Ch 3 World Deserts

Chapter 3: 

Chapter 3 Climates of the World’s Deserts

Some General Properties: 

Some General Properties Meteorological characteristics Surface characteristics Vegetation characteristics

Variety of Properties: 

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

Summary of MeteorologicalCharacteristics (Then we’ll cover physiographic and vegetation characteristics): 

Summary of Meteorological Characteristics (Then we’ll cover physiographic and vegetation characteristics)

Desert Climate Types: 

Desert Climate Types

Warm Versus Cold Deserts: 

Warm Versus Cold Deserts

Daily total solar energy received at top of atmosphere on horizontal surface: 

Daily total solar energy received at top of atmosphere on horizontal surface COLD DESERT WARM DESERT

Slide8: 

Climate % arid lands Coldest mo Warmest mo Examples Hot 43 10-30 andgt;30 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 andlt;0 10-30 Canadian Prairie Gobi Turkestan Deserts of China Great Basin

Coastal/Foggy Desert: 

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

Temperature (solid) and Relative Humidity (dashed), at Different Distances From Namib Desert Coast: 

Temperature (solid) and Relative Humidity (dashed), at Different Distances From Namib Desert Coast 5 km from coast 30 km from coast Far inland FOG

Precipitation: 

Precipitation

Seasonality of Precipitation: 

Seasonality of Precipitation (some/none of each)

A Closer Look: 

A Closer Look

Rule of Thumb: 

Rule of Thumb Summer precip on Equatorial side Winter precip on mid-latitude side

Desert Temperature: 

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

Desert Winds: 

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

Desert Humidity: 

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

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

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

Types: 

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: 

Areas With Interior Drainage

General Vegetation Characteristics: 

General Vegetation Characteristics

Vegetation Types: 

Vegetation Types Small trees Shrubs Succulents Grasses Herbs Lichens

Vegetation Types That are Adapted to Desert Conditions: 

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)

Landscape Types in Terms of Vegetation: 

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)

The Deserts of Africa: 

The Deserts of Africa

African Deserts: 

African Deserts

Orography of the Sahara and Sahel: 

Orography of the Sahara and Sahel

Large-Scale Weather Patterns of the Sahara and Sahel: 

Large-Scale Weather Patterns of the Sahara and Sahel

Slide34: 

Climate of the Horizontal Wind and Sea-level Pressure

Penetration of Monsoon and Frontal Precipitation: 

Penetration of Monsoon and Frontal Precipitation

Monthly Precipitation: 

Monthly Precipitation

Maximum Observed 24-h Precipitation (mm): 

Maximum Observed 24-h Precipitation (mm)

Maximum Observed Annual Precipitation (mm): 

Maximum Observed Annual Precipitation (mm)

Budyko Index (Aridity): 

Budyko Index (Aridity)

Annual Cloudiness (%): 

Annual Cloudiness (%)

Record Maximum Temperature: 

Record Maximum Temperature

Record Minimum Temperature: 

Record Minimum Temperature

Mean Diurnal Temperature Range: 

Mean Diurnal Temperature Range

Annual Range of Daily Mean Temperature: 

Annual Range of Daily Mean Temperature

Orography of SouthwesternAfrica: 

Orography of Southwestern Africa

Budyko Index (Aridity): 

Budyko Index (Aridity)

Temperature Anomaly (C), Summer : 

Temperature Anomaly (C), Summer

Monthly Precipitation: 

Monthly Precipitation

Cross Section of Southern Africa: 

Cross Section of Southern Africa

Orography of the Horn of Africa: 

Orography of the Horn of Africa

The Budyko Index(Aridity): 

The Budyko Index (Aridity)

Monthly Precipitation: 

Monthly Precipitation

The Deserts of North America: 

The Deserts of North America

Slide54: 

Monthly Precipitation: 

Monthly Precipitation

Orography of North America: 

Orography of North America

The Budyko Index (Aridity): 

The Budyko Index (Aridity)

The Deserts of South America: 

The Deserts of South America

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Orography of Western South America: 

Orography of Western South America

Monthly Precipitation: 

Monthly Precipitation

Orography of Southern South America: 

Orography of Southern South America

Monthly Precipitation: 

Monthly Precipitation

BudykoIndex (Aridity): 

Budyko Index (Aridity)

Australian Deserts: 

Australian Deserts

Slide66: 

Orography of Australia: 

Orography of Australia

Budyko Index (Aridity): 

Budyko Index (Aridity)

Monthly Precipitation: 

Monthly Precipitation

Seasonal Distribution of Precipitation: 

Seasonal Distribution of Precipitation

Asian Deserts: 

Asian Deserts

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