scholarly journals Improved Simulation of Tropical Cyclone Responses to ENSO in the Western North Pacific in the High-Resolution GFDL HiFLOR Coupled Climate Model*

2016 ◽  
Vol 29 (4) ◽  
pp. 1391-1415 ◽  
Author(s):  
Wei Zhang ◽  
Gabriel A. Vecchi ◽  
Hiroyuki Murakami ◽  
Thomas Delworth ◽  
Andrew T. Wittenberg ◽  
...  
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Sea Surface ◽  
La Nina

Abstract This study aims to assess whether, and the extent to which, an increase in atmospheric resolution of the Geophysical Fluid Dynamics Laboratory (GFDL) Forecast-Oriented Low Ocean Resolution version of CM2.5 (FLOR) with 50-km resolution and the High-Resolution FLOR (HiFLOR) with 25-km resolution improves the simulation of the El Niño–Southern Oscillation (ENSO)–tropical cyclone (TC) connections in the western North Pacific (WNP). HiFLOR simulates better ENSO–TC connections in the WNP including TC track density, genesis, and landfall than FLOR in both long-term control experiments and sea surface temperature (SST)- and sea surface salinity (SSS)-restoring historical runs (1971–2012). Restoring experiments are performed with SSS and SST restored to observational estimates of climatological SSS and interannually varying monthly SST. In the control experiments of HiFLOR, an improved simulation of the Walker circulation arising from more realistic SST and precipitation is largely responsible for its better performance in simulating ENSO–TC connections in the WNP. In the SST-restoring experiments of HiFLOR, more realistic Walker circulation and steering flow during El Niño and La Niña are responsible for the improved simulation of ENSO–TC connections in the WNP. The improved simulation of ENSO–TC connections with HiFLOR arises from a better representation of SST and better responses of environmental large-scale circulation to SST anomalies associated with El Niño or La Niña. A better representation of ENSO–TC connections in HiFLOR can benefit the seasonal forecasting of TC genesis, track, and landfall; improve understanding of the interannual variation of TC activity; and provide better projection of TC activity under climate change.

scholarly journals Comparison of the Madden–Julian Oscillation-Related Tropical Cyclone Genesis over the South China Sea and Western North Pacific under Different El Niño-Southern Oscillation Conditions

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 183
Author(s):  
Chengyao Ye ◽  
Liping Deng ◽  
Wan-Ru Huang ◽  
Jinghua Chen
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Madden Julian Oscillation ◽  
La Nina

This paper explores the Madden–Julian Oscillation (MJO) modulation of tropical cyclone (TC; hereafter, MJO-TC) genesis over the South China Sea (SCS) and Western North Pacific (WNP) under different El Niño-Southern Oscillation (ENSO) conditions. Analyses used Joint Typhoon Warning Center (JTWC) best-track data, the Real-Time Multivariate MJO (RMM) index, and European Center for Medium-Range Weather Forecasts (ECMWF) Interim (ERA-Interim) reanalysis data. The results showed that the MJO has significant modulation on both the SCS and WNP TC genesis in neutral years, with more (fewer) TCs forming during the active (inactive) MJO phases. However, during the El Niño and La Niña years, the MJO-TC genesis modulation over the two regions differs from each other. Over the SCS, the MJO modulation of TC genesis is stronger in the La Niña years, while it becomes weaker in the El Niño years. Over the WNP, the MJO has a stronger influence on TC genesis in the El Niño years compared to that in the La Niña years. Related Genesis Potential Index (GPI) analysis suggests that midlevel moisture is the primary factor and vorticity is the secondary factor, for the MJO-TC genesis modulation over the SCS in the La Niña years. Over the WNP, midlevel moisture is the dominant factor for the MJO-TC genesis modulation during the El Niño years. These results can be explained by increased water vapor transport from the Bay of Bengal, associated with enhanced westerly wind anomalies, during the active phases relative to the inactive MJO phases; these conditions prevail over the SCS during the La Niña years, and over the WNP during the El Niño years.

scholarly journals Influence of Intraseasonal–Interannual Oscillations on Tropical Cyclone Genesis in the Western North Pacific

2018 ◽  
Vol 31 (12) ◽  
pp. 4949-4961 ◽  
Author(s):  
Jau-Ming Chen ◽  
Ching-Hsuan Wu ◽  
Pei-Hsuan Chung ◽  
Chung-Hsiung Sui
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Relative Vorticity ◽  
La Niña ◽  
Positive Vorticity ◽  
La Nina

Influences of intraseasonal–interannual oscillations on tropical cyclone (TC) genesis are evaluated by productivity of TC genesis ( PTCG) from the developing (TC d) and nondeveloping (TC n) precursory tropical disturbances (PTDs). A PTD is identified by a cyclonic tropical disturbance with a strong-enough intensity, a large-enough maximum center, and a long-enough lifespan. The percentage value of PTDs evolving into TC d is defined as PTCG. The analysis is performed over the western North Pacific (WNP) basin during the 1990–2014 warm season (May–September). The climatological PTCG in the WNP basin is 0.35. Counted in a common period, mean numbers of PTDs in the favorable and unfavorable conditions of climate oscillations for TC genesis [such as equatorial Rossby waves (ERWs), the Madden–Julian oscillation (MJO), and El Niño–Southern Oscillation (ENSO)], all exhibit a stable value close to the climatological mean [~31 (100 days)−1]. However, PTCG increases (decreases) during the phases of positive-vorticity (negative-vorticity) ERWs, the active (inactive) MJO, and El Niño (La Niña) years. PTCG varies from 0.17 in the most unfavorable environment (La Niña, inactive MJO, and negative-vorticity ERW) to 0.56 in the most favorable environment (El Niño, active MJO, and positive-vorticity ERW). ERWs are most effective in modulating TC genesis, especially in the negative-vorticity phases. Overall, increased PTCG is facilitated with strong and elongated 850-hPa relative vorticity overlapping a cyclonic shear line pattern, while decreased PTCG is related to weak relative vorticity. Relative vorticity acts as the most important factor to modulate PTCG, when compared with vertical wind shear and 700-hPa relative humidity.

scholarly journals The roles of ENSO on the occurrence of abruptly recurving tropical cyclones over the Western North Pacific Ocean Basin

2006 ◽  
Vol 6 ◽  
pp. 139-148 ◽  
Author(s):  
N. K. W. Cheung
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
Pressure Field ◽  
El Nino ◽  
North Pacific Ocean ◽  
Ocean Basin ◽  
La Niña ◽  
La Nina

Abstract. The abruptly recurving tropical cyclones over the Western North Pacific Ocean Basin during El Niño and La Niña events are studied. Temporal and spatial variations of these anomalous tracks under different phases of ENSO are shown. The anomalies of the pressure field in relation to ENSO circulation for the occurrence of the abruptly recurving cyclone tracks are investigated using fuzzy method. These are supplemented by wind field analyses. It is found that the occurrence of recurving-left (RL) and recurving-right (RR) tropical cyclones under the modification of the steering currents, including the re-adjustment of the westerly trough, the expansion or contraction of the sub-tropical high pressure, the intensifying easterly flow and the strengthening of the cross-equatorial flow, can be in El Niño or La Niña events. Evidently, there is a higher chance of occurrence of anomalous tropical cyclone trajectories in El Niño rather than La Niña events, but there is not any pronounced spatial pattern of anomalous tropical cyclone tracks. By analyzing the pressure-field, it is seen RL (RR) tropical cyclones tend to occur when the subtropical high pressure is weak (strong) in El Niño and La Niña events. More importantly, how the internal force of tropical cyclones changed by the steering current, which relies upon the relative location of tropical cyclones to the re-adjustment of the weather systems, shows when and where RL and RR tropical cyclones occur in El Niño and La Niña events.

How Much Do Tropical Cyclones Affect Seasonal and Interannual Rainfall Variability over the Western North Pacific?

2009 ◽  
Vol 22 (20) ◽  
pp. 5495-5510 ◽  
Author(s):  
Hisayuki Kubota ◽  
Bin Wang
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Rainfall Variability ◽  
La Niña ◽  
Total Rainfall ◽  
La Nina ◽  
Interannual Rainfall Variability

Abstract The authors investigate the effects of tropical cyclones (TCs) on seasonal and interannual rainfall variability over the western North Pacific (WNP) by using rainfall data at 22 stations. The TC-induced rainfall at each station is estimated by using station data when a TC is located within the influential radius (1000 km) from the station. The spatial–temporal variability of the proportion of TC rainfall is examined primarily along the east–west island chain near 10°N (between 7° and 13°N) and the north–south island chain near 125°E (between 120° and 130°E). Along 10°N the seasonality of total rainfall is mainly determined by non-TC rainfall that is influenced by the WNP monsoon trough. The proportion of the TC rain is relatively low. During the high TC season from July to December, TC rainfall accounts for 30% of the total rainfall in Guam, 15%–23% in Koror and Yap, and less than 10% at other stations. In contrast, along 125°E where the WNP subtropical high is located, the TC rainfall accounts for 50%–60% of the total rainfall between 18° and 26°N during the peak TC season from July to October. In Hualien of Taiwan, TC rainfall exceeds 60% of the total rainfall. The interannual variability of the TC rainfall and total rainfall is primarily modulated by El Niño–Southern Oscillation (ENSO). Along 10°N, the ratio of TC rainfall versus total rainfall is higher than the climatology during developing and mature phases of El Niño (from March to the following January), whereas the ratio is below the climatology during the decaying phase of El Niño. The opposite is true for La Niña, except that the impact of La Niña is shorter in duration. Furthermore, in summer of El Niño developing years, the total seasonal rainfall increases primarily because of the increase of TC rainfall. In the ensuing autumn, an anticyclonic anomaly develops over the Philippine Sea and TC rainfall shifts eastward; as a result, the total rainfall over the Philippines and Taiwan decreases. The total rainfall to the east of 140°E, however, changes little, because the westward passage of TCs enhances TC rainfall, which offsets the decrease of non-TC rainfall. Along the meridional island chain between 120° and 130°E, the total rainfall anomaly is affected by ENSO starting from the autumn to the following spring, and the variation in TC rainfall dominates the total rainfall variation only in autumn (August–November) of ENSO years. The results from this study suggest that in the tropical WNP and subtropical East Asian monsoon regions (east of 120°E), the seasonal and interannual variations of rainfall are controlled by changes in nonlocal circulations. These changes outside the monsoon domain may substantially affect summer monsoon rainfall by changing TC genesis and tracks.

scholarly journals Characteristics of the Onset, Withdrawal, and Breaks of the Western North Pacific Summer Monsoon in the 1949–2014 Period

2020 ◽  
Vol 33 (17) ◽  
pp. 7371-7389
Author(s):  
Inmaculada Vega ◽  
Pedro Ribera ◽  
David Gallego
Keyword(s):  
Interannual Variability ◽  
Summer Monsoon ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
La Niña ◽  
Onset Date ◽  
Central Pacific ◽  
La Nina

ABSTRACTThe western North Pacific summer monsoon (WNPSM) onset and withdrawal dates as well as its breaks have been determined throughout the 1949–2014 period by defining the monsoon daily directional index (MDDI). This index, developed exclusively with wind direction observations, is an upgrade of the monthly western North Pacific directional index. The onset date shows a high interannual variability, varying between early May and early August, whereas the WNPSM withdrawal shows a lower interannual variability, occurring between October and mid-November. The MDDI reflects the multibreak character of the WNPSM. Breaks, which tend to last a few weeks, are more likely to happen from mid-August to early September and from late June to mid-July. This bimodal distribution shows decadal variability. In addition, the monsoon dates determined by the MDDI show very good agreement with relationships previously described in literature, such as the influence of tropical Pacific SST on the monsoon onset/withdrawal and changes in tropical cyclone (TC) tracks related to monsoon breaks. The WNPSM tends to start earlier (later) and finish later (earlier) under eastern Pacific (EP) La Niña (El Niño) conditions, especially from the 1980s on. Central Pacific (CP) ENSO is also associated with the monsoon withdrawal, which is advanced (delayed) under CP El Niño (La Niña). TCs tend to move from the Philippine Sea to the South China Sea during active monsoon days whereas they tend to reach higher latitudes during inactive monsoon days, especially in August and July.

scholarly journals Asymmetric Modulation of Western North Pacific Cyclogenesis by the Madden–Julian Oscillation under ENSO Conditions

2012 ◽  
Vol 25 (15) ◽  
pp. 5374-5385 ◽  
Author(s):  
Richard C. Y. Li ◽  
Wen Zhou ◽  
Johnny C. L. Chan ◽  
P. Huang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
La Niña ◽  
Western Region ◽  
Madden Julian Oscillation ◽  
Asymmetric Modulation ◽  
La Nina ◽  
The Western Region

Abstract The present study investigates the modulation by the Madden–Julian oscillation (MJO) and the impact of the El Niño–Southern Oscillation (ENSO) on tropical cyclone (TC) genesis in the western North Pacific (WNP) during the period 1975–2010. Results reveal a stronger modulation of cyclogenesis by the MJO during El Niño years, while the modulations in neutral and La Niña years are comparable to each other. The asymmetric background modification by ENSO is found to greatly affect the extent of MJO modulation under different ENSO conditions. First, MJO activity is intensified and extends farther eastward during El Niño years, instead of being confined west of 150°E as in neutral and La Niña periods. Thus, the influence of MJO is stronger and more zonally widespread in El Niño years, causing significant differences in cyclogenesis parameters in most parts of the WNP. In El Niño years, cyclogenesis is further enhanced in the active phase due to synchronization of MJO signals with favorable background ENSO conditions. While in the inactive phase, the dominance of the strong MJO signals leads to further suppression in TC formation. This leads to overall enhancement of the MJO–TC relationship during El Niño years. On the other hand, the MJO signals confined to the western region west of 150°E in neutral and La Niña years lead to changes in TC-related parameters mainly in the western region, which contribute to the comparatively weaker TC modulations. It can thus be concluded that the MJO has an asymmetric modulation on cyclogenesis in the WNP under different ENSO conditions.

scholarly journals Modulation of Boreal Summer Intraseasonal Oscillations over the Western North Pacific by ENSO

2016 ◽  
Vol 29 (20) ◽  
pp. 7189-7201 ◽  
Author(s):  
Fei Liu ◽  
Tim Li ◽  
Hui Wang ◽  
Li Deng ◽  
Yuanwen Zhang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Boreal Summer ◽  
Maritime Continent ◽  
La Nina

Abstract The authors investigate the effects of El Niño and La Niña on the intraseasonal oscillation (ISO) in the boreal summer (May–October) over the western North Pacific (WNP). It is found that during El Niño summers, the ISO is dominated by a higher-frequency oscillation with a period of around 20–40 days, whereas during La Niña summers the ISO is dominated by a lower-frequency period of around 40–70 days. The former is characterized by northwestward-propagating convection anomalies in the WNP, and the latter is characterized by northward- and eastward-propagating convective signals over the tropical Indian Ocean/Maritime Continent. The possible mechanisms through which El Niño–Southern Oscillation (ENSO)-induced background mean state changes influence the ISO behavior are examined through idealized numerical experiments. It is found that enhanced (weakened) mean moisture and easterly (westerly) vertical wind shear in the WNP during El Niño (La Niña) are the main causes of the strengthened (weakened) 20–40-day northwestward-propagating ISO mode, whereas the 40–70-day ISO initiated from the Indian Ocean can only affect the WNP during La Niña years because the dry (moist) background moisture near the Maritime Continent during El Niño (La Niña) suppresses (enhances) the ISO over the Maritime Continent, and the ISO propagates less over the Maritime Continent during El Niño years than in La Niña years.

ENSO-Modulated Cyclogenesis over the Bay of Bengal*

2013 ◽  
Vol 26 (24) ◽  
pp. 9806-9818 ◽  
Author(s):  
Clifford S. Felton ◽  
Bulusu Subrahmanyam ◽  
V. S. N. Murty
Keyword(s):  
Tropical Cyclone ◽  
Relative Humidity ◽  
El Niño ◽  
El Nino ◽  
Tropical Cyclone Activity ◽  
La Niña ◽  
Sea Surface ◽  
Cyclone Activity ◽  
La Nina ◽  
Sst Anomalies

Abstract The role of the El Niño–Southern Oscillation (ENSO) on the modulation of tropical cyclone activity over the Bay of Bengal (BoB) for the 1979–2011 period is examined. It is shown that Niño-3.4 sea surface temperature (SST) anomalies are negatively correlated with the BoB tropical cyclone activity to a statistically significant percentage by a lead time of 5 months. Composites of 10-m zonal winds exhibit greater variance during La Niña events, favoring the development of low-level cyclonic vorticity. Low vertical wind shear over the central and northern BoB also aids in the development of tropical cyclones during La Niña events. Increased relative humidity is the result of enhanced moisture transport and higher precipitable water under La Niña conditions. Furthermore, storm-relative composites of relative humidity show stronger moisture pulses over the BoB during La Niña. The enhanced moisture associated with tropical cyclogenesis likely aids in the development and strengthening of the systems. ENSO forces modulations in oceanic conditions as well. The observed negative (positive) SST anomalies during La Niña (El Niño) could be seen as the result of increased (decreased) net heat flux across the sea surface. Tropical cyclone activity varies between El Niño and La Niña as a result of anomalous wind and moisture patterns during each ENSO phase.

scholarly journals The Zonal Oscillation and the Driving Mechanisms of the Extreme Western North Pacific Subtropical High and Its Impacts on East Asian Summer Precipitation

2019 ◽  
Vol 32 (10) ◽  
pp. 3025-3050 ◽  
Author(s):  
Tat Fan Cheng ◽  
Mengqian Lu ◽  
Lun Dai
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
La Niña ◽  
Positive Phase ◽  
La Nina ◽  
Asian Summer ◽  
Zonal Oscillation

Abstract This paper scrutinizes the zonal oscillation of the western North Pacific subtropical high (WNPSH) via diagnosing its two extreme phases, which are defined by the top 10% strongest (positive phase) and the weakest (negative phase) WNPSH index (WNPSHI) days during summers in 1979–2016. Key findings include the following: a tripole pattern consisting of intensified (weakened) precipitation over the Maritime Continent and the East Asian summer monsoon regions, and suppressed (strengthened) precipitation over the western North Pacific summer monsoon region during positive (negative) WNPSH phases; a westward movement of WNPSH-induced precipitation anomalies that subsequently affects eastern China, Japan, and the Korean Peninsula at different time lags; an OLR–vorticity pattern explained by atmospheric responses to thermal sources is suggested to drive the oscillation; and the competitive interaction of local air–sea feedbacks, especially during the positive phase. In addition, moderate-to-strong positive correlations between the WNPSHI and the Niño-3.4 index are found on 1–2-, 2–3-, and 3–6-yr time scales; both exhibit decadal shifts to a higher-frequency mode, suggesting the intensification of both the zonal WNPSH oscillation and the ENSO under the changing climate and their close interdecadal association. A nonlinear quasi-biennial WNPSH–ENSO relationship is identified: the positive (negative) WNPSH phase sometimes occurs during 1) a decaying El Niño (La Niña) in the preceding summer/autumn, and/or 2) a developing La Niña (El Niño) in the current summer/autumn. A full ENSO transition from moderate-to-strong El Niño to La Niña is often seen during the positive phase, offering potential in predicting ENSO events and extreme WNPSH phases and thereby the summer monsoon rainfall in East Asia.

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