digging trough

A colloquial term for an upper-level trough that is amplifying, often deepening, and pushing equatorward due to a jet streak on the upstream side of the trough, causing a net import of cyclonic vorticity into the base of the trough.

Contrast lifting trough.

Figure from Midlatitude Synoptic Meteorology: Dynamics, Analysis, and Forecasting by Gary Lackmann, © 2011 Gary Lackmann, published by the American Meteorological Society. Figure originally from Synoptic–Dynamic Meteorology in Midlatitudes: Volume II: Observations and Theory of Weather Systems by Howard B. Bluestein, © 1993 Oxford University Press, Inc. Reproduced with permission of the Licensor through PLSclear.

Bluestein, H. B., 1993. Synoptic–Dynamic Meteorology in Midlatitudes: Volume II, Observations and Theory of Weather Systems. Oxford University Press, 594 pp.

Lackmann, G., 2011. Midlatitude Synoptic Meteorology: Dynamics, Analysis, and Forecasting. American Meteorological Society, 360 pp.

Term edited 26 February 2024.

In meteorological usage, contrast C is defined by

where L₀ is the luminance of a target object and L_s is that of its immediate visual surroundings.
Both luminances may include airlight or reflected glare, and L_s is always assumed to be greater than zero. Because detection outdoors often depends on luminance rather than chromaticity differences, C is usually calculated from spectrally integrated luminances. Contrast for a perfectly black target is -1 but, in principle, C has no upper limit for a self-luminous target. If is less than a variable threshold contrast, the target is visually indistinguishable from its surroundings.

1. The study of the physics, chemistry, and dynamics of the earth's atmosphere, including the related effects at the air–earth boundary over both land and the oceans. Fundamental topics include the composition, structure, and motion of the atmosphere. The goals ascribed to meteorology are the complete understanding and accurate prediction of atmospheric phenomena.

1. In synoptic meteorology, a detailed study of the state of the atmosphere based on observations, usually including a separation of the entity into its component patterns and involving the drawing of families of isopleths for various elements.

1. In general, pertaining to or affording an overall view.