Petr Chylek Professor of Physics and Atmospheric Science Diploma (1967), Charles University, Prague Ph.D. (1970), University of California, Riverside   Member of the Americal Meteorological Society, American Geophysical Union, Canadian Meteorological and Oceanographic Society, Fellow of the Optical Society of America Atmospheric Science Program Departments of Physics and Oceanography Dalhousie University Halifax, Nova Scotia, Canada B3H-3J5 e-mail: chylek@lanl.gov Office Phone: (902) 494-2337 FAX: (902) 494-5191

My research interests Atmospheric Radiation Atmospheric Aerosols Cloud Physics Ice Core Analysis Paleoclimate Climate Diagnostic Global Change

My research group Petr Chylek I Wayan Sudiarta (Ph. D. student) Xiaobo Chen (Ph. D. student) Dr. Glen Lesins (Research Associate) Dr. W. Kim (Postdoctoral Fellow) Regina Mass (Lab Technician) Nancy Ogden (Lab Technician)

Current Research Projects

Global Change

A common view on the current climate change (global warming) is that it is a result of fossil fuel burning and the following increase in atmospheric concentration of carbon dioxide. In reality there are several factors that produce the current climate change. Some of the most important are:

• natural climate variability
• variability of the incoming solar radiation
• increrase in atmospheric concentration of carbon dioxide
• increase in atmospheric concentration of other greenhouse gases, especially methane

The goal of our research is to understand the relative contributions of the above listed factors to the currently observed global warming. For this purpose we are analyzing existing climate and paleoclimate data, analyzing outputs of general circulation models and creating new approximations to for the various physical processes involved in climate system.To bring together experts holding different views on the current global warming an to faciliate an intense discussion of the related scince, we are organizing The First International Conference on Global Warming and The Next Ice Age, sponsorod by the American Meteorological Society and by the Canadian Meteorological and Oceanographic Society, to take place in Halifax in August 2001.

Atmospheric Aerosols

Atmospheric aerosols (airborne particulate matter) play an important role in atmospheric energy balance and climate change. Aerosols also affect biogeochemical cycles and human health. Man-made aerosols include sulfates, nitrates, black carbon, products of biomass burning, and soil dust (produced by agricultural activities). Main types of natural aerosols are sea salt, soil dust, aerosols produced by volcanos and forest fires, and biogenic sulfates and organic aerosols. Aerosols affect climate through their direct interaction with solar and terrestrial radiation (direct aerosol effect) and through their effect on the optical properties and life cycle of clouds (indirect aerosol effect). Atmospheric aerosols can significantly modify the predicted warming of greenhouse gases. We are investigating the growth of aerosols (sulfates, nitrates, sea salt, mineral dust and black carbon) with relative humidity, their interaction with atmospheric radiation, and their effect on clouds and climate. Our work also include the parameterization of aerosol optical properties as functions of relative humidity for use in climate models.

Clouds

Clouds reflect a considerable portion of incoming solar radiation back to space and they modify outgoing infrared radiation. The interplay between atmospheric radiation and dynamics, cloud microphysics, aerosols, and thermodynamics is not fully understood. In many cases, predicted climate changes (connected to increasing concentration of carbon dioxide and other greenhouse gases) are dependent on the cloud parameterization used in a particular general circulation model. Our current research concerns the effect of atmospheric aerosols on cloudiness and cloud optical properties, and improvement of cloud parameterizations in radiation codes used in climate models. We are also investigating the effect of black carbon on the absorption of solar radiation by clouds.

Laboratory and Field Measurements

In recent years we have seen tremendous progress in computer-based modeling of various atmospheric processes. Laboratory and field measurements are needed to provide suitable checks of our modeling abilities. The discrepancy between the measured and calculated absorption of solar radiation in cloudy atmospheres demonstrates the need of a balanced approach to atmospheric research that includes modeling and measurements. In our laboratory we are currently performing the most accurate measurements of the refractive indices of water, supercooled water, ice, sulfates, and nitrates. Our graduate students have participated in several international field measurement programs like NARE (North Atlantic Regional Experiment), RACE (Radiation, Aerosols and Cloud Experiment) and FIRE.

Ice Core Analysis

Ice core contains a wealth of information concerning past climate. We have developed a method for determining black carbon (soot) concentrations in ice core samples and we were able to detect large forest fires that occured up to about 2000 years ago. We also observed a large increase in biosphere burning (recorded in Antarctic ice core samples) a few thousand years after the end of the last ice age. Our current investigation is directed towards recent changes (last 200 years) in black carbon deposition rates in polar regions, attributed possibly to anthropogenic activities.

Light Scattering and Radiative Transfer

We are using several computational techniques and approximations to calculate the scattering and absorption of radiation by nonspherical and composite atmospheric particles. Ice crystals and mineral dust aerosols are examples of nonspherical particles in the atmosphere. Hailstones, melting snow, and mineral dust or black carbon within sulfate or cloud droplets are common composite particles. The scattering and absorption characteristics of these particles are needed for remote sensing and for climate forcing calculations. Monte Carlo and other radiative transfer techniques are used to determine aerosol climate forcing, and the effect of clouds and aerosols on surface UV fluxes. We are trying to understand interactions between solar and terrestrial radiation, and clouds, aerosols, and climate. The tools used in our research include laboratory and field measurements, computational modeling, and theoretical analysis.

Recently Supervised Ph. D. Thesis

• S. Dobbie (Ph. D., 1999): Radiative Characteristict of Aerosols and Clouds.
• J. Wong (Ph. D., 1998): Radiative Impact of Atmospheric Aerosols and Clouds.
• L. Kou (Ph. D., 1997): Black Carbon: Atmospheric Measurements and Radiative Effects.
• J. Li (Ph. D., 1995): Radiative Transfer in Clouds with Internal Inhomogeneity.

Recently Supervised M. Sc. Thesis

• B. Winter (M. Sc., 1995): Light Scattering by a Sea Salt Aerosol Layer.
• S. Gosse (M. Sc., 1994): Imaginary Part of refractive Index of Ice, Ammonium Sulfate and Sulfuric Acid in the 1.4 to 7.8 micron Range.
• S. Dobbie (M. Sc., 1994): Solar Radiative Transfer in Cirrus Clouds.

Recent Invited Presentations

• Balck Carbon and Absorption of Solar Radiation by Clouds and Aerosols, Seminar, Desert Research Institute, University of Nevada, Reno, April, 1997.
• Absorption of Solar Radiation by Water Vapor Dimers, Seminar at the National Center of Atmospheric Research, Boulder, May 1997.
• Black Carbon in the Atmosphere, Invited presentation at the AGU Spring Meeting, Baltimore, June 1997.
• Black Carbon, Water Vapor Dimers and Absorption of Solar Radoation in the Atmosphere, Seminar, Los Alamos National Laboratory, Los Alamos, NM.
• Possible Causes of Atmospheric Excess Absorption, Invited presentation at the Gordon Research Conference on Solar Radiation and Climate, Plymouth, NH, June 1998.
• Heterogeneous Particles and Effective Medium Approximations, Invited presentation at the Conference on Light Scattering by Nonspherical Particles: Theory, Measurements and Applications, Goddard Institute for Space Studies, New York, Oct. 1998.
• Ice Cores and Mineral Dust Aerosol, Invited presentation at the International Workshop on Mineral Dust, Boulder, June 8-10, 1999.
• Global Warming and the Next Ice Age, Seminar, Environmental Research Laboratory, NOAA, Boulder, January 2000.
• Memorial Lecture in Honor of Prof. Hendrick Van deHulst, Fifth International Conference of Light Scattering by Nonspherical Particles, 28 August - 1 September, 2000, Halifax, Nova Scotia, Canada.
• North Atlantic Oscillations, Global Warming and The Greenland Ice Sheet, Seminar, Air Resources Laboratory, NOAA, Boulder, October 2000.

Recent Publications (1995-2000)

2000

• P. Chylek, G. Lesins and U. Lohmann, Enhancement of dust source area during past glacial periods due to changes in the Hadley circulation, J. Geophys. Res., 2000, in press.
• S. Dobbie, J. Li, R. Harvey and P. Chylek, Sea salt optical property parameterization and GCM forcing at solar wavelengths, Atmos. Res.,2000, in press.
• J. Li, S. Dobbie and P. Chylek, Parameterization of the optical properties and growth of sulfate aerosol, J. Atmos. Sci., 2000, in press.
• I.W. Sudiarta and P. Chylek, Absorption and scattering cross sections of spherical particles in absorbing medium, J. Opt. Soc. Am.,2000, in press.
• P. Chylek, G. Jennings and R. Pinnick, Soot, In: Encyclopedia of Atmospheric Science, Academic, 2000, in press.
• I.W. Sudiarta and P. Chylek, Mie scattering efficiency of a large spherical particle embedded in an absorbing medium J. Opt. Soc. Am.,2000, in press.
• W. Geldart and P. Chylek, Absorption of solar raiation by charged water droplets J. Quant. Chem. Rad. Trans., 2000, in press.
• P. Chylek, G. Videen, W. Geldart, S. Dobbie, and W. Tso, Effective Medium Approximation for Heterogeneous Particles, In Light Scattering by Nonspherical Particles: Theory, Measurements, and Geophysical Applications, 273-308, M. Mishchenko, Editor, Academic, 2000.

  1999

• P. Chylek, Q. Fu, W. Tso and W. Geldart, Contribution of water vapor dimers to clear sky absorption of solar radiation, Tellus 51A, 304-313, 1999.
• P. Chylek, L. Kou, B. Johnson, F. Boudala and G. Lesins, Black carbon concentrations in precipitation and near surface air in and near Halifax, Nova Scotia, Atmos. Environ. 33, 2269-2277, 1999.
• J. S. Dobbie, J. Li and P. Chylek, Two and Four Stream Optical Properties for Water Clouds and Solar Wavelengths J. Geophys. Res., 410 2067-2079, 1999.

  1998

• O. Boucher, S. E. Schwartz, T. P. Ackerman, B. Bergstrom, B. Bonnel, P. Chylek, A. Dahlback, Y. Fouquart, Q. Fu, R. Halthorne, T. Iversen, J. Haywood, S. Kato, S. Kinne, A. Kirkevag, K. Knapp, A. Lacis, I. Laszlo, S. Nemesure, V. Ramaswamy, D. Roberts, P. Russell, M. Schlesinger, G. Stephens, R. Wagener, M. Wang, J. Wong, and F. Yang, Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols, J. Geophys. Res., 103,16979-16998, 1998.
• P. Chylek and J. Wong Erroneous use of modified Kohler equation in cloud and aerosol physics applications, J. Atmos. Sci., 55, 1473-1477, 1998.
• W. Tso, W. Geldart and P. Chylek, Anharmonicity and cross section for absorption of radiation by water dimers, J. Chem. Phys., 108, 5319-5329, 1998.
• P. Chylek, L. Kou, B. Johnson, F. Boudala and G. Lesins, Black carbon concentrations in precipitation and near surface air in and near Halifax, Nova Scotia, Atmos. Environ.,1998, in press.
• Q. Fu, G. Lesins, J. Higgins, T. P. Charlock, P. Chylek and J. Michalsky, Water vapor continuum absorption of solar radiation tested using ARM data, Geophys. Res. Lett., 25, 1169-1172, 1998.
• P. Chylek and J. Wong, Cloud radiative forcing ratio: an analytical model, Tellus ,50A, 259-264, 1998.
• P. Chylek and G. Videen, Scattering by a composite sphere and effective medium approximations, Opt. Comm., 146, 15-20, 1998.
• P. Chylek and G. Videen, Effect of air bubbles on the absorption of solar radiation by cloud droplets, J. Atmos. Sci., 55, 340-343, 1998.
• G. Videen and P. Chylek, Limits of the anomalous diffraction approximation, Atm. Res., 49, 77-80, 1998.

  1997

• P. Chylek and W. Geldart, Water vapor dimers and atmospheric absorption of electromagnetic radiation , Geophys. Res. Lett., 24, 2015-2018, 1997.
• B. Winter and P. Chylek, Contribution of sea salt aerosol to the planetary clear-sky albedo, Tellus , 49B , 72-79.

  1996

• S. Gosse, M. Wang, D. Labrie and P. Chylek, Imaginary part of refractive index of sulfates and nitrates in the 0.7-2.6 micron spectral region, Appl. Opt. , 36 , 3622-3634, 1996.
• S. Gosse, D. Labrie and P. Chylek, Refractive index of ice in the 1.4 to 7.8 micron spectral range, Appl. Opt. , 34 , 6582-6586, 1996.
• P. Chylek, G. Lesins,G. Videen, J. Wong, R. Pinnick D. Ngo and J. Klett, Black carbon and absorption of solar radiation by clouds, J. Geophys. Res., 101, 23365-23371, 1996. (/li>
• P. Chylek, C. Banic, P. Damiano, G. Isaac, B. Johnson, R. Leaitch, P. Liu, D. Ngo, F. Said and B. Winter, Black Carbon: Atmospheric Concentrations and Cloud Water Content Measurements over Southern Nova Scotia, J. Geophys. Res., 101, 29105-29110, 1996.
• S. Hill and P. Chylek, Comment on A Rigorous Explanation for the Resonances Observed in the Scattering from Spherical Ice Particles, IEEE Trans, Antennas and Propagat., 44, 1052-1055, 1996.

  1995

• P. Chylek, B. Johnson, P. Damiano, K. Taylor and P. Clement, Biomass Burning and Black Carbon in the GISP2 Ice Core, Geophys. Res. Lett. , 22 , 89-92, 1995.
• P. Chylek and J. Wong, Effect of Absorbing Aerosol on Global radiation Budget, Geophys. Res. Lett. , 22 , 929-931, 1995.
• P. Chylek, G. Videen, D. Ngo, R. Pinnick, and J. Klett, Effect of black carbon on the optical properties and climate forcing of sulfate aerosols, J. Geophys. Res., 100, 16325-16332,1995.
• P. Chylek and J. Li, Light Scattering by Small Particles in an Intermediate Region, Optics Communications, 117, 389-394,1995.
• G. Videen, J. Li and P. Chylek, Resonances and Poles of Weakly Absorbing Spheres, J. Opt. Soc. Am., A12, 916-921, 1995
• G. Videen, D. Ngo, P. Chylek and R. Pinnick, Light scattering from a sphere with an irregular inclusion, J. Opt. Soc. Am., A12, 922-928, 1995
• P. Chylek and J. Dobbie, Inhomogeneous Cirrus Clouds: Monte Carlo Simulation, J. Atmos. Sci., 52 3512-3522, 1995.
• P. Chylek and J. Wong, Effect of Absorbing Aerosols on Global Radiation Budget, Geophys. Res. Lett., 22, 929-931, 1995.
• J. Li, W. Geldart and P. Chylek, Second Order Perturbation Solution For Radiative Transfer in Clouds, J. Quant. Spectr. Radiat. Transfer., 53, 445-456, 1995.
• P. Chylek, P. Damiano, N. Kalyaniwalla and E. Shettle, Radiative Properties of Water Clouds, Atm. Res., 35, 139-156, 1995.