Australian Satellite Images and El Niño Links

This page will help you get started looking at the wealth of data available on these topics. Enjoy! Links to Internet sites are in green. Areas of North America, Europe and Eurasia experience enhanced (floods, erratic snowfall leads to avalanche or spring flood risk) or decreased precipitation (drought). Deviations from "normal" can be substantial and affect agriculture, fisheries, disease distribution, disaster planning, travel, to name a few influences.

For Australia and other countries surrounding the Indian Ocean, the Australasian monsoon season changes drastically. As for North America and South America, monsoon rains are the difference between food, economic health, and disease. In drought areas, fires spread out of control.

In 1997-98, Australia experienced particularly damaging wildfires. Setting fires to control vegetation in the outback and in other sorts of farming is a frequent practice. Under normal circumstances, Australian burning does not show up on nighttime satellite (temperature differences are recorded) because dew puts out the fires. With water content of the atmosphere reduced, fires burn and spread without the natural buffer of condensation (dew).

ABOVE: NOAA diagram of the ElNiño warm water mass, which pumps more water vapor into the Earth's atmosphere along the equator. Arrows indicate its movement influenced by the west to east spin of the planet when the trade winds stop (see below). A thermocline is the boundary (rapid temperature change with depth) between water masses of different temperature. A sea level satellite series of images is below the next diagram, with expanation by a NOAA scientist. Click on the images to view at full size.

ABOVE: Diagram of the way in which the trade winds keep the warm water mass over by Australia's Great Barrier Reef, allowing the cold water to well up along the Pacific South American coast. These cold waters come from deep in the ocean, where they have been collecting (recycling) nutrients which "rain down" from shallower waters (from the lighted zone of about the top 200 meters) where photosynthesis occurs. When the trades stop, the warm water moves eastward, and because it is less dense than the cold seawater under it, it acts as a "cap" for upwelling. The fisheries dependent on the coastal food web (based on photosynthesis PLUS nutrients to feed the marine algae which zooplankters consume, which are eaten by fish, which are caught by fishermen...) are deprived of the crucial nutrient enrichment needed to support commercial fishing.

This effect is commonly noticed during the Christ Mass season, the Christ Child being called "El Niño" in Spanish. "La Niña" refers to the periods between El Niño episodes.

These three images (ABOVE, shown at 50%, so click on the image to see at full size) depict the evolution of a warm water Kelvin wave1 in the equatorial Pacific Ocean during March and April 1997. Kelvin waves are often precursors to El Niño events which can disrupt global weather patterns. These data were collected by the altimeter onboard the joint US/French TOPEX/Poseidon satellite and these images show sea surface height relative to normal ocean conditions.

The white and red areas indicate unusual patterns of heat storage where the sea surface is elevated up to about 20 centimeters (about 8 inches)2 and 10 centimeters (4 inches) respectively. The El Niño phenomenon is thought to be triggered when the steady westward blowing trade winds weaken and even reverse direction. This change in the winds allows the large mass of warm water (the red and white area) that is normally located near Australia to move eastward3 along the equator until it reaches the coast of South America.

The warm water mass can affect where rain clouds form4 and, consequently, alter the typical atmospheric jet stream patterns around the world. Using these data, the National Oceanic and Atmospheric Administration, (NOAA) has issued an advisory indicating the presence of the early indications of El Niño conditions. A number of El Niño forecast5 activities supported by NOAA indicate the likelihood of a moderate or strong El Niño in late 1997. The forecast model operated at NOAA's National Centers for Environmental Prediction (NCEP) used data collected by the TOPEX/Poseidon satellite.

Stephanie Kenizter
National Oceanic and Atmospheric Administration
Washington, D.C.

NLN Footnotes:
1. The Kelvin wave can be seen as the big red and white band along the equator. The red and white banding in the southern hemisphere during March and April is comes in large part from the southern hemisphere summer heating of ocean water. As the northern hemisphere is still cold from the winter, these satellite images show how the oceans affect global weather by storing heat and releasing it slowly, modifiying climate.

2. Satellite surveys of the oceans show variation in sea level with water temperature (seen in the above images), gravitational forces (such as tides where water responds to the masses of sun and moon), atmospheric pressure and so forth.

3. The earth's spin direction from west to east plus winds affects the movement of water masses, when the winds slacken, the other factors such as the spin of the planet and the density of water masses dominate the sizing and position of the warm masses of sea water in the world's oceans. The biggest mass of shifting warm water is in the equatorial Pacific Ocean. Density of seawater in any given place is a nonlinear interaction of temperature and salinity.

4. More water evaporates into the atmosphere from warm water than cold. This evaporated water is carried aloft by rising air at or near the equator (ITCZ or InterTropical Convergence Zone) and is transported in the general direction of the poles. The ITCZ is a prominant feature of the Earth's atmosphere and results from the temperature differences at the poles (both are cold/northern hemisphere continents trap sea ice/southernhemisphere has a continental platform for ice to accumulate) and the equator (warm). The ITCZ can be identified in appropriate satellite images by the "necklace" of spiral storms which form as warm wet rising air meets cooler air aloft. The net effect of an El Niño episode is to shift rainfall from one region to another, which is why there worries about famine track by this sort of weather. And then there are the droughts (which ruin crops), floods (ruin crops as well), disease (many carriers of disease redistribute themselves as the frost limit moves north or south), ice storms, erratic snow packs and so forth...

5. Forecasting is tricky because of uncertainties inherent in the multitude of factors which interact to produce climate (long term behavior of the atmosphere, sun, earth's orbital geometry and oceans) and weather (short term behaviors).