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 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 Blocking Detection Based on Synoptic Filters

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
Bernd Schalge ◽  
Richard Blender ◽  
Klaus Fraedrich
Keyword(s):  
Case Studies ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
Height Anomaly ◽  
Geopotential Height Anomaly ◽  
Minimum Duration ◽  
Additional Filter ◽  
Blocking Index

The Tibaldi-Molteni blocking index is supplemented by additional filter criteria to eliminate cut-off lows and subsynoptic structures. We introduce three blocking filters and analyse their sensitivities: (i) a quantile filter requiring a minimum geopotential height anomaly to reject cut-off lows, (ii) an extent filter to extract scales above a minimum zonal width, and (iii) a persistence filter to extract events with a minimum duration. Practical filter application is analysed in two case studies and the blocking climatologies for the Northern and the Southern Hemisphere.

scholarly journals The impact of the Southern Annular Mode on future changes in Southern Hemisphere rainfall

2016 ◽  
Vol 43 (13) ◽  
pp. 7160-7167 ◽  
Author(s):  
Eun-Pa Lim ◽  
Harry H. Hendon ◽  
Julie M. Arblaster ◽  
Francois Delage ◽  
Hanh Nguyen ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Southern Annular Mode ◽  
Annular Mode ◽  
The Impact

scholarly journals Southern Hemisphere Annular Mode Variability and the Role of Optimal Nonmodal Growth

2005 ◽  
Vol 62 (6) ◽  
pp. 1947-1961 ◽  
Author(s):  
Harun A. Rashid ◽  
Ian Simmonds
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Positive Feedback ◽  
General Model ◽  
Initial Perturbation ◽  
Low Frequency ◽  
Southern Annular Mode ◽  
Feedback Mechanism ◽  
Annular Mode ◽  
Positive Feedback Mechanism

Abstract The southern annular mode is the leading mode of Southern Hemisphere circulation variability, the temporal evolution of which is characterized by large amplitudes and significant persistence. Previous investigators have suggested a positive feedback mechanism that explains some of this low-frequency variance. Here, a mechanism is proposed, involving transient nonmodal growths of the anomalies, that is at least as effective as the positive feedback mechanism in increasing the low-frequency variance of the southern annular mode. Using the vector autoregressive modeling technique, a number of linear inverse models of southern annular mode variability from National Centers for Environmental Prediction–Department of Energy (NCEP–DOE) Reanalysis 2 is derived. These models are then analyzed applying the ideas of the generalized stability theory. It is found that, as a consequence of the nonnormality of the system matrices, a significant increase in the low-frequency variance of the southern annular mode occurs through optimal nonmodal growth of the zonal wind anomalies. The nonnormality arises mainly from the relative dominance of the eddy forcing, while the nonmodal growth is caused by the interference of the nonorthogonal eigenvectors of the nonnormal system matrix. These results are demonstrated first in a simple model that retains only the two leading modes of the zonally averaged zonal wind and eddy-forcing variability, and then in a more general model that includes all the important modes. Using the more general model the authors have determined, among other things, the optimal initial perturbation and the time scale over which it experiences the maximum nonmodal growth to evolve into the pattern associated with the southern annular mode.

scholarly journals Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode*

2006 ◽  
Vol 19 (6) ◽  
pp. 979-997 ◽  
Author(s):  
Ryan L. Fogt ◽  
David H. Bromwich
Keyword(s):  
High Latitude ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Phase Relationship ◽  
South Pacific ◽  
Southern Annular Mode ◽  
Height Anomaly ◽  
Austral Spring ◽  
Annular Mode ◽  
The Pacific

Abstract Decadal variability of the El Niño–Southern Oscillation (ENSO) teleconnection to the high-latitude South Pacific is examined by correlating the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr Re-Analysis (ERA-40) and observations with the Southern Oscillation index (SOI) over the last two decades. There is a distinct annual contrast between the 1980s and the 1990s, with the strong teleconnection in the 1990s being explained by an enhanced response during austral spring. Geopotential height anomaly composites constructed during the peak ENSO seasons also demonstrate the decadal variability. Empirical orthogonal function (EOF) analysis reveals that the 1980s September–November (SON) teleconnection is weak due to the interference between the Pacific–South American (PSA) pattern associated with ENSO and the Southern Annular Mode (SAM). An in-phase relationship between these two modes during SON in the 1990s amplifies the height and pressure anomalies in the South Pacific, producing the strong teleconnections seen in the correlation and composite analyses. The in-phase relationship between the tropical and high-latitude forcing also exists in December–February (DJF) during the 1980s and 1990s. These results suggest that natural climate variability plays an important role in the variability of SAM, in agreement with a growing body of literature. Additionally, the significantly positive correlation between ENSO and SAM only during times of strong teleconnection suggests that both the Tropics and the high latitudes need to work together in order for ENSO to strongly influence Antarctic climate.

scholarly journals Impacts of a Midlatitude Oceanic Frontal Zone for the Baroclinic Annular Mode in the Southern Hemisphere

2021 ◽  
pp. 1-63
Author(s):  
MORIO NAKAYAMA ◽  
HISASHI NAKAMURA ◽  
FUMIAKI OGAWA
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
Frontal Zone ◽  
Circulation Model ◽  
Southern Annular Mode ◽  
Internal Dynamics ◽  
Near Surface ◽  
Annular Mode ◽  
Major Mode ◽  
Sst Gradient

AbstractAs a major mode of annular variability in the Southern Hemisphere, the baroclinic annular mode (BAM) represents the pulsing of extratropical eddy activity. Focusing mainly on sub-weekly disturbances, this study assesses the impacts of a midlatitude oceanic frontal zone on the BAM and its dynamics through a set of “aqua-planet” atmospheric general circulation model experiments with zonally uniform sea-surface temperature (SST) profiles prescribed. Though idealized, one experiment with realistic frontal SST gradient reasonably well reproduces observed BAM-associated anomalies as a manifestation of a typical lifecycle of migratory baroclinic disturbances. Qualitatively, these BAM features are also simulated in the other experiment where the frontal SST gradient is removed. However, the BAM-associated variability weakens markedly and shifts equatorward, in association with the corresponding modifications in the climatological-mean stormtrack activity. The midlatitude oceanic frontal zone amplifies and anchors the BAM variability by restoring near-surface baroclinicity through anomalous sensible heat supply from the ocean and moisture supply to cyclones, although the BAM is essentially a manifestation of atmospheric internal dynamics. Those experiments and observations further indicate that the BAM modulates momentum flux associated with transient disturbances to induce a modest but robust meridional shift of the polar-front jet, suggesting that the BAM can help maintain the southern annular mode. They also indicate that the quasi-periodic behavior of the BAM is likely to reflect internal dynamics in which atmospheric disturbances on both sub-weekly and longer time scales are involved.

Extratropical Southern Hemisphere Synchronous Pressure Variability in the Early 20th Century

2021 ◽  
pp. 1-41
Author(s):  
Ryan L. Fogt ◽  
Charlotte J. Connolly
Keyword(s):  
Southern Hemisphere ◽  
Historical Data ◽  
Austral Summer ◽  
Southern Annular Mode ◽  
Early 20Th Century ◽  
Annular Mode ◽  
Tropical Variability ◽  
Zonal Wavenumber ◽  
Meteorological Observations ◽  
Statistical Relationships

AbstractBecause continuous meteorological observations across Antarctica did not start until the middle of the 20th century, little is known about the full spatial pattern of pressure variability across the extratropical Southern Hemisphere (SH) in the early 20th century, defined here as the period from 1905-1956. To fill this gap, this study analyzes pressure observations across the SH in conjunction with seasonal pressure reconstructions across Antarctica, which are based on observed station-to-station statistical relationships between pressure over Antarctica and the southern midlatitudes. Using this newly generated dataset, it is found that the early 20th century is characterized by synchronous, but opposite signed pressure relationships between Antarctica and the SH midlatitudes, especially in austral summer and autumn. The synchronous pressure relationships are consistent with the Southern Annular Mode, extending its well-known influence on SH extratropical pressure since 1957 into the early 20th century. Apart from connections with the Southern Annular Mode, regional and shorter-duration pressure trends are found to be associated with influences from tropical variability and potentially the zonal wavenumber three pattern. Although the reduced network of SH observations and Antarctic reconstruction capture the Southern Annular Mode in the early 20th century, reanalyses products show varying skill in reproducing trends and variability, especially over the oceans and high southern latitudes prior to 1957, which stresses the importance of continual efforts of historical data rescue in data sparse regions to improve their quality.

Seasonal southern hemisphere multi-variable reflection of the southern annular mode in atmosphere and ocean reanalyses

2017 ◽  
Vol 50 (3-4) ◽  
pp. 1451-1470 ◽  
Author(s):  
Zhaoru Zhang ◽  
Petteri Uotila ◽  
Achim Stössel ◽  
Timo Vihma ◽  
Hailong Liu ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Southern Annular Mode ◽  
Annular Mode ◽  
Ocean Reanalyses

scholarly journals Relationship between the southern annular mode and southern hemisphere atmospheric systems

2009 ◽  
Vol 24 (1) ◽  
pp. 48-55 ◽  
Author(s):  
Michelle Simões Reboita ◽  
Tércio Ambrizzi ◽  
Rosmeri Porfírio da Rocha
Keyword(s):  
South America ◽  
Southern Hemisphere ◽  
Southern Annular Mode ◽  
South Atlantic ◽  
Positive Anomaly ◽  
The South ◽  
Rainfall Distribution ◽  
Atlantic Sector ◽  
Annular Mode ◽  
Atmospheric Systems

Seasonal relationship between the Southern Annular Mode (SAM) and the spatial distribution of the cyclone systems over Southern Hemisphere is investigated for the period 1980 to 1999. In addition, seasonal frontogenesis and rainfall distribution over South America and South Atlantic Ocean during different SAM phases were also analyzed. It is observed that during negative SAM phases the cyclone trajectories move northward when compared to the positive one, and in the South America and South Atlantic sector there is intense frontogenetic activity and positive anomaly precipitation over the Southeast of the South America. In general, SAM positive phase shows opposite signals.

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