Wind is the horizontal movement of air along the earth's surface. Which side it blows depends on the distribution of pressure zones in the planet’s atmosphere. The article discusses issues related to wind speed and direction.
Weather vane or anemone
Perhaps a completely quiet weather will be a rare occurrence in nature, because you can constantly feel that a gentle breeze is blowing. Since ancient times, mankind has been interested in the direction of air movement, so the so-called weathervane or anemone was invented. The device is an arrow that rotates freely on a vertical axis under the influence of wind. She indicates his direction. If you define a point on the horizon from where the wind blows, then the line drawn between this point and the observer will show the direction of air movement.
In order for the observer to transmit wind information to other people, concepts such as north, south, east, west, and various combinations thereof are used. Since the totality of all directions forms a circle, the verbal wording is also duplicated by the corresponding value in degrees. For example, a north wind means 0 o (the blue compass needle points exactly north).
The concept of a wind rose
Speaking about the direction and speed of the air masses, a few words should be said about the wind rose. It is a circle on which lines are shown showing how air flows. The first mention of this symbol was found in the books of the Latin philosopher Pliny the Elder.
The whole circle, reflecting the possible horizontal directions of translational air movement, is divided into 32 parts on a wind rose. The main ones are north (0 o or 360 o ), south (180 o ), east (90 o ) and west (270 o ). The resulting four lobes of the circle are divided further, forming the northwest (315 o ), northeast (45 o ), southwest (225 o ) and southeast (135 o ). The resulting 8 parts of the circle are again divided each in half, which forms additional lines on the wind rose. Since the result is 32 lines, the angular distance between them is equal to 11.25 o (360 o / 32).
Note that a distinctive feature of the wind rose is the image of a heraldic lily located above the north icon (N).
Where does the wind blow from?
Horizontal movements of large air masses are always carried out from areas of high pressure to areas with lower air density. At the same time, it is possible to answer the question of what wind speed is by studying the location on the geographic map of isobars, that is, wide lines within which the air pressure is constant. The speed and direction of movement of air masses are determined by two main factors:
- The wind always blows from the areas where the anticyclone stands, in the areas that the cyclone covers. You can understand this if you remember that in the first case we are talking about areas of high pressure, and in the second case - low.
- Wind speed is in direct proportion to the distance that separates two adjacent isobars. Indeed, the greater this distance, the weaker the pressure drop will be felt (in mathematics they say the gradient), which means that the translational movement of air will be slower than in the case of small distances between isobars and large pressure gradients.
Factors Affecting Wind Speed
One of them, and the most important one, has already been voiced above - this is the pressure gradient between neighboring air masses.
In addition, the average wind speed depends on the topography of the surface over which it blows. Any irregularities on this surface significantly inhibit the translational movement of air masses. For example, everyone who has been at least once in the mountains should have noticed that there are weak winds at the foot of the wind. The higher you climb the mountainside, the stronger the wind is felt.
For the same reason, winds blow more strongly over the sea surface than over land. It is often corroded by ravines, covered with forests, hills and mountain ranges. All these heterogeneities, which are not above the seas and oceans, slow down any gusts of wind.
High above the surface of the earth (of the order of several kilometers) there are no obstacles to the horizontal movement of air, so the wind speed in the upper layers of the troposphere is large.
Another factor that is important to consider when talking about the speed of movement of air masses is the Coriolis force. It is generated due to the rotation of our planet, and since the atmosphere has inertial properties, any movement of air in it is deviated. Due to the fact that the Earth rotates from west to east around its own axis, the action of the Coriolis force causes the wind to deflect to the right in the northern hemisphere, and to the left in the southern.
Curiously, the indicated effect of the Coriolis force, which is insignificant at low latitudes (tropics), has a strong influence on the climate of these zones. The fact is that the deceleration of wind speed in the tropics and at the equator is offset by an increase in upward flows. The latter, in turn, lead to the intense formation of cumulus clouds, which are sources of strong tropical showers.
Wind speed meter
It is an anemometer, which is three cups located at an angle of 120 o relative to each other, and mounted on a vertical axis. The principle of operation of the anemometer is quite simple. When the wind blows, the cups experience its pressure and begin to rotate on the axis. The stronger the air pressure, the faster they rotate. By measuring the speed of this rotation, you can accurately determine the wind speed in m / s (meters per second). Modern anemometers are equipped with special electrical systems that independently calculate the measured value.
A cup speed wind device is not the only one. There is another simple tool called the pitot tube. This device measures the dynamic and static wind pressure, the difference of which can accurately calculate its speed.
Beaufort Scale
Information about wind speed, expressed in meters per second or kilometers per hour, says little to most people - and especially to sailors. Therefore, in the XIX century, the English admiral Francis Beaufort proposed to use some empirical scale for assessment, which consists of a 12-point system.
The higher the score on the Beaufort scale, the stronger the wind blows. For instance:
- The number 0 corresponds to the absolute calm. With it, the wind blows at a speed not exceeding 1 mile per hour, that is, less than 2 km / h (less than 1 m / s).
- The middle of the scale (number 6) corresponds to a strong breeze, the speed of which reaches 40-50 km / h (11-14 m / s). Such a wind is capable of raising large waves at sea.
- The maximum on the Beaufort scale (12) is a hurricane, the speed of which exceeds 120 km / h (more than 30 m / s).
Major winds on planet Earth
They are usually classified in one of four types in the atmosphere of our planet:
- Global. They are formed as a result of the different ability of continents and oceans to heat from sunlight.
- Seasonal These winds change depending on the season of the year, which determines how much solar energy a certain area of the planet receives.
- Local. They are associated with the features of the geographical position and topography of the area in question.
- Rotating These are the most powerful movements of the air masses that lead to the formation of hurricanes.
Why is it important to study the wind?
In addition to the fact that wind speed information is included in the weather forecast that every inhabitant of the planet takes into account in his life, air movement plays a big role in a number of natural processes.
So, it is a carrier of plant pollen and is involved in the distribution of their seeds. In addition, wind is one of the main sources of erosion. Its destructive effect is most pronounced in deserts, when during the day the terrain changes dramatically.
It should also not be forgotten that the wind is the energy that people use in economic activity. According to general estimates, wind energy accounts for about 2% of all solar energy falling on our planet.