QUESTION = What causes the trail behind jets at high altitude? GENERATION = The same thing that causes the clouds you see at the start of a storm to form in the first place. The air pressure changes as the jet moves through the air, causing it to cool down and condense into water droplets. These droplets are in fact a lot bigger than the water droplets in the clouds, so when the plane passes through them, they can cause the air pressure to change, causing the water droplets to condense into clouds. This is what you see when you look at a cloud formation from the ground. In addition to this, when the plane passes through the clouds, it also moves through the air, causing it to change its temperature, causing the water droplets to condense and form clouds. These clouds are often quite large, and can block out the sun. This is what you see when you look at a contrail. Finally, the water vapor that forms at high altitudes is cooled by the air above, and as it cools, it condenses into clouds. This is what you see when you look at a cumulonimbus cloud. These clouds are even larger than the water droplets in the clouds, and they block out the sun. RETRIEVAL #0 = Contrail---sometimes called cirrus aviaticus. Persistent spreading contrails are suspected to have an effect on global climate. Section::::Condensation from engine exhaust. The main products of hydrocarbon fuel combustion are carbon dioxide and water vapor. At high altitudes this water vapor emerges into a cold environment, and the local increase in water vapor can raise the relative humidity of the air past saturation point. The vapor then condenses into tiny water droplets which freeze if the temperature is low enough. These millions of tiny water droplets and/or ice crystals form the contrails. The time taken for the vapor to cool enough to condense accounts for the contrail forming some distance behind the aircraft. At high altitudes, supercooled water vapor requires a trigger to encourage deposition or condensation. The exhaust particles in the aircraft's exhaust act as this trigger, causing the trapped vapor to condense rapidly. Exhaust contrails usually form at high altitudes; usually above , where the air temperature is below . They can also form closer to the ground when the air is cold and moist. A 2013–2014 study jointly supported by NASA, the German aerospace center DLR, and Canada's National Research Council NRC, determined that biofuels could reduce contrail generation. This reduction was explained by demonstrating that biofuels produce fewer soot particles, which are the nuclei around which the ice crystals form RETRIEVAL #1 = Contrail (disambiguation)---Contrail (disambiguation) A contrail is a condensation trail caused by an aircraft. Contrail or Contrails may also refer to: BULLET::::- Contrail (company), a defunct video game developer BULLET::::- Contrail (software), a Cloud Federation computing project BULLET::::- "Contrail" (song), a song by Namie Amur BULLET::::- "Contrails" (book), a handbook issued to new cadets entering the United States Air Force Academy Section::::See also. BULLET::::- Distrail BULLET::::- Vapor Trail (disambiguation) RETRIEVAL #2 = Contrail---at cruising altitude with a sample-gathering aircraft flying in trail. In these samples, the contrail-producing soot particle count was reduced by 50 to 70 percent, using a 50% blend of conventional Jet A1 fuel and HEFA (hydroprocessed esters and fatty acids) biofuel produced from camelina. Section::::Condensation from decreases in pressure. As a wing generates lift, it causes a vortex to form at the wingtip, and at the tip of the flap when deployed (wingtips and flap-boundaries are discontinuities in airflow.) These wingtip vortices persist in the atmosphere long after the aircraft has passed. The reduction in pressure and temperature across each vortex can cause water to condense and make the cores of the wingtip vortices visible. This effect is more common on humid days. Wingtip vortices can sometimes be seen behind the wing flaps of airliners during takeoff and landing, and during landing of the Space Shuttle. The visible cores of wingtip vortices contrast with the other major type of contrails which are caused by the combustion of fuel. Contrails produced from jet engine exhaust are seen at high altitude, directly behind each engine. By contrast, the visible cores of wingtip vortices are usually seen only at low altitude where the aircraft is travelling slowly after takeoff or before landing, and where the ambient humidity RETRIEVAL #3 = Mirage---mirages explained BULLET::::- China daily, rare mirage in Penglai BULLET::::- The superior mirage BULLET::::- The inferior mirage BULLET::::- The highway mirage BULLET::::- Fata Morgana Mirage from the Continental Divide Trail RETRIEVAL #4 = Contrail---suggesting that examination of historic weather data could help study these effects. Section::::Head-on contrails. A contrail from an airplane flying towards the observer can appear to be generated by an object moving vertically. On 8 November 2010 in the US state of California, a contrail of this type gained media attention as a "mystery missile" that could not be explained by U.S. military and aviation authorities, and its explanation as a contrail took more than 24 hours to become accepted by U.S. media and military institutions. Section::::Distrails. Where an aircraft passes through a cloud, it can disperse the cloud in its path. This is known as a distrail (short for "dissipation trail"). The plane's warm engine exhaust and enhanced vertical mixing in the aircraft's wake can cause existing cloud droplets to evaporate. If the cloud is sufficiently thin, such processes can yield a cloud-free corridor in an otherwise solid cloud layer. An early satellite observation of distrails that most likely were elongated, aircraft-induced fallstreak holes appeared in Corfidi and Brandli (1986). Clouds form when invisible water vapor ( in gas phase) condenses into microscopic water droplets ( in liquid phase) or into microscopic ice crystals ( in solid phase). This may happen when air with a high proportion of gaseous water cools. A RETRIEVAL #5 = Vapor Trail (disambiguation)---Vapor Trail (disambiguation) A vapor trail or contrail is a condensation trail made by the exhaust of an aircraft engine. Vapor Trail or Vapour Trail may also refer to: Section::::Music. Section::::Music.:Albums. BULLET::::- "Vapour Trails" (album), an album by Tuxedomoon BULLET::::- "Vapor Trails", a 2002 album by Rush or its title song Section::::Music.:Songs. BULLET::::- "Vapour Trail" (song), a 1990 song by Ride from "Nowhere" BULLET::::- "Vapor Trail" (The Crystal Method song) BULLET::::- "Vapour Trails", a song by the Tragically Hip from "Phantom Power" Section::::Other uses. BULLET::::- Vapor Trail (roller coaster), a roller coaster at Sesame Place BULLET::::- "", a 1989 video game by Data East Section::::See also. BULLET::::- Contrail (disambiguation) RETRIEVAL #6 = Mountain jet---Mountain jet Mountain jets are a type of jet stream created by surface winds channeled through mountain passes, sometimes causing high wind speeds and drastic temperature changes. Section::::Central America jets. The North Pacific east of about 120°W is strongly influenced by winds blowing through gaps in the Central American cordillera. Air flow in the region forms the Intra-Americas Low-Level Jet, a westward flow about 1 km above sea level. This flow, trade winds, and cold air flowing south from North America contribute to winds flowing through several mountain valleys. Along Central America are three main wind jets through breaks in the American Cordillera, on the Pacific Ocean side due to prevailing winds. BULLET::::- Tehuano wind blows from the Gulf of Mexico through Chivela Pass in Mexico's Isthmus of Tehuantepec and out over the Gulf of Tehuantepec on the Pacific coast. Chivela Pass is a gap between the Sierra Madre del Sur and the Sierra Madre range to the south. BULLET::::- Papagayo wind shrieks over the lakes of Nicaragua and pushes far out over the Gulf of Papagayo on the Pacific coast. The Cordillera Central Mountains rise to the south, gradually descending to Gatun Lake and the Isthmus of Panama. BULLET::::- Panama winds slice through to the Pacific through the Gaillard Cut in Panama, which also holds the Panama