Footprints of Tropical Cyclones in WNP Summer Monsoon Variability

2020 ◽  
Author(s):  
Huang-Hsiung Hsu
Keyword(s):  
Climate Variability ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Climate Models ◽  
Southern Oscillation ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Monsoon Trough ◽  
Teleconnection Pattern ◽  
Large Scale Circulation

<p>Tropical cyclones (TCs) in the western North Pacific (WNP) are modulated by large-scale circulation systems such monsoon trough, intraseasonal oscillation, teleconnection pattern, El Niño and Southern Oscillation, and some interdecadal oscillations. While the low-frequency, large-scale circulation produces a clustering effect on TCs, the latter in return leave marked footprints in climate mean state and variability because of large amplitudes in circulation and strong heating. In this study, we applied PV inversion technique to remove TCs from reanalysis and evaluate their contribution to mean circulation and climate variability. It is found that the mean climatological circulation (e.g., low-level monsoon trough and upper-tropospheric anticyclone) would be much weaker with TCs removed. Intraseasonal and interannual variance of certain variables could decrease by as much as 40–50 percent. An accompanied study indicated that TCs had slowed down the sea surface warming in the WNP for the past few decades because of TC-induced cooling. Our results suggest that TC effect has to be considered to understand the climate variability in the tropical atmosphere and ocean. The ensemble effect of TCs, at least in the statistical sense, has to be resolved in climate models to better simulate climate variability and produce more reliable climate projection in the TC-prone regions.</p>

scholarly journals Interannual Variability of the Intraseasonal Oscillation and Its Impact on the Summertime Wave Patterns and Tropical Cyclones over the Western North Pacific

2017 ◽  
Vol 145 (9) ◽  
pp. 3465-3483 ◽  
Author(s):  
Ken-Chung Ko ◽  
Jyun-Hong Liu
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Mean Flow ◽  
Background Flow ◽  
Wave Patterns ◽  
Intraseasonal Oscillations ◽  
The Mean ◽  
Local Weather

In this study, intraseasonal oscillations (ISOs) and submonthly wave patterns were separated into maximal variance (MaxV) and minimal variance (MinV) years on the basis of ISO variance from July to October. The mean-state 850-hPa streamfunction for submonthly cases indicated that, in the MinV years, tropical cyclones (TCs) formed near areas southeast of those in the MaxV years. ISOs propagated northward in the MaxV years, whereas a weaker westward-propagating tendency was observed in the MinV years. Track analysis of the centers of the submonthly cyclonic anomalies suggested that the background flow dictated the propagation routes of the easterly cyclonic anomalies in the MaxV years. However, the propagation routes of the westerly cyclonic anomalies were barely affected by the background flow. Further analysis of the ISO mean flow patterns showed that in the MaxV years, the propagation routes of the westerly cyclonic anomalies were more likely controlled by the anomalous easterly flow generated by the ISO westerly cyclonic anomalies. Moreover, rainfall was heavier in Taiwan in the MaxV years because the background flow in the MinV years caused the submonthly cyclonic anomaly tracks to shift away from Taiwan. Therefore, low-frequency large-scale circulations can affect smaller-scale phenomena and local weather.

scholarly journals Climate Variability, Fish, and Fisheries

2006 ◽  
Vol 19 (20) ◽  
pp. 5009-5030 ◽  
Author(s):  
P. Lehodey ◽  
J. Alheit ◽  
M. Barange ◽  
T. Baumgartner ◽  
G. Beaugrand ◽  
...  
Keyword(s):  
Climate Variability ◽  
Time Scales ◽  
Large Scale ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Fish Population ◽  
Marine Ecology ◽  
Fish Populations ◽  
Global Ocean ◽  
Close Link

Abstract Fish population variability and fisheries activities are closely linked to weather and climate dynamics. While weather at sea directly affects fishing, environmental variability determines the distribution, migration, and abundance of fish. Fishery science grew up during the last century by integrating knowledge from oceanography, fish biology, marine ecology, and fish population dynamics, largely focused on the great Northern Hemisphere fisheries. During this period, understanding and explaining interannual fish recruitment variability became a major focus for fisheries oceanographers. Yet, the close link between climate and fisheries is best illustrated by the effect of “unexpected” events—that is, nonseasonal, and sometimes catastrophic—on fish exploitation, such as those associated with the El Niño–Southern Oscillation (ENSO). The observation that fish populations fluctuate at decadal time scales and show patterns of synchrony while being geographically separated drew attention to oceanographic processes driven by low-frequency signals, as reflected by indices tracking large-scale climate patterns such as the Pacific decadal oscillation (PDO) and the North Atlantic Oscillation (NAO). This low-frequency variability was first observed in catch fluctuations of small pelagic fish (anchovies and sardines), but similar effects soon emerged for larger fish such as salmon, various groundfish species, and some tuna species. Today, the availability of long time series of observations combined with major scientific advances in sampling and modeling the oceans’ ecosystems allows fisheries science to investigate processes generating variability in abundance, distribution, and dynamics of fish species at daily, decadal, and even centennial scales. These studies are central to the research program of Global Ocean Ecosystems Dynamics (GLOBEC). This review presents examples of relationships between climate variability and fisheries at these different time scales for species covering various marine ecosystems ranging from equatorial to subarctic regions. Some of the known mechanisms linking climate variability and exploited fish populations are described, as well as some leading hypotheses, and their implications for their management and for the modeling of their dynamics. It is concluded with recommendations for collaborative work between climatologists, oceanographers, and fisheries scientists to resolve some of the outstanding problems in the development of sustainable fisheries.

scholarly journals Influence of large-scale circulation and interannual modes of climate variability on seasonal drought characteristics over Pakistan

2021 ◽  
Author(s):  
Irfan Ullah ◽  
Xieyao Ma ◽  
Jun Yin ◽  
Farhan Saleem ◽  
Sidra Syed ◽  
...  
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Statistical Significance ◽  
Influential Factors ◽  
Drought Severity ◽  
Monthly Precipitation ◽  
Large Scale Circulation ◽  
Drought Characteristics ◽  
Cropping Seasons

Abstract The long-term drought monitoring and its assessment are of great importance for meteorological disaster risk management. The recurrent spells of heatwaves and droughts have severely affected the environmental conditions worldwide, including Pakistan. The present work sought to investigate the spatiotemporal changes in drought characteristics over Pakistan during Rabi and Kharif cropping seasons. The role of large-scale circulation and interannual mode of climate variability is further explored to identify the physical mechanisms associated with droughts in the region. Monthly precipitation and temperature data (1983–2019) from 53 meteorological stations were used to study drought characteristics, using the standardized precipitation evapotranspiration index (SPEI). The non-parametric Mann-Kendall (MK), Sen’s Slope (SS), and Sequential Mann-Kendall (SQMK) tests were applied on the drought index to determine the statistical significance and magnitude of the historical trend. The state-of-the-art Bayesian Dynamic Linear (BDL) model was further used to analyze large scale climate drivers of droughts, analysis revealed an increase in drought severity mostly over arid to semi-arid regions for both cropping seasons. Temperature played a significant role in defining droughts over dry and hot seasons, while rainfall is influential over the western disturbances (WD) influenced region. The analysis of atmospheric circulation patterns revealed that large-scale changes in wind speed, air temperature, relative humidity and geopotential height anomalies are the likely drivers of droughts in the region. We found that Niño4, Sea Surface Temperature (SST), and multivariate El Niño-Southern Oscillation (ENSO4.0) Index are the most influential factors for seasonal droughts across Pakistan. Overall, the findings provide a better understanding of drought-prone areas in the region, and this information is of potential use for mitigating and managing drought risks.

scholarly journals The Role of Natural Climate Variability in Recent Tropical Expansion

2017 ◽  
Vol 30 (16) ◽  
pp. 6329-6350 ◽  
Author(s):  
Robert J. Allen ◽  
Mahesh Kovilakam
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Climate Models ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Forced Response ◽  
Natural Climate Variability ◽  
Sst Variability ◽  
Natural Climate

Observations show the tropical belt has widened over the past few decades, a phenomenon associated with poleward migration of subtropical dry zones and large-scale atmospheric circulation. Coupled climate models also simulate tropical belt widening, but less so than observed. Reasons for this discrepancy, and the mechanisms driving the expansion remain uncertain. Here, the role of unforced, natural climate variability—particularly natural sea surface temperature (SST) variability—in recent tropical widening is shown. Compared to coupled ocean–atmosphere models, atmosphere-only simulations driven by observed SSTs consistently lead to larger rates of tropical widening, especially in the Northern Hemisphere (NH), highlighting the importance of recent SST evolution. Assuming the ensemble mean SSTs from historical simulations accurately represent the externally forced response, the observed SSTs can be decomposed into a forced and an unforced component. Targeted simulations with the Community Atmosphere Model, version 5 (CAM5), show that natural SST variability accounts for nearly all of the widening associated with recent SST evolution. This is consistent with the similarity of the unforced SSTs to the observed SSTs, both of which resemble a cold El Niño–Southern Oscillation/Pacific decadal oscillation (ENSO/PDO)-like SST pattern, which is associated with a wider tropical belt. Moreover, CAM5 coupled simulations with observed central to eastern tropical Pacific SSTs yield more than double the rate of widening compared to analogous simulations without prescribed tropical Pacific SSTs and reproduce the magnitude of tropical widening in atmosphere-only simulations. The results suggest that the bulk of recent tropical widening, particularly in the NH, is due to unforced, natural SST variability, primarily related to recent ENSO/PDO variability.

scholarly journals Historical drought patterns over Canada and their teleconnections with large-scale climate signals

2018 ◽  
Vol 22 (6) ◽  
pp. 3105-3124 ◽  
Author(s):  
Zilefac Elvis Asong ◽  
Howard Simon Wheater ◽  
Barrie Bonsal ◽  
Saman Razavi ◽  
Sopan Kurkute
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Kendall Test ◽  
Wavelet Coherence ◽  
Climate Indices ◽  
Data Sets ◽  
Canadian Prairies ◽  
Agriculture Industry ◽  
Spatio Temporal

Abstract. Drought is a recurring extreme climate event and among the most costly natural disasters in the world. This is particularly true over Canada, where drought is both a frequent and damaging phenomenon with impacts on regional water resources, agriculture, industry, aquatic ecosystems, and health. However, nationwide drought assessments are currently lacking and impacted by limited ground-based observations. This study provides a comprehensive analysis of historical droughts over the whole of Canada, including the role of large-scale teleconnections. Drought events are characterized by the Standardized Precipitation Evapotranspiration Index (SPEI) over various temporal scales (1, 3, 6, and 12 consecutive months, 6 months from April to September, and 12 months from October to September) applied to different gridded monthly data sets for the period 1950–2013. The Mann–Kendall test, rotated empirical orthogonal function, continuous wavelet transform, and wavelet coherence analyses are used, respectively, to investigate the trend, spatio-temporal patterns, periodicity, and teleconnectivity of drought events. Results indicate that southern (northern) parts of the country experienced significant trends towards drier (wetter) conditions although substantial variability exists. Two spatially well-defined regions with different temporal evolution of droughts were identified – the Canadian Prairies and northern central Canada. The analyses also revealed the presence of a dominant periodicity of between 8 and 32 months in the Prairie region and between 8 and 40 months in the northern central region. These cycles of low-frequency variability are found to be associated principally with the Pacific–North American (PNA) and Multivariate El Niño/Southern Oscillation Index (MEI) relative to other considered large-scale climate indices. This study is the first of its kind to identify dominant periodicities in drought variability over the whole of Canada in terms of when the drought events occur, their duration, and how often they occur.

scholarly journals Observational Analysis of Tropical Cyclone Formation Associated with Monsoon Gyres

2013 ◽  
Vol 70 (4) ◽  
pp. 1023-1034 ◽  
Author(s):  
Liguang Wu ◽  
Huijun Zong ◽  
Jia Liang
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Monsoon Trough ◽  
Cyclonic Circulation ◽  
Tropical Cyclone Formation ◽  
Monsoon Gyre

Abstract Large-scale monsoon gyres and the involved tropical cyclone formation over the western North Pacific have been documented in previous studies. The aim of this study is to understand how monsoon gyres affect tropical cyclone formation. An observational study is conducted on monsoon gyres during the period 2000–10, with a focus on their structures and the associated tropical cyclone formation. A total of 37 monsoon gyres are identified in May–October during 2000–10, among which 31 monsoon gyres are accompanied with the formation of 42 tropical cyclones, accounting for 19.8% of the total tropical cyclone formation. Monsoon gyres are generally located on the poleward side of the composited monsoon trough with a peak occurrence in August–October. Extending about 1000 km outward from the center at lower levels, the cyclonic circulation of the composited monsoon gyre shrinks with height and is replaced with negative relative vorticity above 200 hPa. The maximum winds of the composited monsoon gyre appear 500–800 km away from the gyre center with a magnitude of 6–10 m s−1 at 850 hPa. In agreement with previous studies, the composited monsoon gyre shows enhanced southwesterly flow and convection on the south-southeastern side. Most of the tropical cyclones associated with monsoon gyres are found to form near the centers of monsoon gyres and the northeastern end of the enhanced southwesterly flows, accompanying relatively weak vertical wind shear.

Ocean carbon storage uniquely linked to ocean heat 

2021 ◽  
Author(s):  
Ben Bronselaer ◽  
Laure Zanna
Keyword(s):  
Carbon Storage ◽  
Large Scale ◽  
Climate Models ◽  
Circulation Pattern ◽  
Secondary Importance ◽  
Large Scale Circulation ◽  
Excess Carbon ◽  
Excess Heat ◽  
Surface Ocean ◽  
Ocean Carbon

<p>As the climate warms due to greenhouse gas emissions, the ocean absorbs excess heat and carbon. The patterns of ocean excess heat and carbon storage appear tightly linked when the large-scale circulation is fixed. This unique link is not shared with any other ocean tracer, such as <span>Chlorofluorocarbons</span> (CFCs). At the same time, ocean excess carbon storage patterns are mostly unchanged whether the large-scale circulation is free to evolve, or fixed to the pre-industrial circulation pattern, as the climate warms. Here, we interpret the reason for this behavior by breaking ocean carbon storage into two parts: uptake of atmospheric anomalies by the surface ocean, and subsequent internal storage by the ocean’s circulation. We show that the patterns of surface ocean carbon anomalies are dictated by mean state biogeochemical properties and therefore mostly unchanged by circulation changes. Furthermore, surface biogeochemical properties are strongly shaped by the ocean temperature, providing a link between ocean heat and carbon uptake. CFCs on the hand, lack chemical buffering and therefore the patterns of CFC storage do not correlate with heat as much as carbon patterns do. The patterns of surface anomalies ultimately explain most of the differences in how temperature, carbon and CFCs are stored by the ocean, while changes in internal pathways are of secondary importance. Furthermore, the ratio of total ocean carbon and heat storage is roughly constant across warming scenarios and climate models, which might have further implications for relating ocean carbon storage to important climate metrics, such as the transient response to cumulative emissions.</p>

scholarly journals Synchronous combined effects of fishing and climate within a demersal community

2012 ◽  
Vol 70 (2) ◽  
pp. 319-328 ◽  
Author(s):  
Antoni Quetglas ◽  
Francesc Ordines ◽  
Manuel Hidalgo ◽  
Sebastià Monserrat ◽  
Susana Ruiz ◽  
...  
Keyword(s):  
Climate Variability ◽  
Age Structure ◽  
Large Scale ◽  
Southern Oscillation ◽  
Climatic Variability ◽  
Early Period ◽  
Combined Effects ◽  
Population Fluctuations ◽  
Fishing Activity ◽  
The Mediterranean

Abstract Quetglas, A., Ordines, F., Hidalgo, M., Monserrat, S., Ruiz, S., Amores, Á., Moranta, J., and Massutí, E. 2013. Synchronous combined effects of fishing and climate within a demersal community. – ICES Journal of Marine Science, 70: 319–328. Accumulating evidence shows that fishing exploitation and environmental variables can synergistically affect the population dynamics of exploited populations. Here, we document an interaction between fishing impact and climate variability that triggered a synchronic response in the population fluctuations of six exploited species in the Mediterranean from 1965–2008. Throughout this period, the fishing activity experienced a sharp increase in fishing effort, which caused all stocks to shift from an early period of underexploitation to a later period of overexploitation. This change altered the population resilience of the stocks and brought about an increase in the sensitivity of its dynamics to climate variability. Landings increased exponentially when underexploited but displayed an oscillatory behaviour once overexploited. Climatic indices, related to the Mediterranean mesoscale hydrography and large-scale north Atlantic climatic variability, seemed to affect the species with broader age structure and longer lifespan, while the global-scale El Niño Southern Oscillation index (ENSO) positively influenced the population abundances of species with a narrow age structure and short lifespan. The species affected by ENSO preferentially inhabit the continental shelf, suggesting that Mediterranean shelf ecosystems are sensitive to the hydroclimatic variability linked to global climate.

scholarly journals Interannual Variability of Summer Tropical Cyclone Rainfall in the Western North Pacific Depicted by CFSR and Associated Large-Scale Processes and ISO Modulations

2018 ◽  
Vol 31 (5) ◽  
pp. 1771-1787 ◽  
Author(s):  
Jau-Ming Chen ◽  
Pei-Hua Tan ◽  
Liang Wu ◽  
Hui-Shan Chen ◽  
Jin-Shuen Liu ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Interannual Variability ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Monsoon Trough ◽  
Tropical Eastern Pacific

This study examines the interannual variability of summer tropical cyclone (TC) rainfall (TCR) in the western North Pacific (WNP) depicted by the Climate Forecast System Reanalysis (CFSR). This interannual variability exhibits a maximum region near Taiwan (19°–28°N, 120°–128°E). Significantly increased TCR in this region is modulated by El Niño–Southern Oscillation (ENSO)-related large-scale processes. They feature elongated sea surface temperature warming in the tropical eastern Pacific and a southeastward-intensified monsoon trough. Increased TC movements are facilitated by interannual southerly/southeasterly flows in the northeastern periphery of the intensified monsoon trough to move from the tropical WNP toward the region near Taiwan, resulting in increased TCR. The coherent dynamic relations between interannual variability of summer TCR and large-scale environmental processes justify CFSR as being able to reasonably depict interannual characteristics of summer TCR in the WNP. For intraseasonal oscillation (ISO) modulations, TCs tend to cluster around the center of a 10–24-day cyclonic anomaly and follow its northwestward propagation from the tropical WNP toward the region near Taiwan. The above TC movements are subject to favorable background conditions provided by a northwest–southeasterly extending 30–60-day cyclonic anomaly. Summer TCR tends to increase (decrease) during El Niño (La Niña) years and strong (weak) ISO years. By comparing composite TCR anomalies and correlations with TCR variability, it is found that ENSO is more influential than ISO in modulating the interannual variability of summer TCR in the WNP.

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