Southeast Asia summer monsoon and rainfall seasons over climatic zones of

Vietnam

Southeast Asia summer monsoon and rainfall seasons over climatic zones of

Vietnam

Presented by Nguyen Thi Hien Thuan

Melbourne, 9-14 Dec 2012

INSTITUTE OF METEOROLOGY AND HYDROLOGY AND ENVIRONMENT (IMHEN)

OutlineOutline

1. Overview on summer monsoon (focusing on Vietnam region)

2. Relationship between summer monsoon and rainfall seasons of Vietnam

3. Summer monsoon and ENSO

4. Remarks

Pham and Phan before 1990s, showed the basic feature of two distinct monsoon subsystems of the Asian monsoon: the south Asian monsoon and the east Asian monsoon

Nguyen and Nguyen (2004) analyzed the influence of Asia monsoon on climate

Nguyen and Thuan, 2007: define a new monsoon circulation index for studies of interannual variability of South Vietnam summer monsoon

Pham et al., 2010 focused on predictability of monsoon onset based on relationship of rainfall and monsoon indices

Overview on summer monsoon Overview on summer monsoon

The summer monsoon brings major amount of rainfall to south of Vietnam:- Major source of rainfall: wet season

brings ~90% of total annual

- The summer monsoon – Southwest monsoon season: May-Sep, traditional summer/rainy season: May-Oct (May-Nov)

- Critical issues: the onset of the rainy season/ dry spells

Overview on summer monsoon Overview on summer monsoon

Overview on summer monsoon Overview on summer monsoon

* Traditionally: rainfall characteristics: rainfall amount (monthly, seasonal, yearly) or their anomalies – rainfall variation

* But: rainfall data: influenced by local conditions, other factors, not always reliable

* Worldwide and in the region: various monsoon indices – objective – representative of a large scale circulations of the monsoon (circulation index – dymamic index, convection index, …

Mean summer monsoon onset date based on rainfall(Wang and Linho, 2001)

Overview on summer monsoon Overview on summer monsoon

Summer monsoon onset and withdraw date over Vietnam change region to region

(Lanh.N.V et. al., 2007)

20

50

46

72

monsoon onset pentad monsoon withdrawal pentad

Overview on summer monsoon Overview on summer monsoon

Summer monsoon onset date over Vietnam change year to year over southern Vietnam, (Pham et. al., 2010)

Overview on summer monsoon Overview on summer monsoon

Relationship between summer monsoon and rainfall seasons

Rainfall seasons of 7-sub climatic regionRainfall seasons of 7-sub climatic region

Double-peaks

Corr. coefficient between monthly rainfall with..Corr. coefficient between monthly rainfall with..

Monsoon index: U850 (2.5N-12.5N, 95E-110E)-(20.0N-27.5N, 105E-120E), V-IX. Nguyen and Thuan (2006)

Corr. coefficient between monthly rainfall with..Corr. coefficient between monthly rainfall with..

SCSSM index

over east seaCI index

Over south of VN

Lien.T.V (2010)

Relationship between summer monsoon and ENSO

• Rainfall data: Two data sets: • The Climate Prediction Center (CPC) Merged Analysis

of Precipitation (CMAP) data. • Pentad and monthly CMAP rainfall averaged over 8o –

15oN, 104o – 110oE, for Jan 1979 - Dec 2006, on 2.5o x 2.5o.

• Station rainfall data over South Vietnam

0

2

4

6

8

10

12

14

1 11 21 31 41 51 61 71Pentad

Ra

infa

ll, m

m/d

ay

R_Obs CMAP

* Circulation index: CI

Summer monsoon index for SVN

Summer monsoon index for SVN

Map of correlation coefficients of U850 hPa & seasonal CMAP SVN (8o-15oN, 104o-110oE).

The areas with the highest correl. coeff. are selected

CI = U850 (2.5-12.5oN, 95-115oE and 20.0 - 27.5oN, 105- 120oE)

RCMAP&U850 (V-IX)

Anomalies of Circulation index over SVN

Anomalies of Circulation index over SVN

Summers 1961-2004Light yellow color: Non_ENSO, red: El Nino, blue:

La Nina,

Circulation index anomalies

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

1961 1966 1971 1976 1981 1986 1991 1996 2001

Ano

mal

ies (

m/s

)

Average CI anomaliesAverage CI anomalies

EL Nino developing

(E0)

EL Nino decaying

(E1)

La Nina developing

(L0)

La Nina decaying

(L1)

Non-ENSO (Non)

(1) (2) (3) (4) (5) (6)

Ave 0.11 -2.03 -0.59 0.17 0.64

Min -1.2 -3.2 -2.5 -0.8 -1.5

Max 1.3 0 0.8 1.4 2.1

Ave El Nino : - 0.55(m/s) La Nina: - 0.16 (m/s)Non-ENSO

0.64

RemarksRemarks- The influence of ENSO on monsoon

circulations- Different impact according to ENSO

development- El Nino summers: weak monsoon. - La Nina summers: strong monsoon. - But: stronger impact in the decaying

summers, especially in El Nino decaying summers (‘83, ‘87, ‘98)

• Monsoon plays a crucial role on Vietnam climate

• Rainfall over southern Vietnam has a close relationship with summer monsoon activities

• There is no universal monsoon index for all seven climatic zones of Vietnam

• Impacts of ENSO on the summer monsoon are different according to ENSO phases: development or decaying: stronger impacts are in ENSO decaying year, especially in El Nino cases.

ConclusionsConclusions

Thank you for your attention!