bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring heat storage changes in the equatorial Pacific: A comparison between TOPEX altimetry and Tropical Atmosphere‐Ocean buoys
Authors: Chambers D. P. , Tapley B. D. , Stewart R. H.
Published: September 2002

Heat storage variations in the equatorial Pacific have been studied from December 1992 through February 1997, using sea level data from the TOPEX altimeter and temperatures measured by 42 tethered buoys that are part of the Tropical Ocean‐Atmosphere (TAO) array. The TOPEX measurements are converted to heat storage anomalies using a coefficient determined from mean climatological values. For 30‐day averages the two measurements agree well over most of the region, except for the southwestern quadrant of the warm pool and a small region of the north‐central equatorial Pacific. In the southwestern quadrant the TOPEX measurements indicate a smaller long‐term heating rate than the TAO measurements, differing by as much as 30%. After examining conductivity‐temperature‐depth data in this region, it appears that the difference is due to a change in ocean salinity which is reflected in the TOPEX sea level measurements but not in the TAO heat measurements. The signal in the north‐central region is predominately at an annual period, but there is not enough external measurements to determine what the source of the difference is. In the remainder of the equatorial Pacific, the agreement between the data suggests that the TOPEX measurements can be used to measure heat storage variations in the upper layer with reasonable accuracy. Thus TOPEX altimeter data can provide information about the heat budget of the equatorial Pacific in regions where there are few or no direct measurements.
Picoplankton and nanoplankton aggregation by appendicularians: Fecal pellet contents ofMegalocercus huxleyiin the equatorial Pacific
Authors: Gorsky G. , Chrétiennot‐Dinet M. J. , Blanchot J. , Palazzoli I.
Published: September 2002

The content of fecal pellets of the freshly collected warm water appendicularianMegalocercus huxleyiwas studied by light and electron microscopy and by flow cytometry in the superficial 100 m of the water column at 2°N, 165°E, in September 1994, during the Flux dans l'Ouest du Pacifique Equatorial (Joint Global Ocean Flux Study‐France) oceanographic cruise. Microscopic observations showed that the fecal pellet contents ofM. huxleyireflected the natural composition of the nanophytoplankton and small microphytoplankton (<50 μm). Larger cells were excluded from entering the filtering system by the inlet filters. Coccolithophorids appeared as the main component found in the feces. Evidence for ingestion of “naked” cells by this appendicularian is given. Analysis of picoplankton in fecal pellets by flow cytometer confirmed that appendicularians efficiently collect small particles. Cyanobacteria, ∼1 μm in diameter, were found in large quantities and showed high fluorescence in the fecal pellets. Most of these cyanobacteria in the pellets appeared to be intact, and thus may be good indicators of the appendicularian ingestion rate. The situation was different for the prochlorophyteProchlorococcusabundant in the seawater and for picoeucaryotes (<2 μm). These were found at very low quantities in the larvacean fecal pellets. The calculations showed that with an average concentration of 5M. huxleyim−3, >7% of the small particulate matter will be daily removed from the water. Some of this matter will be assimilated, some trapped in the houses, and the rest aggregated into rapidly sinking fecal pellets. Ingestion of large quantities of coccolithophorids indicates that appendicularians are important not only in the cycle of organic carbon but also of inorganic carbon. Moreover, if appendicularians successfully aggregate and assimilateProchlorococcusand picoeucaryotes, then their grazing activity can represent a major pathway of carbon transformation in the tropical ecosystem
Phycoerythrins in the southern tropical and equatorial Pacific Ocean: Evidence for new cyanobacterial types
Authors: Neveux Jacques , Lantoine François , Vaulot Daniel , Marie Dominique , Blanchot Jean
Published: September 2002

Quantitative and qualitative investigations of phycoerythrins (PE) were achieved in the central southern tropical and equatorial Pacific during the Flux dans l'ouest du Pacifique equatorial (FLUPAC: September‐October 1994) and Oligotrophie en Pacifique (OLIPAC: November 1994) cruises. We observed mainly high‐phycourobilin (PUB) PE related to small Synechococcus spp. (0.6–1.4 μm). This PE was characterized by fluorescence excitation peaks at 496 and 550 nm in 50% glycerol. Highest concentrations (0.1–0.2 μg L−1) were recorded either in the mixed layer (nutrient‐enriched area) or at depth in the vicinity of the 0.1 μM NO3− isopleth (oligotrophic waters). Maximum abundance of Synechococcus did not exceed 31 × 103 cell mL−1. No subpopulations of Synechococcus were evidenced by flow cytometry. Nevertheless, in a few samples, two new PE spectral types were observed. The first type was a high‐PUB PE with two fluorescence excitation peaks at 494 and 564 nm. It appears to be attributable to nonmotile round cells, 2–3 μm in size and easily detected by flow cytometry, likely cyanobacteria. They were only observed in very oligotrophic waters south of 15°30′S along 150°W in the top 60 m. In this area, nitrate, nitrite, and ammonia were undetectable above 120 m, while phosphate was always recorded. This suggests that these larger cyanobacteria may fix dinitrogen (N2) to supply their growth and therefore possibly play a significant role in oceanic new production. The second type, a high‐phycoerythrobilin (PEB) PE was observed in three samples obtained at or near the equator. It displayed two fluorescence excitation peaks at 496 and 536 nm. The organisms that contained this PE type were not identified. These data suggest that PE is more diverse in oceanic waters than was previously assumed.
Statistical distribution of wind speeds and directions globally observed by NSCAT
Authors: Ebuchi Naoto
Published: September 2002

In order to validate wind vectors derived from the NASA scatterometer (NSCAT), statistical distributions of wind speeds and directions over the global oceans are investigated by comparing with European Centre for Medium‐Range Weather Forecasts (ECMWF) wind data. Histograms of wind speeds and directions are calculated from the preliminary and reprocessed NSCAT data products for a period of 8 weeks. For wind speed of the preliminary data products, excessive low wind distribution is pointed out through comparison with ECMWF winds. A hump at the lower wind speed side of the peak in the wind speed histogram is discernible. The shape of the hump varies with incidence angle. Incompleteness of the prelaunch geophysical model function, SASS 2, tentatively used to retrieve wind vectors of the preliminary data products, is considered to cause the skew of the wind speed distribution. On the contrary, histograms of wind speeds of the reprocessed data products show consistent features over the whole range of incidence angles. Frequency distribution of wind directions relative to spacecraft flight direction is calculated to assess self‐consistency of the wind directions. It is found that wind vectors of the preliminary data products exhibit systematic directional preference relative to antenna beams. This artificial directivity is also considered to be caused by imperfections in the geophysical model function. The directional distributions of the reprocessed wind vectors show less directivity and consistent features, except for very low wind cases.
Geophysical validation of NSCAT winds using atmospheric data and analyses
Authors: Atlas R. , Bloom S. C. , Hoffman R. N. , Brin E. , Ardizzone J. , Terry J. , Bungato D. , Jusem J. C.
Published: September 2002

A detailed geophysical evaluation of the initial NASA scatterometer (NSCAT) wind data sets was performed in order to determine the error characteristics of these data and their applicability to ocean surface analysis and numerical prediction. The first component of this evaluation consisted of collocations of NSCAT data to ship and buoy wind reports, special sensor microwave imager wind observations, and National Centers for Environmental Prediction and Goddard Earth Observing System (GEOS) model wind analyses. This was followed by data assimilation experiments to determine the impact of NSCAT data on analysis and forecasting. The collocation comparisons showed the NSCAT wind velocity data to be of higher accuracy than operational ERS 2 wind data. The impact experiments showed that NSCAT has the ability to correct major errors in analyses over the oceans and also to improve numerical weather prediction. NSCAT data typically show the precise locations of both synoptic‐scale and smaller‐scale cyclones and fronts over the oceans. This often results in significant improvements to analyses. Forecast experiments using the GEOS model show approximately a 1‐day extension of useful forecast skill in the southern hemisphere, in good agreement with the results of Observing System Simulation Experiments conducted prior to launch.
Intercomparison of ground‐based NOy measurement techniques
Authors: Williams E. J. , Baumann K. , Roberts J. M. , Bertman S. B. , Norton R. B. , Fehsenfeld F. C. , Springston S. R. , Nunnermacker L. J. , Newman L. , Olszyna K. , Meagher J. , Hartsell B. , Edgerton E. , Pearson J. R. , Rodgers M. O.
Published: September 2002

An informal intercomparison of NOy measurement techniques was conducted from June 13 to July 22, 1994, at a site in Hendersonville, Tennessee, near Nashville. The intercomparison involved five research institutions: Brookhaven National Laboratory, Environmental Science and Engineering, Georgia Institute of Technology, NOAA/Aeronomy Laboratory, and Tennessee Valley Authority. The NOy measurement techniques relied on the reduction of NOy species to NO followed by detection of NO using O3‐chemiluminescence. The NOy methods used either the Au‐catalyzed conversion of NOy to NO in the presence of CO or H2 or the reduction of NOy to NO on a heated molybdenum oxide surface. Other measurements included O3, NOx, PAN and other organic peroxycarboxylic nitric anhydrides, HNO3 and particulate nitrate, and meteorological parameters. The intercomparison consisted of six weeks of ambient air sampling with instruments and inlet systems normally used by the groups for field measurements. In addition, periodic challenges to the instruments (spike tests) were conducted with known levels of NO, NO2, NPN, HNO3 and NH3. The NOy levels were typically large and highly variable, ranging from 2 ppbv to about 100 ppbv, and for much of the time was composed mostly of NOx from nearby sources. The spike tests results and ambient air results were consistent only when NOx was a substantial fraction of NOy. Inconsistency with ambient air data and the other spike test results is largely attributed to imprecision in the spike results due to the high and variable NOy background. For the ambient air data, a high degree of correlation was found with the different data sets. Of the seven NOy instrument/converters deployed at the site, two (one Au and one Mo) showed evidence of some loss of conversion efficiency. This occurred when the more oxidized NOy species (e.g., HNO3) were in relatively high abundance, as shown by analysis of one period of intense photochemical activity. For five of the instruments, no significant differences were found in the effectiveness of NOy conversion at these levels of NOy with either Au or Mo converters. Within the estimated uncertainty limits there was agreement between the sum of the separately measured NOy species and the NOy measured by the five of the seven techniques. These results indicate that NOy can be measured reliably in urban and suburban environments with existing instrumentation.
Model correlations for ozone, reactive nitrogen, and peroxides for Nashville in comparison with measurements: Implications for O3‐NOx‐hydrocarbon chemistry
Authors: Sillman Sanford , He Dongyang , Pippin Margaret R. , Daum Peter H. , Imre Daniel G. , Kleinman Lawrence I. , Lee Jai Hoon , Weinstein‐Lloyd Judith
Published: September 2002

We present an analysis of correlations between O3, NOxreaction products (NOz), and peroxides in photochemical models for polluted environments in comparison with measurements in the vicinity of Nashville, Tennessee. This analysis is associated with the use of O3/NOz, H2O2/NOz, and similar ratios as indicators for the relative impact of NOxand hydrocarbons (volatile organic compounds, VOC) on ozone formation. The measurements are used both to evaluate the NOx‐VOC indicator theory and to identify NOx‐VOC chemistry in Nashville. Results show that a linear correlation exists between O3and the sum 2H2O2+ NOz, consistent between models and measurements. The ratio O3/2H2O2+ NOzhas a near‐constant value in both the Nashville urban plume and surrounding rural area. A similar correlation is found with total peroxides (O3versus 2peroxides + NOz) but with greater scatter. The correlations between O3, NOz, and peroxides are consistent with an assumed dry deposition rate of 5 cm s−1for H2O2and HNO3. Changes in dry deposition and RO2reaction rates cause minor adjustments in the NOx‐VOC‐indicator analysis for H2O2/NOz. Measured indicator ratios for Nashville are close to the NOx‐VOC transition predicted by models and form an intermediate point between previous measurements for Atlanta (NOxsensitive) and Los Angeles (VOC sensitive). The model ozone production efficiency (P(O3)/L(NOx)) is 3–4, significantly lower than would be derived from the O3‐NOzslope (5–8).
Relative production of ozone and nitrates in urban and rural power plant plumes: 1. Composite results based on data from 10 field measurement days
Authors: Gillani Noor V. , Meagher James F. , Valente Ralph J. , Imhoff Robert E. , Tanner Roger L. , Luria Menachem
Published: September 2002

A rather limited number of large power plants are responsible for about 2/3 and 1/3 of the U.S. anthropogenic emissions of SO2 and NOx, respectively. Considerable uncertainty continues to prevail about the local and regional impact of their potentially harmful secondary products (e.g., ozone, sulfates, nitrates), We have analyzed state‐of‐the‐art data of the Southern Oxidant Study (SOS)‐Nashville Field Study (1994, 1995) for 10 days of summer daytime field measurements by instrumented aircraft in the plumes of three large, tall‐stack, base‐load, Tennessee Valley Authority (TVA) coal‐fired power plants in northwestern Tennessee: Gallatin (G), located within the Nashville urban ozone nonattainment area, and Cumberland (C) and Johnsonville (JV) in rural isoprene‐rich forested areas about 100 km to the west of Nashville. The average 1995 emissions of NOx from these three sources ranged over more than an order of magnitude. In this paper, we have explored plume chemical evolution and the magnitude, efficiency, and yield of ozone and NOz, (NOx oxidation products, mostly inorganic and organic nitrates) production in a broad variety of plume transport and chemistry scenarios within the convective boundary layer (CBL) in rural and urban settings. The results show that (1) plume chemical maturity and peak production capacities of ozone and NOz were realized quite close to the sources, within 30–40 km and 4 hours of daytime transport for Gallatin (smallest NOx emission rate, QNOx, and suburban environment) and typically within 100 km and 6 hours of CBL transport for Cumberland (highest QNOx and rural environment rich in isoprene); (2) the ozone impact of Gallatin on Nashville can exceed that of Cumberland, and under favorable transport and chemical conditions, both power plants can contribute as much as 50 ppb of excess ozone to the urban area, raising local peak levels well in excess of 100 ppb; (3) an estimated 3.1±0.7 molecules of ozone and more than 0.6 molecules of NOz, may be produced in large isolated rural power plant plumes (PPPs) per molecule of NOx release, and the corresponding peak yields of ozone and NOz may be significantly greater in urban PPPs; (4) the rate of NOz production ≈ 10–15% h−1 in isolated rural PPPs, and higher in urban PPPs; (5) NOz production is favored in all PPPs at first when the chemistry is VOC‐limited; later, with increasing VOC ingestion from the background, the chemistry increasingly favors NOx‐limited ozone production, starting at plume edges, and ultimately throughout the diluted plume. These results have major implications on outstanding issues related to the environmental impact and regulatory control of electric utility industry NOx emissions.
Role of anthropogenic NOx and VOC as ozone precursors: A case study from the SOS Nashville/Middle Tennessee Ozone Study
Authors: St. John J. C. , Chameides W. L. , Saylor R.
Published: September 2002

Using data collected on July 11, 1995, from the Tennessee Valley Authority (TVA) instrumented Bell 205 helicopter during the 1995 SOS Nashville/Middle Tennessee Ozone Study, we examine the relative roles of NOx and volatile organic compound (VOC) emissions on ozone photochemical production in the Nashville area. On this day, instruments onboard the helicopter separately sampled air from within a plume emanating from a nearby coal‐fired power plant and air from the Nashville urban plume. Using SO2 concentrations and latitude to discriminate between the plumes, we compare the effects on O3 production of only adding NOx to the background air (i.e., the power plant plume) to that of adding both NOx and VOC (i.e., the urban plume). Our analysis indicates that NOx was the prime anthropogenic precursor causing the generation of O3 during the experiment, with anthropogenic VOC perhaps playing a secondary but significant role. The addition of VOC emissions from the urban area had no appreciable effect on peak O3 concentrations, clearly demonstrating that anthropogenic NOx emissions by themselves can produce elevated O3 concentrations in the Nashville area. Anthropogenic VOC emissions, however, may have enhanced the ozone production efficiencies and the rate at which O3 reached its peak values. While not conclusive, the data also suggested that the highest O3 concentrations in the Nashville area on July 11, 1995, appeared within embedded plumes that combined the effects of both urban and power plant precursor emissions.
Nighttime isoprene chemistry at an urban‐impacted forest site
Authors: Starn T. K. , Shepson P. B. , Bertman S. B. , Riemer D. D. , Zika R. G. , Olszyna K.
Published: September 2002

Isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were measured over a 4 week period in July of 1995 at a rural/forest site near Nashville, Tennessee, as part of the 1995 Southern Oxidants Study (SOS) field intensive. High nighttime isoprene mixing ratios, measured during a 3 day period of stagnant high pressure, are reported. These high nighttime isoprene events are interpreted as a result of continuing emission of isoprene into a developing shallow nocturnal boundary layer in the early evening, followed by advective transport under the inversion to the measurement site. During some evenings, there is very rapid decay of isoprene just after sunset. These events occurred when the product [O3]·[NO2] was relatively large, consistent with loss via reaction with NO3. A chemical box model showed that isoprene decays were consistent with the NO3 mechanism but only for relatively high NOx conditions. This study indicates that nighttime processing of isoprene can be important for forested regions susceptible to high‐NOx transport events. We also find that this nighttime NO3 chemistry can lead to conditions where, at least at the surface, a significant fraction of the NOy is in the form of organic nitrates that are products of the NO3‐isoprene reaction and that the NO3‐isoprene reaction can be the dominant NO3 sink.
Observations of isoprene chemistry and its role in ozone production at a semirural site during the 1995 Southern Oxidants Study
Authors: Starn T. K. , Shepson P. B. , Bertman S. B. , White J. S. , Splawn B. G. , Riemer D. D. , Zika R. G. , Olszyna K.
Published: September 2002

Isoprene and its oxidation products, methyl vinyl ketone (MVK) and methacrolein (MACR), were measured in a semirural environment that was occasionally heavily impacted by urban emissions. At this site, isoprene was the most important hydrocarbon in terms of kOH·[hydrocarbon], but the aldehydes HCHO and CH3CHO also appear to be very important. The local isoprene photochemistry appears to be occasionally enhanced in NOx‐rich urban plumes that are adverted to the site over intermediate forested land. When O3 was being rapidly produced in urban plumes adverted to this forested site, isoprene was found to contribute ≈28% of the total ozone production. We observe that many of the peaks in isoprene oxidation products at this surface site arise from downward mixing of more photochemically processed air aloft, as the nocturnal inversion breaks up in the morning. We estimate that, in the daytime, typically 1–2% of the NOy at this NOx‐rich site is composed of isoprene nitrates.
Atmospheric trace element concentrations over the eastern Mediterranean Sea: Factors affecting temporal variability
Authors: Güllü Gülen H. , Ölmez Ilhan , Aygün Sezer , Tuncel Gürdal
Published: September 2002

Concentrations of elements and ions were measured in aerosol samples collected between March 1992 and December 1993 at a rural station on the Mediterranean coast of Turkey. Concentrations of pollution‐derived elements are lower than corresponding concentrations reported for the western Mediterranean region, due to the longer distances traveled by the particles to reach the eastern Mediterranean region. Concentrations of elements vary on timescales ranging from days to seasons. Short‐term variations in the concentrations of pollution‐derived elements are explained by transport from source regions. Short‐term variations in the concentrations of sea‐salt and crustal elements, on the other hand, are due to the episodic nature of wind‐induced particle generation mechanisms. Transport failed to explain long‐term variations due to lack of seasonal changes in air mass transport patterns. The seasonal variations in the concentrations of anthropogenic elements are determined by the wet deposition of particles, which is more extensive in the wet season, and distances between source regions and the sampling site. The long‐term variations in the concentrations of crustal and sea‐salt elements are explained by seasonal changes in their source strengths. Distant rains on the path of the air masses which transport anthropogenic particles to the eastern Mediterranean are more influential on the observed seasonal behavior of pollution‐derived elements than local rain events.
An assessment of cloud effects on photolysis rate coefficients: Comparison of experimental and theoretical values
Authors: Crawford J. , Davis D. , Chen G. , Shetter R. , Müller M. , Barrick J. , Olson J.
Published: September 2002

An assessment of the effects of clouds on photolysis rate coefficients was carried out using three different experimental methods involving two different aircraft platforms. This evaluation was based on data recorded during NASA's Pacific Exploratory Mission (PEM)‐Tropics A program in August‐October 1996. On the NASA DC‐8, upward and downward looking J(NO2) filter radiometers and spectroradiometers were employed. For the NASA P‐3B, the instrumentation consisted of Eppley radiometers. Although each aircraft typically sampled the same geographic region, coincident measurements occurred for only one brief period in the marine boundary layer near Christmas Island (2°N, 157°W). All three methods were compared for this flight period; however, only the J(NO2) filter radiometers and spectroradiometers could be compared for the entire campaign. For the Christmas Island sampling period, all three radiometric measurements disagreed in magnitude but exhibited trends consistent with model‐calculated photolysis rate coefficients. Overall, the results showed that the J(NO2) filter radiometers and spectroradiometers exhibited a consistent disagreement of 30%, the J(NO2) filter radiometers being higher. Eppley‐derived values of J(NO2) fell between those of the J(NO2) filter radiometers and spectroradiometers. An examination of the variation in J(O1D) and J(NO2) based on the output from the spectroradiometers and J(NO2) filter radiometers suggests that differences between each photolysis rate coefficient's response to cloud effects tend to be smaller than model uncertainties. Thus J(O1D) and other photolysis rate coefficients can be corrected for cloud effects based on the response of J(NO2).
Humidification factors for atmospheric aerosols off the mid‐Atlantic coast of the United States
Authors: Kotchenruther Robert A. , Hobbs Peter V. , Hegg Dean A.
Published: September 2002

The light‐scattering coefficients of aerosols as a function of relative humidity (RH) and wavelength were measured in flights off the mid‐Atlantic coast of the United States during July 1996. At a wavelength of 550 nm the ratio of the total light‐scattering coefficient at RH = 80% to that at RH = 30% in westerly airflows had a mean value of 2.30 with a standard deviation of 0.24; in northerly and southerly airflows the mean value was 1.81 with a standard deviation of 0.37. This ratio generally decreased with increasing altitude and with increasing mass ratio of aerosol carbon to sulfate, and it increased with increasing wavelength. The aerosol hemispheric backscatter ratio decreased by 30 to 40% as the RH increased from 30 to 80%. Direct radiative forcing by aerosols advected off the mid‐Atlantic coast of the United States is strongly dependent on RH. At a RH of 80%, direct radiative forcing by the aerosol is roughly twice that of the dry aerosol.
A ground‐based microwave radiometer dedicated to stratospheric ozone monitoring
Authors: de La Noë J. , Lezeaux O. , Guillemin G. , Lauqué R. , Baron P. , Ricaud P.
Published: September 2002

A microwave radiometer has been developed for long‐term measurements of strato‐mesospheric ozone profiles at midlatitudes. The instrument located at the Bordeaux Observatory, France (45°N) is operated in the framework of the French atmospheric station, of the European Alpine station belonging to the Network for the Detection of Stratospheric Change. The instrument detects an ozone spectral line at 110.836 GHz, enabling the retrieval of ozone profiles from ∼25 to ∼75 km. The technical parameters are described as the observing technique, calibration procedures, and data acquisition. Two retrieval methods are used: the Backus‐Gilbert method and the optimal estimation method. Strong emphasis is placed on the error analysis including a detailed characterization of errors. To improve the retrieval, we discuss which errors have to be taken into account in the retrieval process. Three cases have been selected for which retrieval errors due to time stochastic and time systematic errors are calculated. First, only the thermal noise is introduced in the retrieval code; second, all errors are introduced; and finally, a selection among errors is searched in order to provide a good compromise between the retrieval error and the vertical resolution. Diurnal variations of mesospheric O3 are compared with results from a photochemical model. The agreement is within 5–10%. During the February‐March 1996 period the temporal evolution of ozone at an altitude of 30 km is in good agreement with both satellite and three‐dimensional model data. There is a good correlation with the potential vorticity field calculated at the 850 K isentropic temperature. A crossing of the polar vortex over the site is associated with an O3 decrease observed in the three data sets.
Horizontal wavenumber spectra of winds, temperature, and trace gases during the Pacific Exploratory Missions: 1. Climatology
Authors: Cho John Y. N. , Zhu Yong , Newell Reginald E. , Anderson Bruce E. , Barrick John D. , Gregory Gerald L. , Sachse Glen W. , Carroll Mary Anne , Albercook George M.
Published: September 2002

Aircraft‐based meteorological and chemical measurements from NASA's Pacific Exploratory Missions provide a suitable database for studying the climatology of horizontal wavenumber spectra in the troposphere overlying an ocean. The wavenumber spectra of trace gas and meteorological quantities aid in identifying the physical processes producing atmospheric structures as well as provide diagnostics for general circulation models. Flight segments were distributed over altitudes ranging from about ∼50 m to 13 km and 70°S to 60°N in latitude. The spectra were averaged according to altitude and latitude regions. The wavelength range covered was typically ∼0.5–100 km. Quantities processed in this way were horizontal velocity, potential temperature, specific humidity, and the mixing ratios of ozone, methane, carbon monoxide, and carbon dioxide. Spectral power and slope (in log‐log coordinates) corresponding to the wavelength regime of 6–60 km were tabulated for those measured quantities. The spectral slopes of horizontal velocity and potential temperature were generally close to −5/3 with no transition to a steeper slope at short wavelengths as seen in some other studies. Spectral slopes of the tracer species also ranged around −5/3. This agreement in form of the dynamical and tracer spectra is consistent with both the gravity‐wave advection and quasi two‐dimensional turbulence models. In the upper troposphere the spectral power for all quantities except specific humidity tended to be greater at latitudes higher than 30° compared to latitudes lower than 30°. This latitudinal trend confirms the earlier results of the Global Atmospheric Sampling Program.
Sequestration of HNO3 in polar stratospheric clouds and chlorine activation as monitored by ground‐based Fourier transform infrared solar absorption measurements
Authors: Wegner A. , Stiller G. P. , von Clarmann T. , Maucher G. , Blumenstock T. , Thomas P.
Published: September 2002

Solar absorption infrared spectra measured with the ground‐based Michelson Interferometer for Passive Atmospheric Sounding‐Laboratory Model (MIPAS‐LM) at the Esrange research station near Kiruna, North Sweden, were analyzed for zenith column amounts of stratospheric trace gases. Time series of HF, HCl, ClONO2, HNO3, and O3 measured in the winter of 1991–1992, the summer of 1992, and the winter of 1992–1993 were studied for anomalies indicating a perturbed stratospheric chemistry in the Arctic winter. Indications of chlorine activation were found in both winters, inside the stratospheric polar vortex as well as at the vortex edge, as was indicated by the ratio of stratospheric HCl to the HF zenith column amount. This ratio decreased from values higher than 3 for chemically undisturbed stratospheric conditions to 1.1–1.3 in January 1992 and 0.8 in February 1993, inside the polar vortex when maximum chlorine activation took place. Sequestration of HNO3 in polar stratospheric clouds (PSCs) was found on several days of observation inside the polar vortex; it leads to a decrease of the HNO3 zenith column amounts by up to 50% on February 10, 1993. From comparison to model calculations we conclude that the HNO3 loss can only be explained by formation of nitric acid trihydrate (NAT) PSCs on January 18, 1992, and February 10, 1993, whereas on January 19, 1992, January 28, 1993, and February 11, 1993, the formation of ternary solutions can also explain the HNO3 loss.
Winter warming over Dome Fuji, East Antarctica and semiannual oscillation in the atmospheric circulation
Authors: Enomoto Hiroyuki , Motoyama Hideaki , Shiraiwa Takayuki , Saito Takashi , Kameda Takao , Furukawa Teruo , Takahashi Shuhei , Kodama Yuji , Watanabe Okitsugu
Published: September 2002

An abrupt warming was observed in the winter around Dome Fuji (3810 m above sea level (asl)) in East Antarctica. The air temperature increased from −73° C to −36° C in two days, from June 13 to 14, 1994. Warming occurred first in the coastal region near the Lambert Glacier, East Antarctica, then progressed inland to Dome Fuji. During the warming, a blocking high was observed in the middle troposphere and it persisted for several weeks. This circulation pattern brought warm air inland. A blocking high over East Antarctica also appeared in the upper troposphere; this high‐pressure area corresponded to a ridge of stratospheric circulation. This condition occurred after a displacement of the polar vortex from East Antarctica to West Antarctica. Warming at the surface of the ice sheet occurred suddenly; however, in the stratosphere the circulation pattern began to change on a seasonal scale prior to the warming as part of the first phase of the semiannual oscillation.
Snow breezes in the boreal forest
Authors: Taylor Christopher M. , Harding Richard J. , Pielke Roger A. , Vidale Pier L. , Walko Robert L. , Pomeroy John W.
Published: September 2002

This study examines thermally induced flows (or “snow breezes”) associated with snow cover in the boreal forests of Canada. Observations from a lake less than 4 km across were made as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS) winter field campaign. These are interpreted with the aid of idealized three‐dimensional mesoscale model simulations representing the forest‐lake contrast. Typically, strong forest‐lake temperature contrasts develop in the lowest 50 m of the atmosphere during the morning. The resulting pressure gradients induce low‐level onshore wind components across the lake. This snow breeze persists into the afternoon provided that large‐scale winds remain light. A characteristic snow breeze signature is clearly evident in wind observations averaged over 27 days of data, in agreement with model simulations. The study suggests that snow breezes will regularly develop over the many larger lakes and other unvegetated areas in the region.
Infrared radiative forcing and atmospheric lifetimes of trace species based on observations from UARS
Authors: Minschwaner K. , Carver R. W. , Briegleb B. P. , Roche A. E.
Published: September 2002

Observations from instruments on the Upper Atmosphere Research Satellite (UARS) have been used to constrain calculations of infrared radiative forcing by CH4, CCl2F2, and N2O and to determine lifetimes of CCl2F2 and N2O. Radiative forcing is calculated as a change in net infrared flux at the tropopause that results from an increase in trace gas amount from preindustrial (1750) to contemporary (1992) times. Latitudinal and seasonal variations are considered explicitly, using distributions of trace gases and temperature in the stratosphere from UARS measurements and seasonally averaged cloud statistics from the International Satellite Cloud Climatology Project. Top‐of‐atmosphere fluxes calculated for the contemporary period are in good agreement with satellite measurements from the Earth Radiation Budget Experiment. Globally averaged values of the radiative forcing are 0.550, 0.132, and 0.111 W m−2 for CH4, CCl2F2, and N2O, respectively. The largest forcing occurs near subtropical latitudes during summer, predominantly as a result of the combination of cloud‐free skies and a high, cold tropopause. Clouds are found to play a significant role in regulating infrared forcing, reducing the magnitude of the forcing by 30–40% compared with the case of clear skies. The vertical profile of CCl2F2 is important in determining its radiative forcing; use of a height‐independent mixing ratio in the stratosphere leads to an overprediction of the forcing by 10%. The impact of stratospheric profiles on radiative forcing by CH4 and N2O is 2% or less. UARS‐based distributions of CCl2F2 and N2O are used also to determine global destruction rates and instantaneous lifetimes of these gases. Rates of photolytic destruction in the stratosphere are calculated using solar ultraviolet irradiances measured on UARS and a line‐by‐line model of absorption in the oxygen Schumann‐Runge bands. Lifetimes are 114±22 and 118±25 years for CCl2F2 and N2O, respectively.
Cirrus layer microphysical properties derived from surface‐based millimeter radar and infrared interferometer data
Authors: Mace Gerald G. , Ackerman Thomas P. , Minnis Patrick , Young David F.
Published: September 2002

Observational data regarding the properties of cirrus clouds are needed to aid in the development of accurate, physically based parameterizations in climate models. The Atmospheric Radiation Measurement (ARM) program, sponsored by the U.S. Department of Energy, is providing continuous observations of cirrus clouds with a suite of instrumentation at several locales. In this paper, we describe an algorithm to derive the microphysical properties of optically thin cirrus clouds. This algorithm uses radar reflectivity and infrared emission spectra from an interferometer and is tailored for the specific instruments at the ARM sites. We present in situ validation of the technique and examine a cirrus case study to illustrate the sensitivity of the algorithm. In the case study, solar fluxes calculated from the retrieved microphysical parameters are compared to observed fluxes to build confidence in the algorithm results. Comparison of the retrieved quantities to microphysical parameters retrieved from satellite data is also presented.
Radiative effect of cirrus clouds in Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager channels
Authors: Wiegner Matthias , Seifert Peter , Schlüssel Peter
Published: September 2002

Radiances at the top of the atmosphere are calculated for three channels at λ = 0.635, 3.8 and 8.7 μm of the Spinning Enhanced Visible and Infrared Imager which is to be flown as part of the Meteosat Second‐Generation Programme. Special emphasis is put on the influence of natural cirrus clouds. Their optical properties are determined by means of a geometric ray‐tracing code assuming hexagonal ice crystals. Radiative transfer is modeled by a successive order of scattering program in the visible spectral range and a combination of the radiance sampling method and the discrete ordinate method in the infrared. It is found that significant errors are introduced if spherical particles are assumed and if the small particle fraction of the size spectrum is neglected. A comparison of several realistic particle size distributions of cirrus clouds shows that the radiances at the top of the atmosphere do not differ significantly. Thus the derivation of cirrus microphysics certainly has to meet very demanding requirements on signal‐to‐noise ratio and cloud homogeneity. Further work is recommended to study the possibility of using spectrally averaged radiances for deriving cirrus cloud properties before designing any detailed retrieval algorithm.
Nucleation in the equatorial free troposphere: Favorable environments during PEM‐Tropics
Authors: Clarke A. D. , Eisele F. , Kapustin V. N. , Moore K. , Tanner D. , Mauldin L. , Litchy M. , Lienert B. , Carroll M. A. , Albercook G.
Published: September 2002

A combination of aerosol and gas phase instrumentation was employed aboard the NASA‐P3B as part of the Pacific Exploratory Mission‐Tropics (PEM‐T) in the eastern equatorial Pacific during August‐October 1996. Recent particle production was found in cloud‐processed air over extended regions aloft (6–8 km). These were clearly associated with clean marine air lofted by deep convection and scavenged of most aerosol mass in the Intertropical Convergence Zone (ITCZ) and in more aged cloud‐scavenged air influenced by a distant continental combustion near the South Pacific Convergence Zone (SPCZ). Recent particle production was evident in regions where sulfuric acid concentrations were about 0.5 to 1 × l07 molecules cm−3, when surface areas were near or below 5 µm2 cm−3, and when relative humidity (RH) was elevated over adjacent regions. In regions of recent particle production, the calculated critical sulfuric acid concentrations, based upon classical binary nucleation theory and corrected for in situ conditions near cloud, were generally consistent with nearby observed sulfuric acid concentrations. This indicates that classical binary nucleation theory and natural sources of sulfuric acid can account for nucleation in the near‐cloud environment. Data from six equatorial flights between 20°N and 20°S demonstrate that this process populates extensive regions of the equatorial free troposphere with new particles. Vertical profiles suggest that nucleation, subsidence, and mixing into the MBL can supply the MBL with new aerosol.
On the origin of tropospheric ozone and NOx over the tropical South Pacific
Authors: Schultz Martin G. , Jacob Daniel J. , Wang Yuhang , Logan Jennifer A. , Atlas Elliot L. , Blake Donald R. , Blake Nicola J. , Bradshaw John D. , Browell Edward V. , Fenn Marta A. , Flocke Frank , Gregory Gerald L. , Heikes Brian G. , Sachse Glen W. , Sandholm Scott T. , Shetter Richard E. , Singh Hanwant B. , Talbot Robert W.
Published: September 2002

The budgets of ozone and nitrogen oxides (NOx = NO + NO2) in the tropical South Pacific troposphere are analyzed by photochemical point modeling of aircraft observations at 0–12 km altitude from the Pacific Exploratory Mission‐Tropics A campaign flown in September‐October 1996. The model reproduces the observed NO2/NO concentration ratio to within 30% and has similar success in simulating observed concentrations of peroxides ( H2O2, CH3OOH), lending confidence in its use to investigate ozone chemistry. It is found that chemical production of ozone balances only half of chemical loss in the tropospheric column over the tropical South Pacific. The net loss is 1.8 × 1011 molecules cm−2 s−1. The missing source of ozone is matched by westerly transport of continental pollution into the region. Independent analysis of the regional ozone budget with a global three‐dimensional model corroborates the results from the point model and reveals the importance of biomass burning emissions in South America and Africa for the ozone budget over the tropical South Pacific. In this model, biomass burning increases average ozone concentrations by 7–8 ppbv throughout the troposphere. The NOx responsible for ozone production within the South Pacific troposphere below 4 km can be largely explained by decomposition of peroxyacetylnitrate ( PAN) transported into the region with biomass burning pollution at higher altitudes.
Interactive coupling of regional climate and sulfate aerosol models over eastern Asia
Authors: Qian Yun , Giorgi Filippo
Published: September 2002

The NCAR regional climate model (RegCM) is interactively coupled to a simple radiatively active sulfate aerosol model over eastern Asia. Both direct and indirect aerosol effects are represented. The coupled model system is tested for two simulation periods, November 1994 and July 1995, with aerosol sources representative of present‐day anthropogenic sulfur emissions. The model sensitivity to the intensity of the aerosol source is also studied. The main conclusions from our work are as follows: (1) The aerosol distribution and cycling processes show substantial regional spatial variability, and temporal variability varying on a range of scales, from the diurnal scale of boundary layer and cumulus cloud evolution to the 3–10 day scale of synoptic scale events and the interseasonal scale of general circulation features; (2) both direct and indirect aerosol forcings have regional effects on surface climate; (3) the regional climate response to the aerosol forcing is highly nonlinear, especially during the summer, due to the interactions with cloud and precipitation processes; (4) in our simulations the role of the aerosol indirect effects is dominant over that of direct effects; (5) aerosol‐induced feedback processes can affect the aerosol burdens at the subregional scale. This work constitutes the first step in a long term research project aimed at coupling a hierarchy of chemistry/aerosol models to the RegCM over the eastern Asia region.
Modeling clouds and radiation for the November 1997 period of SHEBA using a column climate model
Authors: Pinto James O. , Curry Judith A. , Lynch Amanda H. , Persson P. O. G.
Published: September 2002

A column version of the Arctic regional climate system model (ARCSYM) has been developed for testing general circulation model parameterizations in the Arctic. The ARCSYM column model has been employed for a 23‐day period in November to simulate conditions over a multiyear ice floe that has been the site of intensive observations as part of the Surface Heat Budget of the Arctic (SHEBA) project. The large‐scale tendencies of temperature, moisture, and wind are specified with values obtained from a special column data set obtained from the European Centre for Medium‐Range Weather Forecasting. Comparisons between the ARCSYM column simulations and SHEBA data reveal that modeled temperature profiles are too cold aloft and generally too warm in the boundary layer. The occurrence of low clouds is severely underpredicted while the high cloud fraction is over predicted. The modeled longwave radiative cooling at the surface is 1.5–3 times as large as that observed. Much of this bias is related to problems with the treatment of clear‐sky radiative transfer and in the simulated cloud optical properties. At the same time, the magnitude of modeled downward sensible heat flux at the surface is much too large. This has been related, in part, to the method for scaling temperature at the lowest modeled level to its surface air value under conditions of strong static stability. The importance of properly treating longwave radiative transfer under extremely cold, clear‐sky conditions is evident in the sensitivity studies. The best simulation of cloud properties was achieved by assuming liquid cloud processes and properties at temperatures above 255 K. This temperature is significantly colder than that used in many climate models. The occurrence of supercooled clouds in the simulation dramatically reduced longwave cooling at the surface due to increases in the optical depth and fractional coverage of clouds. Results from a coupled sea ice‐atmosphere simulation reveal that improvements in the atmospheric parameterizations are enhanced when the system is coupled.
Observations of H2SO4 and MSA during PEM‐Tropics‐A
Authors: Mauldin R. L. , Tanner D. J. , Heath J. A. , Huebert B. J. , Eisele F. L.
Published: September 2002

Results are presented of measurements of the concentration of gas phase H2SO4 and methane sulfonic acid (MSA) performed aboard the NASA P3‐b aircraft during the Pacific Exploratory Mission (PEM) Tropics study using the selected ion chemical ionization mass spectrometry (SICIMS) technique. During a nighttime portion of one flight the [H2SO4] was found to increase with decreasing relative humidity (RH). When compared to laboratory measurements of H2SO4 vapor pressure as a function of RH and particle neutralization (NH4+ and SO42− ionic composition) and model predictions using a liquid drop hydrate model, these measurements indicate that the particles from which the H2SO4 is evaporating are relatively unneutralized, a result which is in good agreement with filter measurements. Overall, the same increase in the gas phase [MSA] with decreasing RH or decreasing [NH4+] (obtained from filter measurements) was also observed, indicating a high volatility of MSA at low RH values or particle neutralization. When gas phase MSA values are compared to methane sulfonate (MS) values obtained from filter measurements, it was found that MSA was totally volatilized at low RH values, while MSA resides mainly in the particulate form at high RH values. Combining the gas phase and filter measurements, the boundary layer MS/(MS + SO42−) ratio showed a distinct increase with decreasing temperature and suggests that little or no MS or MSA is produced in the boundary layer at temperatures above 300 K.