Module 1 Flashcards
Weather vs Climate
Weather relates to hourly, daily atmospheric conditions such as precipitation, hours of sunshine, cloud cover, temperature and humidity. The most important fact is that it is short-term.
The climate of a place is based on the average weather conditions for a particular place taken over a minimum of a 30-year period. It is a general
picture and the weather received for a place can be vastly different from its usual climate.
What is the Atmosphere
The Earth’s atmosphere consists of air-a mixture of various gases surrounding the Earth to a height of many kilometres.
There are four vertical layers within the atmosphere:
1) Troposphere
2) Stratosphere
3) Mesosphere
4) Thermosphere
The outer limit of the atmosphere is set at 1000km, but the vast majority of our weather and climate is found within the lower 12km.
Radiation
Insolation is solar radiation received in the Earth’s atmosphere or at its surface, in the form of short-wave solar energy.
Only approximately 52% of this insolation reaches the earth’s surface.
The rest is absorbed by water vapour, dust and clouds or is reflected by the Earth’s surface and scattered by particles in the air.
This reflection is called the albedo. The albedo of an object is the extent to which it diffusely reflects light from the Sun.
Reflected heat, in the form of long-wave radiation, is trapped in our atmosphere and keeps our planet warm (this is known as the natural greenhouse effect).
Albedo
Albedo is the measure of how much of the incoming solar radiation that is reflected back into space from a surface without being absorbed.
The albedo of a surface depends on various factors such as its color, texture, and composition.
For example, a surface that is white or light-colored typically has a higher albedo than a dark or black surface because it reflects more light.
Albedo plays an important role in Earth’s climate system as it influences the amount of energy absorbed by the planet and the temperature of its surface.
Temperature
Air Temperature refers to the temperature of the air as observed at 1.2 m (4ft) above the ground surface.
The temperature of the Earth’s surface is the outcome of two processes:
i. The inward receipt of solar energy or insolation
ii. The outward loss of heat by radiation or exsolation
The volume or level of each process decreases from the Equator to the poles and so does the resulting energy budget.
Since the trend in insolation receipts being more than that of exsolation, the energy balance changes at around latitude 35° from surplus to deficit.
This spatial variation in the global energy budget is the principal factor determining the spatial pattern of temperatures over the Earth’s surface.
Factors affecting temperature
1) Latitude:
Latitude is the distance (measured in degrees) to the north and south of the Equator. The further away the location is from the equator, the smaller the angle
at which the sun’s rays strike the earth.
This means that there is a greater distance in the atmosphere through which the rays have to pass. Therefore, away from the equator, where the angle of incidence of the sun’s ray is less than 90°, the solar radiation is spread over a larger area. Therefore, less intense heating takes place, causing temperature to become lower.
2) Altitude:
Altitude is the height of a point above the sea level.
Temperature decreases by 6.5°C for every increase in 1,000m increase in altitude.
The air at high altitudes is thin. Thin air is unable to absorb heat as effectively as the dense air at sea
level because it has a smaller concentration of gases to trap heat. Thus places at higher altitudes have a lower temperature.
3) Cloud Cover
When there is high humidity, the cloud cover is greater. In equatorial regions with thick cloud cover, incoming solar radiation will be absorbed, reflected and scattered. Thus keeping the land cool and the heating effect is less intense. At night clouds reflect heat radiated by the ground back to the earth’s surface, preventing heat from escaping into outer space. This keeps the temperature of the ground high at night. As such there is a smaller difference in day and night temperatures.
However, in areas such as deserts, there is less cloud cover so there is more insolation reaching the surface resulting in intense heating with temperatures easily reaching 40oC. At night, the absence of cloud cover causes the rapid escape of heat resulting in very low temperatures of 15oC. Thus there is a greater diurnal range
Global Heat Budget & Energy Balance
The global heat budget is the balance between incoming and outgoing solar radiation.
At the Equator, there is an energy surplus (net gain), whereas at the poles there is an energy deficit. To keep energy balanced at the Earth’s surface, excess energy is transferred from lower latitude energy surplus areas to higher latitude energy deficit areas by atmospheric circulation.
If there was no atmospheric circulation, lower latitudes would get hotter and hotter and higher latitudes colder and colder.
Heat Transfers
Horizontal heat transfers:
The transfer of heat from the equator to the poles occurs via winds - 80% (large scale to small scale) and ocean currents (20%).
Vertical heat transfers:
Exist to stop the atmosphere from cooling and the Earth’s surface from overheating. They include:
1) Conduction: The process through which the air receives heat from contact with the ground. Requires a medium
2) Radiation: The process by which heat energy is transferred without requiring a medium
3) Convection: Hot air, being lighter than cold air raises as convection currents. It requires a medium
4) Latent Heat: It is the quantity of heat energy needed to change state. When solar radiation changes liquid water to water vapour, latent heat is absorbed but the atmosphere’s temperature does not change.
Factors affecting Wind Speed & Direction
- Pressure-Gradient
Differences in air temperature, due to the unequal heating of the atmosphere, cause differences in air pressure.
A frequent cause of a horizontal difference in air pressure is a difference in air temperature and resulting difference in air density. When air
warms, it tends to rise and expand. This causes low pressure. When cooling occurs, the air tends to sink and contract, causing high pressure.
When there is pressure gradient, it produces a force that causes air to move from the place of higher pressure to a place of lower pressure.
This force is known as the pressure-gradient force and it increases as the difference in air pressure across a specified distance increases.
The direction of the pressure-gradient force is ALWAYS oriented from high to low pressure at a 90° angle to isobars (isobars that are close together indicate a larger force faster/stronger winds). - Coriolis Effect
Due to the Earth’s rotation, winds are deflected by the Coriolis effect (force). In the Northern Hemisphere the Coriolis effect deflects movement to the right and in the Southern Hemisphere it deflects movement to the left.
The magnitude of the Coriolis force varies directly with the wind speed and the rate of the Earth’s rotation.
The force also varies with the latitude and it is a maximum at the poles and minimum (zero) at the equator (no deflection at the equator).
Eventually, the pressure-gradient force and the Coriolis force acting on the wind balance each other out.
This results in a wind known as a geostrophic wind. It has a constant speed and follows a relatively straight path that minimizes deflection.
Geostrophic winds occur in the upper atmosphere, above the surface layer
3.Friction (frictional drag)
This affects air flows in the atmosphere, near the
Earth’s surface. The closer individual air molecules are to the surface, the more they are slowed by surface drag, creating a frictional force.
The direction of the frictional force is always OPPOSITE to the direction of air movement.
The magnitude of the frictional force depends primarily on the “roughness” of the surface (there is less frictional force with movement across a smooth snow or water surface than across a mountainous
terrain, forested area)
Friction affects wind direction (surface winds vs. upper winds) as well as modifies the Coriolis force.
Tricellular Model- Surface Circulation
On a rotating Earth’s surface, the driving force of the global circulation is again the intense heating received at equatorial areas. This produces deep convection with the rising air carried up to the tropopause by the
release of latent heat.
The tropopause (and its associated inversion) force
the rising air to spread out horizontally towards the poles. The Coriolis force results in this air being deflected to become part of the global flow of upper-air westerlies.
The system is caused by UNEQUAL heating of the Earth’s atmosphere at different latitudes.
The Hadley Cell:
This cell exist on either side of the Equator. Hot air at the Equator rises as the north-easterly and south easterly trade winds meet to the form the Intertropical Convergence Zone (ITCZ). The convergence of these two air masses of warm moist air results in large cumulus and cumulonimbus clouds as the air rises and cools rapidly. This produces afternoon thunderstorms. (LOW PRESSURE ZONE) Near the equator, at the ITCZ, winds tend to be light and the air is very stable in the known as the doldrums. The rising air eventually moves away from the equator and flow to towards the poles and with increasing density it subsides to form the descending limb of the Hadley cell.
The air subsides and diverges at about 30 degrees north and south of the Equator creating subtropical high pressure belts resulting in dry stable conditions with clear skies. The air currents return to the Equator as the north-easterly and south-easterly trade winds
Ferrel Cell:
This cell stretches between 30 and 60 degrees north and south of the Equator. Here, the air flows poleward. The relatively warm, sub-tropical air flows at low altitudes towards the poles in the Ferrel Cell until it meets cooler polar air, at which point it rises.
This is an area of low pressure, known as the Polar Front (depressions are formed along the Polar Front). The resultant unstable conditions produce the heavy cyclonic rainfall associated with mid-latitude depressions. The air then returns to 30 degrees north and south of the Equator where it descends to form an area of high pressure.
Polar Cell:
Air from the cell rises at 60 degrees north and south of the Equator, at the polar front and then flows to the north and south poles. Dry air sinking at the poles then blows along the surface toward 60 degrees north and south where the cycle is repeated.
Jet Streams
Jet streams are narrow bands of strong wind or air currents that generally move eastward in the
mid to upper troposphere tropopause). Jet streams are some of the strongest winds in the atmosphere, with speeds usually ranging from 129 to 225 kilometers per hour
Jet streams form when warm air masses meet cold air masses in the atmosphere. They exist largely because of a difference in heat. Dramatic temperature differences between the warm and cool air masses can cause jet streams to move at much higher speeds.
The fast-moving air currents in a jet stream can transport weather systems across countries in the northern hemisphere, affecting temperature and precipitation.
Rossby Waves
Rossby waves are large horizontal atmospheric undulation that is associated with the polar-front jet stream and separates cold polar air from warm tropical air.
Rossby waves form as a result of one, the uneven/differential heating of the Earth’s surface due to the different sizes and shapes the land masses
and two, the inability of air to travel through a mountain, causing it to rise up, go over or go around it.
They are created when air masses move northward or southward, causing variations in atmospheric pressure and creating areas of high and low pressure. These pressure variations in turn cause the jet stream to meander in a wave-like pattern, with troughs and ridges forming along its path.
The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones) that are important in producing
the weather of the middle and higher latitudes.
Sometimes, the waves can also stall and can lead to heatwaves, droughts and floods as the regions of hot and cold air hover over the same regions
for days, or even weeks.
What causes local winds?
Local winds are caused by small scale temperature and pressure differences.
They affect a much smaller geographical area compared to large scale systems such as depressions and tropical cyclones.
Two examples of local winds are land and sea breezes and valley winds.
Land & Sea Breezes
This is a wind system that develops over coastal areas.
It is caused by the different specific heat capacities of water and land to absorb and retain heat from the Sun.
During the day, if the weather is sunny and calm, the land quickly absorbs shortwave solar radiation and starts to warm. Some of this heat is transferred to the air above, which starts to rise.
By contrast, over the sea, the temperature does not rise so much because water warms relatively slowly.
The temperature difference between sea and lad sets up a pressure gradient, with relatively low pressure over the land and relatively high pressure over the sea.
This causes air to blow inland as a SEA BREEZE. Typically, the breeze starts in the mid-morning and strengthen during the afternoon, subsiding in the evening when the Sun’s rays are weaker.
Overnight, the land cools more quickly than the sea.
This causes a reversal in the temperature and pressure gradient and a breeze develops from the land onto the sea, known as a LAND BREEZE.
Valley Winds
At night, the ground surface cools. This is particularly marked when the sky is clear because cloud cover
acts as a ‘blanket’ and reduces the heat loss from radiation cooling.
In mountain regions, the ground and air is coldest over snow and ice fields. The cold air is relatively dense and it starts to sink. If this flow continues, a cold wind, known as a KATABATIC WIND, develops down the valley.
During the day, the wind flow is reversed. The sun’s rays heat the valley floor and slopes, causing relatively warm air to rise. If the flow develops up the valley, it is known as an ANABATIC WIND.
Microclimates
A microclimate is the climate in the lower few metres of the atmosphere, over a relatively small area, for example on a valley slope, in an urban
area or within a woodland area.
Local factors such as:
- slope angle
- quantity and type of vegetation cover
- building material
- heat conductivity
are all important influences.
Valley Microclimates
It is dependent on aspect, slope angle and altitude.
Relatively cool air tends to sink downwards at night, valley bottoms are often cooler than higher slopes. Night time radiation from the Earth’s surface escapes upwards and there are no turbulent winds to cause air at different levels to mix.
Frost hollow (low lying areas in which frost is most likely) can form on the valley floor. The effect of frost hollows on farming is important. Plants that are
sensitive to frost have to be grown on valley slopes rather than on the valley bottom.
Within hilly and mountainous regions, the different angle and aspect of slope creates different microclimates on opposite sides of valleys. This is especially true for valleys that trend east-west because there is a marked difference in intensity of solar radiation that the north and south facing slopes receive.
Woodland Microclimates
On hot days, it is often cooler in woodland or forests.
This is because there is a distinct microclimate under the trees.
Typically, between 5 and 15% of incoming solar radiation is reflected by leaves and much of the rest is absorbed by the tree canopy.
It is not only the temperature that is affected. Trees provide shelter from winds so air is often still in a woodland. Because air movement is weak, moisture from transpiration is not quickly dispersed and humidity tends to be high.
At night, the effect of a tree canopy is to retain heat, causing the range of temperature inside the
woodland to be less than elsewhere.
The exact microclimate within woodland depends upon the type of tree and season. Trees that provide a very dense canopy cut out most of the light, while deciduous trees in winter provide very little cover and a high proportion of light reaches the ground.
In general, the darker the conditions, the fewer plants will grow (therefore there is little vegetation on the floor of trees with a dense canopy cover).
Under deciduous trees there are often very dense vegetation in spring and then the vegetation tends to die in high summer, when the tree canopy is left.
What is absolute humidity?
It is the total mass of water vapour in a given volume of air(g/m^3)
What is adiabatic cooling/warming?
This is an internal change in the pressure and temperature of a gas whereby no heat is gained or lost to an external source. There is a decrease in pressure accompanied by an associated increase in volume and a decrease in temperature as a parcel of air rises. Conversely, descending air experiences a rise in pressure and a decrease in volume resulting in a rise in temperature.
What is advection cooling?
This refers to the drop in temperature resulting from warm moist air moving over a cooler land or sea surface.
What is the carbon cycle?
This is a circulation revolving around the storage of carbon dioxide in the atmosphere. It involves the movement of carbon through the atmosphere, rivers, oceans, sedimentary rocks, and living organisms. The amount of atmospheric carbon can be increased by such activities as the burning of forest and fossil fuels and reduced by photosynthesis.
What is conditional instability?
When such conditions are prevalent, the ELR is lower than the DALR but higher than the SALR. Rising air that might otherwise sink continues to rise as the release of latent heat resulting from condensation keeps the parcel of air warmer than the surrounding air.
What is dew?
It is the condensation of water directly onto ground surfaces, vegetation or objects. Rapid heat loss at night causes the air closest to the surface to reach its dew point.
What is the dew point?
This is the temperature at which air becomes saturated. Once the dew point has been reached, the process of condensation will commence forming dew, fog and cloud. (Relative humidity of 100%)
What is the dry adiabatic lapse rate (DALR) ?
The rate at which an unsaturated parce of air cools as it rises, or warms as it descends.
As a bubble of air forms and rises from the ground (example over a small island), it becomes warmer than the surrounding sea. As the bubble of air rises, it EXPANDS because atmospheric pressure is LOWER. This causes it to cool. (9.8 C per 1000m)
What is the environmental lapse rate (ELR) ?
The environmental lapse rate refers to the actual rate at which the temperature of the surrounding air changes with respect to altitude in the atmosphere.
It is measured or observed in the atmosphere and can vary depending on various factors such as time of day, season, weather patterns, and location.
The environmental lapse rate can be either positive (temperature decreases with altitude) or negative (temperature increases with altitude), and it can vary significantly from the adiabatic lapse rates.
What is instability?
The continued rising of an air mass that is warmer than the surrounding - environmental air. It results in large storm clouds.
What is relative humidity?
The ratio of water vapour that is actually present in air to the amount of moisture that the air can hold when saturated
What is the saturated adiabatic lapse rate (SALR) ?
The rate of fall in air temperature by adiabatic change as saturated air gains altitude (5.4 C per 1000m). It is less than DALR as latent heat is released as a result of condensation.
If a rising air bubble falls in temperature below its dew point, condensation occurs and this reduces the lapse rate. This is because water vapour releases latent heat when it changes to a liquid. The heat has the effect of slowing the rate at which the rising air cools.
What is an urban heat island?
An effect in which temperatures within an urban area are often significantly higher than those of surrounding rural areas.
Stability (Stable Air)
This is where a parcel of air rises and cools at a faster rate than the air surrounding it. The parcel of air is colder and denser than its surroundings so cannot
rise further and sinks.
Condensation and then subsequent rainfall does not occur. Stability is most commonly associated with high pressure and anticyclones.
Instability (Unstable Air)
If a parcel of air is then heated (by conduction, etc.) it leads to a high lapse rate and the air rises and cools less quickly than its surroundings.
If it remains warmer than its surroundings, the air parcel will continue to rise. If dew point is reached, clouds and thunderstorms may result.
Conditional Instability
This means that the parcel of air is stable as long as it DOES NOT fall in temperature to its dew point.
Above the height where condensation occurs (i.e., the condensation level), the air starts to cool more slowly (at the SALR). It may reach a point where it becomes warmer than surrounding air and is then unstable.
This situation can arise if air is forced upwards over high ground or over a cooler mass of air. It occurs if the ELR is between the DALR and SALR.
What is advection fog?
This is caused when relatively warm, moist air passes over a colder surface. The lower layers of air are cooled and, if they go below the dew point, condensation occurs.
This can happen on coastlines where a cold ocean current cools the air above. An onshore breeze can then blow the fog inland where it can persist for
several kilometres.
Eventually, the warmer land heats the air and the water droplets evaporate.
What is radiation fog?
This occurs when the Earth’s surface cools at night, particularly in cloudless conditions.
The cold ground cause the temperature of overlying air to fall below its dew point. The resulting condensation creates fog.
It does not form in windy conditions because turbulent air does not stay in contact with the ground long enough for sufficient cooling to occur.
In hilly or mountainous regions, cold air tends to flow downhill at night thereby causing the temperature to be lower in valleys than on higher slopes. This is why fog forms in hollows and valleys. Fog can persist all day if the cold air is trapped beneath warmer air in a
temperature inversion.
Under normal daytime conditions, the ground warms causing air to rise. But if it is foggy, the sunlight might not penetrate to the ground and there is no uplift of warm air to break the inversion.
When this happens in urban areas, the combination of fog, smoke and vehicle exhausts can create SMOG. Only wind that is strong enough to mix the air can clear the fog under these circumstances.
Collision and Coalescence Theory
In this theory, raindrops form from cloud droplets as a result of the two processes of collision and coalescence, causing droplets to merge into
each other.
This theory is associated with warm clouds, where the temperatures are still high enough for no ice to be present (water is in it liquid state). However, it also works in combination with the ice-crystal process in cool and cold clouds if a part of the temperature profile is above freezing.
According to this theory, precipitation forms when small water droplets in a cloud collide and merge with each other, eventually growing large enough to fall to the ground as raindrops.
The process of collision and coalescence begins when tiny water droplets in a warm cloud collide with each other, sticking together and forming larger droplets. As these larger droplets fall through the cloud, they continue to collide and merge with smaller droplets, growing in size and eventually becoming large enough to overcome the upward air currents that keep them suspended in the atmosphere. Once the droplets become heavy enough, they fall to the ground as precipitation.
Ice-Crystal Theory
This process is associated with clouds where at least some of the water present exists in its solid state (requires both liquid droplets and ice particles in the cloud). As a result, it occurs in cold clouds (clouds whose tops rise above the freezing level).
Most cold clouds have a mixed composition; with water droplets in the lower layers and supercooled water and ice above. In clouds like these, the rainfall can be intense.
According to this theory, precipitation forms when ice crystals in the upper atmosphere grow in size through the process of deposition, in which water vapor freezes onto the surface of the crystals. As the ice crystals become heavier, they fall through the atmosphere, and if they encounter a layer of air with a temperature above freezing, they will begin to melt, forming raindrops.
Short term variations in the global heat budget
Weather Systems: For example, during a high-pressure system (anticyclone), air descends, resulting in clear skies and dry weather, which allows more solar radiation to reach the Earth’s surface, increasing the heat budget. In contrast, during a low-pressure system (cyclone), air ascends, leading to cloud formation and precipitation, which can reflect or absorb incoming solar radiation, reducing the heat budget.
Atmospheric Aerosols: Atmospheric aerosols are tiny particles suspended in the atmosphere. Aerosols can originate from natural sources like volcanic eruptions, forest fires, or human activities such as burning fossil fuels and industrial processes. Aerosols can reflect and scatter incoming solar radiation, reducing the amount of solar radiation reaching the Earth’s surface, and hence decreasing the heat budget. They can also absorb and re-emit outgoing longwave radiation from the Earth’s surface, affecting the radiative balance.
Aspect
Convectional Rainfall
Very common in areas where the ground is heated by the hot sun, such as the Tropics. This is why those areas experience heavy rainfalls most afternoons.
Convectional rainfall occurs when:
- The surface of the earth is heated by the sun.
- The warm surface heats the air above it. Hot air always rises so this newly heated air does so.
- As it rises the air-cools and begins to condensate.
- Further rising and cooling causes a large amount of condensation to occur and rain is formed.
Convection tends to produce towering cumulonimbus clouds, which produce heavy rain and possible thunder and lightning.
Frontal Rainfall
Frontal rainfall occurs when:
- There is the movement of depressions over the country
- Two air masses meet, one a warm air mass and one a cold air mass.
- The lighter, less dense, warm air is forced to rise over the denser, cold air.
- This causes the warm air to cool and begin to condense.
- As the warm air is forced to rise further condensation occurs and rain is formed.
Frontal rain produces a variety of clouds, which bring moderate to heavy rainfall.
Relief/Orographic Rainfall
Relief Rainfall occurs when:
- The prevailing winds pick up moisture from the sea as they travel across it, making the air moist.
- The moist air reaches the coast and is forced to rise over mountains and hills.
- This forces the air to cool and condense, forming clouds.
- The air continues to be forced over the mountains and so it drops its moisture as relief rain.
- Once over the top of the mountain the air will usually drop down the other side, warming as it does so. This means it has a greater ability to carry water moisture and so there is little rain on the far side of the mountain. This area is called the rain shadow.
Weather conditions associated with depressions
Clouds: Depressions are often associated with extensive cloud cover, as rising air cools and condenses, forming clouds. (stratus, nimbostratus, or cumulonimbus)
Precipitation: Precipitation is often widespread and can be heavy, especially near the center of the depression.
Wind: Low-pressure systems are characterized by cyclonic or counterclockwise rotation of winds in the Northern Hemisphere (clockwise in the Southern Hemisphere). Winds blow towards the center of the depression, which is known as the eye or the center of the cyclone, and can be strong, especially near the center.
Instability: Depressions are often associated with unstable weather conditions, including rapidly changing weather patterns, thunderstorms, and sometimes severe weather events such as tornadoes or waterspouts.
Weather conditions associated with anticyclones
Clear skies: Anticyclones are generally associated with clear skies and minimal cloud cover. As air descends and compresses in a high-pressure system, it becomes more stable, inhibiting the formation of clouds and promoting clear weather.
Dry weather: Anticyclones tend to bring dry weather, as the descending air in high-pressure systems inhibits the formation of clouds and precipitation. This can result in prolonged periods of dry weather and low relative humidity.
Light winds: Anticyclones are typically characterized by calm or light winds. The descending air in a high-pressure system tends to suppress the formation of strong winds, resulting in generally light and variable winds.
How are Inter-Tropical Convergence Zones(ITCZ) formed?
The ITCZ is an area of low pressure that forms due to the action of the Hadley Cell, where the Northeast Trade Winds meet the Southeast Trade Winds near the Earth’s equator.
Northeast and Southeast Trade Winds converge along the equatorial trough of low pressure. The rising air that results is responsible for the cloudiness and precipitation that mark the ITCZ.
Weather conditions associated with ITCZs
Convectional rainfall: The ITCZ is known for its abundant rainfall due to the convergence of trade winds and the resulting uplift of warm, moist air. As the warm air rises, it cools and condenses, leading to convectional rainfall. This can result in heavy rainfall and thunderstorms, especially during the peak of the rainy season.
Clouds: The ITCZ is often characterized by extensive cloud cover. The rising warm air leads to the formation of cumulus and cumulonimbus clouds, which can contribute to the rainy and sometimes stormy conditions associated with the ITCZ.
Intense solar heating: The ITCZ is located near the equator, where the sun’s rays are most direct and intense. This can result in strong solar heating of the surface, leading to high temperatures and high humidity.
How are hurricanes formed?
Stage 1 - Trade winds become unstable because of northward movement of the ITCZ
Stage 2 - Warm, moist air is forced upwards and cools rapidly
Stage 3 - The Earth rotation causes spiral motion
Stage 4 - Lower-level winds spiral inwards towards the eye
Weather conditions associated with hurricanes
1) Strong Winds: Hurricanes are characterized by powerful winds that can reach sustained speeds of over 74 miles per hour (119 kilometers per hour) or more.
2) Heavy Rainfall: Hurricanes are also known for their heavy rainfall, which can result in widespread and prolonged precipitation.
3) Thunderstorms and Lightning: Along with strong winds and heavy rainfall, hurricanes often generate numerous thunderstorms and lightning.
4) Storm Surges: They are large and powerful oceanic waves that are driven by the strong winds and low atmospheric pressure associated with hurricanes.
Warm fronts
Warm fronts are formed when warm air rises over a mass of cold air.
As the air lifts into regions of lower pressure, it expands, cools and condenses the water vapour as wide, flat sheets of cloud.
Warm fronts are shown on synoptic charts by a solid line with semicircles pointing towards the colder air and in the direction of movement.
On coloured weather maps, a warm front is drawn with a solid red line with red semicircles.
