🌍 What meteorology is and why pilots need it
The atmosphere is the air envelope around Earth. The air is a mix of gases, which 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 milibar = 102 Pa = 1 hPa An older unit called atmosphere represent 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 mili bar (~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…
