scholarly journals Relationships between Southeast Australian Temperature Anomalies and Large-Scale Climate Drivers

2014 ◽  
Vol 27 (4) ◽  
pp. 1395-1412 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Lance M. Leslie
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Power Spectra ◽  
Warm Season ◽  
Principal Component ◽  
Temperature Variability ◽  
Maximum Temperature ◽  
Past Century ◽  
Tasman Sea ◽  
Australian Continent

Abstract Over the past century, particularly after the 1960s, observations of mean maximum temperatures reveal an increasing trend over the southeastern quadrant of the Australian continent. Correlation analysis of seasonally averaged mean maximum temperature anomaly data for the period 1958–2012 is carried out for a representative group of 10 stations in southeast Australia (SEAUS). For the warm season (November–April) there is a positive relationship with the El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO) and an inverse relationship with the Antarctic Oscillation (AAO) for most stations. For the cool season (May–October), most stations exhibit similar relationships with the AAO, positive correlations with the dipole mode index (DMI), and marginal inverse relationships with the Southern Oscillation index (SOI) and the PDO. However, for both seasons, the blocking index (BI, as defined by M. Pook and T. Gibson) in the Tasman Sea (160°E) clearly is the dominant climate mode affecting maximum temperature variability in SEAUS with negative correlations in the range from r = −0.30 to −0.65. These strong negative correlations arise from the usual definition of BI, which is positive when blocking high pressure systems occur over the Tasman Sea (near 45°S, 160°E), favoring the advection of modified cooler, higher-latitude maritime air over SEAUS. A point-by-point correlation with global sea surface temperatures (SSTs), principal component analysis, and wavelet power spectra support the relationships with ENSO and DMI. Notably, the analysis reveals that the maximum temperature variability of one group of stations is explained primarily by local factors (warmer near-coastal SSTs), rather than teleconnections with large-scale drivers.

scholarly journals Links between Central West Western Australian Rainfall Variability and Large-Scale Climate Drivers

2013 ◽  
Vol 26 (7) ◽  
pp. 2222-2246 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Lance M. Leslie
Keyword(s):  
Western Australia ◽  
Large Scale ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Winter Season ◽  
Principal Component ◽  
Southern Annular Mode ◽  
Reanalysis Data ◽  
Past Century ◽  
Drying Trend

Abstract Over the past century, and especially after the 1970s, rainfall observations show an increase (decrease) of the wet summer (winter) season rainfall over northwest (southwest) Western Australia. The rainfall in central west Western Australia (CWWA), however, has exhibited comparatively much weaker coastal trends, but a more prominent inland increase during the wet summer season. Analysis of seasonally averaged rainfall data from a group of stations, representative of both the coastal and inland regions of CWWA, revealed that rainfall trends during the 1958–2010 period in the wet months of November–April were primarily associated with El Niño–Southern Oscillation (ENSO), and with the southern annular mode (SAM) farther inland. During the wet months of May–October, the Indian Ocean dipole (IOD) showed the most robust relationships. Those results hold when the effects of ENSO or IOD are excluded, and were confirmed using a principal component analysis of sea surface temperature (SST) anomalies, rainfall wavelet analyses, and point-by-point correlations of rainfall with global SST anomaly fields. Although speculative, given their long-term averages, reanalysis data suggest that from 1958 to 2010 the increase in CWWA inland rainfall largely is attributable to an increasing cyclonic anomaly trend over CWWA, bringing onshore moist tropical flow to the Pilbara coast. During May–October, the flow anomaly exhibits a transition from an onshore to offshore flow regime in the 2001–10 decade, which is consistent with the observed weaker drying trend during this period.

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 Comparing precipitation and temperature trends between inland and coastal locations

2019 ◽  
Vol 60 ◽  
pp. C109-C126 ◽  
Author(s):  
Joshua Hartigan ◽  
Shev MacNamara ◽  
Lance M Leslie
Keyword(s):  
Climate Change ◽  
Minimum Temperature ◽  
Southern Oscillation ◽  
Power Spectra ◽  
Maximum Temperature ◽  
P Value ◽  
Wet Season ◽  
Intergovernmental Panel ◽  
The Past ◽  
The Mean

Motivated by the Millennium Drought and the current drought over much of southern and eastern Australia, this detailed statistical study compares trends in annual wet season precipitation and temperature between a coastal site (Newcastle) and an inland site (Scone). Bootstrap permutation tests reveal Scone precipitation has decreased significantly over the past 40 years (p-value=0.070) whereas Newcastle has recorded little to no change (p-value=0.800). Mean maximum and minimum temperatures for Newcastle have increased over the past 40 years (p-values of 0.002 and 0.015, respectively) while the mean maximum temperature for Scone has increased (p-value = 0.058) and the mean minimum temperature has remained stable. This suggests mean temperatures during the wet season for both locations are increasing. Considering these trends along with those for precipitation, water resources in the Hunter region will be increasingly strained as a result of increased evaporation with either similar or less precipitation falling in the region. Wavelet analysis reveals that both sites have similar power spectra for precipitation and mean maximum temperature with a statistically significant signal in the two to seven year period, typically indicative of the El-Nino Southern Oscillation climate driver. The El-Nino Southern Oscillation also drives the Newcastle mean minimum temperature, whereas the Scone power spectra has no indication of a definitive driver for mean minimum temperature. References R. A., R. L. Kitching, F. Chiew, L. Hughes, P. C. D. Newton, S. S. Schuster, A. Tait, and P. Whetton. Climate change 2014: Impacts, adaptation, and vulnerability. Part B: Regional aspects. Contribution of Working Group II to the Fifth Assessment of the Intergovernmental Panel on Climate Change. Technical report, Intergovernmental Panel on Climate Change, 2014. URL https://www.ipcc.ch/report/ar5/wg2/. Bureau of Meteorology. Climate Glossary-Drought. URL http://www.bom.gov.au/climate/glossary/drought.shtml. K. M. Lau and H. Weng. Climate signal detection using wavelet transform: How to make a time series sing. B. Am. Meteorol. Soc., 76:23912402, 1995. doi:10.1175/1520-0477(1995)0762391:CSDUWT>2.0.CO;2. M. B. Richman and L. M. Leslie. Uniqueness and causes of the California drought. Procedia Comput. Sci., 61:428435, 2015. doi:10.1016/j.procs.2015.09.181. M. B. Richman and L. M. Leslie. The 20152017 Cape Town drought: Attribution and prediction using machine learning. Procedia Comput. Sci., 140:248257, 2018. doi:10.1016/j.procs.2018.10.323.

A Methodological Approach to Assess the Co-Behavior of Climate Processes over Southern Africa

2019 ◽  
Vol 32 (9) ◽  
pp. 2483-2495 ◽  
Author(s):  
Kwesi A. Quagraine ◽  
Bruce Hewitson ◽  
Christopher Jack ◽  
Izidine Pinto ◽  
Christopher Lennard
Keyword(s):  
Southern Africa ◽  
Large Scale ◽  
Southern Oscillation ◽  
Methodological Approach ◽  
Principal Component ◽  
Self Organizing Maps ◽  
Circulation Patterns ◽  
Climate Forcings ◽  
The Impact ◽  
Precipitation And Temperature

Abstract The study develops an approach to assess co-behavior of climate processes. The regional response of precipitation and temperature patterns over southern Africa to the combined roles (co-behavior) of El Niño–Southern Oscillation (ENSO), Antarctic Oscillation (AAO), and intertropical convergence zone (ITCZ) is evaluated. Self-organizing maps (SOMs) classify circulation patterns over the subcontinent, and principal component analysis (PCA) is used to identify related patterns across the data. The tropical rain belt index (TRBI), a measure of the ITCZ, is generally in phase with the AAO but mostly out of phase with ENSO. The phases of AAO may enhance or suppress ENSO impact on the location and distribution of regional precipitation and temperature over the region. This understanding of the co-behavior of large-scale processes is important to assess the impact these processes collectively have on precipitation and temperature, especially under future climate forcings.

Influences of the seasonal Indian monsoons, 1790-1993 CE: Sub-annual sea surface temperature and precipitation reconstructed from laminated Pakistan Margin sediments

2020 ◽  
Author(s):  
Tiffany J. Napier ◽  
Lars Wӧrmer ◽  
Jenny Wendt ◽  
Andreas Lückge ◽  
Kai-Uwe Hinrichs
Keyword(s):  
Sediment Core ◽  
Temporal Resolution ◽  
River Runoff ◽  
Southern Oscillation ◽  
Power Spectra ◽  
Principal Component ◽  
Summer Monsoon Rainfall ◽  
Winter Monsoon ◽  
Sea Surface ◽  
Annual Range

<p>Sub-decadal to annual climate oscillations are particularly relevant to human climate perception, including such well-known phenomena as the seasonal monsoons and El Niño-Southern Oscillation (ENSO). To assess the variability of these oscillations in the past, proxies for climate parameters that are influenced by these oscillations (e.g., temperature, precipitation) and geologic materials with a temporal resolution able to record them are both needed. However, even in settings where these two criteria are met, the sample size needed for laboratory analysis can limit temporal resolution.</p><p>We utilize a novel mass spectrometry imaging technique to measure and map distributions of climate-relevant biomarkers (e.g., GDGTs, alkenones) from intact sediment core surfaces in sub-mm increments, unlocking the ability to reconstruct sub-annual paleoclimate. These same sediment sample surfaces are analyzed with micro-XRF mapping to enable congruent examination of complementary elemental- and biomarker-derived paleoenvironmental proxies at ultra-high spatial resolution, both down-core and along-lamination.</p><p>We applied our biomarker and elemental mapping techniques to annually-laminated Pakistan Margin (northeastern Arabian Sea) sediment core SO90-58KG, spanning 1790-1993 CE. Laminated Pakistan Margin marine sediments are excellent archives of past climate and oceanographic conditions that are influenced by the summer (Southwest) and winter (Northeast) monsoons of India. We measured alkenones and GDGTs at 200 µm resolution, and elemental abundances at 50 µm resolution. Reconstructed sea surface temperatures (SSTs) were calculated from alkenone (U<sup>K'</sup><sub>37</sub>) and GDGT (CCaT) ratios, respectively, with sample resolution up to four points per year. Principal component analysis was applied to the elemental measurements. The first principal component (PC1) is associated with siliciclastic elements (Al, Si, K, Ti, Fe), and is used as a proxy for sub-annual precipitation-driven river runoff.</p><p>Reconstructed SSTs for both biomarker proxies contain congruent trends, and align with the annual range of instrumental measurements (23 to 30 °C). The annual cycles in SST, with low temperatures driven by mixing during the winter monsoon, are prominent in the time series and highly significant in their power spectra. Using this annual cycle in SST and our paired elemental measurements, we determine the season(s) of river runoff. PC1 is typically highest when SST is low, suggesting runoff/deposition usually occurs during the winter monsoon, consistent with precipitation from westerly storms. However, some years contain PC1 peaks that occur in-phase with warm SSTs, suggesting expansion of summer monsoon rainfall west of Karachi during these years. This work demonstrates the cutting edge of high-resolution paleoclimate science, and provides new insights into the variability of the Indian monsoon from its sensitive western edge.</p>

Climate Change on the Northern Tibetan Plateau during 1957–2009: Spatial Patterns and Possible Mechanisms

2013 ◽  
Vol 26 (1) ◽  
pp. 85-109 ◽  
Author(s):  
Lan Cuo ◽  
Yongxin Zhang ◽  
Qingchun Wang ◽  
Leilei Zhang ◽  
Bingrong Zhou ◽  
...  
Keyword(s):  
Wind Speed ◽  
Tibetan Plateau ◽  
Large Scale ◽  
Southern Oscillation ◽  
Warm Season ◽  
The Arctic ◽  
Climate Indices ◽  
High Mountain ◽  
Gridded Data ◽  
Northern Tibetan Plateau

Abstract Gridded daily precipitation, temperature minima and maxima, and wind speed are generated for the northern Tibetan Plateau (NTP) for 1957–2009 using observations from 81 surface stations. Evaluation reveals reasonable quality and suitability of the gridded data for climate and hydrology analysis. The Mann–Kendall trends of various climate elements of the gridded data show that NTP has in general experienced annually increasing temperature and decreasing wind speed but spatially varied precipitation changes. The northwest (northeast) NTP became dryer (wetter), while there were insignificant changes in precipitation in the south. Snowfall has decreased along high mountain ranges during the wet and warm season. Averaged over the entire NTP, snowfall, temperature minima and maxima, and wind speed experienced statistically significant linear trends at rates of −0.52 mm yr−1 (water equivalent), +0.04°C yr−1, +0.03°C yr−1, and −0.01 m s−1 yr−1, respectively. Correlation between precipitation/wind speed and climate indices characterizing large-scale weather systems for four subregions in NTP reveals that changes in precipitation and wind speed in winter can be attributed to changes in the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), the East Asian westerly jet (WJ), and the El Niño–Southern Oscillation (ENSO) (wind speed only). In summer, the changes in precipitation and wind are only weakly related to these indices. It is speculated that in addition to the NAO, AO, ENSO, WJ, and the East and South Asian summer monsoons, local weather systems also play important roles.

scholarly journals Investigation of hydrological variability in the Korean Peninsula with the ENSO teleconnections

2016 ◽  
Vol 374 ◽  
pp. 165-173 ◽  
Author(s):  
Sunkwon Yoon ◽  
Taesam Lee
Keyword(s):  
El Niño ◽  
Korean Peninsula ◽  
El Nino ◽  
Southern Oscillation ◽  
Singular Spectrum Analysis ◽  
Warm Season ◽  
Principal Component ◽  
Lag Time ◽  
Climate Indices ◽  
Atmospheric Teleconnections

Abstract. This study analyzes nonlinear behavior links with atmospheric teleconnections between hydrologic variables and climate indices using statistical models during warm season (June to September) over the Korean Peninsula (KP). The ocean-related major climate factor, which is the El Niño-Southern Oscillation (ENSO) was used to analyze the atmospheric teleconnections by principal component analysis (PCA) and a singular spectrum analysis (SSA). The nonlinear lag time correlations between climate indices and hydrologic variables are calculated by Mutual Information (MI) technique. The nonlinear correlation coefficients (CCs) by MI were higher than linear CCs, and ENSO shows a few months of lag time correlation. The warm season hydrologic variables in KP shows a significant increasing tendency during the warm pool (WP), and the cold tongue (CT) El Niño decaying years shows a significant decreasing tendency, while the La Niña year shows slightly above normal conditions, respectively. A better understanding of the relationship between climate indices and streamflow, and their local impacts can help to prepare for the river discharge management by water managers and scientists. Furthermore, these results provide useful data for policy makers and end-users to support long-range water resources prediction and water-related policy.

scholarly journals Regression-based season-ahead drought prediction for southern Peru conditioned on large-scale climate variables

2017 ◽  
Author(s):  
Eric Mortensen ◽  
Shu Wu ◽  
Michael Notaro ◽  
Steven Vavrus ◽  
Rob Montgomery ◽  
...  
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Local Level ◽  
Principal Component ◽  
Spatiotemporal Variability ◽  
Climate Indices ◽  
Southern Peru ◽  
Drought Prediction

Abstract. Located at a complex topographic, climatic, and hydrologic crossroads, southern Peru is a semi-arid region that exhibits high spatiotemporal variability in precipitation. The economic viability of the region hinges on this water, yet southern Peru is prone to water scarcity caused by seasonal drought. Droughts here are often triggered during El Niño episodes; however, other large-scale climate mechanisms also play a noteworthy role in controlling the region’s hydrologic cycle. An extensive season-ahead drought prediction model is developed to help bolster existing capacity of stakeholders to plan for and mitigate the deleterious impacts of this hydrologic extreme. In addition to existing climate indices, large-scale climatic variables, such as sea surface temperature, are investigated to identify potential drought predictors. A principal component regression framework is applied to eleven potential predictors to produce an ensemble forecast of January-March precipitation. Model hindcasts of 51 years, compared to climatology and another model conditioned solely on an El Niño-Southern Oscillation index, achieve notable skill and perform better for several metrics, including ranked probability skill score and a hit-miss statistic. Extending the lead time and spatially disaggregating precipitation predictions to the local level may further assist regional stakeholders and policymakers preparing for drought.

scholarly journals Large-Scale Influences on the Evolution of Winter Subtropical Maritime Cyclones Affecting Australia’s East Coast

2013 ◽  
Vol 141 (7) ◽  
pp. 2416-2431 ◽  
Author(s):  
Stuart A. Browning ◽  
Ian D. Goodwin
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
East Coast ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Winter Period ◽  
Evolutionary Trajectory ◽  
Late Autumn ◽  
Tasman Sea ◽  
Eastern Seaboard

Abstract Subtropical maritime low pressure systems frequently impact Australia’s eastern seaboard. Closed circulation lows in the Tasman Sea region are termed East Coast Cyclones (ECC); they can evolve in a range of climatic environments and have proven most destructive during the late autumn–winter period. Using criteria based on pressure gradients, inferred wind field, and duration, an objectively determined database of ECC occurrences is established to explore large-scale influences on ECC evolution. Subclassification based on evolutionary trajectory reveals two dominant storm types during late autumn–winter: easterly trough lows (ETL) and southern secondary lows (SSL). Synoptic composites are used to investigate the climatological evolution of each storm type. ETL cyclogenesis occurs along the eastern seaboard at the confluence of warm moist subtropical easterlies and cool air over the continent that is advected from higher latitudes. SSL develop when a cold extratropical cyclone moves equatorward and interacts with warm moist conditions in the Tasman Sea. At seasonal time scales, a complex interplay of tropical and extratropical influences contributes to high-frequency storm seasons. ETL are more frequent during neutral or positive phases of the El Niño–Southern Oscillation, cool sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean, and neutral to positive southern annular mode phases. SSL are more frequent during years with warm SSTAs in the eastern Indian Ocean, warm SSTAs in the western Pacific, and high-latitude blocking.

scholarly journals Multi-century cool- and warm-season rainfall reconstructions for Australia's major climatic regions

2017 ◽  
Vol 13 (12) ◽  
pp. 1751-1770 ◽  
Author(s):  
Mandy Freund ◽  
Benjamin J. Henley ◽  
David J. Karoly ◽  
Kathryn J. Allen ◽  
Patrick J. Baker
Keyword(s):  
World War Ii ◽  
Large Scale ◽  
Rainfall Variability ◽  
Warm Season ◽  
Seasonal Rainfall ◽  
Spatial Extent ◽  
The Past ◽  
Millennium Drought ◽  
Australian Continent ◽  
Regional Rainfall

Abstract. Australian seasonal rainfall is strongly affected by large-scale ocean–atmosphere climate influences. In this study, we exploit the links between these precipitation influences, regional rainfall variations, and palaeoclimate proxies in the region to reconstruct Australian regional rainfall between four and eight centuries into the past. We use an extensive network of palaeoclimate records from the Southern Hemisphere to reconstruct cool (April–September) and warm (October–March) season rainfall in eight natural resource management (NRM) regions spanning the Australian continent. Our bi-seasonal rainfall reconstruction aligns well with independent early documentary sources and existing reconstructions. Critically, this reconstruction allows us, for the first time, to place recent observations at a bi-seasonal temporal resolution into a pre-instrumental context, across the entire continent of Australia. We find that recent 30- and 50-year trends towards wetter conditions in tropical northern Australia are highly unusual in the multi-century context of our reconstruction. Recent cool-season drying trends in parts of southern Australia are very unusual, although not unprecedented, across the multi-century context. We also use our reconstruction to investigate the spatial and temporal extent of historical drought events. Our reconstruction reveals that the spatial extent and duration of the Millennium Drought (1997–2009) appears either very much below average or unprecedented in southern Australia over at least the last 400 years. Our reconstruction identifies a number of severe droughts over the past several centuries that vary widely in their spatial footprint, highlighting the high degree of diversity in historical droughts across the Australian continent. We document distinct characteristics of major droughts in terms of their spatial extent, duration, intensity, and seasonality. Compared to the three largest droughts in the instrumental period (Federation Drought, 1895–1903; World War II Drought, 1939–1945; and the Millennium Drought, 1997–2005), we find that the historically documented Settlement Drought (1790–1793), Sturt's Drought (1809–1830) and the Goyder Line Drought (1861–1866) actually had more regionalised patterns and reduced spatial extents. This seasonal rainfall reconstruction provides a new opportunity to understand Australian rainfall variability by contextualising severe droughts and recent trends in Australia.

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