S. Jothiganesh Ph.D.

Team Leader – Climate Application

Regional Integrated Multihazard Early Warning System

Email: jothiganesh@rimes.int

Overview of Northeast monsoon over South Asian region

SASCOF-15 Winter Session and CSUF

23 September 2019

OCEAN

(Bay of Bengal & Indian Ocean)

Evaporation

Ocean

rainfall

Ocean to land Evaporation,

Transpiration

ATMOSPHERE

Moisture transport

Land

rainfall

LAND (peninsular India)

Subsurface

River runoff

Percolation

Cyclones

Easterly waves

(Singh 1995, Kripalani & kumar 2004, Raj 2012, Yadav 2013, Lekshmy et al. 2015, Xi et al. 2015, Kishatwal et al. 2013)

Dynamics of Northeast Monsoon

Rainfall during OND months – NE Monsoon

Rainfall mm/day (1981-2010)

2 3 4 5 6

Oct Nov Dec

Day

Seasonal NEIMR fluctuations 1982-2015Intra-seasonal NEIMR fluctuations 2007

Rain

fall

in

mm

Chaotic variations - Zooming down to Southeastern peninsular India

Out of 17 El Niño years in 1901-2010, 15

(89%) enhanced Oct-Dec rainfall

Oct

-De

c R

ain

fall

ind

ex

SOI Vs Oct-Dec rainfall

Extreme wet years and ENSO linkages

(mm)

Rainfall anomaly during El

Nino years from climatology

Remembering 2015 SASCOF and Floods in Chennai, Tamil Nadu

Source: thehindu.com

Probability of rainfalloccurrence

Rainfall states• S1(State-1):

Wet conditions • S2 (State-2):

Coastal wet conditions

• S3 (State-3): Dry conditions

S1 S2 S3

Rainfall States characterization using Hidden Markov Model

• State-1 (Wet): Often during 03-

08 Oct. to 11-16 Nov.

• State-3 (Dry): Often during 22-

27 Nov. until the end of the

NEIMR season.

• State-2 (Coastal wet): random

in between the State-1 and the

State-3 throughout season.

Pentads during Oct-Dec

Variability in rainfall States

• State-1 and NEIMR

total are positively

correlated: Increased

occurrences of the

wet state during flood

years.

• State-3 and NEIMR

total are negatively

correlated.

No. of occurrence of rainfall states and seasonal NEIMR

Synoptic patterns of wet rainfall condition (State-1)

Surface air temperature Mean sea level pressure @850 hPa

Moisture convergence @850 hPaVorticity @850hPa

(°C)

(10-5 S-1)

(hPa)

(gkg-1s-1)

Synoptic patterns of dry rainfall condition (State-3)

Surface air temperature Mean sea level pressure @850hPa

Moisture convergence @850hPaVorticity @850hPa

(°C)

(10-5 S-1)

(hPa)

(gkg-1s-1)

Composite differences – VIMF convergence and moisture transport vector (Integrated over 1000-850 hPa)

VIMF convergence (10-3

kg m-2 s-1; shaded) and

moisture transport

vectors (kg m-1s-1)

Same pentad

Moisture Transport processes during wet spells of NE monsoon

Correlation - Sea Surface Temperature and NEIMR

Indian Ocean:

Positive at lag-

2, 3, 4

Bay of Bengal:

Positive at all

time

R-value

Wet conditions and lagged SST and latent heat flux

Correlation - Latent heat flux and NEIMR

Indian Ocean:

Positive at

same, lag-1, 2

Bay of Bengal:

Negative at all

time

R-value

Wet conditions and lagged SST and latent heat flux

Composite differences - Latent heat flux

(Wm-2).

Indian Ocean:

Increased at

lag-1, 2

Bay of Bengal:

Decreased at

all time

Wet conditions and lagged SST and latent heat flux

Thanks