Glossary

Climate Change: A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use. (IPCC, 2013: Climate Change 2013: The Physical Science Basis. Cambridge University Press, 1535 pp.).

Extreme weather event: An extreme weather event is an event that is rare at a particular place and time of year. Definitions of rare vary, but an extreme weather event would normally be as rare as or rarer than the 10th or 90th percentile of a probability density function estimated from observations. By definition, the characteristics of what is called extreme weather may vary from place to place in an absolute sense. When a pattern of extreme weather persists for some time, such as a season, it may be classed as an extreme climate event, especially if it yields an average or total that is itself extreme (e.g., drought or heavy rainfall over a season). (IPCC, 2013: Climate Change 2013: The Physical Science Basis. Cambridge University Press, 1535 pp.).

Haboob: A dust or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into air.

Lidar: Lidar means light detection and ranging. An instrument that uses a laser to generate intense pulses that are reflected from atmospheric particles of dust and smoke. Lidars have been used to determine the amount of particles in the atmosphere as well as particle movement that has been converted into wind speed. (Ahrens, C.D., 1999. Meteorology today: an introduction to weather, climate and the environment. 6th ed. ISBN: 0-534-37201-5.).

Mixing layer: The unstable atmospheric layer that extends from the surface up to the base of a thermal inversion. Within this layer, the air is well stirred. The lower the vertical extent of the mixing layer (the mixing depth), the higher the concentration of the atmospheric pollutants at surface level.

PM₁₀: shall mean particulate matter which passes through a size-selective inlet as defined in the reference method for the sampling and measurement of PM₁₀, EN 12341, with a 50 % efficiency cut-off at 10 µm aerodynamic diameter. (DIRECTIVE 2008/50/EC on ambient air quality and cleaner air for Europe).

PM_2.5: shall mean particulate matter which passes through a size-selective inlet as defined in the reference method for the sampling and measurement of PM_2,5, EN 14907, with a 50 % efficiency cut-off at 2,5 µm aerodynamic diameter. (DIRECTIVE 2008/50/EC on ambient air quality and cleaner air for Europe).

Radiosonde: A ballon-borne instrument that measures and transmits pressure, temperature and humidity to a ground-based receiving station. A radiosonde observation that includes wind data is called rawinsonde.