Barometric pressure, often referred to as atmospheric pressure, is the force exerted by the weight of the air pressing down on the Earth’s surface. This weight constantly changes based on temperature, altitude, and weather systems. Understanding a high reading provides insight into current weather conditions and potential subtle effects on the human body. This measurement serves as a fundamental data point for meteorologists and an indicator of atmospheric stability.
Understanding Air Pressure and Measurement
The tool designed to measure atmospheric pressure is called a barometer. Early versions of this instrument used a column of mercury to balance the air’s weight, which is why some units of measurement still reference mercury. Modern barometers often use an aneroid mechanism, which consists of a sealed metal cell that expands and contracts with pressure changes.
Globally, the most common units are the millibar (mb) and the hectopascal (hPa), which are numerically identical. In the United States, pressure is frequently expressed in inches of mercury (inHg). Readings are typically adjusted to sea level to allow for standardized comparison across different elevations.
The Numerical Definition of “High”
The atmosphere’s average pressure at sea level is 1013.25 hPa, equivalent to 29.92 inches of mercury. This figure acts as the baseline, or “normal” reading, around which daily fluctuations occur. A high barometric pressure reading is defined as any value significantly above this average baseline.
A reading that exceeds 1020 hPa (or 30.12 inHg) is generally categorized as high pressure. Readings over 1022 hPa (or 30.20 inHg) designate the presence of a strong high-pressure system. While pressures rarely exceed 1040 hPa, the highest barometric pressure ever recorded was 1085.7 hPa in Mongolia in 2001.
Meteorological Significance of High Pressure
A high barometric pressure reading signals the presence of an anticyclone, a weather system characterized by sinking air. Air high in the atmosphere cools, becomes dense, and descends toward the surface. As the air descends, it warms and dries out, suppressing the formation of clouds and precipitation.
When the air reaches the surface, it diverges and flows outward, resulting in light winds and stable atmospheric conditions. This leads to the clear, calm weather typically associated with a high-pressure system. The stability of the air mass often traps existing pollution or haze near the surface, and the absence of cloud cover allows for larger temperature swings between day and night.
High Barometric Pressure and the Human Body
Although the human body constantly adapts to subtle pressure changes, fluctuations in barometric pressure can affect certain physiological systems. The body’s internal air-filled cavities, such as the sinuses and the middle ear, are normally in equilibrium with the external pressure. When the external pressure rises, this can create a temporary pressure differential if the body’s internal cavities cannot equalize quickly enough.
For some individuals, this pressure change can be a trigger for headaches or migraine attacks. The increased external pressure may also subtly affect the fluid and tissue surrounding joints, particularly in those with pre-existing conditions like arthritis or previous injuries. These effects are thought to relate to the compression of tissues and changes in nerve sensitivity. High pressure has also been noted to influence the cardiovascular system, potentially causing a slight resistance to blood flow due to the denser air.