RICE

HORSE LATITUDES

Introduction

The horse latitudes are subtropical regions located at around 30 degrees north and south of the equator. They are also known as subtropical highs or ridges and are characterized by calm winds, little precipitation, and warm and pleasant weather

Western horse latitudes The story goes like so, under the right conditions sailors would leave horses in a boat (in this case transport them across bodies water).

Why Did Early European Sailors Call It the Horse Latitudes?

  • Stranded Ships: In the era of sailing ships, the calm winds in this zone could leave ships stranded for weeks or even months, unable to make progress.
  • Water Shortages: The lack of wind meant sailors couldn’t use their sails to generate water through evaporation, leading to severe water shortages
  • More than one school of thought, including among some desperate sailors who introduced their own “ship husbandry” by throwing the horses overboard in order to conserve water and food. It is from this practice that the name “Horse Latitudes” derived.

Characteristics of the Horse Latitudes:

  • High Pressure Zones: The Horse Latitudes create high pressure when the air descends. This descending air inhibits cloud formation and results in the calm winds and clear skies.
  • Hot and Dry Climate : The lack of clouds allows for intense solar radiation, leading to hot, dry weather in these regions.
  • No Wind at All: Sailors depend on wind to move their ships, so lack of it often feels especially maddening.
  • Subtropical Deserts: Subtropical deserts like the Sahara Desert and Atacama Desert are also formed under Horse Latitudes.

Why the Calm Winds Exist?

  • This calmness in the wind is a feature of global atmospheric circulation patterns. A simple explanation would be the following:
  • Equatorial Low: At the equator, warm wet air rises to form low pressure zones and a lot of rainfall.
  • Hadley Cells: The rising air bounded for the poles cools and descends towards Earth at roughly 30° latitude. This descending air is the origin of the high-pressure zones in which are situated at approximately 30 and forms what’s known as Horse Latitudes.
  • Trade Winds: The air then circulates toward the equator generating trade winds which mariners have always used to sail across oceans.

Impact on Weather and Climate:

  • Subtropical Highs: Various high pressure cells are responsible for triggering sub-tropical highs that bring warm weather with clear skies and little to no moisture.
  • Desert Formation: The dryness, lack of moisture and the uneven rainfall in this area help form deserts.
  • Ocean Currents: The Horse Latitudes also influence the formation of ocean currents, including the Gulf Stream and the Kuroshio Current.

Why Most of the World’s Hot Deserts are Located near 20-30 degree N and on the Western Side of the Continents:   

Oceanic currents:

  • Cold ocean currents along the west coasts of continents at these latitudes often create an inversion layer, trapping moist air and preventing it from reaching the land.
  • Leading to stable atmospheric conditions, this further reduces precipitation and enhances desert conditions.

Hadley Cells and Descending Air:

  • The Earth’s atmosphere is constantly in motion, driven by the uneven heating of the planet by the sun.
  • Warm, moist air rises at the equator and creates a low-pressure zone. This warm air rises and heads towards the poles, cools back down and drops to Earth around 30 degrees latitude
  • This descending air is dry because it has already released its moisture as it rose and cooled near the equator. This descending, dry air creates a high-pressure zone, leading to clear skies and limited cloud formation.

Lack of Precipitation:

  • The descending air in the Horse Latitudes inhibits cloud formation, making it difficult for precipitation to occur.
  • As the air descends, it warms and becomes more stable, further discouraging cloud formation and rain.

Rain Shadow Effect:

  • Mountains on the western side of the continents act as barriers to moisture-laden winds. When these winds encounter mountains, they rise, cool, and release their moisture as rainfall.
  • As a result, the eastern side of the mountains receives abundant rainfall, while the western side is left relatively dry, creating desert conditions.
PYQ Q. Consider the following statements: (UPSC 2007)
1. Either of the two belts over the oceans at about 30°–35° N and S latitudes is known as Horse Latitude.
2. Horse latitudes are low-pressure belts. Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2