Future southern African summer rainfall variability related to a southwest Indian Ocean dipole in HadCM3

2008 ◽  
Vol 35 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
Gillian Kay ◽  
Richard Washington
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Southwest Indian Ocean

scholarly journals The Role of Mesoscale Convective Complexes in Southern Africa Summer Rainfall

2013 ◽  
Vol 26 (5) ◽  
pp. 1654-1668 ◽  
Author(s):  
R. C. Blamey ◽  
C. J. C. Reason
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
Rainfall Variability ◽  
Warm Season ◽  
Tropical Rainfall Measuring Mission ◽  
Summer Rainfall ◽  
Spatial And Temporal Variability ◽  
Eastern Region ◽  
Southwest Indian Ocean ◽  
Mesoscale Convective

Abstract A combination of numerous factors, including geographic position, regional orography, and local sea surface temperatures, means that subtropical southern Africa experiences considerable spatial and temporal variability in rainfall and is prone to both frequent flooding and drought events. One system that may contribute to rainfall variability in the region is the mesoscale convective complex (MCC). In this study, Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) data is used to document the precipitation produced by MCCs over southern Africa for the 1998–2006 period. Most of the rainfall associated with MCCs is found to occur over central Mozambique, extending southward to eastern South Africa. High precipitation totals associated with these systems also occur over the neighboring southwest Indian Ocean, particularly off the northeast coast of South Africa. MCCs are found to contribute up to 20% of the total summer rainfall (November–March) in parts of the eastern region of southern Africa. If the month of March is excluded from the analysis, then the contribution increases up to 24%. In general, the MCC summer rainfall contribution for most of the eastern region is approximately between 8% and 16%. Over the western interior and Botswana and Namibia, the MCC contribution is much less (<6%). It is also evident that there is considerable interannual variability associated with the contribution that these systems make to the total warm season rainfall.

scholarly journals Influence of Indian Ocean dipole on rainfall variability and extremes over southern Africa

MAUSAM ◽  
2021 ◽  
Vol 71 (4) ◽  
pp. 637-648
Author(s):  
OGWANG B. A. ◽  
ONGOMA V. ◽  
SHILENJE Z. W. ◽  
RAMOTUBEI T. S. ◽  
LETUMA M. ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Indian Ocean Dipole ◽  
Rainfall Variability ◽  
Dominant Mode ◽  
Empirical Orthogonal Functions ◽  
Extreme Weather Events ◽  
Orthogonal Functions ◽  
Upper Level ◽  
The Relationship

Extreme weather events; floods and droughts are common in southern Africa (SA) consisting of 8 countries (Botswana, Namibia, South Africa, Lesotho, Swaziland, Mozambique, Zimbabwe, parts of Angola and Zambia). This study examines the linkage between the SA October-December (OND) rainfall, the Indian Ocean Dipole (IOD) and the South Atlantic Oscillation Dipole (SAOD). Empirical Orthogonal Functions (EOF) technique is used to establish the dominant mode of variability of OND rainfall, as correlation analysis is applied to quantify the relationship between the indices; IOD [Dipole Mode Index (DMI)], SAOD Index (SAODI) and OND rainfall variability. Results show that the dominant mode of variability of OND rainfall exhibits a dipole pattern over SA and there exists a significant correlation at 95% confidence level between the area average OND rainfall (rainfall index (RFI)) and DMI, with a correlation coefficient of -0.3. The relationship between the mean SA OND rainfall and the positive phase of IOD varies greatly in space, ranging from one country to another. Further analysis of the dry and wet of SAOND rainfall years reveal that wet years are associated with convergence at  surface level (850 hPa) and divergence at upper level (200 hPa), depicting rising motion in the region, whereas dry years are associated with divergence at low level and convergence at upper level, implying descending motion. The study recommends further research on a reduced spatial scale, for instance at a country level to ascertain the effect of IOD on individual country’s weather. This will help in accurate monitoring of the evolution of IOD events to improve quality of seasonal weather forecasts in the region.

The Influence on Summer Rainfall in the Lesotho Lowlands from Indian Ocean SSTs

2002 ◽  
Vol 33 (4) ◽  
pp. 305-318 ◽  
Author(s):  
Lars Hydén
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Rainfall Variability ◽  
Austral Summer ◽  
Equatorial Indian Ocean ◽  
Summer Rainfall ◽  
Significant Negative Correlation ◽  
Annual Rainfall ◽  
Ocean Area ◽  
The Indian Ocean

Lesotho is located approximately at latitude 30 degrees south in the interior of Southern Africa. The mesoscale climate is complicated and governed by various weather systems. The inter-annual rainfall variability is great, resulting in low food security, since the growing of crops in the Lesotho Lowlands is almost exclusively rain-fed. Reliable forecasts of austral summer rainfall are thus valuable. Earlier research has shown that the sea surface temperatures (SST) in the Indian Ocean to some extent govern rainfall in Southern Africa. The research presented is part of an on-going project to find suitable oceanographic and meteorological predictors, which can be used in a forecast model for summer rainfall, to be developed later. The first part of this paper investigates the correlation between the average SSTs in the Equatorial Indian Ocean, the Central Indian Ocean, and the Agulhas Gyre, respectively, and rainfall two months later in the Lesotho Lowlands during early austral summer, October until December for the period 1949-1995. No significant correlations have been found, probably because the three ocean areas are too large. In the second part of this paper the monthly SST in 132 grid squares in the Indian Ocean were investigated and found to be correlated with rainfall in the Lesotho Lowlands two months later, October until March. Significant correlations have been found between the SSTs and certain ocean areas and December, January, and February rainfall, respectively. There is significant negative correlation between December rainfall and October SST in an ocean area between Kenya and Somalia across the Indian Ocean to Sumatra. In the area where the Somali Current flows there is also significant correlation between December SST and December rainfall. January rainfall is significantly negatively correlated with November SST in an ocean area, northeast of Madagascar. February rainfall is significantly, but weakly, negatively correlated with SST in a narrow north-south corridor in the Eastern Indian Ocean from the equator down to latitude 40 degrees south.

Signals of the South China Sea summer rainfall variability in the Indian Ocean

2015 ◽  
Vol 46 (9-10) ◽  
pp. 3181-3195 ◽  
Author(s):  
Zhuoqi He ◽  
Renguang Wu ◽  
Weiqiang Wang
Keyword(s):  
Indian Ocean ◽  
South China Sea ◽  
South China ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
The Indian Ocean

Change in Coherence of Summer Rainfall Variability over the Western Pacific around the Early 2000s: ENSO Influence

2020 ◽  
Vol 33 (3) ◽  
pp. 1105-1119 ◽  
Author(s):  
Zhuoqi He ◽  
Weiqiang Wang ◽  
Renguang Wu ◽  
In-Sik Kang ◽  
Chao He ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Rainfall Anomaly ◽  
Western Pacific ◽  
Northern Indian Ocean ◽  
Central Pacific ◽  
Enso Events ◽  
The Western Pacific ◽  
Sst Anomalies

AbstractThis study is the second part of a two-part series investigating a recent decadal modulation of interannual variability over the western Pacific Ocean around the early 2000s. Observational evidence shows that the anomalous Philippine Sea cyclonic circulation retreats eastward, with the western Pacific rainfall anomaly distribution changing from a north–south tripole pattern to an east–west dipole pattern after 2003–04. These changes are attributed to a change in El Niño–Southern Oscillation (ENSO) properties and the associated Indo-Pacific sea surface temperature (SST) anomaly pattern. Before the early 2000s, slow-decaying ENSO events induce large SST anomalies in the northern Indian Ocean during the following summer. The northern Indian Ocean SST anomalies act together with the opposite-sign SST anomalies in the tropical central Pacific, leading to a zonally extended anomalous lower-level cyclonic (anticyclonic) circulation and an elongated rainfall anomaly band over the western Pacific. After the early 2000s, ENSO events have a shortened period and a weakened amplitude, and the eastern Pacific SST anomalies tend to undergo a phase transition from winter to summer. Consequently, the influence of ENSO on the Indian Ocean SST anomalies is weakened and the contribution of the northern Indian Ocean SST anomalies to the western Pacific summer rainfall variability becomes insignificant. In this case, the western North Pacific summer rainfall is mainly dominated by the well-developed tropical Pacific SST forcing following the early decay of ENSO events. The potential physical mechanism for the two types of ENSO influences is validated with regional decoupled Community Earth System Model experiments.

scholarly journals Change in Coherence of Interannual Variability of Summer Rainfall over the Western Pacific around the Early 2000s: Role of Indo-Pacific Ocean Forcing

2018 ◽  
Vol 31 (9) ◽  
pp. 3525-3538 ◽  
Author(s):  
Zhuoqi He ◽  
Renguang Wu
Keyword(s):  
Indian Ocean ◽  
North Pacific ◽  
General Circulation ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
General Circulation Models ◽  
North Indian Ocean ◽  
Western Pacific ◽  
Sst Forcing ◽  
The Western Pacific

The observations show that the covariability between the western North Pacific (WNP) and the South China Sea (SCS) summer rainfall has experienced an obvious weakening since the early 2000s. During the period 1982–2003, the combined north Indian Ocean (NIO), central North Pacific (CNP), and central equatorial Pacific (CEP) sea surface temperature (SST) forcing results in a high coherence between the WNP and SCS summer rainfall variations via a zonally elongated anomalous lower-level cyclone over the western Pacific. During the period 2004–16, the Indian Ocean SST contribution is largely weakened, and the WNP rainfall variability is dominated by the enhanced Pacific SST forcing with an eastward retreated lower-level wind and rainfall anomalies, whereas the SCS rainfall variability is mainly associated with local air–sea interaction processes. The results obtained from observational analysis are supported by numerical experiments with atmospheric and coupled general circulation models. The change in the coherence of interannual summer rainfall variability over the WNP and SCS has important implications for regional climate prediction in South and East Asia.

scholarly journals A Time-Scale Decomposition Approach to Statistically Downscale Summer Rainfall over North China

2012 ◽  
Vol 25 (2) ◽  
pp. 572-591 ◽  
Author(s):  
Yan Guo ◽  
Jianping Li ◽  
Yun Li
Keyword(s):  
Time Scale ◽  
North China ◽  
Climate Models ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Present Climate ◽  
Decomposition Approach ◽  
Southwest Indian Ocean ◽  
Interannual Rainfall Variability ◽  
Time Scale Decomposition

Abstract A time-scale decomposition (TSD) approach to statistically downscale summer rainfall over North China is described. It makes use of two distinct downscaling models respectively corresponding to the interannual and interdecadal rainfall variability. The two models were developed based on objective downscaling scheme that 1) identifies potential predictors based on correlation analysis between rainfall and considered climatic variables over the global scale and 2) selects the “optimal” predictors from the identified potential predictors via cross-validation-based stepwise regression. The downscaling model for the interannual rainfall variability is linked to El Niño–Southern Oscillation and the 850-hPa meridional wind over East China, while the one for the interdecadal rainfall variability is related to the sea level pressure over the southwest Indian Ocean. Taking the downscaled interannual and interdecadal components together the downscaled total rainfall was obtained. The results show that the TSD approach achieved a good skill to predict the observed rainfall with the correlation coefficient of 0.82 in the independent validation period. The authors further apply the model to obtain downscaled rainfall projections from three climate models under present climate and the A1B emission scenario in future. The resulting downscaled values provide a closer representation of the observation than the raw climate model simulations in the present climate; for the near future, climate models simulated a slight decrease in rainfall, while the downscaled values tend to be slightly higher than the present state.

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