Seasonal Variation of the Surface Kuroshio Intrusion into the South China Sea Evidenced by Satellite Geostrophic Streamlines

2021 ◽  
Author(s):  
Yisen Zhong ◽  
Meng Zhou ◽  
Joanna J. Waniek ◽  
Lei Zhou ◽  
Zhaoru Zhang
Keyword(s):  
Lateral Wall ◽  
Reanalysis Data ◽  
Frictional Stress ◽  
Kuroshio Intrusion ◽  
Wind Stress Curl ◽  
Positive Vorticity ◽  
Seasonal Characteristics ◽  
Axis Position ◽  
The Kuroshio

AbstractThe long-term satellite altimeter and reanalysis data show that large seasonal variations are associated with geostrophic Kuroshio intrusion, but not with the current intensity, width and axis position east of Philippine. To address this issue, we examine the seasonal variability of surface intrusion patterns by a new streamline-based method. The along-streamline analysis reveals that the seasonality of geostrophic intrusion is only attributed to the cyclonic shear part of the flow, while the anticyclonic shear part always leaps across the Luzon Strait. A possible physical mechanism is proposed to accommodate these seasonal characteristics based on globally the vorticity (torque work) balance between the basin-wide negative wind stress curl and the positive vorticity fluxes induced by the lateral wall, as well as locally loss of balance between the torques of frictional stresses and normal stresses owing to the boundary gap. Through modifying the nearshore sea surface level, the northeasterly/southeasterly monsoon increases/decreases the positive vorticity fluxes in response to global vorticity balance, and simultaneously amplifies/alleviates the local imbalance by enhancing/reducing the positive frictional stress torque within the cyclonic shear layer. Therefore, in winter when the positive torque is large enough, the Kuroshio splits and the intrusion occurs, while in summer the stress torque is so weak that the entire current keeps flowing north.

scholarly journals A Strong Kuroshio Intrusion into the South China Sea and Its Accompanying Cold-Core Anticyclonic Eddy in Winter 2020–2021

2021 ◽  
Vol 13 (14) ◽  
pp. 2645
Author(s):  
Zhenyu Sun ◽  
Jianyu Hu ◽  
Zhaozhang Chen ◽  
Jia Zhu ◽  
Longqi Yang ◽  
...  
Keyword(s):  
Kuroshio Current ◽  
Anticyclonic Eddy ◽  
Ekman Transport ◽  
Maximum Diameter ◽  
Current Loop ◽  
Coastal Current ◽  
Kuroshio Intrusion ◽  
Wind Stress Curl ◽  
The Kuroshio ◽  
Cold Core

Multiple remote sensing datasets, combined with in-situ drifter observations, were used to analyze the Kuroshio intrusion through the Luzon Strait (LS). The results showed that a strong Kuroshio Current Loop (KCL) and accompanying anticyclonic eddy (ACE) existed in winter 2020–2021. As quantitatively demonstrated by the Double Index (DI), the Kuroshio Warm Eddy Index (KWI) had low values during a long sustained period compared to those in all other years in the available historical records. Remarkable kinematic properties (i.e., amplitude, diameter, propagated distance, lifespan and propagating speed) of the accompanying ACE were extracted by automatic eddy detection algorithms, showing that the ACE had a maximum diameter of 381 km and a peak amplitude of 50 cm, which significantly exceeded the previous statistics in winter. The orographic negative wind stress curl southwest of Taiwan Island and the westward Ekman transport through the LS during the winter half year of 2020–2021 both had large values beyond their historical maxima. Hence wind forcing is regarded as the primary forcing mechanism during this event. Alternating cyclonic eddies (CEs) and ACEs approaching on the east of the LS were identified, indicating that the interaction between the Kuroshio and the impinging CEs at proper locations made extra contributions to enhancing the KCL. The accompanying ACE had a distinctive feature of a cold-core structure at the surface layer, so as to be categorized as a cold core ACE (CC-ACE), and the temperature difference between the cold core and outer warm ring was maintained for three months. The generation and long duration of the CC-ACE may be due to the sustaining entrainment supported by the warm water from Kuroshio intrusion and the Northwest Luzon Coastal Current (NWLCC) successively.

scholarly journals Long-Term Variations of the Kuroshio Extension Path in Winter: Meridional Movement and Path State Change

2014 ◽  
Vol 27 (15) ◽  
pp. 5929-5940 ◽  
Author(s):  
Yasuharu Seo ◽  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Kuroshio Extension ◽  
Thermocline Depth ◽  
Aleutian Low ◽  
Large Meander ◽  
Wind Stress Curl ◽  
Latitudinal Position ◽  
Anticyclonic Eddies ◽  
The Kuroshio ◽  
Main Thermocline

Abstract As an indicator of the Kuroshio Extension (KE) path, the KE northern boundary (KENB) was detected based on the position of the strong winter sea surface temperature (SST) gradient between 142° and 155°E, using high spatial resolution satellite-derived SST for the 30 winters (January to March) from 1982 to 2011. The KE path showed meridional movement with a period of 10–15 yr and an amplitude of about 2° latitude. The changes in latitudinal position of the KE path were initiated by a north–south shift of the Aleutian low (AL). Negative wind stress curl anomalies around 35°N in the eastern North Pacific associated with a northward shift of the AL induced a deepening of the main thermocline depth, and then this deepening signal propagated westward, reaching the KE region after about 3 yr, where it caused the KE path to move northward. The path state of the KE (straight path/convoluted path) modulated on a time scale of 8–12 yr, but this was not significantly correlated with the meridional movement of the KE path. The anticyclonic eddies containing warm-salty water that detached northward from the convoluted KE exerted a strong influence on oceanic conditions in the Kuroshio–Oyashio Confluence (KOC) region. The changes in path state of the KE were related to the path of the Kuroshio south of Japan over the long term; a convoluted (straight) KE path was associated with the Kuroshio taking the offshore nonlarge (nearshore nonlarge or typical large) meander path.

scholarly journals Impacts of the Kuroshio Intrusion through the Luzon Strait on the Local Precipitation Anomaly

2021 ◽  
Vol 13 (6) ◽  
pp. 1113
Author(s):  
Wen-Pin Fang ◽  
Ding-Rong Wu ◽  
Zhe-Wen Zheng ◽  
Ganesh Gopalakrishnan ◽  
Chung-Ru Ho ◽  
...  
Keyword(s):  
Kuroshio Current ◽  
Precipitation Anomaly ◽  
Luzon Strait ◽  
Sea Surface ◽  
Research Quality ◽  
Northwestern Pacific ◽  
Kuroshio Intrusion ◽  
Vertical Advection ◽  
Budget Analysis ◽  
The Kuroshio

The Kuroshio Current has its origin in the northwestern Pacific, flowing northward to the east of Taiwan and the northern part of Luzon Island. As the Kuroshio Current flows northward, it quasi-periodically intrudes (hereafter referred to as Kuroshio intrusion (KI)) into the northern South China Sea (SCS) basin through the Luzon Strait. Despite the complex generation mechanisms of KI, the purpose of this study is to improve our understanding of the effects of KI through the Luzon Strait on the regional atmospheric and weather variations. Long-term multiple satellite observations, including absolute dynamic topography, absolute geostrophic currents, sea surface winds by ASCAT, multi-scale ultra-high resolution sea surface temperature (MURSST) level-four analysis, and research-quality three-hourly TRMM multi-satellite precipitation analysis (TMPA), was used to systematically examine the aforementioned scientific problem. Analysis indicates that the KI is interlinked with the consequential anomalous precipitation off southwestern Taiwan. This anomalous precipitation would lead to ~560 million tons of freshwater influx during each KI event. Subsequently, independent moisture budget analysis suggests that moisture, mainly from vertical advection, is the possible source of the precipitation anomaly. Additionally, a bulk formula analysis was applied to understand how KI can trigger the precipitation anomaly through vertical advection of moisture without causing an evident change in the low-level flows. These new research findings might reconcile the divisiveness on why winds are not showing a synchronous response during the KI and consequential anomalous precipitation events.

Quantifying the Effects of Long-Term Climate Change on Tropical Cyclone Rainfall Using a Cloud-Resolving Model: Examples of Two Landfall Typhoons in Taiwan

2014 ◽  
Vol 28 (1) ◽  
pp. 66-85 ◽  
Author(s):  
Chung-Chieh Wang ◽  
Bo-Xun Lin ◽  
Cheng-Ta Chen ◽  
Shih-How Lo
Keyword(s):  
Climate Change ◽  
Reanalysis Data ◽  
Budget Analysis ◽  
Sensitivity Tests ◽  
Cloud Resolving Model ◽  
Typhoon Rainfall ◽  
Climate Background ◽  
Rain Rates ◽  
Long Term Trend

Abstract To quantify the effects of long-term climate change on typhoon rainfall near Taiwan, cloud-resolving simulations of Typhoon (TY) Sinlaku and TY Jangmi, both in September 2008, are performed and compared with sensitivity tests where these same typhoons are placed in the climate background of 1950–69, which is slightly cooler and drier compared to the modern climate of 1990–2009 computed using NCEP–NCAR reanalysis data. Using this strategy, largely consistent responses are found in the model although only two cases are studied. In control experiments, both modern-day typhoons yield more rainfall than their counterpart in the sensitivity test using past climate, by about 5%–6% at 200–500 km from the center for Sinlaku and roughly 4%–7% within 300 km of Jangmi, throughout much of the periods simulated. In both cases, the frequency of more-intense rainfall (20 to >50 mm h−1) also increases by about 5%–25% and the increase tends to be larger toward higher rain rates. Results from the water budget analysis, again quite consistent between the two cases, indicate that the increased rainfall from the typhoons in the modern climate is attributable to both a moister environment (by 2.5%–4%) as well as, on average, a more active secondary circulation of the storm. Thus, a changing climate may already have had a discernible impact on TC rainfall near Taiwan. While an overall increase in TC rainfall of roughly 5% may not seem large, it is certainly not insignificant considering that the long-term trend observed in the past 40–50 yr, whatever the causes might be, may continue for many decades in the foreseeable future.

RETROSPECTIVE ASSESSMENT OF UNREGULATED LATERAL INFLOWS OF THE KUIBYSHEVSKY (NOW ZHIGULYOVSKAYA HYDROPOWER PLANT) HYDRAULIC UNIT OF THE VOLGA RIVER BASIN

2021 ◽  
pp. 87-99
Author(s):  
G. KH. ISMAIYLOV ◽  
◽  
N. V. MURASCHENKOVA ◽  
I. G. ISMAIYLOVA
Keyword(s):  
River Basin ◽  
Air Temperature ◽  
Atmospheric Precipitation ◽  
Total Precipitation ◽  
Volga River ◽  
Hydraulic Unit ◽  
Seasonal Characteristics ◽  
Lateral Inflow ◽  
Increasing Trend

The results of the analysis and assessment of changes in annual and seasonal characteristics of hydrometeorological processes in a private catchment area of the Kuibyshev hydroelectric complex of the Volga river are presented. To analyze the temporal dynamics of the variability of the annual and seasonal characteristics of the hydrometeorological processes in the considered territory of the river basin we used more than 100 years of observations of annual and seasonal fluctuations of lateral inflow, total atmospheric precipitation and air temperature regimes on the Volgariver. Relationship equations for annual and seasonal changes in hydrometeorological characteristics in time are obtained. It was found that long-term fluctuations of hydrometeorological processes (lateral inflow, total atmospheric precipitation and air temperature) are characterized by tendencies (trends). The analysis of these trends showed that the non-standard climatic situation, starting from the 70s of the last century, had a very significant impact on the distribution of annual and especially on the seasonal (low-water and winter) characteristics of hydrometeorological processes. It has been established that non-standard unidirectional changes are found in the fluctuations in the total atmospheric precipitation. If the winter total precipitation is characterized over the 100-year period in question by a continuously decreasing trend,the summer-autumn period is an increasing trend. This leads to the fact that long-term fluctuations in total precipitation during the period of low water are formed as a stationary process. At the same time, the total precipitation of the spring flood and inflowing to the Kuibyshev hydroelectric unit is characterized by a constantly increasing trend.

scholarly journals Long-Term and Seasonal Trends in Global Wave Height Extremes Derived from ERA-5 Reanalysis Data

2020 ◽  
Vol 8 (12) ◽  
pp. 1015
Author(s):  
Alicia Takbash ◽  
Ian R. Young
Keyword(s):  
Southern Hemisphere ◽  
Wave Height ◽  
Significant Wave Height ◽  
Reanalysis Data ◽  
Extreme Value Analysis ◽  
Winter Storms ◽  
Value Analysis ◽  
Weather Forecasts ◽  
Significant Wave

A non-stationary extreme value analysis of 41 years (1979–2019) of global ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis) significant wave height data is undertaken to investigate trends in the values of 100-year significant wave height, Hs100. The analysis shows that there has been a statistically significant increase in the value of Hs100 over large regions of the Southern Hemisphere. There have also been smaller decreases in Hs100 in the Northern Hemisphere, although the related trends are generally not statistically significant. The increases in the Southern Hemisphere are a result of an increase in either the frequency or intensity of winter storms, particularly in the Southern Ocean.

scholarly journals Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex

2017 ◽  
Vol 30 (18) ◽  
pp. 7125-7139 ◽  
Author(s):  
Nicholas J. Byrne ◽  
Theodore G. Shepherd ◽  
Tim Woollings ◽  
R. Alan Plumb
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Summer ◽  
Stratospheric Polar Vortex ◽  
Time Symmetry

Abstract Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using reanalysis data, that this variability is rendered highly nonstationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed.

scholarly journals Influence of Early Winter Upward Wave Activity Flux on Midwinter Circulation in the Stratosphere and Troposphere

2004 ◽  
Vol 17 (22) ◽  
pp. 4443-4452 ◽  
Author(s):  
Alexei Karpetchko ◽  
Grigory Nikulin
Keyword(s):  
Heat Flux ◽  
Reanalysis Data ◽  
Wave Activity ◽  
Heat Fluxes ◽  
Early Winter ◽  
Polar Night ◽  
Wave Refraction ◽  
Eddy Heat Flux ◽  
Wave Flux

Abstract Using NCEP–NCAR reanalysis data the authors show that the November–December averaged stratospheric eddy heat flux is strongly anticorrelated with the January–February averaged eddy heat flux in the midlatitude stratosphere and troposphere. This finding further emphasizes differences between early and midwinter stratospheric wave flux behavior, which has recently been found in long-term variations. Analysis suggests that the intraseasonal anticorrelation of stratospheric heat fluxes results from changes in the upward wave propagation in the troposphere. Stronger (weaker) upward wave fluxes in early winter lead to weaker (stronger) upward wave fluxes from the troposphere during midwinter. Also, enhanced equatorward wave refraction during midwinter (due to the stronger polar night jet) is associated with weak heat flux in the early winter. It is suggested that the effect of enhanced midwinter upward wave flux from the troposphere in the years with weak early winter heat flux overcompensates the effect of increased equatorward wave refraction in midwinter, leading to a net increase of midwinter upward wave fluxes into the stratosphere.

scholarly journals Impact of the Kuroshio intrusion on the nutrient inventory in the upper northern South China Sea: insights from an isopycnal mixing model

2013 ◽  
Vol 10 (10) ◽  
pp. 6419-6432 ◽  
Author(s):  
C. Du ◽  
Z. Liu ◽  
M. Dai ◽  
S.-J. Kao ◽  
Z. Cao ◽  
...  
Keyword(s):  
South China Sea ◽  
Water Column ◽  
South China ◽  
Water Mass ◽  
Northern South China Sea ◽  
Mixing Model ◽  
Nutrient Concentrations ◽  
Kuroshio Intrusion ◽  
China Sea ◽  
The Kuroshio

Abstract. Based on four cruises covering a seasonal cycle in 2009–2011, we examined the impact of the Kuroshio intrusion, featured by extremely oligotrophic waters, on the nutrient inventory in the central northern South China Sea (NSCS). The nutrient inventory in the upper 100 m of the water column in the study area ranged from ∼200 to ∼290 mmol m−2 for N + N (nitrate plus nitrite), from ∼13 to ∼24 mmol m−2 for soluble reactive phosphate and from ∼210 to ∼430 mmol m−2 for silicic acid. The nutrient inventory showed a clear seasonal pattern with the highest value appearing in summer, while the N + N inventory in spring and winter had a reduction of ∼13 and ∼30%, respectively, relative to that in summer. To quantify the extent of the Kuroshio intrusion, an isopycnal mixing model was adopted to derive the proportional contribution of water masses from the SCS proper and the Kuroshio along individual isopycnal surfaces. The derived mixing ratio along the isopycnal plane was then employed to predict the genuine gradients of nutrients under the assumption of no biogeochemical alteration. These predicted nutrient concentrations, denoted as Nm, are solely determined by water mass mixing. Results showed that the nutrient inventory in the upper 100 m of the NSCS was overall negatively correlated to the Kuroshio water fraction, suggesting that the Kuroshio intrusion significantly influenced the nutrient distribution in the SCS and its seasonal variation. The difference between the observed nutrient concentrations and their corresponding Nm allowed us to further quantify the nutrient removal/addition associated with the biogeochemical processes on top of the water mass mixing. We revealed that the nutrients in the upper 100 m of the water column had a net consumption in both winter and spring but a net addition in fall.

scholarly journals Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations

2021 ◽  
Author(s):  
Gunter Stober ◽  
Ales Kuchar ◽  
Dimitry Pokhotelov ◽  
Huixin Liu ◽  
Han-Li Liu ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Lower Thermosphere ◽  
Winter Season ◽  
General Circulation Models ◽  
Meteor Radar ◽  
Radar Observations ◽  
Seasonal Characteristics

Abstract. Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable to compare climate models or long term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observations from six meteor radars at two conjugate latitudes to validate the corresponding mean winds and atmospheric diurnal and semidiurnal tides from three GCMs, namely Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Community Climate Model Extension (Specified Dynamics) (WACCM-X(SD)) and Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate that there are interhemispheric differences in the seasonal characteristics of the diurnal and semidiurnal tide. There also are some differences in the mean wind climatologies of the models and the observations. Our results indicate that GAIA shows a reasonable agreement with the meteor radar observations during the winter season, whereas WACCM-X(SD) shows a better agreement with the radars for the hemispheric zonal summer wind reversal, which is more consistent with the meteor radar observations. The free running UA-ICON tends to show similar winds and tides compared to WACCM-X(SD).

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