Showing papers on "Microphysics published in 1992"

The schumann resonance: a global tropical thermometer.

Abstract: The Schumann resonance, a global electromagnetic phenomenon, is shown to be a sensitive measure of temperature fluctuations in the tropical atmosphere. The link between Schumann resonance and temperature is lightning flash rate, which increases nonlinearly with temperature in the interaction between deep convection and ice microphysics.

3D mesoscale numerical studies of cirrus and stratus clouds by their time and space evolution

Abstract: Recently available algorithms describing (parameterizing) the cloud microphysics are combined and implemented in the three dimensional non-hydrostatic mesoscale model GESIMA (GEesthachter SImulationsModell der Atmosphare). All three water phases are taken into account. Clouds are represented by two groups of prognostic equations describing the changes in cloud mass and particle number concentration. The radiation scheme uses the mass and the particle number concentration to compute the optical cloud properties

Error Estimates for Retrieval of Cloud-Top Pressure Using Absorption in the A Band of Oxygen

Abstract: This paper examines the feasibility of remotely sensing cloud-top pressure from observations of reflected sunlight at frequencies in the A band of absorption of oxygen (13 070 cm−1, 765 nm). The data are assumed to consist of several channels within the A band and one reference channel outside the A band. The principal difficulty is that the reflected radiance is attenuated by absorption by O2 not only in the atmosphere above the cloud, but also along photon trajectories within the cloud. The extent of the extra absorption is unknown a priori because the microphysics structure of the cloud is unknown. This paper investigates the possibility of simultaneously retrieving both cloud-top pressure and parameters that determine the distribution of photon pathlength within the cloud. Estimates are derived for the errors in the retrieved parameters induced by instrumental noise and uncertainties in the profiles of temperature and aerosol extinction. The study investigates the sensitivity of the errors to...

Cirrus microphysics and radiative transfer : cloud field study on 28 October 1986

Abstract: The radiative properties of cirrus clouds present one of the unresolved problems in weather and climate research. Uncertainties in ice particle amount and size and, also, the general inability to model the single scattering properties of their usually complex particle shapes, prevent accurate model predictions. For an improved understanding of cirrus radiative effects, field experiments, as those of the Cirrus IFO of FIRE, are necessary. Simultaneous measurements of radiative fluxes and cirrus microphysics at multiple cirrus cloud altitudes allows the pitting of calculated versus measured vertical flux profiles; with the potential to judge current cirrus cloud modeling. Most of the problems in this study are linked to the inhomogeneity of the cloud field. Thus, only studies on more homogeneous cirrus cloud cases promises a possibility to improve current cirrus parameterizations. Still, the current inability to detect small ice particles will remain as a considerable handicap.

Simulation of retrieval of the base height and thickness of cirrus clouds from satellite data

Abstract: On the basis of the theory of scattering and radiative transfer in atmospheres with cirrus clouds, a physical retrieval method for the base height and thickness of cirrus clouds is developed in this simulation study. A complicated nonlinear equation is derived and solved, the radiative properties of cirrus clouds are parameterized, and the transmittance profile in atmospheres with cirrus clouds is developed. Two numerical techniques, Muller iteration and a Monte Carlo method, are used. Retrieval results are presented for various atmospheric models and ice-water contents. Detailed analyses of observation errors and theoretical model errors, especially for the cloud microphysics, are carried out. Our analyses of the sensitivity of the method to ice-water content include vertical homogeneities and inhomogeneities. The preliminary study shows that the method developed here is feasible and that the VAS satellite’s IR channels 7 (12-μm H2O window) and 8 (11-μm atmospheric window) are important and useful for passive remote sensing of atmospheres with cirrus clouds from satellites.

Analytic functions for modeling vertical profiles of extinction in and beneath very low stratus clouds

Abstract: A theoretically based microphysics model developed by the authors was used to simulate a large number of vertical drop size distribution profiles in very low stratus clouds and subcloud regions. These drop size distributions were used with Mie calculations to simulate vertical profiles of extinction coefficients at wavelengths of 0.55, 1.06, 4.0, and 10.6 micrometers . These profiles were then fit with smooth analytic functions in order to develop a model that can be used quickly and easily to simulate gross behavior of vertical profiles of extinction coefficients. Values of parameters that appear in two selected analytic functions were determined from fitting simulated data and are presented for a few cases in this work. It is proposed that one of these analytic functions with associated parameter values be considered for possible worldwide application in modeling very low stratus clouds.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Numerical simulation of precipitation scavenging and comparison with observation of prescribed forest fires

Abstract: The primary mechanism by which aerosol particles are removed from the atmosphere is precipitation scavenging. Because of our interest in understanding the processes by which aerosol particles are scavenging as well as basic cloud dynamic and microphysical interactions, we have developed a numerical model that simulates these processes. This model was developed as part of our study of the global climatic effects of smoke from a large number of massive fires. One of the ways that we have attempted to validate the accuracy of the model is to perform simulations of prescribed forest burns where there is information on the source characteristics and fire morphology, and observations of the cloud dynamics and microphysics. In this paper we describe simulations of the Hardiman township and Batterby township Ontario, Canada, prescribed fires. Our numerical model, OCTET, is a system of eight progressively more complex models designed to simulate plumes, clouds, and mesoscale system. OCTET has a three-dimensional, nonhydrostatic, compressible dynamic framework originally based on a convective storm model.

Cloud CCN feedback

Abstract: Cloud microphysics affects cloud albedo precipitation efficiency and the extent of cloud feedback in response to global warming. Compared to other cloud parameters, microphysics is unique in its large range of variability and the fact that much of the variability is anthropogenic. Probably the most important determinant of cloud microphysics is the spectra of cloud condensation nuclei (CCN) which display considerable variability and have a large anthropogenic component. When analyzed in combination three field observation projects display the interrelationship between CCN and cloud microphysics. CCN were measured with the Desert Research Institute (DRI) instantaneous CCN spectrometer. Cloud microphysical measurements were obtained with the National Center for Atmospheric Research Lockheed Electra. Since CCN and cloud microphysics each affect the other a positive feedback mechanism can result.