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Click here to Order your Radar Equipment Online Streamline-Isotach Analysis This method consists of two sets of lines: streamlines, representing the wind direction, and isotachs (labeled in knots), representing the wind speed. The two sets of lines give a continuous representation of the wind field, from which wind direction and wind speed can be determined at any point on the chart. Familiarity with circulation patterns is a necessity when using this method of analysis. ASYMPTOTES. These are streamlines in the wind field away from which neighboring streamlines diverge (positive asymptotes) or toward which they converge (negative asymptotes). We are primarily interested in the negative asymptotes lying between converging currents since, in the lower levels, they are most frequently associated with bad weather. Significant negative asymptotes are frequently found in the convergent flow around well-developed cyclonic indrafts and in the broad zone of convergence between the trade wind currents of the two hemispheres (ITCZ of the doldrums). Asymptotes may or may not represent lines of true horizontal mass divergence and convergence. Typical examples of asymptotesFigure 9-2-6.Streamline asymptotes of difluence (divergence) left; of confluence (convergence) right. are shown in figure 9-2-6. Difluent asymptotes are drawn in blue and confluent asymptotes in red. They begin and end 1 inch before and after the first and last converging or diverging streamline. See figure 9-2-7. WAVES. These are perturbations in the streamlines similar to the wavelike arrangements of troughs and ridges in isobaric patterns. Waves that do not extend across the entire width of the current in which they are embedded are called damped waves. In this case, the streamlines on one or both sides of the current have smaller amplitude than those in which the wave is more pronounced. Figure 9-2-8 illustrates a damped wave in the streamlines.SINGULAR POINTS. These are points into which more than one streamline can be drawn or about which streamlines form a closed curve. The
Cusps.
Figure 9-2-10.Vortices in the streamlines (Northern
Hemisphere). Vortices. These are
centers, outdrafts, and indrafts of anticyclonic or cyclonic circulation. Figure 9-2-10 shows six of the most commonly
seen vortices. Anticyclonic outdrafts and cyclonic indrafts are frequently found at low levels in the
atmosphere. Data is usually too sparse at the upper levels to determine outdraft or indraft
characteristics of vortices. Therefore, many upper level vortices are drawn as pure cyclones or anti-cyclones,
for lack of more detailed information. Satellite pictures reveal even the weaker, smaller-scale
vortices, but conventional data is required to determine the level of most intense circulation. Neutral Points. |
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