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METEOROLOGY AND ITS IMPORTANCE

Meteorology studies the behaviour of the atmosphere. The barometer, thermometer and rain gauge are still the basic instruments of meteorology, although radar, electronic and most recently the orbiting weather satellites which observe clouds, radiation and other phenomena in space have appeared. The very recent success made in space science will produce further development in the science of meteorology.

It is necessary to use all these data to predict with any degree of accuracy the weather for the coming week or even for the next few days. The trans-pacific or trans-atlantic flights cannot be left to chance. The route forecast is very essential to the safety of these flights.

The scientific forecasting of weather depends not only on local observations, but also on observations taken at the same time over a wide area of the Globe, both at the surface and high into the atmosphere. The data collected must be analysed by trained meteorologists who then use them in forecasts of the weather. The quality of the forecast depends on the quality of the observations taken by the meteorological technician.

THE ATMOSPHERE

The atmosphere, in the dry state, is a mixture of many gases three parts of nitrogen and one of oxygen-almost 99% of the whole, and than argon, hydrogen, neon, carbon dioxide, ozon, helium and some others.

But the atmosphere is never entirely dry, as water vapour is always present in varying proportions. The vapour bahaves as a gas, but frequently the vapour condenses into liquid or solid form as fog and mist, cloud and precipitation. The composition of the atmosphere is unchanged up to great heights.

For the lower layer-the temperature changes with height. The layer characterized by marked fall of temperature with height is called the troposphere, its upper boundary is tropopause.

The height of the tropopause is the greatest near the equator and decreases in higher latitudes.

The layer above the tropopause is stratosphere. It is characterised by a temperature, which is practically constant with height or perhaps increases slightly.

There are great differences in the weather conditions between troposphere and stratosphere.

After stratosphere begins mesosphere and thermosphere.

METEOROLOGICAL SERVICE FOR AVIATION

Meteorological service for international aviation is provided by meteorological authorities designated by States. Details of the services to be provided for international aviation are determined by each State in accordance with provisions of ICAO Annex 3 and with air navigation agreement. Meteorological offices and stations provide information required for operational planning, flight operations, the protection of aeronautical equipment on the ground, and for various other aeronautical users. The information provided includes observation of actual weather and forecast, it is made at aerodrome meteorological offices and is disseminated to aeronautical users.

Forecasts of en-route conditions issued by meteorological offices are normally those prepared by world area forecast centres and regional area forecast centres. It permits meteorological watch offices to concentrate on keeping watch on weather conditions in their flight information regions and meteorological offices at aerodromes to concentrate on local aerodrome forecasting, keeping watch over local (aerodrome) conditions and issuing warnings of weather conditions (e.g. wind shear, thunderstorms).

PUBLIC WEATHER SERVICE

Objective: To contribute to the safety, health, welfare, comfort, and convenience of the public, and to meet the needs of all segments of the national economy for general weather information.

Description of Service: The Public Weather Service provides for the general public current weather information, forecasts, and warnings which are distributed in cooperation with the news media. These products also serve as the starting point for most interpretive and specialized forecast services, including the many detailed services provided by industrial and consulting meteorologists. For long-range weather planning needs, nonperishable climatological information is available at each public service office.

Approximately 320 offices cooperate directly and indirectly in serving the public. These include the National Meteorological Centre, the National Hurricane Center, the National Hurricane

Center, Eastern Pacific and Central Pacific Hurricane Centers, the National Severe Storms Forecast Center, the State Forecast Offices, and the local and zone forecast offices.

The principal products are state, zone, and local forecasts. These and the functions of the Regional Weather Center and Warning Coordination Centers are discussed on the next few pages.

METEOROLOGICAL OFFICES

Meteorological offices serving aviation are normally located at aerodromes in which case they are called aerodrome meteorological offices. These offices provide briefing, consultation and flight documentation or other meteorological information: often they also display weather charts, reports and forecasts. Much of their information is obtained from regional area forecast centres (RAFCs) or from other meteorological offices which may be located in different countries. However, not all aerodromes have a meteorological office and for such aerodromes the national aeronautical information publications (AlPs) indicate the name and location of meteorological office designated to supply meteorological information to operators and other users.

Certain meteorological offices are designated by regional air navigation agreement to maintain a watch over meteorological conditions in a specified FIR or control area. They issue inlormation on the occurrence or expected occurrence of potentially hazardous en-route weather conditions which may affect the safety of aircraft operations (SIGMET) and supply this and other weather information to their associated units.

SURFACE OBSERVER

There are two kinds of surface weather observations-synoptic and aviation. Synoptic observations are complete general observatios made every six hours and transmitted in an international code to all major forecast centres throughout the world. The code is concise and independent of all language barriers.

The aviation observations are more specialized observations which are made hourly except in poor flying conditions, when many additional observations may be required.

In making surface observations, the observer must observe and record the pressure, temperature, humidity, wind speed, precipitation, cloud types etc.

The observer is constantly watching the developing weather systems. It is a very responsible job. A number of meteorological instruments are used: hydrogenfilled balloons, cellorneter (for measuring cloud heights), transmissometer (for measuting horizontal visibility).

ATMOSPIIERIC CONDITIONS CAN BE MEASURED BY INSTRUMENTS

The changes in temperature, humidity and the speed of air masses can be measured by instruments made for that purpose.

However, before instruments were invented to measure atmospheric conditions, man made his own observations of wind and sky, the behaviour of birds and animals, and came to associate certain phenomena with types of weather.

The task of the meteorologist is no easy one. A good forecast for a given region can be made up to 24 hours ahead and sometimes longer by taking into account the character of that region.

Weather forecast is now a regular feature of radio and TV broadcasts. The weather bureau supplies the information, and sometimes the wrong one.

Air observations and accurate forecasts are necessary for the safety of ships and aircraft.

The layer of the earth's atmosphere which begins about 9 to I I km above the earth is known as the stratosphere. Weather phenomena, as commonly understood, do not occur in the stratosphere.

Nearly all weather phenomena occur in the lower level of the atmosphere up to a height of about 9,11 km at the poles and 17 km at the equator. This is the region of most interest to the forecaster studying temperature, humidity, wind-speed and the movement of air masses.

TEMPERATURE Heat is a form of energy. It is an expression of molecular activity. Temperature is a measurement of heat and thus experesses the degree of molecular activity. Since different substances have different molecular structures, equal amounts of heat applied to equal masses of two different substances will cause one substance to get hotter than the other. This characteristic is expressed by saying that the substances have different heat capacities (specific heat). Every substance has its own unique specific heat. For example, a land surface becomes hotter than a water surface when equal amounts of heat are added to each. The degree of "hotness"or "coldness-of a substance as measured with a thermometer is known as its tem perature.

The earth's surface is heated during the day by the sun_ Incoming radiation to the earth is called "insolation". Heat is radiated from the earth by outgoing radiation, called "terrestrial radiation". Cooling results at night as terrestrial radiation continues and insolation ceases.

The earth's daily rotation about irs axis, its yearly motion about the sun (revolution), the tilt of the earth's axis, and the uneven heating of the earth's surface are the basic causes of seasonal and geographical variations in general weather conditions over the world. The heat energy radiated by the sun is indirectly the major motivating force for all weather phenomena over the earth.

MOISTURE

Water, an important part of the atmosphere, is found in three states: solid, liquid and gaseou.s. As a solid, it takes the form of snow, hail, sleet, frost, ice-crystal clouds, ice-crystal fog. As a liquid, it is found as rain, drizzle, dew, and as the minute water droplets composing clouds and fog. In the geseous state, water forms an invisible vapour.

Water vapour is the most important element in the production of clouds and other visible weather phenomena. The availability of water vapour for the production of precipitation largely determines the ability of a region to support life. At the same time, however, it creates problems and sometimes hazards For the pilot when it changes into the liquid or solid state.

Most of the atmosphere's moisture is concentrated in the lower troposphere, and only rarely is it found in significant amounts above the tropopause.

The oceans are the primary source of moisture for the atmosphere but it is also furnished by lakes, rivers, swamps, moist soil, snow, ice fields and vegetation. Moisture is introduced into the atmosphere as water vapour, and may then be carried at great distances by the wind befor it is eventually removed as liquid or solid precipitation.

CLOUD FORMS AND CLOUD AMOUNT

The observation of clouds begin by identification of all cloud forms present. This should be based primarily on the definitions, specifications and descriptions given in the International Cloud Atlas (WMO, 1956). The Atlas also provides illustrations of the various cloud forms for comparison and gives detailed coding instructions. For general use at stations where cloud observations are regularly made, the Atlas, which was specially prepared for the use of observers, is a very good guide. The specifications of cloud forms are also given in WMO Publication.

The problem of identifying cloud forms is not always easy: the classification of clouds into typical forms is of very great use. Observations of cloud can be made by keeping as close and continuous a watch as possible on their development. It is not enough to make a short examination of the sky at the observation hour.

The scale which should be used for recording the amount of cloud is given in the international meteorological Code 2700, which is shown in the table. The unit of measurement is the "okta" (meaning one eighth of the area of the sky), and ball (meaning one tenth of the area of the sky).

WIND

Pressure and temperature variations result in two kinds of motion in atmosphere: the movement of air in ascending and descending currents (vertical motions), and the horizontal flow of air known as "wind".

But now these motions are of primary interest to the pilot because they affect the flight of aircraft in takeoff, landing, climbing, speed, and direction. They also affect the degree of smoothness of the air and bring about changes in weather which may make a difference between safe flight and disaster.

It is difficult to distinguish between cause and effect of wind, pressure and temperature because of their close interrelationship. Actually, wind affects the very thing that causes it in a never ending struggle to obtain equilibrium-just as the ocean tends to maintain a constant level. Wind occurs because there are horizontal pressure differences in the atmosphere. But horizontal pressure differences, are primarily the result of uneven temperature distribution. On the other hand, wind very definitely affects both the horizontal and vertical distribution of temperature. It also is the main mechanism through which the mass (weight) of the atmosphere is redistributed, thus causing pressure to change.

At the transportation agency for water vapour, wind has an important effect of the formation of fogs and clouds and on the production of precipitation.

DEW POINT

The dew point is that temperature, at a given pressure, to which air must be to become saturated. When this temperature is below freezing, it is sometimes called the "frost point". The difference between the actual air temperature and the dew point temperature is an indication of how close the air is to saturation

The dew point is included in Aviation Weather Reports because it is a critical temperature, indicating the behaviour of

water in the atmosphere. When the surface air temperature is higher than the dew point, and the difference between the temperatures is increasing, an existing fog and low clouds are likely to dissipate because the air is becoming capable of holding much lower than the freezing point, and sometimes even below - 60°C, but rarely below - 40°C. This situation called "supercooling", is prevalent in clouds to a temperature of about - 15°C. Aircraft penetrating supercooled clouds are likely to accumulate ice because the impact of the aircraft may induce freezing of the droplets.

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166 Кб, 20 октября 2014 в 18:29 - Россия, Москва, АГЗ МЧС России, 2014 г., pdf
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