What a sailor needs to know about meteorology

What a sailor needs to know about meteorology

Everyone who went to sea under sail knows perfectly well how important it is to know the weather forecast, especially for those who want to take yacht for rent so as not to waste your money and ruin your weekend. Going to sea on a yacht without thinking about the weather forecast may not be a safe idea. Over time, a beginner yachtsman gradually begins to "read" signs that indicate possible changes in the strength and direction of movement of air masses. This helps to prepare in advance for various atmospheric "surprises", and to ensure safe sailing. Usually, wind speed can be determined by the changes that occur under its influence. This can be the roughness of the sea, the strength of the flag waving, the swaying of branches, and even the spread of smoke from chimneys. The yachtsman needs to constantly learn to observe and analyze.

But in order to correctly determine possible weather changes, you need to know about the basics of meteorology, to know why the wind occurs, what its speed and strength depend on, what cyclones and anticyclones are.

The general name for meteorology, adopted in many countries, is "physics of the atmosphere", which fully corresponds to its meaning. Meteorology, as a scientific and applied area of knowledge about the processes occurring in the earth's atmosphere, began with descriptions of various observations of the weather. The types of clouds, their combinations, sequence of weather changes, depending on certain atmospheric phenomena, were studied and classified. The study of such records, which were kept continuously for many decades, revealed the annual frequency of recurrence of weather phenomena. This made it possible to compile the world's first weather calendar, which has been successfully used by sailors for almost 100 years. The invention of the thermometer, hygrometer, anemometer, weather vane and rain gauge made it possible to bring scientific justification for the study of weather.

The development of technological progress required more specific forecast weather maps. In terms of economic and technological advancements, the creation of an international meteorological organization has become imperative. The draft of a new World Meteorological Convention, prepared back in 1939, was never adopted due to the outbreak of war.

The World Meteorological Convention, under the auspices of the UN, was signed on October 11, 1947, but the harmonization of common codes, nodes, schemes, symbols, instruments and methods of observation, legal and administrative issues delayed the start of the work of the international organization of meteorology. WMO (World Meteorological Organization) officially began its work on March 17, 1951.

The physical state of the atmosphere can be characterized using meteorological elements, which include: temperature, humidity and air pressure, wind direction and speed, and other quantities. Meteorological stations around the world, under the authority of WMO, send observational data to a single focal point at WMO, where they are studied and systematized. A certain combination of several meteorological quantities can affect atmospheric processes, which can result in rain, snow, thunderstorm, fog or blizzard. The totality of meteorological quantities and phenomena gives the concept of "weather". Today meteorology is an independent science closely related to mathematics, physics, geography, chemistry, hydrology and oceanology. The development of space technologies has found application in meteorology.

But what should a yachtsman know without data from the weather service? First of all, you need to have knowledge about the cause of the winds, about their characters. Wind arises in the process of moving air masses. Air mass is a huge volume of air, several kilometers thick. On the horizontal plane, the air mass covers areas up to several thousand kilometers. The temperature and humidity of such a mass is approximately the same throughout the volume.

According to physical laws, the ratio of atmospheric pressure and temperature in gases (and air is a gaseous mixture) are closely interrelated. In areas where the air warms up more, there is a low pressure, and vice versa, high when it cools.

Due to physical laws, air masses always tend to move from areas with high pressure to areas with lower pressure. This movement of air relative to the surface of the earth is called wind. To study the distribution of atmospheric pressure at the earth's surface, special isolines of atmospheric pressure values are used - isobars. They are usually plotted on a geographic map, first fixing the pressure values for a certain period (for a given area), and then connecting places with the same values with lines - isobars. Isobars are used to map neotectanic movements. On isobaric maps, you can find areas of high and low pressure in certain areas. Air is accelerated in direct proportion to the rate of pressure drop, taking the shortest path, at right angles to the isobar. This angle (perpendicular) is called the normal. The sphericity of the Earth and its rotation act on the wind with the same force as on all other moving objects - the so-called Karyolis force, which affects the direction of movement of the transported air. The wind deviates from the normal, spinning clockwise (in the northern hemisphere), and counterclockwise (in the southern hemisphere), relative to the direction of travel.

Mariners should be aware that over the sea, where the air friction against the surface is much less, this deflection increases, and the wind blows almost along the isobar. Wind speed is measured in meters per second. Mariners determine the strength of the wind in knots (nautical miles per hour). The wind speed in knots corresponds to twice the m / s of the indicated speed. Sometimes the strength of the wind is measured in points (according to the Beaufort scale), according to which, complete calm is indicated by 0 points, and a hurricane - 12 points.

Usually, indicating the direction of the wind, they call the side of the light from where it blows. Waves and eddies of enormous size, arising on the surface of the Earth, form cyclones and anticyclones, the occurrence of which provokes strong winds, followed by a storm.

Cyclones occur when huge air vortices revolve around a center with the lowest atmospheric pressure, sucking in air, and an anticyclone, in which air is blown out of a center with high atmospheric pressure. The scale of such phenomena is enormous, even by planetary standards. Powerful tropical cyclones (typhoons) have always attracted the attention of meteorologists. Terrifying in their destructive power, these cyclones form in the tropics, between 5 and 20 degrees latitude, in both hemispheres of the Earth. A satellite photo allows you to see this giant thundercloud pulling in spiral banks of clouds. Tropical cyclones arise only above the sea surface, due to the rise of warm and humid air from the heated area of the ocean. The wind speed is rapidly increasing, and on average, near the water surface reaches 40-50 m / s, with individual gusts up to 100 m / s.

Huge waves, 10-15 meters high, sweep away everything in their path, and flooding coastal areas bring death and destruction. About 80 tropical cyclones with storm and hurricane winds occur on Earth every year. These atmospheric disasters are so extraordinary that it is even customary to give names to typhoons . The approach of a cyclone is predicted by the appearance of cirrus filamentous clouds in the sky, floating across the sky in parallel stripes. Over time, cloudiness increases and low and dense clouds appear.

There are areas in which air masses of different temperatures collide when moving. Such areas are called a front, which can be either warmer or colder. Although in any case, approaching the front promises a change in weather and precipitation.

This phenomenon is explained by physical processes when warm (and therefore lighter) air mixes with oncoming, colder air. Mixing and creeping on top of each other, air masses generate condensation, which falls down in the form of precipitation. If warm air passes over cold, lingering rain in summer, or fine snow in winter, guaranteed.

If cold air passes over warm air, it gradually heats up by itself, and condensed moisture forms huge cumulus clouds that carry torrential thunderstorms. There is a so-called "onclosure front" - a closed front of two cyclones. Three air currents interact in it - two colder ones displace the warmer air upward, which leads to precipitation of different intensity.

According to experts 2yachts, there are winds arising from the large temperature difference between land and sea. Such winds are called breezes. The land is known to be warmer than the sea surface. But the land also cools faster than the sea. When heated during the day, warm air over land, according to the laws of physics, rises up. A reduced pressure is created over land, where colder air masses rush from the sea. At night, the process is exactly the opposite, the direction of the air changes to the opposite. Such winds have a speed of 3-5 m / s, but in the tropics, due to the large temperature difference, the breeze speed can be higher.

There are belts of constant east winds - trade winds. The trade winds are near the equator, in both hemispheres. The speed of trade winds near the sea surface is 5-8 m / s, and these winds do not carry precipitation. The temperature difference serves as the basis for the emergence of another cold and gusty wind. This is bora, the wind blowing from land. It occurs when a cold wind passes over mountain ranges and rushes rapidly towards the heated sea surface. Gathering a significant storm speed, bora causes strong excitement, sometimes not abating for a week. There is a bora in our latitudes, and it blows in the Caspian (Baku) and Black (Novorossiysk) seas, in Croatia and Montenegro, sometimes covering the entire Adriatic Sea. Yachtsmen who travel in those parts are warned about this, but the sailors themselves must constantly monitor changes in the atmosphere.

Clouds have always helped in this, observing the shape of which one can fairly accurately determine the coming weather changes.

  • Stratus clouds. Dark gray, "heavy" clouds bring with them rains or snowfalls, moderate in intensity, but lasting about 10 hours;
  • Stratus clouds. Looks like a gray fog hanging high above the ground, not very dense. Usually these clouds foreshadow the falling of fine snow, ice needles, drizzle or snow grain;
  • Cumulonimbus clouds. The majestic mountains and towers that these clouds look like portend intense but short-term rainfall. Sometimes, when the cloud is black in color and "ragged" edges, it can be a squall cloud. A yacht that is not prepared for a heavy gust of wind can be overturned, so the sails must be removed in advance. Sometimes a squall cloud accompanies the appearance of a tornado. This vortex moves with the cloud, and can move by the sea for several kilometers. The duration of its existence is short, only a few minutes. Although its destructive power is much less than that of a land tornado, it should be avoided.

Showers and thunderstorms that carry cumulonimbus clouds usually end in a beautiful rainbow. Modern technologies help people to monitor various natural phenomena in the most careful way. There are already known cases when, based on the conclusion of meteorologists, thousands of people were evacuated, fleeing hurricanes and typhoons, hundreds of ships and yachts, thanks to warnings from weather stations, avoided encounters with danger. But even in our century, the century of technological progress, the old, time-tested knowledge about natural phenomena, every yachtsman needs to know.

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