Anticyclones Cause Weather Too: An Understanding of Worldwide Strong Anticyclones and Anticyclogenesis

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Anticyclones Cause Weather Too An Understanding
of Worldwide Strong Anticyclones and
Anticyclogenesis
NROW VIII 1-2 November, 2006

• Matthew L. Doody, Lance Bosart and Daniel Keyser
• Department of Earth and Atmospheric Sciences,
  University at Albany, State University of New
  York, Albany, New York

NSF ATM-0434189
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Purposes

• Examine global regions where strong anticyclones
  and anticyclogenesis occur.
• Determine various thresholds and timescales to
  enhance the climatology.
• Find any possible interannual variability.
• Link strong anticyclones to geographical
  features.
• Lead into a study of predictability of strong
  anticyclones and anticyclogenesis.

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Data and Methodology

• Data used consisted of
• NCEP/NCAR Global Reanalysis at 2.5
  resolution.
• ECMWF ERA-40 Global Reanalysis at 2.5
  resolution.
• Both data sets were used from 1958 2000
• Thresholds were set for the MSLP.
• At each gridpoint a counter was used to sum the
  number of times the MSLP the threshold.
• Counts were only done at 0000 and 1200 UTC to
  mitigate double counting.

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Data and Methodology

• After tabulation of the data it was then
  contoured objectively to show the regions where
  the threshold was met or exceeded.
• It is important to note that the figures that
  follow do not count coherent closed anticyclones,
  but simply the number of times the MSLP met or
  exceeded the defined threshold.

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Outline

• Compare and contrast the two datasets.
• Examine the Northern Hemisphere (NH) at various
  thresholds as well as at monthly timescales.
• Same as above for the Southern Hemisphere (SH).
• Interannual variability.
• Time series of maximum count for 1050 hPa for
  each year throughout the datasets.

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http//www.lpi.usra.edu/education/fieldtrips/2005/
maps/index.html
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ERA-40 MSLP 1050 hPa from 19582000
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NCEP/NCAR MSLP 1050 hPa from 19582000
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NCEP/NCAR MSLP 1050 hPa from 19582000
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ERA-40 MSLP 1040 hPa from 19582000
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ERA-40 MSLP 1060 hPa from 19582000
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Northern Hemisphere Winter Threshold 1050 hPa
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ERA-40 MSLP 1050 hPa for October
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ERA-40 MSLP 1050 hPa for November
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ERA-40 MSLP 1050 hPa for December
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ERA-40 MSLP 1050 hPa for January
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ERA-40 MSLP 1050 hPa for February
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ERA-40 MSLP 1050 hPa for March
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ERA-40 MSLP 1050 hPa for April
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Northern Hemisphere Summer Threshold 1035 hPa
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ERA-40 MSLP 1035 hPa for May
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ERA-40 MSLP 1035 hPa for June
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ERA-40 MSLP 1035 hPa for July
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ERA-40 MSLP 1035 hPa for August
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ERA-40 MSLP 1035 hPa for September
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Southern Hemisphere
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ERA-40 MSLP 1040 hPa from 19582000
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Hoskins and Hodges (2005)
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ERA-40 MSLP 1050 hPa from 19582000
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Southern Hemisphere Winter Threshold 1040 hPa
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ERA-40 MSLP 1040 hPa for May
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ERA-40 MSLP 1040 hPa for June
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ERA-40 MSLP 1040 hPa for July
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ERA-40 MSLP 1040 hPa for August
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ERA-40 MSLP 1040 hPa for September
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ERA-40 MSLP 1040 hPa for October
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Southern Hemisphere Summer Threshold 1035 hPa
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ERA-40 MSLP 1035 hPa for November
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ERA-40 MSLP 1035 hPa for December
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ERA-40 MSLP 1035 hPa for January
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ERA-40 MSLP 1035 hPa for February
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ERA-40 MSLP 1035 hPa for March
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ERA-40 MSLP 1035 hPa for April
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Interannual Variability
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ERA-40 MSLP 1050 hPa for 1962
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ERA-40 MSLP 1050 hPa for 1963
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ERA-40 1050 for 1983 Western Hemisphere
ERA-40 MSLP 1050 hPa for 1983
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ERA-40 MSLP 1050 hPa for 1984
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Time Series Of Maximum Count In The NH For Each
Year
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Conclusions

• ERA-40 was better at masking terrain than
  NCEP/NCAR.
• Cool season maxima occurred primarily over the
  continents while warm season maxima occurred
  primarily over the oceans in the NH.
• Distinct variability on the interannual timescale
  between the eastern and western halves of the NH.
• SH strong anticyclones tend to occur along
  time-mean storm track.
• Seasonal threshold contrast much smaller in SH
  due to oceans.
• SH contintental maxima tend to occur on lee of
  higher terrain.
• Both data sets support a decline in high
  threshold count during latter half of twentieth
  century.

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Future Work

• Understand dynamical reasons for SH strong
  anticyclones remaining in time-mean storm track.
• Relate interannual variability to global
  teleconnections.
• Learn role of arctic-extratropical interactions
  to strong anticyclones and anticyclogenesis.
• Discuss key predictability issues associated with
  these anticyclones and their associated cold
  surges.

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Thank You

• doody_at_atmos.albany.edu

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NCEP/NCAR 1000hPa Heights 375 m
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