🌍 What meteorology is and why pilots need it
The atmosphere is the air envelope around Earth. The air is a mix of gases whose molecules move around by different processes, but are also pulled down by gravity. The net effect of air molecule’s interaction with surrounding objects and surfaces is called atmospheric pressure. In the atmosphere, the pressure represents the weight force of the molecules above certain level. The higher we go, the less molecules weight above, thus pressure decreases with altitude. 📏 1. Measuring Pressure Pressure is measured in Pa (Pascal) and represents the effect of 1 N force applied to 1 m2. Pressure is also measured in bar. 1 millibar = 10² Pa = 1 hPa An older unit called the atmosphere (atm) represents the pressure at sea level and this is the pressure equalizing the weight of 760 mm column of mercury: 1 atm = 760 mm Hg = 101 325 Pa ≈ 1 bar 📊 2. Pressure in Aviation & Weather Charts On weather charts, altitude is given in pressure instead of meters above sea level. One reason is that in the past, airplanes used barometric altimeters to maintain certain altitude above ground. Nowadays, use of pressure as a vertical coordinate simplifies thermodynamic computations used for weather forecasts and charts. The main charts are: ► 850 millibar (~1500 meters above sea level) ► 500 mb (~5500 m ASL) ► 300 mb (~8000 m ASL)
☀️ Solar energy and how air circulates
As the air is transparent, the main source of energy in the atmosphere comes from Sun’s heating of Earth’s surface. Usually, the higher we go, the colder it gets. Again, the Sun is the main engine of processes in the atmosphere and there is a big variety of them because of Earth’s irregularities (land and water, mountains and flatlands, white snow and dark fields, etc.) and also because of daily and seasonal changes of sun’s radiation for different location on Earth’s sphere. 🔄 1. The Temperature Circulation Cell For example, when the Sun shines on a dry dark field, it will heat the air above, expand it and lifts number of molecules up. At certain level, there will be more molecules above and thus higher pressure, compared to a neighbor unheated area at the same altitude. Air moves from higher pressure (H) to the lower pressure (L). The adding of air above the unheated neighboring area will increase the pressure at ground level there and again air will move along the surface to the heated area. As long as there is a temperature difference between two neighboring surfaces, there will be a constant generation of low pressure over the warmer surface and high-pressure above the colder surface. This elementary temperature circulation cell explains a lot of events like sea breeze circulation, valley-mountain circulation, monsoons, global circulation…
🌬️ Wind: where it comes from and how to read it
Air circulation depends on the temperature difference and air mass properties like instability, moisture, etc. The temperature difference circulation cells appear in all kind of sizes and often suppress or enhance each other. Most visible effect on us is the horizontal airmass movement along the ground surface, which we call wind. 🪂 1. Wind and Paragliding Wind has great effect on the very light paragliders with relatively big surface. Strong winds create big forces during takeoff and landing, high groundspeeds and turbulence during flight. At the same time, pilots are looking for wind and air circulations to fly higher and further. Thus, studying the wind is essential for their safety and progress. First, beginners start with measuring the wind on take off, then gradually making the habit of constant observation for building mental models of the wind’s character until being able to find, explain and even predict the wind and circulations. 🧭 2. Wind Direction & Measurement Wind direction is given from where wind comes from: Pilots on the ground often help landing paragliders by showing them with one or two hands where wind comes from, especially when there is no windsock nearby. The wind strength is measured by anemometers (wind meters) in [m/s], [km/h] or [kt]. 1 m/s = 3.6 km/h = 2 knots 📈 3. Wind Classifications in Paragliding ►Calm: up to 1 m/s (forward launch; a lot of running = big launch area) ►Light: 1-3 m/s; (both forward and reverse launch; still good running is needed) ►Moderate: 4-6 m/s; (reverse launch, but forward also possible, some running needed) ►Strong: 7-10 m/s; (reverse launch; only experienced pilots can fly; turbulence in the air; wind is close to the paraglider's airspeed = chance to be lifted upward in front of the hill and blown backward after takeoff) ►Very strong: 11-13 m/s; (too strong to take off; strong turbulence in the air; landing backward; difficult to control the canopy on landing and pilot dragged on ground) ►Squall: above 14 m/s. (too dangerous to fly) 🧐 4. Wind Character ►Constant: speed doesn’t change with more than 2 m/s within 2 minutes. ►Gusty: speed changes more than 2 m/s within 2 minutes. ►Steady: direction doesn’t change more than 1 rumb (22.5°) within 2 minutes. ►Variable: direction changes more than 22.5° within 2 minutes. ►Laminar: doesn’t change speed and direction. Note: Gusty and variable winds are signs of turbulence! It is important to distinguish average wind speed from momentary gusts. For example, the gusts can make you fly backward for a moment, but if the average wind is less than your airspeed, then you still go forward. If gusts exceed 100% of average wind speed, then air is probably too turbulent for beginners. The same is valid if moderate or strong wind changes its direction by more than 45°. Wind can be lifty or sinky i.e. wind is not horizontal but has upward or downward vertical component.
🚀 Launch tactics and wing control
The most critical part of a flight is getting away from the ground after take off. Taking off in lifty air increases your height and gives you more time for reaction and recovery from unpredictable situations. Common reason for accidents is when beginners ignore the message of wind cycles and just look for easy wind for inflation. Experienced pilots spend years of studying the wind cycles and build intuition when it’s good to take off and when it’s better to wait. You should think of the bigger picture, including what happens after take off, not just of having an easy takeoff. Many accidents happen during inflation, because beginners cannot control their wing efficiently and let it take them in undesired directions. There are even good pilots who’ve grown on easy take offs and when they go to different places and conditions, they have surprisingly bad take offs. Air time is not substitute for good control of wing on ground, which require weeks and months of training ground handling.
📉 Wind gradient
When we measure wind on the ground, we should be aware of the wind gradient – change of wind strength and direction with height. Wind gradient occurs, because the lower layers of the moving air mass are slowed down by the friction with the ground. Thus, we should expect increase of wind with height. It’s a common reason for accidents to take off in strong wind, being lifted up and blown backward by the stronger higher winds into the turbulence behind the hill. Wind gradient also changes our gliding trajectory close to the ground and we should expect increase of our groundspeed before landing. Wind gradient can be easily seen outside: if you lay in the grass, you don’t feel much wind, but when you sit or stand up you’ll feel more wind, and if you climb something high like a car, a building or a hill, then you will feel the increase of wind with height. Isolated gusts can cause sudden lift or sink due to increase or decrease of airspeed flow around the wing. Layers with strong wind gradient can cause the same but for longer time and magnitude. The wind is just a wind for the beginner, but for the experienced pilot wind has direction, strength (temporary and average, min and max), character (laminar, gusty, variable), gradient, ascending or descending component. Additionally, the experienced pilot is sensitive about wind tendencies of change of its parameters. Befriending with the wind happens after understanding the big picture – the circulations which drive the wind.