A Climatology of the Extratropical Transition of Tropical Cyclones in the Western North Pacific

Transcription

1 A Climatology of the Extratropical Transition of Tropical Cyclones in the Western North Pacific Naoko KITABATAKE (Meteorological Research Institute / Japan Meteorological Agency) 1

2 Outline 1. Topic 1: Three landfalling TCs in Japan in Topic 2: Economical loss due to TCs in Japan 3. Data used for climatological study on ET: JRA-25 reanalysis year climatology of ET in the western North Pacific and TCs landfalling Japan 2

3 Three landfalling TCs in 2011: (1) TY Ma-on TY Ma-on 00z20Jul hPa wind(m/s) Typhoon Ma-on rapidly weakened and was steered by a large-scale NW-ly flow after the landfall on July 20 JMA designated that it completed ET on July 25

4 Three landfalling TCs in 2011 (2): STS Talas 00z01Sep hPa wind(m/s) Severe Tropical Storm (weaker than TY) Talas consisted of a loosely organized ring of clouds and a very large eye It moved northward very slowly, and brought an extreme amount of rainfall in Japan on the right side of its track It weakened after the landfall in Japan

5 Three landfalling TCs in 2011: (3) TY Roke 00z20Sep hPa wind(m/s) TY Roke rapidly intensified in the south of Japan, rapidly moved NE-ward, and underwent ET PRE-like systems along the Japan Islands increased the total amount of precipitation on the left side of the track

6 CPS of three landfalling TCs in 2011 (Data: JRA-25) TY Ma-on Cold-core dissipater? STS Talas Slowly undergoing ET TY Roke Rapidly completing ET 6

7 Conceptual model of ET (JMA 1990) JMA defined the cold-core dissipater as a type of ET In this study, we call it a non-frontal ET

8 Ten largest claims paid by insurance companies for TCs, windstorms, and heavy rainfalls in Japan (billions of JPY 12.5 million USD) Earthquake and tsunami on 11 March 2011: 1,208.1 Name of disaster Date Total claims paid 1 TY Mireille (1991) Sep TY Songda (2004) 4-8 Sep TY Bart (1999) Sep TY Vicki (1998) 22 Sep TY Tokage (2004) 20 Oct TY Shanshan (2006) Sep TY Chaba (2004) Aug Heavy rainfall (PRE induced by TY Saomai?) Sep TY Yancy (1993) 3 Sep TY Roke (2011) (and PREs?) Sep

9 Ten largest claims paid by insurance companies for TCs, windstorms, and heavy rainfalls in Japan (billions of JPY 12.5 million USD) CPS of TCs at the time of Name of disaster Date the landfall Total claims paid 1 TY Mireille (1991) Sep TY Songda (2004) 4-8 Sep TY Bart (1999) Sep TY Vicki (1998) 22 Sep TY Tokage (2004) 20 Oct TY Shanshan (2006) Sep TY Chaba (2004) Aug Heavy rainfall (PRE induced by TY Saomai?) 1. Mireille 9. Yancy 4. Vicki Sep Bart 6. Shanshan 9 TY Yancy (1993) 3 Sep TY Roke (2011) (and PREs?) Sep Tokage 10. Roke 2. Songda 7. Chaba 9

10 Average frequency of TC landfall in Japan ( ) J F M A M J J A S O N D Although TCs make landfall in Japan most frequently in August, damage is significant in September. The structure of the landfalling TC in Japan, which often undergoes ET, differs from case to case.

11 What we want to know Climatological characteristics of ET (including the non-frontal ET) of TCs landfalling in Japan TCs in the western North Pacific 11

12 Purpose of this study To clarify the climatological characteristics of ET in the western North Pacific Using an objective analysis dataset JRA-25 (Onogi et al. 2007) Using an objective definition of ET CPS (Hart 2003; Evans and Hart 2003) 12

13 Data for objective analysis Japanese 25-year Reanalysis dataset (JRA-25) from 1979 through 2004 (26 years) at 6-hour intervals and 1.25 x 1.25 horizontal resolution (Onogi et al. 2007) A bogus vortex is implemented for each TC 925 hpa surface in place of 900 hpa 687 storms (> 34 kts) in the JMA best track data during in the western North Pacific basin (Eq 60N, 100E-180E) 13

14 Bogus employed in JRA-25 Wind profile data are inserted at the cyclone center and at 2- degree away from the center in the 4 cardinal directions from 1000 hpa to 400 hpa levels TC motion (blue) An estimated large-scale environmental flow based on the storm motion is added to the axisymmetric wind field to represent an asymmetric storm structure These data are assimilated together win various observational data Symmetric wind component (red) retrieved asymmetric wind component (purple) Radius of ~200 km for the bogus implementation Radius of 500 km for calculation of the CPS parameters 14

15 TC structures in JRA-25 Composite of 266 TCs at the time of the last bogus implementation Although the bogus implementation is terminated at the time of the ET completion, the resultant discontinuity seems to be negligible in the composite analysis TC motion 6 hours after the time of the last bogus The warm core structure becomes indistinct in the strong vertical shear environment 15 Kitabatake (2010 SOLA)

16 CPS parameters of composited TCs With bogus Without bogus T=0 : termination of bogus implementation Discontinuity due to the bogus removal seems to be negligible

17 JRA-25 reanalysis dataset Although a bogus vortex is implemented for each TC, its impact is negligible in climatological studies.

18 TCs in the western North Pacific in the best track data TCs in 2001 Positions of ET completion defined in the best track data (closed circle) and that is defined by the CPS parameter(-vtl<0) (open circle) Tracks of tropical cyclones (solid) and extratropical cyclones (dashed) defined in the best track data 18

19 Difference of the time when a TC is identified as completing ET (-VTL<0)from the time of the ET completion defined in the best track data Negative time difference means that the ET timing defined by the CPS parameter is earlier than that defined in the best track data 19

20 Frequency of TCs (white) and ETs (black) in the western North Pacific in 26 years ( ) Annual frequency Monthly frequency ET is defined by -VTL<0 Including TCs that completes ET after they were downgraded to be TDs (<34kt) In 26 years, 274 (40%) out of 687 TCs completed ET The ET probability fluctuates between 17% (in 1983) and 60% (in 1997) Monthly ET probability remarkably decreases in June, July and August 20 (Baiu season and midsummer)

21 TC motion Composite of TCs 48 hrs before the ET completion (T = -48 hr) Radii of outer and inner circles in each panel are 500 km and 200 km, respectively

22 TC motion T=-24 hr Thermal asymmetry increases

23 TC motion T=0 hr (at the time of ET completion) The TC loses the warm core

24 TC motion T=+24 hr The TC moves into a cooler airmass

25 Composite of non-frontal ET storms (B<10 at T=0 hr) JMA (1990)

26 Frequency of non-frontal ET events Non-frontal ET (white bar) / all ET (black bar) Non-frontal ET events may occur in any month in a TC season, but is less frequent in Sep and Oct when the background baroclinicity is relatively strong

27 Latitude and central pressure of TCs at the time of ET completion ( ) Average 35.4N Average 987hPa TCs that underwent the non-frontal ET ( ) are relatively weak Although the mean latitude of ET events in the Baiu season (June- July) was almost equal to that in October, the storm intensity are remarkably different between these seasons, suggesting some difference between their background 27

28 Background environment: Monthly-mean SST and Eady growth rate ( ) June Black line: Eady growth rate(hoskins and Valdes 1990) f du σ = 0.31 N dz In August, many TCs complete ET after they weaken over a cool sea surface In October, some TCs may start baroclinic development (reintensification) over a warm sea surface, which may result in intense ET storms in October August October 28

29 81 landfalling TCs in Japan in 26 years ( ) Most landfalling TCs in midsummer ( ) had the structure typical of the tropical cyclone Most landfalling TCs in autumn (from mid-sep through Nov; ) had the structure of a TC undergoing ET (, and they sometimes coused great damage to Japan) 29

30 Conclusion ET in the western North Pacific basin: 40 % of all TCs completed ET TC generation occurs most frequently in August, whereas ET occurs most frequently in September Latitude and intensity of the TCs at the time of the ET completion vary with season About 16% of all TCs that completed ET were transformed into a cold-core structure before they were transformed into a thermally-asymmetric structure Landfalling TCs in Japan: A considerable number of them (particularly in autumn) have the structure of thermally asymmetric structure undergoing ET 30

31 31

32 Tracks of TCs in the western North Pacific in 2001 (JMA best track data) Solid: tropical cyclone Dashed: extratropical cyclone :ET completion defined in the best track data Most TCs moving near Japan is undergoing ET, but its timing in the best track data is subjectively defined 32

33 Difference of the time when a TC is identified as completing ET (-VTL<0)from the time when a TC bogus is removed (T diff ) Negative T diff means that parameter VTL becomes negative before the termination of bogus implementation (127 TCs, 48%)

34 Composite of TCs relative to the time of ET completion (-VTL<0) By definition, -VTL > 0 at T = -6 hr, and VTL<0 at T=0 hr -VTL may increase after T > 6 hr (reintensification after ET) Mean transition period of ET is estimated to be about 18 hrs Some TCs may have thermally-symmetric (non-frontal) structure (B<10) at T = 0 hr

35 Frequency distribution of the transition period from the beginning (B>10) through the completion (-VTL<0) of ET 39 TCs (14.5%) out of 268, of which B<10 at the time of ET completion (-VTL<0), have negative transition period. They are defined as nonfrontal ET in this study.

36 An example of the non-frontal ET: TY Meranti in August 2004 SST Bogus implementation was terminated at 0600 UTC 8 Aug ET completion defined by CPS was 78 hours later than that of the best track data

37 T=0 hr (at the time of ET completion) Composite of non-frontal ET storms (B<10 at T=0) Composite of all ET storms

38 T= +24 hr Composite of non-frontal ET storms Composite of all ET storms

39 A landfalling TC that had structure typical of the mature TC: TY Songda in 2004 (the 2 nd largest claim paid) Bogus was implemented through 1800 UTC 07 Sep Although Songda had a structure typical of a mature TC at the time of landfall, damage was also caused during the period when it underwent ET

40 Another example: Super Typhoon Tip in 1979 Bogus was implemented through 1200 UTC 18 Oct Although the bogus was not implemented on 19 Oct, the warm core structure was analyzed based on the upper-air observation data ET completion defined by CPS parameter was 30 hours later than that defined in the best track data