Lecture 5/6 - Mass Movement and Depression Flashcards
What is convergence?
Convergence is the process whereby streams of elements come together into a much smaller central area, either by opposing flow directions or by some faster elements catching up to those ahead.
In the atmosphere, when winds converge over a relatively small area, the push of the air-molecule forces those in the centre to form an upward air current (updraft).
What areas see convergence zones?
Surface air convergence may be initiated by topography or solar heating. They also form when surface air masses (sometimes) of contrasting properties are forced into each other by the winds (fronts).
What is divergence?
Air moves outwards away from a centre of high pressure. In the lower atmosphere, surface divergence causes air to sink from above to replace that moving outward from the divergence zone.
What is vorticity?
Vorticity implies the spin or angular velocity of a body.
Vorticity is said to be positive when in the same sense of the earth (Cyclonic) and negative when in the opposite sense of the earth (Anticyclonic).
What is absolute vorticity?
Absolute vorticity is a conservative property (sun doesn’t change form place to place) total spin in the system.
What is different to horizontal motion compared to vertical motion in regards to the atmosphere?
Can be up to 100x greater, horizontal motion accounts for the majority of the destructive systems in the overall system. It expands vast amounts of energy and drives the worlds ocean circulation systems in upper layers.
What is the pressure gradient force for horizontal movement?
Once pressure differences exist motion takes place from areas of high pressure (high mass) to areas of low pressure (low mass). Air attempts to re distribute mass to become equal.
What is the Coriolis force for horizontal movement?
Force caused when a body moves over the spinning earth. Such a body experiences a deflection to the right in the north hem and left in the south hemisphere
What is Geostraphic Wind in horizontal movement?
The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force. This condition is called geostrophic balance. The geostrophic wind is directed parallel to isobars.
What is Centripetal Acceleration in horizontal movement?
Motion around an area of high or low pressure causes the motion of the air to be curved, this implies a force acting toward the centre of the system which is known as the Centripetal Acceleration.
What are the frictional forces for horizontal movement?
Acts as a drag on air movement and slows it down in proportion to surface roughness.
How can an air mass be modified? (4)
From Below
Heated/Cooled
Moisture Content
Dynamic Changes – forced advection etc.
What are the characteristics of a Tropical Maritime stream?
Warm Moist – High Td Stable Drizzle Low Cloud Poor visibility
What are the characteristics of a Polar Maritime stream?
Cool/Cold Dry - low Td Unstable Cumuliform clouds Showers Good visibility
When do fronts occur?
These are a result from Zones of Mixing/Boundaries. These occur when two different air masses meet.
