Atmospheric Layers: Properties, Pressure, and Weather Variables

Atmosphere: Layers and Properties

The atmosphere is a gaseous and tiered layer with vertical physical properties surrounding our planet. It extends super above 1000km.

Troposphere

The troposphere extends up to 13km and contains 75% of the total mass of the atmosphere. Most atmospheric phenomena occur here, with abundant vertical flows. The lower troposphere is followed by the tropopause, a transition layer where jet streams flow, influencing weather patterns. The location and intensity of these systems change with time and latitude.

Stratosphere

The stratosphere spans from 13 to 50km. In Caracas, the isotherm is practically at its lowest point, around -40°C. This layer contains ozone (O3), which absorbs UV radiation and heats the air.

Mesosphere

The mesosphere extends from 50 to 85km. Temperature decreases with height, reaching -90°C. Pressure is around 1hPa. The thermosphere starts at 85km, where the air becomes less dense, composed of O2 and N2. Above 200km, atomic oxygen is heated by UV photons, reaching temperatures of +1200°C.

Exosphere

The exosphere ranges from 500 to 1000km and transitions into the magnetosphere. This zone is the boundary between Earth's atmosphere and interplanetary space. Artificial satellites orbit here. Temperature and density are inappropriate for polar regions.

Ionosphere

The ionosphere is divided into D (50-90km), E (90-140km), and F (140-210km) layers. It contains a high concentration of electrons and atoms, influenced by solar radiation. These ionized particles interact with electromagnetic waves.

Variables

Key atmospheric variables include:

• Temperature (Tª): Measured using thermometers, based on liquid dilation, electrical resistance, material volume variation, and gas pressure.
• Pressure: The weight per unit area of the air column above a given point. It decreases with altitude (1hPa/9m). Measured using barometers (mercury and aneroid) and barographs. Corrections are needed for instrumentation, temperature, and gravity. 1 atm = 101.325 hPa = 1 mb.

Barometric Tide

The barometric tide is a regular daily pressure change. Instability is higher in the tropics, with an amplitude of around 3mb. Barometric pressure tendency is the variation between two observations.

Isobars and Related Concepts

• Isobars: Lines connecting points of equal pressure.
• Isallobars: Lines connecting points of equal pressure tendency.
• Isohypses: Represent relief in geopotential height, connecting points of equal pressure at different altitudes.
• Gradient: Pressure difference per unit distance.

Wind and Pressure Systems

Buys-Ballot Law: Wind direction is tangent to isobars. In the Northern Hemisphere, low pressure is to the left of the wind direction. The greater the pressure gradient, the stronger the wind. High-pressure regions are associated with good weather, while low-pressure regions are associated with clouds and precipitation.

Pressure Systems

• Tropical Cyclones: Intense low-pressure systems with strong wind gradients.
• Secondary Depression: A smaller low-pressure system within a larger one.
• Trough (Vaguada): Isobars in a V-shape.
• Pass (Desfiladero): A low-pressure area connecting two depressions.
• Ridge (Dorsal): Isobars in a U-shape, associated with high pressure.
• Bridge: A high-pressure band connecting two anticyclones.
• Swamp (Pantano): A region of uniform pressure.
• Col (Collado): A region between two highs and two lows.

Gas Laws and Density

Gay-Lussac's Law: The pressure of a gas is a function of temperature. Warm air has a higher pressure than cold air. Density increases with pressure and decreases with temperature.

Weather and Climate

Variables: Temperature, pressure, density, water vapor, clouds, precipitation, and winds.

Weather: Atmospheric conditions at a particular place and time.

Climate: Accumulation of weather conditions over a longer period.

Humidity

Air can retain water vapor, with the amount increasing with temperature. When the air is saturated, vapor begins to condense. Relative humidity is the ratio between the partial vapor pressure and its saturation limit. The dew point is the temperature at which air must be cooled to reach saturation.