The power of the air can go from being barely noticeable to producing catastrophic damage. Air on a calm day can be hardly noticed and only really felt when running or driving into the air. When the wind speed is extreme such as in a tornado or hurricane, the power of the air can be very destructive. The force that is produced from the air increases exponentially as the wind speed increases. Thus, a doubling in wind speed will much more than double the force produced by the wind speed. The force of the air significantly reduces the fuel efficiency of a car. The air can be thought of as a wall of air the car is continuously driving through. This produces a frictional drag that slows the car down. Thus, the accelerator has to be pressed harder (and more gas used) to counteract this. The friction between the tires and road also slows the car down. For these two reasons (friction with the air, and friction with the road), a car will slow down when the accelerator is no longer pressed. Any time someone goes driving with the windows down, they will experience what a strong wind feels like. A car driving 60 mph into a calm wind will produce a relative wind to the driver that is 60 mph. This produces a significant force on the car! Future cars driving on roads on the moon or on Mars will be more fuel efficient since there is very little wind resistance there. The force of the wind is very important in meteorology because of the immediate influence it has on our daily lives. Windy days can be more uncomfortable than light wind days. Gusty winds from thunderstorms can produce damage. Extreme winds of a tornado and hurricane can produce catastrophic damage. Windy days can feel colder than light wind days when the temperature is cold. A nice breeze can be refreshing on a hot day. A windy day can lead to a bad hair day. Assessing the power of the wind was been a challenge in the field of meteorology. The challenge lies is labeling how dangerous a particular wind speed is. Any wind speed can be dangerous. For example, a 30 mph wind could blow a branch down onto a car. As wind speed increases, then it becomes increasing more likely that the wind will produce damage, especially in populated areas. The challenge is where to draw the line between a severe thunderstorm wind and a non-severe thunderstorm wind. For an extended period of time, the line has been drawn at 58 mph. At or above 58 mph, the convective winds from a thunderstorm are considered severe. Keep in mind though, wind speeds below 58 mph can also produce damage but the damage tends to be less. The challenge of labeling the threat of the wind has happened with tornadic winds. For many years the standard was the Fugita scale (F-scale). The use of the enhanced Fugita scale (EF-scale) has followed to try to correct problems with the original Fugita scale such as what range of wind speed best correlates with a particular observed damage. Hurricane winds have not been immune from the controversy also. For many years the standard for analyzing the destructive power of the wind in a hurricane is the Saffir-Simpson hurricane scale. The threshold for a hurricane is 74 mph while the threshold for a significant hurricane is 111 mph. Controversies have occurred when labeling a hurricane using this scale. The CAT value of a hurricane is based on limited observations from aircraft, buoy reports and other data. Typically the hurricane has a higher CAT that what the vast majority of observations experience due to surface friction slowing the wind and the hurricane CAT wind being based on a maximum sustainable wind (and not a typical wind within the eye wall). The CAT value of a hurricane can change rapidly. As a hurricane approaches land the wind can decrease significantly. Also, more surface friction is experienced over land as compared to open ocean and this slows the wind. Thus, it is not uncommon for the wind speed to decrease as a hurricane makes landfall. Exceptions to this can occur when a hurricane is developing rapidly as it approaches land. Another exception can happen when a hurricane approaches relatively small islands in the open ocean. The winds from a weaker hurricane can produce significant damage also since the winds can blow for many hours and from different directions. The quality of the building construction can determines which structures survive the hurricane and which do not. |