Indian Summer Monsoon Rainfall Characteristics During Contrasting Monsoon Years

HAMZA VARIKODEN,1 M. R. RAMESH KUMAR,2 and C. A. BABU3

Abstract—The present paper presents a diagnostic study of two

recent monsoon years, of which one is dry monsoon year (2009)

and the other is wet monsoon year (2010). The study utilized the

IMD gridded rainfall data set in addition to the Reynolds SST,

NCEP-NCAR reanalysis wind and temperature products, and

NOAA OLR. The study revealed that the months July and August

are the most crucial months to decide whether the ISMR is wet or

dry. However, during July 2009, most of the Indian subcontinent

received more than 60 % in the central and western coastal regions.

In a wet monsoon year, about 35–45 % of rainfall is contributed

during June and July in most parts of India. During these years, the

influence of features in the Pacific Ocean played vital role on the

Indian summer monsoon rainfall. During 2009, Pacific SST was

above normal in nino regions, characteristic of the El Nino struc-

ture; however, during 2010, the nino regions were clearly below

normal temperature, indicating the La Nina pattern. The associated

atmospheric general circulation through equatorial Walker and

regional Hadley circulation modulates the tropospheric tempera-

ture, and hence the organized convective cloud bands. These cloud

bands show different characteristics in northward propagation

during dry and wet years of ISMR. During a dry year, the propa-

gation speed and magnitudes are considerably higher than during a

wet monsoon year.

Key words: Contrasting monsoon, sea surface temperature,

monthly contribution, tropospheric temperature.

1. Introduction

One of the main characteristics of the Indian

summer monsoon rainfall (ISMR) is the year-to-year

variation. This variation is subject to many atmo-

spheric and oceanic parameters in fast and slow

response. India is an agrarian country, and therefore

its economy mainly depends upon the seasonal rain-

fall from June to September. About 75–90 % of the

rainfall is received during these four months, and

hence the reduction/excess in rainfall will affect the

economy of the country (MOOLEY et al. 1981). This

year-to-year variation of the ISMR is a physical

manifestation of the interannual variability, and this

interannual variability is subject of intense research

(MOOLEY and PARTHASARATHY 1984; PARTHASARATHY

1984; MOOLEY and SHUKLA 1987; PANT et al. 1988;

PARTHASARATHY et al. 1988, 1991). The variation of

the ISMR from year to year is not coherent over the

Indian region, both spatially and temporally (GADGIL

et al. 2003). In general, some regions experience

above-normal rainfall and others below-normal. Thus

the anomalies of rainfall from the climatology are

positive over some of the meteorological subdivisions

and negative in others. In a flood year, the rainfall is

above normal in most of the subdivisions, and vice

versa during drought years (SHUKLA 1987; GREGORY

1989; GADGIL et al. 2007).

RAMESH KUMAR et al. (1986) have looked into the

SST variability during the monsoon season over the

Indian Ocean and its relation with the summer

monsoon rainfall from a predictive point of view,

using satellite-derived fields of SST for two con-

trasting monsoon years (1979 and 1983). Their study

showed that the zonal anomaly of SST off the coast

of Somalia and the central Indian Ocean are highly

correlated with the monsoon rainfall over the western

and central parts of India during the same week,

based on a 80 years of data; RAO and GOSWAMI

(1988) have shown that the pre-monsoon anomalies

of SST in the western and southern Arabian Sea have

a predictive value for the monsoon rainfall. Most of

these studies presumed that higher values of SST lead

to higher rates of evaporation, which in turn can

contribute to a normal or even excessive monsoon

1 Indian Institute of Tropical Meteorology, Dr. Homo Bhabha

Road, Pashan, Pune 08, India. E-mail: hamza@tropmet.res.in2 National Institute of Oceanography, Dona Paula, Goa,

India.3 Cochin University of Science and Technology, Cochin 16,

India.

Pure Appl. Geophys.

� 2013 Springer Basel

DOI 10.1007/s00024-013-0691-9 Pure and Applied Geophysics

rainfallRAMESH KUMAR and SCHLUESSEL (1998) has

obtained similar result for two contrasting monsoon

years, namely 1987 (deficit) and 1988 (excess).

In another study, RAMESH KUMAR et al. (2005)

looked at the air–sea interaction over the tropical

Indian Ocean during two contrasting monsoon years

2002 (deficit) and 2003 (normal). They found that

evaporation rates were lower (higher) over the Ara-

bian Sea during active (weak) monsoon conditions.

Water vapor contents decreased substantially prior to

the break over the Arabian Sea, and low values pre-

vailed throughout the break period. RAMESH KUMAR

(2009), using a suite of data sets, have shown that

there is an increased propensity towards breaks in

monsoon conditions over the Indian subcontinent

during recent decades. They attributed this to large-

scale changes in the atmospheric circulation and

warming of the eastern equatorial Indian Ocean at the

rate of 0.015 8C year-1. Their study further showed

that this warming in turn has altered the ocean

atmospheric processes over the Indian Ocean so as to

intensify the Southern Hemisphere equatorial trough,

and also led to the weakening of the moisture flow

into the Indian subcontinent during recent decades.

The Indian summer monsoon is influenced by

local and large-scale atmospheric and oceanic fea-

tures. The Indian Ocean dipole (IOD) is one of the

factors which influences the ISMR (SAJI et al. 1999;

ASHOK et al. 2004). The influence of El Nino–

Southern Oscillation (ENSO) on the Indian monsoon

rainfall has been a subject of intense research during

the last three decades (SIKKA 1980; RASMUSSEN and

CARPENTER 1983; SHUKLA 1987; ASHOK et al. 2001).

The Indian summer monsoon is influenced by ENSO

through equatorial Walker circulation, and thus

through the regional Hadley circulation (WEBSTER

et al. 1998; GOSWAMI 1998). ASHOK et al. (2001)

further determined that the IOD modulates the ENSO

influence on ISMR through regional circulation. The

atmospheric part of IOD called EQUINOO (Equato-

rial Indian Ocean Oscillation) also plays a vital role

in modulating the ISMR.

It is well known that the ISMR has considerable

interannual variability (PARTHASARATHY et al. 1995)

with different periodicities, such as biennial, inter-

decadal, decadal and multidecadal periods. The 2009

and 2010 Indian summer monsoons highly contrast in

rainfall amounts and associated atmospheric and

oceanic features. The 2009 Indian summer monsoon

was abnormally below the climatological mean

rainfall and was reported as the third major drought

year in the recent century (IMD report 2009). During

2009, the ISMR has departed about 23 % from its

normal value; however, in certain regions, the ISMR

has departed 48 % from its normal value. This mas-

sive departure of ISMR leads to a drastic deficit

condition in the Indian peninsula. FRANCIS and

FRANCIS (2010) reported that the non-cooperative

behaviour of Bay of Bengal meridional SST leads to

a suppressed condition. It inhibits organized con-

vection over the monsoon regime, and thus the

rainfall during the year. In the case of the 2010

ISMR, the rainfall itself is above normal in most parts

of the country, and was reported as 103 % of the

long-term mean of the rainfall. WEBSTER et al. (2011)

studied the Pakistan floods that occurred during the

peak month of the 2010 summer monsoon period, and

they argued that these deluges were highly predict-

able, at least 6–8 days in advance. HONG et al. (2011)

have pointed out that the anomalous rainfall activity

over the Indo-Pak region during 2010 was related to

persistent activity of European blocking and the co-

occurrence of tropical monsoon surges. All these

studies revealed that ISMR is above normal over the

Asian monsoon regions in addition to the Indian

continent. In the present study, we made an attempt to

bring out the contrasting features in the atmospheric

and oceanic parameters associated with the contrast-

ing monsoons of 2009 and 2010.

2. Data and Methodology

The present study utilizes daily gridded rainfall

data set with a 1� latitude 9 1� longitude grid spatial

resolution, available from the India Meteorological

Department (IMD) for 2009 and 2010. The clima-

tology of the rainfall was made from 1974–2004 as

the base period. In this data set, a geographical area

from 6.5�N to 37.5�N and 66.5�E to 101.5�E was

considered, and the station rainfall data was inter-

polated to gridded rainfall data. The interpolation

method is based on the weights calculated from the

distance between the station and the grid point and

H. Varikoden et al. Pure Appl. Geophys.

also the directional effects (SHEPARD 1968). Standard

quality controls were performed before carrying out

the interpolation analysis (RAJEEVAN et al. 2006;

RAJEEVAN and BHATE 2009). For the present work, we

considered the daily data for ISMR (June–September)

and it has been converted to monthly values.

Daily Reynolds SST data was also used to

understand the ocean temperature features during the

contrasting years (2009 and 2010) of ISMR. This data

set has a spatial resolution of a 0.258 latitude 9

0.258 longitude grid and has been developed using

the optimum interpolation (OI) technique (REYNOLDS

et al. 2007). In addition to the Reynolds SST data set,

the NCEP-NCAR (National Centre for Environmen-

tal Prediction , National Centre for Atmospheric

Research) wind and temperature data sets were used

at different levels in order to understand the behavior

of the atmosphere during contrasting years of ISMR.

These data sets have a spatial resolution of a

2.58 9 2.58 latitude–longitude grid with and a tem-

poral resolution of a day. Even though the wind and

temperature data sets are a reanalysis data set, it is

well related to observed data, and hence it is in the

most reliable class of measured wind observations

(KALNAY 1996). Tropospheric temperature is the

average temperature between 200 and 700 hPa. This

tropospheric temperature is also analyzed. Daily

NOAA (National Oceanic and Atmospheric Admin-

istration) interpolated OLR (Outgoing Longwave

Radiation) with the same spatial resolution (LIEBMANN

and SMITH 1996) was also used to study the propa-

gation of convection in different time scales over the

summer monsoon domain. This interpolated OLR can

be used as a proxy for convection and the values of

OLR \220 Wm-2 represent to indicate convection

and precipitation in the tropics (ARKIN and MEISNER

1987).

3. Results and Discussion

3.1. Mean Rainfall During 2009 and 2010

Indian summer monsoon rainfall (ISMR) on an

average during 2009 is below normal and during

2010 is above normal in most parts of the Indian

subcontinent. The spatial distribution of the seasonal

rainfall during 2009 and 2010 is given in Fig. 1.

During 2009 ISMR, only the western coast gets

rainfall above 200 mm, and rest of the country

received rainfall below 75 mm. This is less than the

normal in the country as a whole. In the northwestern

regions, the rainfall is below 25 mm in the southwest

monsoon season. However, during the 2010 south-

west monsoon, the entire subcontinent received

above-normal rainfall, especially in the Konkan

coasts and eastern regions. There, the monsoon

rainfall is about 300 mm. In central India, the rainfall

is above 100 mm/season.

3.2. Monthly Contribution to the Seasonal Rainfall

Monthly distributions of rainfall during summer

monsoon months are clearly different in the two

contrasting years (Fig. 2). In 2009, a deficit year,

maximum contribution of rainfall occurred in July in

most part of the country. During this month, most

part of the western coast and central India received

more than 60 % of rainfall. However, in other months

the contribution of rainfall is too low, especially

during June. In the June, most parts of the peninsular

India and central India contributed\15 % of the total

seasonal rainfall. During August, the foothills of

Himalaya and eastern regions received more rainfall

than in the western coastal regions. In the 2010

monsoon, June rainfall contributed a small amount

compared with other months in the southwest mon-

soon period. During the months of July and August,

35–45 % of the rainfall is contributed in most of the

Indian regions, indicating that these two months are

contributing most of the rainfall to the total seasonal

rainfall (70–90 % of annual rainfall). The contribu-

tion of rainfall in the month of September is \20 %

in all the regions, except some northern areas.

FENNESSY and SHUKLA (1994) brought out similar

rainfall characteristics for two contrasting monsoon

years 1987 (deficit) and 1988 (excess).

3.3. Departures from Normal for Two Contrasting

Monsoon Years

Monthly departures of ISMR during 2009 and

2010 are presented in Fig. 3. In 2009, as we expected,

most part on the Indian subcontinent experienced dry

Indian Summer Monsoon Rainfall Characteristics

condition in all the months. The departure during

June is negative everywhere, except for some parts of

the southeastern regions. During the July, August and

September, rainfall departures are greater in the

northern and northwestern regions. Only in the

Konkan coasts during July and September, and over

Figure 1Spatial pattern of summer monsoon seasonal rainfall in mm per season (June–September) during 2009 and 2010

Figure 2Spatial pattern of ISMR departures for each month during June to September for 2009 and 2010

H. Varikoden et al. Pure Appl. Geophys.

the western ghats during August, are rainfall depar-

tures above normal. In the case of a wet year (2010

monsoon), we observed above-normal rainfall over

the Indian subcontinent in all the summer monsoon

months except during June. In the month of June,

central India received below-normal rainfall.

3.4. Tropospheric Temperature During 2009

and 2010

In order to understand the reasons for the

persistent rainfall in 2010 and decreased rainfall in

2009, we tried to explore the possibility of the

tropospheric temperature (TT). The tropospheric

temperature is one of the factors governing the

southwest monsoon. A warm TT indicates high

heating, which ultimately draws the moisture towards

its core, and hence produces a good amount of

rainfall. LIU and YANAI (2001) stated that the good

monsoon over the Asian region is linked with a high

TT over the Asian region. During the 2009 southwest

monsoon season, the TT shows low values compared

with the 2010 southwest monsoon period (Fig. 4).

The abnormally high rainfall during the 2010 mon-

soon is due to the high TT. The difference of TT

between the two contrasting monsoons is given in

Fig. 4 (bottom panel). During the 2010 southwest

monsoon, the TT is increased everywhere in the

Indian subcontinent, and this high TT causes pulling

of the atmospheric moisture through the westerly jet,

and produces organized convection over the entire

Indian region. The TT values are greater during July

and August, during which the TT values are more

than -5� C, however, during 2009, the TT is\-6� C

for the same months. The high values of TT

contribute to the organization of high amounts of

monsoon clouds over the Indian subcontinent

through the mid-tropospheric heat flux. The studies

of GOSWAMI and XAVIER (2005) and YU et al. (2004)

support the present analysis.

Figure 3Spatial pattern of ISMR contribution for each month during June to September for 2009 and 2010

Indian Summer Monsoon Rainfall Characteristics

3.5. Seasonal SST for 2009 and 2010

Sea surface temperatures from the Reynolds data

set have been studied for the Indo-Pacific regions for

the two contrasting monsoon years (Fig. 5). During

the 2009 summer monsoon period, it is clear that a

strong El Nino developed in the eastern Pacific Ocean

with a considerable magnitude. The SST pattern

shows a typical El Nino with a magnitude of more

than 1 �C in the equatorial belt up to 150 W, and the

magnitude exceeds more than 1.5 �C over the nino 1

and nino 2 regions. This clearly shows the influence of

Pacific SST on the ISMR over the Indian subcontinent

by governing general atmospheric circulation. This

circulation descends over the Indian subcontinent and

leads to dryness in the upper atmosphere, as we

showed in the TT. Therefore, during 2009 the

combined TT and Pacific SST anomaly leads to the

abnormally low rainfall over the Indian regions.

However, during 2010 ISMR, the SST pattern is

different from that of the 2009 SST anomaly pattern.

This SST anomaly pattern shows negative, indicating

La Nina with moderate intensity, as reported by

MUJUMDAR et al. (2012). The negative SST anomaly

spreads all over the nino 4 region in addition to the

nino 1 and nino 2 regions, with maximum intensity

over nino 3.4 regions. This negative pattern of SST

anomaly over the Pacific region leads to an inverse

general circulation in the atmosphere from that of the

2009 circulations. This opposite circulation leads to a

sinking motion over the equatorial Indian Ocean

through Walker circulation, and the descended com-

ponent rises over the Indian peninsular region through

regional Hadley circulations. This upward motion of

the regional Hadley circulation helps to maintain the

TT warmth, and this maintains the organized mon-

soon clouds over the region, ultimately resulting in a

high amount of rainfall over the monsoon domain.

RAMESH KUMAR et al. (1986) and PATTANAIK and

PATTANAIK (2000) studied the SST features during

different contrasting monsoon years and they reached

similar conclusions. Our results were also coherent

with the previous findings.

Figure 4Spatial pattern of TT during June to September for 2009 and 2010

H. Varikoden et al. Pure Appl. Geophys.

3.6. Anomalies of Wind and OLR

Understanding the low-level circulation anoma-

lies during recent contrasting monsoon years is

interesting because the circulation pattern is very

different from the climatological pattern. Climatol-

ogy of OLR (shaded) and wind at the 850 hPa level

(top panel) and the anomalies of OLR and wind at the

850 hPa are given in Fig. 6. During the dry year, the

wind anomaly shows easterlies in the entire LLJ

(low-level jet stream) zone, indicating that the LLJ is

very much weakened during the year 2009; this is

coherent with the results of GADGIL et al. (2003) for

the 2002 monsoon. Over the land mass of the Indian

Peninsula, we observed that the divergent pattern in

the low-level circulation, and therefore the OLR

anomaly, is high over the regions (Fig. 6b). The

anomaly over the land mass region is more than 15

Wm-2 , indicating the absence of convection due to

the divergence in the low-level circulation. However,

during 2010, an abnormally high rainfall year, the

low-level circulation anomalies are different from

those expected during the wet years (expecting

intense LLJ to carry the moisture from the oceanic

region to the land mass, Fig. 6c). Even though the

strength of the LLJ is weak, the organized convection

anomalies (OLR anomaly) are favorable over the

peninsular region, Arabian Sea and the Bay of Bengal

regions. The OLR anomaly is above -15 Wm-2 in

all these regions. This organization of clouds is due to

the convergent pattern of the low-level circulation

and is clear from Fig. 5c. Due to the convergence in

the low-level circulation fields causes rising motion

(upward limb of Hadley circulation) and this also

favours the increase of the tropospheric temperature.

This increased TT maintains the organization of

monsoon clouds over the region and thereby occur-

rence of abnormal rainfall.

3.7. Intraseasonal Oscillation of OLR During

Contrasting Monsoons

Here, we tried to explore the intraseasonal features

of the organized convection (OLR anomaly) during

Figure 5Spatial pattern of SST for monsoon period for 2009 and 2010

Indian Summer Monsoon Rainfall Characteristics

two contrasting monsoon seasons. In this, we are

attempting to the northward propagation of the OLR

bands over the area averaged 72.5�E to 85�E. To get

the correct signal for both the contrasting years, we

filtered the data with a band-pass filter between 30 and

90 days. The oscillation features are clearly different

for both the years (Fig. 7). For the 2009 southwest

monsoon, the northward propagation of the convec-

tion bands are very distinct and clear with high

magnitudes. The propagation speed from south to

north is also faster during the 2009 monsoon period.

The northward propagation of the cloud bands starts

from around the equatorial regions and covers the

entire region within 15 days. However, during the wet

year, the northward propagation is slower and does

not occur in a well-organized manner, even though the

propagation is present. The propagation starts from

about 10�S and covers the entire region within about

30 days. The slow propagation of the 30–90 day band

of organized cloud bands causes the persistent rainfall

Figure 6Spatial pattern of LLJ and OLR for monsoon period for 2009 and 2010

H. Varikoden et al. Pure Appl. Geophys.

over the entire regions of Indian subcontinent during

2010, and fast propagation causes short spells of

rainfall, and therefore during 2009 the monsoon is

abnormally below normal. It is reported that during

weak monsoon periods, the 30–60 day mode of

oscillation is strong and it is opposite in the intense

monsoon year (KULKARNI et al. 2011). This result

matches with the 30–60 day oscillations of summer

monsoon years during 2009 and 2010.

3.8. Role of Convective Systems over the North West

Pacific (NWP)

KANAMITSU and KRISHNAMURTI (1978) found that

the excess system days over the NWP was one of the

reasons for the deficient monsoon rainfall for the year

1972. They pointed out that when the NWP becomes

convectively active with excess system days, intense

atmospheric heating leads to a shift in the Tibetan

anticyclone southeastwards and weakens the Indian

summer monsoon. VINAY KUMAR and KRISHNAN

(2005) showed that there is a greater tendency for the

cyclones which from the NWP to recurve and move

northwards during the deficit monsoon years. RAMESH

KUMAR (2009) studied the characteristics of the

convective systems such as frequency, geographical

location, duration of the systems and the direction of

movement of the systems over the NWP have been

examined in relation to breaks in monsoon conditions

over the Indian subcontinent during several

Figure 7Time latitude variation of OLR during 2009 and 2010 summer monsoon period. The OLR is subjected to 30–90 day band pass filter

Indian Summer Monsoon Rainfall Characteristics

contrasting monsoon years. They found that the low-

level wind flow at 850 hPa was substantially more

(less) and directed towards the Indian subcontinent

(equatorial region) during the excess (deficit) mon-

soon years. Further, it was found that during the

deficit years and prolonged breaks in monsoon

conditions, more systems (about 69 %) formed

further south than in the case of excess monsoon

years.

In order to look into the relative role of the

convective systems over the Bay of Bengal and

NWP, we analysed the data from the website

(http://www.weather.unisys.com/hurricane) for the

contrasting years 2009 and 2010. Our study showed

that there were four (three) systems over the Bay of

Bengal during 2009 (2010), respectively. Further

analysis of the systems over the NWP, revealed that

more systems formed over the NWP during a dry

monsoon year (2009). Further, there were about 16

convective systems formed over this region, and the

majority of them travelled in a northward or north-

eastward direction, whereas during the wet monsoon

year (2010) only 11 convective systems formed over

the NWP region, and most of them travelled in a

westward or north-westward direction. Our results are

thus in good agreement with the previous results of

RAMESH KUMAR (2009), who found that convective

systems were about 1.83 times greater over the NWP

than the Bay of Bengal while analyzing the results for

several contrasting monsoon years.

4. Summary and Conclusion

Here, we studied the features of contrasting

monsoons, of which one is dry (2009) and the other

one is wet (2010). The 2009 monsoon is 23 %

below normal and 2010 monsoon is 3 % above

normal rainfall over the Indian subcontinent. During

the dry monsoon, most of the rainfall contributed

during the month of July and contribution of rainfall

during other months is relatively low. During the

wet year the contribution is about 35–45 % in the

peak monsoon months (June and July) over the most

parts of India. During 2009, the departure of rainfall

from climatological pattern is below everywhere in

the county except some parts in the western coastal

belts during the months of July and September. In

2010, almost everywhere receives above-normal

rainfall.

The SST in the Pacific is crucial to regulating the

ISMR during these two years, through the equatorial

Walker and regional Hadley circulations. El Nino is

associated with dry monsoon (2009) and La Nina is

associated with wet monsoon (2010). In the 2009 dry

monsoon, the sinking component of regional Hadley

circulation is more prominent, and this creates

divergence at a low level and thus produces the low

values of tropospheric temperature. The low values of

TT are unfavourable for organized convection. In the

case of the 2010 wet monsoon, the rising limb of

regional Hadley circulation is generated as a result of

La Nina, which helps the low-level wind to converge

and thus results in organized convection through the

heat flux from the enhancement of tropospheric

temperature. The intraseasonal behavior of these

convective cloud bands is also different during the

two contrasting years. During the dry year, the

northward propagation is too fast and may be due to

the frequent evolution and propagation of monsoon

surges, leading to the occurrence of active and break

phases of the Indian summer monsoon. In contrast to

the dry phase, during the wet phase the speed and

magnitude of the northward propagating mode is

slow and low. This indicates that during the wet

phase, the rainy phase is prolonged and stagnant.

Therefore, the movement of the northward propa-

gating band is slow. The present studies of

contrasting monsoon years are also in good agree-

ment with earlier studies.

Acknowledgments

The first author acknowledges the Director, Indian

Institute of Tropical Meteorology, Pune, for support.

Dr. M. R. Ramesh Kumar acknowledges the Director,

National institute of Oceanography for support, and

the third author is grateful to the Cochin University of

Science and Technology for providing facilities and

other required support. The data sets used in this

study are properly acknowledged. Comments from

the editor and reviewers helped greatly to improve

the manuscript.

H. Varikoden et al. Pure Appl. Geophys.

REFERENCES

ARKIN, P.A., and MEISNER B.N. (1987), The relationship between

large-scale convective rainfall and cold cloud over the western

hemisphere during 1982-84. Mon. Wea. Rev., 115, 51–74.

ASHOK, K, GUAN Z., SAJI, N.H, and YAMAGATA T. (2004) Individual

and combined influences of the ENSO and Indian Ocean Dipole

on the Indian summer monsoon. J. Climate, 17, 3141–3155.

ASHOK K., GUAN Z., and YAMAGATA T. (2001), Impact of the Indian

Ocean Dipole on the relationship between the Indian monsoon

rainfall and ENSO. Geophys. Res. Lett., 28, 4499–4502.

FENNESSY, M.J., SHUKLA, J. (1994), GCM Simulations of active and

break monsoon periods, Proc. International Conf. on moon

variability and prediction, Int. Centre for Theoretical Physics,

Trieste, Italy, 9 ± 13 May 1994, Vol. II, WCRP-84, WMO/TD-

No 619.

FRANCIS, P.A, and GADGIL, S. (2010) Towards understanding the

unusual Indian monsoon in 2009, J. Earth Syst. Sci. 119,

397–415.

GADGIL, S., RAJEEVAN, M., and FRANCIS, P.A. (2007) Monsoon

variability: Links to major oscillations over the equatorial

Pacific and Indian oceans, Current Science, 93, 182–194.

GADGIL, S., VINAYACHANDRAN, P.N., and FRANCIS, P.A. (2003),

Droughts of Indian summer monsoon: Role of clouds over the

Indian Ocean, Curr. Sci., 85, 1713–1719.

GOSWAMI, B.N. (1998), Physics of ENSO-Monsoon connection, Ind.

J. Marine Sci., 27, 82–89.

GOSWAMI, B.N., and XAVIER, P.K. (2005), ENSO control on the

south Asian monsoon through the length of the rainy season,

Geophys. Res. Lett., 32, L18717, doi:10.1029/2005GL023216.

GREGORY S., 1989. Macro-regional definition and characteristics of

Indian summer monsoon rainfall, 1871–1985. lnt. J. Climatol., 9,

465–483.

HONG, C-C., HSU, H-H., LIN, N-H., CHIU, H. (2011), Roles of

European blocking and tropical-extratropical interaction in the

2010 Pakistan flooding. Geophysical Research Letters 38,

L13806, doi:10.1029/2011GL047583.

KALNAY, E., et al. (1996), The NCEP/NCAR 40-year reanalysis

project, Bull. Am. Meteorol. Soc., 2, 437– 471.

KANAMITSU, M., KRISHNAMURTI, T.N. (1978), Northern summer

tropical circulations during drought and normal rainfall months.

Mon. Wea. Rev., 106, 331–347.

KULKARNI, A.A., KRIPALANI, R.H., SABADE, S., and RAJEEVAN M.

(2011), Role of intra-seasonal oscillations in modulating the

Indian summer monsoon rainfall. Clim. Dyn. 36, 1005–1021.

LIEBMANN, B., and SMITH, C.A. (1996), Description of a complete

(Interpolated) Outgoing Longwave Radiation data set. Bull.

Amer. Meteor. Soc., 77, 1275–1277.

LIU X.D. and YANAI, M. (2001), Relationship between the Indian

monsoon precipitation and the tropospheric temperature over the

Eurasian continent, Quarterly Journal of the Royal Meteoro-

logical Society, 127, 909–937.

MOOLEY, D.A,, and PARTHASARATHY, B. (1984), Fluctuations in all-

India summer monsoon rainfall during 1871–1978. Climatic

Change. 6, 287–301.

MOOLEY, D.A., PARTHASARATHY, B., SONTAKKE, N.A., and MUNOT,

A.A. (1981), Annual rain-water over India, its variability and

impact on the economy. J. Climatol., 1, 167–186.

MOOLEY, D.A., and SHUKLA, J. (1987), Variability and forecasting

of the summer monsoon rainfall over India. Monsoon

Meteorology. Editors: C. P. Chang and T. N. Krishnamurti.

Oxford University Press, pp. 26–59.

MUJUMDAR, M., PREETHI, B., SABIN, T.P., ASHOK, K., SAEED, S., PAI,

D.S. and KRISHNAN, R. (2012), The Asian summer monsoon

response to the La Nina event of 2010. Met. Apps, 19, 216–225.

doi:10.1002/met.1301.

Pant, G.B., Rupa Kumar, K., Parthasarathy, B., Borgaonkar, H.P.

(1988), Long term variability of the Indian summer monsoon and

related parameters. Advances in Atmospheric Sciences, 5,

469–481.

PARTHASARATHY, B. (1984), Some aspects of large scale fluctuations

in the summer monsoon rainfall over India during 1871–1978,

PhD Thesis,University of Poona, 370 pp.

PARTHASARATHY, B., MUNOT, A.A., and KOTHAWALE, D.R. (1988),

Regression model for estimation of Indian food grain production

from Indian summer rainfall. Agric. For. Meteorol., 42, 167–182.

PARTHASARATHY, B., MUNOT, A.A., and KOTHAWALE, D.R. (1995),

All India monthy and seasonal rainfall series: 1871–1993. Theor.

Appl. Climatol., 49, 217–224.

PARTHASARATHY, B., RUPA KUMAR, K., and MUNOT, A.A. (1991),

Evidence of secular variations in Indian monsoon rainfall–cir-

culation relationships. J. Climate, 4, 927–938.

PATTANAIK, D.R., SATYAN, V. (2000), Effect of cumulus parame-

terization on the Indian summer monsoon simulated by the COLA

general circulation model. J Meteor Soc Japan 78, 701–717.

RAJEEVAN, M., BHATE, J. (2009), A high resolution daily gridded

rainfall dataset (1971–2005) for mesoscale meteorological

studies. Curr. Sci., 96, 558–562.

RAJEEVAN, M., BHATE, J., KALE, J.D., LAL, B. (2006), High reso-

lution daily gridded rainfall data for the Indian region: Analysis

of break and active monsoon spells. Curr. Sci., 91: 296–306.

RAMESH KUMAR, M.R., and SCHLUESSEL, P. (1998) Air-sea interac-

tion over the Indian Ocean during two contrasting monsoon

years 1987 and 1988 studied with satellite data. Theor. Appl.

Climatol., 60, 219–231.

RAMESH KUMAR, M.R., ANU K. BABU, and CHRIS REASON (2009), On

the role of convective systems over the northwest Pacific and

monsoon activity over the Indian subcontinent. Meteorol. Appl.,

DOI: 10.1002/met.131.

RAMESH KUMAR, M.R., SATHYENDRANATH, S., VISWAMBHARAN, N.K.,

GANGADHARA RAO, L.V. (1986), Sea surface temperature vari-

ability over the north Indian Ocean - A Study of two contrasting

monsoon seasons. Proceedings of the Indian Acdemy of Sci-

ences, Earth and Planetray Science, 95, 435–446.

RAMESH KUMAR, M.R., SHENOI, S.S.C., and SCHULZ, J. (2005),

Impact of convection over equatorial trough and on the summer

monsoon activity over India. Int. J. Remote Sens., 26,

4747–4762.

RAO, K.G., GOSWAMI, B.N. (1988), Interannual variations of SST

over the Arabian Sea and the Indian Monsoon: A new perspec-

tive. Mon. Wea. Rev., 116, 558–568.

RASMUSSEN, E.M., and CARPENTER, T.H. (1983), The relationship

between eastern equatorial Pacific SST and rainfall over India

and Sri Lanka. Mon Wea. Rev., 111 517–528.

REYNOLDS, R.W., SMITH, T.M., LIU, C., CHELTON, D.B., CASEY, K.S.,

and SCHLAX, M.G. (2007), Daily high-resolution blended analy-

ses for sea surface temperature. J. Climate, 20, 5473–5496.

SAJI, N.H., GOSWAMI, B.N., VINAYACHANDRAN, P., and YAMAGATA, T.

(1999), A dipole mode in the tropical Indian Ocean, Nature, 401,

360–363.

Indian Summer Monsoon Rainfall Characteristics

SHEPARD, D. (1968), A two-dimensional interpolation function for

irregularly- spaced data, in Proceedings of the 1968 23rd ACM

National Conference, pp. 517– 524, Assoc. Comput. Mach., New

York.

SHUKLA, J. (1987), Interannual variability of monsoon, in Mon-

soons, edited by J. S. Fein and P. L. Stephens, pp. 399–464,Wiley

and Sons, New York, 1987.

SIKKA, D.R. (1980), Some aspects of large-scale fluctuations of

summer monsoon rainfall over India in relation to fluctuations in

the planetary and regional scale circulation parameters. Proc

Ind Acad Sci (Earth Planet Sci), 89, 179–195.

VINAY KUMAR, KRISHNAN R. (2005), On the association between the

Indian summer monsoon and the tropical cyclone activity over

the Northwest Pacific. Current Science 88, 602–612.

WEBSTER, P.J. et al. (1998) Monsoons: Processes, predictability,

and the prospects for prediction. J. Geophys. Res., 103, 14,451 –

14,510.

WEBSTER, P.J., TOMA, V.E., KIM, H.-M. (2011) Were the 2010

Pakistan floods predictable? Geophysical Research Letters 38,

L04806, doi:10.1029/2010GL046346.

YU, R., WANG, B., and ZHOU, T. (2004), Tropospheric cooling and

summer monsoon weakening trend over East Asia, Geophys. Res.

Lett., 31, L22212, doi:10.1029/2004GL021270.

(Received November 15, 2012, revised May 14, 2013, accepted June 12, 2013)

H. Varikoden et al. Pure Appl. Geophys.