³ÉÈËVRÊÓƵ

Physical Meteorology

Office: Burnside Hall 810
Tel.: (514) 398-6079
Fax.: (514) 398-6115
henry.leighton [at] mcgill.ca (E-mail)

Research interests

Cloud chemistry and atmospheric aerosols

The interactions between atmospheric aerosol particles and clouds and precipitation have important implications for climate and air quality. Aerosols influence cloud properties. The chemical composition, size distribution and concentration of the aerosol will affect the concentration of cloud droplets, which in turn may impact on the radiative properties of the cloud, the cloud lifetime and the precipitation efficiency of the cloud. On the other hand clouds may impact on aerosol properties. Aerosols that are dissolved in cloud droplets may undergo chemical changes. Subsequent evaporation of the cloud will result in an aerosol that contains larger particles and with altered chemical composition. Precipitation carries the aerosol to the surface. The significance of the wet deposition of the aerosols will depend on the chemical composition of the aerosol and its concentration. We are studying these interactions by means of high resolution numerical models and are comparing the results of these simulations with results from aircraft measurements of aerosols.

Radiation, clouds and precipitation

Regional climate models are important tools to increase understanding of the processes that determine regional climate, fluctuations in the local climate, extremes and the regional climate change in response to global warming. In the Canadian context, a major study of the hydrology of the Mackenzie River Valley (Mackenzie GEWEX Study - MAGS) has recently concluded and currently there is a research network exploring the recent Prairie drought of 1999-2003 (Drought Research Initiative – DRI). In both of these studies the Canadian Regional Climate Model was used to help understand the processes that determined the hydrology of the region in the former study and the characteristics of the drought in the latter. In order to have confidence in the analyses resulting from the model it is useful to compare the model results as extensively as possible with observations. Precipitation is an important variable in both studies and so it is essential that the models reproduce the cloud fields, and their radiative impacts as observed by satellites, and also the relationships between cloud properties as measured from satellites and precipitation measured at the surface. We are contributing to understanding the Prairie drought by combining out analyses of satellite and surface observations with the output from CRCM simulations.

Some recent publications

Guo, Song and H.G. Leighton. Satellite-Derived Aerosol Radiative Forcing from the 2004 British Columbia Wildfires. Atmosphere-Ocean, 46,203-212, 2008.

Ivanova, Irena T. and H.G. Leighton. Aerosol–Cloud Interactions in a Mesoscale Model. Part I: Sensitivity to Activation and Collision–Coalescence. Journal of the Atmospheric Sci ences, 65, 2, 298-308, 2008.

Ivanova, Irena T. and H.G. Leighton. Aerosol–Cloud Interactions in a Mesoscale Model. Part II: Sensitivity to Aqueous-Phase Chemistry. Journal of the Atmospheric Sciences, 65, 2, 309-330, 2008.

Guo, Song, H.G. Leighton and M.D. MacKay. Surface absorbed and top-of-atmosphere radiation fluxes for the Mackenzie River Basin from satellite observations and a regional climat e model and an evaluation of the model. Atmosphere- Ocean, 45, 129-139, 2007.

Koziol, A. and Leighton, H.G. The moments method for multi-modal multi-component aerosols. Quart. J. of the Royal Meteor. Soc., 133, 1057 – 170, 2007.

MacKay, M.D., Bartlett, P., Chan, E., Derksen, C., Guo, S., and Leighton, H.G. On the simulation of regional scale sublimation over boreal and agricultural landscapes in a clima te model. Atmosphere – Ocean 44, 289 – 304, 2006.

Feng, J. and H.G. Leighton. Broadband solar radiances from visible band measurements: a method based on ScaRaB observations and model simulations. International J. of Rem. Sensi ng, 26, 5125 – 5148, 2005.