Ventilation

ventilation

1. In the equation for the time constant of a thermometer, a quantity equal to the product of wind speed and air density.
   The time constant varies inversely with ventilation. The concentration of an air pollutant is inversely proportional to the ventilation, the mass flux of "clean air" moving past the observer. Stagnation, a condition caused by the lack of ventilation, is historically associated with major air pollution episodes. It occurs due to the lack of horizontal wind speed and the lack of vertical wind speed, for example, caused by an inversion.
   
2. The exchange of properties with the surface layer such that property concentrations are brought closer to equilibrium values with the atmosphere.
   Such exchange may occur without water mass formation.
   
3. In weather-observing terminology, the process of causing "representative" air to be in contact with the sensing elements of observing instruments; especially applied to producing a flow of air past the bulb of a wet-bulb thermometer.
   
4. For tropical cyclones (TCs), ventilation refers to the exchange of air between the environment and inner core of a TC. When driven by background vertical wind shear, this process can import low-entropy air into the TC, resulting in weakening of the TC or reduced probability of genesis. Ventilation can also refer to the net evacuation of mass in the upper levels of TCs, such as when interacting with an upper-level trough, which may intensify a TC.
   

Simpson, R., and R. Riehl, 1958: Mid-tropospheric ventilation as a constraint on hurricane development and maintenance. Preprints, Tech. Conf. on Hurricanes, Miami Beach, FL, Amer. Meteor. Soc., D4-1–D4-10.

Term edited 15 November 2022.

A series of operational polar-orbiting meteorological satellites launched by the former Soviet Union since 1969.