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Climatology Flashcards

1
Q

What is created over the city due to warm air rising?

A

Heat dome

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2
Q

Why, besides being near a colder ocean, are the conditions on the west coast more dry?

A
  1. There is decending air at the horse lattitudes
    1. This results in warm air above the cold ocean.
    2. Consequently, there is a temp inversion and no large-scale rising of air can take place.
  2. Anticlockwise rotation
    1. SW winds
    2. Retain moisture (colder to warmer lattitudes)
    3. // to coast and are not onshore
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3
Q

Describe the weather conditions experienced at the cold front of a mid-lattitude cyclone

A
  • Temperature falls rapidly
  • Pressure increases quickly
  • Warm air rises sharply
  • Cumulonimbus clouds form
  • Heavy showers over a small area
  • Decrease in humidity
  • Wind “backs”
  • Later, clouds clear but it is still cold
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4
Q

Where is the angle of incidence measured from?

A

The ground

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5
Q

Why must there be divergence in upper air in order for tropical cyclones to form?

A

Removes air at high altitudes which maintains surface LP

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6
Q

What do the westerlies in a mid-lattitude cyclone become?

A

Northwesterlies

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7
Q

What is the term for “backing” in the context of the NH?

A

Veer / veering

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8
Q

What is the wind-direction in the warm sector of a mid-lattitude cyclone?

A

NW

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9
Q

Name the three HP cells around South Africa

A
  • South Atlantic HP
  • South Indian HP
  • Kalahari HP
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10
Q

In which season is the effect of aspect the greatest?

A

In winter

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11
Q

Where do gales occur in the formative stage of a tropical cyclone?

A

50 km from eye

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12
Q

What does a cold snap on the plateau look like on a synoptic chart?

A
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13
Q

What happens once cold air collects at the bottom of the valley?

A

A temperature inversion occurs

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14
Q

What season is it if there is a interior HP?

A

Winter

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15
Q

Describe the movement of air associated with a LP cell

A

Rising air

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16
Q

Where is pressure the lowest in a tropical cyclone?

A

In the eye

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17
Q

What is unstable air?

A

A pocket of air that rises

Warmer than surrounding air

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18
Q

Why must there be a steep pressure gradient in order for a tropical cyclone to form?

A
  1. Strengthens Coriolis force
  2. Causes air to rotate
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19
Q

Why does a anti-cyclonic temperature inversion occur?

A

Subsiding air is warmer than the air on the plateau which is rising and cooling

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20
Q

During which months do mid-lattitude cyclones form in the SH?

A

April to October

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21
Q

What is the movement of warm air at both the warm front and the cold front?

A

Warm air rises

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22
Q

What is the average pressure in the eye of a tropical cyclone?

A

940 hPa

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23
Q

Where does the pollution done lie during the day?

A

Higher altitudes

The heating of the city causes the pollution to rise

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24
Q

What else can a mid-lattitude cyclone be called?

A
  • Temperate cyclones
  • Extra-tropical cyclones
  • Temperate depressions
  • Frontal depressions
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25
Q

Why is there local air circulation over cities?

A

Warmer air is less dense and rises and cooler air from rural areas blows in

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26
Q

Why is there more cloud cover over a city?

A
  1. Warm unstable air rises easily
  2. Winds that converge on the city (due to it being hotter) bring moisture in from rural areas
  3. More condensation nuclei over the city as a result of pollution
  4. Higher levels of smog (which can be almost like cloud cover)
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27
Q

What is the speed of winds circulating in the system of a tropical cyclone?

A

200 -300 km/h

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28
Q

Describe the cloud formation in the immature stage of a tropical cyclone

A

Spiral bands of clouds

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29
Q

Is the direction that mid-lattitude cyclones travel dependent on the hemisphere they are in?

A

No. Mid-lattitude cyclones ALWAYS travel from W to E

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30
Q

What speed are the winds within 50 km of the eye in the immature stage of a tropical cyclone?

A

Hurricane speed winds

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31
Q

In which season the Kalahari HP (and thus the inversion layer) rise?

A

Summer

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32
Q

Why is there often fog over the West Coast of SA?

A

Warm air (from subsiding air) is cooled over the cold ocean

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33
Q

What is the only way in which areas fallling in the shadow zone of a slope heated?

A

By reflection

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34
Q

What is a tropical cyclone called in its immature stage of development?

A

A tropical storm

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35
Q

Define temperature inversion

A

When the temperature of the atmosphere is colder than the temperature of the atmosphere higher up

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36
Q

Why is the air of a berg wind hot?

A

The air of a berg wind heats adiabatically as it moves down the escarpment

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37
Q

Why does wind “back” in a mid-lattitude cyclone?

A

Air rotates around the LP in a clockwise direction in the SH

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38
Q

What kind of wind (local winds) does aspect influence?

A

Anabatic winds

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39
Q

Where do tropical cyclones develop?

A
  • Over tropical oceans
  • 5° N&S of the equator
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40
Q

What are anabatic winds?

A

Upslope winds

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41
Q

How long does one experience the conditions of the eye in a tropical cyclones

A

For up to two hours

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42
Q

Why should faactories not be constructed in valleys?

A

There is stable air above the temperature inversion

Chimney stacks of factories in valleys should extend above the inversion layer

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43
Q

_____ can form on the valley floor.

A

Frost pockets

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44
Q

Where does the worst weather occur in the mature stage of a tropical cyclone?

A

In the SW in the SH

In the NW in the NH

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45
Q

The position of the HPs that affect SA vary with ____ and ____.

A

The seasons and the position of the overhead sun

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46
Q

How does a line thunderstorm develop?

A
  1. A trough of low presssure develops (NW to SE)
  2. The dry and moist air masses converge
  3. Moist NE air is lighter (so rises and cools)
  4. Rain falls to the NE of the trough axis
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47
Q

Which direction do tropical cyclones move?

A

From East to West

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48
Q

Why do mountain tops cool rapidly?

A

Due to terrestrial radiation

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49
Q

Name some negative impacts of tropical cyclones on people

A
  • Flooding of rivers
  • Storm surges
  • Ships destroyed
  • Soil salty (bad for agriculture)
  • Tourism negatively affected
  • Fertile soil is eroded
  • Vegetation uprooted (loss of habitat)
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50
Q

Where do mid-lattitude cyclones occur?

A

In the middle, or temperate lattitudes

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51
Q

What is a tropical cyclone called in its formative stage of development?

A

A tropical depression

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52
Q

What do the polar easterlies become in a mid-lattitude cyclone?

A

Southwesterlies

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53
Q

What does it mean if the difference between air temp and dew point temp. is large?

A

The air is dry

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54
Q

What are tropical cyclones named according to?

A

People’s names

Starting with A

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55
Q

What are tertiary (or local) winds caused by?

A

The heating and cooling of slopes

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56
Q

What is the approximate pressure in the eye of the mature stage of a tropical cyclone?

A

940 hPa

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57
Q

Why must there be no friction in order for tropical cyclones to form?

A
  1. Causes the winds to reach great speeds
  2. Enables Coriolis force to remain active (which maintains rotation)
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58
Q

What does a deflection of a mid-lattitude cyclone look like on a synoptic chart?

A
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59
Q

What would a station model look like showing berg wind conditions?

A
  • IT WOULD BE ON THE COAST
  • No clouds
  • Low dew point temperature
  • High air temperature
  • Wind direction from land
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60
Q

Why do coastal LPs occur?

A

They lie between the two HP cells

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61
Q

What are some strategies to prepare for the event of a trropical cyclone?

A
  1. Monitor by weather bureaus
  2. Observed via:
    1. Satellite
    2. Reconnaissance aircraft
    3. Weather reports
  3. US National Hurricane Center
  4. Vacate low ground
  5. Board up windows
  6. Move to concrete storm shelters
  7. Sand bags in coastal areas
  8. Disaster management schemes
  9. Conservation of wetlands
  10. Concrete sea walls
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62
Q

What is the precipitation in the immature stage of a tropical cyclone?

A

Light rain

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63
Q

Which slopes (warmer or colder) are preferred for settlement?

A

Warmer

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64
Q

What season is it if there is a coastal low?

A

Summer

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65
Q

Describe the weather conditions experienced in the warm sector of a mid-lattitude cyclone

A
  • Temp increases to a maximum
  • Pressure reaches its lowest just before the cold front arrives
  • Scattered cloud
  • Decreasing rain
  • Increasing sunshine
  • Wind drops
  • Wind - NW
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66
Q

What happens to the temperature inside the eye of a tropical cyclone?

A

It increases slightly

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67
Q

Does moist air have a high or low dew point temperature?

A

High dew point temperature

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68
Q

Which direction does Coriolis Force deflect air?

A

To the RHS in the NH

To the LHS in the SH

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69
Q

Name the four stages of development of a tropical cyclone

A
  1. Formative stage
  2. Immature stage
  3. Mature stage
  4. Dissipation stage
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70
Q

Explain the development of a berg wind

A
  1. Air subsides onto the plateau
  2. Air heats, warm and dry
  3. Moves down the escarpment to converge on the LP that is over the ocean
  4. This wind warms adiabatically (and all moisture evaporates)
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71
Q

Approximately how far towards the poles do tropical cyclones travel?

A

Approximately 25° - 30° N&S

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72
Q

In which season in the berg wind most common?

A

In winter

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73
Q

Describe the vertical movement of air in the formative stage of a tropical cyclone

A

The air rises

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74
Q

What is the life-span of a mid-latitude cyclone?

A

4 - 14 days

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75
Q

In which season does fog most regularly occur?

A

Winter

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76
Q

How do buildings affect the wind in an urban climate?

A
  • Friction (slows down wind speeds)
  • Cause gusty winds
  • Channel the wind down streets (very strong here)
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77
Q

In which season are mid-lattitude cyclones best developed?

A

In winter and spring

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78
Q

What can the heat dome be compared to, on a global scale?

A

The greenhouse effect

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79
Q

Why does a temperature inversion lead to stable air?

A

The cold dense air is unable to rise as the air above it is warmer and lighter

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80
Q

Where does air subside in the mature stage of a tropical cyclone?

A

In the eye

This causes the eye to be cloudless

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81
Q

What are EIGHT conditions required for the formation of a tropical cyclone?

A
  1. Sea temp. >27 °C
  2. High humidity
  3. Unstable air
  4. Very low pressure
  5. Steep pressure gradient
  6. Coriolis force
  7. Divergence in upper air
  8. No friction
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82
Q

What is a berg wind?

A

Hot, dry winds occuring when there is a steep pressure gradient between the KHP and depression

83
Q

Why do line thunderstorms occur in summer?

A

The inversion layer has risen above the escarpment and the moist air is able to reach the plateau

84
Q

Where does air divergence take place in a tropical cyclone?

A

In the upper air

85
Q

In which stage is a tropical cyclone given a name?

A

In the mature stage

86
Q

Which way do tropical cyclones tropical cyclones curve when travelling polewards in each hemisphere?

A
  • SH
    • Travel polewards
    • Curve to left
  • NH
    • Travel polewards
    • Curve to right
87
Q

Why are HP cells associated with cloudless skies?

A

Warming air causes the clouds to evaporate

88
Q

Why is temperature hotter in a city?

A
  1. There are activities in the city which generate surplus heat
  2. Concrete, tar and steel absorb more heat
  3. High-rise buildings
    1. larger surface area
    2. more direct rays on the sides
  4. Multiple reflection, less heat being radiated out to space
  5. Pollution limits abount of heat lost by terrestrial radiation
  6. Fewer water sources which absorb heat
  7. Less evapotranspiration which cools down the city
  8. Greater CO2 levels cause greater absorption of terrestrial radiation
89
Q

What is the pressure in the formative stage of a tropical cyclone?

A

More than 1000 hPa

Drops in this stage

90
Q

How does a trough of low pressure develop in summer in South Africa?

A

Land is heated and warm air rises

91
Q

What two ways can rain occur on the plateau?

A
  • LP over the land causes moist air (from Indian) to converge
  • Line thunderstorms can develop
92
Q

Where can a berg wind develop?

A

On either the W or E coast

93
Q

Why do storms last longer in cities?

A

The air has a greater water vapour capacity

94
Q

Why does an occlusion happen in a mid-lattitude cyclone?

A

The cold front moves more quickly:

  • it displaces the warm air ahead of it easliy.
  • it only uses energy to move horizontally - not to rise
95
Q

What is a vortex?

A

The area where air is circulating around the core of low pressure

96
Q

Which side of continents do tropical cyclones affect?

A

The east coast

97
Q

When do katabatic winds occur most frequently?

A

After noon

98
Q

What is a moisture front?

A

A line marking the boundary between the moist NE air and the dry SW air

99
Q

What are katabatic winds?

A

Downslope winds

100
Q

Give TWO reasons for why the plateau is cloudless in winter

A
  1. Air descends from the Kalahari HP and warms adiabatically
  2. It is cold in winter (no rising convection currents)
101
Q

What is the warmest part of the valley called?

A

Thermal Belt

102
Q

Name the four stages of development of a mid-lattitude cyclone

A
  1. Initial
  2. Mature
  3. Occlusion
  4. Dissipation
103
Q

What precipitaition is associated with cumulonimbus clouds?

A

Torrential rain, hail, thunder and lightning

104
Q

Do mid-lattitude cyclones develop closer to SA in summer or winter?

A

Winter

105
Q

Why is there less latent heat released as a tropical cyclone reaches over land?

A

There is less moisture

106
Q

What is the study of valley climates referred to as?

A

Microclimatology

107
Q

What kind of crops should be planted on the valley floor?

A

Frost-resistant crops

108
Q

Why does air above the slope at night move downwards?

A

It is cold and dense

109
Q

Which pressure belt are the three high pressure cells that affect SA found in?

A

The sub-tropical HP belt (30° N&S)

110
Q

When is the heat dome most noticeable?

A

At night

In winter

111
Q

In what season do tropical cyclones occur?

A

late summer to early autumn

112
Q

What is the diameter of a tropical cyclone?

A

500 km

113
Q

What will happen to tropical cyclones as global warming increases?

A

The frequency and intensity of tropical cyclones will increase

114
Q

Describe the movement of air associated with a HP

A

Descending air

115
Q

Does air diverge from a HP or LP?

A

HP

116
Q

Why does a cold snap happen?

A

The SAAC “ridges in” behind the cold front, thus reinforcing the SW air behind the cold front

117
Q

Why must there be Coriolis force in order for tropical cyclones to form?

A

Causes rotating winds which drops the pressure

118
Q

What is the pressure in the immature stage of a tropical cyclone?

A

Less than 1000 hPa

119
Q

What is smog?

A

A comination of fog and smoke

120
Q

What are some strategies that could be used to reduce the urban heat island effect?

A
  • Use reflective building materials
  • Increase vegetaion
    • plants on buldings insulate
    • plants cool environment
    • shade on buildings (no air-con)
    • reduce CO2
    • give tax rebates to people if a certain % of property includes plants
  • Reduce the energy consumption
121
Q

What is aspect

A

The direction in which the slope faces

122
Q

What usually happens, a warm front occlusion or a cold front occlusion?

A

A cold front occlusion

123
Q

How fast do tropical cyclones move?

A

20 - 25 km/h

124
Q

How big is a tropical cyclone in its immature stage of development?

A

Still small in size

125
Q

Give SIX negative impacts of mid-lattitude cyclones on human activities

A
  1. Snow on Cape Fold Mountains can endanger livestock
  2. Very cold conditions can disrupt human activities (power cuts etc.)
  3. Berg winds experienced ahead of a cold front can cause veld fires
  4. SW winds can cause stormy conditions (danger to ships)
  5. Heavy rain causes poor visability
  6. Snow on mountain passes
126
Q

When does a Southeaster occur?

A

When the SAAC ridges to the south of South Africa

127
Q

Over what range do squall line thunderstorms occur?

A

They occur over hundreds of kilometers

128
Q

What are temperature inversions caused by in valley climates?

A

Cold air collecting at the bottom of the valley

129
Q

What can a person call a city, in terms of climate?

A

A heat island

130
Q

Describe the cloud formation when you see a tropical cyclone approaching (first vortex)

A
  1. Cirrus
  2. Cumulus
  3. Cumulonimbus
131
Q

Why does the inversion layer over the interior of SA rise in summer?

A

Convection currents from the plateau being warm lift the descending air of the HP

132
Q

Give TWO positive impacts of mid-lattitude cyclones on human activities

A
  • Winter rainfall - cultivation of grapes
  • Replenishes water in dams
133
Q

Give the weather conditions that change due to the presence or an urban climate

A
  1. Temperature
  2. Humidity
  3. Cloud cover
  4. Precipitaiton
  5. Wind
134
Q

When do katabatic winds occur?

A
  • Usually after midnight
  • Cold, clear and calm nights
135
Q

What is the diameter of a mid-lattitude cyclone?

A

3000 km

136
Q

In which months do tropical cyclones occur in the SH?

A

Jan - April

137
Q

What is the shape of the isobars surrounding a mid-lattitude cyclone?

A

Oval-shaped

138
Q

In which wind belt do tropical cyclones travel?

A

Tropical Easterly winds

They are then picked up by the Westerly wind belt

139
Q

Why does a mid-lattitude cyclone dissipate?

A

All the warm air has been displaced

Thus, only the cold air is on the surface

And all pressure differences are reduced

140
Q

What TWO things happen at the Initial stage of the development of a mid-lattitude cyclone?

A
  1. A front exists
  2. Friction develops and rotary air movement begins (wave stage)
141
Q

When does frost form in a valley climate?

A

At night, when the air directly above the earth’s surface cools to below freezing

142
Q

Why must there be a high humidity for tropical cyclones to form?

A

Latent heat is released in the process of condensation (this provides energy)

143
Q

What is the angle at which the sun’s rays strike a slope?

A

The angle of incidence

144
Q

What is the gradient of a warm front of a mid-lattitude cyclone?

A

1:150 - 1:300

145
Q

What is a storm surge?

A

Large waves caused by the very strong winds and low pressure in a tropical cyclone

146
Q

What is the speed of the katabatic wind mainly caused by?

A

The steepness of the slope

147
Q

Why must the sea temp be greater than 27 °C for the formation of tropical cyclones?

A
  1. Evaporation occurs
  2. Thermal energy is provided
  3. Convection currents (when warm air rises)
  4. Low pressure (when warm air rises)
148
Q

Where is the polar front found?

A

Where the warm westerly winds and the cold polar easterly winds converge at the sub-polar LP

149
Q

When is there the most pollution in a city, summer or winter? Why?

A

Winter

  • More artificial heating
  • Inversion layer is lower down (stable air which does not rise)
150
Q

How does fog form?

A

If there is light wind and the earth’s surface is cold.

151
Q

What is a tropical cyclone called in its mature stage of development?

A

A tropical cyclone

152
Q

Give THREE reasons why frost is common over the Highveld in winter

A
  1. Cloudless nights (terrestrial radiation)
  2. Calm conditions (no mixing of warm and cold air)
  3. Low humidity (little absorption of terrestrial radiation)
153
Q

What kind of sun rays do slopes facing the poles recieve?

A

Oblique rays

154
Q

What is a squall line thunderstorm?

A

Thunderstorms accompanied by sudden and violent gusts of wind

155
Q

When does dew form?

A

When the earth’s surface cools to above freezing

156
Q

Why must there be unstable air for tropical cyclones to form?

A
  1. Air must rise
  2. Rising air causes condesation (release of latent heat)
157
Q

What is the wind direction behind the cold front of a mid-latitude cyclone?

A

SW

158
Q

What kind of crops will be found above the inversion layer (in the thermal belt) in a valley climate?

A

Frost-sensitive crops

159
Q

Can a berg wind be caused by a frontal depression or a coastal low?

A

Both

160
Q

What is different about the weather experienced in the first vortex and the second vortex of a tropical cyclone?

A

The wind direction is reversed

161
Q

What THREE important factors are there to consider when working with valley climates?

A
  1. Aspect
  2. Tertiary (local) winds
  3. Temperature inversions
162
Q

The lattitude where mid-lattitude cylones form is dependent on the position of …

A

the ITCZ

163
Q

Is the pressure gradient of a mid-lattitude cyclone steep?

A

No.

164
Q

Where do grasses thrive? On slopes facing the equator or on slopes facing the poles?

A

On slopes facing the equator

165
Q

Describe the temperature and humidity in the formative stage of a tropical cylone

A

Hight temp

High humidity

166
Q

Winds stronger than ___ cause the heat island to dissipate

A

20 km/h

167
Q

What can occur at either the cold or the warm front of a mid-lattitude cyclone?

A

A frontal inversion

168
Q

Which season is it if there is a tropical cyclone present?

A

Summer

169
Q

Why do katabatic winds occur most frequently after noon?

A
  1. Sun’s rays warm the slops during the day
  2. Air warms and becomes lighter
170
Q

What two things can cause a tropical cyclone to dissipate?

A
  • When they reach cooler lattitudes
  • When they cross the land
171
Q

When does orographic rain occur?

A

When air of the warm sector is caused to rise up the mountains

172
Q

What are the different names that tropical cyclones are known by in different parts of the world?

A
  • Hurricane
    • North America
  • Willy-willies
    • Eastern Austrailia
  • Typhoons
    • North Pacific and around China
  • Tropical Cyclones
    • Madagascar
173
Q

What does it mean if the ITCZ is further S?

A

It is summer

174
Q

Explain what is meant when it is said that mid-lattitude cyclones occur in “families”

A

The cold from of an older depression is joined to the warm front of a younger depression

175
Q

Where does the pollution dome of a city lie during the night?

A

Low altitude

  • Due to inversion that develops during the night
  • Little rising air (concentrated at surface)
176
Q

Describe the effect of line thunderstorms to the precipitation over the interior of SA

A
  1. Continual rainfall
  2. Large area
  3. Most of summer rainfall
177
Q

When is the effect of aspect least noticeable?

A

At noon

178
Q

Where are hurricane winds found in the mature stage of a tropical cyclone?

A

Within 160 km of the eye

179
Q

What causes the coastal LP to move around the coast of SA?

A

The movement (ridging) of the SAAC draws the coastal low with it

180
Q

What is often is followed after a costal low pressure?

A

A mid-lattitude cyclone often follows a berg wind

181
Q

Which direction does air move around a HP cell in the SH?

A

anticlockwise

182
Q

What is the diameter of the eye of a tropical cyclone?

A

30 - 50 km

183
Q

What direction is the wind blowing on a station model?

A

FROM the direction of the arrow

184
Q

Why does pressure rise as a tropical cyclone reaches land?

A

Friction weakens Coriolis force and air converges on the low pressure

185
Q

What season is it if there is a cold front close to the land?

A

Winter

186
Q

In what way do mid-lattitude cyclones travel (besides going from W to E)?

A

First, travel towards the equator

Then, curve towards the poles

187
Q

What is another term for a front?

A

A discontinuity

188
Q

What is the vertical extent of the cloud wall in a tropical cyclone?

A

15 km

189
Q

Where do gales occur in the immature stage of a tropical cyclone?

A

500 km from the eye

190
Q

Does air converge or diverge at the surface of a tropical cyclone?

A

Converge

191
Q

What is the speed of movement of a mid-lattitude cyclone?

A

30 - 50 km/h (from W to E)

192
Q

What is the pattern of the isobars around a tropical cyclone?

A

circular

193
Q

What are the lattirudes in which the sub-tropical high pressure cells are found sometimes referred to?

A

Horse lattitudes

194
Q

Describe the clouds in the mature stage of a tropical cyclone

A

Cumulonimbus clouds

195
Q

Describe the weather experienced in the warm front in a mid-lattitude cyclone

A
  • Temp ahead is low (rises gradually)
  • Pressure drops
  • Cirrus clouds, then cirrostratus, then altostratus, then nimbostratus
  • Gentle widespread rain
  • Wind - NE (in SH)
196
Q

Where do ferns thrive? On slopes facing the equator or on slopes facing the poles?

A

Slopes facing the equator

197
Q

Where do mid-lattitude cylones form?

A

At the polar front (40° - 60° N&S)

198
Q

In which wind belt do mid-lattitude cyclones travel?

A

In the belt of the westerly winds

199
Q

Why is relative humidity lower in a city?

A
  • Fewer open water sources
    • Storm-water drains
  • Warmer air (due to it being an urban heat island) has greater capacity to hold water vapour
200
Q

What two winds can the SIAC cause?

A

SE and NE winds over the E parts of SA

201
Q

Why can’t tropical cyclones develop within 5° N&S of the equator?

A

There is no coriolis force

202
Q

What is a nocturnal plateau inversion?

A

Where the earth’s surface cools, causing the air above it to cool.

This happens becuase of terrestrial radiation

This traps warm air as follows:

  • Cold air from the clear night-time conditions
  • Warm air from the air which heated up adiabatically
  • Cold air from loss of heat due to terrestrial radiation
203
Q

What is the gradient of the cold front of a mid-lattitude cyclone?

A

1:50 - 1:150

204
Q

What is the difference between fog and mist?

A

Fog is more dense than mist

Geography (5 decks)

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