Oceanography of the New Zealand subantarctic region

2021 ◽  
Author(s):  
◽  
Aitana Forcén-Vázquez
Keyword(s):  
New Zealand ◽  
Interannual Variability ◽  
Water Column ◽  
Large Scale ◽  
Southern Oscillation ◽  
Complex Structure ◽  
Positive Trend ◽  
Intermediate Water ◽  
Subantarctic Region

<p>Subantarctic New Zealand is an oceanographycally dynamic region with the Subtropical Front (STF) to the north and the Subantarctic Front (SAF) to the south. This thesis investigates the ocean structure of the Campbell Plateau and the surrounding New Zealand subantarctic, including the spatial, seasonal, interannual and longer term variability over the ocean properties, and their connection to atmospheric variability using a combination of in-situ oceanographic measurements and remote sensing data.  The spatial and seasonal oceanographic structure in the New Zealand subantarctic region was investigated by analysing ten high resolution Conductivity Temperature and Depth (CTD) datasets, sampled during oceanographic cruises from May 1998 to February 2013. Position of fronts, water mass structure and changes over the seasons show a complex structure around the Campbell Plateau combining the influence of subtropical and subantarctic waters.  The spatial and interannual variability on the Campbell Plateau was described by analysing approximately 70 low resolution CTD profiles collected each year in December between 2002 and 2009. Conservative temperature and absolute salinity profiles reveal high variability in the upper 200m of the water column and a homogeneous water column from 200 to 600m depth. Temperature variability of about 0.7 °C, on occasions between consecutive years, is observed down to 900m depth. The presence of Subantarctic Mode Water (SAMW) on the Campbell Plateau is confirmed and Antarctic Intermediate Water (AAIW) reported for the first time in the deeper regions around the edges of the plateau.  Long-term trends and variability over the Campbell Plateau were investigated by analysing satellite derived Sea Level Anomalies (SLA) and Sea Surface Temperature (SST) time series. Links to large scale atmospheric processes are also explored through correlation with the Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). SST shows a strong seasonality and interannual variability which is linked to local winds, but no significant trend is found. The SLA over the Campbell Plateau has increased at a rate of 5.2 cm decade⁻¹ in the last two decades. The strong positive trend in SLA appears to be a combination of the response of the ocean to wind stress curl (Ekman pumping), thermal expansion and ocean mass redistribution via advection amongst others.  These results suggest that the variability on the Campbell Plateau is influenced by the interaction of the STF and the SAF. The STF influence reaches the limit of the SAF over the western Campbell Plateau and the SAF influence extends all around the plateau. Results also suggest different connections between the plateau with the surrounding oceans, e.g., along the northern edge with the Bounty Trough and via the southwest edge with the SAF. A significant correlation with SOI and little correlation with SAM suggest a stronger response to tropically driven processes in the long-term variability on the Campbell Plateau.  The results of this thesis provide a new definitive assessment of the circulation, water masses and variability of the Campbell Plateau on mean, annual, and interannual time scales which will support research in other disciplines such as palaeoceanography, fisheries management and climate.</p>

Oceanography of the New Zealand subantarctic region

2021 ◽  
Author(s):  
◽  
Aitana Forcén-Vázquez
Keyword(s):  
New Zealand ◽  
Interannual Variability ◽  
Water Column ◽  
Large Scale ◽  
Southern Oscillation ◽  
Complex Structure ◽  
Positive Trend ◽  
Intermediate Water ◽  
Subantarctic Region

<p>Subantarctic New Zealand is an oceanographycally dynamic region with the Subtropical Front (STF) to the north and the Subantarctic Front (SAF) to the south. This thesis investigates the ocean structure of the Campbell Plateau and the surrounding New Zealand subantarctic, including the spatial, seasonal, interannual and longer term variability over the ocean properties, and their connection to atmospheric variability using a combination of in-situ oceanographic measurements and remote sensing data.  The spatial and seasonal oceanographic structure in the New Zealand subantarctic region was investigated by analysing ten high resolution Conductivity Temperature and Depth (CTD) datasets, sampled during oceanographic cruises from May 1998 to February 2013. Position of fronts, water mass structure and changes over the seasons show a complex structure around the Campbell Plateau combining the influence of subtropical and subantarctic waters.  The spatial and interannual variability on the Campbell Plateau was described by analysing approximately 70 low resolution CTD profiles collected each year in December between 2002 and 2009. Conservative temperature and absolute salinity profiles reveal high variability in the upper 200m of the water column and a homogeneous water column from 200 to 600m depth. Temperature variability of about 0.7 °C, on occasions between consecutive years, is observed down to 900m depth. The presence of Subantarctic Mode Water (SAMW) on the Campbell Plateau is confirmed and Antarctic Intermediate Water (AAIW) reported for the first time in the deeper regions around the edges of the plateau.  Long-term trends and variability over the Campbell Plateau were investigated by analysing satellite derived Sea Level Anomalies (SLA) and Sea Surface Temperature (SST) time series. Links to large scale atmospheric processes are also explored through correlation with the Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). SST shows a strong seasonality and interannual variability which is linked to local winds, but no significant trend is found. The SLA over the Campbell Plateau has increased at a rate of 5.2 cm decade⁻¹ in the last two decades. The strong positive trend in SLA appears to be a combination of the response of the ocean to wind stress curl (Ekman pumping), thermal expansion and ocean mass redistribution via advection amongst others.  These results suggest that the variability on the Campbell Plateau is influenced by the interaction of the STF and the SAF. The STF influence reaches the limit of the SAF over the western Campbell Plateau and the SAF influence extends all around the plateau. Results also suggest different connections between the plateau with the surrounding oceans, e.g., along the northern edge with the Bounty Trough and via the southwest edge with the SAF. A significant correlation with SOI and little correlation with SAM suggest a stronger response to tropically driven processes in the long-term variability on the Campbell Plateau.  The results of this thesis provide a new definitive assessment of the circulation, water masses and variability of the Campbell Plateau on mean, annual, and interannual time scales which will support research in other disciplines such as palaeoceanography, fisheries management and climate.</p>

Harvest rate of sooty shearwaters (Puffinus griseus) by Rakiura Māori: a potential tool to monitor population trends?

2004 ◽  
Vol 31 (3) ◽  
pp. 319 ◽  
Author(s):  
Jane Catherine Kitson
Keyword(s):  
New Zealand ◽  
Cross Section ◽  
Large Scale ◽  
Population Change ◽  
Population Trends ◽  
Harvest Rate ◽  
General Index ◽  
Careful Screening ◽  
Potential Tool

Sooty shearwaters (tītī, muttonbird, Puffinus griseus) are highly abundant migratory seabirds, which return to breeding colonies in New Zealand. The Rakiura Māori annual chick harvest on islands adjacent to Rakiura (Stewart Island), is one of the last large-scale customary uses of native wildlife in New Zealand. This study aimed to establish whether the rate at which muttonbirders can extract chicks from their breeding burrows indicates population trends of sooty shearwaters. Harvest rates increased slightly with increasing chick densities on Putauhinu Island. Birders' harvest rates vary in their sensitivities to changing chick density. Therefore a monitoring panel requires careful screening to ensure that harvest rates of the birders selected are sensitive to chick density, and represents a cross-section of different islands. Though harvest rates can provide only a general index of population change, it can provide an inexpensive and feasible way to measure population trends. Detecting trends is the first step to assessing the long-term sustainability of the harvest.

scholarly journals Explaining the trends and variability in the United States tornado records using climate teleconnections and shifts in observational practices

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Niloufar Nouri ◽  
Naresh Devineni ◽  
Valerie Were ◽  
Reza Khanbilvardi
Keyword(s):  
Population Density ◽  
Large Scale ◽  
Southern Oscillation ◽  
The United States ◽  
Anthropogenic Factors ◽  
Climate Variables ◽  
Term Trend ◽  
Cyclical Variability ◽  
Long Term Trend

AbstractThe annual frequency of tornadoes during 1950–2018 across the major tornado-impacted states were examined and modeled using anthropogenic and large-scale climate covariates in a hierarchical Bayesian inference framework. Anthropogenic factors include increases in population density and better detection systems since the mid-1990s. Large-scale climate variables include El Niño Southern Oscillation (ENSO), Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO), and Atlantic Multi-decadal Oscillation (AMO). The model provides a robust way of estimating the response coefficients by considering pooling of information across groups of states that belong to Tornado Alley, Dixie Alley, and Other States, thereby reducing their uncertainty. The influence of the anthropogenic factors and the large-scale climate variables are modeled in a nested framework to unravel secular trend from cyclical variability. Population density explains the long-term trend in Dixie Alley. The step-increase induced due to the installation of the Doppler Radar systems explains the long-term trend in Tornado Alley. NAO and the interplay between NAO and ENSO explained the interannual to multi-decadal variability in Tornado Alley. PDO and AMO are also contributing to this multi-time scale variability. SOI and AO explain the cyclical variability in Dixie Alley. This improved understanding of the variability and trends in tornadoes should be of immense value to public planners, businesses, and insurance-based risk management agencies.

scholarly journals The Interannual Variability of the Haines Index over North America

2013 ◽  
Vol 52 (11) ◽  
pp. 2396-2409 ◽  
Author(s):  
Lejiang Yu ◽  
Shiyuan Zhong ◽  
Xindi Bian ◽  
Warren E. Heilman ◽  
Joseph J. Charney
Keyword(s):  
United States ◽  
Pacific Ocean ◽  
North America ◽  
Interannual Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southeastern United States ◽  
Lower Atmosphere ◽  
The Arctic ◽  
Fire Weather Index

AbstractThe Haines index (HI) is a fire-weather index that is widely used as an indicator of the potential for dry, low-static-stability air in the lower atmosphere to contribute to erratic fire behavior or large fire growth. This study examines the interannual variability of HI over North America and its relationship to indicators of large-scale circulation anomalies. The results show that the first three HI empirical orthogonal function modes are related respectively to El Niño–Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the interdecadal sea surface temperature variation over the tropical Pacific Ocean. During the negative ENSO phase, an anomalous ridge (trough) is evident over the western (eastern) United States, with warm/dry weather and more days with high HI values in the western and southeastern United States. During the negative phase of the AO, an anomalous trough is found over the western United States, with wet/cool weather and fewer days with high HI, while an anomalous ridge occurs over the southern United States–northern Mexico, with an increase in the number of days with high HI. After the early 1990s, the subtropical high over the eastern Pacific Ocean and the Bermuda high were strengthened by a wave train that was excited over the tropical western Pacific Ocean and resulted in warm/dry conditions over the southwestern United States and western Mexico and wet weather in the southeastern United States. The above conditions are reversed during the positive phase of ENSO and AO and before the early 1990s.

scholarly journals A Hydroclimatological Analysis of Precipitation in the Ganges–Brahmaputra–Meghna River Basin

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1359 ◽  
Author(s):  
Scott Curtis ◽  
Thomas Crawford ◽  
Munshi Rahman ◽  
Bimal Paul ◽  
M. Miah ◽  
...  
Keyword(s):  
Interannual Variability ◽  
River Basin ◽  
Significant Relationship ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Wave Train ◽  
Principal Component ◽  
South Atlantic ◽  
The Ganges

Understanding seasonal precipitation input into river basins is important for linking large-scale climate drivers with societal water resources and the occurrence of hydrologic hazards such as floods and riverbank erosion. Using satellite data at 0.25-degree resolution, spatial patterns of monsoon (June-July-August-September) precipitation variability between 1983 and 2015 within the Ganges–Brahmaputra–Meghna (GBM) river basin are analyzed with Principal Component (PC) analysis and the first three modes (PC1, PC2 and PC3) are related to global atmospheric-oceanic fields. PC1 explains 88.7% of the variance in monsoonal precipitation and resembles climatology with the center of action over Bangladesh. The eigenvector coefficients show a downward trend consistent with studies reporting a recent decline in monsoon rainfall, but little interannual variability. PC2 explains 2.9% of the variance and shows rainfall maxima to the far western and eastern portions of the basin. PC2 has an apparent decadal cycle and surface and upper-air atmospheric height fields suggest the pattern could be forced by tropical South Atlantic heating and a Rossby wave train stemming from the North Atlantic, consistent with previous studies. Finally, PC3 explains 1.5% of the variance and has high spatial variability. The distribution of precipitation is somewhat zonal, with highest values at the southern border and at the Himalayan ridge. There is strong interannual variability associated with PC3, related to the El Nino/Southern Oscillation (ENSO). Next, we perform a hydroclimatological downscaling, as precipitation attributed to the three PCs was averaged over the Pfafstetter level-04 sub-basins obtained from the World Wildlife Fund (Gland, Switzerland). While PC1 was the principal contributor of rainfall for all sub-basins, PC2 contributed the most to rainfall in the western Ganges sub-basin (4524) and PC3 contributed the most to the rainfall in the northern Brahmaputra (4529). Monsoon rainfall within these two sub-basins were the only ones to show a significant relationship (negative) with ENSO, whereas four of the eight sub-basins had a significant relationship (positive) with sea surface temperature (SST) anomalies in the tropical South Atlantic. This work demonstrates a geographic dependence on climate teleconnections in the GBM that deserves further study.

scholarly journals West African Summer Monsoon Precipitation Variability as Represented by Reanalysis Datasets

Climate ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 111
Author(s):  
Kwesi Akumenyi Quagraine ◽  
Francis Nkrumah ◽  
Cornelia Klein ◽  
Nana Ama Browne Klutse ◽  
Kwesi Twentwewa Quagraine
Keyword(s):  
Summer Monsoon ◽  
Southern Oscillation ◽  
West African Monsoon ◽  
West African ◽  
Positive Trend ◽  
In Situ Data ◽  
Dry Conditions ◽  
Long Term Trends

Focusing on West Africa, a region riddled with in situ data scarcity, we evaluate the summer monsoon monthly rainfall characteristics of five global reanalysis datasets: ERA5, ERA-Interim, JRA-55, MERRA2, and NCEP-R2. Their performance in reproducing the West African monsoon (WAM) climatology, interannual variability, and long-term trends for the main monsoon months are compared to gauge-only and satellite products. We further examine their ability to reproduce teleconnections between sea surface temperatures and monsoon rainfall. All reanalyses are able to represent the average rainfall patterns and seasonal cycle; however, regional biases can be marked. ERA5, ERA-Interim, and NCEP-R2 underestimate rainfall over areas of peak rainfall, with ERA5 showing the strongest underestimation, particularly over the Guinea Highlands. The meridional northward extent of the monsoon rainband is well captured by JRA-55 and MERRA2 but is too narrow in ERA-Interim, for which rainfall stays close to the Guinea Coast. Differences in rainband displacement become particularly evident when comparing strong El Niño Southern Oscillation (ENSO) years, where all reanalyses except ERA-Interim reproduce wetter Sahelian conditions for La Niña, while overestimating dry conditions at the coast except for NCEP-R2. Precipitation trends are not coherent across reanalyses and magnitudes are generally overestimated compared to observations, with only JRA-55 and NCEP-R2 displaying the expected positive trend in the Sahel. ERA5 generally outperforms ERA-Interim, highlighting clear improvements over its predecessor. Ultimately, we find the strengths of reanalyses to strongly vary across the region.

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.

Revisiting the factors that drive interannual variability in stratospheric entry water vapour

2020 ◽  
Author(s):  
Shlomi Ziskin Ziv ◽  
Chaim I. Garfinkel
Keyword(s):  
Water Vapor ◽  
Interannual Variability ◽  
Large Scale ◽  
Trace Gases ◽  
Transport Processes ◽  
Tropospheric Temperature ◽  
Stratospheric Water Vapor ◽  
Cold Point ◽  
Stratospheric Trace Gases

&lt;p&gt;Understanding the sinks, sources and transport processes of stratospheric trace gases can improve our prediction of mid to long term climate change. In this study we consider the processes that lead to variability in stratospheric water vapor. We perform a Multiple Linear Regression(MLR) on the SWOOSH combined anomaly filled water vapor product with ENSO, QBO, BDC, mid-tropospheric temperature, and CH4 as predictors, in an attempt to find the factors that most succinctly explain observed water vapor variability. We also consider the fraction of entry water vapor variability that can be accounted for by variations of the cold point temperature as an upper bound on how much water vapor variability is predictable from large scale processes. Several periods in which the MLR fails to account for interannual variability are treated as case studies in order to better understand variability in entry water not governed by these large scale processes.&lt;/p&gt;

Influence of Atmospheric Teleconnections on Interannual Variability of Boreal Fires

2020 ◽  
Author(s):  
Zhiyi Zhao ◽  
Zhongda Lin ◽  
Fang Li
Keyword(s):  
Interannual Variability ◽  
Large Scale ◽  
Driving Forces ◽  
Southern Oscillation ◽  
Burned Area ◽  
East Atlantic ◽  
Local Climate ◽  
Atmospheric Teleconnection ◽  
Teleconnection Patterns ◽  
Global Carbon

&lt;p&gt;Wildfires are common in boreal forests around the world and strongly affect regional ecosystem processes and global carbon cycle. Previous studies have suggested that local climate is a dominant driver of boreal fires. However, the impacts of large-scale atmospheric teleconnection patterns on boreal fires and related physical processes remain largely unclear. This study investigates the influence of nine leading atmospheric teleconnection modes and El Ni&amp;#241;o-Southern Oscillation (ENSO) on the interannual variability of simultaneous summer fires in the boreal regions based on 1997-2015 GFED4s burned area, NCEP/NCAR atmospheric reanalysis, and HadISST sea surface temperature. Results show that ENSO has only a weak effect on boreal fires, distinct from its robust influence on the tropical fires. Instead, the interannual variability of burned area in the boreal regions is significantly regulated by five teleconnection patterns. Specifically, East Pacific-North Pacific (EP/NP) and East Atlantic/West Russia (EA/WR) patterns affect the burned area in North America, North Atlantic Oscillation (NAO) and East Atlantic (EA) patterns for Asia, and the Pacific-North American (PNA) pattern for Europe. Related to the teleconnections, the larger burned area is attributable to warmer surface by an anomalous high-pressure above and drier surface due to less moisture transport from the neighboring oceans. The results improve our understanding of driving forces of interannual variability of boreal fires and then regional and global carbon budgets.&lt;/p&gt;

scholarly journals Spatial Coherence of Monsoon Onset over Western and Central Sahel (1950–2000)

2009 ◽  
Vol 22 (5) ◽  
pp. 1313-1324 ◽  
Author(s):  
Romain Marteau ◽  
Vincent Moron ◽  
Nathalie Philippon
Keyword(s):  
Burkina Faso ◽  
Interannual Variability ◽  
Large Scale ◽  
Spatial Coherence ◽  
Daily Rainfall ◽  
Local Scale ◽  
Monsoon Onset ◽  
Onset Date ◽  
Dry Spell

Abstract The spatial coherence of boreal monsoon onset over the western and central Sahel (Senegal, Mali, Burkina Faso) is studied through the analysis of daily rainfall data for 103 stations from 1950 to 2000. Onset date is defined using a local agronomic definition, that is, the first wet day (&gt;1 mm) of 1 or 2 consecutive days receiving at least 20 mm without a 7-day dry spell receiving less than 5 mm in the following 20 days. Changing either the length or the amplitude of the initial wet spell, or both, or the length of the following dry spell modifies the long-term mean of local-scale onset date but has only a weak impact either on its interannual variability or its spatial coherence. Onset date exhibits a seasonal progression from southern Burkina Faso (mid-May) to northwestern Senegal and Saharian edges (early August). Interannual variability of the local-scale onset date does not seem to be strongly spatially coherent. The amount of common or covariant signal across the stations is far weaker than the interstation noise at the interannual time scale. In particular, a systematic spatially consistent advance or delay of the onset is hardly observed across the whole western and central Sahel. In consequence, the seasonal predictability of local-scale onset over the western and central Sahel associated, for example, with large-scale sea surface temperatures, is, at best, weak.

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