Climates of the World

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Chapter 3

• Climates of the Worlds Deserts

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Some General Properties

• Meteorological characteristics
• Surface characteristics
• Vegetation characteristics

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Variety of Properties

• Cold deserts and hot deserts
• Deserts with winter precipitation and deserts
  with summer precipitation and deserts with
  virtually no precipitation
• Perpetually foggy deserts and deserts with near
  the maximum possible sunshine
• Barren deserts and heavily vegetated deserts
• Sand-dune deserts and deserts with rocky plains

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Summary of MeteorologicalCharacteristics (Then
well cover physiographic and vegetation
characteristics)
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Desert Climate Types
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Warm Versus Cold Deserts
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Daily total solar energy received at top of
atmosphere on horizontal surface
COLD DESERT
WARM DESERT
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Climate arid lands Coldest mo Warmest
mo Examples Hot 43
10-30 gt30 Central
Sahara Great Sandy (Aust) Mild Winter
18 10-20 10-30
Southern Sahara Kalahari
Mexico Deserts Simpson (Aust) Cool
Winter 15 0-10
10-30 Northern Sahara
Atacama Mojave Cold Winter 24
lt0 10-30
Canadian Prairie Gobi
Turkestan Deserts of China
Great Basin
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Coastal/Foggy Desert

• Summer temperatures are not especially high, but
  the winters are not cold because the ocean is
  close
• Can be very uncomfortable because of high humidity

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Temperature (solid) and Relative Humidity
(dashed), at Different Distances From Namib
Desert Coast
FOG
30 km from coast
5 km from coast
Far inland
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Precipitation
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Seasonality of Precipitation
(some/none of each)
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A Closer Look
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Rule of Thumb

• Summer precip on Equatorial side
• Winter precip on mid-latitude side

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Desert Temperature

• Why is it high?
• Lack of evaporation from surface
• Lack of vegetation (transpiration)
• Not much cloud cover

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Cloud Cover
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Desert Winds

• Subtropical deserts
• - High pressure areas are generally
  characterized by weak winds
• - Thunderstorms can produce high winds
• - Mid-latitude disturbances (lows) with high
  winds can penetrate into deserts
• Cold deserts in mid-latitudes, experience
  mid-latitude cyclones (lows) that can have strong
  winds
• Lack of vegetation near-surface winds higher
• Winds are very desiccating high temperature
  coupled with high winds

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Desert Humidity

• Relative humidity can be as low as a few percent,
  or as high as 100 (foggy coastal desert)
• Specific humidity
• Compared to hot humid tropics, desert air is
  drier
• But desert air of 95 F and 15 RH has more water
  vapor than does saturated air at 32 F in a winter
  storm

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Humidity Calculations

• Use the table on the previous slide to find vapor
  pressure, saturation vapor pressure, and relative
  humidity for
• Temperature 38 C, Dew point 7 C
• Temperature -1 C, Dew point -4 C
• Which location is more humid?
• It depends on how you define humidity!!!!

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Desert Humidity

• Compare the relative and absolute humidity of a
  desert and winter storm
• Desert
• 95 F and 15 RH
• Find dew point temperature for these conditions
• Winter storm
• 32 F and 100 RH
• Find dew point temperature for these conditions
• Which location is more humid?

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General Physiographic Characteristics(Why do we
care in a meteorology course?)
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Types

• Sand sheets and sand dunes
• Bare flat rock
• Desert pavement matrix of pebbles cemented
  together on the surface
• Salt flats
• Large rocks and mountains
• Clay plains

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Mojave
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Northern Chihuahuan Desert
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Areas With Interior Drainage
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General Vegetation Characteristics
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Vegetation Types

• Small trees
• Shrubs
• Succulents
• Grasses
• Herbs
• Lichens

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Vegetation Types That are Adapted to Desert
Conditions

• Phreatophyte long roots
• Xerophyte mechanisms for conserving water
• Halophytes adapted to saline soils
• Psammophytes grow in sandy soils
• Therophytes (annuals) seeds remain dormant in
  soil during dry season or dry years (contrast
  with perennial)

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Landscape Types in Terms of Vegetation

• Steppes grassland without trees, generally in
  midlatitudes
• Savannas also open grassland, but there are
  scattered shrubs and trees (subtropical,
  representing a transition between tropical
  forests and grassland of arid areas)

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The Deserts of Africa
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African Deserts
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Orography of the Sahara and Sahel
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Large-Scale Weather Patterns of the Sahara and
Sahel
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Climate of the Horizontal Wind and Sea-level
Pressure
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Penetration of Monsoon and Frontal Precipitation
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Monthly Precipitation
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Maximum Observed 24-h Precipitation (mm)
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Maximum Observed Annual Precipitation (mm)
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Budyko Index (Aridity)
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Annual Cloudiness ()
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Record Maximum Temperature
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Record Minimum Temperature
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Mean Diurnal Temperature Range
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Annual Range of Daily Mean Temperature
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Orography of SouthwesternAfrica
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Budyko Index (Aridity)
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Temperature Anomaly (C), Summer
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Monthly Precipitation
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Cross Section of Southern Africa
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Orography of the Horn of Africa
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The Budyko Index(Aridity)
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Monthly Precipitation
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The Deserts of North America
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Monthly Precipitation
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Orography of North America
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The Budyko Index (Aridity)
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The Deserts of South America
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Orography of Western South America
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Monthly Precipitation
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Orography of Southern South America
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Monthly Precipitation
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BudykoIndex (Aridity)
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Australian Deserts
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Orography of Australia
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Budyko Index (Aridity)
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Monthly Precipitation
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Seasonal Distribution of Precipitation
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Asian Deserts
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