Saturday, October 17, 2015

El-Nino: North East Monsoon: Quantum:

“Whether El Niño gets slightly stronger or a little weaker is not statistically significant now. This baby is too big to fail,”...2015 El Nino !

It has been known for some time that an El Nino has very different effects on the south-west and north-east monsoons. This abnormal warming of the central and eastern Pacific waters has often been associated with failure of the south-west monsoon. But sometimes, the very same phenomenon appears to have just the opposite effect on the north-east monsoon, leading to more bountiful rain.

Research that was published recently by Pankaj Kumar and M.Rajeevan of the Indian Institute of Tropical Meteorology (IITM) in Pune, K. Rupa Kumar, currently with the World Meteorological Organisation in Geneva and A.K. Sahai, also of IITM, examined the relationship between the “El Nino/Southern Oscillation” (ENSO) and the North-East Monsoon between 1901 and 2000.

They found that the correlation between ENSO and the north-east monsoon had fluctuated during this period. The relationship was positive and strong from 1930 to 1950, and then became weak for the next two and a half decades. But since 1976, the relationship has picked up and become strong again. This, the scientists noted, was “diametrically opposite” to the relationship between ENSO and the south-west monsoon, which has weakened greatly in recent decades.

Moreover, North-East Monsoon rainfall during the El Nino years after 1976 had on average become considerably more copious than during the period from 1950 to 1976. The scientists pointed to evidence that changes in atmospheric circulation during an El Nino were now strengthening easterly wind flows, thus bringing more moisture to the subcontinent and increasing rainfall during the North-East Monsoon.

El Nino:

This year, however, an El Nino, is fully developing. An El Nino is generally weak for the south-west monsoon but could it strengthen the north-east monsoon? 

NASA Earth Observatory map 

The maps above show a comparison of sea surface heights in the Pacific Ocean as observed at the beginning of October in 1997 and 2015.  Shades of red indicate where the ocean stood higher (in tens of millimeters) than the normal sea level because warmer water expands to fill more volume. Shades of blue show where sea level and temperatures were lower than average (contraction). Normal sea-level conditions appear in white.

The latest analyses from the National Oceanic and Atmospheric Administration and from NASA confirm that El Niño is strengthening and it looks a lot like the strong event that occurred in 1997–98. Observations of sea surface heights and temperatures, as well as wind patterns, show surface waters cooling off in the Western Pacific and warming significantly in the tropical Eastern Pacific.

“Whether El Niño gets slightly stronger or a little weaker is not statistically significant now. This baby is too big to fail,” said Bill Patzert, a climatologist at NASA. October sea level height anomalies show that 2015 is as big or bigger in heat content than 1997.

In its October monthly update, scientists at NOAA’s Climate Prediction Center stated: “All multi-model averages predict a peak in late fall/early winter. The forecaster consensus unanimously favors a strong El Niño...Overall, there is an approximately 95 percent chance that El Niño will continue through Northern Hemisphere winter 2015–16.”

NOAA Climate Prediction Center (2015, October 8) El Niño/Southern Oscillation Diagnostic Discussion. 
NASA Earth Observatory] 

As mentioned in our previous article, the NEM arrival is delayed this year. NEM may arrive as a weak current around the 27th of October. 

Though there is no direct connection with the El Nino, it is possible, however, that this year the north-east monsoon may be above normal.

For Tamil Nadu, Vagaries' estimates around 110%-115% rainfall of the Long Term Average (LTA). LTA as worked out by IMD for Tamil Nadu is 438 mms for Oct-Nov-Dec.

Chennai expectations are around +10% more than the average. Chennai receives around 850 mms (Average for both Stations) rains in these 3 months...

As yet, in October, Both Stations have measured 85 mms...


Narayanan Ky said...

Interesting to know that Pacific ocean has an influence even in our bay. Only today we started to feel easterly breeze getting slightly picking up with some isolated pre nem rains in central tn. Thanks for a very nice written article.

Nilay Wankawala said...

Very informative write up.NEM and El Niño correlation I came to know first time...I thought El Niño has only impact on swm.

Majid Ahmad said...

I am surprised at the number of, and intensity, of tropical cyclones in the Western Pacific Ocean this year, although you have written that waters in the Western Pacific are cooler this year as a result of El-Nino. But, it is normally the case that cyclones are formed by hotter sea surface temperatures. This year has seen lots of cyclones in the Eastern, Central and Western Pacific, maybe the highest number till date.

Shiva HEAD said...

Excellent write up. Kudos.
In short the term "Vagaries of weather" aptly suits, fits NEM more than SWM for the many surprises it throws year after year.