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 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 The Relationship between the Southern Hemisphere Annular Mode and Antarctic Peninsula Summer Temperatures: Analysis of a High-Resolution Model Climatology

2008 ◽  
Vol 21 (8) ◽  
pp. 1649-1668 ◽  
Author(s):  
Nicole P. M. van Lipzig ◽  
Gareth J. Marshall ◽  
Andrew Orr ◽  
John C. King
Keyword(s):  
High Resolution ◽  
Surface Temperature ◽  
Southern Hemisphere ◽  
Antarctic Peninsula ◽  
Windward Side ◽  
Ice Shelf ◽  
Near Surface ◽  
Annular Mode ◽  
Surface Mass ◽  
Southern Hemisphere Annular Mode

Abstract The large regional summer warming on the east coast of the northern Antarctic Peninsula (AP), which has taken place since the mid-1960s, has previously been proposed to be caused by a trend in the Southern Hemisphere Annular Mode (SAM). The authors utilize a high-resolution regional atmospheric model climatology (14-km grid spacing) to study the mechanisms that determine the response of the near-surface temperature to an increase in the SAM (ΔT/ΔSAM). Month-to-month variations in near-surface temperature and surface pressure are well represented by the model. It is found that north of ∼68°S, ΔT/ΔSAM is much larger on the eastern (lee) side than on the western (windward) side of the barrier. This is because of the enhanced westerly flow of relatively warm air over the barrier, which warms (and dries) further as it descends down the lee slope. The downward motion on the eastern side of the barrier causes a decrease in surface-mass balance and cloud cover. South of ∼68°S, vertical deflection across the barrier is greatly reduced and the contrast in ΔT/ΔSAM between the east and west sides of the barrier vanishes. In the northeastern part of the AP, the modeled ΔT/ΔSAM distribution is similar to the distribution derived from satellite infrared radiometer data. The region of strongest modeled temperature sensitivity to the SAM is where ice shelf collapse has recently taken place and does not extend farther south over the Larsen-C Ice Shelf.

Sign in / Sign up

Export Citation Format

Share Document