The atmospheric pressure – it is a force exerted upon the surface of the Earth by the weight of the air (a column of air one square centimeter in cross-section and one kilometer in height).
The atmospheric pressure at the sea level equals 1,0333kg/1m2 = 1kgf (kilogram-force). It decreases non-linearly with height:
– 1013,2 hpa at the sea level
– 795 hpa at 2-kilometer altitude
– 233,4 hpa at 10-kilometer altitude.
It was established that the standard atmospheric pressure is measured at the sea level, at the latitude of 45 degrees and in temperature of 0 degrees Celsius and it is 1013,2 hpa. The area of the pressure measured in the exact same moment is illustrated with isobaric lines (drawn every 5 hpa) in a synoptic map. They are defined by the measurements taken at the meteorological stations on different altitudes. The results must therefore be equalized – reduced to the standard level. To do that, the pressure, which would be in all the measuring points if they were all at the same altitude, must be calculated.
The pressure systems
Low-pressure area is where the zone is surrounded by the areas with higher pressure. On barometric maps a low pressure area is recognizable by at least one closed isobar. In a low pressure area one can observe a cyclonic circulation which means that it has the same direction as the rotational movement of the Earth. In the Northern Hemisphere it is counter-clockwise whereas in the Southern Hemisphere it is clockwise. In the low-pressure area there exists a certain arrangement of fronts as well as constantly changing weather where most of the time there are clouds on the whole sky or on most of it with rain and strong wind. The low-pressure area is an elongated valley where the pressure is low, surrounded by the higher pressure from three sides and connected with another low-pressure area on the fourth. It shows itself on the map as isobars with big curvature between two areas of higher pressure or as isobars arranged in the letter V (in this case the valley is the wanted low-pressure area). Movement of the valley above the surface in the temperate climate of the Northern Hemisphere (for example in Poland) changes the direction of the air flowing in to this point form South West to North West and the drop in temperature follows. A high-pressure area is an area surrounded by the low-pressure area from every side. On synoptic maps it has the shape of concentric isobars with irregular borders, but mostly round. The maximal pressure (on the sea level) in the center of the high-pressure area can even be bigger than 1070 hpa (for example during a winter in Asia). In Poland during a winter the pressure can be bigger than 1050 hpa. The pressure gradient in the high-pressure area are relatively smaller than in the low-pressure area and there is a silent zone in the center. There is a lack of fronts, small clouds and weak winds in the high-pressure area. The high-pressure area wedge is an increased pressure area without the closed isobars, surrounded by the low pressure from three sides and the high pressure from the remaining side. In the area of wedges axis the weather is always improving and after it passes (above the temperate climate in the Northern Hemisphere) there is a change of direction of the air flowing in – usually from South West to North West.
Measurements of the atmospheric pressure
Mercury barometer – the structure: a glass tube 900 mm long and 10mm in diameter, filled with mercury. The upper end of the tube is closed and the lower one is dipped in metal dish filled with mercury. There is a vacuum in the tube above the mercury. Next to the mercury column in the tube, there is a scale in hectopascals or milliliters. When the pressure increases, the mercury column gets longer. Some of the mercury goes from the dish to the tube. When the pressure decreases it moves on the opposite direction. The measurements have to be corrected because of the imperfection of the device. Aneroid – balancing the atmospheric pressure using the resilience of two thin tin discs (diaphragm box). Pressure increases – discs are getting close together, pressure decreases – they’re moving away. The spring and levers transport those changes to the indicator (hpa or mm hg). The structure: elastic properties of metals were used. The main part of this device is a closed metal box made of resilient tin with a vacuum inside. The fluctuations of the atmospheric pressure cause bigger or smaller deflection of the cans walls. It is then transferred through the system of levers into the pointer moving on the round disk calibrated to the pressure units.
Impact of the pressure changes on man
On average, the body surface of an adult human is 18 000 cm2 which means that the force of the pressure equals 18 000 kgf. External pressure is balanced by the internal pressure of the body (resilience of the tissues, osmotic, hydrodynamic and hydrostatic pressure). Thanks to this, the body is in homeostasis with the environment. The change of the atmospheric pressure over 8 hpa a day is disadvantageous for a human body. It occurs during the movement of the atmospheric fronts, especially cold ones. They bring changes of the atmospheric pressure and a low temperature. The consequence is contraction of the blood vessels and the impairment of the circulatory system.
The reaction of the nerve system
Sudden drops of the atmospheric pressure lead to disorganization in the functioning of the nerve system, as a cause of oxygen deficiency and damage to the cells. Exterior symptoms: excitement, euphoria, being uncritical, blocked senses, faulty posture, diseases of the locomotor system.
A sudden drop of the atmospheric pressure also causes:
• Troubles with the proper functioning of the circulatory system, especially the heart.
• Minor increase of the blood pressure and filling the bodies spaces with gas (middle ear – muffled hearing, stomach and intestines – flatulence)
• Oxygen deficiency caused by worsening of the oxygen diffusion from the pulmonary alveoli to the erythrocytes. Too low atmospheric pressure and low oxygen content may result in, for example: increase of the pulse in the mountains, excessive sweating, sleepiness, feeling of fatigue, weakening of the metabolism, weakening of the physical efficiency, worsening of eyesight, troubles with the balance.
Organisms that have adapted to the low pressure and oxygen deficiency: fast heart beats, deep breaths, increase of the amount of hemoglobin, erythrocytes and proteins in blood, increase of the plasmas viscosity.