1. A Closer Look at Divergence and ConvergenceUpper-level divergence
and convergence are changes in the horizontal area occupied by an air
parcel and result from changes in vorticity as air flows. This
relationship between divergence and vorticity can be summarized in the
simple equation...where ... is the standardized chanqe (here, the
decrease) in absolute vorticity (ξ) with respect to time (t), and div =
divergence. If absolute vorticity increases, convergence must result. If
absolute vorticity decreases, divergence must result.Divergence and
convergence can occur in two ways. The first is by an increase or a
decrease in the speed of air as it flows. The second is by a stretching
out or pinching inward of the air, in a direction perpendicular to the
direction in which it is moving. The divergence and convergence
described earlier in this chapter can take either form.Speed Divergence
and Speed Convergence Speed divergence and speed convergence occur when
air moving in a constant direction either speeds up or slows down.
Consider the two parcels of air, A and B, in Figure 10-3-1a. Both
parcels are moving in the same direction, but parcel B moves faster, as
indicated by the length of the arrows. Because the leading parcel has
greater speed than the one behind it, the distance between the two
increases with time Figure 10-3-1b. This is an example of speed
divergence.This form of divergence is analogous to what might happen in a
race with many entrants at the starting line. Initially, the runners
cluster together, with little space between them, When the starting gun
goes off, the people at the front of the pack dash away from those
farther back, who shuffle along as they wait for the crowd to move
forward. The cluster of people gradually thins out as the faster runners
pull away from the slower ones, and the same number of people now
occupy a greater area.Because wind speed on an upper-level weather map
is directly proportional to the spacing of height contours, we can use
these maps to identify regions of speed divergence. Specifically, speed
divergence occurs where contour lines come closer together in the
downwind direction. In Figure 10-3-1c, the wind speed, indicated by the
length of the arrows, increases in the direction of flow and causes
speed divergence.FIGURE 10-3-1 Speed Divergence and Convergence, (a) Two
hypothetical parcels of air are moving in the same direction, with the
one in front moving faster, (b) At some interval of time later, the
leading parcel has moved even farther ahead, creating speed divergence.
This is also illustrated in (c), with the tighter spacing of height
contours to the east creating speed divergence. Speed convergence is
occurring in (d). Note that the values shown on the lines in (c) and (d)
represent the height of the 500 mb level in meters....Speed convergence
occurs when faster-moving air approaches the slower-moving air ahead.
In the example of runners in the race, convergence might occur behind a
muddy part of the track that slows the runners. The fastest runners, who
have pulled ahead of the others, are the first to encounter the muddy
spot. As they slog through the muck, the trailing runners have the
opportunity to catch up. The entire pack bunches up in a smaller area
and convergence occurs. A similar phenomenon is illustrated in Figure
10-3-1d.Diffluence and ConfluenceA second type of divergence and
convergence, diffluence and confluence, occurs when air stretches out or
converges horizontally due to variations in wind direction.In Figure
10-3-2a, a certain amount of air is contained in the shaded area between
points 1 and 3. As it passes to the region between points 2 and 4, the
same amount of air occupies a greater horizontal area. This is
diffluence, a pattern that commonly appears wherever vorticity changes
cause divergence. Confluence is shown in Figure 10-3-2b.Close inspection
of Figure 10-3-2 reveals an interesting relationship between the
different types of convergence and divergence. Diffluence occurs where
height contours on an upper-level map spread apart in the upwind
direction (confluence occurs where they converge).But where height
contours are spread farther apart, there is a lesser horizontal pressure
gradient, and therefore weaker winds.So diffluence (a type of
divergence) in the upper figure occurs at the same time that speed
convergence is occurring; that is, two opposite processes are occurring
at once. We know that divergence occurs downwind of a trough axis. How
does divergence actually occur downwind of a trough axis when diffluence
and speed convergence occur simultaneously? The answer is that in most
instances the diffluence is greater in magnitude than the accompanying
speed convergence, so the sum of the two yields: a net divergence.FIGURE
10-3-2 (a) Diffluence and (b) Confluence....What are diffluence and
speed divergence? Get solution
2. A Closer Look at Divergence and ConvergenceUpper-level divergence and convergence are changes in the horizontal area occupied by an air parcel and result from changes in vorticity as air flows. This relationship between divergence and vorticity can be summarized in the simple equation...where ... is the standardized chanqe (here, the decrease) in absolute vorticity (ξ) with respect to time (t), and div = divergence. If absolute vorticity increases, convergence must result. If absolute vorticity decreases, divergence must result.Divergence and convergence can occur in two ways. The first is by an increase or a decrease in the speed of air as it flows. The second is by a stretching out or pinching inward of the air, in a direction perpendicular to the direction in which it is moving. The divergence and convergence described earlier in this chapter can take either form.Speed Divergence and Speed Convergence Speed divergence and speed convergence occur when air moving in a constant direction either speeds up or slows down. Consider the two parcels of air, A and B, in Figure 10-3-1a. Both parcels are moving in the same direction, but parcel B moves faster, as indicated by the length of the arrows. Because the leading parcel has greater speed than the one behind it, the distance between the two increases with time Figure 10-3-1b. This is an example of speed divergence.This form of divergence is analogous to what might happen in a race with many entrants at the starting line. Initially, the runners cluster together, with little space between them, When the starting gun goes off, the people at the front of the pack dash away from those farther back, who shuffle along as they wait for the crowd to move forward. The cluster of people gradually thins out as the faster runners pull away from the slower ones, and the same number of people now occupy a greater area.Because wind speed on an upper-level weather map is directly proportional to the spacing of height contours, we can use these maps to identify regions of speed divergence. Specifically, speed divergence occurs where contour lines come closer together in the downwind direction. In Figure 10-3-1c, the wind speed, indicated by the length of the arrows, increases in the direction of flow and causes speed divergence.FIGURE 10-3-1 Speed Divergence and Convergence, (a) Two hypothetical parcels of air are moving in the same direction, with the one in front moving faster, (b) At some interval of time later, the leading parcel has moved even farther ahead, creating speed divergence. This is also illustrated in (c), with the tighter spacing of height contours to the east creating speed divergence. Speed convergence is occurring in (d). Note that the values shown on the lines in (c) and (d) represent the height of the 500 mb level in meters....Speed convergence occurs when faster-moving air approaches the slower-moving air ahead. In the example of runners in the race, convergence might occur behind a muddy part of the track that slows the runners. The fastest runners, who have pulled ahead of the others, are the first to encounter the muddy spot. As they slog through the muck, the trailing runners have the opportunity to catch up. The entire pack bunches up in a smaller area and convergence occurs. A similar phenomenon is illustrated in Figure 10-3-1d.Diffluence and ConfluenceA second type of divergence and convergence, diffluence and confluence, occurs when air stretches out or converges horizontally due to variations in wind direction.In Figure 10-3-2a, a certain amount of air is contained in the shaded area between points 1 and 3. As it passes to the region between points 2 and 4, the same amount of air occupies a greater horizontal area. This is diffluence, a pattern that commonly appears wherever vorticity changes cause divergence. Confluence is shown in Figure 10-3-2b.Close inspection of Figure 10-3-2 reveals an interesting relationship between the different types of convergence and divergence. Diffluence occurs where height contours on an upper-level map spread apart in the upwind direction (confluence occurs where they converge).But where height contours are spread farther apart, there is a lesser horizontal pressure gradient, and therefore weaker winds.So diffluence (a type of divergence) in the upper figure occurs at the same time that speed convergence is occurring; that is, two opposite processes are occurring at once. We know that divergence occurs downwind of a trough axis. How does divergence actually occur downwind of a trough axis when diffluence and speed convergence occur simultaneously? The answer is that in most instances the diffluence is greater in magnitude than the accompanying speed convergence, so the sum of the two yields: a net divergence.FIGURE 10-3-2 (a) Diffluence and (b) Confluence....Explain why you can have one kind of divergence and one kind of convergence occurring at the same location. Get solution
2. A Closer Look at Divergence and ConvergenceUpper-level divergence and convergence are changes in the horizontal area occupied by an air parcel and result from changes in vorticity as air flows. This relationship between divergence and vorticity can be summarized in the simple equation...where ... is the standardized chanqe (here, the decrease) in absolute vorticity (ξ) with respect to time (t), and div = divergence. If absolute vorticity increases, convergence must result. If absolute vorticity decreases, divergence must result.Divergence and convergence can occur in two ways. The first is by an increase or a decrease in the speed of air as it flows. The second is by a stretching out or pinching inward of the air, in a direction perpendicular to the direction in which it is moving. The divergence and convergence described earlier in this chapter can take either form.Speed Divergence and Speed Convergence Speed divergence and speed convergence occur when air moving in a constant direction either speeds up or slows down. Consider the two parcels of air, A and B, in Figure 10-3-1a. Both parcels are moving in the same direction, but parcel B moves faster, as indicated by the length of the arrows. Because the leading parcel has greater speed than the one behind it, the distance between the two increases with time Figure 10-3-1b. This is an example of speed divergence.This form of divergence is analogous to what might happen in a race with many entrants at the starting line. Initially, the runners cluster together, with little space between them, When the starting gun goes off, the people at the front of the pack dash away from those farther back, who shuffle along as they wait for the crowd to move forward. The cluster of people gradually thins out as the faster runners pull away from the slower ones, and the same number of people now occupy a greater area.Because wind speed on an upper-level weather map is directly proportional to the spacing of height contours, we can use these maps to identify regions of speed divergence. Specifically, speed divergence occurs where contour lines come closer together in the downwind direction. In Figure 10-3-1c, the wind speed, indicated by the length of the arrows, increases in the direction of flow and causes speed divergence.FIGURE 10-3-1 Speed Divergence and Convergence, (a) Two hypothetical parcels of air are moving in the same direction, with the one in front moving faster, (b) At some interval of time later, the leading parcel has moved even farther ahead, creating speed divergence. This is also illustrated in (c), with the tighter spacing of height contours to the east creating speed divergence. Speed convergence is occurring in (d). Note that the values shown on the lines in (c) and (d) represent the height of the 500 mb level in meters....Speed convergence occurs when faster-moving air approaches the slower-moving air ahead. In the example of runners in the race, convergence might occur behind a muddy part of the track that slows the runners. The fastest runners, who have pulled ahead of the others, are the first to encounter the muddy spot. As they slog through the muck, the trailing runners have the opportunity to catch up. The entire pack bunches up in a smaller area and convergence occurs. A similar phenomenon is illustrated in Figure 10-3-1d.Diffluence and ConfluenceA second type of divergence and convergence, diffluence and confluence, occurs when air stretches out or converges horizontally due to variations in wind direction.In Figure 10-3-2a, a certain amount of air is contained in the shaded area between points 1 and 3. As it passes to the region between points 2 and 4, the same amount of air occupies a greater horizontal area. This is diffluence, a pattern that commonly appears wherever vorticity changes cause divergence. Confluence is shown in Figure 10-3-2b.Close inspection of Figure 10-3-2 reveals an interesting relationship between the different types of convergence and divergence. Diffluence occurs where height contours on an upper-level map spread apart in the upwind direction (confluence occurs where they converge).But where height contours are spread farther apart, there is a lesser horizontal pressure gradient, and therefore weaker winds.So diffluence (a type of divergence) in the upper figure occurs at the same time that speed convergence is occurring; that is, two opposite processes are occurring at once. We know that divergence occurs downwind of a trough axis. How does divergence actually occur downwind of a trough axis when diffluence and speed convergence occur simultaneously? The answer is that in most instances the diffluence is greater in magnitude than the accompanying speed convergence, so the sum of the two yields: a net divergence.FIGURE 10-3-2 (a) Diffluence and (b) Confluence....Explain why you can have one kind of divergence and one kind of convergence occurring at the same location. Get solution
