actual precision in comparison to the error values.
Optical properties of the Indo‐Asian haze layer over the tropical Indian Ocean
Authors: Franke Kathleen , Ansmann Albert , Müller Detlef , Althausen Dietrich , Venkataraman Chandra , Reddy M. Shekar , Wagner Frank , Scheele Rinus
Published: May 2003

Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4°N, 73°E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532‐nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000‐m height. On average, the free‐tropospheric aerosol layers contributed 30–60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm−1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction‐to‐backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50–80 sr for highly absorbing particles from northern India. The shift of the lidar‐ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent with an aerosol black‐carbon content of up to 20%. The Ångström exponent (for short wavelengths 355/400/532 nm) ranged mostly from 1 to 1.6 for Southeast Asian particles, from 0.8 to 1.4 for North Indian pollution, and from 0.6 to 1 for South Indian air masses. The comparably low Indian Ångström exponents (indicating a comparably large mean particle radius) are possibly caused by the high contribution of biomass combustion to the aerosol formation in India. Results of a correlation analysis based on the lidar ratio, extinction coefficient, Ångström exponents, and relative humidity are presented. In most cases only a weak relationship or no relationship was found between the different parameters.
Ozone in background and photochemically aged air over central Europe: Analysis of long‐term ozonesonde data from Hohenpeissenberg and Payerne
Authors: Naja Manish , Akimoto Hajime , Staehelin Johannes
Published: May 2003

Long‐term ozonesonde data (1970–1999) from Hohenpeissenberg, Germany (48°N, 11°E) and Payerne, Switzerland (47°N, 7°E) have been studied for the boundary layer (from 900 to 750 hPa) and lower troposphere (from 750 to 550 hPa) using back air trajectory analysis. The residence times of air masses over central Europe have been estimated for each day utilizing the trajectory data and are tagged with the corresponding mixing ratios of ozone. It is shown that mixing ratios increase with increasing residence time in summer at a rate of about 2 ppbv/day, but stabilize after about 6 days. Mixing ratios corresponding to central European residence times of 4–6 days are defined as “photochemically aged” ozone. Correlation and slope analysis is made between ozone and residence time (1–6 days) using a statistical regression model, and ozone mixing ratios extrapolated to zero day are defined as “background” ozone. The maximum in “photochemically aged” ozone occurs in summer. “Background” ozone shows lower values and generally a broad maximum extending from spring to summer. Absolute values and variations of ozone in “photochemically aged” and “background” air are quite similar at Hohenpeissenberg and Payerne, indicating their good regional representativeness for central Europe. Regional monthly averaged ozone build‐up (above the “background” value) over central Europe is about 10 ppbv in summer. Central Europe is found to be a net source of ozone throughout the year, except in winter. However, an increasing trend of ozone in “background” and “photochemically aged” air has been observed in winter during the 1980s. Only the boundary layer “photochemically aged” ozone showed a decreasing trend (−1.6 ± 0.2 ppbv/year), consistent with the NOx emissions trend over central Europe during the 1990s. Long‐term changes in “photochemically aged” and “background” ozone suggest that intercontinental transport has a significant effect on ozone mixing ratios in the lower troposphere as well as in “background” ozone in the boundary layer over central Europe. The present analysis ignores transport of ozone from the stratosphere, which might also contribute to interannual variations and changes.
Characterization of secondary atmospheric photooxidation products: Evidence for biogenic and anthropogenic sources
Authors: Spaulding Reggie S. , Schade Gunnar W. , Goldstein Allen H. , Charles M. Judith
Published: May 2003

Measurements of the biogenic hydrocarbons isoprene and 2‐methyl‐3‐buten‐2‐ol (MBO), their first‐, second‐, and third‐generation photooxidation products methacrolein (MACR), methyl vinyl ketone (MVK), acetone, 2‐hydroxy‐2‐methylpropanal (2‐HMPR), glycolaldehyde, hydroxyacetone, methylglyoxal, and glyoxal, and carbon monoxide (CO), were obtained above a ponderosa pine plantation, near the Blodgett Forest Research Station, California on 15–19 August and 11–15 September 2000. Diurnal cycles for all the compounds were similar, with maximum mixing ratios in the afternoon and minimum mixing ratios in the early morning. The diurnal cycles of the second‐generation isoprene photooxidation products were similar to their precursors, while changes in 2‐HMPR, a compound unique to MBO photooxidation, lagged behind corresponding changes in MBO. These observations are consistent with transport of isoprene and its photooxidation products from a strong source several hours upwind, and a predominantly local source of MBO with in situ photochemical production of 2‐HMPR. Glycolaldehyde and hydroxyacetone mixing ratios exceeded the mixing ratios of their biogenic precursors on days with high CO, and were generally correlated more strongly with CO than with their biogenic precursors. The agreement between measured product ratios and ratios predicted by a box model improved when anthropogenic precursors were added to the model. Quantification of the source apportionment demonstrated that photooxidation of anthropogenic precursors contributed significantly to the mixing ratios of glycolaldehyde and hydroxyacetone measured in this rural environment. More research into the photochemistry and yields of multifunctional carbonyl compounds from hydrocarbon photooxidation is needed in order for models to accurately predict their role in tropospheric chemistry.
Size‐resolved particle emission indices in the stratospheric plume of an Athena II rocket
Authors: Schmid O. , Reeves J. M. , Wilson J. C. , Wiedinmyer C. , Brock C. A. , Toohey D. W. , Avallone L. M. , Gates A. M. , Ross M. N.
Published: May 2003

Simultaneous measurements of carbon dioxide (CO2) mixing ratio and alumina (Al2O3) particle abundances between 0.004 and 1.2 μm were obtained in the stratospheric plume wake of an Athena II solid‐fueled rocket motor (SRM). A multimode model of the particle size distribution is used to determine the number (N) and surface area (SA) emission indices as 8.7 ± 2.0 × 1015 per kg and 6.9 ± 2.1 × 1014 μm2 per kg, respectively. Integration of the size distribution shows that 37% of the total SA and 8% of the total mass (M) are contained in the submicron size range (diameter < 1μm) that most influences the stratospheric impact of alumina particles emitted by SRMs. These values are significantly greater than reported by most previous studies and they imply that the annual global ozone loss associated with SRM alumina emissions is about half of the ozone loss from SRM chlorine emissions alone. Comparison of our results to previous studies raises the possibility that submicron M and SA fraction, and therefore global ozone loss, are inversely related to SRM thrust.
The visible absorption spectrum of NO3 measured by high‐resolution Fourier transform spectroscopy
Authors: Orphal J. , Fellows C. E. , Flaud P.‐M.
Published: May 2003

The visible absorption spectrum of the nitrate radical NO3 has been measured using high‐resolution Fourier transform spectroscopy. The spectrum was recorded at 294 K using a resolution of 0.6 cm−1 (corresponding to 0.026 nm at 662 nm) and covers the 12600–21500 cm−1 region (465–794 nm). Compared to absorption spectra of NO3 recorded previously, the new data show improvements concerning absolute wavelength calibration (uncertainty 0.02 cm−1), and spectral resolution. A new interpretation and model of the temperature dependence of the strong (0‐0) band around 662 nm are proposed. The results are important for long‐path tropospheric absorption measurements of NO3 and optical remote sensing of the Earth's atmosphere from space.
Stratosphere‐troposphere exchange: A review, and what we have learned from STACCATO
Authors: Stohl A. , Bonasoni P. , Cristofanelli P. , Collins W. , Feichter J. , Frank A. , Forster C. , Gerasopoulos E. , Gäggeler H. , James P. , Kentarchos T. , Kromp‐Kolb H. , Krüger B. , Land C. , Meloen J. , Papayannis A. , Priller A. , Seibert P. , Sprenger M. , Roelofs G. J. , Scheel H. E. , Schnabel C. , Siegmund P. , Tobler L. , Trickl T. , Wernli H. , Wirth V. , Zanis P. , Zerefos C.
Published: May 2003

This paper provides a review of stratosphere‐troposphere exchange (STE), with a focus on processes in the extratropics. It also addresses the relevance of STE for tropospheric chemistry, particularly its influence on the oxidative capacity of the troposphere. After summarizing the current state of knowledge, the objectives of the project Influence of Stratosphere‐Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO), recently funded by the European Union, are outlined. Several papers in this Journal of Geophysical Research–Atmospheres special section present the results of this project, of which this paper gives an overview. STACCATO developed a new concept of STE in the extratropics, explored the capacities of different types of methods and models to diagnose STE, and identified their various strengths and shortcomings. Extensive measurements were made in central Europe, including the first monitoring over an extended period of time of beryllium‐10 (10Be), to provide a suitable database for case studies of stratospheric intrusions and for model validation. Photochemical models were used to examine the impact of STE on tropospheric ozone and the oxidizing capacity of the troposphere. Studies of the present interannual variability of STE and projections into the future were made using reanalysis data and climate models.
Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust
Authors: Cattrall Christopher , Carder Kendall L. , Gordon Howard R.
Published: May 2003

The single‐scattering albedo and phase function of African mineral dust are retrieved at 14 wavelengths across the visible spectrum from ground‐based measurements of the aerosol optical thickness and the sky radiance taken in the solar principal plane. The retrieval algorithm employs the radiative transfer equation to solve by iteration for these properties that best reproduce the observed sky radiance, and is therefore independent of particle shape. The estimated error in the retrieved single‐scattering albedo is less than 0.02 due to the precision of the solar‐reflectance‐based calibration of the radiometer. The phase function retrieved at 860 nm is robust under simulations of expected experimental errors and may be used to characterize aerosol scattering at the directly measured scattering angles (i.e., Θ ≤ 155°). The phase function retrieved at 443 nm, however, is too sensitive to such errors to confidently describe the angular scattering at blue wavelengths. The single‐scattering albedo displays a spectral shape expected of iron‐bearing minerals but is much higher than climate models have assumed, indicating that wind‐blown mineral dust cools Earth more than is generally believed. The method may be applied to any combination of airborne and ground‐based measurements over the ocean and can complement more involved ground‐based retrievals through its insensitivity to particle shape and ability to retrieve aerosol properties at relatively small aerosol optical depths.
Adjustment of global gridded precipitation for systematic bias
Authors: Adam Jennifer C. , Lettenmaier Dennis P.
Published: May 2003

Systematic biases in gauge‐based measurement of precipitation can be substantial. Of the sources of bias, wind‐induced undercatch of solid precipitation is by far the largest. A methodology for producing gridded mean monthly catch ratios (CRs) for the adjustment of wind‐induced undercatch and wetting losses is developed, which is suitable for application to continental or global gridded precipitation products. The adjustments for wind‐induced solid precipitation were estimated using gauge type‐specific regression equations from the recent World Meteorological Organization Solid Precipitation Measurement Intercomparison. Wind‐induced undercatch of liquid precipitation and wetting losses were estimated using methods employed in previous global bias adjustment efforts. Due to the unique nature of Canada's precipitation measurement network, the Canadian adjustments were determined using more detailed information than for the rest of the domain, and are therefore expected to be more reliable. The gridded gauge adjustment products are designed to be applicable both to climatological estimates and to individual years during the 1979 through 1998 reference period. Application of the CRs to an existing precipitation product yielded an increase in mean annual global terrestrial precipitation of 11.7%. As compared with recent (but more localized) studies that used a similar method to account for wind‐induced catch deficiencies, our estimates of wind‐induced undercatch are 1.6–7.9% higher on a mean annual basis. Compared to a previous global precipitation bias adjustment effort, our adjusted data set results on average in slightly greater warm season and lower cold season precipitation increases, greater precipitation increases over North America, and lower precipitation increases over Eurasia.