Synoptic climatology, and intrahemispheric associations, of cold air mesocyclones in the Australasian sector

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Abstract

Satellite IR images for seven months in 1992 are interpreted for cold air mesoscale cyclones (mesocyclones) occurring in the Australasian sector (∼70°E-150°W) of the Southern Ocean. Time-averaged (monthly, seasonal) distributions of mesocyclogenesis, mesocyclolysis, and tracks of movement, along with statistical summaries of mesocyclone attributes (e.g., cloud vortex size, speeds of movement), are presented and discussed in the context of the larger-scale atmospheric circulation. Maximum frequencies of mesocyclones occurred in the transitional months of April and October 1992, with a secondary peak in July. Statistically significant differences in mesocyclone track length between months appear related dominantly to changes in speed of the background flow, associated with the semiannual oscillation (SAO) of tropospheric pressure/height. The associations of mesocyclone "outbreaks" with composite anomaly fields of pressure and height are identified for three subareas of the Australasian sector suggested by the analysis of mesocyclone spatial patterns. Outbreaks occur in the strong southerly geostrophic airflow located between pressure and height anomalies that are negative (positive) to the eastward (westward). When outbreaks occurred in the New Zealand subarea in 1992, a similarly strong couplet of pressure/height anomalies developed in the southern South America/ Antarctic Peninsula sector but not when outbreaks occurred south of Australia. The mesocyclone remote association that is suggested is evaluated by using polar orbiter IR imagery for the southeastern Pacific region. Frequencies of mesocyclones increase (decrease) west of Chile but decrease (increase) through Drake Passage when mesocyclone outbreaks occur near New Zealand (south of Australia). These long distance associations of mesocyclone outbreaks are consistent with the connectivity of the baroclinic waves and might prove useful in the development of techniques to forecast mesocyclones over the Southern Ocean.

Original languageEnglish (US)
Article number96JD03357
Pages (from-to)13873-13887
Number of pages15
JournalJournal of Geophysical Research Atmospheres
Volume102
Issue numberD12
DOIs
StatePublished - Jan 1 1997

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Climatology
cyclones
climatology
cold air
cyclone
sectors
air
Air
South Australia
oceans
atmospheric circulation
air flow
Chile
oscillation
New Zealand
anomalies
anomaly
baroclinic waves
semiannual oscillation
baroclinic wave

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Cite this

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title = "Synoptic climatology, and intrahemispheric associations, of cold air mesocyclones in the Australasian sector",
abstract = "Satellite IR images for seven months in 1992 are interpreted for cold air mesoscale cyclones (mesocyclones) occurring in the Australasian sector (∼70°E-150°W) of the Southern Ocean. Time-averaged (monthly, seasonal) distributions of mesocyclogenesis, mesocyclolysis, and tracks of movement, along with statistical summaries of mesocyclone attributes (e.g., cloud vortex size, speeds of movement), are presented and discussed in the context of the larger-scale atmospheric circulation. Maximum frequencies of mesocyclones occurred in the transitional months of April and October 1992, with a secondary peak in July. Statistically significant differences in mesocyclone track length between months appear related dominantly to changes in speed of the background flow, associated with the semiannual oscillation (SAO) of tropospheric pressure/height. The associations of mesocyclone {"}outbreaks{"} with composite anomaly fields of pressure and height are identified for three subareas of the Australasian sector suggested by the analysis of mesocyclone spatial patterns. Outbreaks occur in the strong southerly geostrophic airflow located between pressure and height anomalies that are negative (positive) to the eastward (westward). When outbreaks occurred in the New Zealand subarea in 1992, a similarly strong couplet of pressure/height anomalies developed in the southern South America/ Antarctic Peninsula sector but not when outbreaks occurred south of Australia. The mesocyclone remote association that is suggested is evaluated by using polar orbiter IR imagery for the southeastern Pacific region. Frequencies of mesocyclones increase (decrease) west of Chile but decrease (increase) through Drake Passage when mesocyclone outbreaks occur near New Zealand (south of Australia). These long distance associations of mesocyclone outbreaks are consistent with the connectivity of the baroclinic waves and might prove useful in the development of techniques to forecast mesocyclones over the Southern Ocean.",
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Synoptic climatology, and intrahemispheric associations, of cold air mesocyclones in the Australasian sector. / Carleton, Andrew Mark; Song, Yudong.

In: Journal of Geophysical Research Atmospheres, Vol. 102, No. D12, 96JD03357, 01.01.1997, p. 13873-13887.

Research output: Contribution to journalArticle

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