ridging

Ridging refers to the development of a ridge of high atmospheric pressure aloft, typically in the mid- to upper troposphere, often identified as positive anomalies in geopotential height maps such as those at 500 hPa. A ridge represents a northward bulge of the jet stream and is usually associated with sinking air, stable stratification, and clearer skies at the surface.

Formation and dynamics: Ridging arises from large-scale atmospheric waves in the westerlies. When the jet stream amplifies and arches northward, a ridge forms downstream of the trough. Blocking patterns, including persistent high pressure known as blocking highs, can reinforce ridging and extend its duration. Surface temperature contrasts between land and sea, and continental features, can influence the location and strength of ridges. The persistence of ridges is often linked to quasi-stationary atmospheric wave trains.

Weather effects: Ridging tends to suppress mid-latitude storm activity in the region beneath or downstream of the ridge, leading to drier, clearer conditions and potential heat waves in warm seasons. In winter, ridging can divert storms away from the high-pressure zone, resulting in colder or more variable conditions on the downwind side depending on orientation.

Observations and forecasting: Ridging is diagnosed on weather maps by positive geopotential-height anomalies and by shifts in the jet stream pattern. Climate and weather models simulate ridging and its evolution, with regional impacts on precipitation and temperature.

Research notes: There is ongoing study of how ridging patterns may shift with long-term climate change and natural variability such as ENSO, the Pacific-North American pattern, and Atlantic multidecadal oscillation.