The diurnal cycle of rainfall in South Africa in the austral summer

2012 ◽  
Vol 33 (3) ◽  
pp. 770-777 ◽  
Author(s):  
Mathieu Rouault ◽  
Shouraseni Sen Roy ◽  
Robert C. Balling
Keyword(s):  
South Africa ◽  
Diurnal Cycle ◽  
Austral Summer

scholarly journals Circulation pattern controls of wet days and dry days in Free State, South Africa

2021 ◽  
Author(s):  
Chibuike Chiedozie Ibebuchi
Keyword(s):  
South Africa ◽  
Indian Ocean ◽  
Atmospheric Circulation ◽  
Southern Africa ◽  
Austral Summer ◽  
Free State ◽  
Austral Spring ◽  
Study Region ◽  
Southwest Indian Ocean ◽  
South Indian

AbstractAtmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the atmospheric circulation. This paper investigates synoptic situations in southern Africa that can be associated with wet days and dry days in Free State, South Africa, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (variable is time series and observation is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of being associated with dry days in Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of being associated with wet days in Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced low-level moisture transport by southeast winds was found to have the highest probability of being associated with above-average rainfall in most regions in Free State. On the other hand, the synoptic state associated with enhanced transport of cold dry air, by the extratropical westerlies, was found to have the highest probability of being associated with (winter) dryness in Free State.

Identifying the drivers of the pelagic ecosystem of an oligotrophic bight (KwaZulu–Natal, South Africa) using stable isotopes (δ13C, δ15N) and C : N ratio analysis

2016 ◽  
Vol 67 (11) ◽  
pp. 1750 ◽  
Author(s):  
Ander M. de Lecea ◽  
Rachel Cooper ◽  
Albertus J. Smit
Keyword(s):  
South Africa ◽  
East Coast ◽  
Austral Summer ◽  
Ratio Analysis ◽  
Wet Season ◽  
Terrestrial Organic Matter ◽  
Pelagic Ecosystem ◽  
Riverine Input ◽  
Kwazulu Natal ◽  
Marine System

The international literature highlights the importance of understanding the role and fate of terrestrial organic matter (OM) in the marine system, yet little is known about this on the oligotrophic east coast of South Africa. Within the Bight, three important processes make OM biologically available: (1) a topographically induced upwelling cell (north), (2) a Cyclonic Eddy (south), and (3) riverine input. We hypothesise that: (i) these OM sources differ substantially in their isotope ratios, and (ii) zooplankton at the inshore region has an isotope signature linked to localised fluvial fluxes. Particulate OM samples were collected at five locations along the Bight and in three main estuaries during austral summer and winter seasons in 2010 and subjected to isotopic and mixing model analysis. Riverine input played an important role in this ecosystem inshore during the wet season. Only marine OM played a role as a biological driver offshore and at all sites during the dry season. Although there were indications that the upwelling cell did occur, it was not confirmed as active in either season. The current study provides valuable insights into the Bight's biological functioning and principle insights into the fate of terrestrial organic carbon on the east coast of southern Africa.

scholarly journals Diurnal Cycle in Different Weather Regimes and Rainfall Variability over Borneo Associated with ENSO

2013 ◽  
Vol 26 (5) ◽  
pp. 1772-1790 ◽  
Author(s):  
Jian-Hua Qian ◽  
Andrew W. Robertson ◽  
Vincent Moron
Keyword(s):  
Diurnal Cycle ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Austral Summer ◽  
Weather Types ◽  
Sea Breezes ◽  
Rainfall Anomalies ◽  
Dipolar Structure

Abstract The interannual variability of precipitation over the island of Borneo in association with El Niño–Southern Oscillation (ENSO) has been studied by using the Global Precipitation Climatology Centre (GPCC) gridded rain gauge precipitation, the NOAA Climate Prediction Center (CPC) Morphing Technique (CMORPH) satellite estimated precipitation, the Quick Scatterometer (QuikSCAT) satellite estimated sea winds, and the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis data. Analysis of the GPCC precipitation shows a dipolar structure of wet southwest versus dry central and northeast in precipitation anomalies associated with El Niño over Borneo Island during the austral summer [December–February (DJF)]. By using the 0.25° and 3-hourly CMORPH precipitation, it is found that rainfall over Borneo is strongly affected by the diurnal cycle of land–sea breezes. The spatial distribution of rainfall over Borneo depends on the direction of monsoonal winds. Weather typing analysis indicates that the dipolar structure of rainfall anomalies associated with ENSO is caused by the variability in the frequency of occurrence of different weather types. Rainfall is enhanced in the coastal region where sea breezes head against off-shore synoptic-scale low-level winds (i.e., in the lee side or wake area of the island), which is referred to here as the “wake effect.” In DJF of El Niño years, the northwesterly austral summer monsoon in southern Borneo is weaker than normal over the Maritime Continent and easterly winds are more frequent than normal over Borneo, acting to enhance rainfall over the southwest coast of the island. This coastal rainfall generation mechanism in different weather types explains the dipole pattern of a wet southwest versus dry northeast in the rainfall anomalies over Borneo Island in the El Niño years.

Circulation pattern control of wet days and dry days in Free State, South Africa

2021 ◽  
Author(s):  
Chibuike Chiedozie Ibebuchi
Keyword(s):  
South Africa ◽  
Indian Ocean ◽  
Atmospheric Circulation ◽  
Southern Africa ◽  
Austral Summer ◽  
Free State ◽  
Study Region ◽  
Southwest Indian Ocean ◽  
South Indian ◽  
Circulation Patterns

Abstract Atmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the mechanisms of atmospheric circulation. This paper uses the concept of classifying the recurrent large-scale atmospheric circulation patterns in southern Africa, and the linkage of the classified patterns to wet days and dry days in Free State, South Africa, for the analysis of how the probability of wet and dry events in Free State can be associated with specific synoptic situations, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (column/variable is time series and row is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the recurrent circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of bringing dry days to Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of bringing wet days to Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced moisture transport by southeast winds was found to have the highest probability to bring above-average rainfall in most regions in Free State; while the synoptic state associated with enhanced transport of cold dry air, from the Benguela current, by the extratropical westerlies was found to be associated with the highest probability of (winter) dryness in Free State.

scholarly journals Influence of Subseasonal Variability on the Diurnal Cycle of Precipitation on a Mountainous Island: The Case of New Caledonia

2019 ◽  
Vol 148 (1) ◽  
pp. 333-351 ◽  
Author(s):  
Damien Specq ◽  
Gilles Bellon ◽  
Alexandre Peltier ◽  
Jérôme Lefèvre ◽  
Christophe Menkes
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
New Caledonia ◽  
Austral Summer ◽  
Mountain Range ◽  
Wet Season ◽  
Diurnal Variability ◽  
Synoptic Wind ◽  
Diurnal Cycle Of Precipitation ◽  
Wind Regimes

Abstract The relationship between the large-scale intraseasonal variability, synoptic wind regimes, and the local daily variability of precipitation over the main island of New Caledonia (southwest tropical Pacific) is investigated with a focus on the austral summer wet season (November–April). The average diurnal cycle of precipitation over the island is characterized by a sharp afternoon maximum around 1600 local time, with significant differences between the windward east coast, the leeward west coast, and the mountain range. The afternoon peak is related to the afternoon sea-breeze circulation and to the diurnal cycle of convection over land. In general, its magnitude follows the same evolution as the daily mean. In agreement with past studies, a clear modulation of the Madden–Julian oscillation (MJO) on both the diurnal cycle of precipitation and the probability of occurrence of four robust wind regimes can be identified in the New Caledonia region during the wet season. From the evidence that there is a qualitative correspondence between the effects of both the MJO phases and the wind regimes on features in the diurnal cycle of precipitation, a simple model is proposed to inspect the MJO forcing mediated by wind regimes on the diurnal variability of rain. The complete decomposition of the MJO impact shows that the modulation of diurnal cycle by the MJO relies on complex interactions between the MJO and synoptic winds that involve both large-scale MJO convective anomalies and MJO-induced modification of wind patterns.

scholarly journals Migratory connectivity and conservation of the Amur Falcon Falco amurensis: a stable isotope perspective

2010 ◽  
Vol 20 (2) ◽  
pp. 134-148 ◽  
Author(s):  
CRAIG T. SYMES ◽  
STEPHAN WOODBORNE
Keyword(s):  
South Africa ◽  
South African ◽  
Significant Proportion ◽  
Austral Summer ◽  
Annual Precipitation ◽  
Migratory Connectivity ◽  
Breeding Sites ◽  
American Kestrels ◽  
Global Estimates ◽  
Global Population

SummaryStable isotopes (δD, δ13C, δ15N) were measured in adult and juvenile Amur Falcon Falco amurensis feathers to understand the migratory connectivity of this species. Using the OIPC (Online Isotopes in Precipitation Calculator) and a calibration curve for American Kestrels Falco sparverius we predicted the breeding range of South African Amur Falcons in the Palaearctic. δD values for juvenile feathers (mean ± SE = -58.1 ± 2.5‰, range -83.9 to -25.7‰) and predicted Palaearctic annual precipitation values indicated that juvenile Amur Falcons in South Africa originated from across their entire Palaearctic range. This rejects the leapfrog migration hypothesis and suggests the widespread movement of birds south, with a funnelling effect into the subregion where they become concentrated over a narrower distribution range. Adult δDf values were more depleted (-37.4 ± 1.8‰, range = -71.3 to -9.3‰) than predicted annual precipitation values for sites where feathers moulted in South Africa (-20.2 ± 0.9‰) but there was no correlation between δDp and δDf. This, together with significant variation of δ13C among sites and annual fluctuations in roost sizes, suggests that roost site fidelity is low in the overwintering range. Populations not confined to breeding sites in South Africa are able to move widely across the subregion, feeding on a broad range of arthropods that become seasonally abundant during the austral summer. Total population estimates for South Africa are significantly lower than global estimates so a significant proportion of the population may not overwinter in South Africa or global populations are significantly lower than estimated. In South Africa, roosts that number hundreds to thousands of individuals are often in large exotic trees, e.g. Eucalyptus sp. They are often tolerant of disturbance at roosts which may be of little concern for their conservation. Habitat changes in the overwintering range in South Africa though, particularly due to agriculture, afforestation and strip mining, may affect global population numbers. There is also concern over the persecution of birds along their migratory route.

scholarly journals Environmental controls on marine productivity near Cape St. Francis, South Africa

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1579-1592 ◽  
Author(s):  
Mark R. Jury
Keyword(s):  
South Africa ◽  
Chlorophyll Fluorescence ◽  
Large Scale ◽  
Coastal Upwelling ◽  
Austral Summer ◽  
Heat Fluxes ◽  
Northerly Wind ◽  
Environmental Controls ◽  
Coastal Hydrology ◽  
Marine Productivity

Abstract. This study considers ocean–atmosphere influences on marine productivity over the shelf near Cape St. Francis, South Africa. Multiday estimates of chlorophyll fluorescence in the period 2006–2017 with an area outlined by 34.5–33.75∘ S and 24–26.5∘ E provide the basis for evaluation using data from high-resolution reanalyses. Correlations with the mean annual cycle of chlorophyll fluorescence were significant for salinity, linking marine productivity and the coastal hydrology. A strengthened Agulhas Current induces cyclonic shear that lifts water at the shelf edge. Composite high-chlorophyll-fluorescence events were dominated by a large-scale midlatitude atmospheric ridge of high pressure. The resultant easterly winds caused offshore transport and the upwelling of cool nutrient-rich water in multiday events at the beginning and end of austral summer. Environmental controls on interannual fluctuations of the commercial fishery were also explored. Southwestward currents and diminished heat fluxes favored the squid catch, while anchovy and sardine catches were linked with upper northerly wind, consistent with large-scale weather patterns that underpin coastal upwelling and river discharge. Productivity lags a few days behind cyclonic wind and current shear and the upstream coastal hydrology, which shares a common atmospheric driver.

Recurrent daily rainfall patterns over South Africa and associated dynamics during the core of the austral summer

2010 ◽  
Vol 32 (2) ◽  
pp. 261-273 ◽  
Author(s):  
Julien Crétat ◽  
Yves Richard ◽  
Benjamin Pohl ◽  
Mathieu Rouault ◽  
Chris Reason ◽  
...  
Keyword(s):  
South Africa ◽  
Austral Summer ◽  
Daily Rainfall ◽  
The Core ◽  
Rainfall Patterns
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