Abstract
On 21 September 2012 the entire sky was covered by contrails over the Gulf of Lyon (NW of the Mediterranean basin). These clouds were well recorded by ground observers as well as by Meteosat imagery. The atmospheric characteristics at the levels where these anthropic clouds formed are analyzed by performing a WRF simulation in the area where Meteosat recorded contrail clouds. According to the vertical profiles of temperature and the relative humidity respect to the ice (RHI), the environmental condition favors that the water vapor exhaust emitted by the aircraft engines reaches the deposition point and form crystal clouds, which spread out because the temperature remained below 230 K and the RHI was higher than 70% during the whole episode.
Highlights
In a pioneer study about the condensation trails of aircraft, [1] defined the term contrail as clouds that form when a mixture of warm, unsaturated, engine exhaust gases and cold ambient air reaches saturation with respect to water, forming liquid drops, which quickly freeze
If the environment is saturated with respect to the ice, the ice particles forming the contrail can grow and the contrail spreads out, covering a large area in the sky
Contrail growths will continue and spread out in an environment saturated respect to the ice, and eventually it may transform into cirrus clouds [7,8,9]
Summary
In a pioneer study about the condensation trails of aircraft, [1] defined the term contrail as clouds that form when a mixture of warm, unsaturated, engine exhaust gases and cold ambient air reaches saturation with respect to water, forming liquid drops, which quickly freeze. Temperature and humidity play a key role in spreading out contrails [3]. This author, by using numerical simulations, found that, in order to guarantee persistency of contrails, the air needs to have a relative humidity of. At a given relative humidity, the ice crystal’s growth rate increases with increasing temperature. According to [6], in the initial growth stage of an ice particle, a contrail rapidly evaporate (around tens of second) if the air is dry. Contrail growths will continue and spread out in an environment saturated respect to the ice, and eventually it may transform into cirrus clouds [7,8,9]
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