Teleconnection of Tropical Pacific and Indian Ocean Oscillation with Monsoon Rainfall Variability over Nepal 8/8/20141 Lochan P. Devkota & Ujjwal Tiwari

What is the status of monsoon 2014? 8/8/20142

3 What DHM records?

Weak monsoon in 2014 is due to El Nino Weak monsoon in 2014 is due to El Nino El Niño is the collapse of the Walker Circulation A temporary circulation known as El Niño-Southern Oscillation (ENSO) is replacing it 8/8/20144 SST in El Niño (left) and La Niña (right) phenomenon

Monsoon is influenced by large scale circulations: Hadley Circulation 8/8/20145 Walker circulation

Indian Ocean Dipole (IOD) Difference in SST between western Arabian Sea and eastern Indian Ocean (south of Indonesia) Positive IOD (PIOD): Cold SST anomaly over eastern Indian Ocean Negative IOD (NIOD): Opposite anomalous feature over same region 8/8/20146 PIOD (left) and NIOD (right):

Study Area Study area map 8/8/20147

Data used SST, wind, mslp, specific humidity taken from ERA interim reanalysis dataset produced by ECMWF Out going long-wave radiation (OLR) data obtained from NOAA All-Nepal summer monsoon rainfall (ANSMR) data was derived from APHRODITE 8/8/20148

Spatial and temporal variation of ANSMR Large spatial and temporal variation Northwestern part receive least rainfall Several high rainfall pockets Spatial variation of ANSMR (JA) averaged over the period /8/20149 Interannual variability of summer monsoon (JA) rainfall over Nepal

Spatial and temporal variation of ANSMR ANSMR shows 9-11 years oscillatory characteristics Shrestha et al. (2000) observed significant peaks at an interval of 2.5 and 11 years Mann Kendall trend test did not reveal any trend in ANSMR for the period Below normal rainfall for coincides with prolonged El Niño and 1991 Mount Pinatubo eruption Above normal rainfall for the period coincides with elongated La Niña 8/8/201410

Data Analysis Intensity of El Niño/La Niña measured by Nino 3.4 index Intensity of IOD measured by dipole mode index (DMI) Strength of Walker circulation measured by low level wind at 850hPa averaged over equatorial Pacific (10 0 S-10 0 N, E W) Hadley circulation index was defined as the maximum absolute value of zonal mean meridional mass stream function in the 0 0 to 30 0 N latitude zone Nino 3.4 and walker circulation index Dipole mode index 8/8/201411

Linkage among large scale atmospheric circulations and ANSMR Negative association between Walker and Hadley circulations (r= , p<0.01) Bjerkines (1969) also found an inverse relationship between these two circulations ANSMR anomaly with Walker circulation index and Hadley circulation index. ANSMR is plotted on secondary axis 8/8/201412

El Niño, IOD and ANSMR Nino 3.4 exhibit large inter-annual variability Pacific SST anomaly averaged over Nino3.4 region 13 ANSMR negatively correlated (r=-0.59, p<0.01) with ENSO

El Niño, IOD and ANSMR Rainfall anomaly during El Niño years Rainfall anomaly during La Niña years 8/8/201414

El Niño, IOD and ANSMR Less cloud during El Niño and more cloud cover in La Niña OLR anomaly during El Niño years OLR anomaly during El Niña years 8/8/201415

El Niño, IOD and ANSMR Rainfall anomaly for the year in which El Niño and PIOD co-occurred Rainfall anomaly for the year in which El Niño occurred alone Rainfall anomaly for the year in which La Niña occurred alone Rainfall anomaly for the year in which La Niña and NIOD co-occurred 8/8/201416

El Niño, IOD and ANSMR IOD phenomenon countered the effect of El Niño for ANSMR 8/8/201417

Moisture budget Moisture flux divergence in highest/least rainfall years Moisture flux divergence (10 -5 Kgm -2 S -1 ) due to anomalous wind and average humidity in the highest rainfall years. Moisture flux divergence (10 -5 Kgm -2 S -1 ) due to anomalous wind and average humidity in the least rainfall years 8/8/201418

Analysis of moisture budget Moisture flux divergence in El Niño/La Niña years Figure 3.26: Moisture flux divergence (10 -5 Kgm -2 S -1 ) due to anomalous wind and average humidity in El Niño years Figure 3.27: Moisture flux divergence (10 -5 Kgm -2 S -1 ) due to anomalous wind and average humidity in La Niña years. 8/8/201419

Conclusion Large spatial and temporal variations of ANSMR 9-11 years oscillatory characteristics No trend as per Mann Kendall trend test Negatively correlated with Nino 3.4 index IOD countered the effect of ENSO Driven by the interplay between Walker and Hadley circulations Moisture divergence flux revealed dipole characteristics between western and eastern Indian ocean Convergence around Arabian Sea and western part of Bangladesh in highest ANSMR months Convergence around eastern coast of India in least ANSMR months Similar trend observed during La Nina and El Nino years 8/8/201420

Thank you!!!!!! 8/8/201421