scholarly journals To what extent the presence of real-strength tropical cyclones influences the estimation of atmospheric intraseasonal oscillation intensity?

2015 ◽  
Vol 16 (4) ◽  
pp. 438-444 ◽  
Author(s):  
Mingyu Bi ◽  
Tim Li ◽  
Xinyong Shen ◽  
Melinda Peng
Keyword(s):  
Tropical Cyclones ◽  
Intraseasonal Oscillation ◽  
Oscillation Intensity ◽  
Real Strength

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 Interannual Variability of the Intraseasonal Oscillation and Its Impact on the Summertime Wave Patterns and Tropical Cyclones over the Western North Pacific

2017 ◽  
Vol 145 (9) ◽  
pp. 3465-3483 ◽  
Author(s):  
Ken-Chung Ko ◽  
Jyun-Hong Liu
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Mean Flow ◽  
Background Flow ◽  
Wave Patterns ◽  
Intraseasonal Oscillations ◽  
The Mean ◽  
Local Weather

In this study, intraseasonal oscillations (ISOs) and submonthly wave patterns were separated into maximal variance (MaxV) and minimal variance (MinV) years on the basis of ISO variance from July to October. The mean-state 850-hPa streamfunction for submonthly cases indicated that, in the MinV years, tropical cyclones (TCs) formed near areas southeast of those in the MaxV years. ISOs propagated northward in the MaxV years, whereas a weaker westward-propagating tendency was observed in the MinV years. Track analysis of the centers of the submonthly cyclonic anomalies suggested that the background flow dictated the propagation routes of the easterly cyclonic anomalies in the MaxV years. However, the propagation routes of the westerly cyclonic anomalies were barely affected by the background flow. Further analysis of the ISO mean flow patterns showed that in the MaxV years, the propagation routes of the westerly cyclonic anomalies were more likely controlled by the anomalous easterly flow generated by the ISO westerly cyclonic anomalies. Moreover, rainfall was heavier in Taiwan in the MaxV years because the background flow in the MinV years caused the submonthly cyclonic anomaly tracks to shift away from Taiwan. Therefore, low-frequency large-scale circulations can affect smaller-scale phenomena and local weather.

scholarly journals Heavy Rainfall Induced by Tropical Cyclones across Northern Taiwan and Associated Intraseasonal Oscillation Modulation

2013 ◽  
Vol 26 (20) ◽  
pp. 7992-8007 ◽  
Author(s):  
Jau-Ming Chen ◽  
Pei-Hua Tan ◽  
Ching-Feng Shih
Keyword(s):  
Tropical Cyclones ◽  
Heavy Rainfall ◽  
Intraseasonal Oscillation ◽  
Convergence Result ◽  
Windward Side ◽  
Tropical Western Pacific ◽  
Moisture Supply ◽  
Rainfall Type ◽  
Northern Taiwan

Abstract Tropical cyclones (TCs) moving northwestward/westward across northern Taiwan are defined to have a type-2 track. This study aims to analyze heavy rainfall associated with type-2 TCs in Taiwan, focusing on the modulation processes of the intraseasonal oscillation (ISO). During 1958–2011, 21 summer type-2 TCs are separated into three rainfall types: strong, moderate, and weak. For the strong rainfall type, both 30–60-day and 10–24-day ISOs propagate northwestward across Taiwan. During landfall and the ensuing two days, both ISOs exhibit a cyclonic anomaly centering northwest of Taiwan that causes anomalous westerly flows (or enhance seasonal southwesterly flows) from the South China Sea (SCS) onto Taiwan. Persistent moisture supply and strong moisture convergence result in prolonged heavy rainfall on the windward side over western Taiwan. TCs with weak rainfall are accompanied by a northward-propagating 30–60-day ISO from the tropical western Pacific toward Japan and a westward-propagating 10–24-day ISO along 20°N latitude. During the landfall stage both ISOs have a cyclonic anomaly with its center south of Taiwan. Major anomalous westerly flows are displaced southward across the central SCS, leading to a weak moisture supply and rainfall in Taiwan. The moderate rainfall type features a 30–60-day (10–24 day) ISO resembling that of the weak (strong) rainfall type. The amount of rainfall thus ranges between the strong and weak rainfall types. Major processes regulating the rainfall of type-2 TCs relate to the intensity of the moisture supply associated with anomalous westerly flows from the SCS onto Taiwan, which is jointly modulated by 30–60-day and 10–24-day ISOs.

scholarly journals Association between Northward-Moving Tropical Cyclones and Southwesterly Flows Modulated by Intraseasonal Oscillation

2012 ◽  
Vol 25 (14) ◽  
pp. 5072-5087 ◽  
Author(s):  
Jau-Ming Chen ◽  
Ching-Feng Shih
Keyword(s):  
Tropical Cyclones ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Northern South China Sea ◽  
Intraseasonal Oscillation ◽  
Regulatory Processes ◽  
The North ◽  
Intraseasonal Oscillations ◽  
The Tropics ◽  
Northern Taiwan

Abstract Tropical cyclones (TCs) of a particular track type move northward along the open oceans to the east of Taiwan and later pass over or near northern Taiwan. Their northward movement may be associated with intensified monsoon southwesterly flows from the northern South China Sea (SCS) toward Taiwan. Prolonged heavy rainfall then occurs in western Taiwan across the landfall and postlandfall periods, leading to severe floods. Characteristics of this TC–southwesterly flow association and related large-scale regulatory processes of intraseasonal oscillations (ISOs) are studied. For summers from 1958 to 2009, 16 out of 108 TCs affecting Taiwan exhibit the aforementioned northward-moving track. Among them, four TCs (25%) concur with enhanced southwesterly flows. Intensified moisture supplies from the SCS result in strong moisture convergence and prolonged heavy rainfall in western Taiwan. Both 30–60- and 10–24-day ISOs make positive contributions to the TC–southwesterly flow association. Both ISOs exhibit the northward progress of a meridional circulation pair from the tropics toward Taiwan. During landfall and the ensuing few days, Taiwan is surrounded by a cyclonic anomaly to the north and an anticyclonic anomaly to the south of these two ISOs. The appearance of anomalous southwesterly–westerly flows acts to prolong heavy rainfall in western Taiwan after the departure of a TC. The TC–southwesterly flow association tends to occur during the minimum phase of the 30–60-day ISO featuring a cyclonic anomaly in the vicinity of Taiwan but in various phases of the 10–24-day ISO. Rainfall in western Taiwan increases when these two ISOs simultaneously exhibit a cyclonic anomaly to the north of Taiwan.

Footprints of Tropical Cyclones in WNP Summer Monsoon Variability

2020 ◽  
Author(s):  
Huang-Hsiung Hsu
Keyword(s):  
Climate Variability ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Climate Models ◽  
Southern Oscillation ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Monsoon Trough ◽  
Teleconnection Pattern ◽  
Large Scale Circulation

<p>Tropical cyclones (TCs) in the western North Pacific (WNP) are modulated by large-scale circulation systems such monsoon trough, intraseasonal oscillation, teleconnection pattern, El Niño and Southern Oscillation, and some interdecadal oscillations. While the low-frequency, large-scale circulation produces a clustering effect on TCs, the latter in return leave marked footprints in climate mean state and variability because of large amplitudes in circulation and strong heating. In this study, we applied PV inversion technique to remove TCs from reanalysis and evaluate their contribution to mean circulation and climate variability. It is found that the mean climatological circulation (e.g., low-level monsoon trough and upper-tropospheric anticyclone) would be much weaker with TCs removed. Intraseasonal and interannual variance of certain variables could decrease by as much as 40–50 percent. An accompanied study indicated that TCs had slowed down the sea surface warming in the WNP for the past few decades because of TC-induced cooling. Our results suggest that TC effect has to be considered to understand the climate variability in the tropical atmosphere and ocean. The ensemble effect of TCs, at least in the statistical sense, has to be resolved in climate models to better simulate climate variability and produce more reliable climate projection in the TC-prone regions.</p>

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