vertical motion

VERTICAL MOTION

• the upward or downward movement of air within the atmosphere

• plays a crucial role in development of clouds and precipitation

• typically measured in centimeters per second due to the relatively slow vertical speeds compared to horizontal wind speeds

MECHANISMS THAT DRIVE VERTICAL MOTION

1. Dynamic Processes

2. Thermodynamic Processes

DYNAMIC PROCESSES

refer to mechanisms driven by the movement of air masses and differences in pressure or rotation

PRESSURE GRADIENT FORCE

air naturally moves from high-pressure regions to low-pressure regions, causing convergence and divergence

CORIOLIS FORCE AND VORTICITY

• Coriolis deflect the air motion to the right (left) in the Northern Hemisphere (Southern Hemisphere).

• Vorticity, or the measure of air rotation, also plays a role, with regions of high vorticity often associated with upward motion, as they induce cyclonic flow that promotes rising air (Holton & Hakim, 2012)

FRICTIONAL EFFECTS

at the Earth's surface, friction slows down the wind, leading to changes in its direction and speed

THERMODYNAMIC PROCESSES

related to temperature differences and involve changes in air buoyancy

CONVECTIVE LIFTING

when air near the Earth's surface is heated, it becomes less dense and more buoyant, causing it to rise; common in the development of thunderstorms

OROGRAPHIC LIFTING

when air is forced to rise over a mountain or elevated terrain, it cools adiabatically, often leading to condensation and cloud formation on the windward side of the mountain

FRONTAL LIFTING

occurs when air masses of different temperatures meet, as in cold and warm fronts

ATMOSPHERIC STABILITY

• controls the ability of air to rise or sink, which in turn influences weather

• determines whether vertical motion will continue or be suppressed

3 TYPES OF ATMOSPHERIC STABILITY

1. Unstable

2. Stable

3. Neutral

STABLE ATMOSPHERE

• drizzle; poor air quality

• air that is forced to rise will eventually slow down and sink back to its original position

• associated with temperature inversions and conditions where the environmental lapse rate is less than the adiabatic lapse rate (Holton & Hakim, 2012)

UNSTABLE ATMOSPHERE

• good air quality

• encourages continuous upward motion when air is lifted

• common in warm, humid environments where rising air cools at the adiabatic lapse rate, leading to cloud formation and potentially to convective weather events like thunderstorms (Rogers & Yau, 1989)

NEUTRAL ATMOSPHERE

• displaced air neither returns to its original position nor accelerates upward

• relatively rare but can occur during the mixing of different air masses.

• nice weather despite having too much clouds

ROLE OF VERTICAL MOTION IN WEATHER SYSTEMS

1. Cloud formation and precipitation

2. Cyclogenesis and Fronts

3. Thunderstorms and severe weather

CLOUD FORMATION AND PRECIPITATION

• Rising air cools adiabatically, reaching the dew point and forming clouds

• If rising motion continues, the air may cool enough for condensation to occur, leading to precipitation

CYCLOGENESIS AND FRONTS

• Cyclogenesis, the development or intensification of cyclones, is associated with strong upward motion at the center of low-pressure systems.

• The vertical motion in cyclones is driven by the convergence of air at the surface and divergence aloft, resulting in cloud formation and precipitation along frontal boundaries (Bluestein, 1992)

THUNDERSTORMS AND SEVERE WEATHER

• Thunderstorms are driven by intense upward motion due to convective lifting in unstable atmospheres

• This upward motion can reach heights of up to 12 kilometers in severe thunderstorms, leading to strong downdrafts, lightning, and even tornadoes (Holton & Hakim, 2012)

VORTICITY

• measure of the rotation or "spin" of air parcels in the atmosphere

• Greek letter ζ (zeta), representing the local rotation at a specific point in the atmosphere (Bluestein, 1992)

• vorticity indicates whether an air parcel tends to rotate in a clockwise or counterclockwise direction

TYPES OF RELATIVE VORTICITY

1. Relative

2. Planetary

3. Absolute

RELATIVE VORTICITY

• measures the spin of air relative to the Earth's surface. It can be affected by changes in wind speed or direction over a given distance

• the primary measure when discussing weather systems' local rotation (Bluestein, 1992)

PLANETARY VORTICITY

• also known as the Coriolis parameter, 𝑓

• arises from the Earth's rotation. It depends on the latitude and increases toward the poles

ABSOLUTE VORTICITY

• is the sum of relative vorticity and planetary vorticity, providing a more comprehensive picture of the atmosphere's rotation

• it is a useful quantity in large-scale atmospheric circulation patterns (Holton & Hakim, 2012)

VORTICITY MAXIMA

• (high vorticity values) play a significant role in generating vertical motion

• occur when air experiences intense rotation, often leading to convergence (accumulation) or divergence (spreading) of air masses, which can either support or inhibit vertical movement (Bluestein, 1992)

RISING AIR IN POSITIVE VORTICITY ADVECTION (PVA)

• rising air (cloud formation and precipitation)

• the transport of higher vorticity values into a region

• often promotes upward motion, as it is associated with increasing cyclonic rotation

When air converges near a vorticity maximum, it is forced to rise due to the conservation of mass. This rising air can lead to cloud formation and precipitation if moisture is present, making PVA critical in storm development and frontal systems (Holton & Hakim, 2012)

SINKING AIR IN NEGATIVE VORTICITY ADVECTION (NVA)

• leads to sinking air (clear skies)

• involves the movement of lower vorticity values into a region, often leading to downward motion (subsidence)

As air diverges near a region of low vorticity, it sinks, resulting in clearer and more stable weather. NVA is typically associated with anticyclones and fair-weather conditions (Wallace & Hobbs, 2006).