NCERT Class 11 Geography — Chapter 2: Movements of Ocean Water

The correct option is Narrow diurnal and annual temperature ranges.

Explanation

The climate of the west of continents in tropical and subtropical latitudes (approximately 15°-35° N/S) is heavily influenced by cold ocean currents (e.g., Peru Current, Benguela Current, Canary Current, California Current). These currents modify the coastal climate, creating distinct conditions known as "Cold Coastal Deserts" or "West Coast Deserts."

Option-wise Analysis

• Wide diurnal and annual temperature ranges.: Incorrect.
  While hot deserts located in the continental interiors are characterized by very wide diurnal and annual temperature ranges due to continentality and clear skies, the west are different. The proximity to the ocean and the presence of cold currents moderate the temperature significantly.
• Narrow diurnal and annual temperature ranges.: Correct.
  The cold ocean currents exert a strong maritime influence on the immediate coastal strip.
  • Annual Range: The ocean prevents extreme heating in summer and extreme cooling in winter, resulting in a narrow annual temperature range (often less than 10°C).
  • Diurnal Range: The presence of a cool marine layer, high humidity, and frequent fog (caused by temperature inversion) suppresses the daily temperature variation, keeping the diurnal range narrow compared to the inland desert.
• Heavy rainfall throughout the year.: Incorrect.
  These regions are characterized by aridity (low rainfall), not heavy rainfall. The cold water cools the air above it, creating a temperature inversion (cold air below warm air). This stable condition prevents the vertical uplift of air necessary for cloud formation and precipitation, leading to the formation of deserts (e.g., Atacama, Namib).
• Absence of fog.: Incorrect.
  Fog is a defining characteristic of these coasts. When warm, moist air from the ocean blows over the cold current, it cools to its dew point, forming thick advection fog (e.g., the garúa in Peru or fog in Namibia), even though rainfall is absent.

Key Takeaway

Cold ocean currents on the western margins of the tropics create a unique climate characterized by aridity, frequent fog, and narrow temperature ranges (cool summers and mild winters), distinguishing the coast from the extreme temperatures of the interior deserts.