back to list of extensions Some Comments on El Nino

The principles of cloud formation and the Coriolis effect help in understanding summer  El Nino as a phenomenon that occurs in the equatorial PacificOcean. During EI Nino periods the surface waters of the western equatorial Pacific near Asia are relatively warm while the waters of the eastern equatorial Pacific near South America are relatively cool. This temperature distribution is a result of the easterly winds in tropical regions, the Coriolis effect and the fact that warm water overfies cold water in the ocean.
During El Nino periods the surface water temperatures in the eastern equatorial Pacific get warmer while those in the western equatorial Pacific get somewhat cooler. These periods occur at intervals of 2 to 7 years with varying levels of intensity and varying lengths of occurrence. These changes in the equatorial Ocean temperatures are associated with changes in the atmosphere. During non El Nino periods the air over the warm western equatorial Pacific waters tends to rise (rem
ember that warmer air tends to rise relative to cooler air) and the surface air pressure is relatively low. At the same time in the eastern Pacific the cool surface waters result in cooling of the air and hence sinking air and higher surface air pressures. The rising air in the western Pacific results in clouds and precipitation while sinking air in the eastern Pacific suppresses
During El Nino the surface air pressures increase in the western Pacific and decrease in the eastern Pacific, There is an associated weakening of the easterly equatorial winds. The region of rising air and significant precipitation moves
away from the western Pacific toward the central Pacific resulting in non rain in the central Pacific and drier conditions and often drought in western Pacific areas such as Indonesia and Australia. in the eastern Pacific the warmer surface waters result in non rising air in coastal regions of South America which in turn results in high rainfall regions.The changes in air pressure between El Nino and non EI Nino periods are referred to as the Southern Oscillation. The Southern Oscillation and El Nino are linked occurrences and each influences the other. Due to this linkage the overall phenomenon is referred to as ENSO (El Nino - Southern Oscillation). Although I have not gone into detail about the role of the Coriolis effect ingenerating El Nine, you should note that the principles of cloud formation resulting from conditions of rising air and being suppressed in sinking air help to understand the changes in precipitation in the equatorial Pacific during El Nine periods. El Nino has been big news lately as a result of its alleged global effects. While the effects in the equatorial regions described above are fairly certain and even extend to other other equatorial areas such as drought in parts of Africa, some of the reported more distant effects are less certain, One should he particularly wary of predictions and claimed linkages in th northeast US based on EI Nino, since many other factors affect the weather in our area.
latitudes in both hemispheres. The Earth of course has features such as oceans, continents and mountain chains, so there are further complications to these patterns. Still the easterlies in the tropics and the westerlies in the mid latitudes exist on average. The banding of clouds into certain latitudes is related to these motions and a time lapse picture shows clouds in the mid-latitudes moving west to east. That is why we can often look to the west to know what weather we might expect. Weather systems in our latitudes often move from west to east. We live in mid latitudes, but we know that the wind does not always blow from the west. That is due to the effect of low and high pressure systems which determine the winds over distances of hundreds of miles. The wind resulting from such systems can blow from any direction depending on where you are relative to the center of low or high pressure. The prevailing westerlies represent the average tendency for the winds to blow from west to east in the mid-latitudes. Also the westerlies are the drivers that tend to make pressure systems move from west to east in mid-latitudes. Although storms (low pressure systems) usually move from west to east in mid-latitudes, their approach is generally signaled by winds from the east or northeast or southeast because air is moving toward the approaching low and diverted by the Coriolis effect. On the east coast of the US some severe storms move from southwest to northeast. These are called Nor'easters due to the strong winds from the northeast. Benjamin Franklin was one of the first to realize that although the strong winds were coming from the northeast, the storm was moving in a direction opposite to the winds. He discovered this by comparing storm arrival times in Philadelphia with those observed by his brother in Boston. 
 

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