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Chapter 12

Dynamic Interactions Among Desert Microclimates

Concept§ Contrasts in microclimates, especially temperature,

cause horizontal pressure gradients that force local wind circulations.

§ Examples that can occur in deserts and non-deserts –contrasts in the following can produce mesoscale winds

- land-water (lake/sea breeze), - soil-moisture (irrigation contrasts), - vegetation, - urban-rural, - snow-bare ground (snow breeze), - substrate

§ Desert-only examples that have been discussed- substrate (salt breeze)

A contrast in microclimates –The Nile in Luxor, Egypt

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The dynamics of local circulations

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Why Should We Care About These Local Winds

§ Especially in subtropical deserts, large-scale winds are often benign, and “local” winds are the most-frequent ones.

§ Wildfires are common in semi-arid areas, and local winds must be understood and forecast.

§ Local winds can elevate dust into the air.§ Even light winds can cause heat stress on

the human body.

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Salt-Breeze Circulations

Australian Dry Salt Lake

Surface Temperature

Australian Dry Salt Lake

Low-Level Wind

Climatology For Five-

Month Period

Observed Divergence-Convergence of Low-Level Winds Over the Lake

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Model-Simulated Vertical Motion Caused by the Salt Breeze

1200 LT negative = down

Great Basin Desert

Salt Breeze

Great Basin Desert

Salt Breeze

1500 LT

40 m AGL

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The winds around Lake Kinneret

Lake Kinneret

Orography

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Jordan Valley Lake Kinneret

Wind ClimatologyThe Negev Desert –

What could cause this?

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An Example of Important Weather Consequences That Result From Local Circulations in Arid Areas

Typical Soil

Moisture

Wind

The Elevated Mixed Layer (EML)

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