A pilot Usually, on the leeward mountainside, the terrain drops in elevation at the same rate as the windward side. speed and/or direction) to adjacent layers or columns '. These can produce squall lines near showers. and the velocity of the windcan present a serious hazard during takeoffs The occurrence of CAT can extend to very high levels and can be associated Because of these downdrafts, it is recommended that mountain When the air reaches the mountain or escarpment slopes, it is forced to rise with the elevation of the physical terrain. attempted under gusty conditions should be made at higher speeds, to maintain The consent submitted will only be used for data processing originating from this website. These thermals may displace the airplane from its normal Due to the shear at the lower and upper part of the jet, turbulence may be generated there and/or gravity waves may be excited. Although they are more intense with the highest altitude, orographic waves can occur in any range of mountainous terrain or succession of crests at least 300 feet or more in height. As air flows over the tops of mountains, traveling down the leeward side, a standing mountain wave is formed and air currents oscillate between altitudes. bluffs or mountains are involved. The origin and physical cause may vary: The vertical currents within and around convective clouds are turbulent. thunderstorms develop. Basic fluid dynamics tells us that any fluid such as the atmosphere can support only a maximum of shear between laminar flow layers before breaking down into turbulent flow. The force of the vortex is determined by the weight, velocity and shape of the wing of the generating aircraft. Primarily, they are a function of the weight, size, and aerodynamic properties of the aircraft. Air speed variations are usually large. The impact of turbulence associated with baroclinic waves on cloud water and precipitation formation is well known (Baumgartner and Reichel, 1975; Houze and Medina, 2005; Medina and Houze, 2015 . When applied to mountains, they are important factors in weather and climate . turbulence but somewhat more intense. The vortexes of the turbulence mat generated by airplanes usually persist between one and three minutes after the passage of the aircraft depending on the conditions of air stability and wind speed. A big wave with the complex topography. flying over such terrain needs to be alert for wind shifts, and particularly 3. Types of Turbulence 3. It is located where there are large horizontal differences in temperature between warm and cold air masses. Turbulence threat alert en-route can be sent by company pilots in the form of audio and visual notifications, signaling when and where the belt tightening warning should be turned on and when pilots need to be in charge. Special Clouds (Not associated with thunderstorms) Clouds in unstable air aloft: Castellanus like small castle turrets~ Type of stratiform cloud Sometimes form out of the top . But a region's topography, like the orographic effect, also plays a large role. usually occurs near the mid-level of the storm, between 12,000 and 20,000 feet and is most Severe: Abrupt changes in aircraft attitude and/or height. Orographic precipitation is defined as snow, rain, or other precipitation which is formed when moist air is lifted as it moves over a range of mountains. Such effects will be most pronounced if the aircraft track is parallel with the ridge. Here we find not only a negative vertical wind speed, which by itself pushes the aircraft down; we also observe significant horizontal wind shear. Often, orographic lift occurs where a mountain is situated close to the ocean or large body of water. Plateaus cover 1/3 of the earth's surface and can be found on all continents. Source: National Transportation Safety Board (NTSB). The closer it is to the ground, the less time there is available to react to those accelerations. Vegetation may also cause updrafts and downdrafts, Thermal turbulence caused by surface heating. Please refer to the appropriate style manual or other sources if you have any questions. is an irregular motion of the air resulting from eddies and vertical currents. We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development. Relatively few reports of turbulence are received from fast military jets which are designed to give a high degree of tolerance. anticipate the bumpy and unsteady flight that may be encountered. Those downdraughts usually are caused by cool air sinking in the surrounding rising warmer updraught air. ridges and peaks be cleared by at least 2,000 feet. The only way for the pilot to avoid this invisible hazard is to be forewarned, Heating from below creates unstable conditions, gusty winds and bumpy flying conditions. The following are the seven cloud types that are associated with critical wildfire: 1. Changes in accelerometer readings of 0.5-1.0g at the aircrafts centre of gravity. glide path with the result that it will either overshoot or undershoot the runway. The effects of local convection, however, are less dangerous in advance. marked when the warm air is moist and unstable and will be extremely severe if The Evolution and Stability of Finite-Amplitude Mountain Waves. This study examines the dynamical and microphysical mechanisms that enhance precipitation during the passage of winter midlatitude systems over mountain ranges. Bench forecasters, therefore, have to largely rely upon more general, empirical rules and relationships. As its name suggests, this often though not necessarily always occurs in the absence of cloud, making it difficult to detect visually. Crossing the boundary may result in a period of turbulence, but it is the change of airflow across the wings at low level that may adversely affect lift especially in the landing and take-off phase. irregular terrain and man-made obstacles, causes eddies and therefore turbulence in the Swayne is an editor at Boldmethod, certified flight instructor, and a First Officer on the Boeing 757/767 for a Major US Carrier. The storm cloud is only the visible portion of a turbulent system in a thunderstorm. Focusing of this erosional power onto the . Clear air turbulence is turbulence not associated with cumuliform clouds, including thunderstorms, occurring at or above 15,000 feet. Ultimately, depending on aircraft type, severe turbulence may cause structural damage to an aircraft, especially when combined with inadequate, strong rudder movements. pronounced-effect on the flight path of an airplane approaching a landing area. On the lee side of the mountain range, rainfall is usually low, and the area is said to be in a rain shadow. But updrafts and downdrafts often extend outside the storm, with severe turbulence possible as much as 15 to 30 miles downwind. The downward flow is called a downwelling and the upward flow an upwelling. enough altitude to clear low objects in its path. with sudden changes in speed and directionwhich may be carried along some The wind on the leeward The different axes and scales of the major orographic features combined with the varying vegetation cover create a complex terrain for wind flow modelling. These reports are automatically sent to weather forecast models and made available in real time in the application. turbulence caused by surface heating. In extremes, structural damage to the aircraft may occur. Surface heating during the day causes thermal turbulence violently against their seat belts. Copyright 2020World Meteorological Organization (WMO). Occupants feel strain against seat belts. The wind blowing two opposing air masses produce turbulence in the frontal zone. On a low flight over varying surfaces, the pilot will encounter For every rising current, there is a compensating downward current usually slower in speed, since it covers a broader area, causing turbulence. The most comprehensive definition is high-altitude turbulence encountered outside of convective clouds. surface winds can be significantly modified by this process. It rises due to a variety of factors. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation Advertisement dianan30213021 Answer: orographic turbulence can be associated with what type of terrain Signup for our newsletter to get notified about sales and new products. For civil aviation, passengers may be made uncomfortable, or suffer injuries when not wearing their seat belts. The higher the lapse rate, the more readily vertical gusts develop and thus the more vigorous the turbulence is. But if you're looking to make some quick estimates, here are 8 rules-of-thumb that will help. The and to know where to expect unusual conditions. Quiz: Can You Identify These 6 Uncommon Airport Lighting Systems? Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. Sailplane (glider) pilots, soaring along mountain waves to reach higher altitudes, were among the first to recognize that the air in the vicinity of a mountain range is likely to bear considerable turbulence (Hirth, 1933).Early pilot reports of severe turbulence encounters . Turbulence extends from the base to the top of the convection layer, with smooth conditions found above. An example of a climatological low level jet would be the seasonal development and subsequent decay of the Somali Jet. Often, these slopes receive rain during large parts of the year as a result of a constant source of moisture from the ocean, as well as prevailing winds blowing from the sea. However, once formed, they are known to sink with a speed of 12 m/s, and will be transported with the general wind flow. The descending currents cause the aircraft to be deflected down its normal trajectory, which may cause a touch on the runway before the desired point (undershoot). Clear air turbulence (CAT) is the term used to describe medium- or high-level atmospheric turbulence produced in regions of marked wind shear. Thermal turbulence will have a The intensity of turbulence is categorized by the ICAO as follows: Light: Effects are less than those of moderate intensity. It is not surprising then to find lush vegetation on the windward slopes of mountains. lower levels. turbulence and would tend to force an aircraft into the mountain side. This type of turbulence originates from a strong shear of the wind, that is, great variation of the speed in a few kilometers. There are technologies under development for the detection of CAT that are being tested and improved by NASA, scientific institutions and airlines, such as Delta Airlines. Fatalities have occurred as a result of turbulence encounters. It should be noted that the sting jet is still being studied, and its precise method of formation will be more complex than the simple description above. A pilot flying through such turbulence should Turbulence is generally found along troughs at any altitude, within lows at any altitude, and poleward of lows in the mid and upper altitudes. The more perpendicular to the wind barrier, the more pronounced the effects will be. In this case, it is possible to estimate the turbulence conveyor category of the aircraft that is ahead through the knowledge of the other air carrier's fleet. Turbulence is the name for random gusty fluctuations (vertical and horizontal) of the wind. Light turbulence momentarily causes slight Final Video: Your Questions About Mountain Flying, Coffin Corner And Mach Tuck, Explained: Boldmethod Live, Why Fast Jets Have Swept Wings: Boldmethod Live, 7 Important Things To Remember During A Last Minute Runway Change, 4 Differences Of Learning To Fly A High Wing Vs. Low Wing Aircraft, 5 Things You Learn In Your First 50 Hours Of Instructing, How Airline Pilots Manage Maximum Landing Weight, 8 Tips For Keeping Your Logbooks Clean, Professional, And Interview-Ready, 6 Questions You Should Be Prepared To Answer During Your CFI Interview. This means very little, if any, plant growth can occur in this climate. In the meteorological radar images: the presence of convective clouds in the vicinity of the departure, destination and alternative airports. winds may reverse the direction of usual winds. These clouds also occur in regions lacking mountainous terrain, in areas of turbulence, but are less common. This article was most recently revised and updated by, https://www.britannica.com/science/orographic-precipitation, Institute of Meteorology and Climate Research - Mechanism of Orographic Precipitation Over Complex Terrain, University of Colorado Boulder - Orographic Precipitation. Quiz: Can You Answer These 6 IFR Preflight Planning Questions? It is possible for windsocks at different locations within the perimeter of an airfield to all indicate markedly different wind directions and strengths. The aircraft may be out of control for short periods. present, to a lesser degree, in a warm front as well. In the windward clouds, the airplanes must find elevation of altitude (gain of sustentation) and, to leeward, loss of altitude. Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simplyclicking on this link.Until next time, keep your eye on the weather! Depending on your location, US airline Delta Airlines has launched an application called Flight Weather Viewer that provides turbulence area graphics and real-time forecasts for pilots. Aircraft is violently tossed about and practically impossible to control. Convective Turbulence 2. It's here that friction occurs between the two opposing air masses, producing turbulence in the frontal zone. 1. Quiz: Do You Know These 6 IFR Regulations? Note 2-5 In the case of overflight of a mountainous region with strong surface winds, when faced with a severe turbulence condition, the pilot must request Air Traffic Control to move to a higher flight level, where he will probably find better conditions. So what are the differences? If there is any doubt 15 Common Types of Terrain and Infographic. Jet engine exhaust and rotor blast can produce localized wind speeds with sufficient intensity to cause damage to other aircraft, vehicles and personnel circulating within the affected area. Some Convective currents are often strong enough to produce air mass thunderstorms with which severe turbulence is associated. Friction and air turbulence generated at the surface slow low level winds. over cities, forests, small hills and larger hills, and mountains, the airflow suffers large corresponding displacements from its original level. Lens-shaped clouds (altocumulus lenticularus) may severe wind shear associated with them. When a cold front cuts underneath a warm front, it forces the warm to rise. evaporation and sublimation. Satellite images, weather radar images and significant time charts (SIGWX) help in identifying this phenomenon. The flow of air passing under the wing of an aircraft is conducted around the tip of the wing to the region above the wing, through the larger pressure difference below the wing and smaller above the wing, thus creating a trail of turbulence mats . they develop, and how they are affected by terrain. tend to cause the pilot to land short of the field. Orographic Effect. Turbulence is associated with fronts, wind shear, thunderstorms, etc. This Occupants of the airplane may If a turbo-generator aircraft is rising or falling rapidly, the vortices generated may persist at various flight levels. When air reaches dew point (the temperature at which water can no longer stay in its gaseous state) while still rising along the mountain slopes, condensation takes place. Let's look at some effects of channeling and mechanical turbulence. This application is customized by aircraft type, interpreting that an aircraft 737 and another of type 767 have different impacts on turbulence due to difference in size and weight. Wind Shear. Did you find errors in this content ? The latter is always found close to the surface where wind speed vanishes. Some also falls a short distance downwind of the ridge and is sometimes called spillover. Although ground vortex dissipation of the turbulence belt occurs more rapidly, when issuing authorizations or instructions, air traffic controllers consider the hazards caused by the exhaust of jet engines and rotor blasting, in the case of are taking off or landing, particularly when intersecting tracks are being used. The system automatically sends turbulence reports to nearby operations centers and aircraft. In weather conditions when thermal activity can be expected, many pilots prefer to fly in the early morning or in the evening when the thermal activity is not as severe. Clouds with extensive vertical development. Turbulence is always associated with convection, so for that reason this type is referred to as convective turbulence. If the encounter with the vortex occurs in the approach area, its effect will be greater because the aircraft that follows is in a critical situation with respect to speed, thrust, altitude and reaction time. Moisture is added to a parcel of air by. gc232 2) Thermal Turbulence effects on surface winds, but often makes them gusty and erratic. With ascent rates of around 500 ft per minute they can be very useful in gaining height quickly. How Mixture Control Works On Carbureted Engines. Thermal (Convective) Turbulence. Turbulence can manifest through: The following provides an overview of each of these forms of turbulence. This break-up is enhanced, and occurs earlier, if ambient turbulence is high. There are two sources of turbulence--mechanical and thermal. absorb, reflect, and radiate varying amounts of heat. Microbursts can be especially hazardous because of the . Vortices form on the top surface of each wing, and are left in the aircrafts wake. Your Guide To Minimum VFR Altitudes, The Four Steps Of Spin Recovery, Explained, Ice-Covered Pitot Tube Results In Low-Altitude Alert From ATC, Why You Experience Turbulence When Flying Through A Cloud. On encountering the turbulence, because of its weight the second aircraft will be less responsive to control input and engine power settings, and may well impact the ground. Wake turbulence can impose rolling moments exceeding . Source: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/14_phak_ch12.pdf, Source: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_00-6B.pdf. In Moderate Turbulence changes in altitude or attitude are more . Descending currents prevail above some surfaces and Extreme: Effects are more pronounced than for severe intensity. Quiz: What Should You Do When ATC Says '______'? When the flow of air is interrupted by a hill or mountain and it is forced to rise, it can cause disturbances in the weather system. they affect the rate of descent. Source: New Zealand Air Force Good Aviation Practice Booklet on Wake Turbulence. Moderate turbulence is similar to light Experienced glider pilots look for the updraught side of mountain waves in order to gain altitude. Dependent upon the stability of the air mass, this may result in triggering convection, with its attendant turbulence; it also may generate gravity waves, referred to in that case as mountain waves, or may tend to return the airflow to its original level giving standing waves and rotors. The air continues to cool as it keeps rising along the slopes. The greatest shear, and thus the greatest turbulence, is found at the tops of the inversion layer. Frontal turbulence. Chances are you'll fly both types in your aviation career. Omissions? airplane. mechanical turbulence. As with all turbulence types, the degree of turbulence is categorized by the ICAO definitions. Orography. Another factor which has a great deal of effect on low level wind is thermal The downdraught forces the air close to the ground to spread radially outwards. The leewardor "lee"side is the one sheltered from the wind by the reference point. Loose objects are tossed about. the field. The In this study, WRF v.3.6 model is using for collapsed 1 million m3 of land, mud, rocks and trees prediction heavy showers and hails for different set moved down from the Akhaldaba mountain into of physical options over the regions characterized Tbilisi and dammed up the Vere river. find smooth air above the cloud level. During orographic lifting, however, there are no atmospheric conditions or weather elements that cause the air to rise. size; in stable air, they tend not to grow in size but do dissipate more slowly. Source: FAA - Pilot and Air Traffic Controller Guide to Wake Turbulence. The three basic effects of the turbulence conveyor on the aircraft are: violent swing, height loss or ascensional speed and structure efforts. Source: FAA AC 90-23G - Aircraft Wake Turbulence. The turbulence embodied in this orographically induced cellularity allows a quick response of the precipitation fallout to the orography since aggregation and riming of ice particles in the turbulent layer produce heavier, more rapidly falling pr ecipitation particles. Light aircraft are prone to be buffeted, and are significantly affected even by light turbulence. Surface rotors are extremely hazardous to aircraft. For any given intensity of turbulence, the faster the aircraft flies, the more it will be accelerated. Light turbulence causes slight, erratic changes in the altitude and attitude of the plane. One common cause for unstable air is the vertical air flow known as thermals. Winds on the lee sides of ridges can shift in direction and speed, making In extreme turbulence, the airplane is tossed violently about and is impossible to control. }, abstractNote = {High resolution numerical simulation can provide insight into important physical processes . In the flight planning phase, the occurrence of turbulence at the starting aerodrome, along the route or at the destination aerodrome can be identified by consulting weather reports. Is Flying Through Snow Considered 'Known Icing'? Orographic turbulence Known as mountain wave Can be expected on the windward side and over the crests of mountains, along the downward slope Avoid rotor cloud and strong downdraft on the leeward side of mountain associated with mechanical agencies. The quantitative measures of turbulence consider speed fluctuations (defined as the maximum speed variation from the indicated flying speed under turbulent conditions), the derived bursts (defined as the estimated velocity of a given vertical gust of wind impacting flight altitude due to the impact of a vertical gust of wind on the aircraft) and vertical acceleration (defined as the standard gravity acceleration deviation peak of 1.0 g measured at center of gravity of the aircraft). Send email to, https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/14_phak_ch12.pdf, https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_00-6B.pdf, https://www.bfu-web.de/EN/Service/V180-Video-EN/V180-Video-EN_node.html, A319 / B744, en-route near Oroville WA USA, 2008, B733, en-route, Santa Barbara CA USA, 1999, B735, en-route, North East of London UK, 1996, WW24, vicinity John Wayne Airport Santa Ana CA USA, 1993. When the warm air is moist and unstable, there can be a risk of thunderstorms, leading to more severe turbulence. surfaces create rising currents which tend to cause the pilot to overshoot Convective turbulence. Flying through turbulence can be stressful and fatiguing, so it's good to understand where and how it happens. the larger convection currents form cumulus clouds, the pilot will invariably This sensitivity can be influenced by aircraft type, flight altitude and flight speed. The upward currents force the aircraft up its normal landing path, resulting in a touch beyond the desired point (overrun). In plateau regions, relief can contribute to the occurrence of "mountain circulation" that can trigger deep convection processes and generate orographic turbulence. Contents 1 Effects of orographic lifting Turbulence is located along strong isotach gradient zones. Source: Wake Vortices , C. Lelaie, Airbus Safety First Magazine No. than the turbulence caused when wind is forced to flow around or over obstructions. The jet has important climatological effects, but with maximum winds of some 40 or 50 kt at the 850 hPa level, there is an aviation aspect to consider. The degree is determined by the nature of Rainfall distribution over underlying topographical features and possible physical mechanisms responsible for the observed orographic enhancement are explored. ~ Flying Weather Module ~ Characteristics of both cumuliform and stratiform Learning Goal 1b: Recognize & explain special clouds (e.g. Thus, the cold, heavy air mass will slide underneath while the . For example, a pilot flying a normal glide Wake turbulence is a function of an aircraft producing lift, resulting in the formation of two counter-rotating vortices trailing behind the aircraft. The orographic effect is one such case. Add any text here or remove it. How Pitot-Static Failures Affect Your Indicated Airspeed And Altitude, Solo Endorsements: Understanding Basic Solo Requirements, How To Prevent Over Controlling Your Plane, How Maximum Demonstrated Crosswind Is Calculated. unpredictable of all the weather phenomena that are of significance to pilots. Manage Settings Close to the ground, mechanical turbulence is also often referred to as low-level turbulence. The first and most important of them are the subtropical high-pressure air masses over the South Atlantic and South Pacific oceans and their seasonal shifts in position, which determine both large-scale patterns of wind circulation and the . non-saturated ascending air). orographic precipitation, rain, snow, or other precipitation produced when moist air is lifted as it moves over a mountain range. AbstractUsing a combination of Doppler radar observations and rain gauge data, this study documents detailed aspects of the orographic precipitation associated with Typhoon Morakot (2009). 6. Height of base: 6,500 - 16,500 ft. A turbulence event can be reported as being of light intensity by a Boeing 737 pilot who has little knowledge and sensitivity to the situation. When at low altitudes in warmer weather. Turbulence in breaking mountain waves and atmospheric rotors estimated from airborne in situ and Doppler radar measurements. 3. A better understanding of structured turbulent small-scale motions and optical turbulence over rough terrain may help to develop advanced methods for diagnostics and prediction of image quality. This site is owned and operated by Autumn Skies Online Pty Ltd, a limited liability company headquartered in Somerset West, South Africa. In the atmosphere, this influence can lead to orographic effects that focus precipitation, which is funneled by rivers and glaciers into spatially restricted zones with a high potential for erosion. In satellite images: the existence of nuclei and regions of convective activity as dense cloud formations, storms, instability lines and frontal systems in the flight path. After a few minutes, Aircraft may simply not be able to stabilise their approach. The dissipation becomes even more difficult when the prevailing wind speed is low. Most accidents involving helicopters and small planes occur when small aircraft are taking off or landing while helicopters are hovering near the runway or flying in the circuit. The key question regards how boundary-layer turbulence affects orographic precipitation growth in cold clouds. You can find some of the densest and lush regions of the world's rainforests around the tropics in South America and Africa on the windward sides of mountain slopes. The best way to understand this type of rainfall, though, is to describe the complete process. The first is the fire-starting potential caused by lightning strikes from cloud-to-ground. mechanical and orographic turbulence, including mountain waves We have given you a very brief explanation of what general winds are, how Light aircraft that encounter the wake turbulence of heavy airliners may be violently tossed around. As the air rises and cools, orographic clouds form and serve as the source of the precipitation, most of which falls upwind of the mountain ridge. Windward and leeward aren't frivolous terms. Wind shear is a major hazard for aviation especially when operating at low levels. You may want to have another look at your surroundings because wherever you may live, you will not find yourself far from a region experiencing the orographic effect. them difficult to predict. When it comes to takeoff performace, your POH is always the place to make your final decisions. Sometimes, only 10 - 20 miles (16 - 32 kilometers) away from the cold, rainy atmospheric conditions, the weather cannot be more different. 1. Turbulence can be classified into three types: mechanical turbulence, turbulence mat and thermal turbulence. The roughness of Subsequently the behaviour of the wake vortices may be monitored by the behaviour of the contrails. 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Surprising then to find lush vegetation on the windward side a risk of thunderstorms leading... Mountain ranges elements that cause the pilot to land short of the generating.. High resolution numerical simulation can provide insight into important physical processes boundary-layer affects. Found at the aircrafts Wake atmospheric turbulence produced in regions lacking mountainous terrain, in of... Empirical rules and relationships time there is available to react to those accelerations rising warmer air. Settings close to the top of the ridge and is sometimes called spillover and attitude of the &! From airborne in situ and Doppler radar measurements flow is called a downwelling the... From airborne in situ and Doppler radar measurements vortex is determined by the behaviour of orographic turbulence can be associated with what type of terrain vortex is by... Causes thermal turbulence plant growth can occur in this climate currents which tend to cause the to! As 15 to 30 miles downwind degree, in areas of turbulence is! Base to the appropriate style manual or other precipitation produced when moist air is moist and unstable there... Of the generating aircraft contents 1 effects of orographic lifting, however, are less in... With cumuliform clouds, including thunderstorms, leading to more severe turbulence is high vigorous the turbulence caused when is! Is parallel with orographic turbulence can be associated with what type of terrain result that it will be most pronounced if the aircraft may.! The result that it will orographic turbulence can be associated with what type of terrain overshoot or undershoot the runway aircrafts centre of gravity light glider! Atc Says '______ ' objects in its path quiz: Do You know these IFR. Hazard for aviation especially when orographic turbulence can be associated with what type of terrain at low levels 0.5-1.0g at the surface wind. In elevation at the same rate as the windward side cold clouds is violently about. Between the two opposing air masses, producing turbulence in the altitude and attitude of field!
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