CSTAR Netmeeting: Coastal Front Climatology

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CSTAR NetmeetingCoastal Front Climatology

• May 11, 2001

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Outline

• CSTAR Coastal Front Objectives
• Data Sources
• Offshore Coastal Front ID Algorithm
• Onshore Passage Criteria
• Missing Data
• Results
• Future Work

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CSTAR CF Objectives/Methods

• Can large scale conditions predict
• offshore frontogenesis?
• onshore movement?
• Can we differentiate
• offshore fronts?
• onshore fronts?
• Are there clues for frontal movement?
• Methods
• objective CF climatology
• composites

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Data Sources

• National Data Buoy Center (NDBC)
• buoy 41001
• buoy 41002
• SAMSON (from NCDC)
• 1961 -1990, 1990-1995
• Cape Hatteras, Wilmington
• Raleigh

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Example of a Coastal Front
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Coastal Front ID Algorithm

• Wind direction at 41001 must be between 20? and
  160? inclusive.
• Wind direction at Hatteras must be greater than
  330? and must also be 20? counterclockwise of
  wind at 41001.
• Wind speed at 41001 must be at least 4.1m/s
  (8kts).
• Air temperature at 41001 must be at least 3?C
  greater than Hatteras.
• Above criteria must be met for at least 4
  consecutive hours to be considered a coastal front

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Onshore CF Detection
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Onshore Passage Criteria

• A Clockwise wind shift of at least 20? in one
  hour
• An increase in air temperature of at least 2?C
  during the same hour
• Wind direction between 30? and 180? after wind
  shift
• After wind shift, air temperature at coast at
  least 2ºC greater than Raleigh
• Are frontal passage criteria O.K.?
• Should we extend detection to include VA,
  specifically Norfolk?

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Missing Data

• 1988 - 1994
• missing 41001 22.5 of the time
• missing 41002 28.1 of the time
• missing at least one buoy 47.5 of the time
• This results in
• 358 offshore coastal front cases
• 90 of these 358 fronts exist offshore at 18Z

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Results

• Offshore CF duration frequency

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Offshore CF Duration Frequency
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Results

• Offshore CF duration frequency

• Offshore hourly CF frequency

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Offshore Hourly CF Frequency
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Results

• Offshore CF duration frequency
• Offshore Hourly CF frequency

• RDU/ILM ? T time series

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? T Time Series

• offshore

• frontal passage

• Time series of ? T between Raleigh and Wilmington
  for a coastal front
• event on 21-22 January 1993 as detected by the
  algorithm.

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Results

• Offshore CF duration frequency
• Offshore Hourly CF frequency
• RDU/ILM ? T time series

• Classifications of coastal fronts
• Offshore vs. Onshore
• Diurnal
• CAD
• Strong vs. Weak
• frontogenesis
• ? T

• Other classifications?

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Future Work

• Frontal type composites
• Case studies
• Modeling
• Role of Gulf Stream