Characteristics of Sudden Changes in Tropical Cyclone Tracks over North Indian Ocean. M. Mohapatra and B. K. Bandyopadhyay

Transcription

1 Characteristics of Sudden Changes in Tropical Cyclone Tracks over North Indian Ocean M. Mohapatra and B. K. Bandyopadhyay INDIA METEOROLOGICAL DEPARTMENT MAUSAM BHAVAN, LODI ROAD, NEW DELHI

2 PRESENTATION LAYOUT Introduction Data and Methodology Results and Discussion Translation speed and Track Changes Convection and Track Changes Steering wind and Track Change MJO and Track Changes Conclusion

3 Most of the natural hazards are weather related WINTER (JAN FEB) WESTERN DISTURBANCES COLD WAVE, FOG PRE MONSOON (MAR MAY MONSOON (JUN SEP) POST MONSOON (OCT DEC) CYCLONIC DISTURBANCES HEAT WAVE THUNDER STORMS, SQUALLS HAIL STORM TORNADO SOUTHWEST MONSOON CIRCULATION MONSOON DISTURBANCES NORTHEAST MONSOON CYCLONIC DISTURBANCES

4 Climatology of tropical storms and cyclones F. F. Roux, Roux, Average annual number ( ) of tropical storms/cyclones over each ocean basin (average around the globe : 84 TS / 44 TC) and average track of the disturbances

5 Climatological Characteristics Out of 80 forming over the globe, five form over north Indian Ocean Ratio of TCs between Bay of Bengal and Arabian Sea 4:1 Year to year variation Quite large. Minimum No. of cyclones in a year One (1949), Maximum No.of cyclones in a year Ten (1893,1926,1930,1976)

6 Frequency of Cyclonic disturbances over north Indian Ocean during JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC Depression Cyclonic Storms Severe cyclonic storms 68% of disturbances over Bay of Bengal have landfall over east coast c 30% of disturbances over Arabian Sea have landfall over west coast

7 TROPICAL CYCLONES over NIO as Disaster YEAR COUNTRIES DEATHS 1970 Bangladesh 500, India 300, China 300, Japan 250, Bangladesh 200, Bangladesh 175, Bangladesh 140, Myanmar 138, India 50, India 50, Bangladesh 40, Antilles(West Indies) 22, Bangladesh 19, India 10, Bangladesh 11, Bangladesh 11, Bangladesh 11, India 10, India 10, Cuba 7,196 NARGIS : An Example of recent devastating cyclone Cyclone not only causes loss of life and property on landfall, it i t also causes disaster in aviation and navigation sectors 1900 USA 6, Bangladesh 5, Japan 5, India 5,000

8 Regional Specialised Meteorological Centre (RSMC) Tropical Cyclone, New Delhi Monitoring and prediction of Cyclones over the North Indian Ocean Issue of Tropical weather outlook/ Cyclone Advisories to the WMO/ESCAP Panel Countries (Bangladesh, Myanmar, Thailand, Srilanka, Maldives, Oman and Pakistan) and Tropical Cyclone Advisories for Aviation as per guidelines of ICAO

9 Monitoring and Forecast Process Broad Classification of Observations Space B ased Geoststionary Satellites Polar Orbiting Satellites U pper Air Pilot Balloon R SR W Profiler Ground B ased RAD AR A ircraft Initial conditions (Observations) Surface A WS A RG SYN OP B UOYS A VIATION SHIPS Action Runs of different Models, Consecutive runs from the same model, Ensemble runs ("choosing the best member") Model Model runs Numerical Numerical forecasts forecasts Forecaster End forecast Decision maker Monitoring and Forecast Process of Tropical Cyclone

10 TC track forecasting methods i) Statistical Techniques ii) iii) i) Analogue ii) iii) Persistence Climatology iv) CLIPER, v) Chaos theory and Generic Algorithm method) Synoptic Techniques Empirical Techniques Satellite Techniques Techniques iv) Radar Techniques v) NWP Models Individual models (Global and regional) IMDGFS (382, 574), NCMRWF (254), ARP (MeteoFrance, ECMWF, JMA, UKMO, NCEP, WRF (IMD, IITD, IAF), HWRF (IMD), QLM MME (IMD) and MME based on Tropical Cyclone Module (TCM) EPS (Strike probability, Location specific probability vi) Operational (Consensus) forecast

11 TC intensity forecasting methods i) Statistical Techniques ii) iii) i) Analogue ii) iii) Persistence Climatology iv) CLIPER, Synoptic Techniques Empirical Techniques (as discussed in case of genesis) Satellite Techniques Techniques iv) Radar Techniques v) NWP Models Individual models (Global and regional) IMDGFS (382, 574), NCMRWF (254), ARP (MeteoFrance, ECMWF, JMA, UKMO, NCEP, WRF (IMD, IITD, IAF), HWRF (IMD), QLM Wind probability (To be developed) and risk Threat graphics (To be developed) vi) Dynamical Statistical Model (SCIP) Operational (Consensus) forecast

12 Track forecast error (km) Average ( ) 24 hr 130 km, 48 hr 262 km 72 hr 386 km Skill compared to CLIPER model Year Track forecast skill (%) (b) Track forecast skill (%) Year 24 hr 27%, 48 hr 39% 72 hr 50% North Atlantic(NHC) 24hr 95km, 48hr 150 km 72hr 250 km NW Pacific(JMA) 24hr 113km, 48hr 208 km 72hr 310 km

13 Average direct position error (km) (a) Lead time of forecast (Hrs) Average skill (%) of track forecast Comparison of forecast error and skill of climatological/ straight moving and recurving TCs over NIO Lead time of forecast (Hrs)

14 Comparison of Cone of Uncertainty for climatological/ straight moving and recurving TCs

15 Percentage of forecasts within and outside the cone of uncertainty (COU) (a) Climatological/straigh t moving TCs (b) Recurving/looping TCs Lead period(hr) of forecast

16 Data and Methodology The sudden change in track may occur due to sudden change in direction of movement leading to recurvature of the TC, sudden increase in speed of movement and sudden decrease in speed in movement leading to quasistationarity of the TC. While sudden increase/decrease in speed of movement, especially near the coast caused not only the forecast difficult, but also put the TC disaster management into disarray. So all the three types of sudden changes in track, as mentioned above have, been considered in this study for detailed analysis.

17 Data and Method For the purpose of analysis, the classification of the intense lowpressure systems as adopted by India Meteorological department(imd)/ Regional Specialised Meteorol,ogical Centre (RSMC), New Delhi (IMD, 2003) has been considered Low pressure system Maximum sustained winds Low < 17 knots < 31 kmph Depression kts kmph Deep Depression kts kmph Cyclone kts kmph Severe Cyclone kts kmph Very Severe Cyclone kts kmph Super Cyclone 120 kts & above 222 kmph & above

18 SN Year Life period Maximum intensity Basin of formation Season of formation Type of track of TC May VSCS BOB PM SCD L Nov. SCS AS PS RM D May SCS AS PM RM D May SCS BOB PM SCD L Sept. CS BOB Monsoon SM/RM L Nov. 2 Dec. CS BOB PS SM D Dec. CS BOB PS RM L April VSCS BOB PM RM L May CS BOB PM RM L Nov. VSCS BOB PS RM/SCD L April 3 May VSCS BOB PM SCD L Oct. CS BOB PS RM L Nov. CS BOB PS SM L May SCS BOB PM RM L Dec. CS BOB PS SM/SCD L May SCS BOB PM SM/SCS L May CS AS PM SM D May 7 June VSCS AS PM SCD L Oct 4 Nov CS AS PS SM/SCD L Dec VSCS BOB PS SCD L Landfalling/ dissipating TC CS : Cyclonic storm, SCS : Severe cyclonic storm, VSCS : Very severe cyclonic storm, BOB : Bay of Bengal, AS : Arabian Sea RM : Rapid movement, SM : Slow movement, SCD : Sudden change in direction L : Landfalling, D : Dissipating over sea, PM : Pre monsoon, PS : Post monsoon

19 Data and Methodology 1. Six hourly best track data of cyclones over north Indian Ocean since 1990 in digital form hourly data in cyclone Atlas during (Web E Atlas) E Data from are also available in hard copies in 1979 edition of cyclone Atlas

20 Sudden change in direction of movement Out of 33 TCs developed during , 8 TCs had sudden change in direction of movement It consists of two over the AS and six over the BOB. The analysis indicates that both the sudden changes in tracks over the AS occurred when the TC lay to the north of 15 0 N. On the other hand, there are cases of such changes occurring in the BOB to the south of 13 0 N (2 out of 6) While there has been a single case of looping track (over AS), most of the sudden changes in direction have occurred towards right of the previous direction of movement (6 out of 8, 75%). Considering the season of occurrence of such tracks, It has occurred more frequently during pre monsoon (March May) season (5) than in postmonsoon (October December) season (3)

21 Sudden change in direction of movement Recurvature towards right may be attributed to the fact that the TCs over the NIO, while move towards more northerly latitude may recurve towards right under the influence of the deep trough in middle and upper tropospheric westerlies lying to the left of the TC centre. More cases in pre monsoon season may be due to recurvature under influence of trough in westerlies which is predominant in pre monsoon season. Another feature which contributed to the sudden change in direction of movement towards right is the middle/ upper tropospheric steering ridge/ anti cyclonic circulation lying to the east of the TC centre

22 Translation speed and sudden change in direction of TCs

23 Translation speed and sudden change in direction of TCs

24 Translation speed and sudden change in direction of TCs

25 Translation speed and sudden change in direction of TCs

26 Translation speed and sudden change in direction of TCs To summarise, the translation speed gradually decreases for about 24 hrs period pror to change in direction of movement. Minimum translation speed becomes about 10 kmph in most of the cases This is true for both cases of increase in northerly and southerly components during the change

27 Impact of MJO on sudden change in track : The track is less sensitive than the genesis and intensity of the cyclonic disturbances over the north Indian Ocean Favourable phases for genesis and intensification are 3, 4 and 5 Genesis of Thane occurred when MJO index was in Phase 4(25 Dec,2011) MJO index then gradually moved with amplitude > 1 through phase 5 to phase 6 Though there was northward movement till 27 th, Thane moved west southwestwards during Dec 2011

28 Impact of MJO on sudden change in track : The track is less sensitive than the genesis and intensity of the cyclonic disturbances over the north Indian Ocean as seen in case of NILAM also (28 31 Oct, 2012) Change in direction took place on 29 th and 30 th with more northnorthwestward movement. there was no significant change in location of MJO index. It continued to be in phase 2, though it slightly moved eastwards on 29 th and 30 th.

29 Impact of Convection sudden change in track : 27 Dec 2011/0500UTC 12.2N/87.0E 27 Dec 2011/1000UTC 12.2N/86.6E Area of intense convection changed from morthern sector to soutwest sectior on 27th 28 Dec 2011/0300UTC 12.N/85.5E 28 Dec 2011/1000UTC 12.N/84.0E

30 Impact of Convection sudden change in track 28 Dec 2011/1700UTC 12.1N/84.0E 29 Dec 2011/0300UTC 11.9N/82.3E 28 Dec 2011/1400UTC 12.0N/84.0E 29 Dec 2011/0500UTC 11.8N/82.1E Area of intense convection consolidated around system centre gradually on 29th

31 Impact of convection on sudden change in track Southward shifting of area of intense convection is also seen in DWR imageries

32 Impact of convection on sudden change in track : Area of intense convection again shifted to north at the time of landfall

33 Impact of steering ridge, vorticity and large scale circulation on sudden change in track Example : Very Severe Cyclonic storm Thane

34 Impact of steering ridge, vorticity and large scale circulation on sudden change in track

35 Impact of steering ridge, vorticity and large scale circulation on sudden change in track

36 Impact of steering ridge, vorticity and large scale circulation on sudden change in track

37 Impact of steering ridge, vorticity and large scale circulation on sudden change in track

38 Impact of steering ridge, vorticity and large scale circulation on sudden change in track Example : Cyclonic storm NILAM (28 Oct 01 Nov, 2012) Anti cyclone located to northeast of system Ridge extended southward on 26th

39 Impact of steering ridge, vorticity and large scale circulation on sudden change in track Anti cyclone located to northeast of system Ridge extended southward on 27th

40 Impact of steering ridge, vorticity and large scale circulation Anti cyclone is less marked Extension of ridge to south reduced

41 Impact of steering ridge, vorticity and large scale circulation

42 Track Forecast verification of Cyclonic Storm, NILAM The track of cyclone Thane (28 31 Oct 2012) with rapid change in direction followed the principle of interaction between the TC, convection and anticyclonic circulation Using this principle, the change in track could be predicted well l in advance Considering the NWP models, the track could be better predicted by ECMWF model Track Forecast Error, NILAM Lead Period (hr) Error (km)

43 Track Forecast verification of Very severe Cyclonic Storm, THANE The track of cyclone Thane (25 31 Dec 2011) with rapid change in direction followed the principle of interaction between the TC, convection and anticyclonic circulation Using this principle, the change in track could be predicted well l in advance Considering the NWP models, the track could be better predicted by ECMWF model

44 An examples of landfalling Cyclones Very severe cyclonic storm Thane (25 31 Dec. 2011) Landfall of Thane occurred near Cuddalore on 30 th December 2011(morning) Landfall error : 24 hrs : 20 km, 48 hrs : 160 km, 72 hrs : 140 km k Death toll was only 46 due to improved early warning alongwith preparedness and management Forecast on 26 th Dec Morning (four days prior to landfall) Observed Track

45 Rapid movement near coast There were 9 out of 33 TCs developed during , which moved rapidly while approaching the coast. It consists of two over the AS and seven over the BOB. The analysis indicates that rapid movement took place mostly with the straight movers or with minimal recurvature.. Such TCs are also higher over the BOB (7) than over the AS (2). The rapid movement could take place in all latitudes. There is also no seasonal bias in the occurrence of rapidly moving TCs as almost equal number of such TCs occurred in both pre monsoon and postmonsoon seasons. Rapid movement in case of northeastward recurving system is mainly under influence of the trough in middle and upper tropospheric westerlies,reason for rapid movement in case of westward moving TCs needs further investigation.

46 Translation speed and Rapid movement of TCs Translation speed can go upto kmph

47 Slow movement near coast There were seven out of 33 TCs during which showed slow movement near the coast. It includes 2 over AS and 5 over the BOB. It consisted of one looping TC over the AS and three recurving TCs over the BOB. The slow moving TCs mostly occurred to the south of 15 0 N in both BOB and AS unlike the rapidly moving TCs and TC showing sudden change in direction. The role of land surface processes in accelerating and retarding the speed of TC approaching the coast needs investigation.

48 Characteristics of Rapid Intensification over NIO 20 ( ) 100 Frequency (%) Frequency (%) dv 24 (kt) CS SCS VSCS SUCS ALL TCs 35 Frequency (%) April May October November Month

49 Rapid Intensification over NIO ( ) The composite probability of RI determined for the dependent sample. The probabilities are provided as a function of the total number of the eight RI predictor indices that were satisfied. The sample mean probability of RI is also shown for reference. The number of cases is shown in parentheses beside the total number of RI indices satisfied (Kotal et al, 2012) RI cases are embedded in regions with higher Upper level divergence, Lower level relative vorticity and Relative humidity and low vertical wind shear Initial wind speed of RI cases is higher and tends to move with a faster translational speed than the non RI cases. Probability of RI (%) Dependent Sample mean 0(17) 1(58) 2(117) 3(115) 4(96) 5(41) 6(25) 7(11) 8(3) Total number of RI Indices satisfied

50 Summary Translational speed of TC decreases to less than 10 kmph 24 hrs preceding the sudden change in track The interaction between TC, convection and steering ridge mainly determine the sudden change in direction of movement of TC MJO does not seem to be very influential in causing sudden track changes direction of movement of TCs mostly occur at higher latitudes (north of 15 0 N over AS and north of 13 0 N over BOB). Stationarity of TC near the coast needs further investigation Reason for rapid movement in case of westward moving TCs needs further investigation. Also, the role of land surface processes in accelerating and retarding the speed of TC approaching the coast needs investigation.

51 Conclusions Sudden change in direction before landfall and rapid increase in intensity before landfall creates problems for disaster management apart from increasing the forecast error. Currently, forecasters are able to predict rapid intensification based on nowcasting basis (upto 6 hrs) using microwave products to evaluate the trend in upper tropospheric warming, low level wind and burst of convection in association with favourable factors like low vertical wind shear. But is not sufficient for disaster managers Hence there is need to improve the NWP models and dynamical statistical models for RI Comparing existing models, ECMWF model performs better in predicting sudden change in track and intensity. There is need to factor in the interaction of storm scale with mesoscale and convection scale in the NWP models with better data assimilation and increased resolution.

52 Thank you