If you were to study the movement of the isobars on an 500mb chart over time, you would see that the waves or ridges and troughs of the lines do not stay in one spot but move from left to right. The lines themselves will evolve over time, but the overall movement is to the right. The schematic diagram on pg. 306 in the reader can be helpful in understanding the relationship between upper level divergence and wave cyclones at the ground. The significance of this is that divergence aloft indicates convergence, or an area of low pressure at the ground.
Divergence tends to occur on the eastern side of upper air troughs.
Convergence tends to occur on eastern side of upper air ridges. As discussed above, the waves of the isobars move from left to right. This means that lows and highs at the ground will not remain fixed in one spot, but will move with the jet stream. If you were to study the movement of the isobars on an 500mb chart over time, you would see that the waves or ridges and troughs of the lines do not stay in one spot but move from left to right. The lines themselves will evolve over time, but the overall movement is to the east.