Pre-Lab: Definitions & Types of Streamlines » Singular Points

Singular points are locations where the direction of flow cannot be determined - that is, more than one approach to a streamline can be drawn. This can be a point on the chart into which more than one streamline enters, or where streamlines might form a closed curve. The wind speed is zero at the singular point, and very light in adjacent areas.

Vortex Singular Points are circulation cells that can be cyclonic or anticyclonic. A cyclonic indraft is indicated as a closed circulation where streamlines converge into low pressure.

An anticyclonic outdraft is a closed circulation center where streamlines diverge out of high pressure. See below for examples of each. Note again the color convention of the letters used to indicate anticyclonic and cyclonic circulations.

A cusp is an intermediate pattern that represents a transition phase between a wave and a circulation center. Cusps are generally short-lived on the synoptic scale. An example is shown below.

Neutral Singular Points denote locations where confluent and diffluent asymptotes appear to intersect. In some cases, the neutral point captures an area of nearly pure deformation flow, similar to what is shown below with incoming southeasterlies and northwesterlies deforming to produce exiting northeasterlies and southwesterlies.

Neutral points are transition areas between two like singular points, or they will separate one flow regime from an adjacent flow regime of the opposite direction (e.g., a large area of midlatitude westerly flow adjacent to a large area of tropical easterly trade winds). Examples of a wave train including neutral points are below.

Another commonly observed pattern (necessarily observed, even) is a neutral point that separates prevailing background flow from the opposite-directed flow within an anticyclone or cyclone. See below for an example of a cyclone embedded in tropical easterlies - a neutral point must separate the background easterly flow from the westerly flow somewhere adjacent to the center of circulation.