Constantin Andronache

An empirical parameterization of heterogeneous ice nucleation for multiple chemical species of aerosol

A novel, flexible framework is proposed for parameterizing the heterogeneous nucleation of ice within clouds. It has empirically derived dependencies on the chemistry and surface area of multiple species of ice nucleus (IN) aerosols. Effects from variability in mean size, spectral width, and mass loading of aerosols are represented via their influences on surface area. The parameterization is intended for application in largescale atmospheric and cloud models that can predict 1) the supersaturation of water vapor, which requires a representation of vertical velocity on the cloud scale, and 2) concentrations of a variety of insoluble aerosol species. Observational data constraining the parameterization are principally from coincident field studies of IN activity and insoluble aerosol in the troposphere. The continuous flow diffusion chamber (CFDC) was deployed. Aerosol species are grouped by the parameterization into three basic types: dust and metallic compounds, inorganic black carbon, and insoluble organic aerosols. Further field observations inform the partitioning of measured IN concentrations among these basic groups of aerosol. The scarcity of heterogeneous nucleation, observed at humidities well below water saturation for warm subzero temperatures, is represented. Conventional and inside-out contact nucleation by IN is treated with a constant shift of their freezing temperatures. The empirical parameterization is described and compared with available field and laboratory observations and other schemes. Alternative schemes differ by up to five orders of magnitude in their freezing fractions (30°C). New knowledge from future observational advances may be easily assimilated into the scheme’s framework. The essence of this versatile framework is the use of data concerning atmospheric IN sampled directly from the troposphere.

Improvements to an Empirical Parameterization of Heterogeneous Ice Nucleation and Its Comparison with Observations

AbstractA framework for an empirical parameterization (EP) of heterogeneous nucleation of ice crystals by multiple species of aerosol material in clouds was proposed in a 2008 paper by the authors. The present paper reports improvements to specification of a few of its empirical parameters. These include temperatures for onset of freezing, baseline surface areas of aerosol observed in field campaigns over Colorado, and new parameters for properties of black carbon, such as surface hydrophilicity and organic coatings. The EP’s third group of ice nucleus (IN) aerosols is redefined as that of primary biological aerosol particles (PBAPs), replacing insoluble organic aerosols. A fourth group of IN is introduced—namely, soluble organic aerosols.The new EP predicts IN concentrations that agree well with aircraft data from selected traverses of shallow wave clouds observed in five flights (1, 3, 4, 6, and 12) of the 2007 Ice in Clouds Experiment–Layer Clouds (ICE-L). Selected traverses were confined to temperatur...

Vertical distribution of isoprene in the lower boundary layer of the rural and urban southern United States

An analysis is presented of vertical profiles of isoprene concentration and meteorological parameters measured in the boundary layer (BL) during the daylight hours at a rural site in Alabama and an urban site in Atlanta, Georgia, during the summer of 1990, as part of the Southern Oxidants Study. Of the 37 isoprene profiles recorded at the sites, 16 exhibited complex vertical structure with local maxima within the BL. This complex vertical structure appears to arise from a variety of turbulent processes fostered by horizontal inhomogeneities in the surface emissions of isoprene and by the transient appearance of layers of strong wind shear and/or vertical stability within the BL. A statistical analysis of the data suggests that the complex features observed in the individual profiles are stochastic in nature and tend to cancel out upon averaging over all profiles. Nevertheless, these complex structures can confound attempts to infer the BL abundance of a short-lived hydrocarbon like isoprene from a set of measurements at a single height. Our calculations suggest that measurements made at a height of 40–100 m above the surface will yield the most reliable measure of average BL concentrations of reactive hydrocarbons.

Gas‐to‐particle conversion of tropospheric sulfur as estimated from observations in the western North Pacific during PEM‐West B

Aircraft observations during the Pacific Exploratory Mission in the western Pacific Ocean, phase B (PEM-West B), taken in February–March 1994, have been used to constrain a numerical model that calculates local concentrations of gaseous H2SO4 rates of homogeneous nucleation, and concentrations of newly formed, nanometer-sized particles. The data was selected from 13 flights over the western Pacific Ocean that covered an altitude range from the boundary layer (BL) to the upper troposphere (UT) and latitudes from 10°S to 60°N. The largest nucleation rates were calculated for the data from the flights over the temperate latitudes (λ>30°N). Within these latitudes, homogeneous nucleation rates averaged about 1–100 particles cm−3 s−1. Significantly smaller nucleation rates were calculated for the tropical (λ<20°N) and subtropical (20°N<λ<30°N) regions. In the tropics, average nucleation rates in excess of 10 particles cm−3 s−1 were limited to the UT. In the subtropics, large average nucleation rates in excess of 1 particle cm−3 s−1 were obtained in the BL and in the UT, and average rates of about 10−1 particles cm−3 s−1 were obtained for the rest of the troposphere. The relatively large nucleation rates calculated for the temperate latitudes could be largely attributed to the cold temperatures encountered in this region during the PEM-West B flights. For the data from the tropical and subtropical flights, little or no homogeneous nucleation was calculated for the average conditions encountered in the BL and midtroposphere (MT). Instead, significant nucleation was limited either to the UT or to several small-scale events. These enhanced nucleation events were generally characterized by spikes in relative humidity and low aerosol surface density. However, the strongest nucleation events, with homogeneous nucleation rates of about 10 particles cm−3 s−1, were associated with high concentrations of SO2, most likely as a result of pollution from the Asian continent. Our results imply that in regions in which homogeneous nucleation is dominated by small-scale fluctuations, approaches that attempt to infer nucleation rates using average or typical conditions will grossly underestimate the actual average rate of nucleation.

Atmospheric sulfur and deep convective clouds in tropical Pacific: A model study

A high-resolution limited area nonhydrostatic model was used to simulate sulfate-cloud interactions during the convective activity in a case study from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment, December 20–25, 1992. The model includes a new detailed sulfate-cloud microphysics scheme designed to estimate the effects of sulfate on cloud microphysics and radiative properties and the effects of deep convection on the transport and redistribution of aerosol. The data for SO2 and SO4(2−) species were taken from the Pacific Exploratory Mission West B observations during February-March 1994. Results show that a change in sulfate loading from the minimum to the maximum observed value scenarios (i.e., from about 0.01 to 1 μg m−3) causes a significant decrease of the effective radius of cloud droplets (changes up to 2 μm on average) and an increase of the diagnostic number concentration of cloud droplets (typical changes about 5–20 cm−3). The change in the average net shortwave (SW) radiation flux above the clouds was estimated to be on average −1.5 W m−2, with significant spatial and temporal variations. The horizontal average of the changes in the net SW radiation fluxes above clouds has a diurnal cycle, reaching typical values approximately −3 W m−2. The changes in the average net longwave radiation flux above the clouds were negligible, but they showed significant variations, typically between −10 W m−2 and 10 W m−2 near the surface. These variations were associated mainly with the changes in the distribution of cloud water, which showed typical relative changes of cloud water path of about 10–20%. Other notable changes induced by the increase of aerosol were the variations in air temperature of the order of 1°C. The case study presented here suggests that characteristics of convective clouds in tropical areas are sensitive to atmospheric sulfate loading, particularly during enhanced sulfate episodes.

Interactions between sulfur and soot emissions from aircraft and their role in contrail formation: 1. Nucleation

A numerical model of the time evolution of subsonic aircraft exhaust is used to evaluate the possible activation of soot particles by collisions with SO2 and H2SO4 gas molecules and Brownian coagulation with H2SO4/H2O aerosol formed by homogeneous nucleation. The soluble mass fraction accumulated on soot by the three processes is estimated for emission indices of sulfur from 0.001 to 3 g kg−1. The calculations indicate that the soluble mass fraction of sulfate added to soot particles (assumed to be totally hydrophobic at the point of exhaust) can be large enough to form activated particles within the exhaust plumes of aircraft operating on fuels with typical sulfur contents. However, for emissions from aircraft operating on extremely low sulfur fuels, the soluble material added to soot particles is not sufficient to activate them within the time frame observed for contrail formation. This result, coupled with the Busen and Schumann [1995] observations of contrail formation from an aircraft using 0.004 g S kg−1 fuel, suggests that heterogeneous interactions between soot and sulfur within the exhaust plume are not sufficient to explain the presence of activated particles and contrails in the wakes of high altitude aircraft if the emitted sulfur is in the form of SO2 only. It is probable that soot particles already have enough soluble material when emitted from the engine exhaust, or/and a higher conversion of sulfur into H2SO4 enable them to act as cloud condensation nuclei (CCN) for contrails.

PRINCIPAL COMPONENT ANALYSIS OF SEA SURFACE TEMPERATURE IN THE NORTH ATLANTIC OCEAN

The framework of principal component analysis (PCA) based on singular value decomposition (SVD) is applied to the monthly sea surface temperature (SST) observations in the North Atlantic Ocean for the time interval 1856–2008. Multiyear time series of SST for each month are used to investigate the statistical relationship between SST variations from the 12 months. To obtain approximate stationary conditions, the trend and a multidecadal oscillation are removed from the data. The remaining SST residuals exhibit remarkable correlation between successive months, due largely to persistence. PCA demonstrates the dimension reduction of the data sets and provides a robust way of analyzing multivariate observations describing the climate system.

The effects of atmospheric sulfur on the radiative properties of convective clouds: a limited area modeling study

Abstract. Convective clouds in tropical areas can be sensitive to the atmospheric sulfate loading, particu- larly during enhanced sulfate episodes. This assertion is supported by simulations with a high resolution lim- ited area non-hydrostatic model (LAN) employing a detailed sulfate-cloud microphysics scheme, applied to estimate the effects of sulfate on convective clouds in a case study from the Tropical Ocean Global Atmo- sphere Coupled Ocean Atmosphere Response Experi- ment (TOGA COARE). Results show that a change in sulfate loading for scenarios using the minimum to the maximum observed values produces a change in the average net flux of shortwave radiation above clouds. This time-average change was estimated between -1.1 and-0.3 Wm -2 over the integration domain. Introduction In addition to the direct atmospheric radiative forc- ing [Charlson et al., 1992], sulfate aerosols interact with clouds, primarly by providing cloud condensation nuclei (CCN). An increase of sulfate in the atmosphere pro-

The Potential of Econophysics for the Study of Economic Processes

What will be the challenges and opportunities for physicists and economists to work together in the field of social sciences and economics in the years to come? An attempt to define what is the meaning of Econophysics, a brief historical background, some significant achievements and perspectives, together with the specific method used in physics to analyze economic data and economic processes and finally a short review of major results and new domains in refereed literature are the principal themes or the major content of this paper, which remains nothing else but a modest contribution for starting a debate about the outstanding potential of Econophysics.

Chapter 5 – Characterization of Mixed-Phase Clouds: Contributions From the Field Campaigns and Ground Based Networks

Abstract Clouds and their associated microphysical processes regulate the atmospheric radiative transfer and the hydrological cycle. Mixed-phase clouds are an important component of the Earth cloud system, and their radiative effects are dependent on water phase partitioning. These clouds present particular challenges for observations and modeling, and their accurate representation in numerical models is essential for weather and climate simulations. The physical properties of mixed-phase clouds are derived mainly from aircraft observations, ground-based monitoring networks such as Atmospheric Radiation Measurement (ARM) Program and Cloudnet, and from satellites equipped with remote sensing instruments. This chapter presents a perspective on the main field experiments and ground-based networks during the last decades that resulted in improved characterization of mixed-phase clouds.