Sunday, February 02, 2014

El Nino - La Nina

 Pradeep has put up the Hill Sates rain amounts from F-1 on his Page..

See Update on F-2 and latest as on Wednesday Night on Current weather Page 

What is El-Nino, La-Nina and Normal Scenario...Simplified

The name El Niño is believed to have been coined in the 19th century after Peruvian fisherman observed it around Christmas – the word is Spanish for "boy", in reference to the infant Jesus Christ. La Niña, the word for "girl", was devised later to label the reverse phenomenon.Both are significant markers of global climate fluctuations.




In Normal Scenario, In the vast Pacific Ocean, the water goes West from the Peru Coastline. So does the air. Why? Because the surface of the ocean is joined to the bottom of the air. Now the water is an easterly current going to the west, and so is the air, and this produces easterly winds. Easterly winds bring moisture from the sea and by the time they arrive on the Australian coast they are rain-laden.


The combi-nation of cooler easterlies and lower pressure brings rain. This is the NORMAL situation. 

But it doesn't last. The movement of water to the left eventually makes the sea level higher on the left, just as a very slow-moving ripple wave would in a bath. When it gets to a critical height difference, about 62cms, it wants to go the other way. Slowly the water starts flowing to the RIGHT. Higher pressure now is on the LEFT, above Australia. And higher pressure flows towards lower pressure.The water is joined to the air and produces westerlies. The warmer water arrives at Peru and is called El Niño.

During an El Niño event, the easterly trade winds converging across the equatorial Pacific weaken.  This in turn slows the ocean current that draws surface water away from the western coast of South America and reduces the upwelling of cold, nutrient–rich water from the deeper ocean, flattening out the thermocline and allowing warm surface water to buld in the eastern part of the basin.

El Niño occurs every two to seven years, when the trade winds that circulate surface water in the tropical Pacific start to weaken. The result is a major shift in rainfall, bringing floods and mudslides to usually arid countries in western South America and drought in the western Pacific, as well as a change in nutrient-rich ocean currents that lure fish and make them migrate.

The last El Niño lasted from June 2009 to May 2010.



An enhancement of the "normal situation" is La Nina. Same winds and flow, but stronger. Averaging about 2-3 years after the normal occurrence.

El Niño is often followed by a reverse swing  with La Niña, characterized by unusually cool ocean surface temperatures in the central and eastern tropical Pacific. In fact, very simply put, when the normal situation reaches its maximum point it is called La Niña. 
The last La Nina ended in April 2012.

El Niño and the Southern Oscillation, also known as ENSO is a periodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean.

The Southern Oscillation compares variation in sea level barometric pressure between observation stations at Darwin, Australia and Tahiti.  It is quantified in the Southern Oscillation Index (SOI), which is a standardized difference between the two barometric pressures.  Normally, lower pressure over Darwin and higher pressure over Tahiti encourages a circulation of air from east to west, drawing warm surface water westward and bringing precipitation to Australia and the western Pacific. 
When the pressure difference weakens, it is coincidental with El Niño conditions,

Although the exact initiating causes of an ENSO warm or cool event are not fully understood, the two components of ENSO – sea surface temperature and atmospheric pressure are strongly related.  

The strengthening and weakening of the trade winds is a function of changes in the pressure gradient of the atmosphere over the tropical Pacific.  Ironically, the warming of the sea surface works to decrease the atmospheric pressure above it by transferring more heat to the atmosphere and making it more buoyant.  
So, in summary, the pressure gradient affects the sea surface temperatures, and the sea surface temperatures affect the pressure gradient.


La Nina Summer 


El Nino Summer


Southern Oscillation Index:
The Southern Oscillation Index (SOI) has risen over the past two weeks, though this is thought to be largely due to short term local weather variations rather than larger scale climate shifts. The latest approximate 30-day SOI value to 26 January is +10.0.
(Sustained positive values of the SOI above +8 may indicate a La Niña event, while sustained negative values below -8 may indicate an El Niño event. Values of between about +8 and -8 generally indicate neutral conditions.)

Current Position:
El Niño–Southern Oscillation (ENSO) remains in a neutral state. The latest NINO3.4 sea surface temperature anomaly is -0.3 °C. The 30-day Southern Oscillation Index (SOI) value to 26 January is +10.0. 
Negative OLR anomalies  were observed over Malaysia, Indonesia, the Philippines, and the 
equatorial western Pacific. Positive OLR anomalies were evident over the central equatorial Pacific. 
Low-level (850-hPa) winds were near average across the equatorial Pacific. 

ENSO-neutral conditions continue.
• Equatorial sea surface temperatures (SST) are near average across much of the 
Pacific Ocean, with regions of below average SST in the east-central Pacific. 

What is the Positional Outlook for remaining months of this year  ? Specially for the South West Monsoon -2014 ? 
WMO cautions forecasters-" "Some caution should be exercised when using long-range outlooks made at this time for the middle of the year and beyond," it said

Some International Outlooks:

--"Current model outlooks further suggest an enhanced possibility of the development of a weak El Niño around the middle of 2014," the World Meteorological Organization (WMO) said.

-- For the first few months of this year, meanwhile, the WMO said there was a slight possibility of a weak and brief appearance of the El Niño's mirror image La Nina, which cools the ocean.

-- But overall, there is a strong likelihood that conditions in the Pacific will remain neutral, with neither an El Niño or La Nina observed.

-- Climate models suggest an ENSO-neutral state to persist until at least the end of March, with some warming of the tropical Pacific likely.
-- Some, but not all, models predict this warming may approach El Niño thresholds by early Summer.
-- The picture for the remainder of the year remains hazy, the WMO underlined.

-- Vagaries estimates a neutral State till April/May. Now, we are concerned with the SWM position, and remember, if you go through the MW series (archives), then, ENSO or El-Nino is one of the important parameters for the South West Monsoon.
Vagaries estimates a slight tendency to warm of the SST off the Peru Coast and Nino 3.4 to warm up after June/July. ENSO can be on the threshold of El-Nino in June /July, and may show El-Nino tendency after July/August.
SWM should start of Normal", but can become tardy later...Too early for a forecast, but will get better views when we start our MW series.


Now, we hear from the famous Global Warming quarters...Climate change will cause severe Ninos and Ninas...Wow !..Meteorologists, who understand the science of climate, will vouch for the fact that : The two climate patterns are are not caused by climate change, but cause climate changes !
That's all there is to it. It has nothing to do with global warming, climate change, what make of lightbulbs we should be using. Nor does El Niño slow or speed up global warming, anymore than a wave on the ocean can control a current beneath. It is merely one of the giant cycles that rule the planet.

Excerpts from:Ken Ring  (Predict Weather.com)
ncdc NASA and NOAA. and from  Bur of Met Aust, www.geocurrents.infoand ,http://instructional1.calstatela.edu/



9 comments:

Atul Naik said...

Excellent explanation and video link for El Nino and El Nina phenomena. Thank you very much, Rajeshbhai!

Ron said...

very informative..all in one post..Thank you sir for the detailed explaination

rajesh said...

Some Comments from Social Media on this :
(Delhi)RK Chaudhary excellent....nicely explained
(Ghaziabad)Arpit Sharma Nice...we need more articles like this on various topics...
(Islamabad)Muhammad Waqas me read karny laga hu ehhe
Delhi)RK Chaudhary I hope the el-nino stays away....if it affects second half of monsoon..then nw india will see drought as the region gets proper monsoon only from mid july...
(Ghaziabad)Arpit Sharma Nowadays we are getting proper rain from mid August only...
(Panvel)Mohan Krishnan: Thanks sir
( Badlapur)Abhijit Modak: Wow. Very informative and detailed explanation.. Thank you Sir..
(Islamabad)Muhammad Waqas: thnx bro .... its worth reading article
(Karachi)Jawad Jawed: great intel @ rajesh bhai
(Dombivali)Puneet Bangera: Very detailed and nice explanation by rajesh sir.Truly excellent

ANOOP RAWAT said...

Great information! Thank you sir.

sset said...

what about NEM monsoon? With successive 3 years of failure - EL-NINO may be only saving grace for TN / AP / KAR. If possitive correlation between EL-NINO and NEM holds true.

ANOOP RAWAT said...

sset righty mention in recent comments that SE india getting less rain and Guj / Raj getting above normal monsoon rain . Raj also getting regular WD rains

rajesh said...

Mumbai sees slight fall in pressure..

rajesh said...

Mumbai sees slight fall in pressure..

Hrishikesh said...

do we expect clouds in mumbai due to dropping pressure?