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Southeast Pacific Climate - Windows to the Universe

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VOCALS scientists will be studying the Southeastern Pacific Climate to better understand the interacitons between the oceans, clouds, atmosphere, and land in this region.
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Robert Wood (University of Washington) and the VOCALS Scientific Working Group

Southeast Pacific Climate

There are several regions in the world where low-lying stratus and stratocumulus clouds are frequently present and an important part of climates. It turns out that these regions also play an important role in Earth's global climate. Examples include the subtropical climates off of the coasts of California (US), Namibia (Africa), and Peru and Chile in South America. The climates of these regions involve interactions and feedbacks between the ocean, clouds, atmosphere, and land. Scientists in the VOCALS field campaign are focusing their experiments in the Southeast Pacific (SEP) Ocean off the coasts of Chile and Peru. They have chosen this area because the feedbacks in the regional climate systems are the clearest.

The climate of the SEP is dependent upon interactions between the Andes Mountains, the upper layer of the ocean, and the lower troposphere. In the SEP, clouds form right above the ocean in an area known as the marine boundary layer or MBL. MBL clouds are of the low stratus type. They create continuous cover over extended regions of the SEP. Precipitation from MBL clouds is mostly in the form of drizzle. It is likely that the amount of drizzle influences the structure and dynamics of SEP cloudiness.

Westerly winds blow thousands of miles across the Pacific Ocean toward South America. The winds are forced to turn north along the coast when they encounter the Andes Mountains range. Evaporative cooling occurs as the winds sweep across the water. The winds in this region cause the water at the ocean surface to move perpindicular to the coastlaine (westward) in a process known as the Ekman transport. The displaced surface water is replaced by colder, nutrient-rich ocean water rising from the deep ocean. The process of upwelling in the SEP is associated with the Humboldt Current system. These cold waters, aided by an air mass, made stable in part by effects of the Andes, help support the largest and most persistent subtropical sheet of stratus and stratocumulus clouds on the planet. This cloud deck, affected by aerosols from both natural and human sources, helps in turn to maintain cool ocean waters beneath.

Limited measurements, model results, and satellite observations indicate that the atmosphere over most of the SEP is very clean. However, copper smelters located in Chile and Peru produce pollutants which become aerosols in the atmosphere. Aerosols are also present naturally in this area from sea salt and plankton. Aerosols are known to affect the formation of clouds and precipitation. If the aerosol concentration is high enough, it is thought the amount of drizzle produced by the MBL clouds could be suppressed. Therefore, VOCALS scientists will test hypotheses about the relationship between aerosols, atmospheric processes in clouds, and precipitation.

Last modified September 22, 2008 by Sandra Henderson.

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Stratus (weather symbol - St) clouds consist of water droplets and belong to the Low Cloud (surface-2000m up) group. They are uniform gray in color and can cover most or all of the sky. Stratus clouds...more


Stratocumulus (weather symbol - Sc) clouds consist of water droplets and belong to the Low Cloud (surface-2000m) group. These clouds are low, lumpy, and gray. These clouds can look like cells under a microscope...more

What is VOCALS?

What if you wanted to learn more about the climate system of a very large area such as the Southeast Pacific Ocean? What would be involved in studying how the oceans, land, and atmosphere interact? You...more


Drizzle is light precipitation that is made up of liquid water drops that are smaller than rain drops. Drizzle can be so light that only a millimeter of accumulation is measured at the Earth's surface....more

Winds in the Southeast Pacific

Winds in the Southeast Pacific have a strong influence on regional climate and play an important role in several large-scale, global climate phenomena. The Hadley cell is a global atmospheric circulation...more

Ocean Upwelling

In areas of upwelling, deep ocean water makes its way to the surface. This has an impact on marine life as well as the region's climate. Upwelling happens commonly along coastlines. Winds blowing parallel...more

Aerosols: Tiny Particulates in the Air

Aerosols, also called particulates, are tiny bits of solid or liquid suspended in the air. Some aerosols are so small that they are made only of a few molecules so small that they are invisible because...more

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