scholarly journals Subtropical Cyclogenesis over the Central North Pacific*

2006 ◽  
Vol 21 (2) ◽  
pp. 193-205 ◽  
Author(s):  
Steven J. Caruso ◽  
Steven Businger
Keyword(s):  
Interannual Variability ◽  
North Pacific ◽  
Southern Oscillation ◽  
North Pacific Ocean ◽  
Baroclinic Instability ◽  
Cool Season ◽  
Central Pacific ◽  
Surface Development ◽  
Upper Level ◽  
Central North Pacific

Abstract The occurrence of subtropical cyclones over the central North Pacific Ocean has a significant impact on Hawaii’s weather and climate. In this study, 70 upper-level lows that formed during the period 1980–2002 are documented. In each case the low became cut off from the polar westerlies south of 30°N over the central Pacific, during the Hawaiian cool season (October–April). The objectives of this research are to document the interannual variability in the occurrence of upper-level lows, to chart the locations of their genesis and their tracks, and to investigate the physical mechanisms important in associated surface development. Significant interannual variability in the occurrence of upper-level lows was found, with evidence suggesting the influence of strong El Niño–Southern Oscillation events on the frequency of subtropical cyclogenesis in this region. Of the 70 upper-level lows, 43 were accompanied by surface cyclogenesis and classified as kona lows. Kona low formation is concentrated to the west-northwest of Hawaii, especially during October and November, whereas lows without surface development are concentrated in the area to the east-northeast of Hawaii. Kona low genesis shifts eastward through the cool season, favoring the area to the east-northeast of Hawaii during February and March, consistent with a shift in the climatological position of the trough aloft during the cool season. Consistent with earlier studies, surface deepening is well correlated with positive vorticity advection by the thermal wind. Static stability and advection of low-level moisture are less well correlated to surface deepening. These results suggest that kona low formation, to first order, is a baroclinic instability that originates in the midlatitudes, and that convection and latent-heat release play a secondary role in surface cyclogenesis.

Interannual Variability of the North Pacific Subtropical Countercurrent and Its Associated Mesoscale Eddy Field

2010 ◽  
Vol 40 (1) ◽  
pp. 213-225 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
North Pacific ◽  
Southern Oscillation ◽  
North Pacific Ocean ◽  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Vertical Shear ◽  
North Equatorial Current ◽  
Altimeter Data ◽  
Subtropical Countercurrent ◽  
Eddy Field

Abstract Interannual changes in the mesoscale eddy field along the Subtropical Countercurrent (STCC) band of 18°–25°N in the western North Pacific Ocean are investigated with 16 yr of satellite altimeter data. Enhanced eddy activities were observed in 1996–98 and 2003–08, whereas the eddy activities were below average in 1993–95 and 1999–2002. Analysis of repeat hydrographic data along 137°E reveals that the vertical shear between the surface eastward-flowing STCC and the subsurface westward-flowing North Equatorial Current (NEC) was larger in the eddy-rich years than in the eddy-weak years. By adopting a 2½-layer reduced-gravity model, it is shown that the increased eddy kinetic energy level in 1996–98 and 2003–08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the STCC–NEC’s background flow. The cause for the STCC–NEC’s interannually varying vertical shear can be sought in the forcing by surface Ekman temperature gradient convergence within the STCC band. Rather than El Niño–Southern Oscillation signals as previously hypothesized, interannual changes in this Ekman forcing field, and hence the STCC–NEC’s vertical shear, are more related to the negative western Pacific index signals.

scholarly journals Role of climate variability in the potential predictability of tropical cyclone formation in tropical and subtropical western North Pacific Ocean

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Yu-Lin K. Chang ◽  
Yasumasa Miyazawa ◽  
Swadhin Behera
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
North Pacific Ocean ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Potential Predictability ◽  
Vorticity Anomaly ◽  
Tropical Western North Pacific

AbstractThe out of phase tropical cyclone (TC) formation in the subtropical and tropical western North Pacific associated with local low-level wind vorticity anomaly, driven by the remote central and eastern equatorial Pacific warming/cooling, is investigated based on the reanalysis and observational data in the period of 1979−2017. TC frequencies in the subtropical and tropical western North Pacific appear to be connected to different remote heating/cooling sources and are linked to eastern and central Pacific warming/cooling, which are in turn related to canonical El Niño/Southern Oscillation (ENSO) and ENSO Modoki, respectively. TCs formed in subtropics (SfTC) are generally found to be associated with a dipole in wind vorticity anomaly, which is driven by the tropical eastern Pacific warming/cooling. Tropically formed TCs (TfTC) are seen to be triggered by the single-core of wind vorticity anomaly locally associated with the warming/cooling of central and eastern Pacific. The predicted ENSOs and ENSO Modokis, therefore, provide a potential source of seasonal predictability for SfTC and TfTC frequencies.

scholarly journals An Assessment of Multimodel Simulations for the Variability of Western North Pacific Tropical Cyclones and Its Association with ENSO

2016 ◽  
Vol 29 (18) ◽  
pp. 6401-6423 ◽  
Author(s):  
Rongqing Han ◽  
Hui Wang ◽  
Zeng-Zhen Hu ◽  
Arun Kumar ◽  
Weijing Li ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Tropical Cyclones ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Annual Number ◽  
Central Pacific ◽  
Cp El Niño

Abstract An assessment of simulations of the interannual variability of tropical cyclones (TCs) over the western North Pacific (WNP) and its association with El Niño–Southern Oscillation (ENSO), as well as a subsequent diagnosis for possible causes of model biases generated from simulated large-scale climate conditions, are documented in the paper. The model experiments are carried out by the Hurricane Work Group under the U.S. Climate Variability and Predictability Research Program (CLIVAR) using five global climate models (GCMs) with a total of 16 ensemble members forced by the observed sea surface temperature and spanning the 28-yr period from 1982 to 2009. The results show GISS and GFDL model ensemble means best simulate the interannual variability of TCs, and the multimodel ensemble mean (MME) follows. Also, the MME has the closest climate mean annual number of WNP TCs and the smallest root-mean-square error to the observation. Most GCMs can simulate the interannual variability of WNP TCs well, with stronger TC activities during two types of El Niño—namely, eastern Pacific (EP) and central Pacific (CP) El Niño—and weaker activity during La Niña. However, none of the models capture the differences in TC activity between EP and CP El Niño as are shown in observations. The inability of models to distinguish the differences in TC activities between the two types of El Niño events may be due to the bias of the models in response to the shift of tropical heating associated with CP El Niño.

Development of a Long-Range Lightning Detection Network for the Pacific: Construction, Calibration, and Performance*

2009 ◽  
Vol 26 (2) ◽  
pp. 145-166 ◽  
Author(s):  
Antti T. Pessi ◽  
Steven Businger ◽  
K. L. Cummins ◽  
N. W. S. Demetriades ◽  
M. Murphy ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Long Range ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Cloud Microphysics ◽  
Lightning Flash ◽  
Central Pacific ◽  
The North ◽  
Lightning Detection ◽  
Central North Pacific

Abstract The waveguide between the earth’s surface and the ionosphere allows very low-frequency (VLF) emissions generated by lightning, called sferics, to propagate over long distances. The new Pacific Lightning Detection Network (PacNet), as a part of a larger long-range lightning detection network (LLDN), utilizes this attribute to monitor lightning activity over the central North Pacific Ocean with a network of ground-based lightning detectors that have been installed on four widely spaced Pacific islands (400–3800 km). PacNet and LLDN sensors combine both magnetic direction finding (MDF) and time-of-arrival (TOA)-based technology to locate a strike with as few as two sensors. As a result, PacNet/LLDN is one of the few observing systems, outside of geostationary satellites, that provides continuous real-time data concerning convective storms throughout a synoptic-scale area over the open ocean. The performance of the PacNet/LLDN was carefully assessed. Long-range lightning flash detection efficiency (DE) and location accuracy (LA) models were developed with reference to accurate data from the U.S. National Lightning Detection Network (NLDN). Model calibration procedures are detailed, and comparisons of model results with lightning observations from the PacNet/LLDN in correlation with NASA’s Lightning Imaging Sensor (LIS) are presented. The daytime and nighttime flash DE in the north-central Pacific is in the range of 17%–23% and 40%–61%, respectively. The median LA is in the range of 13–40 km. The results of this extensive analysis suggest that the DE and LA models are reasonably able to reproduce the observed performance of PacNet/LLDN. The implications of this work are that the DE and LA model outputs can be used in quantitative applications of the PacNet/LLDN over the North Pacific Ocean and elsewhere. For example, by virtue of the relationship between lightning and rainfall rates, these data also hold promise as input for NWP models as a proxy for latent heat release in convection. Moreover, the PacNet/LLDN datastream is useful for investigations of storm morphology and cloud microphysics over the central North Pacific Ocean. Notably, the PacNet/LLDN lightning datastream has application for planning transpacific flights and nowcasting of squall lines and tropical storms.

Growth and spatiotemporal distribution of juvenile shortfin mako (Isurus oxyrinchus) in the western and central North Pacific

2015 ◽  
Vol 66 (12) ◽  
pp. 1176 ◽  
Author(s):  
M. Kai ◽  
K. Shiozaki ◽  
S. Ohshimo ◽  
K. Yokawa
Keyword(s):  
North Pacific ◽  
Linear Models ◽  
North Pacific Ocean ◽  
Age Groups ◽  
Growth Curves ◽  
Growth Function ◽  
Gaussian Mixture ◽  
Isurus Oxyrinchus ◽  
Shortfin Mako ◽  
Central North Pacific

This paper presents an estimation of growth curves and spatiotemporal distributions of juvenile shortfin mako shark (Isurus oxyrinchus) in the western and central North Pacific Ocean using port sampling data collected from 2005 to 2013. The monthly length compositions show a clear transition of three modes in the size range of smaller than 150-cm precaudal length (PCL), which were believed to represent the growth of age-0 to age-2 classes, and they were then decomposed into age groups by fitting a Gaussian mixture distribution. Simulation data of lengths at monthly ages were generated from the mean and standard deviation of each distribution, and fit with a von Bertalanffy growth function. Parameters of the estimated growth curves for males and females were 274.4 and 239.4cm PCL for the asymptotic length and 0.19 and 0.25 year–1 for the growth coefficient indicating apparently faster growth than previously reported. Generalised linear models were applied to age-0 to explore the seasonal changes of PCL by area. They were born during late autumn and winter off the coast of north-eastern Japan, an area known to have relatively high productivity compared with other pelagic areas, and gradually expanded their habitat eastward and northward with the seasons as they grew.

scholarly journals Observations of Upper-Tropospheric Influence on a Monsoon Trough over the Western North Pacific

2014 ◽  
Vol 142 (4) ◽  
pp. 1472-1488 ◽  
Author(s):  
Biao Geng ◽  
Kunio Yoneyama ◽  
Ryuichi Shirooka
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Low Pressure ◽  
Monsoon Trough ◽  
Pressure Cell ◽  
Intensive Observations ◽  
Upper Level ◽  
Synoptic Observations ◽  
Eastern Edge

Abstract This study examined the synoptic evolution and internal structure of a monsoon trough in association with the deep equatorward intrusion of a midlatitude upper trough in the western North Pacific Ocean in June 2008. The study was based on data from routine synoptic observations and intensive observations conducted on board the research vessel Mirai at 12°N, 135°E. The monsoon trough was first observed to extend southeastward from the center of a tropical depression. It then moved northward, with its eastern edge moving faster and approaching a surface low pressure cell induced by the upper trough. The distinct northward migration caused the monsoon trough to become oriented from the southwest to the northeast. The monsoon trough merged with the surface low pressure cell and extended broadly northeastward. The passage of the monsoon trough over the Mirai was accompanied by lower pressure, higher air and sea surface temperature, and minimal rainfall. The monsoon trough extended upward to nearly 500 hPa and sloped southward with height. It was overlain by northwesterly winds, negative geopotential height and temperature anomalies, and extremely dry air in the upper troposphere. Precipitation systems were weak and scattered near the monsoon trough but were intense and extensive south of the surface monsoon trough, where intense low-level convergence and upper-level divergence caused deep and vigorous upward motion. It appears that the upper trough exerted important impacts on the development of both the monsoon trough and associated precipitation, which are discussed according to the observational results.

Recent intensified influence of the winter North Pacific sea surface temperature on the withdrawal date of Meiyu

2021 ◽  
pp. 1-53
Author(s):  
Hua Li ◽  
Shengping He ◽  
Ke Fan ◽  
Yong Liu ◽  
Xing Yuan
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Interannual Variability ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Sea Surface ◽  
The North ◽  
Time Period ◽  
The North Pacific ◽  
Sst Anomalies

AbstractThe Meiyu withdrawal date (MWD) is a crucial indicator of flood/drought conditions over East Asia. It is characterized by a strong interannual variability, but its underlying mechanism remains unknown. We investigated the possible effects of the winter sea surface temperature (SST) in the North Pacific Ocean on the MWD on interannual to interdecadal timescales. Both our observations and model results suggest that the winter SST anomalies associated with the MWD are mainly contributed by a combination of the first two leading modes of the winter SST in the North Pacific, which have a horseshoe shape (the NPSST). The statistical results indicate that the intimate linkage between the NPSST and the MWD has intensified since the early 1990s. During the time period 1990–2016, the NPSST-related SST anomalies persisted from winter to the following seasons and affected the SST over the tropical Pacific in July. Subsequently, the SST anomalies throughout the North Pacific strengthened the southward migration of the East Asian jet stream (EAJS) and the southward and westward replacement of the western North Pacific subtropical high (WPSH), leading to an increase in Meiyu rainfall from July 1 to 20. More convincingly, the anomalous EAJS and WPSH induced by the SST anomalies can be reproduced well by numerical simulations. By contrast, the influence of the NPSST on the EASJ and WPSH were not clear between 1961 and 1985. This study further illustrates that the enhanced interannual variability of the NPSST may be attributed to the more persistent SST anomalies during the time period 1990–2016.

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