In long waves, deepening of troughs is associated with cold air advection on the west side of the trough and filling of troughs with warm air advection on the west side of the trough. The converse is true for ridges. Warm air advection on the western side of a ridge indicates intensification, and cold air advection indicates weakening. This rule is least applicable immediate yeast of the Continental Divide in the United States, and probably east of any high mountain range where westerly winds prevail aloft. In short waves, deepening of troughs is associated with cold air advection on the west side of the trough and falling of troughs with warm air advection, particularly if a jet maximum is in the northerly current of the trough and tilling is indicated by warm air advection on the western side.

In reference to the above paragraph, the advection is not the cause of the intensity changes, but rather is a "sign" of what is occurring. High level convergence/divergence is the cause.

Figure 2-1, views (A) through (D), shows the effect of the location of maximum winds on the intensity of troughs and ridges.

Explanation of figure 2-1 is as follows: 

. When the strongest winds aloft are the westerlies on the western side of the trough, the trough deepens [fig. 2-1, view (A)].

. When the strongest winds aloft are the westerlies at the base of the trough, the trough moves rapidly eastward and does not change in intensity [fig. 2-1, view (B)].

. When the strongest winds are on the east side of the trough, the trough fills [fig. 2-1, view (C)].

Figure 2-1.-Effect of super gradient winds on the deepening and filling of troughs. (A) Strongest winds on the west side of trough;(B) strongest winds in southern portion of trough; (C) strongest winds on east side of trough; (D) excessive contour gradients.

. Sharply curved ridges with excessive contour gradients are unstable and rotate rapidly clockwise, causing large height rises and filling in the trough area downstream, and large height falls in the left side of the strong gradient ridge [fig. 2-1, view (D)].

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