scholarly journals Influences of the Pacific–Japan Teleconnection Pattern on Synoptic-Scale Variability in the Western North Pacific

2014 ◽  
Vol 27 (1) ◽  
pp. 140-154 ◽  
Author(s):  
Richard C. Y. Li ◽  
Wen Zhou ◽  
Tim Li
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Wave Train ◽  
Circulation Model ◽  
Environmental Parameters ◽  
Teleconnection Pattern ◽  
Convective Heating ◽  
Synoptic Scale ◽  
The Pacific

Abstract This study investigates the influences of the Pacific–Japan (PJ) teleconnection pattern on synoptic-scale variability (SSV) in the western North Pacific (WNP). The PJ pattern exhibits salient intraseasonal variations, with a dominant peak at 10–50 days. During positive PJ phases, strengthened SSV is found in the WNP, with a much stronger and better organized synoptic wave train structure. Such a synoptic-scale wave train, however, is greatly weakened during negative PJ phases. Examination of the vertical profiles of the observational data suggests that environmental parameters are generally more (less) favorable for the growth of synoptic disturbances under positive (negative) PJ conditions. Observational results are further verified with an anomaly atmospheric general circulation model, which reveals faster (slower) growth of the synoptic-scale wave train when the environmental anomalies associated with positive (negative) PJ phases are incorporated into the summer mean state of the model. In addition, sensitivity experiments indicate that thermodynamic parameters of the planetary boundary layer (PBL) play a determining role in controlling the development of synoptic disturbances in the WNP. The increase (decrease) in background PBL moisture during positive (negative) PJ phases enhances (suppresses) perturbation moisture convergence and thus the convective heating associated with SSV, leading to strengthened (weakened) synoptic-scale activity in the WNP. Serving as potential seed disturbances for cyclogenesis, the strengthened (weakened) synoptic-scale activity may also contribute to the enhancement (suppression) in intraseasonal TC frequency during positive (negative) PJ phases.

scholarly journals Variability of Tropical Cyclone Frequency Over the Western North Pacific in 2018–2020

2021 ◽  
Vol 3 ◽  
Author(s):  
Tomomichi Ogata ◽  
Yuya Baba
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Circulation Model ◽  
Atmospheric Variability ◽  
Convection Scheme ◽  
Planetary Scale ◽  
Ensemble Simulations ◽  
Potential Index

In this study, we examine the tropical cyclone (TC) activity over the western North Pacific (WNP) in 2018–2020 and its relationship with planetary scale convection and circulation anomalies, which play an important role for TC genesis. To determine the sea surface temperature (SST)-forced atmospheric variability, atmospheric general circulation model (AGCM) ensemble simulations are executed along with the observed SST. For AGCM experiments, we use two different convection schemes to examine uncertainty in convective parameterization and robustness of simulated atmospheric response. The observed TC activity and genesis potential demonstrated consistent features. In our AGCM ensemble simulations, the updated convection scheme improves the simulation ability of observed genesis potential as well as planetary scale convection and circulation features, e.g., in September–October–November (SON), a considerable increase in the genesis potential index over the WNP in SON 2018, WNP in SON 2019, and South China Sea (SCS) in SON 2020, which were not captured in the Emanuel scheme, have been simulated in the updated convection scheme.

scholarly journals Boreal Summer Synoptic-Scale Waves over the Western North Pacific in Multimodel Simulations

2016 ◽  
Vol 29 (12) ◽  
pp. 4487-4508 ◽  
Author(s):  
Haikun Zhao ◽  
Xianan Jiang ◽  
Liguang Wu
Keyword(s):  
Spatial Pattern ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Climate Model ◽  
Climate Modeling ◽  
Active Role ◽  
General Circulation Models ◽  
Boreal Summer ◽  
Synoptic Scale

During boreal summer, vigorous synoptic-scale wave (SSW) activity, often evident as southeast–northwest-oriented wave trains, prevails over the western North Pacific (WNP). In spite of their active role for regional weather and climate, modeling studies on SSWs are rather limited. In this study, a comprehensive survey on climate model capability in representing the WNP SSWs is conducted by analyzing simulations from 27 recent general circulation models (GCMs). Results suggest that it is challenging for GCMs to realistically represent the observed SSWs. Only 2 models out of the 27 GCMs generally well simulate both the intensity and spatial pattern of the observed SSW mode. Plausible key processes for realistic simulations of SSW activity are further explored. It is illustrated that GCM skill in representing the spatial pattern of the SSW is highly correlated to its skill in simulating the summer mean patterns of the low-level convergence associated with the WNP monsoon trough and conversion from eddy available potential energy (EAPE) to eddy kinetic energy (EKE). Meanwhile, simulated SSW intensity is found to be significantly correlated to the amplitude of 850-hPa vorticity, divergence, and conversion from EAPE to EKE over the WNP. The observed modulations of SSW activity by the Madden–Julian oscillation are able to be captured in several model simulations.

scholarly journals Interannual Variations in Summer Precipitation in Southwest China: Anomalies in Moisture Transport and the Role of the Tropical Atlantic

2020 ◽  
Vol 33 (14) ◽  
pp. 5993-6007 ◽  
Author(s):  
Chaoxia Yuan ◽  
Mengzhou Yang
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Moisture Transport ◽  
General Circulation ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Circulation Model ◽  
Summer Precipitation ◽  
Tropical Atlantic ◽  
Anomalous Anticyclone

AbstractUsing a Lagrangian trajectory model, contributions of moisture from the Indian Ocean (IO), the South China Sea (SCS), the adjacent land region (LD), and the Pacific Ocean (PO) to interannual summer precipitation variations in southwestern China (SWC) are investigated. Results show that, on average, the IO, SCS, LD, and PO contribute 48.8%, 21.1%, 23.6%, and 3.7% of the total moisture release in SWC, respectively. In summers with the above-normal precipitation, moisture release from the IO and SCS increases significantly by 41.4% and 15.1%, respectively. In summers with below-normal precipitation, moisture release from the IO and SCS decreases significantly by 44.2% and 24.6%, respectively. In addition, the moisture anomalies from the four source regions together explain 86.5% of the total interannual variances of SWC summer precipitation, and the IO and SCS only can explain 75.7%. Variations in moisture transport from the IO, SCS, and LD to SWC are not independent of one another and are commonly influenced by the anomalous anticyclone in the western North Pacific Ocean, which enhances the moisture transport from the IO and SCS by the anomalous southwesterlies over its northwestern quadrant but reduces that from the LD east of SWC by the anomalous westerlies along its northern edge. Anomalous warming in the tropical Atlantic Ocean can modify the Walker circulation, induce anomalous descending motion over the central tropical Pacific, and excite the anomalous anticyclone in the western North Pacific as the classic Matsuno–Gill response. The observed impacts of the tropical Atlantic warming on the anomalous anticyclone and summer precipitation in SWC can be well reproduced in an atmospheric general circulation model.

scholarly journals Dynamics of the Coastal Oyashio and Its Seasonal Variation in a High-Resolution Western North Pacific Ocean Model

2010 ◽  
Vol 40 (6) ◽  
pp. 1283-1301 ◽  
Author(s):  
Kei Sakamoto ◽  
Hiroyuki Tsujino ◽  
Shiro Nishikawa ◽  
Hideyuki Nakano ◽  
Tatsuo Motoi
Keyword(s):  
Seasonal Variation ◽  
Pacific Ocean ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Maximum Velocity ◽  
Circulation Model ◽  
Okhotsk Sea ◽  
Resolution Model

Abstract The Coastal Oyashio (CO) carries the cold, fresh, and relatively light water mass called the Coastal Oyashio Water (COW) westward along the southeastern coast of Hokkaido in winter and spring. To investigate dynamics of the CO and its seasonal variation, model experiments are executed using a western North Pacific general circulation model with horizontal resolutions of approximately 2 and 6 km. The 2-km resolution model reproduces the properties of COW with temperature of 0°–2°C and salinity of 32.2–32.6 and reproduces its distribution. COW is less dense than offshore water by 0.2 kg m−3, and it forms a surface-to-bottom density front with a width of 10 km near the shelf break. The CO appears as a baroclinic jet current along the front with a maximum velocity of approximately 40 cm s−1. The velocity and density structures and the front location relative to bathymetry indicate that the CO can be understood in terms of a simplified dynamical model developed for the shelfbreak front in the Middle Atlantic Bight. In contrast to the 2-km resolution model, the 6-km model cannot realistically reproduce the COW distribution. This is because only the 2-km model can represent the sharp density structure of the shelfbreak front and the accompanying CO. The CO exists during the limited period from January to April. This is directly connected with seasonal variation of the COW inflow from the Okhotsk Sea to the North Pacific Ocean through the Nemuro and Kunashiri Straits, indicating that the seasonal variation of the CO is ultimately controlled by the variation of the circulation in the Okhotsk Sea induced by the monsoon.

scholarly journals Sensitivity of the Simulated Distributions of Water Masses, CFCs, and Bomb 14C to Parameterizations of Mesoscale Tracer Transports in a Model of the North Pacific

2006 ◽  
Vol 36 (3) ◽  
pp. 273-285 ◽  
Author(s):  
Yongfu Xu ◽  
Shigeaki Aoki ◽  
Koh Harada
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Circulation Model ◽  
Water Masses ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The North Pacific

Abstract A basinwide ocean general circulation model of the North Pacific Ocean is used to study the sensitivity of the simulated distributions of water masses, chlorofluorocarbons (CFCs), and bomb carbon-14 isotope (14C) to parameterizations of mesoscale tracer transports. Five simulations are conducted, including a run with the traditional horizontal mixing scheme and four runs with the isopycnal transport parameterization of Gent and McWilliams (GM). The four GM runs use different values of isopycnal and skew diffusivities. Simulated results show that the GM mixing scheme can help to form North Pacific Intermediate Water (NPIW). Greater isopycnal diffusivity enhances formation of NPIW. Although greater skew diffusivity can also generate NPIW, it makes the subsurface too fresh. Results from simulations of CFC uptake show that greater isopycnal diffusivity generates the best results relative to observations in the western North Pacific. The model generally underestimates the inventories of CFCs in the western North Pacific. The results from simulations of bomb 14C reproduce some observed features. Greater isopycnal diffusivity generates a longitudinal gradient of the inventory of bomb 14C from west to east, whereas greater skew diffusivity makes it reversed. It is considered that the ratio of isopycnal diffusivity to skew diffusivity is important. An increase in isopycnal diffusivity increases storage of passive tracers in the subtropical gyre.

Interactions between Boreal Summer Intraseasonal Oscillations and Synoptic-Scale Disturbances over the Western North Pacific. Part II: Apparent Heat and Moisture Sources and Eddy Momentum Transport*

2011 ◽  
Vol 24 (3) ◽  
pp. 942-961 ◽  
Author(s):  
Pang-Chi Hsu ◽  
Tim Li
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Wave Train ◽  
Intraseasonal Oscillation ◽  
Momentum Transport ◽  
Boreal Summer ◽  
Synoptic Scale ◽  
Mean Flow ◽  
The North ◽  
Intraseasonal Oscillations

Abstract The interactions between the boreal summer intraseasonal oscillation (ISO) and synoptic-scale variability (SSV) are investigated by diagnosing the atmospheric apparent heat source (Q1), apparent moisture sink (Q2), and eddy momentum transport. It is found that the synoptic Q1 and Q2 heating (cooling) anomalies are in phase with cyclonic (anticyclonic) vorticity disturbances, aligned in a southeast–northwest-oriented wave train pattern over the western North Pacific (WNP). The wave train is well organized and strengthened (loosely organized and weakened) during the ISO active (suppressed) phase. The nonlinearly rectified Q1 and Q2 fields due to the eddy–mean flow interaction account for 10%–30% of the total intraseasonal Q1 and Q2 variabilities over the WNP. During the ISO active (suppressed) phase, the nonlinearly rectified intraseasonal Q1 and Q2 heating (cooling) appear to the northwest of the ISO enhanced (suppressed) convection center, favoring the northwestward propagation of the ISO. A diagnosis of the zonal momentum budget shows that the eddy momentum flux convergence forces an intraseasonal westerly (easterly) tendency to the north of the ISO westerly (easterly) center during the ISO active (suppressed) phase. As a result, the eddy momentum transport may contribute to the northward propagation of the boreal summer ISO over the WNP.

scholarly journals Synoptic-Scale Influences on Tropical Cyclone Formation within the Western North Pacific Monsoon Trough

2015 ◽  
Vol 143 (9) ◽  
pp. 3421-3433 ◽  
Author(s):  
Huijun Zong ◽  
Liguang Wu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Low Frequency ◽  
Vertical Wind Shear ◽  
Monsoon Trough ◽  
Core Area ◽  
Convective Heating ◽  
Synoptic Scale ◽  
The Core

Abstract Tropical cyclones (TCs) always develop from synoptic-scale disturbances. While early studies suggested that the presence of synoptic-scale disturbances may enhance large-scale conditions for TC formation, recent studies argued that TC-precursor disturbances can establish a rotation-dominant area, which can play a crucial role in organizing convective activity and converting convective heating to rotational energy for storm-scale intensification. To demonstrate the synoptic-scale influence of TC-precursor disturbances, 91 TC formation events within the monsoon trough over the western North Pacific during 2000–10 were examined by separating TC-precursor disturbances from the low-frequency background. The composite analysis shows that the synoptic disturbances indeed enhance the mid- and low-level relative vorticity and convergence, but contribute little to reducing vertical wind shear. The dynamic composite that is conducted with respect to disturbance centers indicates that TC-precursor disturbances within the monsoon trough establish a rotation-dominant region with a radius of less than 550 km. The cyclonic rotation increases with time 72 h prior to TC formation and nearly all air particles keep recirculating in the core area with a radius of about 220 km. Analysis of a specific case suggests that vorticity increase occurs through the merger of mesoscale convective systems in the rotation-dominant area. The enhancing rotation in the core area may efficiently convert diabatic heating to kinetic energy for TC formation. Thus, it is suggested that the important role of TC-precursor disturbances in TC formation is the establishment of a limited, rotation-dominant area.

scholarly journals The Southwest China Flood of July 2018 and Its Causes

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 247 ◽  
Author(s):  
Lijuan Wang ◽  
Lin Wang ◽  
Yuyun Liu ◽  
Wei Gu ◽  
Peiqiang Xu ◽  
...  
Keyword(s):  
Rossby Wave ◽  
North Pacific ◽  
Western North Pacific ◽  
Southwest China ◽  
Wave Train ◽  
Western Pacific Subtropical High ◽  
Water Vapor Transport ◽  
Dynamical Condition ◽  
The Pacific ◽  
Rossby Wave Train

Excessive rainfall was observed over Southwest China in July 2018, leading to floods in several major tributaries of the Yangtze River and landslide and debris flow in the neighboring provinces. The rainfall during 7–11 July was unusually heavy and broke the record that can be traced back to 1961. The occurrence of the excessive rain can be attributed to the anomalous convection over the western North Pacific and the presence of a mid-latitude Rossby wave train. On one hand, the convection over the western North Pacific was anomalously strong in July 2018, and it could have excited the negative phase of the Pacific–Japan pattern and led to a northwestward shift of the western Pacific subtropical high. Hence, the water vapor transport toward inland China including Southwest China was enhanced, providing a favorable moisture environment for precipitation. On the other hand, a mid-latitude Rossby wave train was observed to propagate from Northern Europe towards East Asia, which was conducive to anomalous ascending motion over Southwest China via warm advection and differential vorticity advection, creating a favorable dynamical condition for precipitation. As a result, the combination of the two effects mentioned above led to the occurrence of the flood over Southwest China in July 2018.

scholarly journals Atlantic multidecadal oscillation drives interdecadal Pacific variability via tropical atmospheric bridge

2021 ◽  
pp. 1-46
Author(s):  
Xiaohe An ◽  
Bo Wu ◽  
Tianjun Zhou ◽  
Bo Liu
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Circulation Model ◽  
Atlantic Multidecadal Oscillation ◽  
Tropical Pacific ◽  
Convective Heating ◽  
The North ◽  
The North Pacific ◽  
Sst Anomalies ◽  
The Tropical Pacific

AbstractInterdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Oscillation (AMO), two leading modes of decadal climate variability, are not independent. It was proposed that ENSO-like sea surface temperature (SST) variations play a central role in the Pacific responses to the AMO forcing. However, observational analyses indicate that the AMO-related SST anomalies in the tropical Pacific are far weaker than those in the extratropical North Pacific. Here, we show that SST in the North Pacific is tied to the AMO forcing by convective heating associated with precipitation over the tropical Pacific, instead of by SST there, based on an ensemble of pacemaker experiments with North Atlantic SST restored to the observation in a coupled general circulation model. The AMO modulates precipitation over the equatorial and tropical southwestern Pacific through exciting an anomalous zonal circulation and an interhemispheric asymmetry of net moist static energy input into the atmosphere. The convective heating associated with the precipitation anomalies drive SST variations in the North Pacific through a teleconnection, but remarkably weaken the ENSO-like SST anomalies through a thermocline damping effect. This study has implications that the IPO is a combined mode generated by both AMO forcing and local air-sea interactions, but the IPO-related global-warming acceleration/slowdown is independent of the AMO.

Future Change of Western North Pacific Typhoons: Projections by a 20-km-Mesh Global Atmospheric Model*

2011 ◽  
Vol 24 (4) ◽  
pp. 1154-1169 ◽  
Author(s):  
Hiroyuki Murakami ◽  
Bin Wang ◽  
Akio Kitoh
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Japan Meteorological Agency ◽  
Global Atmospheric Model ◽  
Meteorological Research Institute

Abstract Projected future changes in tropical cyclone (TC) activity over the western North Pacific (WNP) under the Special Report on Emissions Scenarios (SRES) A1B emission scenario were investigated using a 20-km-mesh, very-high-resolution Meteorological Research Institute (MRI)–Japan Meteorological Agency (JMA) atmospheric general circulation model. The present-day (1979–2003) simulation yielded reasonably realistic climatology and interannual variability for TC genesis frequency and tracks. The future (2075–99) projection indicates (i) a significant reduction (by about 23%) in both TC genesis number and frequency of occurrence primarily during the late part of the year (September–December), (ii) an eastward shift in the positions of the two prevailing northward-recurving TC tracks during the peak TC season (July–October), and (iii) a significant reduction (by 44%) in TC frequency approaching coastal regions of Southeast Asia. The changes in occurrence frequency are due in part to changes in large-scale steering flows, but they are due mainly to changes in the locations of TC genesis; fewer TCs will form in the western portion of the WNP (west of 145°E), whereas more storms will form in the southeastern quadrant of the WNP (10°–20°N, 145°–160°E). Analysis of the genesis potential index reveals that the reduced TC genesis in the western WNP is due mainly to in situ weakening of large-scale ascent and decreasing midtropospheric relative humidity, which are associated with the enhanced descent of the tropical overturning circulation. The analysis also indicates that enhanced TC genesis in the southeastern WNP is due to increased low-level cyclonic vorticity and reduced vertical wind shear. These changes appear to be critically dependent on the spatial pattern of future sea surface temperature; therefore, it is necessary to conduct ensemble projections with a range of SST spatial patterns to understand the degree and distribution of uncertainty in future projections.

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