2.3 Weather processes and phenomena Flashcards
What is evaporation?
- transformation of liquid water into water vapour
- due to increase in speed of molecules
What factors affect evaporation rates?
- Temperature: increased kinetic energy, and so become vapour quicker
- Wind speed: removes moist air above water body, also faster winds replace saturated air with drier air, enhancing evaporation rates
- Humidity: low levels increase evaporation, as drier air absorbs more water vapour
- Sunlight exposure: provides energy necessary for evaporation
- Surface area: more water exposed to air
What energy required for evaporation?
- endothermic process, absorbs heat
- latent heat of vaporisation necessary to break molecular bonds
What is condensation?
- water vapor back to liquid
- essential in forming dew, clouds and fog
How does condensation lead to formation of dew, clouds and fog?
Dew: air near ground cools to its dew point, causing water vapour to condense into liquid on surfaces, e.g grass
Cloud: air rises, cools and may reach dew point, water vapour condenses around tiny particles in air, known as condensation nuclei, forming clouds
Fog: similar to clouds, but occurs and ground level
What are condensation nuclei?
- microscopic particles, such as dust, pollen, smoke, and sea salt, that are critical for cloud formation.
- Water vapour condenses around these particles, leading to the formation of cloud droplets.
What is deposition and sublimation?
Deposition: direct transition from water vapour to ice, forming frost
- high humidity and low temperatures
Sublimation: direct transition of ice to water vapor
- snow covered regions/ice caps
How do different types of surfaces affect dew formation?
- different surfaces have varying capacities to radiate heat/cool down
- e.g metal surfaces radiate heat more efficiently than wooden surfaces, thus cooling down faster at night
- rapid cooling can lead to quicker/more extensive dew formation on metal surfaces
- vegetation cools down rapidly compared to bare soil, often leading to more dew accumulation on grassy surfaces
- darker and smoother surfaces tend to cool down faster, promoting more dew formation
What factors influence size/density of fog?
- cooler conditions with higher humidity, fog droplets tend to be smaller and more densely packed
- because cooler air cannot hold as much moisture, leading to a higher concentration of water droplets when saturation occurs
- More condensation nuclei mean more surfaces for water vapour to condense upon, resulting in a higher density of smaller droplets
- dynamics of air movement can impact droplet formation.
- In stagnant air, droplets may grow larger due to less collision and coalescence, while in turbulent air, droplets are more likely to collide, coalesce, and form larger droplets
What is the mechanism of convectional precipitation?
- can occur anywhere where the ground sufficiently heats the air above it
- begins with the sun warming the Earth’s surface
- heat is then transferred to the air directly above the surface
- As air warms, it becomes less dense and begins to rise
- During its ascent, the air cools adiabatically (without heat exchange), and its capacity to hold moisture decreases, leading to condensation when the air reaches its dew point
- result is the formation of cumulus clouds, which can further develop into cumulonimbus clouds if conditions allow
What is frontal uplift?
WARM FRONT:
- warm air above cool air
- warm air squeezes cold air out and warm air gradually rises above it and cools to form clouds
- warm air replacing cold air at surface
- mild rainstorms, more spread out
COLD FRONT:
- cold air moves underneath warm air (denser)
- pushes warm air upwards
- warm air cools and condenses to form clouds
- cold air replacing warm air at surface
- intense local thunderstorms/rainfall
OCCLUDED FRONT:
- occur when cold front ‘catches up’ with warm front
- will lift warm air, trapping it as a wedge between 2 cold air masses
- air will condense and create rainfall
- band of thick cloud/rain
What is orographic uplift of air?
- in mountainous regions
- When moist air is forced to ascend over a mountain range, it expands and cools, leading to condensation and precipitation.
- Windward Side: The side of the mountain where the wind ascends receives significant rainfall, often characterised by lush, green vegetation
- Leeward Side: where the air descends, becomes warmer and drier, often resulting in semi-arid or arid conditions. This is known as the rain shadow effect.
What is radiation cooling ?
- most pronounced during clear, calm nights.
- Earth’s surface, which absorbs heat during the day, radiates this heat back into space at night
- leads to a cooling effect, particularly near the ground
How does altitude affect convectional precipitation?
- As altitude increases, the air becomes cooler and can hold less moisture
- means that highland areas can experience more frequent convectional precipitation due to the air reaching its dew point more quickly as it rises and cools
- in mountainous regions, the terrain can enhance the lifting and cooling of air, further promoting cloud formation and precipitation
- However, the intensity of the precipitation might decrease with increasing altitude beyond a certain point, as the air becomes too cold and dry to support heavy rainfall.
What are the different kinds of clouds?
Cumulus: fluffy, white clouds + flat bases: stable weather
Stratus: uniform grey clouds: light rain/drizzle
Cirrus: wispy clouds at high altitudes: indicate change in weather
Nimbus: dense/dark: heavy precipitation
