In the past, compiling weather forecasts was much more difficult. Many activities had to be done manually, from observation data to a synoptic map, so that the current situation could be analyzed, and to provide the final forecast, which the synoptic was developing based on the knowledge of processes controlling the atmosphere movement, own intuition and experience. Known in the meteorological environment is the fact that on the basis of the same synoptic maps, each synoptician can give a slightly different prognosis, and this is due to the two last factors (intuition and experience) that make such a forecast very subjective.
Currently, thanks to the hydrodynamic models of the atmosphere and the availability of high-performance computers, it became possible to create Numerical weather prediction, ie forecasts calculated using supercomputers on the basis of equations describing the behavior of the atmosphere. Such forecasts are objective forecasts, i.e. no matter how many times the calculations for the same initial state of the atmosphere were made, the obtained result would be the same.
The earth’s atmosphere is a complex dynamic system. Equations that describe its behavior are so complex (non-linear partial differential equations) that accurate (analytical) their solution is not possible.
Weather forecasting instruments
A Stevenson screen or instrument shelter is a wooden box set at a height of 2 m above ground level, having airy walls, painted white to reflect sunlight, housing a set of meteorological instruments. Located in the meteorological garden, on an even and flat surface, far from water reservoirs, river banks or streams, should not be on any kind of elevations, there should not be buildings in the nearby environment, tall trees, so that the air has an easy opportunity to exchange . The lawn within the meteorological garden should have a height of no more than 5 cm. The size of the cage is 50cm / 50cm / 75cm, the bottom of 3 boards (the middle a little higher – to ensure the airflow of the cage, and thus the accuracy of measurements), the walls of the so-called. blinds, white color, roof sloping towards the south, ventilation holes in the ceiling, door on the north side; inside measuring instruments.
Wind speed and direction
The Anemometer is an instrument used to observe the direction and speed of the wind. The indication of the anemometer is read from the deflection of the plate, and in the cup anemometer from the speed of the fan rotation, these are measured by the intensity of the current generated by the generator, coupled with the fan. The wind direction is read on the basis of the setting of a tin flag, called a tap, or a sleeve, i.e. a heavily elongated bag.
Wind measurements are one of the most difficult due to the rapid changes in direction and speed that occur even in such a small area as the medium-sized area of the city. On one street it can blow from the north at a speed of 25 km / h while on another at the same time from the south at a speed of 10 km / h. Such significant differences arise due to the urban areas, which cause strong turbulence of the air and, as a result, the actual wind speed and direction difficult to measure.
Barometer is used to measure air pressure. The barometer is equipped with a flexible box with pumped air. The external pressure causes the box lid to bend, which resists its elasticity. The movement of the lid moves to the movement of the pointer, which shows the pressure on the scale.
The barometer can be additionally equipped with a writing device that allows you to follow the pressure changes recently. Such a barometer is a barograph (aneroid self-writing), and the entry is called a barogram.
The mercury barometer consists of an open mercury container and a vertical glass tube inserted in it, topped and voided. The pressure pushes mercury into the tube to the height at which the weight of the post balances the air pressure. The mercury barometer does not record the history of pressure changes.
A rain gauge (also known as an udometer, pluviometer, or an ombrometer) is a device used to measure the sum of rainfall. It is equipped with a cylindrical vessel with a defined area of the upper opening and a measuring cup to measure the amount of water. The self-recording device for quoting the sum of rainfall is a pluvograph (ombrograph).
Totalizator is a rain gauge with a device for automatic emptying of the water bottle and recording the amount of rainfall. It is set in hard to reach places, for example on mountain peaks, and its records are read once a month or even less frequently.
Hygrometer – a device for observing the relative humidity of the air using the properties of elongation of the human hair due to increased humidity. A self-describing hygrometer is called a hygrograph and its recording is called an higrogram.
Psychrometer – a device for observing the relative humidity of the air. It consists of two thermometers: dry and wet. The dry thermometer indicates the current air temperature, the wetted thermometer has on the tank stretched with a batiste „shirt” with the other end immersed in water. It indicates the temperature is basically lower than the current air temperature. Its temperature reduces the loss of heat for evaporation of water – latent heat of evaporation. The difference between the indications of both thermometers is the greater, the drier the air, the more intense the evaporation of water.
The evaporometer – a device for measuring the evaporation capacity from the free water surface by weighing the water loss.
Lysimeter – a device for measuring evaporation and transpiration from soil covered with vegetation. It is a device of great size. The whole block of soil and vegetation is on a great weight.
The thermometer is a well-known temperature measuring instrument.
The meteorology uses a station thermometer to measure the current air temperature. It is equipped with a Celsius scale. It consists of a container with mercury and a tube connected to it, which is sealed at the top. Under the influence of warming up, mercury increases its volume, raises it as a pole in the tube and indicates the temperature of its post. In case of strong freezing temperatures, because mercury freezes at -39 ° C, alcohol thermometers are used.
In the Stevenson screen, there is also a maximum thermometer – it is a mercury thermometer with a narrowed tube above the reservoir. After lifting the mercury bar at the highest temperature, after cooling the bar does not drop – so it shows the highest temperature between observations. After reading, the thermometer is flicked off, so that the bar returns to the lower position.
The third thermometer is the minimum thermometer, indicating the lowest temperature in the period between observations. It is filled with a liquid – toluene or alcohol. The rod has a rod ending with an enlarged head. The thermometer sets almost horizontally; when the temperature decreases, the alcohol (toluene) shrinks and draws the rod with it; when the temperature rises, the alcohol bar lengthens, but does not push the rod but flows around it – the rod still indicates the lowest temperature.
In addition, self-describing thermometers – thermographs are used. They are provided with a clock device that moves the drum, on which the feather records the temperature course. The thermogram recording is called a thermogram.
Weather balloon is a tiny balloon equipped with necessary meteorological instruments released in order to examine the atmospheric conditions that prevail in the upper atmosphere. Such a balloon is released twice a day at 1,100 points around the world. The measurement results (temperature, humidity, atmospheric pressure) are sent to the meteorological station via radio, where they are further processed, and also used in forecasts.
Radar is a device that uses radio waves to detect and determine the position of objects. In meteorology, radar detects rainfall, clouds, storms and other atmospheric phenomena.
Artificial satellites circling high above the Earth allow observation of clouds at all levels of the atmosphere over oceans and lands. Based on images from artificial satellites, very dangerous meteorological phenomena can be detected, such as hurricanes, and their movement can be monitored, which allows meteorological services to warn given areas of possible threat.
How meteorological data is collected and recorded
Meteorological data is collected in the network of stations and meteorological stations. In meteorological stations, at least eight measurements per day of many different weather parameters are made. Based on data from the station, weather forecasts are developed. The station network is complemented by meteorological stations in which the state of the atmosphere is recorded at least three times a day, and only a few parameters. Data obtained at meteorological stations are not used for weather forecasting, but for conducting scientific research and describing the local climate.