[, Music ]. This lesson will cover weather theory, understanding the theories behind weather helps a pilot make sound weather decisions based on the reports and forecasts obtained from a flight service station weather specialists and other aviation weather services.

The atmosphere is in constant motion. Certain factors combine to set the atmosphere in motion, but a major factor is the uneven heating of the Earth’s. Surface earth is warmed by energy radiating from the Sun.

The process causes a circular motion that results when warm air rises and is replaced by cooler air, because the earth has a curved surface that rotates on a tilted axis. While orbiting the Sun. The equatorial regions of the earth receive a greater amount of heat from the Sun than the polar regions.

Solar heating causes higher temperatures in the equatorial areas, which causes the air to be less dense and rise. As the warm air flows toward the poles, it cools becoming denser and sinks back toward the surface.

The unequal heating of the Earth’s surface, not only modifies air density and creates circulation patterns. It also causes changes in air pressure or the force exerted by the weight of air molecules. The actual pressure at a given place and time differs with altitude, temperature and density of the air.

These conditions also affect aircraft performance, especially with regard to takeoff rate of climb and landings to provide a common reference. The international standard atmosphere eisah has been established.

These standard conditions are the basis for certain flight instruments and most aircraft performance data standards. Sea level pressure is defined as 29.92 inches of mercury and a standard temperature of 59 degrees, Fahrenheit 15 degrees Celsius.

Atmospheric pressure is also reported in millibars, with one inch of mercury equal to approximately 34 millibars standard. Sea-Level pressure is one zero one: 3.2 millibars typical millibar pressure. Readings range from nine fifty two one: zero four zero millibars since weather stations are located around the globe.

All local barometric pressure. Readings are converted to a sea-level pressure to provide a standard for records and reports to achieve this. Each station converts its barometric pressure by adding approximately one inch of mercury for every thousand feet of elevation, for example, as shown above a station at five thousand feet above sea level.

With a reading of twenty-four point, nine two inches of mercury reports, a sea-level pressure reading of 29.92 inches of mercury using common sea level, pressure readings helps ensure aircraft altimeter ZAR, set correctly based on the current pressure readings.

As pressure decreases, the air becomes less dense or thinner. This is the equivalent of being at a higher altitude and is referred to as density altitude da as pressure decreases da increases and has a pronounced effect on aircraft performance.

The resulting uneven heating of the air creates small areas of local circulation called convective currents. Convective currents caused the bumpy turbulent air, sometimes experienced when flying at lower altitudes during warmer weather on a low-altitude flight.

Over varying surfaces, updrafts are likely to occur over pavement or barren places and downdrafts often occur over water or expansive areas of vegetation. Like a group of trees, this same condition is even more noticeable when flying in mountainous regions, as shown above, while the wind flows smoothly up the windward side of the mountain and the upward currents help to carry an aircraft over the peak of the mountain.

The wind on the leeward side does not act in a similar manner as the air flows down the leeward side of the mountain. The air follows the contour of the terrain and is increasingly turbulent. This tends to push an aircraft into the site of a mountain.

The stronger the wind, the greater the downward pressure and turbulence become wind shear is a sudden drastic change in wind speed, and/or direction over a very small area. Wind shear can subject an aircraft of violent, updrafts and downdrafts, as well as abrupt changes to the horizontal movement of a aircraft while wind shear can occur at any altitude.

Low-Level wind shear is especially hazardous due to the proximity of an aircraft to the ground. Directional, wind changes of 180 degrees and speed changes of 50 knots or more are associated with low-level wind shear low-level wind shear is commonly associated with passing frontal systems, thunderstorms and temperature inversions with strong upper-level winds, greater than 25 knots in general, the most severe type of Low-Level wind shear is associated with convective, precipitation or rain from thunderstorms.

One critical type of shear associated with convective precipitation is known as a microburst. A typical microburst occurs in a space of less than one mile horizontally and within 1,000 feet vertically.

The lifespan of a microburst is about 15 minutes during which it can produce down drafts of up to 6,000 feet per minute fpm. It can also produce a hazardous twin direction, change of 45 degrees or more in a matter of seconds, as shown above during an inadvertent takeoff into a micro burst the plane.

First experiences: a performance increasing headwind, figure 1, followed by performance, decreasing downdrafts figure; 2. Then the wind rapidly shares to a tailwind figure 3 and can result in terrain impact or flight dangerously close to the ground figure.

4. A pilot must be prepared to react immediately to the changes to maintain control of the aircraft. The stability of the atmosphere depends on its ability to resist vertical motion. A stable atmosphere makes vertical movement difficult and small, vertical disturbances dampen out and disappear in an unstable atmosphere.

Small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence. Extensive vertical clouds and severe weather cool dry air is very stable and resists vertical movement, which leads to good and generally clear weather.

The greatest instability occurs when the air is moist and warm as it is in the tropical regions. In the summer, typically, thunderstorms appear on a daily basis in these regions due to the instability of the surrounding air as air rises and expands in the atmosphere the temperature decreases.

There is an atmospheric anomaly that can occur, however, that changes this typical pattern of atmospheric behavior. When the temperature of the air rises with altitude, a temperature inversion exists, inversion layers are commonly shallow layers of smooth, stable air close to the ground.

The temperature of the air increases with altitude to a certain point, which is the top of the inversion. The air at the top of the layer acts as a lid keeping weather and pollutants trapped below. If the relative humidity of the air is high, it can contribute to the formation of clouds, fog, haze or smoke resulting in diminished visibility.

In the inversion layer, surface based temperature inversions occur on clear cool nights when the air close to the ground is cooled by the lowering temperature of the ground. The air within a few hundred feet of the surface becomes cooler than the air.

Above it, frontal inversions, occur when warm air spreads over a layer of cooler, air or cooler. Air is forced under a layer of warmer air. The above image relates to humidity. Humidity refers to the amount of water vapor present in the atmosphere at a given time.

Relative humidity is the actual amount of moisture in the air compared to the total amount of moisture the air could hold at that temperature, for example, if the current relative humidity is 65 %, the air is holding sixty-five percent of the total amount of moisture that it Is capable of holding at that temperature and pressure? The relationship between dewpoint and temperature defines the concept of relative humidity.

The dew point given in degrees is the temperature at which the air can hold no more moisture when the temperature of the air is reduced to the dew point. The air is completely saturated and moisture begins to condense.

Out of the air in the form of fog. Do frost clouds, rain, hail or snow as moist unstable air rises clouds often form at the altitude where temperature and dew point reach the same value when lifted unsaturated air cools at the rate of five point four degrees, Fahrenheit per thousand feet and the dew point temperature Decreases at the rate of one degree, Fahrenheit per thousand feet.

This results in a convergence of temperature and dew point at a rate of four point. Four degrees Fahrenheit apply the convergence rate to the reported temperature and dew point to determine the height of the cloud base.

As shown, above with an outside air temperature of 85 degrees, Fahrenheit at the surface and dew point at the surface of 71 degrees Fahrenheit, the spread is 14 degrees divide. The temperature dew point spread by the convergence rate of four point four degrees Fahrenheit and multiply by 1000 to determine the approximate height of the cloud base.

If air reaches the saturation point, while temperature and dew point are close together, it is highly likely that fog, low clouds and precipitation will form. There are four methods by which air can reach the complete saturation point.

First, when warm air moves over a cold surface, the air temperature drops and reaches the saturation point. Second, the saturation point may be reached when cold air and warm air mix. Third, when air cools at night through contact with the cooler ground air, reaches the saturation point.

The fourth method occurs when air is lifted or is forced upward in the atmosphere on cool calm nights, the temperature of the ground and objects on the surface can cause temperatures of the surrounding air to drop below the dew point.

When this occurs, the moisture in the air condenses and deposits itself on the ground buildings and other objects like cars and aircraft, this moisture is known as Dew and sometimes can be seen on grass in the morning.

If the temperature is below freezing the moisture is deposited in the form of Frost while do poses no threat to an aircraft, frost poses a definite flight safety. Hazard frost, disrupts the flow of air over the wing and can drastically reduce the production of lift.

It also increases drag which, when combined with lowered lift production, can adversely affect the ability to take off an aircraft must be thoroughly cleaned and free of frost prior to beginning a flight fog is a cloud that begins within 50 feet of the surface.

It typically occurs when the temperature of air near the ground is cooled. The airs dew point clouds are visible indicators and are often indicative of future weather for clouds to form there must be adequate water, vapor and condensation nuclei, as well as a method by which the air can be cooled.

When the air cools reaches its saturation point. The invisible water vapor changes into a visible state through the processes of deposition also referred to as sublimation and condensation, moisture, condenses or sublimates onto minuscule particles of matter like dust, salt and smoke known as condensation nuclei cloud type, is determined by its height shape and behavior.

They’re, classified according to the height of their bases as low middle or high clouds, as well as clouds with vertical development shown above low clouds. Are those that form near the Earth’s surface and extend up to 6,500 feet.

Agl, typical low clouds are Stratus, stratocumulus and nimbostratus. Fog is also classified as a type of low cloud formation. Clouds in this family create low ceilings, hamper visibility and can change rapidly.

Because of this, they influence flight planning and can make visual flight rules VFR flight, impossible middle clouds form around 6,500 feet AGL and extend up to 20,000 feet. Agl high clouds form above 20,000 feet.

Agl and usually form only in stable air, they are made up of ice crystals and pose no real threat of turbulence or aircraft. Icing clouds with extensive vertical development are cumulus clouds that build vertically into towering cumulus or cumulonimbus clouds.

The basis of these clouds form in the low to middle cloud based region, but can extend into high-altitude cloud levels. Towering cumulus clouds indicate areas of instability in the atmosphere and the air around and inside them is turbulent.

These types of clouds often develop into cumulonimbus clouds or thunderstorms. Cumulonimbus clouds contain large amounts of moisture and unstable air and usually produce hazardous weather phenomena such as lightning hail, tornadoes, gusty winds and wind shear to pilots.

The cumulonimbus cloud is perhaps the most dangerous cloud type since rising air currents caused cumulonimbus clouds. They are extremely turbulent and pose a significant hazard to flight safety. For example, if an aircraft enters a thunderstorm, the aircraft could experience updrafts and downdrafts that exceed 3,000 feet per minute.

In addition, thunderstorms can produce large hailstones, damaging, lightning tornadoes and large quantities of water, all of which are potentially hazardous to aircraft. We hope you learned a lot. Please help us spread the word about pilot training system and we look forward to further servicing your flight.

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