scholarly journals A Study of Predictable Patterns for Seasonal Forecasting of New Zealand Rainfall

2006 ◽  
Vol 19 (13) ◽  
pp. 3320-3333 ◽  
Author(s):  
Xiaogu Zheng ◽  
Carsten S. Frederiksen
Keyword(s):  
New Zealand ◽  
Indian Ocean ◽  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Summer Rainfall ◽  
Statistical Prediction ◽  
Decomposition Approach ◽  
Annular Mode ◽  
Southern Hemisphere Annular Mode ◽  
Verification Period

Abstract A recently developed variance decomposition approach is applied to study the causes of the predictability of New Zealand seasonal mean rainfall. In terms of predictability, the Southern Oscillation is identified as being the most important cause of variability for both the winter and summer New Zealand rainfall, especially for the North Island. Indian Ocean sea surface temperature variability and the Southern Hemisphere annular mode are the second most important causes of variability for winter and summer rainfall, respectively. Based on this study, a statistical prediction scheme has been developed. May Niño-3 (5°N–5°S, 150°–90°W) SSTs and March–May (MAM) central Indian Ocean SSTs are identified as being the most important predictors for the winter rainfall, while September–November (SON) Niño-3 SSTs, November local New Zealand SSTs, and the SON Southern Hemisphere annular mode index are the most important predictors for the summer rainfall. The predictive skill, in term of the percentage explained variance for the verification period (1993–2000) is nearly 20%, which is considerably higher than that achieved previously.

scholarly journals Australian Rainfall and Surface Temperature Variations Associated with the Southern Hemisphere Annular Mode

2007 ◽  
Vol 20 (11) ◽  
pp. 2452-2467 ◽  
Author(s):  
Harry H. Hendon ◽  
David W. J. Thompson ◽  
Matthew C. Wheeler
Keyword(s):  
Surface Temperature ◽  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Daily Rainfall ◽  
High Index ◽  
Maximum Temperature ◽  
Annular Mode ◽  
Southern Hemisphere Annular Mode ◽  
Southwest Australia ◽  
Australian Rainfall

Abstract Daily variations in Australian rainfall and surface temperature associated with the Southern Hemisphere annular mode (SAM) are documented using observations for the period 1979–2005. The high index polarity of the SAM is characterized by a poleward contraction of the midlatitude westerlies. During winter, the high index polarity of the SAM is associated with decreased daily rainfall over southeast and southwest Australia, but during summer it is associated with increased daily rainfall on the southern east coast of Australia and decreased rainfall in western Tasmania. Variations in the SAM explain up to ∼15% of the weekly rainfall variance in these regions, which is comparable to the variance accounted for by the El Niño–Southern Oscillation, especially during winter. The most widespread temperature anomalies associated with the SAM occur during the spring and summer seasons, when the high index polarity of the SAM is associated with anomalously low maximum temperature over most of central/eastern subtropical Australia. The regions of decreased maximum temperature are also associated with increased rainfall. Implications for recent trends in Australian rainfall and temperature are discussed.

scholarly journals Statistical Prediction of Seasonal Mean Southern Hemisphere 500-hPa Geopotential Heights

2007 ◽  
Vol 20 (12) ◽  
pp. 2791-2809 ◽  
Author(s):  
Xiaogu Zheng ◽  
Carsten S. Frederiksen
Keyword(s):  
Southern Hemisphere ◽  
Geopotential Height ◽  
Southern Annular Mode ◽  
Statistical Prediction ◽  
Height Anomaly ◽  
Height Field ◽  
Decomposition Approach ◽  
Annular Mode ◽  
Mode Index ◽  
Southern Annular Mode Index

Abstract A recently developed variance decomposition approach is applied to predict seasonal mean 500-hPa geopotential height anomalies in the Southern Hemisphere. In terms of predictability of both the winter and summer height fields, the Southern Oscillation and the Southern Annular Mode are identified as the first and second most important factors affecting the variability. Based on this study, a statistical prediction scheme has been developed. The linear trend in the leading empirical orthogonal function of the height field, the November Southern Annular Mode index, the austral spring Niño-3 index, and the November Coral Sea index are identified as the main predictors for the summer height field, while the March–May Southern Annular Mode index, the May Niño-4 index, and the austral autumn central Indian Ocean index are the main predictors for the winter height field. The predictive skill in forecasts of National Centers for Environmental Prediction–National Center for Atmospheric Research and European Centre for Medium-Range Weather Forecasts reanalysis 500-hPa geopotential height anomaly fields, in terms of a spatiotemporal anomaly correlation, is considerably higher than a single prediction achieved by a coupled general circulation seasonal forecast model.

scholarly journals Triggering the Indian Ocean Dipole from the Southern Hemisphere

2021 ◽  
Author(s):  
Lian-Yi Zhang ◽  
Yan Du ◽  
Wenju Cai ◽  
Zesheng Chen ◽  
Tomoki Tozuka ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Indian Ocean Dipole ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Triggering Mechanism ◽  
Phase Development ◽  
The Indian Ocean ◽  
High System ◽  
The Tropics

<p>This study identifies a new triggering mechanism of the Indian Ocean Dipole (IOD) from the Southern Hemisphere. This mechanism is independent from the El Niño/Southern Oscillation (ENSO) and tends to induce the IOD before its canonical peak season. The joint effects of this mechanism and ENSO may explain different lifetimes and strengths of the IOD. During its positive phase, development of sea surface temperature cold anomalies commences in the southern Indian Ocean, accompanied by an anomalous subtropical high system and anomalous southeasterly winds. The eastward movement of these anomalies enhances the monsoon off Sumatra-Java during May-August, leading to an early positive IOD onset. The pressure variability in the subtropical area is related with the Southern Annular Mode, suggesting a teleconnection between high-latitude and mid-latitude climate that can further affect the tropics. To include the subtropical signals may help model prediction of the IOD event.</p>

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.

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