Pressure Map Lab: Barometric Height, Isobars and Gradient Wind over Mountain and Sea

Barometric Height and Pressure

Barometric height refers to the altitude at which a given pressure level occurs in the atmosphere. In the Pressure Map Lab, as you move your barometer up or down a mountain or near the coast, the station pressure changes due to variations in air density with altitude. This principle is governed by the hydrostatic equation: dP = -ρg dz, where P is pressure, ρ is air density, g is gravitational acceleration, and z is height.

The relationship between barometric height and pressure is crucial for weather forecasting as it helps predict changes in atmospheric conditions. For instance, a rapid decrease in station pressure often indicates the approach of a low-pressure system, which can lead to stormy weather.

Isobars and Their Behavior

Isobars are lines connecting points of equal atmospheric pressure on a map. In the Pressure Map Lab, you observe how isobars curve over mountains and coastlines due to the variation in air density with altitude and temperature. The curvature of these lines reflects the gradient of pressure changes across different regions.

The behavior of isobars is governed by the geostrophic wind equation: V = (1/f) x (g/dz) * ∇P, where f is the Coriolis parameter, g is gravitational acceleration, dz is the height change, and ∇P is the pressure gradient. This equation helps explain why isobars curve over mountains and how they interact with coastal areas.

Gradient Wind and Its Effects

A gradient wind is a type of atmospheric flow that balances the Coriolis force, pressure gradient force, and centrifugal force. In the Pressure Map Lab, you can observe how a deep low-pressure system develops over mountainous terrain or coastal areas, creating a strong gradient wind. This phenomenon is particularly evident when air is forced to rise up mountainsides, leading to cloud formation and precipitation.

The dynamics of gradient winds are described by the gradient wind equation: V = (1/f) x (g/dz) * ∇P - (f^2/2) * R, where f is the Coriolis parameter, g is gravitational acceleration, dz is the height change, ∇P is the pressure gradient, and R is the radius of curvature. This equation helps explain why strong winds form in certain atmospheric conditions.

Temperature Variations with Altitude

In the Pressure Map Lab, you can observe how temperature changes with altitude over mountains and coastal areas. As air rises up a mountain, it cools due to expansion, leading to condensation and cloud formation. This process is known as adiabatic cooling and is described by the dry adiabatic lapse rate: dT/dz = -g/cp, where T is temperature, z is height, g is gravitational acceleration, and cp is specific heat capacity at constant pressure.

The boiling point of water also decreases with altitude due to lower atmospheric pressure. This effect can be observed in the simulation as you move your barometer up a mountain or near the coast. The decrease in boiling point explains why high-altitude regions have different cooking times for certain foods and beverages.

Frequently asked questions

Try it live

Everything above runs in your browser — open Pressure Map Lab: Barometric Height, Isobars and Gradient Wind over Mountain and Sea and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.