Geography – Hot Deserts
Essay30th October 2011 Discuss the climatic characteristics of one climate type you have studied. The climatic type of climate I have studies is the hot deserts. These deserts usually consist between 15° and 30°, north and south of the equator normally positions within the trade wind belts with the Sahara as the only exception. Desert temperatures are very extreme; they can be both very hot and cold. The tropical desert has the highest mean annual temperature of any climate on Earth.
The high temperatures are a result of the high sun angles throughout the year and having the highest percentage of sunshine of any climate. No month has an average temperature below 18oC and many places have consecutive average monthly temperatures in the mid 30os Celsius (90oF). Daytime temperatures can reach 50oC at low elevation inland deserts. The sky in the tropical desert remains cloud-free due to the subsiding air of dominant high pressure resulting in large amounts of insolation.
The cloudless skies during the day let insolation in, but also let’s much heat out at night. Without the absorptive blanket of clouds, long wave radiation emitted from the Earth readily escapes to space, chilling the nighttime desert air. The high energy input during the day and large loss at night results in an extremely large daily temperature range also known as the diurnal range. Precipitation in the tropical desert is very irregular and unreliable. Low latitude deserts average less than 25 in a year.
An entire year’s worth of rain may fall in one downpour. The continental location of many tropical deserts places them far from a source of moisture, the ocean. Combine continentality with the strong subsidence of the subtropical high and you have one of the driest places on earth. Air subsiding from the subtropical high is adiabatically warmed which reduces the relative humidity of the air. Relative humidity can drop to 10% or less. The extremely low relative humidity causes evaporation of what little surface water there is.
The subsiding air also promotes atmospheric stability, further inhibiting precipitation. The Arica desert has a monthly temperature of 22°C due to its close cold ocean currents. Although this lack of rainfall causes an enormous water shortage, no desert is truly “dry”. Climatologists describe the desert as an “arid” climate. An arid climate, as defined on the basis of the soil moisture balance, is one in which the annual precipitation is less than half of the annual potential evapotranspiration.
In the tropical desert the only substantial source of surface water other than exotic streams is an oasis, where the groundwater table is near the surface. From the above description, we can clearly see that the desert is a type of extreme climate. The temperatures can reach deadly numbers. Rainfall is sporadic and in some years no measurable precipitation falls at all. The terribly dry conditions of the deserts are due to the year-round influence of subtropical high pressure and continentality.
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