Nucleation Rate Of Droplets Research Articles

Evaluation of a new cloud droplet activation parameterization with in situ data from CRYSTAL‐FACE and CSTRIPE

The accuracy of the 2003 prognostic, physically based aerosol activation parameterization of A. Nenes and J. H. Seinfeld (NS) with modifications introduced by C. Fountoukis and A. Nenes in 2005 (modified NS) is evaluated against extensive microphysical data sets collected on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft for cumuliform and stratiform clouds of marine and continental origin. The cumuliform cloud data were collected during NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL‐FACE, Key West, Florida, July 2002), while the stratiform cloud data were gathered during Coastal Stratocumulus Imposed Perturbation Experiment (CSTRIPE, Monterey, California, July 2003). In situ data sets of aerosol size distribution, chemical composition, and updraft velocities are used as input for the NS parameterization, and the evaluation is carried out by comparing predicted cloud droplet number concentrations (CDNC) with observations. This is the first known study in which a prognostic cloud droplet activation parameterization has been evaluated against a wide range of observations. On average, predicted droplet concentration in adiabatic regions is within ∼20% of observations at the base of cumuliform clouds and ∼30% of observations at different altitudes throughout the stratiform clouds, all within experimental uncertainty. Furthermore, CDNC is well parameterized using either a single mean updraft velocity or by weighting droplet nucleation rates with a Gaussian probability density function of w. This study suggests that for nonprecipitating warm clouds of variable microphysics, aerosol composition, and size distribution the modified NS parameterization can accurately predict cloud droplet activation and can be successfully implemented for describing the aerosol activation process in global climate models.

Non-perturbative computation of the bubble nucleation rate in the cubic anisotropy model

At first order phase transitions the transition proceeds through droplet nucleation and growth. We discuss a lattice method for calculating the droplet nucleation rate, including the complete dynamical factors. The method is especially suitable for very strongly suppressed droplet nucleation, which is often the case in physically interesting transitions. We apply the method to the 3-dimensional cubic anisotropy model in a parameter range where the model has a radiatively induced strong first order phase transition, and compare the results with analytical approaches.

Energetics of small n-pentanol clusters from droplet nucleation rate data

We use nucleation theorems to extract the excess internal energy of small molecular clusters of n-pentanol from experimental droplet nucleation rates. Corrections to the theorems are derived, in order to take into account the nonideality of the vapor phase, but these have only a small effect on our results. Experimental datasets from different groups provide information about clusters of different sizes at a range of temperatures. The analysis shows that there are significant and intriguing deviations from the predictions of the capillarity approximation.

Critical cluster size and droplet nucleation rate from growth and decay simulations of Lennard-Jones clusters

We study a single cluster of Lennard-Jones atoms using a novel and physically transparent Monte Carlo simulation technique. We compute the canonical ensemble averages of the grand canonical growth and decay probabilities of the cluster, and identify the critical cluster, the size for which the growth and decay probabilities are equal. The size and internal energy of the critical cluster, for different values of the temperature and chemical potential, are used together with the nucleation theorems to predict the behavior of the nucleation rate as a function of these parameters. Our results agree with those found in the literature, and roughly correspond to the predictions of classical theory. In contrast to most other simulation studies, we are able to concentrate on the properties of the clusters which are most important to the process of nucleation, namely those around the critical size. This makes our simulations computationally more efficient.

Critical clusters and droplet nucleation rates using Monte Carlo simulation and the second nucleation theorem

Critical clusters and droplet nucleation rates using Monte Carlo simulation and the second nucleation theorem

Thermal nucleation and cavitation in helium-3 fluids

We have investigated droplet nucleation and bubble cavitation in the quantum fluid helium-3 based on a nonlocal density-functional approach. A marked effect of droplet (or bubble) curvature on the rate of droplet nucleation or cavitation has been found. Without considering this curvature effect (as in the classical theory of nucleation) the droplet nucleation rate for helium-3 could be underestimated (i.e., near 1 K) or overestimated (i.e., near 2.5 K) by orders of magnitude, respectively; for bubble cavitation, the rate could be underestimated by more than twenty orders of magnitude (near 1 K).

The nucleation of water vapor in the absence of particulate matter and ions

The nucleation rate of droplets from water vapor in a helium atmosphere was measured with an expansion cloud chamber as a function of temperature, supersaturation, and sensitive time. In addition to homogeneous nucleation, a form of heterogeneous nucleation was observed to occur above the ion limit, presumably upon neutral centers whose concentration is low and seemingly dependent upon the initial partial pressure of water vapor present. The semiphenomenological classical theory was modified to take into account the change in the free energy of formation of the critical cluster brought about by the presence of a single foreign molecule. The temperature dependence of these data closely confirms that found by a number of earlier investigators. The form of heterogeneous nucleation observed here makes the disparity in the temperature dependence of the nucleation rate of previous work understandable. As higher and higher nucleation rates are sampled, the centers upon which heterogeneous nucleation occurs are depleted and homogeneous nucleation becomes dominant. It was definitely established that the nucleation rate of water vapor is higher in an argon atmosphere than in a helium atmosphere. The latter result seems to indicate that the noncondensable gas plays a role in the clustering process and may possibly hydrate under appropriate circumstances.