question: Why is air turbulence more severe over the Atlantic Ocean?
comment: Than over where? What you might be trying to ask is why do aircraft often encounter turbulence when crossing eastward across the Atlantic. The answer to that is that fast moving currents of air called jet streams are useful to pilots as they provide big tail winds to help move the aircraft to its destination faster. Like a fast stream, this fast moving wind swirls and causes bumps. We try to avoid the worst bits but some light chop is worth the time (and fuel) savings.
passages: CAT can be hazardous to the comfort, but rarely the safety, of air travelers.
  
  CAT in the jet stream is expected to become stronger and more frequent because of climate change, with transatlantic wintertime CAT increasing by 59% (light), 94% (moderate), and 149% (severe) by the time of CO2 doubling.
  
  Section::::Detection.
   Detecting and predicting CAT is difficult. At typical heights where it occurs, the intensity and location cannot be determined precisely. However, because this turbulence affects long range aircraft that fly near the tropopause, CAT has been intensely studied. Several factors affect the likelihood of CAT. Often more than one factor is present. 64% of the non-light turbulences (not only CAT) are observed less than away from the core of a jet stream.
  
  Section::::Factors that increase CAT probability.:Jet stream.
   Because aircraft move so quickly, they can experience sudden unexpected accelerations or 'bumps' from turbulence, including CAT - as the aircraft rapidly cross invisible bodies of air which are moving vertically at many different speeds. Although the vast majority of cases of turbulence are harmless, in rare cases cabin crew and passengers on aircraft have been injured when tossed around inside an aircraft cabin during extreme turbulence (and in a small number of cases, killed, as on United Airlines Flight 826 on December 28, 1997). BOAC Flight 911 broke up in flight in 1966 after experiencing severe lee-wave turbulence just downwind of Mount Fuji, Japan.
   BULLET::::- The pilot may issue a Pilot Report (PIREP), communicating position, altitude and severity of the turbulence to warn other aircraft entering the region.
  
  Section::::Effects on aircraft.:Cases.
   A report published in the science journal "Nature Climate Change" forecasts that increasing levels will result in a significant increase in in-flight turbulence experienced by transatlantic airline flights by the middle of the 21st century. The lead author of the study, Paul Williams, a researcher at the National Center for Atmospheric Science, at the University of Reading stated, "air turbulence does more than just interrupt the service of in-flight drinks. It injures hundreds of passengers and aircrew every year – sometimes fatally. It also causes delays and damage to planes."
  
  Section::::Noise.
   From the ground upwards through the troposphere temperature decreases with height; from the tropopause upwards through the stratosphere temperature increases with height. Such variations are examples of temperature gradients.
  
  Section::::Factors that increase CAT probability.:Temperature gradient.:Horizontal.
  
  A horizontal temperature gradient may occur, and hence air density variations, where air velocity changes. An example: the speed of the jet stream is not constant along its length; additionally air temperature and hence density will vary between the air within the jet stream and the air outside.
  
  Section::::Factors that increase CAT probability.:Wind shear.
   Because of the often abrupt changes in horizontal and vertical wind speeds and direction that can occur within these small weather systems they represent a significant hazard to aircraft on landing and taking off. During the climb-out and approach phases of flight, aircraft airspeed and height are near critical values, thus rendering the aircraft especially susceptible to the adverse effects of these wind shears.
   Section::::Characterization of atmospheric turbulence.:The Pasquill atmospheric stability classes.
  
  Pasquill atmospheric stability classes – oldest and, for a great many years, the most commonly used method of categorizing the amount of atmospheric turbulence present was the method developed by Pasquill in 1961. 
  
  He categorized the atmospheric turbulence into six stability classes named A, B, C, D, E and F with class A being the most unstable or most turbulent class, and class F the most stable or least turbulent class. 
  
  BULLET::::- Table 1 lists the six classes
   Section::::Factors that increase CAT probability.:Wind shear.:Horizontal.
  
  When strong wind deviates, the change of wind direction implies a change in the wind speed. A stream of wind can change its direction by differences of pressure. CAT appears more frequently when the wind is surrounding a low pressure region, especially with sharp troughs that change the wind direction more than 100°. Extreme CAT has been reported without any other factor than this.
  
  Section::::Factors that increase CAT probability.:Mountain waves.
  
  Mountain waves are formed when four requirements are met. When these factors coincide with jet streams, CAT can occur:
   BULLET::::- Upper-level jet streams. Associated with upper level jet streams is a phenomenon known as clear air turbulence (CAT), caused by vertical and horizontal wind shear connected to the wind gradient at the edge of the jet streams. The CAT is strongest on the anticyclonic shear side of the jet, usually next to or just below the axis of the jet.
   Such a claim is too broad and again contradicts the fact that updraughts in front of a thunderstorm are often laminar. However, it is true that the upper layers are almost always turbulent. However, in most cases, the aforesaid turbulence is not extreme. Along the same lines, Didier Morieux states:
  
  Dennis Pagen is even more explicit. He states:
  
  The International cloud atlas soothes these claims: it simply states that ""la turbulence is often very strong" " below the cloud.
  
  Section::::Myths and truth about cumulonimbus.:Serious hazard to glider pilots.
   As the result of the accidents due to wind shear and other weather disturbances, most notably the 1985 crash of Delta Air Lines Flight 191, the U.S. Federal Aviation Administration mandated that all commercial aircraft have on-board wind shear detection systems by 1993. Since 1995, the number of major civil aircraft accidents caused by wind shear has dropped to approximately one every ten years, due to the mandated on-board detection as well as the addition of Doppler weather radar units on the ground (NEXRAD). The installation of high-resolution Terminal Doppler Weather Radar stations at many U.S. airports that are commonly affected by wind shear has further aided the ability of pilots and ground controllers to avoid wind shear conditions.
   As the result of the accidents in the 1970s and 1980s, most notably following the 1985 crash of Delta Air Lines Flight 191, in 1988 the U.S. Federal Aviation Administration mandated that all commercial aircraft have on-board wind shear detection systems by 1993. Between 1964 and 1985, wind shear directly caused or contributed to 26 major civil transport aircraft accidents in the U.S. that led to 620 deaths and 200 injuries. Since 1995, the number of major civil aircraft accidents caused by wind shear has dropped to approximately one every ten years, due to the mandated on-board detection as well as the addition of Doppler weather radar units on the ground (NEXRAD). The installation of high-resolution Terminal Doppler Weather Radar stations at many U.S. airports that are commonly affected by wind shear has further aided the ability of pilots and ground controllers to avoid wind shear conditions.
   Wind shear is a difference in relative speed between two adjacent air masses. An excessive wind shear produces vortices, and when the wind shear is of sufficient degree, the air will tend to move chaotically. As is explained elsewhere in this article, temperature decreases and wind velocity increase with height in the troposphere, and the reverse is true within the stratosphere. These differences cause changes in air density, and hence viscosity. The viscosity of the air thus presents both inertias and accelerations which cannot be determined in advance.
  
  Section::::Factors that increase CAT probability.:Wind shear.:Vertical.
   BULLET::::- ADMS 4, – United Kingdom's most advanced model, uses the Monin-Obukhov length, the boundary layer height and the windspeed to categorize the atmospheric turbulence.
  
  Section::::Miscellaneous other terminology.
   BULLET::::- microburst intensity can double in a minute or less,
  
  BULLET::::- the winds can shift to excessive cross wind,
  
  BULLET::::- is the threshold for survivability at some stages of low-altitude operations, and
  
  BULLET::::- several of the historical wind shear accidents involved microbursts.
  
  Wind shear is also a key factor in the creation of severe thunderstorms. The additional hazard of turbulence is often associated with wind shear.
  
  Section::::Where and when it is strongly observed.
  
  Weather situations where shear is observed include:
   Most atmospheric turbulence occurs within the ABL, whereas the free atmosphere is largely non-turbulent. So, in order to have a proper accounting for motions within the ABL, GCMs must properly account for turbulence within the ABL. To do this, GCMs must have some way of achieving turbulence closure.
   Section::::Opinions.
   Section::::Current Considerations.:Critical Turbulence Hypothesis.
   BULLET::::- Bridge supports (piers) in water. In the late summer and fall, when river flow is slow, water flows smoothly around the support legs. In the spring, when the flow is faster, a higher Reynolds number is associated with the flow. The flow may start off laminar but is quickly separated from the leg and becomes turbulent.
   Section::::In popular culture.
  
  In the 1986 film "Top Gun", Lieutenant Pete "Maverick" Mitchell, played by Tom Cruise, suffers two flameouts caused by passing through the jetwash of another aircraft, piloted by fellow aviator Tom "Ice Man" Kazansky (played by Val Kilmer). As a result, he is put into an unrecoverable spin and is forced to eject, killing his RIO Nick "Goose" Bradshaw. In a subsequent incident, he is caught in an enemy fighter's jetwash, but manages to recover safely.
   Section::::Effects on aircraft.:Wake turbulence.
   Associated with jet streams is a phenomenon known as clear-air turbulence (CAT), caused by vertical and horizontal wind shear caused by jet streams. The CAT is strongest on the cold air side of the jet, next to and just under the axis of the jet. Clear-air turbulence can cause aircraft to plunge and so present a passenger safety hazard that has caused fatal accidents, such as the death of one passenger on United Airlines Flight 826.
  
  Section::::Uses.:Possible future power generation.
   Vertical wind shear above the jet stream (i.e., in the stratosphere) is sharper when it is moving upwards, because wind speed decreases with height in the stratosphere. This is the reason CAT can be generated above the tropopause, despite the stratosphere otherwise being a region which is vertically stable. On the other hand, vertical wind shear moving downwards within the stratosphere is more moderate (i.e., because downwards wind shear within the stratosphere is effectively moving against the manner in which wind speed changes within the stratosphere) and CAT is never produced in the stratosphere. Similar considerations apply to the troposphere but in reverse.
   Wind shear refers to the variation of wind over either horizontal or vertical distances. Airplane pilots generally regard significant wind shear to be a horizontal change in airspeed of for light aircraft, and near for airliners at flight altitude. Vertical speed changes greater than also qualify as significant wind shear for aircraft. Low level wind shear can affect aircraft airspeed during take off and landing in disastrous ways, and airliner pilots are trained to avoid all microburst wind shear (headwind loss in excess of ). The rationale for this additional caution includes:
  