El Nino/ La Nina part 1

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I have struggled with how to present this information. El Nino Southern Oscillation (ENSO) is one of the most talked about occurrences going into a winter season. It is also one of the least understood occurrences by most of those who talk about it.


While El Nino and La Nina are factual occurrences, their impacts are theoretical. There are degrees of severity for both and there are different types of each. Generically, El Nino is a condition that refers to warmer than average sea surface temperatures (SSTs) along the equatorial region west of South America. More specifically, the temperatures need to reach .5 degrees Celsius above average for a period of either 3 or 5 months depending on who you listen to.  Most countries that are affected by the phenomenon have their own definition or standard for determining when El Nino conditions have been reached.

El Nino Regions

There are 4 regions of El Nino/La Nina: 1+2, 3, 3.4 and 4.


Credit:  “The Climate Data Guide: Nino SST Indices (Nino 1+2, 3, 3.4, 4; ONI and TNI).”


El Nino/La Nina types

A “typical” El Nino is determined by warming in region 3.4 which is roughly between 120 west and 170 west longitudes and 5 north and 5 south latitudes. This is area is where they determine the ONI or Oceanic Nino Index.

An El Nino Modoki occurs when the anomalous warming occurs in region 4 which is roughly from 160 west to 160 east.

El Nino Modoki conditions can often be similar to La Nina events depending on the severity of the warming and the warming in comparison to the SSTs in the other regions which determine the Trans Nino Index (TNI).

I have to admit I have not been monitoring the ENSO conditions closely the last few months. Our area is only slightly influenced by mild ENSO conditions. I follow people who interpret the data and they pass on their opinion.  While preparing for this post I dug into the latest data and learned some interesting things that I will be sharing over the next couple of posts because it is about to get complicated. Eventually, I will get to the theoretical effects of ENSO.



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