scholarly journals Structures and Northward Propagation of the Quasi-Biweekly Oscillation in the Western North Pacific

2020 ◽  
Vol 33 (16) ◽  
pp. 6873-6888
Author(s):  
Kuiping Li ◽  
Yang Yang ◽  
Lin Feng ◽  
Weidong Yu ◽  
Shouhua Liu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Remote Sensing Data ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Budget Analysis ◽  
Northward Propagation ◽  
Convention Center ◽  
Barotropic Vorticity ◽  
Sst Anomalies

AbstractThis study investigates the northward-propagating quasi-biweekly oscillation (QBWO) in the western North Pacific by examining the composite meridional structures. Using newly released reanalysis and remote sensing data, the northward propagation is understood in terms of the meridional contrasts in the planetary boundary layer (PBL) moisture and the column-integrated moist static energy (MSE). The meridional contrast in the PBL moisture, with larger values north of the convection center, is predominantly attributed to the moisture convergence associated with barotropic vorticity anomalies. A secondary contribution comes from the meridional moisture advection, for which advections by mean and perturbation winds are almost equally important. The meridional contrast in the MSE tendency, due to the recharge in the front of convection and discharge in the rear of convection, is jointly contributed by the meridional and vertical MSE advections. The meridional MSE advection mainly depends on the moisture processes particularly in the PBL, and the vertical MSE advection largely results from the advection of the mean MSE by vertical velocity anomalies, wherein the upper-troposphere ascending motion related to the stratiform heating in the rear of the convection plays the major role. In addition, partial feedback from sea surface temperature (SST) anomalies is evaluated on the basis of MSE budget analysis. SST anomalies tend to enhance the surface turbulent heat fluxes ahead of the convention center and suppress them behind the convention center, thus positively contributing approximately 20% of the meridional contrast in the MSE tendency.

scholarly journals An Examination of the Thermodynamic Impacts of Western North Pacific Tropical Cyclones on Their Tropical Tropospheric Environment

2015 ◽  
Vol 28 (19) ◽  
pp. 7529-7560 ◽  
Author(s):  
Benjamin A. Schenkel ◽  
Robert E. Hart
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Rossby Waves ◽  
Budget Analysis ◽  
Surface Latent Heat Flux ◽  
Static Energy ◽  
Thermodynamic Anomalies ◽  
Meridional Advection ◽  
Gas Effect ◽  
Sst Anomalies

Abstract The present study examines the tropospheric thermodynamic anomalies induced by western North Pacific tropical cyclone (TC) passage using storm-relative composites. Negative moist static energy (MSE) anomalies containing embedded westward-propagating anomalies generally occur only following larger TCs for two months following TC passage in a region extending from the domain center to ~3000 km to its west. Larger TCs force negative MSE anomalies likely because of feedbacks from stronger, broader TC-induced negative sea surface temperature (SST) anomalies and the excitation of TC-induced Rossby waves to the southeast of the TC. The negative MSE anomalies are composed of lower- and midtropospheric negative latent energy anomalies with smaller contributions from boundary layer and upper-tropospheric negative sensible heat anomalies. The lower- and midtropospheric negative MSE anomalies are forced by the TC, whereas the upper-tropospheric negative MSE anomalies are forced by the Madden–Julian oscillation. Vertically integrated MSE budgets at the domain center reveal negative MSE tendencies that are primarily forced by surface latent heat flux anomalies resulting from the TC-induced negative SST anomalies. Smaller negative MSE tendencies are due to 1) zonal and meridional advection of MSE anomalies by the Rossby waves and 2) enhanced top-of-the-atmosphere longwave radiative flux anomalies potentially associated with a reduction in the greenhouse gas effect of water vapor. The budget analysis in the west region is generally similar except that all terms are comparable in magnitude and relatively weaker. These results conservatively suggest that larger TCs can anomalously cool and dry their synoptic-scale environment for ~40 days following TC passage.

Role of Air–Sea Interaction in the 30–60-Day Boreal Summer Intraseasonal Oscillation over the Western North Pacific

2018 ◽  
Vol 31 (4) ◽  
pp. 1653-1680 ◽  
Author(s):  
Tianyi Wang ◽  
Xiu-Qun Yang ◽  
Jiabei Fang ◽  
Xuguang Sun ◽  
Xuejuan Ren
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Intraseasonal Oscillation ◽  
Phase Relationship ◽  
Heat Fluxes ◽  
Boreal Summer ◽  
Northern Portion ◽  
Sst Anomaly ◽  
Sst Anomalies

This study investigates the role of air–sea interaction in the 30–60-day boreal summer intraseasonal oscillation (BSISO) over the western North Pacific with daily outgoing longwave radiation (OLR), CFSR, and OAFlux datasets for 1985–2009. The BSISO events are identified with the first principal component of 30–60-day bandpass filtered OLR anomalies. Composite analysis of these events reveals that during the northward migration of BSISO, the convection can interact with underlying sea surface temperature (SST). A near-quadrature phase relationship exists between the convection and SST anomalies. An active (a suppressed) convection tends to induce a cold (warm) underlying SST anomaly by reducing (increasing) downward solar radiation but a warm SST anomaly in its northern (southern) portion by reducing near-surface wind and upward latent and sensible heat fluxes, resulting in a 10-day delayed maximized warm SST anomaly ahead of the active convection. In turn, this warm SST anomaly tends to increase upward surface sensible and latent heat fluxes via amplifying sea–air temperature and humidity differences. This oceanic feedback acts to heat, moisten, and destabilize the low-level atmosphere, favoring the trigger of shallow convection, which can further develop into deep convection. The maximum warm SST anomaly lies in the southern (northern) portion of the convectively suppressed (enhanced) area, which weakens the anomalous descending motion in the southern portion of convectively suppressed area and preconditions the boundary layer to promote convection development in the northern portion of convectively enhanced area. Such a spatial and temporal phase relationship between the convection and SST anomalies suggest that air–sea interaction can play a delayed negative feedback role in the BSISO cycle and provide an alternative mechanism responsible for its northward propagation.

scholarly journals Climatological Increased Precipitation from July to August in the Western North Pacific Region Simulated by CMIP6 Models

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 664
Author(s):  
Xiao Dong ◽  
Renping Lin
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Coupled Models ◽  
Model Simulations ◽  
Observational Analysis ◽  
Budget Analysis ◽  
Circulation Change ◽  
Precipitation Increase

In this study, the climatological precipitation increase from July to August over the western North Pacific (WNP) region was investigated through observations and simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6), atmospheric model simulations and historical experiments. Firstly, observational analysis showed that the precipitation increase is associated with a decrease in the local sea surface temperature (SST), indicating that the precipitation increase is not driven by the change in SST. In addition, the pattern of precipitation increase is similar to the vertical motion change at 500-hPa, suggesting that the precipitation increase is related to the circulation change. Moisture budget analysis further confirmed this relation. In addition to the observational analysis, the outputs from 26 CMIP6 models were further evaluated. Compared with atmospheric model simulations, air–sea coupled models largely improve the simulation of the climatological precipitation increase from July to August. Furthermore, model simulations confirmed that the bias in the precipitation increase is intimately associated with the circulation change bias. Thus, two factors are responsible for the bias of the precipitation increase from July to August in climate models: air–sea coupling processes and the performance in vertical motion change.

scholarly journals Reintensification of the Anomalous Western North Pacific Anticyclone during the El Niño Modoki Decaying Summer: Relative Importance of Tropical Atlantic and Pacific SST Anomalies

2020 ◽  
Vol 33 (8) ◽  
pp. 3271-3288
Author(s):  
Juan Feng ◽  
Wen Chen ◽  
Xiaocong Wang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
El Nino ◽  
Central Pacific ◽  
El Niño Modoki ◽  
Sst Cooling ◽  
Sst Warming ◽  
Sst Anomalies

AbstractThe El Niño Modoki–induced anomalous western North Pacific anticyclone (WNPAC) undergoes an interesting reintensification process in the El Niño Modoki decaying summer, the period when El Niño Modoki decays but warm sea surface temperature (SST) anomalies over the tropical North Atlantic (TNA) and cold SST anomalies over the central-eastern Pacific (CEP) dominate. In this study, the region (TNA or CEP) in which the SST anomalies exert a relatively important influence on reintensification of the WNPAC is investigated. Observational analysis demonstrates that when only anomalous CEP SST cooling occurs, the WNPAC experiences a weak reintensification. In contrast, when only anomalous TNA SST warming emerges, the WNPAC experiences a remarkable reintensification. Numerical simulation analysis demonstrates that even though the same magnitude of CEP SST cooling and TNA warming is respectively set to force the atmospheric general circulation model, the response of the WNPAC is still much stronger in the TNA warming experiment than in the CEP cooling experiment. Further analysis demonstrates that this difference is caused by the distinct location of the effective tropical forcing between the CEP SST cooling and TNA SST warming for producing a WNPAC. The CEP cooling-induced effective anomalous diabatic cooling is located in the central Pacific, by which the forced anticyclone becomes gradually weak from the central Pacific to the western North Pacific. Thus, a weak WNPAC is produced. In contrast, as the TNA SST warming–induced effective anomalous diabatic cooling is just located in the western North Pacific via a Kelvin wave–induced Ekman divergence process, the forced anticyclone is significant and powerful in the western North Pacific.

scholarly journals Contributions of SST Anomalies in the Indo-Pacific Ocean to the Interannual Variability of Tropical Cyclone Genesis Frequency over the Western North Pacific

2019 ◽  
Vol 32 (11) ◽  
pp. 3357-3372 ◽  
Author(s):  
Ruifen Zhan ◽  
Yuqing Wang ◽  
Jiuwei Zhao
Keyword(s):  
Pacific Ocean ◽  
Tropical Cyclone ◽  
Statistical Model ◽  
Interannual Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
Typhoon Season ◽  
Genesis Frequency ◽  
Sst Anomalies

Abstract This study attempts to evaluate quantitatively the contributions of sea surface temperature (SST) anomalies in the Indo-Pacific Ocean to the interannual variability of tropical cyclone (TC) genesis frequency (TCGF) over the western North Pacific (WNP). Three SST factors in the Indo-Pacific Ocean are found to play key roles in modulating the interannual variability of WNP TCGF. They are summer SST anomaly in the east Indian Ocean (EIO), the summer El Niño–Southern Oscillation Modoki index (EMI), and the spring SST gradient (SSTG) between the southwestern Pacific and the western Pacific warm pool. Results show that the three factors together can explain 72% of the total variance of WNP TCGF in the typhoon season for the period 1980–2015. Among them, the spring SSTG and the summer EIO contribute predominantly to the interannual variability of TCGF, followed by the summer EMI, with respective contributions being 39%, 38%, and 23%. Further analysis shows that the summer EMI was affected significantly by the spring SSTG and thus had a relatively lower contribution to the TCGF than the spring SSTG. In addition, a statistical model is constructed to predict the WNP TCGF in the typhoon season by a combination of the May EIO and the spring SSTG. The new model can reproduce well the observed WNP TCGF and shows an overall better skill than the ECMWF Seasonal Forecasting System 5 (SEAS5) hindcasts. This statistical model provides a good tool for seasonal prediction of WNP TCGF.

scholarly journals Two Distinctive Processes for Abnormal Spring to Summer Transition over the South China Sea

2017 ◽  
Vol 30 (23) ◽  
pp. 9665-9678 ◽  
Author(s):  
Renguang Wu ◽  
Zhuoqi He
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
The South China Sea ◽  
The South ◽  
Maritime Continent ◽  
China Sea ◽  
Tropical Western North Pacific ◽  
Sst Anomalies

The period from April to June signifies the transition from spring to summer over the South China Sea (SCS). The present study documents two distinct processes for abnormal spring to summer transition over the SCS. One process is related to large-scale sea surface temperature (SST) anomalies in the tropical Indo-Pacific region. During spring of La Niña decaying years, negative SST anomalies in the equatorial central Pacific (ECP) and the southwestern tropical Indian Ocean (TIO) coexist with positive SST anomalies in the tropical western North Pacific. Negative ECP SST anomalies force an anomalous Walker circulation, negative southwestern TIO SST anomalies induce anomalous cross-equatorial flows from there, and positive tropical western North Pacific SST anomalies produce a Rossby wave–type response to the west. Together, they contribute to enhanced convection and an anomalous lower-level cyclone over the SCS, leading to an advanced transition to summer there. The other process is related to regional air–sea interactions around the Maritime Continent. Preceding positive ECP SST anomalies induce anomalous descent around the Maritime Continent, leading to SST increase in the SCS and southeast TIO. An enhanced convection region moves eastward over the south TIO during spring and reaches the area northwest of Australia in May. This enhances descent over the SCS via an anomalous cross-equatorial overturning circulation and contributes to further warming in the SCS. The SST warming in turn induces convection over the SCS, leading to an accelerated transition to summer. Analysis shows that the above two processes are equally important during 1979–2015.

scholarly journals Accumulated Effect of Intra-Seasonal Oscillation Convections over the Tropical Western North Pacific on the Meridional Location of Western Pacific Subtropical High

2020 ◽  
Vol 8 ◽  
Author(s):  
Zongci Huang ◽  
Wenjun Zhang ◽  
Xin Geng ◽  
Pang-Chi Hsu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Late Summer ◽  
Western Pacific Subtropical High ◽  
Western Pacific ◽  
Subtropical High ◽  
Boreal Summer ◽  
Seasonal Oscillation ◽  
Tropical Western North Pacific ◽  
Sst Anomalies

An extreme northward displacement of the western Pacific subtropical high (WPSH) was detected during the boreal mid-late summer (July-August) of 2018, bringing record-breaking heat waves over northern East Asia. Negative sea surface temperature (SST) anomalies in the northern India Ocean (NIO) are usually accompanied with a northward shift of the WPSH. However, no prominent NIO SST anomalies were observed during the 2018 boreal summer. It is found that this extreme northward-shifted WPSH event is largely attributed to the accumulated effect of intra-seasonal oscillation (ISO) convection anomalies over the tropical western North Pacific (WNP). The accumulated effect on the WPSH meridional location is further supported by their significant correlation based on the data since 1979. While the relationship between the NIO SST anomalies and WPSH meridional location has substantially weakened since the late 1990s, the accumulated effect of the tropical WNP ISO convections keeps playing a crucial role in modulating the WPSH meridional displacement. The active WNP ISO activities can stimulates a poleward propagating Rossby wave train, which favors a northward shift of the WPSH. Our results suggest that the accumulated effect of the tropical WNP ISO convections should be considered when predicting the WPSH during the boreal mid-late summer season.

Concurrent Decadal Mesoscale Eddy Modulations in the Western North Pacific Subtropical Gyre

2013 ◽  
Vol 43 (2) ◽  
pp. 344-358 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Mesoscale Eddy ◽  
Subtropical Gyre ◽  
Altimeter Data ◽  
Upper Ocean ◽  
North Pacific Subtropical Gyre ◽  
Mode Water ◽  
Budget Analysis ◽  
Salinity Data

Abstract Satellite altimeter data of the past two decades are used to investigate the low-frequency mesoscale eddy variability inside the western North Pacific subtropical gyre. Eddy activity modulations with a decadal time scale are detected concurrently within the 18°–28°N band, including the three branches of the Subtropical Countercurrent (STCC) and the Hawaiian Lee Countercurrent (HLCC). Lagging behind the Pacific decadal oscillation (PDO) index by six months, enhanced eddy activities were detected in 1995–98 and 2003–06, whereas the eddy activities were below the average in 1999–2002 and 2009–11. Analysis of the temperature and salinity data that became available after 2001 via the International Argo Program reveals that the modulating eddy activities are due to the decadal change in the upper-ocean eastward shear in the broad-scale STCC–HLCC band. By conducting an upper-ocean temperature budget analysis, the authors found that this observed eastward shear change can be effectively accounted for by the decadal-varying surface heat flux forcing. Using the Argo-based temperature and salinity data, it is further found that the decadal subsurface potential vorticity (PV) signals to the north and beneath the STCC–HLCC were vertically coherent and not confined to the mode water isopycnals. Adjusting to the PDO-related surface forcing, these subsurface PV anomalies lagged behind the upper-ocean eastward shear signals and likely made minor contributions to generate the decadal-varying eddy signals observed in the western North Pacific subtropical gyre.

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