Molndrift

Molndrift (Swedish: "cloud drift") is a descriptive term for the movement of clouds through the atmosphere. It refers to the advection of cloud masses by wind and larger-scale atmospheric circulation, and is used in meteorology, aviation, and environmental monitoring to characterize how cloud patterns change over time and space.

The behavior of cloud drift depends on wind speed and direction at the cloud-bearing layers, vertical wind shear, atmospheric stability, and local factors such as topography and land–sea contrasts. Convective processes can cause rapid, localized changes, while synoptic-scale flows produce more uniform displacement. Cloud type and altitude also affect observed motion: low stratiform clouds typically move with near-surface winds, whereas high cirrus may be transported by jet-stream winds.

Observation and analysis of molndrift employ ground-based observations, weather radar, and satellite imagery. Techniques such as cloud motion vectors derived from sequential satellite images allow estimation of horizontal wind fields at the altitudes of the observed clouds. These observations support short-term forecasting, nowcasting of precipitation and storms, aviation routing, and assessment of solar irradiance for renewable-energy planning.

Molndrift also has implications for the transport of aerosols, pollution, and moisture, influencing local weather and air quality. In climatology, long-term patterns of cloud motion contribute to understanding atmospheric circulation changes. The term is primarily descriptive and widely applicable across operational meteorology and atmospheric research.