lämpöaallon

lämpöaallon is the genitive form of lämpöaalto, Finnish for "heat wave." The phrase is used to discuss two related concepts in different fields: a climatic heat wave in meteorology and a physical thermal wave in heat transfer. While related in name, the two senses refer to distinct phenomena and measurements.

Climate context: A heat wave is typically defined as a prolonged period of unusually high air temperatures, often specified by thresholds (such as daily maxima above a certain temperature or above the historical percentile) and lasting several days to weeks. Impacts include increased risk of heat-related illness, higher energy demand for cooling, crop stress, and risks to vulnerable populations. Monitoring relies on meteorological stations, humidity measures, and indices like heat index or wet-bulb temperature.

Physical context: In physics and engineering, a thermal or heat wave describes a transient temperature disturbance that propagates through a material. The classical Fourier model describes diffusion of heat, which effectively implies infinite propagation speed. More accurate descriptions at short times use hyperbolic equations (such as the Cattaneo–Vernotte formulation) that yield finite-speed, damped thermal waves. In some materials at low temperatures, actual thermal waves, sometimes referred to as second sound, have been observed, illustrating wave-like heat transport beyond simple diffusion.

Related topics include climate heat waves, heat conduction, Fourier's law, the Cattaneo–Vernotte equation, and second sound.