Meteorological and climatological characteristics of the Andes

Introduction

The Andes extends from Western Venezuela (10°N) in the North, along the western side of the South American continent and across the Equator towards the South of Chile, Patagonia (50°S).  Obviously along this 7000km long mountain range there are a number of different climates.

The Andes are subdivided into three parts: the Northern, the Central and the Southern Andes, each with its specific climate

These climates are mainly determined by two elements:

• Their position in the different zones of the global surface circulation pattern.
• The effect of the Foehn wind which determines the wet/cold  and arid/hot regions

The cold Ocean current, the Humboldt, and the climatological processes El Niño and La Niña are playing an important part too but not explained in the frame of this article.

 

Global Circulation

Due to the thermal unbalance between the Tropics and the Polar regions there is a global circulation which transfers heat from the former to the latter.

The picture below shows the global surface circulation with to the North of the Equator the Northeasterly trade winds, to the South of the Equator the Southeasterly trade winds and South of the subtropical High pressure belt, the Westerlies.

 

 Picture 1: Global surface circulation

 Effect of the Föhn wind

The foehn wind is the thermo dynamical modification of an air mass when it crosses a mountain range.

 Picture 2: The Foehn Wind Process

On the ‘wind ward’ side the air mass is wet and cold:

then air reaches a mountain range it is pushed upward .Air that moves upward becomes gradually colder and finally saturation occurs.  Due to the saturation, condensation starts and clouds are formed. As the air mass further rises, the cloud grows. When the cloud is big enough it starts to produce precipitation

On the ‘lee side’ the air mass becomes dry and warm: As the air mass reaches the summit it has become much drier due to loss of moisture by  precipitation. As a consequence the clouds dissipate and the lee side is in general cloud free. The air mass starts its descend and heats up.

 The different climates of the Andes

With a length of 7000km the Andes crosses three different circulation belts:

The Northeasterly Trade winds - The Southeasterly Trade winds - The Westerlies

 

 Picture 3: South America in the Global Surface Circulation

 

In the Northern and Central Andes the air comes from the Easterly sector (trade winds). Due to the effect of the Fhoen wind, the eastern side of the Andes is in general wet.

Along the western side of the Andes there is a drier area (between the mountains and the Pacific) which corresponds with the ‘lee’side of the mountain range (see picture 2)

 

Picture 4: Precipitation distribution in the vicinity of the Andes. Notice the dry slot between the mountain range and the Pacific Ocean.

 

• 1.Northern Andes 
• Picture 5: Northern Andes region with mountain tops      

Climate

      The coastal area (Peru and South Colombia has an unusual type of dry desert climate, caused by two main features:

o       the Northeasterly trade winds, when crossing the mountain range, become dry due to the Foehn wind effect.

o       The cold waters of the Humboldt Ocean current. This current maintains low temperatures for this tropical latitude.

In this area the El Nino effect may cause every few years a few weeks of torrential rain, causing considerable damage.

In this area the snow line is situated in general between 4500m and 4800m 

On the Eastern slopes of the Andes mountain range it is rainy and dry. An example of a snow covered peak next to the rain forest is the Cotopaxi (see picture below)

Picture 6: Cotopaxi, snow covered summit next to rain forrest

Main mountain tops

•  
  •       Venezuela-Northern Colombia
  • ¨      Pico Bolivar – 16427 (Venezuela)
  • ¨      Pico Cristobal – 18847ft (Colombia)
  •    Central Colombia (vulcanoes)
  • ¨      Nevado del Ruiz – 17405ft
  • ¨      Nevado de Santa Isabel – 16700ft
  • ¨      Nevado del Tolima – 17110ft
  • ¨      Nevado de Huila – 18997ft 
  •       Ecadorian Vulcanoes (Avenue of Vulcanoes)        
  • ¨      Chimborazo – 20703ft
  • ¨      Cotopaxi – 19347ft
  • ¨      Cayambe – 18997ft (Equator)

 

 

 

 

This entry was posted on Friday, August 21st, 2009 at 5:03 pm and is filed under The climate of the Andes. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.