bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloud and rain processes in a biosphere‐atmosphere interaction context in the Amazon Region
Authors: Silva Dias M. A. F. , Rutledge S. , Kabat P. , Silva Dias P. L. , Nobre C. , Fisch G. , Dolman A. J. , Zipser E. , Garstang M. , Manzi A. O. , Fuentes J. D. , Rocha H. R. , Marengo J. , Plana‐Fattori A. , Sá L. D. A. , Alvalá R .C. S. , Andreae M. O. , Artaxo P. , Gielow R. , Gatti L.
Published: October 2002

This paper presents an overview of the results from the first major mesoscale atmospheric campaign of the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA) Program. The campaign, collocated with a Tropical Rainfall Measuring Mission (TRMM) satellite validation campaigns, was conducted in southwest Rondônia in January and February 1999 during the wet season. Highlights on the interaction between clouds, rain, and the underlying landscape through biospheric processes are presented and discussed.
Characteristics of the Amazonian mesoscale convective systems observed from satellite and radar during the WETAMC/LBA experiment
Authors: Laurent Henri , Machado Luiz A. T. , Morales Carlos A. , Durieux Laurent
Published: October 2002

An objective tracking of mesoscale convective systems (MCSs) observed in full‐resolution Geostationary Operational Environmental Satellite (GOES) satellite images has been applied during the Wet Season Atmospheric Mesoscale Campaign/Large‐Scale Biosphere–Atmosphere (WETAMC/LBA) experiment in Amazonia from January to February 1999 to document the characteristics of the convective cloud organization in the southwestern Amazon region. The same tracking methodology was also applied to the National Aeronautical Space Administration (NASA) Tropical Ocean Global Atmosphere (TOGA) C‐Band radar data in order to estimate the propagation of the convective rain cells from constant altitude plan position indicators (CAPPI) at a height of 2 km. The convective activity showed two different patterns named Easterly and Westerly regimes according to the wind flow in the 700–850‐hPa layer. During the Easterly regime, MCSs and rain cells had closely related propagations. MCS as well as rain cell propagations were associated mostly to the midlevel mean flow. During the Westerly regime, the propagations of both MCSs and rain cells were much more disorganized, there was no clear relationship with the mean atmospheric flow at any level, although the rain cells have a slight tendency to propagate eastward, and the low‐level rain cells propagated quite independently of the high‐level cloud cover. MCS initiations were mostly driven by topography, that is, high escarpment and relatively high elevation.
Measurements of drop size distribution in the southwestern Amazon basin
Authors: Tokay Ali , Kruger Anton , Krajewski Witold F. , Kucera Paul A. , Filho Augusto Jose Pereira
Published: October 2002

Simultaneous observations of an optical and an impact type disdrometer and their application in radar rainfall estimation are evaluated. The disdrometers and two collocated rain gauges were operated in the southwest Amazon region of Brazil in 1999 as part of a NASA Tropical Rainfall Measuring Mission (TRMM) field campaign and the hydro‐meteorological component of the Large Scale Biosphere–Atmosphere Experiment (LBA). During the experiment, we observed large drops with diameters greater than 5 mm. These large drops were not adequately detected by the impact disdrometer and resulted in differences in drop size distribution and integral rain parameters derived from the two sensors. Considering coincident observations, we calculated that the impact disdrometer recorded about 11% lower rainfall accumulations than the optical disdrometer. In addition, radar rainfall algorithms, which we derived from the impact and optical disdrometer measurements, showed instrument dependency. Out of four radar rainfall algorithms that we considered, rain rate derived from specific differential phase has the least dependency, while the rain rate derived from reflectivity at horizontal polarization and differential reflectivity combined exhibited the largest. We also observed the characteristics of rainfall and drop size distribution in two distinct wind regimes present during the TRMM–LBA field campaign. Rain was heavier in the easterly regime, with more large drops being present.
Surface diurnal cycle and boundary layer structure over Rondônia during the rainy season
Authors: Betts Alan K. , Fuentes Jose D. , Garstang Michael , Ball John H.
Published: October 2002

An integrated data set with simultaneous observations at the surface, from tethered balloons within the boundary layer and from rawinsonde ascents, was collected during the wet season experiment of the Large‐Scale Biosphere‐Atmosphere (LBA) Experiment in Amazonia during January and February of 1999 in support of the ground validation for the Tropical Rainfall Measuring Mission (TRMM). We analyze the surface diurnal cycles of temperature, humidity, lifting condensation level, equivalent potential temperature, and the surface fluxes of sensible and latent heat, ground heat flux and net radiation, for easterly and westerly wind regimes in the lower troposphere. During the easterly wind regimes, the diurnal evolution of mixing ratio shows that the flux of water vapor through cloud base exceeds the large surface evaporation. There is a trend toward a wetter and cooler subcloud layer as the rainy season progresses. Daytime surface Bowen ratio for this pasture site is about 0.4, and falls slightly as the rainy season progresses. Typically in the afternoon, evaporatively driven downdrafts from convective rainbands transform the boundary layer. The fall of equivalent potential temperature in the boundary layer is similar for both regimes, but the boundary layer cooling by convective events during the westerly regimes is reduced, because the subcloud layer is shallower on average. Tethersonde ascents through the edges of gust fronts show that subcloud air is first cooled and moistened by rainfall evaporation before the arrival of downdraft air at the surface. These measurements provide a detailed observational basis for the validation and improvement of parameterizations for shallow and deep convection in numerical forecast models.
Surface ozone and precursor gases at Gadanki (13.5°N, 79.2°E), a tropical rural site in India
Authors: Naja M. , Lal S.
Published: October 2002

Ozone, nitrogen oxides (NO′x) (this includes NO, NO2 and some of their compounds converted by molybdenum converter; see section 2.2 for details), CO, and CH4 have been measured during the period 1993–1996 at Gadanki (13.5°N, 79.2°E), a rural site in the tropical Indian region. Observations show daytime photochemical ozone production that is initiated by the photooxidation of the precursor gases, with maximum noontime annual average O3 mixing ratios of only 34 ± 13 ppbv. Ozone levels were highest during the winter/spring period and lowest during summer, which differs from observations at sites in other regions. The rate of increase in O3 is greatest around 0900 hours local time, whereas the magnitude of the maximum rate of decrease during the evening is considerably smaller. This feature distinguishes the urban and rural sites since the magnitudes of the rates during morning and evening are more similar at urban sites. At Gadanki, annual averages of oxides of nitrogen (NO′x), CO, and CH4 are observed to be 2.1 ± 1.8 ppbv, 237 ± 64 ppbv, and 1.70 ± 0.11 ppmv, respectively. However, a poor correlation between ozone and NO′x was found, indicating that NO′x levels at this site are not controlled by fresh combustion or emissions and could be due to transport from the nearby major cities. Ozone production efficiency and estimated photochemical ozone production were also found to be lower at this site.
Control and interannual variability of dimethyl sulfide in the Indian Ocean
Authors: Shenoy D. M. , Joseph S. , Dileep Kumar M. , George M. D.
Published: October 2002

Aqueous dimethyl sulfide (DMS) concentrations and its sea‐to‐air fluxes were studied in upper layers (200 m) of the Indian Ocean, as a part of the Indian Ocean Experiment (INDOEX) that centered around the movement of the Intertropical Convergence Zone (ITCZ). Observations during the January–March period revealed significant interannual differences in water column DMS concentrations between 1998 and 1999. DMS concentrations were about five times higher in 1999 (range: 0–14.84 nM; average: 3.32 nM) than 1998 (range: 0.05–4.94 nM; average: 0.70 nM). Similar variation was found with respect to its precursor, dimethylsulfoniopropionate (averages of 3.31 nM in 1998 and 16.36 nM in 1999). DMS exhibited weak relationships with nitrate and chlorophyll but a relatively strong one with mixed layer depths. Our results suggest that physical forcing (wind speed and depth of mixed layer) along with the associated biological processes might have primarily controlled DMS in these waters. The column DMS appears to be a function of mixed layer depth whereas interannual variability in its concentrations might be attributable to changes in wind forcing and plankton composition, Sea‐to‐air fluxes were higher (seven times) because of higher DMS abundance and wind speeds in 1999 (average: 7.2 μM m−2 d−1) than 1998 (average: 1.0 μM m−2 d−1). Higher DMS fluxes coincided with reported higher aerosol optical depths over the Indian Ocean in 1999.
Distribution of optical properties among atmospheric submicrometer particles of given electrical mobilities
Authors: Heintzenberg Jost , Okada Kikuo , Luo Bei Ping
Published: October 2002

With the serial combination of a differential mobility analyzer (DMA) and an optical particle counter (OPC) the optical state of mixture in the suburban aerosol at Tsukuba, Japan, was explored. At mobility diameters between 200‐ and 400‐nm broad optical signal distributions were measured which indicated optically external mixtures, i.e., particles with a given electrical mobility exhibiting different optical properties. On average ∼50% of the analyzed particles were classified as optically external mixtures. The average measured distribution of optical signals was combined with the average size distribution to calculate an estimate of the integral scattering properties of the submicrometer aerosol for the measured state of optical mixture. This estimate yields 71% of the scattering coefficient of a size distribution in which all particles of a given size have the optical properties of ammonium sulfate. However, for extended periods of time this percentage was as low as 41%. With a nonspherical particle model number fractions of nonspherical particles have been retrieved from the OPC signal distributions. The results of the present study demonstrate that the combination of DMA and OPC can quantify the optical state of mixture of submicrometer particles with strong consequences for the quantification of their integral scattering coefficients. Conversely, the study indicates the limitations of conventional DMA size distributions measured in urban aerosols with number fractions of nonspherical particles on the order of 50%. DMA penetrations are dependent on particle shape. Thus information on particle shape appears to be a necessary prerequisite for interpreting DMA measurements.
Large area mapping of land‐cover change in Rondônia using multitemporal spectral mixture analysis and decision tree classifiers
Authors: Roberts D. A. , Numata I. , Holmes K. , Batista G. , Krug T. , Monteiro A. , Powell B. , Chadwick O. A.
Published: October 2002

We describe spatiotemporal variation in land cover over 80,000 km2 in central Rondônia. We use a multistage process to map primary forest, pasture, second growth, urban, rock/savanna, and water using 33 Landsat scenes acquired over three contiguous areas between 1975 and 1999. Accuracy of the 1999 classified maps was assessed as exceeding 85% based on digital airborne videography. Rondônia is highly fragmented, in which forests outside of restricted areas consist of numerous, small irregular patches. Pastures in Rondônia persist over many years and are not typically abandoned to second growth, which when present rarely remains unchanged longer than 8 years. Within the state, annual deforestation rates, pasture area, and ratio of second growth to cleared area varied spatially. Highest initial deforestation rates occurred in the southeast (Luiza), at over 2%, increasing to 3% by the late 1990s. In this area, the percentage of cleared land in second growth averaged 18% and few pastures were abandoned. In central Rondônia (Ji‐Paraná), deforestation rates rose from 1.2% between 1978 and 1986 to a high of 4.2% in 1999. In the northwest (Ariquemes), initial deforestation rates were lowest at 0.5% but rose substantially in the late 1990s, peaking at 3% in 1998. The ratio of second growth to cleared area was more than double the ratio in Luiza and few pastures remained unchanged beyond 8 years. Land clearing was most intense close to the major highway, BR364, except in Ariquemes. Intense forest clearing extended at least 50 km along the margins of BR364 in Ji‐Paraná and Luiza. Spatial differences in land use are hypothesized to result from a combination of economic factors and soil fertility.
Sensitivity of simulated mesoscale atmospheric circulations resulting from landscape heterogeneity to aspects of model configuration
Authors: Weaver Christopher P. , Baidya Roy Somnath , Avissar Roni
Published: October 2002

Recent work has demonstrated the importance of anthropogenic landscape heterogeneity in Amazonia and the central U.S. in forcing mesoscale atmospheric circulations and generating clouds and precipitation. It has been shown that failing to account for this surface heterogeneity may have important implications for the simulation of land–atmosphere interactions in large‐scale atmospheric models. The work presented here shows that, in addition to correctly specifying the surface forcing, accurate simulation of landscape‐induced mesoscale effects with a regional model (e.g., Regional Atmospheric Modeling System, RAMS) depends critically on informed choices of aspects of model configuration. These include horizontal resolution, strength of nudging, and atmospheric initialization. Sensitivity experiments designed to illustrate the impact of varying these factors on RAMS‐simulated, landscape‐induced mesoscale circulations are presented here. These results, supported by dynamical and scaling arguments, suggest that model configuration can have at least as great an impact on the simulated mesoscale circulations, fluxes, and PBL structure as correctly accounting for mesoscale landscape heterogeneity. Such experiments therefore provide crucial guidance for optimally constructing simulations of mesoscale land–atmosphere interaction important for a variety of applications from field campaigns to parameterization development.
Rainfall estimation from TOGA radar observations during LBA field campaign
Authors: Anagnostou Emmanouil N. , Morales Carlos A.
Published: October 2002

The TRMM Large Scale Biosphere‐Atmosphere (LBA) experiment, conducted between January and February of 1999 in Southwest Amazon, deployed among other instruments NASA's C‐band Doppler radar (TOGA) and four dense rain gauge networks. This paper presents a procedure devised to derive surface rainfall rate estimates from combination of TOGA observations and the in situ rain gauge rainfall measurements. The spatial and temporal scales considered are 2 × 2 km2 grids of instantaneous to hourly rain accumulations. The procedure includes evaluation of TOGA calibration through comparisons with TRMM Precipitation Radar (PR) data and implementation of an optimal quantitative precipitation estimation (QPE) algorithm. Comparisons with PR indicated a 4‐dB calibration offset occurring in the later two thirds of the observation period. The implemented QPE algorithm applies a parameter that differentiates the Z‐R conversion in convective and stratiform regimes and a stochastic filtering approach for estimation of mean‐field bias on the basis of radar‐rain gauge comparisons at the hourly timescale. The calibration of the algorithm parameter values is formulated as a global optimization problem, which is solved by minimizing the radar‐rain gauge rainfall accumulation root‐mean‐square (rms) difference at the hourly timescale. A random resampling calibration/validation exercise is performed to evaluate the algorithm performance and its sensitivity to parameter values. Validation against gauges shows that the algorithm produces unbiased estimates with ∼57% relative RMS difference at the hourly scale. Comparison with S‐POL rain estimates showed good correlation (0.9) but some overestimation (9%). Rainfall products are used to derive rainfall statistics for two distinct meteorological low‐level wind regimes (easterly and westerly) that occurred during LBA. Finally, instantaneous rain estimates are compared against TRMM PR rainfall profiles for six coincident storm cases showing high correlation (0.9) and low (7%) systematic difference (PR overestimation).
Analysis of fine‐scale canopy turbulence within and above an Amazon forest using Tsallis’ generalized thermostatistics
Authors: Bolzan Maurício J. A. , Ramos Fernando M. , Sá Leonardo D. A. , Rodrigues Neto Camilo , Rosa Reinaldo R.
Published: October 2002

We analyzed the probability density function (PDF) of velocity and temperature differences in the canopy sublayer of Amazonia based on Tsallis' generalized thermostatistics theory. We show that such a theory provides an accurate framework for modeling the statistical behavior of the inertial subrange above and below the canopy. For this, we compared the experimental PDFs with the theoretically predicted ones. The data were measured during the wet season of the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA), which was carried out during the months of January–March 1999 in the southwestern part of Amazonia region. Measurements were made simultaneously at different heights in a 60 m micrometeorological tower located in the Biological Reserve of Jaru (10°04′S, 61°56′W), Brazil. The fast response wind speed measurements, sampled at 60 Hz rate, were made using three‐dimensional sonic anemometers at the heights of 66 m (above the canopy) and 21 m (below the canopy). The results showed good agreement between experimental data measured above the canopy forest and Tsallis' generalized thermostatistics theory. For below canopy data, the agreement between experimental and theoretical PDFs was fairly good, but some distortion was observed. This is probably due to some peculiar characteristics of turbulent momentum transfer process inside the forest crown. Discussion is presented to explain these results. Conclusions regarding the absence of “universal scaling” in the inertial subrange are also presented in the context of the entropic parameter of Tsallis' theory.
Scale variability of atmospheric surface layer fluxes of energy and carbon over a tropical rain forest in southwest Amazonia 1. Diurnal conditions
Authors: von Randow Celso , Sá Leonardo D. A. , Gannabathula Prasad S. S. D. , Manzi Antonio O. , Arlino Paulo R. A. , Kruijt Bart
Published: October 2002

The aim of this study is to investigate the low‐frequency characteristics of diurnal turbulent scalar spectra and cospectra near the Amazonian rain forest during the wet and dry seasons. This is because the available turbulent data are often nonstationary and there is no clear spectral gap to separate data into “mean” and “turbulent” parts. Daubechies‐8 orthogonal wavelet is used to scale project turbulent signals in order to provide scale variance and covariance estimations. Based on the characteristics of the scale dependence of the scalar fluxes, some classification criteria of this scale dependence are investigated. The total scalar covariance of each 4‐hour data run is partitioned in categories of scale covariance contributions. This permits the study of some statistical characteristics of the scalar turbulent fields in each one of these classes and, thus, to give an insight and a possible explanation of the origin of the variability of the scalar fields close to the Amazonian forest. The results have shown that a two‐category classification is the most appropriate to describe the kind of observed fluctuations: “turbulent” and “mesoscale” contributions. The largest contribution of the sensible heat, latent heat, and CO2 covariance contributions occurs in the “turbulent” length scales. Mesoscale eddy motions, however, can contribute up to 30% of the total covariances under weak wind conditions. Analysis of scale correlation coefficient [r(Tvq)] between virtual temperature (Tv) and humidity (q) signals shows that the scale patterns of Tv and q variability are not similar and r(Tvq) < 1 for all analyzed scales. Scale humidity skewness calculations are negative during the dry season and positive during the wet season. This suggests that different boundary layer moisture regimes occur during the dry and wet seasons.
Active chlorine release from marine aerosols: Roles for reactive iodine and nitrogen species
Authors: McFiggans G. , Cox R. A. , Mössinger J. C. , Allan B. J. , Plane J. M. C.
Published: October 2002

Recent laboratory measurements of the uptake of gaseous hypoiodous acid (HOI) on NaCl, NaBr, and sea‐salt surfaces have been used to aid calculation of the expected liberation of chlorine atoms from sea‐salt aerosol resulting from marine boundary layer (MBL) iodine chemistry. An existing model has been extended to include reactive chlorine chemistry resulting from two activation mechanisms. Measurements of the iodine monoxide (IO) and nitrate (NO3) radicals from three recent field experiments have been used to constrain numerical simulations, investigating the relative importance of the iodine‐and nitrogen‐mediated mechanisms. These calculations show that the reactive uptake of both HOI and N2O5 in the MBL can liberate Cl atoms from sea‐salt aerosol at a significant rate. A characteristic pulse of Cl production leading to several thousand molecules per cubic centimeter after sunrise may prove to be a useful diagnostic for the iodine‐mediated mechanism. Steady daytime production is predicted, leading to steady state [Cl] of several hundred to a few thousand molecules per cubic centimeter, perhaps over wide areas of the oceans. In addition, under certain conditions reactive bromine chemistry due to IBr release from fresh sea salt by reaction of HOI may dominate ICl production.
Formation of an ozone lamina due to differential advection revealed by intensive observations
Authors: Tomikawa Yoshihiro , Sato Kaoru , Kita Kazuyuki , Fujiwara Masatomo , Yamamori Miho , Sano Takuki
Published: October 2002

An intensive observation with ozonesondes, radiosondes, and the Middle and Upper atmosphere (MU) radar was conducted at Shigaraki (34.9°N, 136.1°E), Japan, from 16 through 24 April 1998 to investigate the formation mechanism of ozone laminae in the midlatitude lower stratosphere. In these observations the temporal variation of an ozone lamina at Shigaraki was continuously observed through a short time interval of 8 hours. During the observation period an ozone lamina with a thickness of 2–3 km appeared and ascended with a speed of ∼1 km day−1 in the height region of 18–21 km. It is deduced that inertia gravity waves existing in this height region did not contribute to formation of the ozone lamina, because their amplitudes were too small and their vertical phase propagation was in the opposite direction. The reverse domain filling method was used to reconstruct the “high‐resolution” modified potential vorticity field using backward trajectory calculations. The results indicate that this ozone lamina was caused by differential advection due to the vertical shear associated with the subtropical westerly jet and embedded stationary Rossby wave therein. This means that large‐scale motions concurrent with vertical wind shear can produce much smaller‐scale structures in material fields than those of the large‐scale motions themselves.
Bias correction and random error characterization for the assimilation of high‐resolution Doppler imager line‐of‐sight velocity measurements
Authors: Tangborn Andrew , Ménard Richard , Ortland David
Published: October 2002

The statistical characteristics of the systematic and random observation errors of the line‐of‐sight (LOS) velocity measurements made by the high‐resolution Doppler imager (HRDI) are obtained using collocated and coincident differences between HRDI observations and model‐assimilated data (H‐A). Although these differences have contributions from both observation and model errors, we show how they can be individually characterized. HRDI, a limb sounder on board the Upper Atmosphere Research Satellite (UARS), is the only instrument making global wind measurements in the stratosphere. Doppler shifts in O2 absorption spectra measured by HRDI within two different bands (γ and B) basically provide the line‐of‐sight velocity. The analysis presented here is carried out using the Doppler shifts themselves, rather than the HRDI retrieved (u, v) wind components. The absolute position of the line for zero‐wind conditions in LOS velocity measurement is unknown, and one goal of this paper is to develop a systematic method of determining this position through mean differences (biases) between observed HRDI and LOS model analyses approximately projected onto the line of sight. Biases are separated based on 16 different measurement configurations. The bias dependence on these configurations (plus an altitude dependence) is used to create a bias correction for each instrument configuration. The random error component in H‐A differences is analyzed by separating the γ and B band observations and locating observation pairs where both bands are very nearly looking at the same location at the same time. It is shown that the two observation error streams are uncorrelated. Observation errors are also uncorrelated with the analyses error, and observational and model wind variance (in the stratosphere) are estimated.
Aerosol optical depth at Cape Grim, Tasmania, 1986–1999
Authors: Wilson S. R. , Forgan B. W.
Published: October 2002

The aerosol optical depth at four wavelengths (368, 500, 778, and 868 nm) has been measured automatically at Cape Grim since 1986. The site, on the northwest tip of Tasmania, Australia, was chosen to be representative of much of the Southern Ocean. Fourteen years of measurement have been calibrated and analyzed. The data have been filtered so that only measurements made under onshore wind conditions are considered. The major feature observed in the record is the eruption of Mount Pinatubo, which resulted in the aerosol optical depth at 500 nm rising to 0.2–0.3. If the period of high stratospheric aerosol is ignored, the resulting record shows an average aerosol optical depth near 0.04 for all four wavelengths. In the winter months the observed optical depth correlates well with wind speed. This correlation indicates, that, as an annual average, 40% of the observed aerosol optical depth is due to wind‐generated aerosol. The annual cycle of the aerosol optical depth can be understood in terms of the impact of photochemically generated aerosol in the summer months, and an injection of midtropospheric aerosol in September, presumably due to biomass burning.
Simulation of a biomass‐burning plume: Comparison of model results with observations
Authors: Trentmann J. , Andreae M. O. , Graf H.‐F. , Hobbs P. V. , Ottmar R. D. , Trautmann T.
Published: October 2002

We have simulated the dynamical evolution of the plume from a prescribed biomass fire, using the active tracer high‐resolution atmospheric model (ATHAM). Initialization parameters were set to reflect the conditions during the fire. The model results are compared with airborne remote‐sensing and in situ measurements of the plume. ATHAM reproduces the injection height (250–600 m) and the horizontal extent of the plume (∼4 km) with good accuracy. The aerosol mass concentrations are underestimated but still in the range of the observations. Remaining differences between the model results and the measurements are attributed to limited meteorological and fire emission information. Additionally, radiative transfer simulations using in situ measurements of the aerosol properties are performed. A comparison of the measured and simulated reflected solar flux shows an underestimation by the model over the ocean surface, which is most likely due to an underestimation of the aerosol optical depth in the model. The instantaneous radiative forcing was calculated to −36 W m−2over land and −58 W m−2over the ocean for a solar zenith angle of 47° and an optical depth of unity, consistent with previous studies. Overall, it appears that ATHAM is a valuable tool for the examination of transport processes within biomass‐burning plumes and, together with a chemical and microphysical module, is suitable for studies of the interaction between transport, chemistry, and microphysics within such plumes.
An assessment of the ozone loss during the 1999–2000 SOLVE/THESEO 2000 Arctic campaign
Authors: Schoeberl Mark R. , Newman Paul A. , Lait Leslie R. , McGee Thomas J. , Burris John F. , Browell Edward V. , Grant William B. , Richard Erik C. , von der Gathen Peter , Bevilacqua Richard , Mikkelsen Ib S.
Published: October 2002

Ozone observations from ozonesondes, the lidars aboard the DC‐8, in situ ozone measurements from the ER‐2, and satellite ozone measurements from Polar Ozone and Aerosol Measurement III (POAM) were used to assess ozone loss during the Sage III Ozone Loss and Validation Experiment (SOLVE) and Third European Stratospheric Experiment on Ozone (THESEO) 1999–2000 Arctic campaign. Two methods of analysis were used. In the first method a simple regression analysis of the data time series is performed on the ozonesonde and POAM measurements within the vortex. In the second method the ozone measurements from all available ozone data were injected into a free‐running diabatic trajectory model and were carried forward in time from 1 December to 15 March. Vortex ozone loss was then estimated by comparing the ozone values of those parcels initiated early in the campaign with those parcels injected later in the campaign. Despite the variety of observational techniques used during SOLVE, the measurements provide a fairly consistent picture. Over the whole vortex the largest ozone loss occurs between 550 and 400 K potential temperatures (∼23–16 km) with over 1.5 ppmv (∼55%) lost by 15 March, the end of the SOLVE mission period. An ozone loss rate of 0.04–0.05 ppmv/day was computed for 15 March. The total column loss was between 44 and 57 DU or 11–15%. Ozonesondes launched after 15 March suggest that an additional 0.5 ppmv or more ozone was lost between 15 March and 1 April.
Impact of bogus tropical cyclones on summertime circulation in regional climate simulation
Authors: Ahn Young‐In , Lee Dong‐Kyou
Published: October 2002

Ten‐year (1987–1996) summertime simulations are conducted using a regional climate model to investigate the impact of tropical cyclones on simulated summertime circulation over east Asia. Toward this end, a tropical cyclone‐bogusing scheme is incorporated into a regional climate‐modeling framework to realistically describe tropical cyclone structure and its intensity during seasonal integration. The simulated summertime monsoon climatology with and without bogus tropical cyclones incorporated into the large‐scale forcing of the NCEP/NCAR reanalysis is analyzed. The model with the bogus tropical cyclones shows improvement in the intensity and tracks of the tropical cyclones. In addition, the well‐defined tropical cyclones in the model are sustained for a longer time, so they actually modify the east Asian summer monsoon circulation as well as the extratropical circulation. The bogus tropical cyclones in the model also produce much stronger convection and then a larger amount of precipitation modifying the entire precipitation pattern. Meanwhile, compared with the observations, the intensity of the bogus tropical cyclones weakens more rapidly in the earlier stage of the tropical cyclone development. With the bogus tropical cyclones, the large‐scale features over east Asia are closer to observations. Major results are as follows: (1) The intensity of the North Pacific subtropical high becomes weaker, while it is excessively intensified and shifted northward without the bogus tropical cyclones. (2) The southerly or southwesterly monsoon flows in the lower troposphere are reduced, meanwhile they are too strong, accompanying the northward excessive transport of moisture in the no‐bogus simulation. (3) The midlatitude jets and storm tracks are intensified and shifted southward. (4) Especially, the retreat of the east Asian summer monsoon in late August is well reproduced, which is completely missed in the cases of poorly resolved tropical cyclones. (5) The empirical orthogonal function analysis reveals that the large‐scale variability of the east Asia summertime circulation does appear realistically with the bogus tropical cyclones. (6) The biweekly period related to the life cycle of the intraseasonal monsoon depressions is much weakened, while the period of 5 ∼ 7 days associated with the synoptic or mesoscale disturbances, such as tropical cyclone activities, is intensified. One of the important findings in this study is that with the bogus tropical cyclones, the secondary rainy season in late August associated with the retreat of the east Asian summer monsoon is simulated realistically. The secondary rainy season annually takes place in middle‐latitude east Asia, especially over southern China, Korea, and Japan. This finding strongly suggests that one of the major reasons for the secondary rainy season could be tropical cyclone activities.
Construction of a unified, high‐resolution nitrous oxide data set for ER‐2 flights during SOLVE
Authors: Hurst, Dale F. , Schauffler, Sue M. , Greenblatt, Jeffery B. , Jost, Hansjürg , Herman, Robert L. , Elkins, James W. , Romashkin, Pavel A. , Atlas, Elliot L. , Donnelly, Stephen G. , Podolske, James R. , Loewenstein, Max , Webster, Christopher R. , Flesch, Gregory J. , Scott David C.
Published: October 2002

Four nitrous oxide (N2O) instruments were part of the NASA ER‐2 aircraft payload during the 2000 SAGE‐III Ozone Loss and Validation Experiment (SOLVE). Coincident data from the three in situ instruments and a whole air sampler are compared. Agreement between these instruments was typically good; however, there are several types of important differences between the data sets. These differences prompted a collaborative effort to combine data from the three in situ instruments, using an objective method, to produce a self‐consistent, high‐resolution, unified N2O data set for each SOLVE flight. The construction method developed by the four N2O instrument teams is described in detail. An important step in this method is the evaluation and reduction of bias in each of the in situ data sets before they are combined. The quality of unified N2O data is examined through its agreement with high‐accuracy and high‐precision N2O data from whole air samples collected from the ER‐2 during SOLVE flights. Typical agreement between these two data sets is 2.9 ppb (1.5%), better than the typical agreement between any pair of N2O instruments.
Separating the influence of halogen and climate changes on ozone recovery in the upper stratosphere
Authors: Shindell Drew T. , Grewe Volker
Published: October 2002

While halogens from chlorofluorocarbons (CFCs) dominated past ozone changes, our simulations show climate change playing an increasingly important role over coming decades. Including potential climate‐induced stratospheric water vapor increases, the ozone change relative to 1980 attributable to climate change surpasses that due to halogens in the 2030s for both the upper stratosphere and the total column. Its overall impact may delay recovery of total ozone to 1980 values. These results emphasize that ozone recovery is not only a detection issue but also a detection and attribution issue, as trends must be ascribed to climate and halogens. Exploiting their different spatial patterns, we demonstrate a technique to isolate the halogen signature in the upper stratosphere by contrasting equatorial and midlatitude ozone trends at 40‐km altitude. This may allow early detection of the effectiveness of halogen emission reductions, which would show that a delayed recovery does not represent a CFC treaty failure but rather highlights the growing influence of greenhouse gases on the Earth's atmosphere.
Interannual changes of temperature and ozone: Relationship between the lower and upper stratosphere
Authors: Salby Murry , Callaghan Patrick , Keckhut Philippe , Godin Sophie , Guirlet Marielle
Published: October 2002

Changes of stratospheric dynamical structure and ozone are investigated in observations of the lower stratosphere, from meteorological analyses and Total Ozone Mapping Spectrometer (TOMS) ozone, and in contemporaneous observations of the upper stratosphere and mesosphere, from the French lidar at Observatoire de Haute‐Provence (OHP). Interannual changes in the lower stratosphere are shown to be accompanied by coherent changes in the upper stratosphere and mesosphere. Over the 1980s and 1990s, both operate coherently with anomalous forcing of the residual mean circulation. Changes of temperature and ozone at OHP have sign and structure consistent with interannual changes of meridional transport. They reflect a poleward expansion and contraction of warm ozone‐rich air, compensated by opposite changes of the polar‐night vortex.
On the spatial extent and evolution of coastal aerosol plumes
Authors: O'Dowd Colin D.
Published: October 2002

Airborne mapping and pseudo‐Lagrangian experiments were conducted in coastal and tidal‐induced nucleation plumes along the west coast of Ireland in June 1999. The mapping flights confirmed that the source of the previously reported coastal nucleation events is indeed the tidal zone around the coastline. Additionally, the mapping flights also confirmed that coastal nucleation is typically ubiquitous along the coastline, at least on the Irish coast. Along with the large horizontal extent of coastal nucleation events, these new particles were observed to be mixed up to >1000 m in the vertical despite slightly stable meteorological conditions. On the clean air mapping flight the background particle concentration (r > 1.5 nm) was observed to increase from <1000 cm−3to >100,000 cm−3, while accumulation mode (r > 50 nm) particle concentration remained constant at approximately 50 cm−3. During a semipolluted mapping flight, concentrations increased from 3000 to >100,000 cm−3in places. The enhancement in particle concentration was confirmed to be in the size range 1.5–5 nm radius at the start of the nucleation event, while growth into larger sizes was observed later. During this semipolluted event, owing to favorable wind conditions, it was possible to perform a pseudo‐Lagrangian experiment in a coastal plume advecting out over the northeast Atlantic. This plume was observed to be >60 km in width and >1000 m in the vertical and was encountered for >250 km off the coast. During this plume evolution the growth of the new particle mode at sizes <5 nm up to sizes >40 nm was observed. After the plume had evolved for 3 hours, increases in scattering coefficients were observed along with significant increases in cloud condensation nuclei concentrations. These results confirm that the spatial extent of tidal‐related particle production is regionally significant, and after a few hours, the growth of these recently formed coastal aerosols significantly increase the concentration of radiatively active aerosol particles.
Quantifying the rate of heterogeneous processing in the Arctic polar vortex with in situ observations of OH
Authors: Hanisco T. F. , Smith J. B. , Stimpfle R. M. , Wilmouth D. M. , Perkins K. K. , Spackman J. R. , Anderson J. G. , Baumgardner D. , Gandrud B. , Webster C. R. , Dhaniyala S. , McKinney K. A. , Bui T. P.
Published: October 2002

We present simultaneous in situ observations of OH, HO2, ClONO2, HCl, and particle surface area inside a polar stratospheric cloud undergoing rapid heterogeneous processing. A steady‐state analysis constrained by in situ observations is used to show that concentrations of OH calculated during a processing event are extremely sensitive to the assumptions regarding aerosol composition and reactivity. This analysis shows that large perturbations in the abundance of OH are consistent with the heterogeneous production of HOCl via ClONO2 + H2O → HOCl + HNO3 and removal via HOCl + HCl → Cl2 + H2O in a polar stratospheric cloud. If the cloud is composed of supercooled ternary solution (STS) aerosols and solid nitric acid trihydrate (NAT) particles, comparison with observations of OH show that modifications to surface reactivity to account for high HNO3 content in STS aerosols and low HCl coverage on NAT particles are appropriate. These results indicate that with the low HCl levels in this encounter and in a processed polar vortex in general, reactions on STS aerosols dominate the total heterogeneous processing rate. As a consequence, the formation of NAT does not lead to significantly faster reprocessing rates when HCl concentrations are low and STS aerosols are present. Model calculations that include these modifications to uptake coefficients for STS and NAT will lead to significantly slower reprocessing and faster recovery rates of chlorine in the springtime Arctic polar vortex.
Regional radiative forcing by line‐shaped contrails derived from satellite data
Authors: Meyer R. , Mannstein H. , Meerkötter R. , Schumann U. , Wendling P.
Published: October 2002

The influence of contrails on the radiation budget depends mainly on their coverage and optical depth. This study derives these parameters from data of the advanced very high resolution radiometer sensor onboard the NOAA 14 satellite for a region over western Europe within 40°–56°N and 10°W–23°E during 2 years starting March 1995. The data are classified by an operational contrail detection algorithm with a new evaluation of the detection efficiency. From the classification results, daytime and nighttime coverage by line‐shaped contrails over western Europe are derived. The daytime contrail coverage for the analyzed region is 0.7% in the annual mean, 1.0% during winter, and 0.4% during summer. The daytime contrail cover is 3 times higher than the night‐time contrail cover. An effective optical depth of the observed contrails is derived from the radiation contrasts in the 11 μm channel for contrails and adjacent pixels. The optical depth in the visible spectral range is computed from these results assuming a previously measured size spectrum of ice crystals. The mean visible optical depth is found to be about 0.1, much smaller than that derived from previous case studies. The average radiative forcing at the top of the atmosphere is computed for the derived contrail cloud cover and optical depth. Here contrails mostly cause positive radiative forcing (heating). Larger heating effects during night and summer get partly compensated through more contrail cover during day and winter. The radiative forcing by contrails in the examined region is ∼0.03 W m−2, which is much smaller than was estimated earlier.
Evaluation of the diurnal cycle of precipitation, surface thermodynamics, and surface fluxes in the ECMWF model using LBA data
Authors: Betts Alan K. , Jakob Christian
Published: October 2002

The mean diurnal cycle of precipitation, near‐surface thermodynamics and surface fluxes from short‐term forecasts of the ECMWF model are compared with corresponding observations from the Large‐Scale Biosphere‐Atmosphere Experiment in the Amazonia wet season campaign in 1999 in Rondônia. Precipitation starts about 2 hours after sunrise in the model, several hours earlier than observed, because the model does not simulate well the morning growth of the nonprecipitating convective boundary layer. However, the mean daily precipitation during the wet season compares well with observed rainfall. On most days, maximum early afternoon temperature and cloud base height are lower in the model than observed. Maximum equivalent potential temperature is close to that observed. The model surface evaporative fraction is higher than observed and rises to near unity in the late afternoon. Work is in progress to evaluate and integrate the parameterizations for shallow and deep convection.
Atmospheric effects on insolation in the Brazilian Amazon: Observed modification of solar radiation by clouds and smoke and derived single scattering albedo of fire aerosols
Authors: Schafer J. S. , Holben B. N. , Eck T. F. , Yamasoe M. A. , Artaxo P.
Published: October 2002

Five aerosol and solar flux monitoring sites were established in Brazil for the Large Scale Biosphere–Atmosphere Experiment in Amazônia (LBA) project. The first two sites were developed in the states of Rondonia and Mato Grosso in January 1999, while the others were initiated in September 1999 in Amazonas, Para, and near Brasilia (later relocated to Acre). Daily insolation [photosynthetically active radiation (PAR) and total solar] for 1999 and 9 months of 2000 was determined from flux measurements, and the daily fraction of theoretical cloud‐free, background‐aerosol insolation, fB(day), was evaluated for each site. Observed daily shortfall (MJ m−2 d−1) of PAR insolation due to clouds and aerosols (relative to modeled values for background aerosol), and the instantaneous reductions of PAR irradiance due to high aerosol optical thickness (AOT) smoke events are presented for 1999 at Alta Floresta. The ratio of PAR flux to total solar flux (PAR fraction) was examined for all atmospheric conditions during 1999, and the observed dependence of this parameter on column water vapor and smoke AOT was quantified. No significant relationship with cloud amount (as quantified) was found. Instantaneous PAR irradiance measurements and concurrent, cloud‐cleared aerosol data from collocated CIMEL sunphotometers were used with a radiative transfer model to investigate the optical properties of smoke aerosols during the burning season. In particular, the single scattering albedo (SSA) was evaluated in the PAR spectral range for AOT440 nm values ranging from 0.8 to 3.0. These estimates were compared with the operational retrievals of the same parameter from algorithms developed by AERONET for CIMEL sunphotometer radiance measurements.
Generation of layering in the lower stratosphere by a breaking Rossby wave
Authors: Bradshaw Neil G. , Vaughan G. , Ancellet G.
Published: October 2002

An airborne ozone lidar has been used to observe layering in the ozone field between 350 and 400 K northward of the subtropical jet stream. An ozone‐poor layer between 370 and 400 K was observed over western Europe on 21 April 1999. On this day a Rossby wave was observed to be breaking over the eastern North Atlantic and western Europe, with both poleward and equatorward components. We propose that the low ozone at ∼400 K was caused by a poleward breaking Rossby wave stretching from Spain to the south coast of Britain. Isentropic back‐trajectory calculations suggest a tropical upper tropospheric origin for the air within this wave, over North America. We suggest that Rossby waves generate layering in the lower stratosphere because of vertical gradients in the background wind fields, which govern the growth in amplitude and breaking characteristics of the waves.