The Potential for Orographic Biases in Jan Mayen Gauge Measurements Validation of High-Latitude Ocean Precipitation Grant W. Petty Sarah Davis Longtao Wu University of Wisconsin-Madison

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The Potential for Orographic Biases in Jan Mayen
Gauge MeasurementsValidation of High-Latitude
Ocean PrecipitationGrant W. PettySarah
DavisLongtao WuUniversity of Wisconsin-Madison
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Mid- and high-latitude islands with existing WMO
stations neglected resource?
Thorshavn
Jan Mayen
Nikolskaya
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WMO stations on mid- and high-latitude islands

• Unlike Morrissey's tropical atoll stations, these
  islands are neither very small nor very flat.
• Issues with respect to use as validation for
  ocean precipitation
• Accuracy of measurements of local precipitation
• Undercatch of snowfall, especially when windy
• Representativeness with respect to surrounding
  open ocean
• Orographic enhancement or rain shadows
• Frictionally induced convergence
• Differential heating

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Climatology of snow occurrence Northern Hemis.
Winter
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Jan Mayen
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Jan Mayen - corrected gauge values

• Corrections by Daqing Yang accounts for
• Gauge type and height above ground
• Precipitation phase
• Wind speed at time of precipitation
• Temperature

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Overview

• At 71N, Jan Mayen is ideally situated to validate
  high latitude ocean precipitation.
• For greater confidence in the detailed validation
  results, we are undertaking
• Careful assessment of station biases relative to
  surrounding ocean (e.g., importance of local
  orographic suppression or enhancement of precip)
  using numerical model simulations.
• Correction of gauge biases due to windsnow,
  etc., using methodology of Yang et al.

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WRF Model Simulations

• Digitize topography to 50 m resolution
• Configure WRF model with 3 nested grids 12.5,
  2.5, and 0.5 km
• Utilize WSM6 explicit microphysics option
  (assessed as best of five bulk microphysics
  schemes for polar ocean precip by Wu and Petty,
  2009)
• Run for several episodes of winter precip --
  initially Dec. 14, 2003.

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Potential for Influence by Beerenberg (northeast
of station)
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Conclusions

• At 71N, Jan Mayen is ideally situated to validate
  high latitude ocean precipitation.
• Initial results of numerical simulations suggest
  that local perturbations of the precipitation
  field are important only in the direct wake of
  Beerenberg, which lies to the northeast.
• Climatological wind patterns associated with
  precipitation suggest that the gauge measurements
  are only rarely influenced by Beerenberg.
• Correction of gauge biases due to windsnow,
  etc., using methodology of Yang et al., increase
  station totals by a few percent.

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Recap of Ongoing Work

• Acquire high resolution topography for Jan Mayen
  - done
• Run mesoscale model simulations of precipitation
  events to assess orographic influences - nearly
  done.
• Undertake similar assessment of additional
  islands having high potential - next step.
• Funding permitting Site visits to assess gauge
  siting, maintenance, etc. Also, may place
  additional recording gauges to assess variability.

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Additional High-Latitude Islands(2003 only)
Petty GPROF Wentz
Petty GPROF Wentz
Corr. Ratio
Corr. Ratio
Petty GPROF Wentz
Petty GPROF Wentz
Corr. Ratio
Corr. Ratio