METD WEATHER
AKSHAY DEORAS
SEVERE WEATHER FORECASTER
16TH MAY 2012,
MUSCAT,OMAN
FROM THE DESK-
***METD WEATHER COMPLETES 1,00,000 PAGEVIEWS ON 14TH MAY 2012 SINCE MAY 2010.
Dear Readers,
As a part of the annual forecast of the Indian Monsoon (IndiMO) since 2010, METD WEATHER brings you the 2012 Indian Monsoon Forecast ( IndiMO I). The Summer Monsoon forecast is prepared using multiple parameters which include the Indian Ocean Dipole ( IOD), Madden Julian Oscillation (MJO),El Nino Southern Oscillation (ENSO) and their inter relation. Its widely observed that the Indian Summer Monsoon is largely affected by the atmospheric patterns such as the Madden Julian Oscillation which is directly linked to the El Nino Southern Oscillation. The Indian Ocean Dipole also plays some role in the strength of the monsoon current and subsequently affects the quantum of the monsoon rainfall.
To give a better idea about the monsoon, a portion from the 2011 IndiMO Part 1 is being added. To help more in understanding, the forecast will be issued in two versions which includes a technical version and a public version. Public version is all about the conclusions explained in simple words for the readers.
METD WEATHER has all the rights reserved for this forecast and the matter is (C) 2012 METD WEATHER.
A.Deoras
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CHAPTERS-
1) The Summer Monsoon mechanism
2) Gist of the Summer Monsoon activity
3) Interseasonal Oscillation,IOD
4) IOD-MJO Interaction
5) Discussion on the present conditions
6) 2012 Summer Monsoon Forecast
7) Inference
8) References
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I- The Summer Monsoon mechanism
Indian Summer monsoon is an annual phenomena happening briefly in the Indian Ocean,Arabian Sea and the Bay of Bengal. The summer monsoon is characterized by the development of monsoon current or a band of South West Winds carrying moisture lash the mainland bringing torrential rains.
The summer monsoon has two category on the basis of its splitting at Southernmost India
The Arabian Sea Branch
The Bay of Bengal Branch
This Monsoon current sets up because of differential heating of continental and sea air mass.
As the air over mainland gets heated more in summer period as the sun apparently migrates Northwards of Equator, rising warm air causes a decrease in air pressure over the Northern regions of India. As the Sea air mass has comparatively less cooling, a system of winds from South West develops which carries moisture with it.
The Somali Current plays a very important role in monsoon. The somali current generates the SW Monsoonal flow and the current typically resides in the 10-15N in Arabian Sea during the monsoonal period bending in and then entering bay of bengal.
The Ekman drift comes in effect in Arabian Sea when the ocean waters are directed at an angle of 45 degrees to the wind stress in the region. This arrangement directs the SW Monsoon winds towards mainland of India.
Right-
The IMD GFS Forecast map of 925mb ( Surface Winds) indicating well developed SW Winds as valid for 12UTC 22/05/11
The dark blue region indicate amplified winds pulling in moisture and regarded as SW Monsoon current.
This current originates from the Somali current
** The Inter-Tropical Convergence Zone or ITCZ which is an area of strong convective activity and rainfall can be seen as a region of converging winds as shown South of Sri Lanka.
ITCZ migrates North with torrential heating during summers and is over India during the Monsoon period.
(B)-
At left, The GFS map of 850mb winds Valid 00z Fri,13th May shows Broad Anticyclonic circulation in Arabian Sea offshore India.
This circulation is regarded at "The Great Whirl"
and is present during summer in this region.
You can also see enhanced moisture SW of the Whirl which is the Somali Current developing.
THE GREAT WHIRL MOVEMENT CONTROLS THE DIRECTION OF MONSOON CURRENT AS IT ACTS LIKE A BLOCKING HIGH PRESSURE RESPONSIBLE FOR INCREASE IN HEATING OVER CENTRAL INDIA,WESTERN INDIA. ITS DISAPPEARANCE IMMEDIATELY REGULATES THE MONSOON CURRENT.
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II- GIST OF SUMMER MONSOON ACTIVITY
The summer monsoon activity formation requires following key factors-
1) Ample heating of Northern Plains of India and surrounding regions leading to formation of low pressure area due to land air mass lifting
2) No interference of Tropical Cyclones ( Which mostly forms within Monsoon trough) and limit the Monsoon wind amplification and disturbs the flow
3) An Enhanced Convection phase of Madden Jullian Oscillation ( Inter-Seasonal Variational Wind flowing Eastwards)
4) Reduction in intensity of North-East winds ( Trade Winds) permitting the flow.
5) Positive phase of the Indian Ocean Dipole ( for more than average rainfall).
*The second parameter of Tropical Activity has been a major concern which had disrupted the Monsoonal Winds since many years.
III- Interseasonal Oscillation(MJO),IOD
Madden Julian Oscillation
MJO or Madden Julian Oscillation is a moving variation ( Travelling Variation) in the Tropical Atmosphere having a period of roughly 30-60 days.
This cycle moves Eastwards and is of the form of Enhanced or Suppressed Convection region depending on the Surface temperature of segment of Sea infront of them and behind them geometrically.
For higher latitudes, Jet Stream plays an important role in deciding the weather pattern. However for tropics, interseasonal variations are the deciding factor for the weather.
MJO can be determined studying the Outgoing Longwave Radiation OLR depicting Cloud tops temperature and thus forecasting the location of the phase.
The year 2009 turned to be a major rainfall deficiency year for India because of the absence of Enhanced Convection phase of the MJO. In addition to this years where strong deficiency or rainfall was seen in India, MJO wet phase was absent.
Right-
The 2009 plot showing the MJO. On Y-axis, period is plotted i.e months. On X axis, longitudes are mentioned.
Check the vertical column above 70-100E region.
In the map, Orange-Yellow shading indicates suppressed region of rains while the blue shows wet phase of MJO
For the entire year of 2009, there was a remarkable absence of Wet phase of MJO leading to depreciation in the quantum of rainfall
Above-
Two phase of Madden Julian Oscillation in progress. The top image is of 14th May 2011 of the Outgoing Longwave Radiation showing a suppressed phase over India and South East Asia ( Depicted by the brown region in the right side of image)
Bottom image shows the Enhanced phase of MJO depicted by the precipitation region and green blue area over SE Asia. At the same time, the opposite phase can be seen near Atlantic Ocean.
II- MJO Formation
The air flows out from the suppressed convection region due to the absence of primary lifting required for convection. This air progresses towards the Enhanced convection region.
The circulating air carries moisture with it. When it reaches the area of Enhanced Convection,the development of cyclonic circulation at lower troposphere layers ( Around 850mb) leads to convergence of moist air. The moist air rises inside a convection region and hence a Wet phase of MJO develops.
The dry phase of MJO is a region having Cyclonic spin at the 200mb ( In contrast to wet phase mentioned above having an anticyclonic spin at 200mb) while dry phase has anticyclonic or clockwise spin in lower profiles.
This is a textbook description why a broad region ( The Great Whirl mentioned above) is seen during dry MJO in Arabian Sea.
Indian Ocean Dipole
The Indian Ocean Dipole (IOD) is another major contributor in the summer monsoon. The previous years monsoon forecast hadn't mentioned this Dipole but from IndiMO of 2012, IOD will be considered.
The Indian Ocean Dipole also referred as IOD is a variation in the SST ( Sea Surface Temp) in the Indian Ocean. The variations are seen across the Western and Eastern Indian Ocean where above average or below average sea surface temperatures are recorded. Its an aperiodic variation i.e not of a specific duration or is known to repeat after a specific duration. The IOD is a phenomena similar to ENSO ( El Nino Southern Oscillation) in the Pacific Ocean where there is an interaction of the atmosphere and the ocean. Just like the ENSO, IOD has three phases briefly Positive,Neutral,Negative phase.
Positive Phase-
The Positive Phase happens when the SST across the Western Indian Ocean are above normal (Warmer) and the SST across the Eastern Indian Ocean are below normal (Colder). Due to favored SST, strong convection and cyclogenesis take place across the Western Indian Ocean. The rate of this convection activity is often greater than the normal levels for Western Indian Ocean which impacts areas like India,North Africa and Madagascar as shown in the below image of schematic Positive Dipole Mode..
Negative Phase-
In a negative phase, the scenario is exactly the opposite as during the Positive phase. The SST across Western Pacific is less (cooler) than the SST across Eastern Pacific which is warmer than the normal. As this happens, the convection shifts towards the Eastern Pacific Ocean with more rainfall across Indonesia and vicinity,Australia and some parts of Japan.
The phases are determined from the DMI ( Dipole Mode Index). Below is the schematic diagram of the conditions during the Negative Dipole Mode.
The third stage is a neutral one which will not be discussed. We shall also not discuss the IOD formation.
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4) Relation of Madden Jullian Oscillation with the ENSO
As discussed above, inter-seasonal variation plays a great role in deciding the quantum of monsoon rainfall in India.
However, it has been noted that there is a relation between ENSO and MJO
ENSO refers to the oscillational transition taking place in the Equatorial Central Pacific due to changes in the Sea Surface Temperatures which is attributed to variations in the intensity of trade winds.
ENSO has two phases -
El Nino and La Nina
Above- During a La Nina period in June-August, regions of SE Asia experience Wet and Cool weather.
The Reason is not known why there is such anomaly during La Nina in SE Asia
The Warm Phase of ENSO i.e El Nino
During El Nino,Trade winds weaken leading to accumulation of Sea waters near Indonesia due to which temperature rises ( SST).
During El Nino, there is deficient rainfall in India as shown above.
Relation of the MJO with ENSO-
Considering the ENSO,MJO events since 1978-2010
El Nino Years- ( After 1978) ( S for Strong,M for Moderate,W for Weak)
1982 ( S)
1983 first half (S),
1987(M),
1991(S),
1992(M)
2002(M)
2004,2006 (W)
2009(S)
The MJO was mostly positive (+1.5 to 2) all these years especially during the Summer Monsoon period i.e June-Sept
clearly depicting its direct relation.
All related data can be availed here
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_mjo_index/pentad.shtml
La Nina years
Brief year 1988(S)
1998,1999 (M)
2010(M)
It can be seen that during this period, the MJO phase was mostly Wet or Negative ( Anomaly of -1 to -2)
For images click above
III -
Neutral Phase-
1978-1982 ( Neut)
and some more years like Mid 2012
It has been observed that the MJO wave has a nature depending on the intensity of Neutral.
During the period 1978-1982 when the SST was showing weak negative anomaly,
those years witnessed more number of wet phase of mjo than the dry
4) IOD-MJO Interaction
The Madden Julian Oscillation is observed widely across the Indian Ocean and Pacific Ocean.
As discussed in the above MJO section, conditions favorable for convection lead to the development of "wet phase" of MJO while those areas where strong convection is not possible the dry phase develops.
It can be noted that the MJO formation across the Indian Ocean is much marked than the Pacific Ocean
The animation of the OLR for a period between 19th Nov-19th Dec 2009 can be seen here at the top panel.
http://www.esrl.noaa.gov/psd/map/clim/olr_modes/mapanim2.html
OR CLICK
HERE
As seen in the image, a blue shade area which is represented by a "Red Circle" ( Positive phase of the MJO) is forming across East Central Africa while a developed orange-yellow shade ( Negative phase of MJO) is sweeping across Indonesia.
We now have a look at the DMI ( Dipole Mode Index) for the period of Nov-Dec 2009.
DATE DMI
2009:11:11:0 -0.0511759
2009:11:18:0 -0.199991
2009:11:25:0 -0.0942584
2009:12:2:0 0.152676
2009:12:9:0 0.535976
2009:12:16:0 0.571879
2009:12:23:0 -0.0290021
Here, negative DMI indicates Negative phase of the Indian Ocean Dipole (IOD) where Warmer water (SST) is present across the Eastern Indian Ocean and Cooler water is present across Western Indian Ocean.
The Eastern Indian Ocean during a Negative phase has greater convection activity going on which supports the formation of a Wet Phase of the MJO while across the Western Pacific, a Positive ( DRY) phase of MJO develops.
We consider some more examples of a significant MJO event across the region.
OLR Anomaly March 2010-May end 2010
2
For the Western Indian Ocean, one can note that there is a blue shade region ( Blue shade= greater than normal rain/clouding which is the enhanced phase of MJO). An orange shade is noted across the Eastern Indian Ocean ( orange=lesser clouding i.e dry phase of the MJO).
Here is the DMI for the period
DATE DMI
2010:3:3:0 -0.0212098
2010:3:10:0 0.275377
2010:3:17:0 0.378245
2010:3:24:0 0.201978
2010:3:31:0 0.515495
2010:4:7:0 0.712007
2010:4:14:0 0.447102
2010:4:21:0 0.234534
Here, the DMI values are positive ( Positive Indian Ocean Dipole) from 10th March-April end 2010
Thus the Enhanced ( WET) phase of MJO coincides with the Positive IOD.
2) OLR Anomaly (Oct 2010-Dec 2010)
A significant DRY PHASE of MJO seems over the Western Indian Ocean. Lets see the DMI now
DATE DMI
2010:10:6:0 -0.918562
2010:10:13:0 -0.948848
2010:10:20:0 -0.968341
2010:10:27:0 -0.581541
2010:11:3:0 -0.497689
2010:11:10:0 -0.546642
2010:11:17:0 0.0580557
2010:11:24:0 -0.0620495
2010:12:1:0 -0.119381
2010:12:8:0 -0.297918
2010:12:15:0 -0.0470014
2010:12:22:0 -0.493268
2010:12:29:0 -0.0990546
Here, a significant negative DMI event ( Negative IOD) is in place which is responsible for the DRY PHASE OF MJO
More analysis of MJO events with DMI can be done comparing the two links
http://www.bom.gov.au/climate/mjo/ ( OLR ANOMALY MJO)
http://www.jamstec.go.jp/frcgc/research/d1/iod/DATA/dmi.weekly.ascii ( DMI=IOD)
THUS ONE INFERS THAT THE MJO DRY PHASE DEVELOPS WHEN THE NEGATIVE INDIAN OCEAN DIPOLE IS IN PROGRESS WHERAS ENHANCED MJO DEVELOPS WHEN THE POSITIVE OCEAN DIPOLE IS IN PROGRESS FOR WESTERN INDIAN OCEAN. VICE VERSA FOR EAST INDIAN OCEAN
Reason-
As explained in the MJO,IOD section, a positive IOD will support stronger convection and hence Enhanced MJO across the Western Indian Ocean whereas a negative IOD will support suppressed convection and hence a dry phase of the MJO.
The IOD-ENSO relation is still being studied and shall be mentioned in a separate article-
5) Discussion on the present condition
1) ENSO
After a weak La Nina event in the year 2011 which continued in the 2012 beginning, conditions have turned to ENSO Neutral in the Equatorial Pacific Ocean. The latest weekly departure ( Temp.anomaly) from the Equatorial Central Pacific Ocean and surroundings indicate a well defined ENSO Neutral
The latest weekly SST departures are:
Region Anomaly
Niño 4 -0.3ºC
Niño 3.4 0.0ºC
Niño 3 0.1ºC
Niño 1+2 1.2ºC
Here is the latest SST anomaly ( analysis for 13th May 2012). The large cooler water SST can be seen across the Central Pacific Ocean which is fading now. Simultaneously, a pool of warmer water can be seen across the Indonesia,Australia East coasts as well.
II- MJO
The latest data indicates an ongoing dry phase of MJO across India. A significant MJO event ( DRY PHASE) ended late March 2012.
III- Indian Ocean Dipole
A Positive IOD ended during end of April 2012 and as seen from the data, a Negative IOD ( Weak) is in progress right now.
IV Somali Current
As of 15th May 2012, the Somali current isn't well established across the Equator and India. The above 850mb GFS shows much of moisture across the Somalia region and as seen from the map "The Great Whirl" is located in the Arabian Sea across Southern Arabian Sea which blocks the winds from reaching India coast. The Great Whirl is an indicator of the Dry phase of MJO..
The Ekman drift also is absent as of now!
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6) 2012 Summer Monsoon Forecast
*The Somali Current and Ekman Drift
Above-
The top most image is of the expected wind of 22nd May 2011 as analyzed on 15th May 2011
The below image is of the expected wind of 22nd May 2012 as analyzed on 15th May 2012
In 2011, the Somali current was very well defined across the Arabian Sea and the Bay of Bengal.However in 2012, the Somali Current is absent for Arabian Sea. Across the Bay of Bengal, the 850mb winds from Somali are well defined. As the current is absent this year, Ekman drift is absent this year!
* ENSO
IRI Probabilistic ENSO Prediction for NINO3.4 Region
| Season | La Niña | Neutral | El Niño |
|---|
| AMJ 2012 | 10% | 88% | 2% |
| MJJ 2012 | 9% | 71% | 20% |
| JJA 2012 | 7% | 58% | 35% |
| JAS 2012 | 6% | 50% | 44% |
| ASO 2012 | 6% | 48% | 46% |
| SON 2012 | 7% | 49% | 44% |
| OND 2012 | 6% | 50% | 44% |
| NDJ 2013 | 6% | 53% | 41% |
| DJF 2013 | 6% | 55% | 39% |
The IRI forecast shows the persistance of ENSO Neutral conditions this summer,monsoon period as well.
Majority forecast models show that ENSO Neutral may persists even in the winter but thats pretty long to discuss.
* Conclusion- ENSO Neutral will persist in the Monsoon period for India
* INDIAN OCEAN DIPOLE
THE INDIAN OCEAN DIPOLE FORECAST IS EXPECTED TO BE NEUTRAL IN EARLY MONSOON PERIOD WITH LATER TURNING TO POSITIVE IOD.
THE IOD DOESN'T SEEM TO BE INFLUENCING THE 2012 SUMMER MONSOON THIS YEAR DUE TO ITS INTENSITY.
* MJO
Establishing a relation with IOD which is expected to be slightly negative mode till June mid and then turning positive, the overall MJO activity will be weaker this season. Considering the weak negative activity till June mid, it appears that a weak dry phase will be near India especially across the Western Indian Ocean. In all considering the IOD and ENSO status of Neutrality almost, MJO interference shall be low this year and hence we rule out the excess rainfall possibility.
Above- TOP MOST image shows the MJO forecast as initialized on 15th May 2011 and valid till 24th June 2011. The MJO activity was very strong last year as compared to the 2012 conditions( bottom image). This is related to the IOD,ENSO activity.
Thus till 24th June 2012, a weak phase ( enhanced phase) will linger.
The June rainfall pattern across India where the monsoon reaches shall be
MOSTLY NORMAL (85% NORMAL EXPECTED)
Thus for the monsoon season, NEUTRAL ENSO activity, Weak Positive IOD and lesser interference of MJO is expected.
The Ekman Drift will play a significant role in deciding the rainfall amount in this region. The Great Whirl also will play a significant role as the MJO is expected to be more towards a DRY PHASE resulting in the amount of rains.
Concluding these factors, it appears that for India, the overall ( quantum) of 2012 Summer Monsoon will
be "SLIGHT DEFICIENT" WITH THE QUANTUM ANOMALY FOR THE SEASON EXPECTED TO BE -
~ 85% NORMAL
~ 15% DEFICIENT
REGION WISE FORECAST-
1) SOUTHERN INDIA
The IOD which is expected to be more towards weakly negative will lead to dry phase development which may reduce the rainfall amount in this area. A Slow Monsoon phase shall be likely in June due to no MJO activity. The rainfall amounts shall increase from July.
Region will witness " DEFICIENT" Rainfall with around 75% NORMAL RAIN and 25% DEFICIENT
2) Western India
The same conditions shall apply for Western India also as if the MJO activity remains less, monsoon winds shall be weak in this region. The rainfall pattern is expected to be slow in June month with monsoon making a slow entry. The rainfall amounts shall revive at the mid monsoon stage onwards when a Positive IOD consistency will develop
The region will witness "DEFICIENT" rainfall around 65% to 70% NORMAL and 35-40% DEFICIENT
3) Northern India
The region can expect good rainfall unlike the other areas. The primary reason seems to be the wind patterns expected. The region will receive some rains from the Western Disturbances which may have a southernly dip than normal. This factor was observed in April month also when greater than normal thunderstorm activity was reported across North-East India as the trough dug more southward and brought rains.
Aperiodic rainfall shall be there with 85% NORMAL and 15% DEFICIENT CONDITIONS
4) North East India
NE India will witness "Slightly Weak" Monsoon with the primary reason expected to be the less effective Bay of Bengal current. Due to lesser MJO events the current may not be that strong to produce much rains in the region
Expected 80% NORMAL RAINS AND 20% DEFICIENT
5) East India
Region shall witness SLIGHTLY WEAK MONSOON CONDITION.
Expected 85% NORMAL and 15% DEFICIENT
6) Central India
Lesser Bay systems shall reach this area resulting in lesser precipitation as compared to 2010,2011. The southward dip of Jet stream shall assist is some rainfall.
For South Central India ( Maharashtra parts) rainfall shall be 85% NORMAL and 15% DEFICIENT and for North Central India, rainfall will be 90% NORMAL and 10% DEFICIENT.
7) Andaman and Nicobar Is.
Normal rainfall is expected in this region around 95% i.e 5% deficient
8) Lakshadweep and surrounding
Considering the expected strength of Monsoon current and Ekman Drift this region will witness deficient rainfall
70% NORMAL i.e 30% DEFICIENT
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SINDH REGION
CONSIDERING THE CONDITIONS ACROSS ARABIAN SEA AND LESSER LOW PRESSURE SYSTEMS, SLIGHTLY DEFICIENT MONSOON RAINS ARE BEING EXPECTED IN THIS REGION
AROUND 85-90% NORMAL RAINFALL EXPECTED THIS YEAR
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7) Inference
* METD WEATHER ESTIMATES THAT THE SUMMER MONSOON FOR INDIA WILL BE AROUND 85% NORMAL AND 15% DEFICIENT.
* THE SUMMER MONSOON WILL BE DEFICIENT AS COMPARED TO 2010,2011
* NEUTRAL EL NINO SOUTHERN OSCILLATION, WEAK POSITIVE INDIAN OCEAN
DIPOLE AND LACK OF MADDEN JULIAN OSCILLATION SHALL REDUCE THE RAINFALL
* SOUTHERN AND WESTERN INDIA SHALL GET MORE DEFICIENT RAIN AS COMPARED TO OTHER PARTS
* NORTHERN,CENTRAL INDIA AND ANDAMAN NICOBAR IS. SHALL GET NEARLY NORMAL RAINFALL
*MONSOON WILL BE WEAK IN JUNE AND EXPECTED TO INTENSIFY ACROSS JULY
* VERY LESS LOW PRESSURE SYSTEMS SHALL AFFECT THIS YEAR
* INDIAN OCEAN DIPOLE (IOD) SHALL TURN TO A WEAK POSITIVE AROUND MID MONSOON PERIOD
* ENSO IS EXPECTED TO REMAIN NEUTRAL THROUGHOUT THE PERIOD
* MJO INTERFERENCE SHALL BE WEAK IN BOTH THE PHASES
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8) References
1) METD WEATHER - 2011 IndiMO Part I
http://metdweather.blogspot.com/2011/05/indimo-2011-part-i-indian-monsoon.html
2) INDIA METEOROLOGICAL DEPARTMENT- MAPS RELATED TO SOMALI CURRENT
http://www.imd.gov.in/section/nhac/dynamic/nwp/welcome.htm
3) NCEP COLA GFS FOR 850MB MAPS
http://wxmaps.org/pix/casia.fcst.html
4) CLIMATE PREDICTION CENTER FOR MJO RELATED IMAGES
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml
5) JAMSTEC for Indian Ocean Dipole
http://www.jamstec.go.jp/frsgc/research/d1/iod/iod_home.html.var
http://www.jamstec.go.jp/frcgc/research/d1/iod/DATA/dmi.weekly.ascii
6) BUREAU OF METEOROLOGY,AUSTRALIA FOR OLR MAPS
http://www.bom.gov.au/climate/mjo/
7) http://ggweather.com/enso/oni.htm
8) WIKIPEDIA.ORG FOR ENSO RELATED IMAGES
http://en.wikipedia.org/wiki/El_Ni%C3%B1o-Southern_Oscillation
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The Empirical Wave Propagation shows a weak enhanced phase of MJO arriving this month end and continuing till June. As the IOD is negative, the enhanced phase of MJO will be weak with strong dry phase which can be seen in July. The enhanced phase of MJO shall help the monsoon in June to reach on time and the rainfall intensity will be maintained for most of the places and hence the forecast ( as given in IndiMO 1) will be followed
The JAMSTEC updated models show that the Indian Ocean Dipole is expected to remain mostly positive during the monsoon period favoring the monsoon rainfall as it will enhance the MJO to active or wet phase over India
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