How does convergence affect the atmosphere

See Technical Requirements in the Orientation for a list of compatible browsers. However, to good approximation, density does not change with time for any given horizontal surface.

Sure, density decreases exponentially with height, but for each height level, the density at that level is fairly constant. Thus, horizontal divergence is compensated by vertical convergence and horizontal convergence is compensated by vertical divergence.

Divergence aloft is associated with rising air throughout the troposphere, which is associated with low pressure and convergence at the surface. Convergence aloft is associated with sinking air throughout the troposphere, which is associated with high pressure at the surface and thus divergence at the surface.

So, starting at the surface, the vertical velocity becomes more positive with height when there is surface convergence, reaches some maximum vertical velocity, and then becomes less positive with height again toward the divergence aloft. Similarly, starting again at the surface, the vertical velocity becomes more negative with height when there is surface divergence, reaches some maximum negative velocity, and then becomes less negative with height again near convergence aloft.

The key concepts that allow horizontal divergence to be converted into vertical motion are that mass is conserved, but the air density and density vertical structure are fairly constant with time, and that the vertical wind at Earth's surface and at the tropopause is effectively 0. This means that the total divergence must be approximately 0 so that the air parcel volume remains constant. Thus, changes in the horizontal area cause changes in the vertical height to maintain the air quality.

A key to remember is that the vertical velocity w is partial derivative with respect to height z do not always have the same sign. The second key point to remember is that the partial derivative of w with respect to z is a negative divergence. We would look first at diverging mirror surface. But if there is horizontal convergence, then the air must go somewhere, and it cannot go down, so it goes up.

The equation actually says that the partial derivative of w, the vertical velocity with respect to z, must be positive. But if w equals 0 at Earth's surface and w is increasingly with altitude, than w must be positive. For divergence near Earth's surface, we see that the partial derivative of w with respect to z is negative, which means that w must be negative above the surface since w equals 0 at earth's surface.

So the air velocity w must be downward. Because of this, low pressure centers are generally associated with clouds, precipitation, and what we generally call "bad weather. Surface high pressure systems in the Northern Hemisphere have a clockwise rotation with wind turning slightly outward away from the highest pressure. This causes air to diverge, or move away, from the center of the high near the ground.

Air has to come from above to fill in the void left by the diverging air at the surface. This leads to sinking motion in the center of a high pressure system and generally clear air. This explains why high pressure systems are associated with what we think of as "good weather. They change the television viewing experience from one where the viewer faces a wide range of programs available at a given time, to an arrangement of greater consumer choice about what to view and when.

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