| Modulation of Western North Pacific Tropical Cyclone Genesis by Intraseasonal Oscillation of the ITCZ:A Statistical Analysis |
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| 作者姓名： | CAO Xi HUANG Ping CHEN Guanghu CHEN Wen |
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| 作者单位： | Center |
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| 摘 要： | The present study investigates modulation of western North Pacific(WNP) tropical cyclone(TC) genesis in relation to different phases of the intraseasonal oscillation(ISO) of ITCZ convection during May to October in the period 1979-2008.The phases of the ITCZ ISO were determined based on 30-80-day filtered OLR anomalies averaged over the region(5-20 N,120-150 E).The number of TCs during the active phases was nearly three times more than during the inactive phases.The active(inactive) phases of ISO were characterized by low-level cyclonic(anticyclonic) circulation anomalies,higher(lower) midlevel relative humidity anomalies,and larger(smaller) vertical gradient anomalies of relative vorticity associated with enhanced(weakened) ITCZ convection anomalies.During the active phases,TCs tended to form in the center of the ITCZ region.Barotropic conversion from the low-level mean flow is suggested to be the major energy source for TC formation.The energy conversion mainly depended on the zonal and meridional gradients of the zonal flow during the active phases.However,barotropic conversion weakened greatly during the inactive phases.The relationship between the meridional gradient of absolute vorticity and low-level zonal flow indicates that the sign of the absolute vorticity gradient tends to be reversed during the two phases,whereas the same sign between zonal flow and the absolute vorticity gradient is more easily satisfied in the active phases.Thus,the barotropic instability of low-level zonal flow might be an important mechanism for TC formation over the WNP during the active phases of ISO.
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| 关 键 词： | intertropical convergence zone(ITCZ) intraseasonal oscillation(ISO) tropical cyclone(TC) modulation |
Modulation of Western North Pacific Tropical Cyclone Genesis by
Intraseasonal Oscillation of the ITCZ: A Statistical Analysis |
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| CAO Xi,HUANG Ping,CHEN Guanghu,CHEN Wen.Modulation of Western North Pacific Tropical Cyclone Genesis by Intraseasonal Oscillation of the ITCZ:A Statistical Analysis[J].Advances in Atmospheric Sciences,2012,29(4):744-754. |
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| Authors: | CAO Xi HUANG Ping CHEN Guanghua and CHEN Wen |
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| Institution: | Center for Monsoon System Research, Institute of Atmospheric Physics,
Chinese Academy of Sciences, Beijing 100029,
Graduate University of Chinese Academy of Sciences, Beijing 100049 |
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| Abstract: | The present study investigates modulation of western North Pacific (WNP)
tropical cyclone (TC) genesis in relation to different phases of the
intraseasonal oscillation (ISO) of ITCZ convection during May to October in
the period 1979--2008. The phases of the ITCZ ISO were determined based on
30--80-day filtered OLR anomalies averaged over the region (5o--20oN,
120o--150oE). The number of TCs during the active phases was
nearly three times more than during the inactive phases. The active
(inactive) phases of ISO were characterized by low-level cyclonic
(anticyclonic) circulation anomalies, higher (lower) midlevel relative
humidity anomalies, and larger (smaller) vertical gradient anomalies of
relative vorticity associated with enhanced (weakened) ITCZ convection
anomalies. During the active phases, TCs tended to form in the center of the
ITCZ region.
Barotropic conversion from the low-level mean flow is suggested to be the
major energy source for TC formation. The energy conversion mainly depended
on the zonal and meridional gradients of the zonal flow during the active
phases. However, barotropic conversion weakened greatly during the inactive
phases. The relationship between the meridional gradient of absolute
vorticity and low-level zonal flow indicates that the sign of the absolute
vorticity gradient tends to be reversed during the two phases, whereas the
same sign between zonal flow and the absolute vorticity gradient is more
easily satisfied in the active phases. Thus, the barotropic instability of
low-level zonal flow might be an important mechanism for TC formation over
the WNP during the active phases of ISO. |
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| Keywords: | intertropical convergence zone (ITCZ) intraseasonal
oscillation (ISO) tropical cyclone (TC) modulation |
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