scholarly journals Poleward migration of western North Pacific tropical cyclones related to changes in cyclone seasonality

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiangbo Feng ◽  
Nicholas P. Klingaman ◽  
Kevin I. Hodges
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Walker Circulation ◽  
Lower Latitude ◽  
Annual Average ◽  
Anthropogenic Forcing ◽  
Late Season ◽  
Long Term Trends

AbstractThe average location of observed western North Pacific (WNP) tropical cyclones (TCs) has shifted north over the last several decades, but the cause remains not fully understood. Here we show that, for the annual average, the observed northward migration of WNP TCs is related to changes in TC seasonality, not to a northward migration in all seasons. Normally, peak-season (July–September) TCs form and travel further north than late-season (October–December) TCs. In recent decades, related to less frequent late-season TCs, seasonally higher-latitude TCs contribute relatively more to the annual-average location and seasonally lower-latitude TCs contribute less. We show that the change in TC seasonality is related to the different responses of late-season and peak-season TC occurrence to a stronger Pacific Walker Circulation. Our findings provide a perspective on long-term trends in TC activity, by decomposing the annual-average statistics into seasonal components, which could respond differently to anthropogenic forcing.

scholarly journals Relationship between Early-Stage Features and Lifetime Maximum Intensity of Tropical Cyclones over the Western North Pacific

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 815
Author(s):  
Ren Lu ◽  
Xiaodong Tang
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Early Stage ◽  
Maximum Intensity ◽  
Moisture Distribution ◽  
Coefficient Of Determination ◽  
Lower Latitude ◽  
Composite Analysis ◽  
Translation Speed

The relationship between early-stage features and lifetime maximum intensity (LMI) of tropical cyclones (TCs) over the Western North Pacific (WNP) was investigated by ensemble machine learning methods and composite analysis in this study. By selecting key features of TCs’ vortex attributes and environmental conditions, a two-step AdaBoost model demonstrated accuracy of about 75% in distinguishing weak and strong TCs at genesis and a coefficient of determination (R2) of 0.30 for LMI estimation from the early stage of strong TCs, suggesting an underlying relationship between LMI and early-stage features. The composite analysis reveals that TCs with higher LMI are characterized by lower latitude embedded in a continuous band of high low-troposphere vorticity, more compact circulation at both the upper and lower levels of the troposphere, stronger circulation at the mid-troposphere, a higher outflow layer with stronger convection, a more symmetrical structure of high-level moisture distribution, a slower translation speed, and a greater intensification rate around genesis. Specifically, TCs with greater “tightness” at genesis may have a better chance of strengthening to major TCs (LMI ≥ 96 kt), since it represents a combination of the inner and outer-core wind structure related to TCs’ rapid intensification and eyewall replacement cycle.

What Percentage of Western North Pacific Tropical Cyclones Form within the Monsoon Trough?

2013 ◽  
Vol 141 (2) ◽  
pp. 499-505 ◽  
Author(s):  
John Molinari ◽  
David Vollaro
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Relative Vorticity ◽  
Monsoon Trough ◽  
Easterly Waves ◽  
Suitable Definition ◽  
Definition Of ◽  
Background State

Abstract It is frequently stated that 70%–80% of western North Pacific tropical cyclones form “within the monsoon trough,” but without an objective definition of the term. Several definitions are tested here. When the monsoon trough (MT) is defined as the contiguous region where long-term (1988–2010) mean July–November 850-hPa relative vorticity is positive, 73% of all July–November tropical cyclones form within the MT. This percentage varies interannually, however, from as low as 50% to nearly 100%. The percentage correlates with the Niño-3.4 index, with more storms forming within the MT during warm periods. When the MT is defined instead using long-term monthly mean ζ850, more than 80% of tropical cyclones form within the MT in all months except July and August, when more than 30% of storms form poleward of the MT. It is hypothesized that the known peak in the frequency of upper-tropospheric midlatitude wave breaking in July and August is responsible. It is argued that any long-term mean provides a suitable definition of the MT. Defining it on less than seasonal time scales, however, creates a lack of conceptual separation between the MT and other tropical disturbances such as the MJO, equatorial waves, and easterly waves. The term monsoon trough should represent a climatological feature that provides an asymmetric background state within which other disturbances evolve.

Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific

2018 ◽  
Vol 35 (4) ◽  
pp. 423-434
Author(s):  
Shumin Chen ◽  
Weibiao Li ◽  
Zhiping Wen ◽  
Mingsen Zhou ◽  
Youyu Lu ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
High Frequency ◽  
Western North Pacific ◽  
High Frequency Oscillations

Interactions between Boreal Summer Intraseasonal Oscillations and Synoptic-Scale Disturbances over the Western North Pacific. Part I: Energetics Diagnosis*

2011 ◽  
Vol 24 (3) ◽  
pp. 927-941 ◽  
Author(s):  
Pang-chi Hsu ◽  
Tim Li ◽  
Chih-Hua Tsou
Keyword(s):  
Kinetic Energy ◽  
Energy Conversion ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Intraseasonal Oscillation ◽  
Active Phase ◽  
Boreal Summer ◽  
Synoptic Eddies ◽  
Barotropic Energy Conversion

Abstract The role of scale interactions in the maintenance of eddy kinetic energy (EKE) during the extreme phases of the intraseasonal oscillation (ISO) is examined through the construction of a new eddy energetics diagnostic tool that separates the effects of ISO and a low-frequency background state (LFBS; with periods longer than 90 days). The LFBS always contributes positively toward the EKE in the boreal summer, regardless of the ISO phases. The synoptic eddies extract energy from the ISO during the ISO active phase. This positive barotropic energy conversion occurs when the synoptic eddies interact with low-level cyclonic and convergent–confluent ISO flows. This contrasts with the ISO suppressed phase during which the synoptic eddies lose kinetic energy to the ISO flow. The anticyclonic and divergent–diffluent ISO flows during the suppressed phase are responsible for the negative barotropic energy conversion. A positive (negative) EKE tendency occurs during the ISO suppressed-to-active (active-to-suppressed) transitional phase. The cause of this asymmetric EKE tendency is attributed to the spatial phase relation among the ISO vorticity, eddy structure, and EKE. The southwest–northeast-tilted synoptic disturbances interacting with cyclonic (anticyclonic) vorticity of ISO lead to a positive (negative) EKE tendency in the northwest region of the maximum EKE center. The genesis number and location and intensification rate of tropical cyclones in the western North Pacific are closely related to the barotropic energy conversion. The enhanced barotropic energy conversion favors the generation and development of synoptic seed disturbances, some of which eventually grow into tropical cyclones.

scholarly journals Occurrences of Wintertime Tropical Cyclones in the Western North Pacific under the Background of Global Warming

2009 ◽  
Vol 2 (6) ◽  
pp. 333-338
Author(s):  
He Jie-Lin ◽  
Guan Zhao-Yong ◽  
Qian Dai-Li ◽  
Wan Qi-Lin ◽  
Wang Li-Juan
Keyword(s):  
Global Warming ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific
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