bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of the 1997/1998 El Niño cloud distributions from SAGE II observations
Authors: Wang Pi‐Huan , Minnis Patrick , Wielicki Bruce A. , Wong Takmeng , Cess Robert D. , Zhang Minghua , Vann Lelia B. , Kent Geoffrey S.
Published: May 2003

The present study examines the characteristics of cloud distributions with emphasis on cloud longwave radiative forcing (CLRF) during the peak of the 1997/1998 El Niño in relation to climatological conditions, based on measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II. The observed distinct cloud occurrence and CLRF during this unusual 1997/1998 El Niño constitutes a unique data set for validating and improving cloud‐radiation‐climate interactions in general circulation and climate models. Using the solar occultation technique, the SAGE II satellite instrument is capable of providing measurements with a 1‐km vertical resolution facilitating the analysis with sufficient vertical as well as near global scale (70°S–70°N) details. The present study indicates (1) above normal high‐altitude opaque cloud occurrence over the eastern tropical Pacific and an opposite situation over the Pacific warm pool, leading to a distribution of the cumulative opaque cloud anomalies above 3 km generally consistent with the pattern of observed tropical sea surface temperature and precipitation anomalies; (2) a similar behavior in the subvisual cloud distributions near the tropical tropopause; (3) a zonally averaged cloud distribution that is characterized by reduced opaque clouds at low latitudes, except in the southern tropics below 10 km, and by enhanced opaque clouds at high latitudes, along with increased subvisual clouds in the southern tropics and decreased subvisual clouds in the northern subtropics in the upper troposphere; and (4) a geographic distribution of model‐calculated CLRF anomalies that resembles closely that inferred from the Earth Radiation Budget Experiment and the Clouds and the Earth's Radiant Energy System. A discussion on the influence of the El Niño on large‐scale mean tropospheric circulations is also provided.
Signatures of terminal alkene oxidation in airborne formaldehyde measurements during TexAQS 2000
Authors: Wert B. P. , Trainer M. , Fried A. , Ryerson T. B. , Henry B. , Potter W. , Angevine W. M. , Atlas E. , Donnelly S. G. , Fehsenfeld F. C. , Frost G. J. , Goldan P. D. , Hansel A. , Holloway J. S. , Hubler G. , Kuster W. C. , Nicks D. K. , Neuman J. A. , Parrish D. D. , Schauffler S. , Stutz J. , Sueper D. T. , Wiedinmyer C. , Wisthaler A.
Published: May 2003

Airborne formaldehyde (CH2O) measurements were made by tunable diode laser absorption spectroscopy (TDLAS) at high time resolution (1 and 10 s) and precision (±400 and ±120 parts per trillion by volume (pptv) (2σ), respectively) during the Texas Air Quality Study (TexAQS) 2000. Measurement accuracy was corroborated by in‐flight calibrations and zeros and by overflight comparison with a ground‐based differential optical absorption spectroscopy (DOAS) system. Throughout the campaign, the highest levels of CH2O precursors and volatile organic compound (VOC) reactivity were measured in petrochemical plumes. Correspondingly, CH2O and ozone production was greatly enhanced in petrochemical plumes compared with plumes dominated by power plant and mobile source emissions. The photochemistry of several isolated petrochemical facility plumes was accurately modeled using three nonmethane hydrocarbons (NMHCs) (ethene (C2H4), propene (C3H6) (both anthropogenic), and isoprene (C5H8) (biogenic)) and was in accord with standard hydroxyl radical (OH)‐initiated chemistry. Measurement‐inferred facility emissions of ethene and propene were far larger than reported by inventories. Substantial direct CH2O emissions were not detected from petrochemical facilities. The rapid production of CH2O and ozone observed in a highly polluted plume (30+ parts per billion by volume (ppbv) CH2O and 200+ ppbv ozone) originating over Houston was well replicated by a model employing only two NMHCs, ethene and propene.
Thermal effects of saturating gravity waves in the atmosphere
Authors: Medvedev A. S. , Klaassen G. P.
Published: May 2003

Breaking/saturating gravity waves (GWs) not only exert drag on the mean flow due to their momentum deposition but also affect the background thermally because of the associated energy flux divergence. We present a rigorous derivation of terms describing the thermal effects of GWs on the mean flow, based on the corresponding energy cycle for wave/mean flow interactions. The combined effect of saturating GWs is to produce both differential heating and cooling by inducing a downward wave heat flux, and an irreversible conversion of wave energy into heat. The former effect can also be represented as thermal diffusion acting on the mean potential temperature gradient. This rigorous theory for the thermal exchange between waves and the mean flow can be closed once the mechanism for GW dissipation is parameterized. To illustrate the procedure, we employ our recent nonlinear theory of GW spectra to derive expressions for the wave‐induced heating rates. This yields a parameterization of the thermal effects of GWs, which is suitable for use in general circulation models and requires the source GW spectrum as the only tunable parameter. We present results of numerical calculations of wave heating terms for typical wind and temperature profiles as well as simulations with the full‐scale Canadian Middle Atmosphere Model (CMAM).
Mixing states of individual aerosol particles in spring Arctic troposphere during ASTAR 2000 campaign
Authors: Hara K. , Yamagata S. , Yamanouchi T. , Sato K. , Herber A. , Iwasaka Y. , Nagatani M. , Nakata H.
Published: May 2003

The present study mainly focuses on the mixing states of aerosol constituents and their vertical distribution in spring Arctic troposphere during the ASTAR 2000 campaign (T. Yamanouchi et al., Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) campaign: An overview and first results, submitted to Bulletin of the American Meteorological Society, 2002) (hereinafter referred to as Yamanouchi et al., submitted manuscript, 2002). Sulfate and soot were identified as major aerosol under both Arctic haze and background conditions, and sea‐salts are major only in lower troposphere (<3 km above sea level). Mineral/dusts and unknown species were obtained as minor constituents during the ASTAR 2000 campaign. Airborne aerosol measurements were carried out under the Arctic haze (23 March), and aerosol‐enriched (20 March and 12 April) conditions. The highest relative abundance of soot (∼94.7%) was observed in free troposphere on 23 March, when the heaviest Arctic haze condition during the ASTAR 2000 campaign (Yamanouchi et al., submitted manuscript, 2002) was transported directly from Russian industrial regions to the measuring area for several days. Moreover, whereas the external mixing of soot and sulfate dominated under the Arctic haze and aerosol enriched conditions, in the background conditions the internal mixing is dominant. On the other hand, most of aerosol particles containing sulfate had the external mixing states with soot and other aerosol constituents in the free troposphere under both the Arctic haze and background conditions. Sea‐salts are dominant only in the lower troposphere (<3 km asl), although a few sea‐salt particles were observed in the middle‐upper troposphere (3–7 km). Some sea‐salt particles were modified (Cl− depleted) in the lower troposphere (<3 km) during the ASTAR 2000 campaign.
Thirty years of in situ stratospheric aerosol size distribution measurements from Laramie, Wyoming (41°N), using balloon‐borne instruments
Authors: Deshler T. , Hervig M. E. , Hofmann D. J. , Rosen J. M. , Liley J. B.
Published: May 2003

Vertical profiles of size‐resolved aerosol concentrations above Laramie, Wyoming (41°N), have been measured for the past thirty years, 1971‐2001. During this period, two somewhat different optical particle counters have been used to measure particles with radii ≥0.15 μm, whereas the instrument to measure condensation nuclei (CN) has not changed significantly since the late 1970s. The two optical particle counters measure aerosols ≥0.15, 0.25 μm and aerosols ≥0.15–2.0 μm in twelve size classes. These measurements have concentration (N) uncertainties ∝ ±N−0.5, but with a minimum of ±10%. Sizing uncertainties are about ±10%. The impact of these uncertainties on size distribution fitting parameters and aerosol moments are approximately ±30% and ±40%. The long‐term record from these measurements indicates that volcanoes have controlled stratospheric aerosol abundance for 20 of the past 30 years. The present period, beginning in 1997, represents the longest volcanically quiescent period in the record. These and other measurements clearly show that stratospheric aerosol are now in a background state, a state rarely occurring in recent times, and that this background state is not significantly different than observations in 1979. Aerosol volumes and surface areas, inferred from size distributions fit to the measurements, are compared with SAGE II satellite estimates of surface area and volume. For volume the measurements are in agreement within measurement error throughout the record. For surface area there is good agreement for a volcanic aerosol laden stratosphere, but for background aerosol conditions the SAGE II estimates are about 40% less than the in situ measurements. Present aerosol surface areas are ∼1.0 (0.6) μm2cm−3in the 15–20 (20–25) km layer based on in situ measurements. The Laramie size distribution record is now available to the community over the internet.
The residence times of aircraft emissions in the stratosphere using a mean emission inventory and emissions along actual flight tracks
Authors: Forster Caroline , Stohl Andreas , James Paul , Thouret Valérie
Published: May 2003

Flight routes of commercial aircraft are adjusted to the actual meteorological situation in order to benefit from tail winds and avoid head winds and dangerous flight conditions. This study investigates whether these adjustments have an impact on the partitioning and the residence times of aircraft emissions in the stratosphere and troposphere. A Lagrangian dispersion model is used in combination with a mean emission inventory and emissions along actual flight tracks. Both inventories are established from Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) aircraft position data in the North Atlantic Flight Corridor (NAFC) over a 1‐year period. The results show that stratospheric emissions released in the NAFC are transported in a northeasterly direction towards polar regions on a timescale of a few days. The mean residence time of these emissions is about 23 days, which is shorter than documented in previous studies. The greatest fluxes from the stratosphere into the troposphere occur during the first 10 days and have their maxima over Europe and North Africa. About 62% and 67% of the emissions are directly deposited in the stratosphere in the mean emission inventory and in the inventory of the actual flight tracks, respectively. The deposition in the stratosphere was found to be sensitive to the definition of the tropopause height. However, the transport and partitioning of the emissions in the stratosphere and troposphere are only moderately affected if an inventory of the actual flight tracks is used instead of a mean emission inventory. Therefore, the systematic errors made in chemistry climate models, which use mean inventories, are small and can be tolerated for most applications.
Effects of nonsphericity on mineral dust modeling
Authors: Ginoux Paul
Published: May 2003

The dependency of nonsphericity on gravitational settling of mineral dust particles is parameterized for prolate ellipsoids and Reynolds number lower than 2. The settling speed is numerically solved from the momentum equation as a function of particle diameter and aspect ratio. The reduction of settling speed due to nonsphericity is included in the Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model to simulate dust size distribution for April 2001. Two numerical schemes for solving sedimentation are compared. For particles of diameter greater than 5 μm, the simulated size distribution is sensitive to the numerical sedimentation scheme. Changing the particle shape from spherical to nonspherical with λ = 2 makes little difference to the simulated surface concentration and size distribution except at the periphery of the dust sources. However, when very elongated particles (λ = 5) are simulated, the differences between nonspherical and spherical particles are significant. With limited in situ measurements reporting most frequent λ around 1.5, the overall effects on global modeling is rather negligible and the essential benefit is to relax the CFL condition of Eulerian settling schemes.
Reactivity of BrONO2 and HOBr on sulfuric acid solutions at low temperatures
Authors: Hanson D. R.
Published: May 2003

Uptake of BrONO2 onto bulk sulfuric acid solutions and submicron sulfuric acid aerosol particles was studied in laminar flow cylindrical reactors where a chemical ionization mass spectrometer was used to detect products and reactants. Results from measurements at low temperatures and for sulfuric acid content between 70 and 85 wt.% are presented. These measurements suggest that the reaction probability for BrONO2 on a given sulfuric acid solution does not depend strongly on temperature. The heterogeneous chemistry of HOBr, a product of the hydrolysis of BrONO2, was also studied on bulk sulfuric acid solutions (58–70 wt.%). Measurements of HOBr and HNO3 solubility and the reaction HOBr + HCl → BrCl + H2O are reported. Supplemented with previous measurements, a set of parameters to calculate the reaction probabilities appropriate to the stratosphere are deduced. These measurements confirm earlier assertions that the reaction can be a significant loss process for HCl when aerosol volume in the stratosphere is elevated.
Rapid uplift of nonmethane hydrocarbons in a cold front over central Europe
Authors: Purvis R. M. , Lewis A. C. , Carney R. A. , McQuaid J. B. , Arnold S. R. , Methven J. , Barjat H. , Dewey K. , Kent J. , Monks P. S. , Carpenter L. J. , Brough N. , Penkett S. A. , Reeves C. E.
Published: May 2003

The vertical distribution of 21 C2–C7 nonmethane hydrocarbons (NMHCs) has been determined in planetary boundary layer (PBL) and free tropospheric (FT) air over central Europe under a range of meteorological conditions. High‐frequency whole air sampling was conducted on board the U.K. Meteorological Office C‐130 Hercules aircraft during the European Export of Precursors and Ozone by Long‐Range Transport (EXPORT) experiment in August 2000. When vertical transport by large‐scale flow or convection was weak, the expected large concentration gradient between the PBL and FT was observed for all short and medium lifetime hydrocarbons (e.g., average iso‐butane, PBL 100 pptV, FT 6 pptV). During periods of strong convective activity associated with the passage of a cold front, a rapid uplift of reactive carbon from the boundary layer to the mid free troposphere was observed. Using changing ratios of hydrocarbons with different atmospheric lifetimes, a timescale for transport during this event was determined. Hydrocarbon lifetime measurements suggest that in certain regions of the system, it is convective transport embedded within the cold front rather than larger‐scale advection along the warm conveyor belt that is dominant in transporting ozone precursors into the free troposphere.
A modified formulation of fractional stratiform condensation rate in the NCAR Community Atmospheric Model (CAM2)
Authors: Zhang Minghua , Lin Wuyin , Bretherton Christopher S. , Hack James J. , Rasch Phillip J.
Published: May 2003

This paper describes a modified formulation of stratiform condensation rate associated with fractional cloudiness in the Community Atmospheric Model Version 2 (CAM2). It introduces an equation to link cloudiness change with the variation of total condensate. Together with a diagnostic cloud relationship that represents subgrid‐scale variability of relative humidity, a closed system is formed to calculate the fractional condensation rate. As a result, the new formulation eliminates the two closure assumptions in the Rasch and Kristjànsson [1998] prognostic cloud scheme. It also extends the Sundqvist [1978] scheme by including the influence of convective detrainment and advection of condensates on the fractional cloudiness. Comparison is made between the present formulation and the Rasch and Kristjànsson scheme by using data from the Atmospheric Radiation Measurement Program and through global model simulations with CAM2. It is shown that relative to the Rasch and Kristjànsson scheme, the new formulation produces less clouds and a slightly warmer troposphere, thus reducing the original cold bias in the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM). Even though the overall impact of the new formulation on the model climate is small, the modifications lead to more consistent treatments of fractional cloudiness change, condensation rate, and cloud water change in the model.
Sensitivity of hydrogen peroxide (H2O2) and formaldehyde (HCHO) preservation in snow to changing environmental conditions: Implications for ice core records
Authors: Hutterli Manuel A. , McConnell Joseph R. , Bales Roger C. , Stewart Richard W.
Published: May 2003

Sensitivity studies with physically based numerical air–snow–firn transfer models for formaldehyde (HCHO) and hydrogen peroxide (H2O2) show that even though nonlinear processes determine the preservation of HCHO and H2O2 in snow and firn, changes in atmospheric mixing ratios are linearly recorded in ice cores under otherwise constant environmental conditions. However, temperature, snowpack ventilation, and rate and timing of snow accumulation also affect the ice core records of reversibly deposited species and must be considered when inferring past atmospheric mixing ratios. The results of the sensitivity studies allow quantitative separation of these factors in ice core records. Past temperatures and accumulation rates are generally determined in ice cores and the preservation of HCHO and H2O2 is not highly sensitive to snowpack ventilation, leaving changes in seasonality of snow accumulation as the main source of uncertainty in a reconstruction of past atmospheric mixing ratios.
Optimal surface temperature reconstructions using terrestrial borehole data
Authors: Mann Michael E. , Rutherford Scott , Bradley Raymond S. , Hughes Malcolm K. , Keimig Frank T.
Published: May 2003

We derive an optimal Northern Hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries. The pattern of borehole ground surface temperature (GST) reconstructions displays prominent discrepancies with instrumental surface air temperature (SAT) estimates during the 20th century, suggesting the presence of a considerable amount of noise and/or bias in any underlying spatial SAT signal. The vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors. A sizable share of the variance in the first eigenvector appears to be associated with non‐SAT related bias in the borehole data. A weak but detectable SAT signal appears to be described by a combination of the first two eigenvectors. Exploiting this eigendecomposition, application of optimal signal estimation methods yields a hemispheric borehole SAT reconstruction that is largely consistent with instrumental data available in past centuries, and is indistinguishable in its major features from several published long‐term temperature estimates based on both climate proxy data and model simulations.
Evaluation of upper tropospheric water vapor in the NCAR Community Climate Model (CCM3) using modeled and observed HIRS radiances
Authors: Iacono Michael J. , Delamere Jennifer S. , Mlawer Eli J. , Clough Shepard A.
Published: May 2003

Upper tropospheric water vapor (UTWV) simulated by the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is evaluated by comparing modeled, clear‐sky, brightness temperatures (BTs) to those observed from space by the High‐Resolution Infrared Radiation Sounder (HIRS). The climate model was modified to utilize a highly accurate longwave radiation model (RRTM) and a separate radiance module, which contains physics consistent with RRTM, to calculate BTs in the National Oceanic and Atmospheric Administration (NOAA‐7) HIRS 6.7 μm water vapor channel (CH12) and the 14.2 μm temperature channel (CH04). The CCM3 simulations follow the Atmospheric Model Intercomparison Project (AMIP) protocol for the period 1982–1984 to provide a basis for evaluating the water vapor distribution over a wide range of atmospheric conditions. BT differences of 2 K or less in CH04 indicate that CH12 differences are primarily due to water vapor rather than cloud effects or temperature variations. Regionally, CCM3 exhibits considerable positive and negative differences of 5–10 K in CH12 that are apparent in both convective and dry subtropical areas. This suggests that significant moist and dry discrepancies in UTWV amount of 50% or more are present in CCM3. These biases are also shown to persist through several annual cycles and at shorter timescales, and they are only slightly influenced by the improved longwave radiation model, which suggests a dynamical cause. Comparison to HIRS radiances provides a considerably more effective and comprehensive means of globally evaluating general circulation model (GCM)‐simulated UTWV on various timescales than surface‐based water vapor measurements.
Effect of organics of low solubility on the growth rate of cloud droplets
Authors: Shantz Nicole C. , Leaitch W. Richard , Caffrey Peter F.
Published: May 2003

Organic aerosols represent an important fraction of the fine particle aerosol, yet little is known about the role that these particles play in the indirect effect of aerosols on climate. The growth rates of organic acid particles due to the condensation of water were measured in a cloud condensation nucleus chamber. Delays in the cloud activation of organic acid particles were observed relative to ammonium sulfate, (NH4)2SO4. The inclusion of particle dissolution with time according to its water solubility in a kinetic model of condensational growth of droplets was able to reasonably reproduce the observed delays, indicating that the delays in the growth of the organic acid particles were mainly due to their lower solubilities. Applying the results in an adiabatic simulation of cloud droplet nucleation, the number of cloud droplets nucleated on particles with solubility equivalent to adipic acid were reduced relative to those nucleated on (NH4)2SO4 by up to 85%. The relative solubility of organic species must be considered when simulating the indirect effect of organic aerosol particles.
Stratosphere–troposphere exchange in a changing climate simulated with the general circulation model MAECHAM4
Authors: Land C. , Feichter J.
Published: May 2003

Tracer simulations of 7Be and 10Be have been performed with the general circulation model MAECHAM4 for present and future climatic conditions in order to study possible trends of stratosphere–troposphere exchange (STE). These model simulations suggest an intensification of the mean meridional circulation above 100 hPa in a warmer climate. At extratropical tropopause levels, it increases poleward of 60° and between 30°S and the equator. This is attributed to shifts of the transport pattern. Consequently, large‐scale STE there increases with time, whereas it decreases between 60°S and 30°S and equatorward of 60°N. STE changes also occur due to changes in eddy activity. Our model results suggest that in a warmer climate cyclonic and blocking‐like variability is lower than today poleward of 30°N, and cyclonic activity is stronger at Southern Hemisphere midlatitudes. If the amount of air exchanged per cyclone or cutoff low between stratosphere and troposphere does not change in a warmer climate, our results suggest a decrease of STE poleward of 30°N and an increase at Southern Hemisphere midlatitudes due eddy activity. Extratropical changes in the distributions of 7Be and 10Be are dominated by changes in eddy activity. Due to their short tropospheric lifetime, they are more sensitive to the shorter timescale process. Eddy activity does not play any role in STE in the tropics. Large‐scale STE changes there do occur due to changes in the mean meridional circulation. In the troposphere, the zonal mean 10Be/7Be ratio increases in the Southern Hemisphere and decreases in the Northern Hemisphere as a consequence of STE and tropospheric transport changes. Thus, one has to be cautious in using this ratio as an exclusive measure for STE changes because changes in the tropospheric processes can also affect the climatological mean ratio.
Adjoint modeling for atmospheric pollution process sensitivity at regional scale
Authors: Menut Laurent
Published: May 2003

During the summer 1998, a strong pollution event was documented over Paris as part of the Etude et Simulation de la Qualité de l'air en Ile‐de‐France (ESQUIF) project (second intensive observation period (IOP2)). From 7 to 9 August 1998 the pollution event changes from a well‐marked ozone plume issued from Paris to a more general pollution over the whole Ile‐de‐France region. Using a three‐dimensional chemistry‐transport model and its adjoint part, the sensitivity of ozone, Ox, and NOx peaks to model parameters is investigated. For two locations, Paris and a suburban site, the influence of both meteorological and chemical model parameters on the simulated field concentrations is hourly quantified for each day. Processes leading to a urban polluted event are compared. It is shown that the pollutant concentrations are mainly driven by traffic and solvent surface emissions and meteorological parameters such as temperature. Since the adjoint approach is limited to infinitesimal model perturbation, some scenario simulations are carried out to evaluate the linearity of the impact of the most sensitive parameters within the uncertainty range. It is shown that the sensitivities determined from the adjoint approach can be extrapolated until their uncertainty ranges except for the wind speed.
Direct aerosol radiative forcing in the Yangtze delta region of China: Observation and model estimation
Authors: Xu Jin , Bergin M. H. , Greenwald R. , Russell P. B.
Published: May 2003

The Yangtze delta region of China is a key agricultural area that experiences relatively high aerosol loadings [Xu et al., 2002]. In order to characterize the aerosol radiative properties and estimate direct aerosol radiative forcing in this region, measurements of the multiwavelength aerosol optical depth, τλ, light scattering coefficient, σsp, and absorption coefficient, σap, as well as the downward photosynthetically active radiation (400–700 nm), DPAR, were conducted during November 1999 in Linan, China. The direct aerosol radiative forcing for photosynthetically active radiation (PAR) and total solar radiation (0.2–4.0 μm, TSR) at both the surface and top of atmosphere (TOA) are estimated based on the measurements using two radiative transfer models. The model estimates indicate that the mean cloud‐free instantaneous direct aerosol radiative forcing efficiency (for solar zenith angle < 70°) at the surface for PAR is −73.5 W m−2, which is in agreement with the value of −74.4 W m−2 derived directly from the measurements of DPAR and 500 nm aerosol optical depth (τ500). On the basis of the measured mean τ500 of 0.61, and the estimated cloud optical depth and cloud coverage of 5.0 and 50%, respectively, the 24‐hr mean direct aerosol radiative forcing at the surface for PAR is estimated to be approximately −11.2 W m−2. This suggests that the amount of PAR reaching the surface over the Yangtze delta region is reduced by ∼16% as a result of the direct radiative effect of aerosols. The model results also indicate that the cloud‐free 24‐hr average direct aerosol radiative forcing efficiency at the TOA for TSR is −30.4 W m−2. When the presence of clouds is considered, the mean direct aerosol radiative forcing at the TOA for TSR is estimated to be approximately −12.1 W m−2. This value is roughly an order of magnitude greater than the estimated global mean aerosol radiative forcing of −0.3 to −1.0 W m−2 suggested by the Intergovernmental Panel on Climate Change [1996]. Overall, this study indicates that aerosols have a substantial impact on the amount of radiation reaching the surface as well as the radiation balance at the TOA in the Yangtze delta region.
Implementation of slope irradiance in Mesoscale Model version 5 and its effect on temperature and wind fields during the breakup of a temperature inversion
Authors: Hauge G. , Hole L. R.
Published: May 2003

The atmospheric mesoscale model MM5 has been used at high horizontal resolution to simulate the breakup of a temperature inversion in complex topography. To improve the surface parameterizations during daytime, slope and orientation of the terrain have been taken into account in the calculation of short wave radiation at the surface. As the model resolution becomes higher, slope irradiance becomes increasingly important at high latitude. To evalute MM5 and slope irradiance's effect on the wind and temperature, a situation from 21 September 1994 is chosen. The situation is dominated by high pressure and no clouds, which gives the possibility of investigating the topography's effect on the radiation in greater detail. Compared to observations, results show improvement in both temperature and wind fields after the implementation of slope irradiances in MM5. The breakup period of the temperature inversion is also simulated more correctly. The RMS error is reduced by 35% for wind speed and 13% for temperature. This suggests that the influence of slope irradiance is larger for wind than for temperature in this situation.
Moisture plumes above thunderstorm anvils and their contributions to cross‐tropopause transport of water vapor in midlatitudes
Authors: Wang Pao K.
Published: May 2003

Water vapor in the lower stratosphere may play significant roles in the atmospheric radiative budget and atmospheric chemistry; hence it is important to understand its transport process. The possibility of water vapor transport from the troposphere to the stratosphere by deep convection is investigated using three‐dimensional, nonhydrostatic, quasi‐compressible simulations of a Midwest severe thunderstorm. The results show that the breaking of gravity waves at the cloud top can cause cloud water vapor to be injected into the stratosphere in the form of plumes above a thunderstorm anvil. Meteorological satellites and aircrafts have observed such plumes previously, but the source of water vapor and the injection mechanism were not identified. The present results reveal that there are two types of plumes, anvil sheet plumes and overshooting plumes, in this injection process and that the process is diabatic. A first‐order estimate of this plume transport of water vapor per day from the upper troposphere to the lower stratosphere was made assuming that all thunderstorms behave the same as the one simulated. Other trace chemicals may also be similarly transported by the same mechanism.
Tropopause folds and cross‐tropopause exchange: A global investigation based upon ECMWF analyses for the time period March 2000 to February 2001
Authors: Sprenger Michael , Croci Maspoli Mischa , Wernli Heini
Published: May 2003

A new methodology is proposed to identify folds of the dynamical tropopause (taken as the 2 potential vorticity (PV) units (pvu) isosurface) from global analysis data sets from the European Centre for Medium‐Range Weather Forecasts (ECMWF). It consists of a three‐dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses. The method is applied to a 1‐year period starting in March 2000. Seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics, with maximum frequencies of about 30%. Pronounced maxima are located in the subtropical bands that extend from 20°E to 120°E on both hemispheres during summer. Generally, subtropical folds are comparatively shallow. Deep folds occur most frequently in midlatitudes during winter (over eastern North America and the western North Atlantic), with maximum frequencies of about 1%. Detailed investigation of the relationship between individual folds and cross‐tropopause exchange events reveals that, on the average, individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics. However, due to the much higher frequency of subtropical folds, the percentage of exchange events that are associated with tropopause folds is larger near 20°–40° latitude (50–70%) than further poleward (20–30% during winter and 10–20% during summer). This indicates that tropopause folds are the key feature for cross‐tropopause exchange in the subtropics, whereas in the extratropics other tropopause structures are at least of equal importance.
Thermal variability of the tropical tropopause region derived from GPS/MET observations
Authors: Randel William J. , Wu Fei , Rivera Ríos Waleska
Published: May 2003

Structure and variability of temperatures in the tropical upper troposphere and lower stratosphere (∼10–30 km) are studied based on Global Positioning System Meteorology (GPS/MET) observations during April 1995 to February 1997. Comparisons with several hundred colocated radiosondes demonstrates the high accuracy of GPS/MET retrievals in the tropics. Mean structure and variability of the tropical cold point tropopause is examined, and much of the subseasonal variability in cold point temperature and height appears to be related to wave‐like fluctuations (such as gravity waves or Kelvin waves). Significant correlations are found between the GPS/MET temperatures and daily, gridded outgoing longwave radiation data (a proxy for tropical deep convection), providing independent confirmation of the GPS/MET temperature fluctuations. These correlations quantify the large‐scale tropical temperature response to transient convection, showing coherent wave‐like variations over ∼12–18 km which span a hemisphere in longitude. The GPS/MET data also show clear evidence of the stratospheric quasi‐biennial oscillation (QBO) in temperatures over altitudes ∼16–40 km.
A model study of stratospheric ozone in the troposphere and its contribution to tropospheric OH formation
Authors: Kentarchos A. S. , Roelofs G. J.
Published: May 2003

Results from an 11‐year simulation of the present‐day atmosphere with a coupled tropospheric chemistry‐climate model have been used to investigate the extratropical transport from the stratosphere to the troposphere, the transport and photochemical destruction of ozone from stratospheric origin in the troposphere, and the resulting contribution to tropospheric OH. The simulated stratosphere–troposphere exchange (STE) is based on the model calculated wind fields, and its seasonality and spatial distribution resemble results derived from other methods. The lifetime of stratospheric ozone in the troposphere is largely determined by transport between the extratropical tropopause where it enters the troposphere and the subtropical lower troposphere where its photochemical destruction rate maximizes. Comparison of the simulated ozone and O3s budgets suggests that ozone from stratospheric origin contributes about 15% to the average oxidation capacity in the Northern Hemisphere (NH), with regional contributions up to 40%. STE has a reverse effect on OH in the extratropical upper troposphere related to the influence of water vapor concentrations. The oxidation capacity of the troposphere may therefore be sensitive to atmospheric dynamic effects of climate change.
Quantifying uptake of HNO3 and H2O by alumina particles in Athena‐2 rocket plume
Authors: Danilin M. Y. , Popp P. J. , Herman R. L. , Ko M. K. W. , Ross M. N. , Kolb C. E. , Fahey D. W. , Avallone L. M. , Toohey D. W. , Ridley B. A. , Schmid O. , Wilson J. C. , Baumgardner D. G. , Friedl R. R. , Thompson T. L. , Reeves J. M.
Published: May 2003

The goal of this study is to quantify uptake of H2O and HNO3 by and estimate their residence time on alumina particles in Athena‐2 rocket plumes. This study uses in situ measurements made in the lower stratosphere with the NASA WB‐57F high‐altitude aircraft on 24 September 1999. Constraining the Atmospheric and Environmental Research, Inc. (AER), plume model with available measurements, we found that (1) H2O uptake coefficient for alumina particles is larger than 3 × 10−4, (2) HNO3 is produced via ClONO2 + HCl → Cl2 + HNO3 on alumina particles and resides on their surfaces for 5–52 min, and (3) alumina particles in the plume are covered by 100–200 monolayers of adsorbed H2O and 0.1–10 monolayers of HNO3 under lower stratospheric conditions. These values are uncertain by at least a factor of 2. We speculate that the H2O coverage remaining on alumina particles accelerates the ClONO2 + HCl → Cl2 + HNO3 reaction, thus leading to a larger than previously thought global ozone loss to solid‐fueled rocket emissions, especially if at least several percent of emitted alumina mass are in submicron particles.
An estimate of the impact of stratosphere‐to‐troposphere transport (STT) on the lower free tropospheric ozone over the Alps using 10Be and 7Be measurements
Authors: Zanis P. , Gerasopoulos E. , Priller A. , Schnabel C. , Stohl A. , Zerefos C. , Gäggeler H. W. , Tobler L. , Kubik P. W. , Kanter H. J. , Scheel H. E. , Luterbacher J. , Berger M.
Published: May 2003

In the framework of the European project STACCATO, combined measurements of 10Be and 7Be were carried out regularly during a full year at the high‐altitude stations, Jungfraujoch (JUN), Switzerland and Zugspitze (ZUG), Germany. Inspection of the variability of the ratio 10Be/7Be in relation to 10Be, 7Be, and relative humidity (RH) reveals that the ratio is independent from processes that have a clear effect on both radionuclides, such as wet scavenging. High ratio values are generally met under cyclonic or northerly advective conditions, which are the synoptic situations mostly related to stratosphere‐to‐troposphere transport (STT) events over central Europe, while the 10‐day back trajectories indicate a stratospheric source for the majority of the cases within the upper 10% quantile of 10Be/7Be ratios. The monthly 10Be/7Be ratios show a clear May and June peak at JUN and a much weaker seasonality at ZUG. A simple mixing model is used for an independent estimate of the strength of STT throughout the year based on the 7Be and 10Be measurements. In spite of the various uncertainties, the results indicate a seasonal cycle of stratospheric ozone percentage contribution with an early spring maximum (3–11%) and autumn minimum (1–2%) at ZUG, while at JUN, a primary maximum in May and June (6–18%), a secondary maximum in March (4–13%), and a minimum again in autumn (1–4%) are revealed. Although the simple method applied here provides an independent estimate for the impact of STT to the lower troposphere, it nevertheless shows relatively good agreement with Lagrangian model calculations, especially for ZUG.
Study of finely divided aqueous systems as an aid to understanding the surface chemistry of polar stratospheric clouds: Case of HCl/H2O and HNO3/HCl/H2O systems
Authors: Bogdan A. , Kulmala M. , MacKenzie A. R. , Laaksonen A.
Published: May 2003

The conditions under which a liquid (quasi‐liquid) or glassy overlayer could form around solid polar stratospheric cloud (PSC) particles have been studied with differential scanning calorimetry (DSC) on nanometer‐size binary HCl/H2O and ternary HNO3/HCl/H2O systems obtained on voluminous powder of fumed silica (SiO2). A HCl/H2O nanosystem of 32 wt % HCl froze heterogeneously, because of the presence of the silica surface, between −70°C and −85°C (203 and 188 K). This suggests that in the absence of any heterogeneous nuclei, a liquid or quasi‐liquid overlayer can exist around solid particles if HCl concentration in the surface layer can reach about 30%. Experiments also showed that the ternary nanosystem freezes more readily (between −52 and −93°C, 221 and 180 K) than the binary HCl/H2O system of similar HCl concentration, except for ternary solutions with excess nitric acid. This finding indicates that in the stratosphere, complex HNO3/HCl/H2O hydrates could be formed within a supercooled liquid overlayer of suitable composition if heterogeneous nuclei, for instance, meteoritic smoke silica particles, are available. A relatively warm glass‐transition temperature region (between −80 and −100°C) observed in one of the ternary samples suggests that in principle, a glassy overlayer could also form from a supercooled liquid overlayer of appropriate composition.
The impact of explicit cloud boundary information on ice cloud microphysical property retrievals from infrared radiances
Authors: Cooper Steven J. , L'Ecuyer Tristan S. , Stephens Graeme L.
Published: May 2003

Cirrus clouds have a profound impact on the radiation balance of the Earth–atmosphere system. Accurate representation of their radiative properties is critical to understanding climate and predicting climate change. This paper casts the split‐window cirrus cloud retrieval technique in an optimal estimation framework facilitating direct inclusion of explicit cloud boundary information from complementary sensors as well as providing a suite of diagnostic tools for evaluating the dominant sources of uncertainty in all retrieved quantities. Errors in retrieved microphysical properties are used to determine the resulting errors in the calculation of global‐scale radiative budgets. Uncertainties in optical depth and effective radius are found to diminish from ∼45% and ∼80%, respectively, in the absence of explicit cloud boundary information to ∼15% and ∼60% when accurate radar‐based or lidar‐based estimates are included. It is demonstrated that the improvements to cirrus cloud optical properties afforded by accurate cloud boundary information may lead to as much as a factor of 3 increase in the accuracy to which their impact on the Earth's radiative balance can be modeled. Colocated infrared radiances from the Moderate‐Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Earth Observing System (EOS) Aqua satellite and cloud radar observations from the CloudSat satellite will soon allow the retrieval presented here to be integrated into an operational retrieval of the vertical distribution of cloud properties on a global scale.
Bimodal radio frequency pulse distribution of intracloud‐lightning signals recorded by the FORTE satellite
Authors: Jacobson Abram R. , Light Tracy E. L.
Published: May 2003

The FORTE satellite's radio frequency receiver payload has made millions of recordings of lightning discharges. The most commonly occurring such radio emission arises from intracloud (IC) electrical breakdown and is usually recognizable by a pulse followed by a delayed echo from the ground reflection. We show that these IC pulses have two polar opposite types that together account for much of the pulse population. One type is a very bright pulse characterized by extended width (>2 μs), deep random fading within the pulse, and lack of prior pulses within a flash to which it belongs. The other type of IC pulse is two orders of magnitude less intense and is characterized by narrow width (<0.1 μs), a simple pulse shape evidencing no random fading, linear polarization, and occurrence in close association with other such pulses within the same flash. We develop the characteristics of these two pulse types by extensive statistical analysis of FORTE data. We relate the two pulse types to prior observations by other instruments.
Effect of stratosphere‐troposphere exchange on the future tropospheric ozone trend
Authors: Collins W. J. , Derwent R. G. , Garnier B. , Johnson C. E. , Sanderson M. G. , Stevenson D. S.
Published: May 2003

This paper investigates the impact of circulation changes in a changed climate on the exchange of ozone between the stratosphere and the troposphere. We have identified an increase in the net transport of ozone into the troposphere in the future climate of 37%, although a decreased ozone lifetime means that the overall tropospheric burden decreases. There are regions in the midlatitudes to high latitudes where surface ozone is predicted to increase in the spring. However, these increases are not significant. Significant ozone increases are predicted in regions of the upper troposphere. The general increase in the stratospheric contribution (O3s tracer) to tropospheric ozone in the climate changed scenario indicates that the stratosphere will play an even more significant role in the future.
Global and regional decreases in tropospheric oxidants from photochemical effects of aerosols
Authors: Martin Randall V. , Jacob Daniel J. , Yantosca Robert M. , Chin Mian , Ginoux Paul
Published: May 2003

We evaluate the sensitivity of tropospheric OH, O3, and O3 precursors to photochemical effects of aerosols not usually included in global models: (1) aerosol scattering and absorption of ultraviolet radiation and (2) reactive uptake of HO2, NO2, and NO3. Our approach is to couple a global 3‐D model of tropospheric chemistry (GEOS‐CHEM) with aerosol fields from a global 3‐D aerosol model (GOCART). Reactive uptake by aerosols is computed using reaction probabilities from a recent review (γHO2 = 0.2, γNO2 = 10−4, γNO3 = 10−3). Aerosols decrease the O3 → O(1D) photolysis frequency by 5–20% at the surface throughout the Northern Hemisphere (largely due to mineral dust) and by a factor of 2 in biomass burning regions (largely due to black carbon). Aerosol uptake of HO2 accounts for 10–40% of total HOx radical (≡ OH + peroxy) loss in the boundary layer over polluted continental regions (largely due to sulfate and organic carbon) and for more than 70% over tropical biomass burning regions (largely due to organic carbon). Uptake of NO2 and NO3 accounts for 10–20% of total HNO3 production over biomass burning regions and less elsewhere. Annual mean OH concentrations decrease by 9% globally and by 5–35% in the boundary layer over the Northern Hemisphere. Simulated CO increases by 5–15 ppbv in the remote Northern Hemisphere, improving agreement with observations. Simulated boundary layer O3 decreases by 15–45 ppbv over India during the biomass burning season in March and by 5–9 ppbv over northern Europe in August, again improving comparison with observations. We find that particulate matter controls would increase surface O3 over Europe and other industrial regions.