# Meteorology and flights

Below is a small FAQ about what is dangerous and what is not for an airplane, and what you need to know about the weather.

As a rule, passengers overestimate the danger of various phenomena, such as turbulence or lightning, which hit the wing of an airplane. But they don’t know anything about the danger of discharge (like static), which arises due to the friction of air particles on the surface of the aircraft. Or about the danger of collecting a couple of tons of ice on the hull during landing and landing a little faster than planned.

Aircraft de-icing prior to departure.

So let's talk about the weather, dear paranoid.

### Why planes fly at high echelons, and not, say, 800 meters from the ground

Because the higher you climb, the less air density there. And the lower the density of air, the lower its resistance, and therefore, the engine thrust is required less, which provides significant savings. That is, the task is to calculate the optimum, which will allow you to spend the least amount of fuel, taking into account three factors:

1. That a glider still needs an environment to rely on.
2. Need oxygen for engines.
3. In this case, the descent and ascent to the desired height should not be more costly than possible fuel economy.

As a result, we have current flight conditions. 75% of the mass of the atmosphere is below the echelons that occupy the passenger sides of Moscow - Petersburg, that is, about 10 kilometers. At 20 kilometers, 95% of the mass will be below, and at an altitude of 100 kilometers - 99.9%. At an altitude of approximately 400 kilometers you can already meet the ISS.

### What is kinetic temperature?

The atmosphere is uneven, and the conditions at the point where the aircraft is located directly affect its flight. For example, kinetic temperature is a characteristic that determines the effect of air gas particles on a ship due to the occurrence of friction. The run length, permissible flight altitude, and fuel consumption are very dependent on the current kinetic temperature.

Basically, bimetallic plates (metal resistance thermometers) are now used to measure temperature near the ground. For radio sounding, semiconductor thermometers are used.

At the airport there are periodic changes in temperature (colder at night than during the day) - this is determined by the heat exchange along the vertical of the atmosphere. Non-periodic are associated with advection (horizontal movement of air masses). Usually coldest in the daily rhythm happens before dawn, and the warmest thing is around 15 o’clock in the afternoon. The amplitude of the diurnal temperature variation changes depending on the type of surface: for example, in troughs as in natural thermal accumulators, it is higher, and in mountains less. The land cools and heats faster than water. In the north, the reflective properties of surfaces (ice, for example) are also important.

In general, the higher the colder. But there are layers (up to 2-3 kilometers) where, due to atmospheric processes, the temperature rises as you climb: these are the so-called inversion zones. At the boundary of the inversion zone, the temperature difference can reach 10 degrees. Accordingly, the density of air changes dramatically. These layers inhibit the movement of air, under them there is a concentration of water vapor and various particles.

### What else do you need to know for educational program?

Humidity is determined by a hygrometer. This is a good old biotech: the greater the humidity, the longer the human hair. An alternative is a psychrometer: measuring the temperature with a dry and wet thermometer, taking into account the difference. The density of moist air is less than the density of dry.

Wind can be caused by Coriolis force, thermal effects. The wind in aviation has an expiration date: the question is where the measurement was taken and how long you can expect it to be relevant. The stronger the wind, the higher the chance of changing its speed and the lower the chance of changing direction. You can fly to the indicated place in 5-6 hours, and there will still be a good good wind.

Cloud- accumulation of vapor particles and ice crystals (a snowflake is a large ice crystal). From clouds from -10 to -40 degrees, the most frequent precipitation begins to pour. At temperatures higher, drizzle is obtained, lower - nothing falls out.

Clouds are dangerous with deterioration of visibility (especially diagonal), thunderstorms, threat of icing, hail, wind shear. At the bottom of the cloud is a transition layer: it begins where the pilot loses the horizon and ends where the ground under the plane is no longer visible. Usually it is from 50 to 200 meters. The height of the lower boundary of clouds above the airfield can change twice in 10 minutes. It is usually measured with a radar.

### Visibility

Eye resolution - 1 arcminute. That is, two points can be separated from each other under this condition. For objects with angular sizes less than 15 minutes, contrast and brightness are very important. The atmosphere reduces brightness and contrast with distance, which is why air transparency is important. The resolution of the eye is considered constant, and the transparency of the atmosphere changes, plus various atmospheric phenomena (fog or rain) can be added. This makes meteorological visibility. There is also an RVR indicator, or visibility on the runway: this is the visibility of marking the strip or its lights. As in the case of meteorological visibility, it does not include things like the glass material of the cockpit, fatigue, direction of light, raindrops on the windshield and so on.

Visibility can be greatly reduced by phenomena such as haze (particles of dust, sand and smoke), sand storms (sand rises to about 15 meters), dust storms (here dust rises to 3 kilometers), sand and dust vortices (rarely above 90 meters) , blizzard, fog, haze and so on. Fog, by the way, can be man-made, for example, as a result of the operation of a thermal power plant in frosts of -20 degrees. The pilot must understand the properties of each of these phenomena and the mechanisms of their formation and development.

Also, the pilot must understand how the flows in the atmosphere are arranged: the principles of formation and movement of cyclones and anticyclones, what happens at their borders and so on. All this affects air currents at various scales.

Take-off and landing during precipitation (turbulence conditions, with a wind of more than 5 m / s) are made with a margin that the flight characteristics of the vessel may deteriorate.

### Icing

This is the deposition of ice on the engines and streamlined parts of the aircraft. Icing degrades aerodynamics, lift, speed, maneuverability, engine power, and interferes with radio communications. The most important thing is the additional mass, which grows as the ice layer increases. When ice is torn off the surface of the fuselage or wing in flight, its pieces can get on rotating blades and seriously damage the engine. Especially if the engine is at the rear.

Icing can occur as a result of freezing of water on the surface of an airplane or as a result of sublimation of water vapor from air on the surface. The second process is more characteristic of sudden changes in temperature, for example, when crossing inversions.

Kinetic heating of the aircraft from friction against air prevents the occurrence of icing. As a rule, most cases (90%) are observed at speeds up to 600 kilometers per hour. That is, takeoff and landing are dangerous. Therefore, before taking off during rain, it is important to treat the aircraft with anti-icing fluid, and at landing, do not pass through hazardous areas.

### Turbulence zones

These are the places where a plane’s chatter is possible. As a rule, wind strength and temperature change there. Simplifying, mechanical or orographic turbulence is when the air mass from acceleration hits an uneven terrain or deforms against the mountains. There is also thermal turbulence due to uneven heating of the surface - remember, we used to talk about the reflective properties of different things like ice on the surface?

Even turbulence can occur in a clear sky "just like that" - with jet flows or due to convection.

Turbulence zones are usually less than 100 kilometers horizontally and 1 kilometer vertically. Strong turbulence in an area of ​​this size is observed in the “core” of 40 kilometers and 30 meters, respectively. There is such a zone most often up to five hours.

They are looking for turbulence zones with radars and geostationary satellite imagery, plus their appearance can be predicted. When entering the zone of strong turbulence, the crew must leave it, and you can independently change the level and report this to the dispatcher.

### Thunderstorm and electrical phenomena

If lightning strikes a plane, then, as a rule, nothing bad will happen: it has no grounding. Rarely there are holes in the structure at the discharge site. But nevertheless, the most dangerous thing in a thunderstorm is precisely electrical phenomena, including disturbing communications.

Lightning strikes on the difference of potentials, therefore you do not see everything from the earth: they happen between clouds, inside clouds or from clouds to the earth. Sometimes even up. The height of the lightning can be up to 95 kilometers, in the case of "ordinary" linear lightning - up to 20 kilometers with a diameter of several tens of centimeters. The current strength of such a lightning will be about 200 thousand amperes, the temperature - about 20 thousand degrees Celsius. Moreover, a weak discharge (leader) clears the way for the strong. Usually a leader hits the ground from a cloud, and the main discharge spreads in the opposite direction.

Near zones of thunderstorms there are strong flows, lightning, hail, squalls, tornadoes and microexplosions. Plus, there are favorable circumstances for icing, so pilots should fly around thunderstorm zones, since they are quite easy to detect.

The plane, even during normal flight (outside the thunderstorm zone), is gaining electric charge. In crystalline clouds, for example, you can charge the board very quickly, because the plane has some properties of a large capacitor, and the cloud is “rough”. When changing the altitude, the electric field strength changes, and discharges between the aircraft and the surrounding air can be obtained. From all the protruding parts of the aircraft (for example, from the ends of the wings), discharges can strike, so there are special devices that reduce this effect.

The discharge itself resembles a flash during electric welding. It can damage communication devices, radar, can burn a hole from 1 to 20 centimeters in the body. From such strong discharges, the protruding parts of the aircraft usually begin to glow noticeably.

Board electrification can be noticed by the behavior of a number of devices in advance. Usually, it is possible to avoid the accumulation of a strong charge, but if suddenly it does begin to form, then the pilots turn off one radio station (so that it is backup in case of a discharge), turn on the cockpit lighting (so that the flash does not blind at night) and leave the danger zone.

### We wish you a pleasant flight!

Most weather events are either predicted or detected from the board, airfield sensors or satellites. It is believed that the technical hazard factor is minimized, that is, the technique allows either to predict any dangerous situation, or to get out of it if its prediction is impossible. The last known major incident with the weather occurred during the sintering of volcanic ash inside the engines, when all four power plants failed at the side. The crew managed to cope with these minor inconveniences and successfully landed the board. An update of locators has been released, new rules for flying around active volcanoes have appeared. With the last major eruption in Europe, everything went relatively smoothly. It is also worth noting the recent disaster RRJ-95B RA-89098, there is a preliminary report on it .

In Russia, pilots and controllers undergo a mandatory meteorology course and deeply professionally understand what happens in flight around an airplane.

Therefore, dear paranoiacs, you can increase the safety of your trip dozens of times if you go to the airport by train. Or transfer from the front seat of the taxi near the driver to the rear and there you can also fasten your seat belt. A simple estimate of the probability suggests that the main threats are in this area, rather than in the air.

The first photo of the post was provided by Yu.V. Filatov (FBO “A-Group”)

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