The Interannual Variability of Tropical Cyclone in the Southern South China Sea.

1
The Interannual Variability of Tropical Cyclone
in the Southern South China Sea.

• Zabani Md. Zuki.
• NATR410 Seminar.

2
Motivation

• Personal observation of Tropical Cyclone over
  South China Sea.
• Consequences from Tropical Cyclone.
• One of the most devasting natural disaster
  (strong wind, storm surge, and flood).

3
Motivation

• Two direct hit from Tropical Cyclone.
• Tropical Storm Greg, 25 Dec. 1996.
• - 238 death and USD 52 million in economy lost.
• Typhoon Vamei, 27 Dec. 2001.
• - develop 1.5 degrees North.
• - 8 death.

4
Outline

• About Tropical Cyclone.
• Data Set.
• Methodology.
• Results.
• Discussion and Conclusion.
• Future Work

5
Tropical Cyclone (TC).

• Definition.
• Deep, convective weather system that develop over
  warm tropical ocean.
• Favorable Environment for TC Development.
• Six environmental factors favorable for TC
  genesis
• High Sea Surface Temperature (SST) gt 26.5 oC and
  deep thermocline.
• Above average moisture in the lower and middle
  troposphere (700-500 hPa).

6
Tropical Cyclone (TC).

• Favorable Environment for TC (continued).
• Convective instability through deep atmosphere.
• Weak vertical shear.
• Large low level vorticity (850 hPa).
• Effect of Coriolis force (at least 5 6 degrees
  poleward of equator).

• Others factor
• Location of the equatorial or monsoon trough.

7
Tropical Cyclone (TC).

• Main Area of TC Activity.
• Tropical Ocean,
• Western North Pacific ocean.
• Eastern Pacific ocean.
• Western Atlantic ocean.
• North Indian Ocean.
• South Indian Ocean.
• South Pacific Ocean.
• Southern South China Sea is part of Western North
  Pacific Ocean

8
Tropical Cyclone (TC).

• Variability.
• 80 90 TC occur annually.
• Seasonal phenomena with active period late summer
  to early autumn.
• Western North Pacific is most active.
• - One third of TC develop in this area.
• - Only region where TC develop in all months.
• - TC very active from July to October.

9
Tropical Cyclone (TC).

• Other factors can cause of TC Variability.
• Large Scale Atmospheric General Circulation
• El-Nino Southern Oscillation (ENSO).
• Quasi-Biennial Oscillation (QBO).
• Madden-Julian Oscillation (MJO).
• North Pacific Oscillation (NPO).

10
Large Scale Atmospheric General Circulation.

• ENSO.
• 3 7 years oscillation.
• El-Nino years warm SST anomalies in Pacific.
• La-Nina years cold SST anomalies in Pacific.
• Alter the ascending and descending branch of
  Walker circulation over equatorial and tropical
  Pacific.

11
Large Scale Atmospheric General Circulation.

• MJO.
• 30 60 days oscillation.
• Significantly effect the atmosphere circulation
  over Tropic.
• Characterized by an eastward propagation of large
  region of descending and uprising air.
• Mainly over Indian Ocean and Pacific Ocean.

12
Large Scale Atmospheric General Circulation.

• NPO.
• 50 70 years oscillation.
• NPO1 relatively cooler western and central
  North Pacific Ocean.
• NPO2 vice versa.
• QBO.
• 24 48 months oscillation.
• Alternating Westerly and Easterly phase at lower
  Stratosphere (100 10 hPa).
• Westerly phase enhance the growth of
  convective cloud.
• Easterly phase vice versa.

13
Data

• TC West North Pacific best track from UNISYS
  website.
• Use data from 1960 USA navy and air force start
  jointly observed and tracking TC over West North
  Pacific on May 1959 by reconnaissance aircraft.
• Sea Surface Temperature (SST) , Sea Level
  Pressure (SLP), and ENSO years from Center for
  Ocean and Atmospheric Prediction Studies (COADS)
  website.

14
Methodology

• Area of study
• - southern South China Sea ( south of 10 degrees
  North and west of 120 degrees East).
• Period of data used
• - 1960 to 2003
• TC category
• Tropical Depression (TD), maximum wind speed
  lt 17 m/s (34 kt).
• Tropical Storm (TS), maximum wind speed
  17 m/s but lt 33m/s (64 kt).
• Typhoon (TY), maximum wind speed 33 m/s.

15
Area of Study
16
Tropical Storm Track (1990)
17
Tropical Storm Track (1996)
18
Methodology

• Count the monthly number of TC.
• Calculate the Monthly Average of SST and SLP.
• Statistical Analysis, Time Series Analysis and
  Fast Fourier Transforms Analysis.

19
Counting the TC
20
Monthly Average
21
ENSO Years
22
Result
Total and Annual Average of TC over Southern SCS
23
Total Number and Percentage of TC occurrence in
Southern SCS by Month

• Total number of TC is 46 compare to 1406 TC in
  West North Pacific.
• contribute only 3 of TC in West North Pacific.
• TC in Southern South China Sea activity more in
  November and December.

24
Result
Bar Graph of Number of TC and Typhoon.
25
Result
Bar Graph of Number of Tropical Storm and
Depression.
26
Result
Times Series of the Number of TC.
Year

• Linear regression analysis, - weak upward trend.

27
Result

• More TCs develop locally in period 1995 2001
• Coincides with increasing TD

28
Result
The Average Annual Occurrence of TC versus ENSO
Year
29
Result
Histogram of Average Annual TC Frequency
Separated by category.
30
Result

• More TC activity during La-Nina year (1.6
  per-year).
• Less TC activity during El-Nino year (0.4
  per-year).
• More TC develop locally during La-Nina (1
  per-year)
• compare to during El-Nino (0.3 per-year) and
• Neutral (0.6 per-year).

31
Result
Time Series of Monthly Mean SLP
Time
32
Result
Fast Fourier Transform Analysis (Unfiltered SLP
Data)
Cycle per decade
Peak shows the annual cycle.
33
Result
Fast Fourier Transform Analysis (Filtered SLP
Data)
Cycle per decade
Second highest amplitude 2 cycle per decade or
1 cycle every 5 years. First highest amplitude
0.25 cycle per decade or 1 cycle every 40 years.
34
Discussion and Conclusion

• TC over southern South China Sea is very few
  compare to the TC over West North Pacific.
• TC most active in November and December compare
  to West North Pacific from July October this
  may be due to equatorward movement of monsoon
  trough.
• Annual variation is not large from zero to
  maximum 4 with annual average 1.

35
Discussion and Conclusion

• The places where TC activity the lowest is likely
  will most influenced by general circulation
  change (Gray, 1984).
• ENSO phenomena influence the TC development over
  southern South China Sea,
• More TC during La-Nina and
• Less TC during El-Nino.

36
Discussion and Conclusion

• Need more study particularly regarding other
  peaks show in Fast Fourier Transforms Analysis
  that may represent other global general
  circulation features.

37
Future Work

• Study other parameters
• Steering wind
• Vorticity
• Monsoon/equatorial trough location.
• Use other methodology like Wavelet Analysis for
  time series analysis.

38
Future Work

• Study the influence of
• Quasi-Biennial Oscillation (QBO)
• Madden Julian Oscillation (MJO)
• North Pacific Oscillation (NPO).

39
Thank You