What is atmospheric pressure?
Atmospheric pressure (also known as air pressure) is the force exerted by air molecules on a unit area of the Earth’s surface. It is generated by the irregular thermal movement of air molecules and is affected by the Earth’s gravity, altitude, temperature and humidity.
The main units of measurement for atmospheric pressure are pascals (Pa) and millimeters of mercury (mmHg). In the International System of Units (SIU), the pascal is the legal unit of measurement, while the mmHg is widely used in some specific fields (e.g. medicine).
At the 10th International Congress of Weights and Measures in 1954, scientists set a “standard” for atmospheric pressure: at sea level at 45° latitude, when the temperature is 0°C, the pressure generated by a high mercury column of 760 millimeters (equivalent to 1013.25 hectopascals) is called the standard atmospheric pressure (also known as normal atmospheric pressure).1 Standard atmospheric pressure = 760 millimeters of mercury = 1,013.25 millibars (mbar) = 101,325 pascals (Pa) = 1,013.25 hundred pascals (hPa).
Atmospheric Pressure Video from @AviationTheory
Barometric pressure VS Atmospheric pressure
Barometric pressure and atmospheric pressure are two terms often used interchangeably, both referring to the pressure exerted by the atmosphere on a unit area of the earth’s surface. And they are measured using the same units, such as pascals (Pa), hectopascals (hPa), millibars (mb), inches of mercury (inHg), or millimeters of mercury (mmHg). However, they have subtle differences:
Barometric pressure usually refers to the pressure obtained by measurement with a barometer. A barometer is an instrument that measures air pressure. Barometric pressure is commonly used in weather forecasting and aviation to describe the current air pressure as measured by a barometer
Atmospheric pressure is the air pressure in the atmosphere at the Earth’s surface. It is a narrower concept compared to the term barometric pressure. It is used to describe pressures in different atmospheric ranges. It is mainly used in weather forecasting, meteorological station and navigational safety.
Why is atmospheric pressure important?
For the environment
Because changes in air pressure can reflect changes in the weather, e.g., when air pressure is high it is sunny, and when air pressure is low there will be rain, so the weather can be predicted by measuring atmospheric pressure. Meteorologists can conduct weather studies based on long-term data. In addition, the value of air pressure varies with temperature and humidity, which can provide data to support the measurement and control of the spread of air pollutants.
For transportation
Atmospheric pressure is closely related to two major transportation systems, maritime and aviation. Accurate air pressure data can help maritime and air transportation to effectively avoid extreme weather and ensure the safety of the routes.
For Human Activities
Atmospheric pressure decreases as the altitude increases, so when human beings carry out certain activities from low altitude to high altitude, such as mountaineering, rock climbing, etc., they will experience different degrees of altitude sickness. Understanding and adapting to changes in atmospheric pressure is important for plateau travelers and climbers.
How is atmospheric pressure measured?
1. Mercury barometer
Mercury barometer is the earliest device used to measure air pressure. The principle of measurement originated from Torricelli’s experiment. Using the principle that the weight of mercury in a glass tube column inverted in a mercury bath balances with the surrounding atmospheric pressure, the height of the mercury column indicates the size of the air pressure. One standard atmospheric pressure is equal to 76 cm of mercury. Modern barometers use other liquids or electronic sensors.
2. Box Barometer
It is made of elastic metal film empty box as a sensing element, the air pressure is converted into empty box elastic displacement, through the lever and transmission mechanism to drive the pointer. When the clockwise direction is deflected, the pointer indicates the amount of change in the increase of air pressure, and vice versa, indicates the amount of change in the decrease of air pressure. It is easy to carry, wide range of pressure measurement and easy to maintain.
3. Electronic barometer
An electronic barometer is a portable device that utilizes semiconductor technology and a pressure sensor to measure barometric pressure. During the measurement process, the sensor converts the pressure change into an electrical signal. The electrical signal is processed and the barometric pressure value is displayed on a digital display.
4. Atmospheric Pressure Sensor
The atmospheric pressure sensor working principle is based on a pressure sensitive element. When the air pressure acts on the sensing element, it causes the resistance or capacitance value of the element to change, and different air pressures produce different resistance or capacitance values. Thus the value of air pressure is obtained. It is often equipped with a wind speed sensor, wind direction sensor, solar radiation sensor, rain gauge, etc. to form an automatic weather station.
What affects atmospheric pressure?
Atmospheric pressure change with temperature
Atmospheric pressure decreases with increasing temperature. When the temperature in the air increases, the movement of molecules is intensified causing the air to become less dense, so the air pressure decreases. Cold air sinks more easily than warm air, so the pressure on cold air molecules is greater.
Atmospheric pressure change with humidity
In addition to temperature, humidity is also a factor in atmospheric pressure change. In a high humidity environment, water vapor molecules are lighter than air molecules and are more likely to occupy the space above them. Air molecules are squeezed underneath and collisions between molecules are intensified, so the pressure increases. Conversely, when the water vapor content is low, the air pressure is low.
Atmospheric pressure change with altitude
Atmospheric pressure decreases with altitude. Higher altitudes are less bound by the Earth’s gravitational pull and contain fewer gases, so the pressure is lower. Atmospheric pressure decreases by about 10% for every 1,000 meters of elevation gain. This is because the number of atmospheric molecules decreases with altitude and there are fewer collisions between them. This is why mountaineers tend to feel short of breath and hypoxic at high altitudes, because there are fewer oxygen molecules in the air.
Atmospheric pressure change with gravity
Gravity affects the density of gas molecules. The greater the gravity, the stronger the force pulling air molecules toward the ground, so the pressure is greater in areas with less gravity. Gravity is not completely uniform on the surface of the Earth, and the effect of gravity is less at the equator than at the poles. This affects the distribution of air pressure.
How does atmospheric pressure affect weather?
High air pressure
Air molecules in an area of high air pressure move toward an area of low pressure, and the air above the high pressure area then falls. As the air falls, it shrinks in size and rises in temperature, causing the condensation in the air to evaporate and dissipate. As a result, there are few clouds in the sky and little rainfall in high-pressure areas, and the climate is usually clear and dry.
Low air pressure
If the air pressure in an area is low, the air from the surrounding area flows horizontally into the area, causing the air in the area to rise. The rising air expands due to the reduced pressure, the temperature decreases, and the water vapor in the air condenses. Therefore, low-pressure areas are often cloudy and rainy.
If the air pressure in an area falls rapidly, a “bomb cyclone” (a weather phenomenon in which the air pressure falls by more than 1‰ of standard atmospheric pressure per hour under natural influences, ultimately resulting in a drop in atmospheric pressure of 10% or more) can form, resulting in supercell winds. gale. In just under a day, it killed four people, injured 356, and almost completely paralyzed traffic in Tokyo and elsewhere. Early last year, the blizzard conditions that hit the United States were also linked to the bomb cyclone.
Wind formation
Changes in atmospheric pressure directly affect the movement of air and the direction of flow, and thus the speed and direction of the wind. The process of air flowing from high pressure to low pressure forms wind. The more pressure difference between the two sides, the faster the air flows and the greater the wind speed. In other words, the size of the wind speed is basically proportional to the air pressure gradient.
How does atmospheric pressure affect the body?
Air pressure affects ears
When an airplane takes off or lands, you may feel discomfort in your ears. This is because the sudden change in ambient air pressure increases the pressure difference between inside and outside the ear, which prevents the Eustachian tubes from opening passively, resulting in pain.
Air pressure affect mood
When in a low-pressure environment, the surrounding oxygen concentration decreases, and people will feel difficulty in breathing. This process also causes a change in the mood of the person, which can be characterized as being very irritable and depressed. The psychological changes can lead to increased heart rate, headaches, nausea, etc. This phenomenon is medically known as “hypothermia”. Medically, this phenomenon is called “altitude sickness”.
Air pressure affect sinuses
There is a direct correlation between low air pressure and the onset and duration of migraine headaches. Low air pressure creates a pressure difference between the atmosphere and the sinuses, which can lead to headaches or migraines. The problem is exacerbated when the sinuses are congested or blocked.
Air pressure affects joints
There is a link between air pressure and changes in the temperature of the surrounding environment and the level of knee pain. This could be due to air pressure affecting the viscosity of the fluid that connects the joint capsule, or it could be that it triggers a pain response in the joint’s nerve endings. In either case, some people will experience joint pain when a storm hits.
Air pressure affects blood pressure
Biometeorologists believe that when air pressure drops, so does blood pressure. For some people, this may mean they experience dizziness or blurred vision. Blood vessels respond to sudden changes in humidity, atmospheric pressure, cloud thickness or wind in the surrounding environment in the same way as they do to cold, and weather-related changes in blood pressure are more common in people over the age of 65.
