On the relationship between ENSO and tropical cyclones in the western North Pacific during the boreal summer

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.

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Rossby Wave Initiation by Recurving Tropical Cyclones in the Western North Pacific

Monthly Weather Review ◽

10.1175/mwr-d-17-0219.1 ◽

2018 ◽

Vol 146 (5) ◽

pp. 1283-1301 ◽

Cited By ~ 7

Author(s):

Jacopo Riboldi ◽

Matthias Röthlisberger ◽

Christian M. Grams

Keyword(s):

Ab Initio ◽

Tropical Cyclones ◽

Rossby Wave ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Rossby Waves ◽

Boreal Summer ◽

Large Scale Flow ◽

Upper Level Jet

Abstract The interaction of recurving tropical cyclones (TCs) with midlatitude Rossby waves during extratropical transition (ET) can significantly alter the midlatitude flow configuration. This study provides a climatological investigation of Rossby wave initiation (RWI) by transitioning TCs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during ET. Recurving TCs interacting with a zonally oriented waveguide in the western North Pacific (WNP) basin from 1979 to 2013 are categorized into cases initiating Rossby waves (TC-RWI) or not (TC-noRWI). Interactions with a zonally oriented waveguide occurred for 22.7% of the recurving TCs, and one-third of these resulted in TC-RWI. In the presence of a TC, the probability of RWI on a zonally oriented waveguide is 3 times larger than in situations without a TC. The occurrence of TC-RWI exhibits a seasonality and is relatively more common during boreal summer than in autumn. We further reveal that a strong preexisting upper-level jet stream, embedded in a deformative large-scale flow pattern, hinders TC-RWI as air from the diabatic outflow of the TC is rapidly advected downstream and does not lead to strong ridge building. In contrast, an enhanced monsoon trough favors TC-RWI as the poleward moisture transport strengthens diabatic outflow and leads to strong ridge building during ET. Thus, we conclude that TC-related ab initio flow amplification over the WNP is governed by characteristics of the large-scale flow more so than by characteristics of the recurving TC.

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Possible Influence of Tropical Indian Ocean Sea Surface Temperature on the Proportion of Rapidly Intensifying Western North Pacific Tropical Cyclones during the Extended Boreal Summer

Journal of Climate ◽

10.1175/jcli-d-20-0087.1 ◽

2020 ◽

Vol 33 (21) ◽

pp. 9129-9143

Author(s):

Jun Gao ◽

Haikun Zhao ◽

Philip J. Klotzbach ◽

Chao Wang ◽

Graciela B. Raga ◽

...

Keyword(s):

Global Warming ◽

Indian Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Tropical Indian Ocean ◽

Sea Surface ◽

Boreal Summer

AbstractThis study examines the possible impact of tropical Indian Ocean (TIO) sea surface temperature anomalies (SSTAs) on the proportion of rapidly intensifying tropical cyclones (PRITC) over the western North Pacific (WNP) during the extended boreal summer (July–November). There is a robust interannual association (r = 0.46) between TIO SSTAs and WNP PRITC during 1979–2018. Composite analyses between years with warm and cold TIO SSTAs confirm a significant impact of TIO SSTA on WNP PRITC, with PRITC over the WNP basin being 50% during years with warm TIO SSTAs and 37% during years with cold TIO SSTAs. Tropical cyclone heat potential appears to be one of the most important factors in modulating the interannual change of PRITC over the WNP with a secondary role from midlevel moisture changes. Interannual changes in these large-scale factors respond to SSTA differences characterized by a tropics-wide warming, implying a possible global warming amplification on WNP PRITC. The possible footprint of global warming amplification of the TIO is deduced from 1) a significant correlation between TIO SSTAs and global mean SST (GMSST) and a significant linear increasing trend of GMSST and TIO SSTAs, and 2) an accompanying small difference of PRITC (~8%) between years with detrended warm and cold TIO SSTAs compared to the difference of PRITC (~13%) between years with nondetrended warm and cold TIO SSTAs. Global warming may contribute to increased TCHP, which is favorable for rapid intensification, but increased vertical wind shear is unfavorable for TC genesis, thus amplifying WNP PRITC.

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A Note on the Relationship between Maximum Surface Wind and Central Pressure in Tropical Cyclones in Western North Pacific

Journal of the Meteorological Society of Japan Ser II ◽

10.2151/jmsj1965.57.4_358 ◽

1979 ◽

Vol 57 (4) ◽

pp. 358-361 ◽

Cited By ~ 1

Author(s):

I. Subbaramayya ◽

S. Fujiwhara

Keyword(s):

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Surface Wind ◽

Central Pressure ◽

Maximum Surface ◽

The Relationship

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Prediction Errors of Tropical Cyclones in the Western North Pacific in the Met Office Global Forecast Model

Weather and Forecasting ◽

10.1175/waf-d-19-0005.1 ◽

2019 ◽

Vol 34 (5) ◽

pp. 1189-1209 ◽

Cited By ~ 5

Author(s):

K. I. Hodges ◽

N. P. Klingaman

Keyword(s):

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Boreal Summer ◽

Lead Times ◽

Forecast Errors ◽

Deterministic System ◽

Ensemble Spread ◽

Location Errors ◽

Ensemble Systems

Abstract The prediction of tropical cyclones (TCs) in the western North Pacific (WNP) and the Philippines Area of Responsibility (PAR) has been explored in the Met Office (UKMO) global forecasting system over a 10-yr period at 0–7-day lead times. Both the high-resolution deterministic and lower-resolution ensemble systems have been considered. Location errors for verification against the observations are comparable for the deterministic, control, and ensemble mean forecasts; however, the ensemble spread indicates the ensemble is underdispersive. Intensity error metrics, for pressure and surface winds, show large biases relative to the observations, with the smallest biases for the deterministic system. For the intensity metrics the ensemble spread shows the ensemble is severely underdispersive primarily due to the large errors relative to the observations. Verification against the analyses shows similar results to verification against the observations for location. This is also the case for the intensities albeit with smaller errors and less underdispersion. The PAR region has larger intensity errors and biases and larger intensity ensemble spread compared with the broader WNP region. Forecast errors for location and intensity have reduced significantly with system upgrades over the period studied (2008–17) for the deterministic and ensemble systems. Intensity errors for the latest configuration of the deterministic system at day 4 are smaller than the initial errors of all the earlier configurations for both pressure and winds. The Madden–Julian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) significantly affect the intensity forecast errors, but not the location errors. Intensity errors are lower at the initiation and for early lead times of the forecasts started in phases 6–7 and 7–8, when the MJO and BSISO are active in the WNP. These reduced errors appear to result mainly from the variations in intensity of the observed storms with MJO and BSISO phases, though the initial states of the forecasts are also affected. Over the studied period, the European Centre for Medium-Range Weather Forecasts (ECMWF) deterministic and ensemble systems have lower errors and biases for both location and intensity than the UKMO forecast systems.

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Factors of boreal summer latent heat flux variations over the tropical western North Pacific

Climate Dynamics ◽

10.1007/s00382-021-05835-4 ◽

2021 ◽

Author(s):

Yuqi Wang ◽

Renguang Wu

Keyword(s):

Heat Flux ◽

Wind Speed ◽

North Pacific ◽

High Frequency ◽

Western North Pacific ◽

Surface Wind ◽

Low Frequency ◽

Boreal Summer ◽

Wind Intensity ◽

Tropical Western North Pacific

AbstractSurface latent heat flux (LHF) is an important component in the heat exchange between the ocean and atmosphere over the tropical western North Pacific (WNP). The present study investigates the factors of seasonal mean LHF variations in boreal summer over the tropical WNP. Seasonal mean LHF is separated into two parts that are associated with low-frequency (> 90-day) and high-frequency (≤ 90-day) atmospheric variability, respectively. It is shown that low-frequency LHF variations are attributed to low-frequency surface wind and sea-air humidity difference, whereas high-frequency LHF variations are associated with both low-frequency surface wind speed and high-frequency wind intensity. A series of conceptual cases are constructed using different combinations of low- and high-frequency winds to inspect the respective effects of low-frequency wind and high-frequency wind amplitude to seasonal mean LHF variations. It is illustrated that high-frequency wind fluctuations contribute to seasonal high-frequency LHF only when their intensity exceeds the low-frequency wind speed under which there is seasonal accumulation of high-frequency LHF. When high-frequency wind intensity is smaller than the low-frequency wind speed, seasonal mean high-frequency LHF is negligible. Total seasonal mean LHF anomalies depend on relative contributions of low- and high-frequency atmospheric variations and have weak interannual variance over the tropical WNP due to cancellation of low- and high-frequency LHF anomalies.

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