El Ninos and La Ninas are at the center of our discussion of climate change. What causes them and what are their effects? These are the two big questions in my mind, though determining the causes of these tropical events will likely prove fruitless, unless we can confirm the cirrus cloud suggestion made by Erl. So, my post will show how El Ninos and La Ninas begin and how they spread, for this seems like a logical place to begin the discussion at this blog. In the future, I’d like to explore the mechanism through which heat released by El Ninos moves after the sea surface temperature (SST) anomaly along the equator disappears. Also, I’d like to determine if we can think of La Ninas and their effects in the same terms. For clarity in this post, I will focus on El Ninos.
The Pacific Ocean:
For this analysis, I used SST anomoly from the region used to calculate the Cold Tongue Index (CTI). I didn’t use the CTI itself, because to calculate it, the trend is removed from the data. The rest of my data is extracted SST with no trend-removal, so to be consistent, I used the raw SST for the region with no trend removed. The CTI is defined to cover the region (6 S to 6 N) (180 W to 90 W). Below is a graph of SST anomalies in the CTI region.
Changes in the temperatuere of the Cold Tongue of the Pacific are not consistently the first signal of an El Nino event. To illustrate this point, here are animations made by NOAA:
As you can see, in the 97/98 El Nino, SST first rose along the Peruvian coast. JISAO provides a SST dataset for Puerto Chicama, Peru. Below are some graphs of the Cold Tongue SST Anomaly vs the Puerto Chicama SST Anomaly.
As you can see, this data also suggests that the 1997/98 El Nino began with changes in SST of the Peruvian Coast. From this analysis, we can conclude a few things. First of all, if cirrus cloud is initiating El Nino events, during specific El Nino events, it is relevant to know if cirrus clouds dissipate first over the Cold Tongue or the Peruvian Coast. Secondly, a topic to pursue in the future is if variations in the temperature off the Peruvian Coast have different effects from variations in the Cold Tongue.
The Atlantic Ocean:
The Atlantic Nino is significantly different from the Pacific Nino, as you will see. I’ve divided the Equatorial Atlantic into several quadrants. Below is a graph of SST separated by Latititde.
Notice how SST above the equator has behaved opposite from SST below the equator since the 97/98 El Nino.
Below is a graph of Atlantic SST separated by Longitude. I haven’t separated the data like I did in the previous graph, because I just intend to show that the behavior of SST does not vary significantly with Longitude.
Below are graphs according to Latitude and Longitude for the 82/83 & 97/98 El Ninos.
Notice that what I am refering to as the 1982/3 El Nino seems to have occured in 1984 in the Atlantic. There was a small rise in SST at the time of the 82/83 El Nino, though the SST anomoly in 1984 in the Atlantic was unusually large, indicating that it may have been related to the El Nino in the Pacific nearly two years earlier, though it may merely be a coincidence.
As you can see, the Atlantic Nino is most apparent in the Eastern Atlantic between 0 and 8 S. The strength of the SST anomaly decreases as you move West and North.
El Ninos in the Indian Ocean resemble El Ninos in the Pacific. Below are graphs of the 1997/8 El Nino according to Latitude and Longitude.
It is clear the El Nino events in the Indian Ocean begin in the West and move East at all latitude bands.
Comparing the Oceans:
Below is a map of where, according to the analysis above, El Ninos begin in each ocean.
I’m leaving out the coast of Peru because the graphs below will use only SST anomalies in the Cold Tongue.
Below are graphs comparing the Pacific, Indian, and Atlantic Nino regions since 1978 and during the 1982/3 Nino and the 1997/8 Nino.
The Atlantic Nino seems to lag behind the Pacific Nino considerably during some events and not at all during others. The Indian Ocean also seems to lag behind the Pacific on some occasions but not others; however, the variable lag time is not as extreme in the Indian Ocean as it is in the Atlantic.
Source: Smith and Reynolds Extended Reconstructed SST (ERSST.v2)
Use the instructions in this post to access the data; however, don’t read the read the rest of the post – it’s wrong.