The southern oscillation and South African summer rainfall

1988 ◽  
Vol 8 (6) ◽  
pp. 577-597 ◽  
Author(s):  
Johan Van Heerden ◽  
Deon E. Terblanche ◽  
Gerhard C. Schulze
Keyword(s):  
South African ◽  
Southern Oscillation ◽  
Summer Rainfall

Elemental proxy evidence for late Quaternary palaeoenvironmental change in southern African sedimentary records: interpretation and applications

2021 ◽  
Author(s):  
M.S. Humphries
Keyword(s):  
Environmental Change ◽  
Southern Africa ◽  
Southern Oscillation ◽  
Late Quaternary ◽  
Rainfall Variability ◽  
Analytical Techniques ◽  
Summer Rainfall ◽  
Geochemical Data ◽  
Complex Nature ◽  
Cape Coast

Abstract Sediments are the most important source of Late Quaternary palaeoclimate information in southern Africa, but have been little studied from a geochemical perspective. However, recent advances in analytical techniques that allow rapid and near-continuous elemental records to be obtained from sedimentary sequences has resulted in the increasing use of elemental indicators for reconstructing climate. This paper explores the diverse information that can be acquired from the inorganic component of sediments and reviews some of the progress that has been made over the last two decades in interpreting the climatic history of southern Africa using elemental records. Despite the general scarcity of elemental records, excellent examples from the region exist, which provide some of the longest and most highly resolved sequences of environmental change currently available. Records from Tswaing crater and marine deposits on the southern KwaZulu-Natal coastline have provided rare glimpses into hydroclimate variability over the last 200 000 years, suggesting that summer rainfall in the region responded predominantly to insolation forcing on glacial-interglacial timescales. Over shorter timescales, lakes and wetlands found in the Wilderness embayment on the southern Cape coast and along the Maputaland coast in north-eastern South Africa have yielded highly-resolved elemental records of Holocene environmental change, providing insight into the changing interactions between tropical (e.g., El Niño-Southern Oscillation) and temperate (e.g., mid-latitude westerlies) climate systems affecting rainfall variability in the region. The examples discussed demonstrate the multiple environmental processes that can be inferred from elemental proxies and the unique insight this can provide in advancing our understanding of past climate change on different timescales. The interpretation of geochemical data can be complicated by the complex nature of sedimentary environments, various proxy assumptions and analytical challenges, and the reliability of sediment-based climate reconstructions is substantially enhanced through multi-proxy approaches.

The Southern Oscillation Index as a predictor of seasonal rainfall in the arable areas of the inland Australian subtropics

1993 ◽  
Vol 44 (6) ◽  
pp. 1337 ◽  
Author(s):  
JS Russell ◽  
IM McLeod ◽  
MB Dale ◽  
TR Valentine
Keyword(s):  
Southern Oscillation Index ◽  
Southern Oscillation ◽  
Linear Trend ◽  
Summer Rainfall ◽  
Seasonal Rainfall ◽  
Four Seasons ◽  
Eastern Australia ◽  
Australian Continent ◽  
Ace Algorithm ◽  
Linear Trends

A detailed study has been carried out in four regions in the subtropics of Eastern Australia to determine the relationship between the Southern Oscillation Index (SOI) and subsequent seasonal rainfall. The period studied was from 1915 to 1991 for 3-monthly periods of spring (SON), summer (DJF), autumn (MAM) and winter (JJA). The 3-monthly prior SOI values were plotted against seasonal rainfall of the four regions and four seasons. These data were widely scattered but with a linear trend showing increased seasonal rainfall as the SOI increased. Linear trends were plotted for each season and region. Comparisons were made between the use of the ACE algorithm, which transforms the SOI and rainfall data, and the use of linear trends. Polynomials were used to calculate equations for each region and season, but only spring and summer produced satisfactory ACE functions. Estimates were made of spring and summer rainfall relative to prior SOI values for each region. While the SOI as a predictor of rainfall broadly estimates spring and summer rainfall, this variable has limited usefulness on its own. One of the options available with the ACE program is that additional independent variables can be added as required. Current research suggests that sea surface temperature data from specific ocean areas surrounding the Australian continent is the most useful additional variable at present. However the complexity of such an analysis is greatly increased.

scholarly journals Interdecadal Changes in the Leading Ocean Forcing of Sahelian Rainfall Interannual Variability: Atmospheric Dynamics and Role of Multidecadal SST Background

2018 ◽  
Vol 31 (17) ◽  
pp. 6687-6710 ◽  
Author(s):  
Roberto Suárez-Moreno ◽  
Belén Rodríguez-Fonseca ◽  
Jesús A. Barroso ◽  
Andreas H. Fink
Keyword(s):  
Southern Oscillation ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Rain Gauge ◽  
Sst Variability ◽  
Cold Events ◽  
Sahel Rainfall ◽  
West African Sahel ◽  
First Time

The atmospheric response to global sea surface temperatures is the leading cause of rainfall variability in the West African Sahel. On interannual periodicities, El Niño–Southern Oscillation, the Atlantic equatorial mode, and Mediterranean warm/cold events primarily drive variations of summer rainfall over the Sahel. Nevertheless, the rainfall response to these modes of interannual SST variability has been suggested to be unstable throughout the observational record. This study explores changes in the leading patterns of covariability between Sahel rainfall and SSTs, analyzing the dynamical mechanisms at work to explain the nonstationary relationship between anomalies in these two fields. A new network of rain gauge stations across West Africa is used for the first time to investigate these instabilities during the period 1921–2010. A hypothesis is raised that the underlying SST background seems to favor some interannual teleconnections and inhibit others in terms of the cross-equatorial SST gradients and associated impacts on the location of the intertropical convergence zone. Results of this study are relevant for improving the seasonal predictability of summer rainfall in the Sahel.

Decadal–Multidecadal Variations of Asian Summer Rainfall from the Little Ice Age to the Present

2019 ◽  
Vol 32 (22) ◽  
pp. 7663-7674 ◽  
Author(s):  
Hui Shi ◽  
Bin Wang ◽  
Jian Liu ◽  
Fei Liu
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Southern Oscillation ◽  
Summer Rainfall ◽  
Ice Age ◽  
Uniform Structure ◽  
Maritime Continent ◽  
Remarkable Change ◽  
Decadal Time Scale ◽  
Asian Summer

Abstract Features of decadal–multidecadal variations of the Asian summer rainfall are revealed by analysis of the reconstructed Asian summer precipitation (RAP) dataset from 1470 to 2013. Significant low-frequency periodicities of the all-Asian rainfall (AAR) index (AARI) are found on decadal (8–10 yr), quasi-bidecadal (22 yr), and multidecadal (50–54 yr) time scales, as well as centennial time scales. The decadal and multidecadal peaks are mainly from the “monsoon Asia” area and the Maritime Continent, while the 22-yr peak is from the “arid Asia” area. A remarkable change of leading frequency from multidecadal to decadal after AD 1700 is detected across the entire Asian landmass. The leading empirical orthogonal function (EOF) modes on the decadal and multidecadal time scales exhibit a uniform structure similar to that on the interannual time scale, suggesting a cross-time-scale, in-phase variation of the rainfall across continental Asia and the Maritime Continent. Enhanced AAR on a decadal time scale is found associated with the mega-La Niña sea surface temperature (SST) pattern over the Pacific. The AARI–mega-ENSO (El Niño–Southern Oscillation) relationship is persistently significant except from 1820 to around 1900. Enhanced decadal AAR is also found to be associated with extratropical North Atlantic warming. The AARI–AMO (Atlantic multidecadal oscillation) relationship, however, is nonstationary. On the multidecadal time scale, the AAR is significantly related to the AMO. Mechanisms associated with the decadal–multidecadal variability of AAR are also discussed.

scholarly journals Interannual Variation of Summer Rainfall in the Taipei Basin

2016 ◽  
Vol 55 (8) ◽  
pp. 1789-1812 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Jenq-Dar Tsay ◽  
Eugene S. Takle
Keyword(s):  
Southern Oscillation ◽  
Summer Rainfall ◽  
Thunderstorm Activity ◽  
River Valley ◽  
Interannual Variations ◽  
Asian Monsoon Region ◽  
Maximum Rainfall ◽  
Vapor Flux ◽  
Taipei Basin ◽  
Northern Taiwan

AbstractThe Taipei basin, located in northern Taiwan, is formed at the intersection of the Tanshui River valley (~30 km) and the Keelung River valley (~60 km). Summer is the dry season in northern Taiwan, but the maximum rainfall in the Taipei basin occurs during 15 June–31 August. The majority of summer rainfall in this basin is produced by afternoon thunderstorms. Thus, the water supply, air/land traffic, and pollution for this basin can be profoundly affected by interannual variations of thunderstorm days and rainfall. Because the mechanism for these interannual variations is still unknown, a systematic analysis is made of thunderstorm days and rainfall for the past two decades (1993–2013). These two variables are found to correlate opposite interannual variations of sea surface temperature anomalies over the National Oceanic and Atmospheric Administration Niño-3.4 region. Occurrence days for afternoon thunderstorms and rainfall amounts in the Taipei basin double during the cold El Niño–Southern Oscillation (ENSO) phase relative to the warm phase. During the latter phase, a stronger cold/drier monsoon southwesterly flow caused by the Pacific–Japan Oscillation weakens the thunderstorm activity in the Taipei basin through the land–sea breeze. In contrast, the opposite condition occurs during the cold ENSO phase. The water vapor flux over the East/Southeast Asian monsoon region converges more toward Taiwan to maintain rainfall over the Taipei basin during the cold ENSO phase than during the warm ENSO phase.

scholarly journals Prospects for Dynamical Prediction of Meteorological Drought

2012 ◽  
Vol 51 (7) ◽  
pp. 1238-1252 ◽  
Author(s):  
Xiao-Wei Quan ◽  
Martin P. Hoerling ◽  
Bradfield Lyon ◽  
Arun Kumar ◽  
Michael A. Bell ◽  
...  
Keyword(s):  
Great Plains ◽  
Climate Model ◽  
Southern Oscillation ◽  
Standardized Precipitation Index ◽  
Summer Rainfall ◽  
Northern Great Plains ◽  
Seasonal Forecasts ◽  
Wet Season ◽  
Antecedent Soil Moisture ◽  
Drought Prediction

AbstractThe prospects for U.S. seasonal drought prediction are assessed by diagnosing simulation and hindcast skill of drought indicators during 1982–2008. The 6-month standardized precipitation index is used as the primary drought indicator. The skill of unconditioned, persistence forecasts serves as the baseline against which the performance of dynamical methods is evaluated. Predictions conditioned on the state of global sea surface temperatures (SST) are assessed using atmospheric climate simulations conducted in which observed SSTs are specified. Predictions conditioned on the initial states of atmosphere, land surfaces, and oceans are next analyzed using coupled climate-model experiments. The persistence of the drought indicator yields considerable seasonal skill, with a region’s annual cycle of precipitation driving a strong seasonality in baseline skill. The unconditioned forecast skill for drought is greatest during a region’s climatological dry season and is least during a wet season. Dynamical models forced by observed global SSTs yield increased skill relative to this baseline, with improvements realized during the cold season over regions where precipitation is sensitive to El Niño–Southern Oscillation. Fully coupled initialized model hindcasts yield little additional skill relative to the uninitialized SST-forced simulations. In particular, neither of these dynamical seasonal forecasts materially increases summer skill for the drought indicator over the Great Plains, a consequence of small SST sensitivity of that region’s summer rainfall and the small impact of antecedent soil moisture conditions, on average, upon the summer rainfall. The fully initialized predictions for monthly forecasts appreciably improve on the seasonal skill, however, especially during winter and spring over the northern Great Plains.

scholarly journals Rainfall Changes over Southwestern Australia and Their Relationship to the Southern Annular Mode and ENSO

2014 ◽  
Vol 27 (15) ◽  
pp. 5801-5814 ◽  
Author(s):  
Bhupendra A. Raut ◽  
Christian Jakob ◽  
Michael J. Reeder
Keyword(s):  
Southern Oscillation ◽  
Summer Rainfall ◽  
Southern Annular Mode ◽  
Winter Rainfall ◽  
Sea Level Pressure ◽  
Annular Mode ◽  
Southwestern Australia ◽  
Synoptic Conditions ◽  
The Mean ◽  
Rainfall Patterns

Abstract Since the 1970s, winter rainfall over coastal southwestern Australia (SWA) has decreased by 10%–20%, while summer rainfall has been increased by 40%–50% in the semiarid inland area. In this paper, a K-means algorithm is used to cluster rainfall patterns directly as opposed to the more conventional approach of clustering synoptic conditions (usually the mean sea level pressure) and inferring the associated rainfall. It is shown that the reduction in the coastal rainfall during winter is mainly due to fewer westerly fronts in June and July. The reduction in the frequency of strong fronts in June is responsible for half of the decreased rainfall in June–August (JJA), whereas the reduction in the frequency of weaker fronts in June and July accounts for a third of the total decrease. The increase in rainfall inland in December–February (DJF) is due to an increased frequency of easterly troughs in December and February. These rainfall patterns are linked to the southern annular mode (SAM) index and Southern Oscillation index (SOI). The reduction in coastal rainfall and the increase in rainfall inland are both related to the predominantly positive phase of SAM, especially when the phase of ENSO is neutral.

scholarly journals ENSO Teleconnection to Eastern African Summer Rainfall in Global Climate Models: Role of the Tropical Easterly Jet

2021 ◽  
Vol 34 (1) ◽  
pp. 293-312
Author(s):  
Amandeep Vashisht ◽  
Benjamin Zaitchik ◽  
Anand Gnanadesikan
Keyword(s):  
Climate Variability ◽  
Climate Models ◽  
Southern Oscillation ◽  
Global Climate ◽  
Summer Rainfall ◽  
Global Climate Models ◽  
Eastern Africa ◽  
Climate Variability And Change ◽  
Tropical Easterly Jet ◽  
Interannual Rainfall Variability

AbstractGlobal climate models (GCMs) are critical tools for understanding and projecting climate variability and change, yet the performance of these models is notoriously weak over much of tropical Africa. To improve this situation, process-based studies of African climate dynamics and their representation in GCMs are required. Here, we focus on summer rainfall of eastern Africa (SREA), which is crucial to the Ethiopian Highlands and feeds the flow of the Blue Nile River. The SREA region is highly vulnerable to droughts, with El Niño–Southern Oscillation (ENSO) being a leading cause of interannual rainfall variability. Adequate understanding and accurate representation of climate features that influence regional variability is an important but often neglected issue when evaluating models. We perform a process-based evaluation of GCMs, focusing on the upper-troposphere tropical easterly jet (TEJ), which has been hypothesized to link ENSO to SREA. We find that most models have an ENSO–TEJ coupling similar to observed, but the models diverge in their representation of TEJ–SREA coupling. Differences in the latter explain the majority (80%) of variability in ENSO teleconnection simulation across the models. This is higher than the variance explained by rainfall coupling with the Somali jet (44%) and African easterly jet (55%). However, our diagnostics of the leading hypothesized mechanism in the models—variability in divergence in the TEJ exit region—are not consistent across models and suggest that a deeper understanding of the mechanisms of TEJ–precipitation coupling should be a priority for studies of climate variability and change in the region.

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