University of British Columbia - ATSC 113 Final Outline. 141 Pages

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University of British Columbia - ATSC 113 Final outline Learning Goal 1a. Identify & classify clouds, and relate them to local and larger-scale weather systems. Normal clouds are classified into t... wo categories:  Convective clouds or cumuliform clouds (Cu) look like stacks of cotton balls, and are associated with updrafts.  Layer clouds or stratiform clouds (St) look like sheets or blankets that can extend hundreds of kilometers horizontally. Cumuliform Stratiform Special Clouds Learning Goal 1b. Recognize special clouds (e.g. castellanus, billow, lenticular, rotor, banner, fractus, etc.) Clouds in unstable air aloft - castellanus — Look like small castle turrets. Are a clue that the atmosphere is becoming unstable; thunderstorms possible later in the day. - billow (K-H wave) clouds — Indicate wind shear (change of wind speed or direction) and clear-air turbulence (CAT) at aircraft altitudes. Clouds associated with strong winds across mountains - lenticular (mountain-wave) clouds — Indicate vertical wind oscillations and possible mountain-wave turbulence. Sailplanes like the updraft portion of the waves, because they can "surf" the wave and fly very long horizontal distances. Commercial aircraft hate the waves because they often mean a very bumpy ride at all altitudes for the whole time while flying over the mountains. - rotor clouds — Indicate severe or extreme turbulence at low altitudes due to mountain waves. The rotors can break off aircraft wings and cause pilots to lose control of their aircraft during take-off and landing. Can also affect sailors if the rotors occur over water (lakes or coastal regions) downwind of mountains. - banner clouds — (Click here for another photo.) Form on downwind side of mountain peak. Indicate strong turbulence touching the downwind side of a tall, isolated mountain peak. Clouds formed by extra heat, updrafts, or turbulence - pyrocumulus — Form over forest fires and volcanoes. Indicate a forest fire so strong that the heat and moisture released can make a thunderstorm in the smoke. - pileus — Form over fast-growing cumulus clouds. Interesting to watch, but they are harmless, and don't affect flying, sailing or snow sports. - fractus / scud — Form in turbulent humid air near the ground. These scud clouds indicate high humidity (such as due to drizzle falling from higher clouds) and strong winds at low altitude. Clouds formed by humans - fumulus — Water-droplet clouds over cooling towers. Interesting to see, though harmless for flying, sailing, or snow sports. - contrails — Aircraft condensation trail. Indicate the turbulent wing-tip vortices behind aircraft. Small aircraft can be flipped upside down if they accidently fly into a wing-tip vortex. Military pilots hate contrails, because they reveal the aircraft to the enemy. Cloud Coverage Learning Goal 1c. Relate cloud coverage amounts to the visual appearance of the sky. The fraction of the sky (celestial dome) covered by cloud is called sky cover, cloud cover, or cloud amount. It is measured in eights (oktas) according to the World Meteorological Organization (WMO). Table 6-7 gives the definitions for different cloud amounts, the associated symbol for weather maps, and the abbreviation (Abbr.) for aviation weather reports (METARs = Meteorological Aviation Reports). For aviation, the altitude of cloud base for the lowest cloud with coverage ≥ 5 oktas (i.e. lowest broken or overcast clouds) is considered the ceiling (see Learning Goal 1d). Sometimes the sky is obscured, meaning that there might be clouds but the observer on the ground cannot see them (see Learning Goal 1i). For obscurations, the vertical visibility (VV) distance is reported as a ceiling instead (see Learning Goal 1e). How observers on the ground try to estimate sky cover by eye A tricky aspect of estimating cloud cover is that lower-altitude clouds block the view of higher-altitude clouds that might or might not really be there. To be conservative (i.e. extra safe), weather observers should always assume that if any clouds are visible at mid or higher levels, then clouds at those same levels are assumed to exist even if they are hidden by lower-altitude clouds. Also, the white arc in Figure 3-4 represents altitudes (feet), and this assumes that the weather observer can correctly measure or estimate the altitudes. While vertically pointing ceilometers can give accurate cloud base directly over the airport, there are no accurate measures off-vertical, unless pilots coming in to land or taking off radio in pilot reports (PIREPs) of cloud base heights. As discussed in Learning Goal 1d, unfortunately, cloud height estimates by eye are rarely accurate. With this conservative method, weather observers always never underestimate the cloud coverage, but often overestimate the coverage. So when cloud "observations" are reported, such as in a Meteorological Aviation Report (METAR), the actual cloud coverage might not be as bad as reported. But you cannot count on this always being the case. Cloud coverage as viewed from an aircraft If you are flying at an altitude just above or just below the clouds, then in your slant or oblique view, the sky will look much more overcast than it really is. Learning Goal 1d. Define the cloud ceiling, estimate its altitude, and relate it to cloud coverage amounts. Pilots flying according to visual flight rules (VFR, see Learning Goal 1g) need to see where they are going. But in clouds, you can't see anything — so VFR pilots need to stay out of clouds. If a layer of clouds covers more than half the sky, then these clouds act like a lid or ceiling for VFR aviation, and constrains VFR flights to fly in the clear air below it (with some exceptions). According to the International Civil Aviation Organization (ICAO), ceiling is the height above ground level (AGL) of the lowest cloud base (bottom of the cloud) that is below 20,000 ft (6,000 m) that is covering more than half the sky (i.e. cloud coverage amount is either "broken" or "overcast" —see Learning Goal 1c). Ceilings are reported as a height, e.g. the ceiling is 500 feet above ground level. In cases where there are such poor visibilities at ground level that a ground-based weather observer cannot see whether there are any clouds or not, then ceiling is reported as the vertical visibility (see Learning Goal 1e) within that surface-based poor-visibility layer. Examples would be in fog, or in forest-fire smoke, or in a dust storm. Even pilots flying under instrument flight rules (IFR, see Learning Goal 1g) are concerned with ceilings, in order to be able to land at airports. Ceilings are measured with:  Laser ceilometers — Send up a burst of light, and measure how long it takes the light from cloud base to reflect back.  Ceiling balloons — Watch a red helium-filled latex balloon as it rises, record the balloon flight time until it disappears into the cloud, and then calculate the ceiling altitude based on typical rise rates of those balloons.  Pilot reports — Ascending planes after take-off or descending planes approaching to land can report their altitude when they passed through cloud base.  Weather-observer estimates — These are the worst estimates, because it is difficult to judge distance by eye, UNLESS the estimates are from tall towers or mountain tops that stick up into the clouds. CAVOK = Ceiling and Visibility are OK (i.e. good for VFR flight) Visibility Learning Goal 1e. Contrast horizontal visibility, vertical visibility, and runway visual range (RVR), and discuss how they affect aviation. Aviation defines horizontal visibilities, vertical visibilities, and slant visibilities. Horizontal visibilities are the ones measured and reported at airports, because it is the one most relevant for safety. If you hear the word "visibility" without any adjectives in front, then assume it is a horizontal visibility. Horizontal Visibility Visibility is a measure of how far away you can see a black object during daytime, or how far away you can see a bright light at night. It is measured as a distance. The World Meteorological Organization (WMO)recommends kilometres or metres. For this reason, visibility rules exist for flight safety. If visibility is good and exceeds a certain threshold (a condition called visual meteorological conditions, VMC), then the pilot is allowed to fly under the Visual Flight Rules (VFR). However, when visibility is poor (instrument meteorological conditions, IMC), only specially-trained pilots flying aircraft with special instruments can fly, on instrument flight rules (IFR), and following specific directions given by air traffic control (people on the ground with radar and other tracking methods to make sure you don't hit other aircraft, and can get where you want to go without hitting any obstacles). Measuring Visibility The word "transmitted" is used in opposite ways in some of the figures above. For the transmissometer, the transmitted light is the dimmed light that is received at the detector. For the scattering visibility meters, "transmitted" is the incident laser light that is emitted from the laser, i.e. the transmitter refers to the light source. Runway Visual Range (RVR) For busy airports, sometimes these automated visibility sensors are installed close to a runway to measure runway visual range (RVR). This indicates how far (in meters or feet) ahead a pilot can see along a runway centerline. RVR is usually reported only when visibilities are poor (i.e. less than about 2,000 m or less than 6,000 feet). RVR 2600 feet ≈ 0.5 statuate mile. RVR 1200 feet ≈ 0.25 statuate mile. Vertical Visibility (VV) In the diagram below, the top frame shows clouds (grey) and non-cloudy air (blue). The height of the cloud base above ground defines the ceiling altitude. In the bottom frame is an obscuration (e.g. dust, smoke, fog, mist, etc., sketched as bluish grey) that reduces visibility in all directions. In obscuration conditions (i.e. an indefinite ceiling), the limit that you can see vertically is the vertical visibility (VV), and is used instead of the normal ceiling height. Vertical visibility is determined by either: 1 The distance that an observer can see vertically into an indefinite ceiling; 2 The height corresponding to the top of a ceiling light projector beam; 3 The height at which a ceiling balloon (a bright red balloon filled with helium) completely disappears during the presence of an indefinite ceiling; or 4 The height determined by the sensor algorithm at automated stations (based on horizontal visibility). Symbols on Weather Maps Learning Goal 1f. Recognize and interpret weather and obscuration glyphs on weather charts. In the tables below, the glyph is the symbol that is used on weather maps. Also listed for completeness is the text abbreviation for the same phenomenon, which is used in Meteorological Aviation Reports (METARs). For this course, focus only on the glyphs. Weather and Storm Glyphs Precipitation Glyphs The intensity of the precipitation is indicated by the number and arrangement of those glyphs, as described in Table 9-3b. Also, the descriptor for the precipitation can be included. Obscuration Glyphs Storm Glyphs Regulations: VFR vs. IFR Learning Goal 1g. Explain the difference between visual & instrument flight rules (VFR, IFR) and meteorological conditions (VFC, IFC), and how they affect aviation. VFR = Visual Flight Rules means that you fly by mostly looking out the window. You need good visibility and need to stay out of clouds. By looking with your eyes, you can:  navigate (see where you are relative to landmarks on the ground) so you can go toward your destination without hitting mountains, tall towers, other aircraft, or flying through airspace where you are not allowed;  control the aircraft — namely, see whether it is climbing (nose up), descending (nose down), or turning (banked left or right);  find airports and land on the appropriate runway. Visual Flight Conditions (VFC) is the name given to weather that is good enough for you to fly VFR. Conditions for which VFR is allowed, but for which visibility is poor and/or cloud-base is low, are called Marginal VFR (MVFR). IFR = Instrument Flight Rules mean that you can conduct most of the flight by NOT looking out the window. Instead, you:  navigate using onboard GPS map displays and other navigation signals  control the aircraft by looking at the instruments on your dashboard (called a control panel on aircraft)  get to airports by following the instructions and clearances given by air traffic controllers(ATC) who keep track of your flight and make sure you arrive at your distination without hitting anything (mountains or other aircraft or tall towers). You are required to file a flight plan before you start, so that ATC knows where you want to go. To fly IFR, you need to:  be specially trained to believe the instruments and to ignore your normal physiological stimuli like inner-ear signals (that could cause vertigo) and "seat of the pants" feelings of pressure or G-forces on your body  have an aircraft with the proper instruments and radios, all in good working order  have the proper charts (paper or electronic)  You can fly IFR in good and in bad weather. Bad weather is called Instrument Meteorological Conditions (IMC), i.e. weather for which VFR flight is not allowed.  Nonetheless, even IFR pilots must stay out of thunderstorms (due to violent turbulence, hail, lightning, etc.) and out of volcanic ash (which sandblasts the engines, causing them to fail). Also, not all aircraft are built with the equipment to remove ice that forms on the wings and propellors, so even IFR pilots without the right aircraft need to stay out of clouds with supercooled cloud and rain drops. Generic Rules for Determining IFR vs. VFR from ceiling and visibility Category Ceiling (AGL = above ground level) Visibility (SM = statute miles) IFR less than 1,000 ft AGL and/or less than 3 SM MVFR between 1,000 ft and 3,000 ft AGL and/or between 3 and 5 SM VFR more than 3,000 ft AGL AND more than 5 SM Fog Learning Goal 1h. Anticipate when fog might occur based on location, humidity, temperature, winds, and cloudcover, and how fog affects aviation. Fog Formation and Dissipation Fog is a cloud that touches the ground. Most fog is made of tiny liquid water droplets that are falling so slowly through the air that they seem suspended. If the fog is made of supercooled tiny liquid water droplets (unfrozen liquid water at temperatures below freezing), then it is called freezing fog, because the supercooled droplets can freeze instantly when they touch something like an airplane or runway. Ice fog is made of tiny ice crystals (water that is already frozen). Fog can form due to two mechanisms: 1. When water is added to unsaturated (non-foggy) air, or 2. When unsaturated air is cooled to its dew-point temperature (the temperature at which water vapor starts to condense into liquid droplets). Sometimes both mechanisms work together to make or maintain fog. Cooling is common at night, which is why fog is most likely during late night and early morning. If the air is not very humid, then fog is less likely, because (1) there might not be enough water available to add to the air to make it saturated (foggy), or (2) the air might not get cold enough to reach its dew-point temperature. Conversely, fog is more likely in humid air, and most likely in cool humid air. Cool air is denser (heavier) than warm air, so the cool air often flows downhill and settles into valleys. For this reason, many fogs form in low spots or valleys as valley fog. Unfortunately, airports are often in valleys. On windy nights, the wind makes turbulence that mixes cool humid air near the ground with warmer drier air aloft. The resulting mixture is often too warm and dry to become fog. So, fog usually forms when the winds are relatively slow or near calm. Conversely, if fog already formed at night when winds were light, then the fog will dissipate if the wind speed increases. On nights with clear skies, the ground surface radiates heat upward to space. As the ground loses heat, it gets colder, and the cold ground cools the air above it by contact. If the air is cooled sufficiently, and has sufficiently high humidity, then fog can form. If there is a deep layer of humid air near the ground, then the ground surface does not cool as much, but the deep layer of humid air cools directly by radiating heat to space. If this humid layer cools enough, then a deep fog layer can form that is difficult to dissipate. On nights with substantial cloud cover, the clouds prevent the ground from cooling rapidly, because the clouds are radiating heat back to the ground.This blanketing effect by the clouds often prevents the ground (and the air touching the ground) from cooling sufficiently to make fog. Types of fog: Radiation: During clear, nearly-calm nights the ground cools by infra-red radiation to space. The cold ground cools the air that touches the ground. These fogs often form first as a very shallow fog, and gradually get thicker (deeper, and lower visibility) as the night progresses. If the fog gets deep enough, then IR cooling happens from fog top instead of from the ground, which quickly creates a deep fog layer that is difficult to dissipate. Advection: Humid air blows over a colder surface, causing the air temperature to decrease to the dew-point temperature. - Example: Warm humid air over the Pacific ocean flows over a cold Alaska ocean current just offshore of the west coast of North America. An example is the fog near San Francisco, California, as sometimes partially obscures the Golden Gate Bridge. - Another example: Humid cool air flows over snowy ground, causing the air to cool to its dew point. These fogs can form as thick layers, sometimes with sharp, well-defined front edges Upslope: When the wind blows air against a hill slope, the air is pushed upward. But upward-moving air cools adiabatically (without the transfer of heat) about 10°C for each 1 kilometer that it goes up. When the air rises sufficiently high and gets sufficiently cold, then fog can form. - As the top photo shows, these fogs often appear as if the mountain top is in a cloud. If you were on the mountain top, you would be in fog. If you were at sea level in this photo, you would see the same phenomenon as a cloud that the mountain sticks up into. - In the second photo example here, winds from the top left of the photo are blowing humid air toward mountains in the bottom right of the photo. As this air is funneled into the valleys and up the mountain slopes, upslope fog has formed. Precipitation or frontal: Precipitation fog or frontal fog is formed by adding moisture, via the evaporation from warm rain drops falling down through the initially-unsaturated cooler air below cloud base. It also forms from evaporation of other water drops, such as at waterfalls that produce large amounts of spray. Steam: Steam fog occurs when cold air moves over warm humid surfaces such as unfrozen lakes or oceans during early winter. The lake warms the air touching it by conduction, and adds water by evaporation. However, this thin layer of moist warm air near the surface is unsaturated (not foggy). But the warm humid air is more buoyant than the rest of the cold air that is flowing over the lake. The warm air rises, creating a shallow (5 to 100 m) layer of convective turbulence touching the ground. As turbulence causes the humid air to mix with the colder air higher above the surface, the mixture becomes saturated, which we see as steam fog. - One of the photos here shows steam fog over the warm water of a cooling pond next to a power plant. - You can also see steam fog after a rain storm when the sun comes out and heats the wet surfaces, such as roofs, docks, and farm fields. What you can do about fog Unfortunately, fog and aviation do not play well together. Fog is considered to be an "obscuration" that reduces horizontal visibility to 0.5 statute miles or less. Fog prevents pilots from seeing where they are going (i.e. very reduced visibilty), and prevents weather observers from seeing the sky condition and weather above the fog. Fog can eventually dissipate (disappear / evaporate) or lift (change from fog into a low cloud). This improvement to the flying conditions can happen as the sunlight starts to warm the earth's surface, or as winds pick up and blow the fog away or turbulently dilute it with drier air. The thicker the fog, the longer it takes to dissipate. If conditions are really bad, the fog can persist all day. Sometimes, the heat of a large nearby city, or the heat and turbulence from many commercial aircraft take-offs and landings at an airport, can delay the onset of fog, and can help dissipate it faster if it already exists Fog depends so strongly on local conditions that many of the national weather prediction models do not forecast it very well. However, local forecasters with knowledge and experience with their local fogs can do a reasonable job estimating when fog will disappear. Fog forecasting is extremely difficult, and I commend the forecasters. Obscurations Learning Goal 1i. Explain the nature of these obscurations: haze, smoke, blowing dust/sand, blowing snow, volcanic ash, and how they affect aviation. Obscurations (and their abbreviations) include: mist [BR; horizontal visibilities ≥ 1 km (i.e. ≥ 5/8 of a statute mile)], fog [FG; visibilities < 1 km (i.e. < 5/8 statute mile)], smoke (FU), volcanic ash(VA), sand (SA), haze (HZ), spray (PY), and widespread dust (DU). Snow and blowing snowcauses many hazards, one of which is as an obscuration. Mist Mist is when very small precipitation particles (small rain drops, only slightly larger than 0.5 mm) are gently falling through the air. Visibility is usually greater than 1 km, as compared to fog, which has lower visibilities. Mist can exist in air having a relative humidity between 95% and 100%. (Relative humidity is the ratio of actual water vapor in the air to the maximum water vapour possible in the air, expressed as a percentage.) Mist creates a thin grey-colored partial obscuration Smoke Smoke can come from factories, cars, and forest fires. The figure below shows smoke from the Fort McMurray, AB, forest fire in 2016. Volcanic Ash Ash from a volcanic eruption is not like the soft, fluffy ashes from a fireplace. Instead, volcanic ash consists of microscopic rocks with sharp edges. The smallest ash particles are so small that they settle out very slowly due to gravity. But while they are suspended in the air, they can cause serious problems to aircraft that accidently fly through the ash clouds. Volcanic ash is very abrasive, like sandpaper. If it gets in an aircraft internal combustion engine, it can cause bearings and gears to wear-out very quickly and fail or seize (stop turning). It can clog or contaminate the air filter, the oil filter, and the aircraft and passenger ventillation systems. It can sandblast the windscreen, making it difficult to see through. If it sticks to wings and other surfaces, it adds weight and changes the balance of the aircraft. Also, as ash hits the aircraft, it causes a static electric charge to build up, which at night can be seen as St. Elmo's fire (sparks writhing across the windscreen). And, as an obscuration, ash clouds reduce your visibility. If volcanic ash gets in jet/turbine engines, it can not only abrade the turbine components, but can also melt and re-solidify into glass-like coatings and protuberances that cause the turbines to break. Sand Strong winds over deserts and sandy regions can create sand storms, also called haboobs. Some of these haboobs are created by outflow winds from thunderstorms (Learning Goal 4b). Most of this sand falls out of the atmosphere fairly quickly after the winds subside. However, the finer sand particles can stay suspended for hours after the wind has decreased. The sand storms have a similar abrasive effect on aircraft and engines as does volcanic ash (but perhaps not melting in jet engines). The sand storms also greatly reduce visibilities and create large static electric charges, making flying and using navigation instruments difficult — so don't fly into haboobs. Sadly, even if your aircraft is tied down on the ground, the strong winds associated with a haboob can sandblast your aircraft. ::::::::::::::::::::::::::::::::::::::::CONTENT CONTINUED IN THE ATTACHMENT::::::::::::::::::::::::::::::::::::::::::::::::::: [Show More]

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