Oscillating waves which affect the phases of summer monsoon of India is explained with some case studies.

1. University of Agricultural Sciences, Dharwad
Department of Agricultural Meteorology
Master’s seminar- I
On
“ Intraseasonal Variations of Indian Summer
Monsoon and its influence on Agriculture”
Presented by
Hemareddy T
PGS19AGR8073

2. Sequence of Presentation
Introduction
Indian Summer Monsoon
Intraseasonal Variations
Madden Julian Oscillation
Research papers
Conclusion
Future line of work

3. Introduction
Word “Monsoon” is derived from the Arabic word for
season.
Monsoon is defined as seasonal reversing of wind system
accompanied by seasonal changes in atmospheric circulation
and precipitation.
Indian summer monsoon is a branch of Asiatic monsoon.
Primary theories behind the cause of monsoon is the
differential heating of ocean and land (Halley,1686) and shifts
in inter tropical conversion zone.

4. Fig 1:The Thermal Theory of Monsoons
Edmond Halley(1686)
Jun Jian, 2005

5. Indian Summer Monsoon (Jun-Sept)
• Also called the Southwest monsoon is due to northward movement of ITCZ
along with the movement of the sun.
• A very deep low pressure (~994mb) develops over the Tibetan plateau and a
high pressure (~1025mb) build up over the Mascarene island in the
Southern Indian Ocean near Madagaskar, and it is called the Mascarene
high.
• This environmental condition creates a strong pressure gradient force
between the Tibetan low and the Mascarene high. Hence the moisture laden
winds will start blowing from the Mascarene high (Southern Indian Ocean)
to the Tibetan low.
• As the air is coming from the ocean it carries enough moisture in it and
these moisture laden winds are allowed to lift up by the mountain ranges of
India and produce heavy rainfall over Indian sub continent.

6. Fig 2: A map showing the circulation of surface
winds during the summer monsoon in India
Source: NROER

7. Fig 3: Advance of Southwest Monsoon-2020
IMD, 2020

8. Climatic Variabilities On Indian Summer
Monsoon
Intra-seasonal monsoon variability
Inter-annual monsoon variability
Decadal monsoon variability
Active and break spells
Cyclonic disturbances
ENSO & LNSO
Climate change

9. Intraseasonal variations of monsoon
• The Intra seasonal variations of monsoons are characterised by the
several atmospheric waves (oscillation patterns) which are present in
the tropical region.
• This is also called the Monsoon Intra Seasonal Oscillations (MISO)
and Boreal Summer Intra Seasonal Oscillations (BSISO).
• Outgoing long wave radiation(OLR), Temperature, Sea Surface
Temperature(SST), Wind movement and Atmospheric pressure are
some of the factors which vary the monsoons.

10. The salient features of Intraseasonal variation
1. Northward movement of the rainbelt from the equatorial Indian
Ocean onto the continent during the onset phase of the monsoon,
during late May or early June.
2. Persistence of the rainbelt in the northern monsoon zone (~ 25°N).
3. Disappearance of the rainbelt from the northern monsoon zone for
periods ranging from a few days to a few weeks.
4. Revival of the rainbelt from break spells either by genesis within the
monsoon zone or by northward propagation of the oceanic rainbelt.
The mean period between northward propagations is about forty
days.(Ravi S. Nanjundiah, 2006)

11. • The main waves responsible for the intra seasonal oscillations are
Madden-Julian Oscillation (MJO), Quasi-Biennial Oscillation
(QBO) and other atmospheric waves such as Gravity waves (GW),
Equatorial Rossby waves (ER), Kelvin waves and Mixed Rossby
Gravity waves (MRG) etc.
• Since the Madden-Julian Oscillation (MJO) originates from the west
Indian Ocean and disappears over the central Pacific Ocean
(International Date Line) it play a very important role in the intra
seasonal variations of Indian Summer Monsoon rainfall.

12. Madden Julian Oscillation (MJO)
• It was discovered in the early 1970s by Dr. Roland Madden and Dr. Paul Julian.
• It is a large scale coupling between the atmospheric circulations and tropical
convection.
• It is a 30-60 day oscillation cycle originating from the West Indian Ocean and
moving eastward and disappears over the central Pacific Ocean somewhere around
the International Date Line.
• Enhanced and suppressed rainfall observed mainly over Indian and Pacific ocean.
• After rotating the globe it again re-generats at lower amplitudes over the Atlantic
Ocean and in higher amplitudes over the western Indian Ocean and begins a new
spell.

13. Fig 4: MJO movement from west Indian ocean to
central Pacific.

14. MJO is having two phases namely
Wet/Active phase: Characterised by the enhanced convections and
rainfall anomalies.
Dry/Break phase: Characterized by the suppressed convection and
dry atmospheric conditions.
• Its primary peak season is Austral (southern) summer season when the
strongest MJO signals are south of the equator. The second peak
season is the Boreal (northern) summer season when the strongest
MJO signals are north of the equator.
• During the northern winter the MJO is propagating eastward and in the
northern summer it is propagating north-eastward and hence it is
having a direct inter relationship with the south-westerly monsoon
flow and in turn it can regulate the Indian summer monsoon rainfall.

15. MJO link to the ENSO & LNSO oscillations
• There is strong season to season(intraseasonal) and year-to-year
(interannual) variability in Madden–Julian oscillation activity, with
long periods of strong activity followed by periods in which the
oscillation is weak or absent.
• In the Pacific, strong MJO activity is often observed 6 to 12 months
prior to the onset of an El Niño episode, but is virtually absent during
the maxima of some El Niño episodes, while MJO activity is typically
greater during a La Niña episode.
• Strong events in the Madden–Julian oscillation over a series of months
in the western Pacific can speed the development of an El Niño or La
Niña.

16. Impact of climate change on MJO
• The MJO travels a stretch of 12,000–20,000 km over the tropical
oceans, mainly over the Indo-Pacific warm pool, which has ocean
temperatures generally warmer than 28 °C.
• This Indo-Pacific warm pool has been warming rapidly, altering the
residence time of MJO over the tropical oceans. While the total
lifespan of MJO remains in the 30–60 day timescale, its residence time
have shortened over the Indian Ocean by 3–4 days (from an average of
15 days to 19 days) and increased by 5–6 days over the West Pacific
(from an average of 18 days to 23 days).
• This change in the residence time of MJO has altered the rainfall
patterns across the globe.

17. The active and break spells of South-west
monsoon
• The south west monsoon rainfall is having two phases namely the active phase
and the break phase.
• The monsoon is said to be in ‘‘active phase’’ when the central parts and the west
coast of India get normal or above normal rainfall.
• The ‘‘break phase’’ it is defined as the rain fall below normal over most parts of
India except in the hills in the north and in the southeast corner.
• The active and break monsoon conditions are also modified by the influence of the
MJO and other oscillation patterns. The break phase of the south-west monsoon
has a large impact on rain fed agriculture. In general most of the breaks occur
with duration of about 3–5 days(Rajeevan et al.,2010).

18. Fig 5:

19. Monsoon trough
• The monsoon trough is a portion depicted by a line on
a weather map showing the locations of minimum sea level
pressure.
• If the monsoon trough is extended along the foot hills of
Himalaya it is called an “Active monsoon” condition.
• When the monsoon trough crosses the Himalayan ranges their
will reduction in the amount of Indian Summer Monsoon
Rainfall and this environmental condition is called the “Break
monsoon” condition.

20. Fig 6: Active and Break phases influenced by monsoon
trough
Weatherview.in

21. Quasi Biennial Oscillation
• The quasi-biennial oscillation (QBO) is a quasi-periodic oscillation of the equatorial zonal
wind between easterlies and westerlies in the tropical stratosphere with a mean period of
28 to 29 months(Baldwin et al., 2001).
• The alternating wind regimes develop at the top of the lower stratosphere and propagate
downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical
tropopause.
• Downward motion of the easterlies is usually more irregular than that of the westerlies.
The amplitude of the easterly phase is about twice as strong as that of the westerly phase.
• And the another important oscillation type is the quasi-biweekly oscillation (QBW). This
oscillation is having a periodicity of 12–20-days. It is one of the major systems that affect
the seasonal mean climate of the tropical and subtropical countries.
• Hence the Indian summer monsoon is also getting affected by these oscillation pattern
and results in reduction in the seasonal and annual rainfall over Indian sub continent.

22. Fig 7: QBO
Smith et al., 2012

23. Research papers

24. Fig 8. Regional mean intraseasonal precipitation (mm day-1 ; black solid curves) and intraseasonal SST
anomalies (0C; blue solid curves) in (a) WCI and (b) NBB. The time mean of precipitation (black dotted
lines) and one std dev above the mean (black solid lines) are superimposed. The beginning of each heavy
precipitation event is marked with a red dot.
Jingyuan et al., 2015 China

25. Fig 9: (a) Thick black solid curve: 30-yr mean TT index (from 1982 to 2011) from March to December. Thin dash curves:
mean TT index plus and minus one std dev. Gray curve: std dev of TT index. The gray curve is 5 times larger than
the actual std dev of the TT index for clarity. On each day, the mean and std dev are calculated with the data on that
day from 1982 to 2011. (b) Std devs of intraseasonal OLR and intraseasonal precipitation, which are averaged within
the northern region for calculating the TT index.
Lei and Raghu, 2013 China & Maryland

26. Fig 11: All-India daily rainfall anomalies (bars), 30-60 days (red curve) and 10-20 days (blue curve) filtered
anomalies for 1 June to 30 September for the period 1901-2005. The scale for daily rainfall anomalies is
left Y axis while that of daily filtered anomalies is right Y axis. Figures in the bracket indicate AIMR for
corresponding year
IITM, Pune Ashwini et.al. 2006

27. Fig 12: Composite mean of daily rainfall departure from normal (in %) for (a) 10 excess
monsoon years and (b) 10 deficient monsoon years for data period 1951 – 2003.
IITM, Pune Kakade et.al, 2008

28. Fig 13: Daily TRMM precipitation averaged over (a) the EAS and (b) the BoB. Gray
shadings denote the ISM season of 15 May–15 October. The red lines with circles
denotes the ISM-mean precipitation for each year.
Yuonlong et al., 2016 USA & India

29. Fig 14: Maps showing 20–90-day TRMM precipitation (mm day-1 ) for the (c) developing
stage (15 May–30 June), (d) mature stage (1 July–31 August), and (e) decaying stage
(1 September–15 October) of the ISM.
Yuonlong et al., 2016 USA & India

30. Fig 15: TMI and CFSR products of 1998–2010. The black rectangles define the
areas of the EAS (108–208N, 658–758E) and the BoB (108–208N, 858–
958E).
Wang et al., 2016 Maryland & India

31. Impact of MJO on Indian Summer monsoon

32. Fig. 16: Frequency of MJO phases 1 to 8 (≥6 days) during onset period for the
data period 1979– 2015.
Bhatla et al., 2016 BHU, Varanasi

33. Fig 17: Day-to-day variation of MJO amplitude/mean amplitude for the a pre-onset, b normal-onset, and c
post-onset years during the period1979–2015
Bhatla et al., 2016, BHU Varanasi

34. Fig 18: 800, 400 &200(hpa) pressure variations for the years 2013 &
2014.
2013
2014
Hussain et.al., 2015, Hyderabad

35. Active and Break Spells of Monsoon

36. Fig 19: Composites of OLR anomalies (Wm−2) during (a) break
and (b) active spells. Period of analysis: 1979–2007
Rajeevan et al., 2010, India

37. Fig 20: Time series of (a) active days and (b) break days
during July and August. Period: 1951–2007
Gadgil et al., 2010, India

38. Conclusion
• The intra-seasonal variability makes up an extremely important part of
the character and evolution of Indian summer monsoon . Its most
pronounced influence is associated with its direct connection to active
and break phases of monsoon.
• Fluctuating monsoons due to ISVs influence on Cropping Pattern and
Evapotranspiration.
• MJO has the dominant role on intraseasonal variability in the tropical
atmosphere and also with onset of the Indian summer monsoon.

39. Future Line Of Work
• Further understanding of the relation between the ISVs and ISM will
be helpful for the study of the interannual variability of ISM and the
prediction skill on the ISM.
• More attention and effort should be paid to understand oceanic
processes in the tropical Indian Ocean and incorporate the knowledge
into the monsoon prediction.
• Studies on ISVs of Monsoon in relation with Agriculture should be
strengthened.

40. THANK YOU