geostrofisen

Geostrofisen is a theoretical concept in geophysical fluid dynamics that describes a systematic deviation from strict geostrophic balance in rotating fluids, such as Earth's oceans and atmosphere. The term combines geostrophic balance with a suffix used in some languages to name phenomena, signaling a distinct but related effect.

In commonly used models, geostrofisen arises when friction, boundary effects, or rapid spatial changes in topography generate a small but persistent ageostrophic component of motion. This residual flow interacts with the dominant geostrophic field, enabling cross-isobaric transport and localized vertical motion. As a result, near boundaries such as coastlines or seafloor features, the flow can exhibit enhanced upwelling, downwelling, or the generation of secondary circulations that are not captured by a purely geostrophic description.

Geostrofisen is discussed mainly in idealized theoretical frameworks and in interpretations of observations where deviations from perfect geostrophy are evident near boundaries. Its practical significance lies in improving coastal current forecasts, refining the representation of boundary layers in ocean and atmospheric models, and aiding the study of mesoscale dynamics where friction and topography play a non-negligible role.

Mathematically, the concept is treated by incorporating frictional terms, boundary-forcing, or nonlinear and beta-plane effects into the governing equations, yielding velocity fields that contain both geostrophic and ageostrophic components. Related concepts include geostrophic balance, ageostrophic flow, boundary layer dynamics, and frictional geostrophy.