Mid- and high-latitude islands with existing WMO stations – neglected resource?

1. The Potential for Orographic Biases in Jan Mayen Gauge MeasurementsValidation of High-Latitude Ocean PrecipitationGrant W. PettySarah DavisLongtao WuUniversity of Wisconsin-Madison

2. Mid- and high-latitude islands with existing WMO stations – neglected resource? Thorshavn Jan Mayen Nikol’skaya

3. 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

4. Climatology of snow occurrence – Northern Hemis. Winter

5. Jan Mayen

6. 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

7. 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 wind+snow, etc., using methodology of Yang et al.

9. 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.

12. Potential for Influence by Beerenberg (northeast of station)

13. 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 wind+snow, etc., using methodology of Yang et al., increase station totals by a few percent.

14. 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.

15. 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