V ol.14 No.1 JOURNAL OF TROPICAL METEOROLOGY June 2008
Article ID: 1006-8775(2008) 01-0069-04
PRELIMINARY STUDY ON STRUCTURE OF WINTERTIME TYPHOON
NANMADOL IN 2004
HE Jie-lin (何洁琳)1, 2
, GUAN Zhao-yong (管兆勇)1
, NONG Meng-song (农孟松)
3
(1. KLME, Nanjing University of Information Science & Technology, Nanjing 210044 China; 2. Yulin City
Meteorological Bureau of Guangxi, Yulin 537000 China; 3. Guangxi Meteorological Obrvatory,
Nanning 530022 China)Abstract: Using NCEP/NCAR reanalysis, the structure of a wintertime typhoon
named Nanmadol that landed on Taiwan 4 December, 2004 has been examined in this paper. It is found that Nanmadol looks similar in structure and time evolution to summer typhoons; the central part of it is warm and humid, and the convergence is obrved in the lower troposphere while there is divergence in the upper troposphere.The differences between wintertime and summertime typhoons are found. The southwest stream flow in the lower troposphere and cyclonic disturbance in the upper troposphere em significantly weaker in Nanmadol than in summertime typhoons. The EOF analysis performed for a level pressure (SLP) of Nanmadol shows that about 90% of the total variance of temporal changes in typhoon circulation can be explained by two leading EOF modes of EOF1 and EOF2. EOF1 shows the structure and intensity variations of Nanmadol while EOF2 shows the changes in environmental SLP distributions that influences the moving direction of Nanmadol.
Key words: typhoon; wintertime; nature; structure CLC number: P444 Document code: A
Received date: 2007-12-24; revid date: 2008-04-16
Foundation item: 2006BAC02B, Guangxi meteorologyical bureau rearch foundation (QK200603)
Biography: HE Jie-lin, female, native from Guangxi Zhuang Autonamous region, Ph.D. candidate, mainly undertaking the rearch on monsoon dynamics.E-mail:******************
1 INTRODUCTION
As shown in rearch and statistical results [1 – 6],Typhoon Nanmadol (No.0428), which made landfall on Taiwan Dec. 4, 2004, is the storm moving on land at the latest time of year in China since 1949. Summer is a ason when typhoons are the most active while winter es few cyclonegenesis and fewer landfalls in China. It is then important to study typhoons making landfall in winter. Previous study focus on typhoons in summer with few on tho in autumn or winter.Statistical characteristics, track change and relationships between the cold air movement and the cyclonegenesis and evolution of typhoons have been the main topics [1 – 10]. In this work, efforts are mainly on the structural features of Nanmadol, a west Pacific typhoon that formed in early winter and made landfall,and its evolution, for its similarities to and differences from wintertime typhoons, so that future study can be done with better basis.
2 STRUCTURAL CHARACTERISTICS OF
THE TYPHOON The reanalysis data of NCEP/NCAR is ud to study the circulation structure and thermodynamic structure of Nanmadol and Imbudo (No.0307), a summertime typhoon. It is shown in comparison and analysis that Nanmadol ’s warm and humid structure is well defined and there is low-
level convergence in association with high-level divergence, though with heights lower than the summertime counterpart to which complete cyclonic circulation reaches. In fact, it is poorly en at levels higher than 200 hPa and low-level convergence and high-level divergence are weaker than normal. In the ca of Nanmadol, the southeasterly and southwesterly converge with the northeasterly, with the easterly playing a major role.For Imbudo, however, the westerly is dominant among the converging flow and an inten southwesterly jet stream appears. The low-level southwesterly
70 Journal of Tropical Meteorology Vol.14 converging flow is poorly defined for Nanmadol and
transports water vapor just moderately.
3 USE OF EOF METHOD IN ANALYZING
THE STRUCTURE OF TYPHOON
STRUCTURE
The center of typhoon is t at that of the
gridpoints and 22 time levels of the SLP field going
through the whole cour of life cycle are taken to
constitute original temporal ries for EOF
decomposition of the anomalous field of SLP over the
whole process of Nanmadol. The contribution is nearly
90% from the accumulated variance of the first two
eigenvectors (referred to as EOF1 and EOF2), which
pass the significance test [11] and are good indicators of
the variation of typhoon’s spatial structure. EOF1
(Fig.1a) gives a structure in which the middle has
higher values than the part surrounding it, i.e. the
center is the eye. It shows a basic pattern of large
pressure gradient at the periphery of the typhoon,
tartywhich is a typical distribution of the pressure field
courier
during the mature pha of typhoon. Its corresponding
first temporal coefficient ries does well in depicting a
main process of pressure field variation for the life
cycle of typhoon, i.e. the change in intensity. EOF2
(Fig.1b) shows that the eye is located at a symbol of
the designated typhoon, with the enclod circle and the
part to its west being positive and that to its north
negative. From the evolution of the cond temporal
ries, it is known that pressure falls over the continent
southwest of the typhoon but ris northeast of it,
which is just the distribution of pressure field during
the westward movement of the typhoon, i.e. the change
in movement.
Temporal coefficients of EOF1 and EOF2 and the
distribution of coefficients of their correlation with the fields of surface temperature anomaly, humidity and 500-hPa vorticity are respectively determined (Fig.2). The results show that there is substantial change in the fields with the variation of life cycle intensity and track of the typhoon. The typhoon intensifies over the ocean where SST is relatively warm and moves in this direction. The variation of the 500-hPa vorticity field agrees with that of pressure and the variation of ambient field around the typhoon is shown during the movement. During the variation of typhoon intensity, a main area of positive correlation of the relative humidity field is over the ocean to the east of the typhoon. Humidity is decreasing as the typhoon evolves, which is unfavorable for the supply of water vapor from the southeast. During the movement of the typhoon, a main area of humidity correlation is to th
e distant west of it, suggesting that the condition of water vapor there be favorable to the formation and development of local convection. When the typhoon weakens and dissipates, however, relative humidity gets smaller to the west of the storm, reflecting the strengthening of dry and cold continental air during the ending pha of the typhoon.
For analys of other aspects, refer to the Chine edition of the journal.
4 CONCLUSIONS AND DISCUSSIONS
As shown in the results of the analysis here, the wintertime typhoon Nanmandol is characteristic of the
following:
Fig.1 The modes of EOF-analyzed a level
pressure anomalies with Typhoon
Nanmandol. (a) and (b) are for EOF1
and EOF2, respectively (unit: ×0.1).北京遇上西雅图插曲
No.1 HE Jie-lin (何洁琳) and GUAN Zhao-yong (管兆勇) et al. 71
曾子曰士不可以不弘毅(1) Like summertime typhoons, it has well-defined warm and humid core and dynamic and thermodynamic structure of low-level convergence versus high-level divergence. The warm core is destroyed and weakened to dissipation when cold air intrudes into it as the typhoon turns to head for the north to get clo to the continent.
(2) The low levels of the typhoon are dominated by the convergence of the northeasterly with the southeasterly and southwesterly. What is different is that Nanmandol does not have a well-defined southwesterly in low-level converging flows and brings
about relatively few water vapor. The cyclonic circulation does not reach as high as its summertime counterpart and exerts weaker disturbance to the atmosphere.
(3) As shown in the EOF analysis, the variation of the pressure field structure of the typhoon is mainly
shown by the first two eigenvectors of EOF, one being
Fig.2 The distribution of the correlation
between the first and cond temporal coefficients between surface temperature anomaly (a, b), 500-hPa vorticity (c, d) and relative humidity at a level (e, f). Unit: ×0.01.
suggest72 Journal of Tropical Meteorology Vol.14
an “intensity mode” and the other a “movement mode”.
The two eigenvectors are well correlated with the
variation of temperature, vorticity and humidity,
shaggyreflecting the changes associated with the internal
dynamic structure and movement of the typhoon during
the generation and development.
It must be noted that Typhoon Nanmandol is
studied in terms of general thermodynamic and
dynamic structure with the reanalysis data of
NCEP/NCAR. As the resolution is relatively low, the
fitting of the intensity of typhoon center is also
relatively weak, resulting in unsatisfactory analysis of
the actual typhoon, and fitting of pressure especially, at
the center. At prent, results have been desirable with
pc是什么的缩写the study of the variation of intensity, track and
structure of typhoons using the latest obrvations like
英文广告
the Doppler and high-resolution TRMM satellite data [12 - 14]and the latest means and methods of measurement can be ud to conduct intensive rearch
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Citation: HE J L, GUAN Z Y and NONG M S. Preliminary study on structure of wintertime typhoon N
anmadol in 2004. J. Trop. Meteor., 2008, 14(1): 69-72.
