Vol.15 No.1 JOURNAL OF TROPICAL METEOROLOGY June 2009

Article ID: 1006-8775(2009) 01-0049-05 IMPACTS OF TWO TROPICAL CYCLONES EXPERIENCING EXTRATROPICAL TRANSITION DURING NORTHWARD PROGRESSION ON THE RAINFALL OF

1 2 2 1 LIANG Jun (梁军) , CHEN Lian-shou (陈联寿) , LI Ying (李英) , ZHU Jing (朱晶)

(1. Dalian Meteorological Observatory, Dalian 116001 ; 2. Chinese Academy of Meteorological Sciences/LaSW, 100081 China)

Abstract: Both of (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.

Key words: synoptics; typhoon rainstorm; diagnostic analysis; extratropical transition; tropical cyclone; Liaodong Peninsula CLC number: P444 Document code: A doi: 10.3969/j.issn.1006-8775.2009.01.007

1 INTRODUCTION the transformed TC is released so that the TC evolves to an and TC rainstorm is When the tropical cyclone (TC) goes northward to intensified. According to statistical analyses by Li et reach the immediate neighborhood of an area of intense al.[3] and Yuan et al.[4] on northbound TCs, the Yellow baroclinity in the mid-latitudes, the warm and moist air Sea and Bohai Sea are the waters over which TCs to the east of it will be pushed northward to enable the undertake frequent transformations during landfall and establishment of a thermodynamic structure in TC that northbound movement. The severe regional is colder in the west than in the east so as to increase precipitation from 1980 to the present over the the frontal zone inside the system experiencing the ET, Liaodong Peninsula were all caused by the tropical if cold air moved in at this point [1]. The ET process of [2] cyclones of 8109 (international code), Mimie, Polly, the TC can be divided into two stages , the first being Ellie, Winnie and Matsa that experienced ET [5]. What the interactions between the TC and the baroclinic belt is different is that some of the TCs intensified through leading to the alteration of the initial structure and the ET while the others weakened and dissipated after ET. second being a reinforcing stage (second stage) in The ET happening in TCs are closely correlated with which the transformed storm is deepened into a the activity of cold air [6, 7]. When north-going TCs baroclinic cyclone. Triggered by the descending cold meet mild cold air in the mid-latitudes, a frontal zone air and ascending warm air, the baroclinic energy of

Received date: 2007-08-22; revised date: 2008-12-29 Foundation item: National Key Fundamental Project for Research Development and Plan (2004CB418301); Natural Science Foundation of China (40575018, 40675033) Biography: LIANG Jun, senior engineer, B.S., mainly undertaking short-range weather forecast. E-mail for correspondence author: [email protected]

PDF created with pdfFactory trial version www.pdffactory.com 50 Journal of Tropical Meteorology Vol.15 will appear in the middle part of the lower-level TCs to 2 SYNOPTIC SUMMARIES FOR WINNIE induce the process of ET. The structure is half-cold, AND MATSA half-warm, being favorable for the release of geopotential energy and its transformation to kinetic Making landfall on province at 21:00 energy to increase the cyclonic circulation at lower (L.T., same below) August 18, 1997, Typhoon Winnie levels and intensify the TC. When the TC interacts was as intense as 960 hPa near the . After landfall, with intense cold air, its warm core will disappear the storm moved into province via Zhejiang completely to fill up the TC quickly. Cold air moved and provinces and split into two centers; the into the middle and lower layers of Typhoon Mamie original one disappeared over southern Shandong while (8509) from the northwest to result in both increased a new sub-center formed in central Shandong and ascending motion and strengthened instability of the moved to the northeast to make the second landfall on storm’s atmospheric stratification, which are the two province after passing through the Bohai Bay, main reasons and prerequisites for the development via and evolved into an extratropical cyclone in Northeast ET, as shown in a diagnostic study of the typhoon’s ET China. Fig.1a presents the distribution of Winnie’s by Sun et al.[8]. The descent of colder air from the precipitation for the whole course over the peninsula. middle and higher levels of the troposphere and warm advection at lower levels are the key to the ET development of Typhoon Winnie (9711), as suggested in Zhu et al. [9, 10] addressing the reinforcing mechanism associated with ET. During the ET, the intrusion of cold air intensified the low-level convergence and increased the divergent wind and its ability to produce kinetic energy; while the positive feedback mechanism for the interactions between Winnie and upper-level jet stream converted the available geopotential energy, the TC intensified into an extratropical cyclone. During its northward journey, Winnie coupled with the mid-latitude westerly trough as significant frontal development was observed inside the low pressure circulation of the TC with the downward transport of upper-level geopotential vorticity, as shown in a diagnostic study and numerical simulation on the TC by Li et al. [11, 12]. The stronger the upper-level trough, the more obviously Winnie intensified during the ET and the faster the extracyclone developed. The relationships between the ET of landing typhoons and Fig.1 Distribution of total rainfall from landfalling frontogenesis in the deformation field were also typhoons Winnie (a) and Matsa (b) for the [13] whole course over the Shandong Peninsula. discussed by Han et al. . Though there have been Unit: mm. much research on the issue of ET for the TC at home and abroad [14 - 18], how the ET process affects the Making landfall on Zhejiang at 02:00 August 6, precipitation of the TC remains unclear. Many issues 2005, Typhoon Matsa was as strong as 950 hPa near need to be further worked on to investigate into the the eye. Weakened to a tropical storm after a passage effects of transformation of TCs on precipitation with over the provinces of Anhui, and Shandong, it varying degree of ET. entered into the Bohai Sea via the Laizhou Bay before Typhoon Matsa (0509) was a transformed TC that heading towards the northeast. It made the second had landed on the Liaodong Peninsula with half as landfall, with pressure at 995 hPa, on Dalian at 07:20 much rainfall total as that of Winnie. How does the ET August 9 before reduction and dissipation. Fig.1b process (of either intensification or weakening) of a TC shows the distribution of Matsa’s precipitation for the relate with the rainfall? In this study, Typhoons Winnie whole course over the peninsula. Fig.2 gives the and Matsa are used as the examples to study it by using variation of the track of Winnie and Matsa and the the NCEP reanalysis data, which is available four pressure near the eyes after landfall. times daily, at a horizontal 2.5°×2.5° resolution and with 17 vertical layers, and comparing the distribution 3 LARGE-SCALE CIRCULATION of large and meso scale physical fields as they exerted BACKGROUND FOR THE ET OF WINNIE influence on the Liaodong Peninsula. AND MATSA

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By comparison and study (Fig.3), it is further 4 MESOSCALE STRUCTURES OF WINNIE proved that the ET is related with the upper-level AND MATSA DURING ET trough in mid-latitudes and the coupling between the northbound Winnie and Matsa and 200-hPa During the northward journey of the TC, an upper-level jet stream was favorable for their inverted trough is prone to extend ahead of its moving re-intensification after the ET [19]. direction. Inside the trough there are strong shears of the northeasterly and southeasterly, with huge amount of wet air accumulated after being transported by the southeasterly from the ocean. With the intrusion into the mid-level atmosphere of small streaks of cold air from the north, the atmospheric stratification becomes so unstable and cumulus convection develops so vigorously that it is likely for rain clusters to form. Usually, a TC-induced rainstorm is composed of one or more rain clusters evolving continuously [1]. Based on a the 3-hourly TBB data from the Japanese GMS satellite and hourly FY-2 satellite (See Fig.4), the TC

Winnie Matsa β 1a 005 rainstorm is of significant meso- scale over the

P h

/ 990 . Liaodong Peninsula. During the early stage of Winnie s e

r 975

p effect for the peninsula, convective cloud clusters kept

e 960 y

E moving north from the southeastern coast and colder air 945 b 012243648607284 entrained into the periphery of the TC when precipitation began over the peninsula. With the Fig.2 Variations of the track (a) and sea surface movement to the east and south of cold air from the pressure near the eyes (b, in which 0 stands northwest near 50°N and the ET gradually intensifying, for the time of landfall and in the unit of hour) after landfall for TCs Winnie and Winnie began approaching the upper-level trough at Matsa, plotted using 6-hourly positioning 19:00 August 21 (Figure omitted), attaining the data. maximum intensity of its life cycle. During Winnie’s For details of the analyses on the evolution of the process of ET, a -50°C TBB persisted for 15 hours vertical distribution of zonal and meridional winds, while severe precipitation lasted nearly 20 hours over their vertical structures and the vertical distribution of the peninsula, resulting in a heavy rainstorm on the moist potential vorticity, see the Chinese edition of the regional scale (Fig.1a). As shown in the evolution of journal. the infrared cloud imagery for the northbound

Fig.3 Geopotential height fields at 200 hPa for Winnie and Matsa after the ET. Unit: gpm; the shades stand for wind speeds ≥28 m/s and the solid circles indicate where the TC is.

PDF created with pdfFactory trial version www.pdffactory.com 51 52 Journal of Tropical Meteorology Vol.15 movement of Matsa, the cloud clusters associated with 5 CONCLUSIONS the TC rainstorm over the peninsula were of MCC (Fig.4). By 02:00 August 8, external cloud regimes had Next is a summary on the effect of Winnie and already affected Dalian with two inner cores inside the Matsa, two northbound TCs, on the precipitation of cluster and their brightness temperature at cloud tops Liaodong Peninsula during the ET. cooler than -77°C and -81°C, respectively, as revealed (1) When Winnie went northward and interacted by FY-2 (Figure omitted). With the northward with the mid-latitude upper-level trough and two advancement of the cloud cluster, precipitation began streaks of cold air intruded into the periphery of the TC to intensify significantly over the area of Dalian at from the east and west, there was frontogenesis over 04:00 August 8 and ended in southeastern Dalian at the region of Liaodong Peninsula. It was the 12:00. Meanwhile, another MCC, split from the MCS, upper-level divergence, transfer of positive vorticity moved toward the northeast with the ambient wind to and lower-level cold and warm advection that exposed affect the northeastern Dalian. This cluster was not the peninsula to Winnie during the ET, resulting in reinforced with more convective cloud clusters so that relatively large amount of rainfall. When Matsa convection developed only moderately and for a life approached the mid-latitude upper-level trough, cycle shorter than its precedent body. As a result, however, the intruding cold air from its periphery was severe precipitation ended as early as 16:00 in this part weaker and frontogenesis was less pronounced; the of Dalian after persisting for 10 hours, with rainfall interactions between weak upper-level divergence, much less than that with Winnie (Fig.1b). The principal negative advection of vorticity and warm and humid affecting system for TC rainstorm of the Liaodong lower-level airflow rapidly weakened Matsa right after Peninsula is cloud clusters on the meso-β scale, as strengthening it a little, producing only half as much demonstrated in the analysis. rainfall over the peninsula as Winnie. (2) As Winnie went northward after landfall, MPV

1997.8.20.02 1997.8.20.08 1997.8.20.14

2005.8.7.20 2005.8.8.02 2005.8.8.08

Fig.4 Evolutions of TBB with TC Winnie and TC Matsa. Unit: °C.

PDF crea52 ted with pdfFactory trial version www.pdffactory.com No.1 LIANG Jun (梁军) and CHEN Lian-shou (陈联寿) et al. 53 perturbation in upper troposphere, lower-level cyclonic [8] SUN Li, ZHEN Xiu-ya. A diagnostic analysis on a circulation and frontal zone had positive feedback northerward neutercance in its developing process [J]. Meteor. effects to transform it into an extratropical cyclone, Mon., 1991, 17(10): 3-8. [9] ZHU Pei-jun, ZHENG Yong-guang, TAO Zu-yu. Analysis resulting in long-lasting and heavy rainfall over the of the extratropical transition of tropical cyclone over peninsula area. With Matsa, however, there was mainland of China [J]. J. Trop. Meteor., 2003, 19(2): 157-162. neither downward transfer of positive MPV [10] ZHU Pei-jun, ZHENG Yong-guang, TAO Zu-yu. Kinetic perturbations from the upper levels nor appearance of energy budget of typhoon during extratropical transition [J]. frontal surfaces in lower-level circulation during the Acta Sci. Natur. Univ. Pekinesis, 2005, 41(1): 93-103. [11] LI Ying, CHEN Lian-shou, LEI Xiao-tu. Moisture ET, resulting in short and light rainfall in the region. potential vorticity analysis on the extratropical transition processes of Winnie (1997) and Bilis (2000) [J]. J. Trop. REFERENCES: Meteor., 2005, 21(2): 142-152. [12] LI Ying, CHEN Lian-shou, LEI Xiao-tu. Numerical study [1] CHEN Lian-shou, DING Yi-hui. Introductory Summary on on impacts of upper-level westerly trough on the extratropical West Pacific Typhoons [M]. Beijing: Science Press, 1979: transition process of typhoon Winnie (1997) [J]. Acta Meteor. 423-428; 462-474. Sinica, 64(5): 552-563. [2] KLEIN P M, HARR P A, ELSBERRY R L. Extratropical [13] HAN Gui-rong, HE Jin-hai, FAN Yong-fu, et al. The transition of western North Pacific tropical cyclone: transfiguration frontogenesis analyses on 0108 landfall Midlatitude contributions to intensification [J]. Mon. Wea. typhoon extratropical transition and heavy rain structure [J]. Rev., 2002, 130(9): 2 240-2 259. Acta Meteor. Sinica, 2005, 63(4): 468-476. [3] LI Ying, CHEN Lian-shou, ZHANG Sheng-jun. Variations [14] HART R E, EVANS J L. A Climatology of the in frequency and intensity of landfall tropical cyclones over Extratropical Transition of Atlantic Tropical Cyclones [J]. J. China during 1951 – 2004 [J]. Mar. Forecasts., 2008, 25(1): Climate, 2001, 14(4): 546-564. 65-73. [15] SINCLAIR M R. Extratropical Transition of Southwest [4] YUAN Zi-peng, ZHANG Li-xiang. Analysis of climatic Pacific Tropical Cyclone I: Climatology and Mean Structure characteristics on activities of tropical cyclones landing from Changes [J]. Mon. Wea. Rev., 2002, 130(3): 590-609. the or Bohai Sea [J]. Meteor. Mon., 2005, 31(6): [16] ZHAO Yu, WU Zeng-mao, LIU Shi-jun, et al. Potential 39-42. vorticity analysis of an torrential rain triggered by a neutercane [5] LIANG Jun, CHEN Lian-shou. Motion and intensity and in Shandong province [J]. J. Trop. Meteor., 2005, 21(1): 34-43. impact characteristics of tropical cyclone affecting the [17] WEN Li-juan, CHENG Lin-sheng, ZUO Hong-chao, et al. Liaodong Peninsula [J]. J. Trop. Meteor., 2005, 21(4): Diagnostic analysis of moist potential vorticity anomaly during 410-419. the may 1998 heavy rainfall of South China in the flood season [6] CHEN Lian-shou. Advances in the Research on Typhoon [J]. J. Trop. Meteor., 2006, 22(5): 447-453. Landfall [C]// Proceedings of Abstracts of the 11th National [18] WU Hai-ying, SHOU Shao-wen. Potential vorticity Science Symposium on Tropical Cyclones. Beijing: Chinese disturbance and cyclone development [J]. J. Nanjing Inst. Academy of Meteorological Sciences, 1999: 11-13. Meteor., 2002, 25(4): 510-517. [7] CHEN L S. An overview on the impact of interaction [19] SINCLAIR M R. Synoptic-scale diagnosis of the between low-mid latitude circulation on rainfall and tropical extratropical transition of a southwest Pacific tropical cyclone cyclone behavior [C]// 24th Conference on Hurricane and [J]. Mon. Wea. Rev., 1993, 121(4): 941-960. Tropical Meteorology. Am. Meteor. Soc., 2000: 63-65.

Citation: LIANG Jun, CHEN Lian-shou and LI Ying et al. Impacts of two tropical cyclones experiencing extratropical transition during northward progression on the rainfall of Liaodong Peninsula. J. Trop. Meteor., 2008, 15(1): 49-53.

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