Essay On Wind Shear

Wind Shear

Wind shear is a change in wind speed and/or direction over a short distance (including the downdraughts and updraughts.) It may cause an aircraft to displace abruptly from its intended flight path. Wind shear can occur either horizontally or vertically and is often associated with strong temperature inversions or density gradients. It can occur at either high or low altitude but the ones that mainly affect the aircraft performance is the low altitude wind shear, also known as low level wind shear and it will be the one that we will consider in this report.

Sources and Formation Process

Wind shear can be produced from these four main sources
• Weather front
• Thunderstorm
• Temperature Inversion
• Surface Obstruction

Weather

When a downdraft caused by a thunderstorm flows down to the surface with an unusually high speed, downburst is generated. As the air reaches the ground it will separate out in different direction and will lose its vertical speed component rapidly which is dangerous to aircrafts. The speed of the downbursts can reach over 100 mph. There are two types of downburst, wet downburst and dry downburst. Wet downbursts are created by thunderstorms with high amount of rainfall while dry downbursts are created by thunderstorms that have little amount of rain.

Figure 2 is the diagram that illustrates the downburst and gust front. It also shows the affect of these wind shears on an aircraft as flying through it.

Temperature Inversion

Temperature inversion is a condition when the air above the ground is warmer than the air below it. This often happens when a less dense, warm air mass moves over on top of the cold air mass, which is more dense (cold front). This situation can occur during nighttime when the air near the ground loses its heat and cooled down rapidly. Since the air higher above the ground did not cool down, the temperature of this air is