著者

YANG Huadong WU Liguang XIE Tong

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-020, (Released:2020-01-22)

被引用文献数

15

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The tropical cyclone (TC) center position is often needed in the study of the inner-core processes although there is currently no consensus on the definition of the TC center. While previous studies evaluated center-detecting methods in terms of the center position, vertical tilt and decomposed symmetric and asymmetric circulations, this study used the 1-km resolution output of the predicted Hurricane Wilma (2005) at 5-minute intervals to evaluate the four TC centers that are frequently used in the diagnostic analysis of the inner-core dynamics processes: the pressure centroid center (PCC), the potential vorticity (PV) centroid center (PVC), the maximum tangential wind center (MTC) and the minimum pressure variance center (MVC) by focusing on the evolution of the small-scale track oscillation and vortex tilt. The differences in the detected center position and vertical tilt are generally small during the course of rapid intensification and eyewall replacement. The four methods all lead to similar small-scale track oscillations that rotate cyclonically around the mean track. While the MVC and PVC lead to a relatively smooth rotation, abrupt changes exist in the track oscillation of the MTC; the track oscillation of the PCC contains amplified embedded rotations that are associated with the PV mixing in the eye region. The tracks of the MVC and PVC relative to the lower-level center (vertical tilt) are generally smooth, while the relative tracks of the MTC and PCC contain abrupt changes. The MVC also leads to the strongest symmetric structure in the tangential wind, PV, and radial PV gradient in the eyewall region. This study suggests that the MVC should be selected in the study of inner-core processes.

著者

ZHAO Haikun WU Liguang WANG Chao KLOTZBACH Philip J.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-039, (Released:2019-03-11)

被引用文献数

8

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Most studies have focused on variations of tropical cyclone (TC) frequency, intensity, and track over the western North Pacific (WNP), while variability of WNP TC season onset date (TCSO) has been less studied. Recent research has indicated a close association between WNP TCSO and sea surface temperature (SST) over the tropical Indian Ocean and the tropical central-eastern Pacific. This study finds the relationship between TCSO and SST underwent an interdecadal change in the late 1990s, likely due to a climate shift that occurred around that time. An observed significant correlation between TCSO and SST before the late 1990s and has been insignificant since that time. It was confrimed by the fact that ENSO positively correlates at 0.46 with TCSO from 1965-1999 (significant at the 95 % level), while the correlation becomes insignificant (0.16) during 1998-2016. Further analysis suggests that the close association between TCSO and SST is robust only for major El Niño events, with consistently extreme late TCSO following major El Niños during the satellite era. Accompanying the decay of major El Niños, tropical equatorial easterly anomalies in the WNP are driven by a Matsuno-Gill-type response to the specific SST anomaly pattern over the tropical Indo-Pacific sector. This in turn induces an anomalous anticyclone, anomalous westerly vertical wind shear, reduced mid-level moisture and suppressed convection over the WNP basin – all of which are unfavorable for WNP TCs, resulting in delayed TCSO following major El Niño events. These inter-decadal changes in the inter-annual correlation between TCSO and ENSO are largely due to the changing influence of moderate El Niño events on TCSO before and after the late 1990s. This study improves understanding of the ENSO-TC relationship, which should aid seasonal outlooks of WNP TC activity.

著者

ZHOU Xingyang WU Liguang LIU Qingyuan ZHENG Yan

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-063, (Released:2020-08-28)

被引用文献数

3

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Previous studies suggested that the entrainment of the low-level, high-entropy eye air can provide additional energy for tropical cyclone (TC) intensification, but the previous trajectory analysis only indicated that considerable air parcels below the eye inversion can be entrained into the eyewall. In this study, the one-minute output data from a semi-idealized experiment are used to quantitatively evaluate the relative importance of the entrainment of the high-entropy eye air by enhancing the eyewall convection. It is confirmed that considerable amount of high-entropy eye air below the eye inversion can be entrained into the eyewall. The entrainment occurs favorably on the quandrants of enhanced eyewall convection and is enhanced in the presence of small-scale disturbances in the inner edge of the eyewall. However, the eyewall air parcels below 3 km experience a fast cycling. There are 84.4 % and 7.7 % eyewall air from the low-level boundary inflow and the middle-level dry environment, respectively. The low-level, high-entropy eye air only accounts for 1.7 % of the eyewall air, while 6.2 % eyewall air remains in the eyewall below 3 km during the 90-minute period. The eye air from the low-level, high-entropy reservoir accounts for 5.8 % of the equivalent potential temperature change below 3 km and 4.5 % of the total mass transport at 3 km in the TC eyewall. This study suggests that the low-level, high-entropy air from the eye has little direct influence on TC intensity through enhancing the eyewall convection by providing relatively small mass and thermodynamic contributions.