What is upper-level divergence?
Divergence occurs when a stronger wind moves away from a weaker wind or when air streams move in opposite directions. When divergence occurs in the upper levels of the atmosphere it leads to rising air. First, strong wind is moving into weaker wind.
What happens when upper-level winds converge?
The convergence of horizontal winds causes air to rise, whereas the divergence of horizontal winds causes downward motion of the air (subsidence). Ground-level atmospheric pressure is not affected by convergence if divergence of an equal magnitude occurs simultaneously at higher levels.
What does upper-level convergence cause?
Convergence aloft, caused by increasing vorticity, promotes sinking air, and surface high pressure. Upper-level divergence causes the formation and intensification of surface mid-latitude cyclones. Upper-level convergence causes high pressure at the the surface.
What happens when the upper-level divergence of air is greater than the lower level convergence of air in a storm?
When upper-level divergence is stronger than lower-level convergence, more air is taken out at the top than is brought in at the bottom. Surface pressure drops, and the low intensifies, or “deepens.”
How are upper level divergence and surface lows related?
While air swirls inward and converges into the center of surface low pressure, an “upper-level disturbance” causes divergence aloft that allows air columns to shed weight. The end result is rising air, and usually clouds and precipitation associated with a low.
Where does divergence aloft typically occur relative to an upper level trough?
The strongest divergence aloft occurs on the northeast side of the trough, where a surface low pressure tens to develop. The strongest convergence aloft occurs on the northwest side of the trough, where a surface high pressure tends to develop.
What air motion is expected with upper level convergence?
* Negative vorticity advection (NVA) results in convergence at that level Page 42 Vorticity Advection and Vertical Motion Remember that convergence at upper levels is associated with downward vertical motion (subsidence), and divergence at upper levels is associated with upward vertical motion (ascent).
Does warm air converge or diverge?
From our discussion of thermal circulations we recognize that warm air results in a rising column of air. As the air rises, some of it spreads out, diverges, aloft thus reducing the surface pressure. At the surface, colder surrounding air moves in to replace the rising air.
What happens when an upper-level low lies directly above a surface low?
When an upper-level low lies directly above a surface low, the pressure of the surface low will decrease. a wave cyclone will begin to form.
How are upper-level divergence and surface lows related?
Why strong upper-level divergence will cause the pressure in the center of a surface low to decrease?
Divergence is removing more air than is being added by surface convergence. The surface low pressure will decrease. The decrease in surface pressure will cause the converging surface winds to blow faster.
Why is upper air divergence important to the development of midlatitude cyclones?
If the upper levels are favorable for cyclone development, then there is a region of divergence aloft above the developing Low-pressure center. This will help pull the air that is converging at the surface upward and continue to develop the surface cyclone.
What happens to the surface pressure at upper level divergence?
Upper level divergence removes air from the cylinder and would decrease the weight of the cylinder (and that would lower the surface pressure) We need to determine which of the two (converging winds at the surface or divergence at upper levels) is dominant. That will determine what happens to the surface pressure.
How do upper level fronts cause severe weather?
Severe weather becomes more likely if the upper level front moves in before the surface front. Cold air above warm surface air promotes thermodynamic instability. This situation is common with a strong mid-latitude cyclone. Use Skew-T diagrams and the upper level charts to see how a front slopes with height.
What is the definition of a wind divergence?
Divergence -The condition that exists when the distribution of winds within a given area results in a net horizon tal outflow of air from the region. In divergence at upper level s, the resulting deficit is compensated by an upward movement of air from below, favoring cloud formation and precipitation. [>>>] ~[ ⇑] – Going apart.
How accurate are upper level weather charts at reporting fronts?
With a large number of reporting stations at the surface, a fairly accurate position of fronts is possible. With far less reporting stations on upper level charts it is more difficult to obtain exact frontal position. Besides, there are only two upper air charts per day.
