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June 30th 198
Anna Mani - The Weather Woman of India
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1989 Article News... Just for Information⬇⬇
Deadly Glacier Flow in Uttarakhand ...8th February 2021 February 2021
Increased Warming in Latest Generation of Climate Models Likely caused by Clouds....25th June 2020
Forecasting Bird Migration with Weather Radar and Models...2nd May 2020
Climate v/s Weather v/s Climate Change...10th Dec 2019
MW-1 2019...8th April 2019
MW-2 2019...17th April
MW-3 2019... 4th May
MW-4 2019 ...17th May
Importance of Monsoon Forecast for India...31st march 2019
The Ozone Hole..Depleting.....20th February 2019
Climate Related Deaths Down.....29th January 2019
Kerala Floods and Heavy Rains August 2018
MW-1 2018...10th April
MW-2 2018...22nd April
MW-3 2018...3rd May
MW-3 Part 2... MW-4 2018 Quantum...20th May
Annual Summary ....2017
Importance of 200 jet streams...The Initial Weather maker...the King:....27th December 2017
A rare and unusual phenomena few days ago...Pink Auroras !...25th November 2017
von Karman Vortices....26th October 2017
Why the Yellow Colour before a ThunderStorm ?...13th October 2017
Secrets of Weather Forecasting Models....Exposed !...27th April 2017
10 years Celebrations of vagaries....17th July 2016
The Crucial 2016 Monsoon....3rd June 2016
Historical High for India..51c on 19th May 2016
World Water Day...22nd March 2016
More first time snow in New Regions...Kuwait and Thailand...30th January 2016
El Nino 2015/2016...Event of the Century...28th January 2016
Hopes Rise if El Nino Eases: ...23rd february 2016
Wither Global Warming... 2014 v/s 2015 Antartic Ice Extent...11th January 2015
There's a Heat Wave in the North Pole..Storm hit the Pole ...2nd january 2016
Achievment of 1 Million Hits...15th October 2015
Weather Events of 2013....
El Nino La Nina and Enso..Simplified 2nd Febraury 2014
SWM Withdrawal note..article of 19th August 2013
What is a drought Year ?....article of 27th March 2013
Indian Monsoon: What’s brewing in the Pacific is more likely a Modokai than a normal El Niño
Indian Monsoon: What’s brewing in the Pacific is more likely a Modokai than a normal El Niño...Article written by Rajan and Vagaries.....17th July 2012
Is India Really Water Starved ?.....July 2012
Importance of Monsoon Forecast for India..March 19th 2012
North Pole Pics.....taken from aircraft over the North Pole on 5th April 2012.
MW-1 2016...10th April
MW-3 2015...30th April
MW-3 Add...2nd May 2015
MW-1 to MW-6 2015
MW-1 2014 10th April
MW-1 2013 ..10th April
MW-3 Add...2013...30th April
MW-4 Part I 2013...6th May
MW-5 ..2013...17th May
MW-6 2013..24th May
NEM Notes 2010
NEM Notes 2011
Direct Links to Previous Articles written in 2009 by the author on :Global Warming"..if it exists !
Ice cover of Artic (Jan 2016) shown in a Satellite image..Though this winter was "Above Normal"..This Image and Recent Events speak in differently.. 2nd March 2016
What is the Rationale behind GW ?...March 2013
Global Warming..Note on...Dec 2009
Global Warming -2...Dec 2009
Global Warming -3..Dec 2009
Global Warming -4 ..Dec 2009
Global Warming - 5 Dec -2013
Harshest Winter ..Dec 2009
Cold days in Gujarat maybe records but no confirmation...winter 2010/2011
Highest variation in scruz 23.9c...5th March 2013
El Nino and its effect on Indian Monsoon....and El Nino Explanation....March 2014
THE 300 / 200 MB CHART
METEOROLOGIST JEFF HABY
One of a forecaster's first thoughts when confronted with the 300/200 mb chart is the jet stream. The jet stream is a high velocity river of air that flows completely around the Earth at the mid-latitudes. During winter, the jet core is located generally closer to 300 millibars since the air is more cold and dense in the vicinity of the jet stream during the cool season. The 200 millibar chart is used for the jet stream in the warm season but either chart in most instances will suffice. Many hot air balloonists have tried to ride this river of air around the world with not much success for most. The river of air is not continuous. Embedded within the jet stream are higher velocity jet streaks. Jet streaks are segments of faster wind speed within the jet stream.
At 300 mb, the air density is much smaller than near the surface. A 100-knot wind at the 200/300 millibar level does not feel as strong as a 100 knot wind at the surface. Even though the density is smaller, these air currents have the power to drive the movement of storm systems and build troughs and ridges.
One jet streak can turn a beautiful Monday into a severe storm Tuesday, as we will see in an example later. Troughs and ridges are not only carved by warm air and cold air advection but also by the high momentum air of jet streaks. A significant jet streak has winds over 100 knots. Look at the 300 mb chart in this section labeled "Time 1". A jet streak exists from Colorado to Montana. The highest wind speeds in the jet streak (aka jet core, jet surge) are 130 knots (150 miles per hour) in southern Wyoming.
Parcels within the jet streak are diving to the southeast. The air's momentum forces a trough to develop across the Central US. In "Time 2", the chart from 12 hours later, the jet streak has moved further to the southeast and the associated trough is becoming more amplified. At "time 3" the jet streak has turned the corner and is in the base of the trough. The trough is at maximum amplification. The trough will now move to the east and eventually to the northeast. It is difficult to determine the four quadrants of a jet streak when one "turns the corner". Divergence and rising motion are strongest to the north of the jet axis, such as in Tennessee during highly curved jet streaks. RULE OF THUMB: If a jet streak exists on the left side of a trough and winds are stronger to the left of the trough (as it is in our example in "Time 1"), the trough will become more amplified with time and will "dig" in a southerly direction. If a jet streak exists on the right side of a trough and winds are stronger to the right of the trough, the trough will become less amplified with time and "lift out" in a northeasterly direction. If the winds are about the same on each side of the trough, it will stay at about the same amplification. This knowledge will make you a better forecaster! A jet streak progression is shown below.
The jet stream is useful for the prediction of temperature. The jet stream divides colder air to the north from warmer air to the south. The transition between temperatures on each side of the jet is very abrupt. Heights are higher to the south of the jet and lower to the north. In the upper levels, this creates relatively high heights to the south of the jet and relatively low heights to the north. The Pressure Gradient Force flows from a southerly to northerly direction. However, the Coriolis force shifts the wind flow to the right of the path of motion. Therefore, the jet stream flows from the west to east. When a trough builds over a region it often indicates cooler temperatures due to cloudier weather and northerly winds. A ridge builds by low level (between the surface and 700-mb) warm air advection and upper level forcing (negative vorticity). Air in a ridge is sinking and is thus expanding and creating higher heights. Therefore, temperatures are warmer than normal in a ridge due to warmer temperatures and sunnier weather. This is especially true when a ridge occurs in high latitudes. Below is a diagram showing the development of the polar jet and the wind pattern the PGF and Coriolis produce.
Certain regions of jet streaks are more favorable for rising or sinking air. Where convergence occurs in the upper levels, sinking motion results. Where divergence (evacuation of mass) occurs in the upper levels, rising motion result. Convergence and divergence in a jet streak is caused by an imbalance of forces as a parcel accelerates into a jet streak then decelerates out of the jet streak. The depiction below shows the balance and imbalance of forces in a jet streak. Lets look at each of the 5 numbers and letters.
MOTION WITHIN A JET STREAK
(1) Pressure Gradient Force and Coriolis are in balance. Wind is geostrophic (parallel to height contours)
(2) Parcel enters region of higher wind speed. This increases the Pressure gradient force at the same time the Coriolis has not been changed much. Wind will tend to flow toward the longest vector, which is the PGF. This causes convergence in the Left Rear Quad (sinking air at letter A) and divergence in the Right Rear Quad (rising air at letter D). The tropopause is just above jet stream level. Convergence at the jet stream level forces air to sink because the highly stable tropopause prevents air from rising.
(3) The Coriolis once again balances the Pressure Gradient Force.
(4) As a parcel leaves the jet streak it must decelerate. The Pressure Gradient Force weakens at the same time the Coriolis has not had time to adjust and decrease. This causes convergence in the Right Front Quad (sinking air at letter B) and divergence in the Left Front Quad (rising air at letter C).
(5) Pressure Gradient Force and Coriolis once again balance
This example has been for a jet streak in a zonal flow. A jet streak in a curved flow, such as the case when a jet streak is in the base of a trough, will have divergence and rising air to the north of the jet and convergence and sinking air to the south of the jet.
The jet stream is a powerful forecasting tool. Not that it can give exact highs/ lows/ and precipitation chances, but because it gives information such as when to expect the next storm system and whether temperatures will be above or below normal. It gives clues to how the upper levels will promote rising air or sinking air. It gives clues to the character of the next storm system. Jet streaks alone provide much information of how a trough or ridge will develop over the next couple of days.
WHAT TO LOOK FOR ON 300/250/200 chart:
(1) Jet stream
*The jet stream is a river of air with segments of higher speed winds embedded within the mean flow
*Areas North of jet stream tend to have cooler than normal temperatures especially in the mid-latitudes
*Areas South of jet stream tend to have warmer than normal temperatures, especially in higher latitudes
(2) Jet Streaks
*Rising air occurs in the right rear and left front quadrants of jets
*Sinking air occurs in the left rear and right front quadrants of jets
*Rising air occurs north of jet axis if jet is in a highly curved flow
*Winds over 120 miles per hour constitute a significant jet streak
*Upper level divergence enhances rising air, especially if warm air advection is occurring in lower levels of atmosphere
(3) General trough/ridge pattern
*Momentum of jet stream carves the trough ridge pattern. If the jet stream winds are greater on the LEFT side of a trough, the trough will become more amplified and move further south. If the jet stream winds are greater on the RIGHT side of a trough, the trough will become less amplified with time and move further north.
Hot Day: Whenever the maximum temperature remains 40o C or more and minimum remains 5o C or more above normal, provided, it is not satisfying the heat wave criteria.
Heat wave Departure of maximum temperature from normal is + 4o C to + 5o C or more for the regions where the normal maximum temperature is more than 40o C and departure of maximum temperature from normal is + 5o C to + 6o C for regions where the normal maximum temperature is 40o C or less (Heat Wave is declared only when the maximum temperature of a station reaches at least 40O C for plains and at least 30O C for Hilly regions). When actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heat wave is declared.
Severe heat wave conditions Departure of maximum temperature from normal is +6 OC or more for the regions were the normal maximum temperature is more than 40 OC and +7 OC or more for regions were the normal maximum temperature is 40 OC or less. (Heat Wave is declared only when the maximum temperature of a station reaches at least 40O C for plains and at least 30O C for Hilly regions)
Cold Day In the plains of north India, foggy conditions prevail during winter for several days or weeks. The minimum temperature on these days remains above normal, while maximum temperature remain much below normal. This creates cold conditions for prolonged period. When maximum temperature is less than or equal to 16°C in Plains, it will be declared “Cold Day”.
Cold Wave Wind chill factor is taken into account while declaring the cold wave situation. The wind chill effective minimum temperature (WCTn) is defined as the effective minimum temperature due to wind flow. For ex. When the minimum temperature is 15 OC and the 6 wind speed is 10 mph, WCTn will be 10.5 OC. Departure of WCTn from normal minimum temperature is from –5 oC to–6 oC where normal minimum temperature > 10oC and from –4 oC to –5 oC elsewhere, Cold Wave is declared.. For declaring cold wave etc. WCTn only is used and when it is < 10OC only, cold wave is considered (this criteria does not hold for coastal stations). Also cold wave is declared when WCTn is < 0oC irrespective of the normal minimum temperature for those stations.
Severe cold wave Departure of WCTn from normal minimum temperature is –7 oC or less for the regions where normal minimum temperature is > 10oC and –6 oC or less elsewhere. (departure of WCTn from normal minimum temperature is from –5 oC to –6 oC where normal minimum temperature > 10oC and from – 4 oC to –5 oC elsewhere)
The forces, or if you like, the equations governing the weather are also non-linear. Over short timescales, weather can be quite predictable, but over longer timescales, very small variations in conditions can produce dramatically different outcomes. MIT physicist Edward Lorenz found this in modeling weather systems on a computer. He found that if he changed the least significant bit of the input that designates the starting point, he obtained dramatically different results. In finding this exquisite sensitivity to tiny changes in the initial conditions, Lorenz asked the famous question, “Does the flap of a butterfly’s wings in the Brazil set off a tornado in Texas?”
What is a Drought Year ? With 7.6% Deficient (All India), would 2012 be termed as a drought Year ?..27th March 2013 (comments on that page)
Droughts in India has resulted in tens of millions of deaths over the course of the 18th, 19th, and 20th centuries. Indian agriculture is heavily dependent on the Monsoons in India: a favorable southwest summer monsoon is critical in securing water for irrigating Indian crops.
Some of the major drought-prone regions are southern and eastern Maharashtra, northern Karnataka, Andhra Pradesh, Orissa, Gujarat, Bengal, Bihar and Rajasthan.
But why has this been repeatedly happening since the last 200 years? 200 years is a long enough period given to overcome the situation and prevent the people's suffering by providing adequate means and inter regional water storage and transfer.
And knowing the weather, it is almost natural, that either of the above mentioned regions is bound to get below normal deficient rainfall in any year. Do we literally have to wait for a surplus rainfall in each and every region of the country. If yes, than thats poor management and governance of water resources.
We should be capable with providing the shortfall by the excess available in some other region. Nature's bounty is always merciful on us, but are we ever ready?
Do we know how to store and preserve water, rather than just let it drain in the two seas on either side. Most of the SWM rains drain off in the seas.
Is India really water starved ? This article ( July 2012) published in Vagaries is most apt and suited for the topic under discussion....and the article ended with ..otherwise .....Otherwise we see the same old story in parts of the country today.
Then what is a drought Year ? Was 2012 a drought Year ?
Out of the total 36 meteorological subdivisions, 23 subdivisions constituting 67.3% of the total area of the country received excess/normal season rainfall and the remaining 13 subdivisions (32.7% of the total area of the country) received deficient season rainfall.
To really analyse the "drought" situation this year, let us take into consideration of the five Peninsula states... TN, Kerala, Gujarat, Maharashtra and Karnataka, which, the officials tell us are the worst effected...
Karnataka: End Season, Coastal Karnatak was 0%, N.I.Karnataka was -36% and S.I.Karnataka was -23%.
Average deficiency for the state: -19.6%.
Maharashtra: End Season: Konkan -3%, Madhya Maharashtra -25%, Marathwada -33% and Vidharbha +8%.
Average State deficiency: -17.6%
Gujarat: Saurashtra and Kutch:-34%, Gujarat Region: -28%.
Average State deficiency: -31%.
Tamil Nadu State Deficiency: -23%. And Kerala -24%.
It can be noticed, from the above figures and map, that the drought regions are all "linked " to each other North/South. Providing and implementing the waters from the coastal regions to the interiors would have been a boon and would have mitigated the losses.
The severest amongst them is Gujarat. However, Gujarat has somewhat marginally lessened the woes by diverting the river waters to water starved Saurashtra and Kutch. Remember, Saurashtra by itself is deficient by -43% !
Maharashtra reservoirs are showing levels as follows as per latest levels available..
Konkan Reservoirs 55%full (last year at this date 49%), Marathwada 10% (24%), Nagpur 37% (35%), Pune 35% (39%).
Overall Maharastra Reservoirs: 32% (36% in 2012 and 50% in 2011).
Situation is manageable and could be kept under control.
Now, in the modern day and era, we have to consider the average of all the regions. The overall Monsoon performance is taken considering India as a whole..Excess and deficient regions. Any developing and established nation like ours would have considered the excess rains that its coastal/mountainous belt gets, to divert the huge amounts of water to its interiors.
The coastal regions of Maharashtra and Karnataka get between 2000-6000 mms, and a few places even boast of over 7500-8000 mms as normal..now that's a fantastic amount of rain by any standards.
Maharashtra has Mahableshwar with five rivers running and originating from there, and from Nasik district the state has the Godavri river, running through the water starved regions of Marathwada !
The State has ample scope to put things in perspective, by irrigating the "normally" low rainfall regions. The state would never complain of a water scarcity !!
July 17th 2012 from Rajan'Take:
Indian Monsoon: What’s brewing in the Pacific is more likely a Modokai than a normal El Niño
Just when it looked as if a traditional El Niño was getting its sea legs, the event is now looking a bit less canonical. This prompted the following analysis. This post is jointly written by Rajan Alexander who administers the blog, Rajan’s Take: Climate Change and Rajesh Kapadia who administers the blog, Vagaries of the Weather.
The Indian press has been going gaga, spreading hysteria about the supposedly El Niño effect messing up the current monsoon. After June whetted their appetites of gloom with very poor rains, their prophecy of doom has now hit a huge speed break with the apparent monsoon revival seen so far this month.Bob Tisdale is perhaps one of the world’s best known authorities on sea-surface temperatures and related oceanic climate phenomena. In his blog he observed that an analysis of historical data suggests that the (summer) El Niño usually crossed its threshold values by late May. This year, it did so only by June second week. Since theoretically there is a time lag of at least 3 months for any El Niño effect to significantly impact the monsoon, this delay could give the current monsoon season a reprieve of sort.Going by the current rate of El-Nino development, the earliest it can impact the monsoon is most likely by beginning of September, a month which accounts for less than 16% of total rainfall of the South West Monsoon (SWM). This also raises hope that August rainfall may have a fair chance of recording “near” normal rainfall viz. around 93-95% of Long Period Average (LPA).Comparison of the evolutions of El Niño eventsBob Tisdale’s latest post compared the current El Niño’s evolution with others historically. The following are his findings:1. NINO3.4 sea surface temperature anomalies (a commonly used ENSO index) have been above the +0.5 deg C threshold of an El Niño for 4 weeks. While it’s far from an “official” El Niño, it appears that it’s likely to become one.
The first thing that stands out in the graph is how there really is nothing typical about the evolution of El Niño events. Five started from ENSO-neutral conditions; that is, with NINO3.4 sea surface temperature anomalies between -0.5 and +0.5 deg C.
Five, including the current one, started from La Niña conditions, with the NINO3.4 sea surface temperatures cooler than -0.5 deg C. And there’s the outlier, the 1987/88 portion of the 2-year 1986/87/88 El Niño.Other than having the coolest NINO3.4 sea surface temperature anomalies at one point, there’s nothing remarkable about the evolution of the NINO3.4 sea surface temperature anomalies this year.
2. The graph below compares the evolution of the El Niño events that started from La Niña conditions. This year’s NINO3.4 sea surface temperature anomalies had been tracking along at the pace of the most recent El Niño, the one that occurred in 2009/10, until recently. Over the past two weeks, NINO3.4 sea surface temperature anomalies have been cooling.
3. NINO3.4 sea surface temperature anomalies appear as though they’re being suppressed by the cooler-than-normal waters being circulated southward from the North Pacific, which should be feedback from the back-to-back La Niña events.It will be interesting to see how long the cooler waters from the North Pacific can suppress the central sea surface temperatures in the east-central equatorial Pacific.
4. The NINO1+2 region is in the eastern tropical Pacific, just south of the equator. The coordinates are 10S-0, 90W-80W. This year the NINO1+2 sea surface temperature anomalies warmed before the NINO3.4 region, but they also have been cooling.
5. There’s still a pocket of elevated anomalies at depth in the eastern equatorial Pacific, and there’s a long way to go before the peak of the ENSO season.
El Niño Modokai
Till recently, it was thought that the El Niño had only one mode - a periodic warming in the eastern tropical Pacific that occurs along the coast of South America. In 2004, it was discovered to have also a second mode that occurs around 12% of the time.A Japanese team led by T. Yamagata (that included a prominent Indian climatologist, Dr Venkata Ratnam) noticed the 2004 El Niño was warming more strongly in the Central Pacific region and accordingly stumbled on the discovery of its second mode by sheer accident. They called such an El Nino as Modokai, which is a classical Japanese word which means“similar but different”. The phenomenon is also known as a Pseudo or Central Pacific (CP) El Niño. It was then adopted by K Ashok and colleagues in a 2007 Journal of Geophysical Research paper to refer to central-Pacific–weighted El Niños more generally. Its basic signature is as follows:1. Weakening of equatorial easterlies related to weakened zonal sea2. Surface temperature gradient lead to more flattening of the thermocline.The US, CPC-International Research Institute in a press note said average sea sub-surface temperatures persisted in thefar eastern Pacific and had recently spread westwards. This has taken place in the eastern half of the equatorial Pacific but recent values of upper ocean heat anomalies continue to reflect ENSO neutral conditions. Equatorial sea surface temperatures (SST) are greater than 0.5°C above average across the eastern Pacific Ocean though the atmospheric circulation over the tropical Pacific reflects cool-to-neutral ENSO conditions.So there we have sort of a confirmation that the Niño is moving westwards instead of the typical eastward direction.
Further - just when it looked as if a traditional El Niño was getting its sea legs, the event is now looking a bit less canonical. Just take a look at last week’s US-CFS v2 forecasts for Niño regions 1+2 from where it could be observed that the warmest anomalies have been centred in the eastern portion of the ENSO monitoring area.
However, as also seen in the forecast, there is now more of a potential for the temperatures to be much lower. One explanation is that the Niño maybe dying off!! The only other explanation is that the heat is merely transferring westwards - a fact validated through the latest SST departures. The western bias to this summer’s warming pattern is what brings to suspect an El Niño Modoki development rather than a typical El Niño.
The question is that if the heat transfer is taking place westward instead of eastward as typically, are we seeing an El Niño Modoki developing instead of a normal El Niño as commonly assumed? This is not easy to answer as Niño regions 1+2 also appears now to be cooling off along with NINO3.4 SSTs. However such cooling could be temporary and not unusual.So what’s an El Niño Modokai?But before we can understand El Niño Modokai variant we need to have to understand El Niño itself. It is part of the El Niño-Southern Oscillation (ENSO) that alternately gives us warm El Niños and cool La Niñas.An ENSO is a physical oscillation of ocean waters from side to side of the tropical Pacific Ocean. It is kept going by trade winds that push the water westwards along the north and south equatorial currents. Between these two currents is the equatorial counter current and the water piled up in the western Pacific eventually comes back east via that counter current. It does so periodically as a massive wave, observable as a Kelvin wave, because the oscillation is caused by wave resonance and the resonance period is determined by the dimensions of the ocean basin.As and when an El Niño wave reaches South America at the equator it splashes ashore and spreads out. This creates a large area of warm water, the air above gets warm, an updraft forms that interferes with trade winds, and global temperature rises by half a degree Celsius. But any wave that runs ashore must also pull back. As the El Niño wave retreats water level behind it drops half a meter or more, cold water from below wells up to fill the space, and a La Niña gets started.But in the case of Modokai, only 20% of the time a La Niña emerges. More often, the Niño dips below the La Niña threshold, but do not remain there long enough to be considered an official La Niña. So if an El Niño Modokai is indeed confirmed this year, it is most likely next year we should be having an ENSO neutral year, rather than a La Niña year. This means, if the El Niño factor is considered as the prime one, we can expect 2013 monsoon season to be within the normal-above average range.Modokai is but a chaotic variation of a typical El Niño pattern, absent the current gyres that usually form at the eastern terminus. This unique warming in the central equatorial Pacific associated with a horse-shoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. This year, as seen in the above graph, there is a lot of cold water circulating from Alaska down the west coast of Canada, the US and Mexico. This cold water is mixing with equatorial Pacific waters and keeping SSTs in equatorial Pacific down.The real difference between the normal El Niño and El Niño Modokai isn’t their locale within the Pacific, it is the mode of energy release and it’s spreading out. The former is predominantly a localised event at the sea surface, because a huge spike in humidity which traps emerging energy and spreads it globally via the resulting winds.Whereas El Niño Modokai is more a global emission of energy from the ocean, resulting in a general humidity increase worldwide rather than a localised blanket of water vapour around a localised emission event, followed by rapid heat loss to space once the warm air is spread out. That is why lower tropospheric temperatures can be expected to remain high as long as 4-6 months after the Pacific event petered out.So from this month to maybe first quarter next year, global temperatures maybe expected to spike moderately and maybe the last hurrah for global warmists. Once the event is over, global lower tropospheric temperatures can be expected to fall very fast, particularly once the NH winter kicks in. Due to the loss of humidity over the cold land masses; the 2014 northern hemisphere winter could be expected to be extremely cold.El Nino Modokai’s Effect on WeatherIn a paper by Venkata Ratnam et al entitled “Pacific Ocean Origin for the 2009 Indian Summer Monsoon Failure”; effect the following were postulated as effects of El Niño Modokai on weather:
During the boreal (northern hemisphere) summer season rainfall anomalies during the June-September season of the seven positive El Niño Modoki years 1986, 1990, 1991, 1992, 1994, 2002, and 2004. Statistically significant surplus rainfall anomalies are seen in the central equatorial Pacific region flanked on both sides by the negative rainfall anomalies in the equatorial western and eastern Pacific.The atmospheric condition associated with the western pole located in the equatorial western Pacific is strongly suspected of influencing rainfall from Indonesia, Malaysia, Singapore etc, with the teleconnection extending northwest up to south India and also Sri Lanka.The teleconnection associated with the positive rainfall anomaly in the central pole (equatorial central Pacific) seems to extend westward via the Philippines, Myanmar to northern eastern India.In the East Asian region, southern Japan suffers droughts during these years owing to the Pacific-Japan pattern [cf. Nitta, 1987]. The deficit rainfall in the western Pacific region is seen to extend southward to southeastern Australia, influencing a significant part of eastern Australia. The negative rainfall anomalies over the equatorial eastern Pacific extend over western coast of North America.The result in the Pacific Ocean is less wind shear and therefore more hurricanes/cyclones - the warmer water is also a necessary factor. The result in the Atlantic Ocean is more wind shear and fewer hurricanes/cyclones.El Niño Modokai Index (EMI)
The Japan Agency for Marine-Earth Science & Technology (Jamstec) developed an El Niño Modokai Index (EMI) as above. The index currently shows that the EMI is still weakly negative but expected to turn weakly positive by this month end or during August.
An El Nino Modoki event is called ‘typical’ when its amplitude of the index is equal to or greater than 0.7α, where α is the seasonal standard deviation. This means even if what is developing is indeed an El Nino Modoki though presently mistakenly assumed an El Niño , this could be confirmed at the earliest only by end of September or October though we could possibly have the first preliminary indication by August end.Past Impact of El Niño Modokai (summer) on Indian Monsoon
Seasonal rainfall wise, there seem to be alot of variation within El Niño Modokai years ranging 769.9 (87%) to 1,001 mm (113%) of rainfall of Long Period Average (LPA). The average however is 845 mm or 95% of LPA.
Instead of around 175 mm average rainfall for June, this year the country received 115.5 mm or a 29% deficiency. If this year is indeed an El Niño Modokai year, then this should be a new record low relegating 1986 to second place.With June rainfall poor, does it mean rainfall would get progressively worse? Let’s look at 1992, presently occupying the bottom rung with a 27% rainfall deficiency in June. At the end of the season it still managed to reduce the deficiency to 6% overall. So it is possible that July-September rains to be normal even if June rains fail.However, this is a simplistic analysis. The performance of the monsoon will depend on other variables such the behaviour of the Indian Ocean Dipole (IOD); Madden Julian Oscillation (MJO), summer temperatures, snow cover, Mascaerne Highs, etc. Nevertheless let’s use the same technique to understand what possible impact El Niño Modoki could have in relation spatial distribution of rainfall as demonstrated historically.
We find that North India, both east and west, relatively tend to suffer a higher rainfall deficiency as compared to the Southern Peninsular with Central India coming out practically unscathed.ConclusionWhat we can conclude with high confidence is that with the El Niño crossing threshold values two weeks later than normal, this is likely to be a positive development in relation to rainfall for rest of the monsoon season.Should the El Niño be of the Modokai variant, then its adverse impact on rainfall is most likely to be relatively weaker than those of a normal El Niño.It is too early to confirm the development of an El Niño Modikai this season. We should have better idea by mid August but an official confirmation would be possible only after the monsoon season ends.
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