Professor Robert (Bob) J. Sica

Department of Physics & Astronomy

The university of western Ontario

London, canada


My primary research tool is the Purple Crow Lidar (PCL), which measures temperature and composition of the Earth's atmosphere from the surface to 110 km altitude. The PCL is able to make these measurements at unprecedented accuracy by using a 2.65 m diameter liquid mirror telescope. The liquid mirror is a Canadian technology which allows large mirrors to be built at a fraction of the cost of traditional glass mirrors. Our expertise in these mirrors is due to our longstanding collaboration with Professor E. Borra’s group at the Université Laval, world leaders in this technology.

The long-term objectives of this research program are to search for atmospheric change and to help improve weather forecasting. Temperature change in the middle atmosphere is not directly affected by land, cities or oceans like surface temperature measurements, and in this region of the atmosphere surface heating corresponds to cooling (due to increased radiation of heat from CO2). The PCL measures water vapor composition change will be measured at both middle and high latitudes. In the middle atmosphere water vapor is an important part of the ozone cycle. We also measure layers of smoke particles at 14 to 16 km altitude associated with forest fires, injected into the stratosphere via a process called pyroconvection. The smoke particles can travel great distances, and affect both ozone concentration and temperature. With the number and severity of forest fires increasing, forest fires play a more complex role in global warming than anticipated, and we are trying to understand these effects.

The PCL also measures disturbances in the air density similar to waves on the surface of a lake called gravity waves. These waves break like ocean waves on a beach, primarily at altitudes above 50 km. Remarkably, even waves that break 100 km above the surface play an important role in determining the behaviour of weather systems which affect us on the surface. Furthermore, the gravity waves alter composition and thus affect ozone.

I am currently also involved with Dr. K. Strawbridge (Environment Canada) in the operation of an ozone lidar as part of the Canadian Network for the Detection of Atmospheric Change’s Polar Environment Research Laboratory (PEARL) in Eureka, Nunavut. The suite of instruments at PEARL are participating in the current International Polar Year, a major international program focussing on all aspects of polar science.


research overview

A main focus of my research is studying the affects of atmospheric waves on weather and climate. Top right: photo of noctilucent clouds shows waves in the mesosphere (85 km altitude); lower right: density changes in the atmosphere as a function of height and time for a single wave measured by the Purple Crow Lidar.

Graduate student opportunities available.