EFFECT OF NATURAL PHENOMENON ON MACHINES.

Abstract

In this lecture, we will be looking at a certain natural phenomenon that lurks in the upper and lower atmosphere waiting for the right condition to unleash havoc on man, its environment and one of its greatest machine made to make life and transportation safer and faster. We will also look at its causes ,effects and methods of handling it.

Introduction

In the recent years, some giants and unforeseen dangers lies in the sky which has the capabilities of  taking lives and wrecking havoc to aircraft and empowering other natural disaster like thunderstorm and tornadoes to do the utter damage unimaginable to man. One of this unpopular but seemingly dangerous weather phenomenon is known as wind shear. Windshear causes air crashes, empowers tornadoes that always wreck havoc on people property especially in the gulf coast area and the Florida keys of the united state and other part of the tropics and temperate regions of the world and causes interference to radio waves and satellite signals thereby hampering communication.

What is wind shear?

Wind shear refers to a change in wind speed or direction with height in the atmosphere. Wind shear, sometimes referred to as wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere.
Wind shear can also be referred to a rapid change in winds over a short horizontal distance experienced by aircraft, conditions that can cause a rapid change in lift, and thus the altitude, of the aircraft.
Some amount of wind shear is always present in the atmosphere, but particularly strong wind shear wind shear is important for the formation of tornadoes and hail.
Larger values of wind shear also exist near fronts, extra tropical cyclones, and the jet stream.
Wind shear in an atmospheric layer that is clear, but unstable, can result in clear air turbulence. wind shear itself is a micro scale meteorological phenomenon occurring over a very small distance, but it can be associated with mesoscale or synoptic scale weather features such as squall lines and cold fronts. It is commonly observed near microburst and downbursts caused by thunderstorms, fronts, areas of locally higher low level winds referred to as low level jets, near mountains, radiation inversions that occur due to clear skies and calm winds, buildings, wind turbines, and sailboats.

EFFECT OF WINDSHEAR

·         Sound movement through the atmosphere is affected by wind shear, which can bend the wave front, causing sounds to be heard where they normally would not, or vice versa.

·         Strong vertical wind shear within the troposphere also inhibits tropical cyclone development, but helps to organize individual thunderstorms into longer life cycles which can then produce severe weather. The thermal wind concept explains how differences in wind speed at different heights are dependent on horizontal temperature differences, and explains the existence of the jet stream.

·         Wind shear has a significant effect during take-off and landing of aircraft due to their effects on control of the aircraft, and has been a significant cause of aircraft accidents involving large loss of life within the United States and other part of the world.

TYPES OF WIND SHEAR

DIRECTIONAL WIND SHEAR

Directional wind shear is the change in wind direction with height. In the image (below), the view is looking north. The wind near the surface is blowing from the southeast to the northwest. As the elevation increases the direction veers (changes direction in a clock-wise motion) becoming south, then southwest, and finally, west.

SPEED SHEAR

Speed shear is the change in wind speed with height. In the illustration below, the wind is increasing with height. This tends to create a rolling affect to the atmosphere and is believed to be a key component in the formation of mesocyclone which can lead to tornadoes.

Strong vertical shear is the combination of a veering directional shear and strong speed shear and is the condition that is most supportive of super cell.

VERTICAL SPEED AND DIRECTIONAL WIND SHEAR

This is a significant increase in wind speed with height and a significant change of wind direction with height.

                        CLASSIFICATION OF WIND SHEAR

WET WINDSHEAR

These are wind shear that often occur during thunderstorm and rainfall

DRY WINDSHEAR

These are windshear that often occur in the absence of rain near the ground.

CAUSES OF WINDSHEAR

Microburst

A microburst is a small very intense downdraft that descends to the ground resulting in a strong wind divergence. When rain falls below cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. The cool air descend and accelerates as it approaches the ground, when this cool air approaches the ground , it spread out in all direction and the divergence of the wind is the signature of the microburst. In humid climates, microburst can also generate from heavy precipitate. The size of the event is typically less than 4 kilometers across and is capable of producing wind of more than 100mph causing significant damage. Their lifespan is around 5-15minutes. This condition has been linked to commercial plane crashes especially during taking off and landings. Researchers believe that a 15 to 45 seconds warning will allow the pilot to deal with this hazard.

TORNADOES

·         A tornado is a rotating funnel shaped loud that snakes toward the ground from the base of a thunder cloud. Tornadoes usually form in connection with thunderstorm

 Microburst  schematic from NASA. Note the downward motion of the air until it hits ground level, then spreads outward in all directions. The wind regime in a microburst is completely opposite to a tornado.

Downburst

A downburst is defined as a strong downdraft

WINDSHEAR AND HOW IT AFFECTS AN AIRPLANE

Windshear is a generic term referring to any rapidly changing wind currents or a strong outflow from thunderstorm causing rapid changes in the three dimensional wind velocity just above ground level. A type of weather phenomenon called "microburst" can produce extremely strong windshear, posing great danger to aircraft. Microbursts are local, short-lived downdrafts that radiate outward as they rush toward the ground. As a downdraft spreads down and outward from a cloud, this outflow causes a headwind that increases airspeed and also creates an increasing headwind over the wings of an oncoming aircraft. This headwind causes a sudden leap in airspeed, and the plane lifts. If the pilots are unaware that this speed increase is caused by windshear, they are likely to react by reducing engine power and this increases the descent rate. However, as the plane passes through the shear, the wind quickly becomes a downdraft and then a tailwind reducing lift generated by the wings. This reduces the speed of air over the wings, and the extra lift and speed vanish. Because the plane is now flying on reduced power and low speed descent it is vulnerable to sudden loss of airspeed and altitude. The pilots may be able to escape the microburst by adding power to the engines. But if the shear is strong enough, they may be forced to crash.

Greatest danger: Takeoff and landing

Windshear poses the greatest danger to aircraft during takeoff and landing, when the plane is close to the ground and has little time or room to maneuver. During landing, the pilot has already reduced engine power and may not have time to increase speed enough to escape the downdraft. During takeoff, an aircraft is near stall speed and thus is very vulnerable to windshear.

METHOD OF DETECTING WINDSHEAR

There are three airborne predictive and detective windshear sensor systems. Pilots need 10 to 40 seconds of warning to avoid windshear. Fewer than 10 seconds is not enough time to react, while more than 40 seconds is too long, atmospheric conditions can change in that time. Three systems are being flight-tested to give advance warning of windshear:

MICROWAVE RADAR

This system sends a microwave radar signal ahead of the aircraft to seek raindrops and other moisture particles. The returning signal represents the motion of those raindrops and moisture particles, and this is translated into wind speed. Microwave radar works better than other systems in rain but less well in dry conditions. Because it points toward the ground as the plane lands, it picks up interfering ground returns, or "clutter." However, researchers are progressing in efforts to eliminate this interference. The radar transmitter is made by Rockwell International's Collins Air Transport division in Cedar Rapids, Iowa. NASA's Langley Research Center has developed the research signal-processing algorithms and hardware for the windshear application.

DOPPLER LIDAR:

 This is a laser system called Doppler LIDAR (light detecting and ranging) which reflects energy from "aerosols" (minute particles) instead of raindrops. This system can avoid picking up ground clutter and noises like (moving cars, etc.) and thus has fewer interfering signals. However, it does not work as well in heavy rain. The system is made by Lockheed Corp.'s Missiles and Space Co., Sunnyvale, Calif.; United Technologies Optical Systems Inc., West Palm Beach, Fla.; and Lassen Research, Chico, Calif.

INFRARED

This is a system that uses an infrared detector to measure temperature changes ahead of the airplane. The system monitors the thermal signatures of carbon dioxide to look for cool columns of air, which can be a characteristic of microburst. This system is less costly and not as complex as others, but does not directly measure wind speeds. This system is made by Turbulence Prediction Systems in Denver, Colo.

WIND SHEAR ALERT SYSTEM USING GROUND BASED RADAR.

This uses a low-level wind-shear alert system has been installed on the ground at more than 100 U.S. airports. Wind speed and directional sensors report to a central computer, and controllers can alert pilots in the event windshear is detected. But the systems cannot predict when wind shears are approaching. However, a ground-based radar (Terminal Doppler Weather Radar) system has been tested at Orlando, Fla., and Denver Stapleton airports and is scheduled to be stationed at more than 40 other airports. Even with such systems installed, however, airborne detection will still be needed because windshear is a global phenomenon and most airports will not have predictive, ground-based systems installed.

FAA mandate: Airlines must install windshear sensors

The FAA directed that all commercial aircraft must have onboard wind shear detection systems by the end of 1993. Three„ American, Northwest and Continental„ received exemptions until the end of 1995 in order to install and test predictive wind shear sensors rather than "reactive" systems that do not report the condition until an airplane already has encountered it.

CONCLUSION

Windshear over the years has done great damage by causing air crashes, empowering storm and cyclone and causing interference to radio signals which is necessary for communication and satellite television network, though vulnerability of man has been reduced to the barest minimum, much still needs to be done to curtail the effect of windshear and its aftermath.