Characteristics of southern hemisphere blocking as determined from a time series of observational data

Lejenäs, Harald

doi:10.1002/qj.49711046610

Cited by 70 publications

(76 citation statements)

References 7 publications

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“…Here, we have adopted a threshold of five consecutive blocked days to the circulation constraints defined by equations (1) and (2) and criteria given by expressions (3) and (4). Finally, it may be noted that similar temporal criteria to ours have been adopted in operational centers such as NCEP (http://www.cpc.ncep.noaa.gov/ products/precip/CWlink/MJO/block.shtml) and that we have compared our results against those obtained by other authors for the Southern Hemisphere (LEJENAS, 1984;TIBALDI et al, 1994;MARQUES, 1996;MARQUES and RAO, 2001;WIEDENMAN et al, 2002;ADANA and COLLUCI, 2005).…”

Section: Blocking Definitionsupporting

confidence: 52%

“…Previous works dealing with the whole SH (LEJENAS, 1984;TRENBERTH and MO, 1985;KAYANO and KOUSKY, 1990;RUTHLAND and FUENZELIDA, 1991) agree on the predominance of blocking episodes over the Australian-New Zealand sector, followed by the Southeastern Pacific, a considerably less number of episodes occurring over the Southern Atlantic and the Indian Ocean. These works have also considered the Pacific Ocean as a single sector, whereas following the work of SINCLAIR (1996) and RENWICK and REVELL (1999), authors started considering a partition of the Southern-Pacific Ocean into the southwestern and the southeastern sectors.…”

Section: Introductionmentioning

confidence: 85%

“…Nevertheless, only six out of seventeen papers employ time series with periods of 30 yrs or more. From the methodological point of view most of these analyses have used blocking definition algorithms based on either a) geopotential height gradients (LEJENAS, 1984;TIBALDI et al, 1994;MARQUES, 1996;MARQUES and RAO, 2001;WIEDENMANN et al, 2002;ADANA and COLLUCI, 2005), and b) persistent positive anomalies of pressure (TRENBERTH and MO, 1985;RUTHLAND and FUENZELIDA, 1991;SINCLAIR, 1996;RENWICK, 1998RENWICK, , 2005RENWINCK and REVELL, 1999;MONTECINOS and ACEITUNO, 2003;DAMIÃ O et al, 2005). A few papers have used less common blocking definition techniques, e.g., Empirical Orthogonal Functions (KAYANO, 1999;RAPHAEL, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

Mendes

Trigo

Cavalcanti³

et al. 2008

Pure appl. geophys.

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Abstract-This work presents an updated climatology of blocking episodes for the Southern Hemisphere between 1960 and 2000, based on data from NCEP/NCAR reanalysis. Five contiguous areas of blocking activity are considered; Southeastern Pacific, Southwestern Pacific, Atlantic, Indian and Oceania. The impact of the three most important areas of onset blocking episodes (Southeastern Pacific, Atlantic and Oceania) upon the climate of the adjacent continental areas (South America and Australia) was evaluated. Composites of the meteorological variables (temperature and precipitation) were obtained for periods of diagnosed blockings. The impact of the blocking episodes over the climate of South America and Australia is highlighted whenever anomaly fields of temperature and precipitation are significant at the 5% and 10% levels, respectively. Impacts of Southeastern Pacific and Atlantic blockings are observed on the temperature field over several regions of South America. Significantly higher (lower) temperatures than climatology occur in southern Brazil, northern Argentina, Uruguay and Paraguay, and lower (higher) than climatology in the extreme south of South America for the Southeastern Pacific (Atlantic) blocking episodes. Precipitation over South America is also affected by the Southeastern Pacific and Atlantic blockings in different ways. The Southeastern Pacific blocking has higher impact on precipitation in summer (dry conditions in northeast Brazil) and spring (wet conditions in central and southern Brazil), while the Atlantic blocking affects precipitation in autumn and winter (wet conditions in parts of central and southern Brazil). The blocking cases over Oceania affect southeastern Australia with normal to higher than climatological precipitation and with negative temperature anomalies in that region. Finally we provide a detailed analysis of a South Atlantic blocking episode, which occurred between the 4 th and the 8 th of June 1997. This event shows clearly the split of the jet stream into two branches (subtropical and polar) surrounding the anticyclonic sector, and satellite imagery revealed the presence of transient systems in the periphery of the blocking anticyclone responsible for high values of precipitation in the southeastern sector of South America.

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Section: Blocking Definitionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

Mendes

Trigo

Cavalcanti³

et al. 2008

Pure appl. geophys.

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“…This could also be coincidental, but it is interesting to note that these sectors where dipole anomalies develop correspond in both hemispheres to the sector where double-jet or blockings occur more frequently [Lejenas, 1984]. This suggests further excitation of the regional mode.…”

Section: Temporal Structurementioning

confidence: 90%

Variability of the polar night jet in the northern and southern hemispheres

Kuroda¹,

Kodera²

2001

J. Geophys. Res.

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Abstract. The spatial and temporal characteristics of the month-to-month variability of the polar night jet and its relationship with tropospheric circulation is investigated for both the Northern and Southern Hemispheres. The variabilities of the hemispheres have many common characteristics of the Polar Night Jet Oscillation (PJO). These common characteristics include the following: (1) the anomalous zonal-mean zonal winds shift poleward and downward; (2) the anomalous polar temperatures propagate downward from the stratopause to the upper troposphere; and (3) they are made through a wave-mean flow interaction with mainly the planetary wave of zonal wave number one. Annular modes associated with the PJOs appear in both hemispheres when the zones of maximum polar temperature anomaly descend to the lowermost stratosphere and upper troposphere. The major difference in the PJOs of the two hemispheres is found in their temporal characteristics. In the Southern Hemisphere, the phase of the PJO is closely locked to the annual cycle, while in the Northern Hemisphere it exhibits quasiperiodic variability with its envelope controlled by the annual cycle. The origin of the differences between the PJOs is discussed based on the theory of the wave-mean flow interaction

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“…In a D+ event, the large variance zone around the South Pacific is not clear and seems to shift toward low latitudes in the south of Australia. This shift or block of the storm track might be due to blocking events in the New Zealand sector where blocking events in the Southern Hemisphere prefer to occur (Trenberth and Mo, 1983;Lejenas, 1984).…”

Section: Datamentioning

confidence: 99%

Low-frequency Variations of the Zonal Mean State of the Southern Hemisphere Troposphere

Shiotani

1990

Journal of the Meteorological Society of Japan

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Characteristics of southern hemisphere blocking as determined from a time series of observational data

Cited by 70 publications

References 7 publications

Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

Variability of the polar night jet in the northern and southern hemispheres

Low-frequency Variations of the Zonal Mean State of the Southern Hemisphere Troposphere

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