|George R. Kasica
METEO 241 Portfolio #2: The 1982-83 El Nino and it's effect on the Walker Circulation in the Pacific Ocean between October 1, 1982 and February 28, 1983
As you can see in the above images provided courtesy of the Earth Systems Research Laboratory's Monthly/Seasonal Composite Web Page there are several areas of differences from the normal values in both the 700mb vertical motion as well as the mean sea-level atmospheric pressure. These differences have a direct effect on the Walker Circulation (note the preceding link is an external link to the on-line AMS Glossary).
In the top pair of images you are looking at the 700mb vertical motion anomaly plot provided by the Earth Systems Research Laboratory's Monthly/Seasonal Composite Web Page and in it you can see that from October 1, 1982 through February 28, 1983 there are two areas of interest indicated: One, an area of ascending motion in the eastern Pacific and a second area of descending motion in the western Pacific. As we know, in order to generate convective activity and ultimately precipitation you need to have some form of rising motion in the atmosphere. You can clearly see that the area in the eastern Pacific has this characteristic, which since it is being shown on an anomaly plot it is clearly an abnormal event for this time period. Looking to the other area in the western Pacific you can see an area of descending motion, and as we know, these areas generally area areas of fair weather and no precipitation. Again, since it is shown on the anomaly plot it is not the expected condition for this time period.
Looking at the bottom pair of images showing mean sea-level pressure anomaly plots provided by the Earth Systems Research Laboratory's Monthly/Seasonal Composite Web Page you can see that from October 1, 1982 through February 28, 1983 there are again two areas of interest indicated in nearly the same places as we saw on the top two 700mb vertical motion plots. In the eastern Pacific we can see as you would expect with an area of rising motion a corresponding area of lower than normal mean sea-level pressure. In the western Pacific you can see an area of higher than normal mean sea-level pressure corresponding to roughly the same area as the area of 700mb descending motion.
As we know, areas of low pressure tend to be generally associated with areas of areas of poorer weather and precipitation and areas of higher pressure tend to be associated with areas of fair weather and little to no precipitation. Therefore these 4 plots show more evidence of the abnormalities in the Walker Circulation (note the preceding link is an external link to the on-line AMS Glossary) and as a result the potentially increased precipitation areas in the eastern Pacific in association with El-Nino.
To look further at what else was occurring at the time return to the main page and lets look at another item of data that may give us a clue as to what El Nino was doing to other aspects of the ocean or atmosphere.