Detection and occurrence of low-level jets over Testbed area

1
Detection and occurrence of low-level jets over
Testbed area

• T. Roschier
• A-J Punkka

2
motivation and goals

• Use and evaluation of wind profiler data in
  low-level jet detection
• Comparison between sounding and profiler data
• Low-level jet occurrence (11/2005-10/2006)

3
definition of low-level jet

• Glossary of meteorology A jet stream that is
  typically found in the lower 2-3 km of the
  troposphere.
• Climatology of the low level jet (Bonner 1968)
  Criterion 1 The wind at the level of maximum
  wind must equal or exceed 12 m/s and must
  decrease at least 6 m/s to the next higher
  minimum or to the 3 km level.
• LLJ climatologyin the Southern Great Plains
  (Whiteman et al. 1997) Criterion 1 Maximum
  wind speed greater than 10 m/s in the lowest 3 km
  and the wind speed must decrease by at least 5
  m/s before the 3 km level is reached.
• Definition of Whiteman et al. used in this study.

4
methods

• Primary data source Vantaa soundings (via
  Researchers interface)
• Comparisons to Jokioinen and Tallinn soundings
  (UWyo) and to Malmi wind profiler (RI)
• Stages
• collecting of cases
• statistics of found cases monthly distribution,
  wind speed at LLJ core, LLJ core height etc.
• comparisons

5
data problems

• irregular soundings from Vantaa
• coarse temporal resolution of Jokioinen and
  Tallinn soundings
• bad raw data from Malmi wind profiler
• discontinuities in measurements
• poor signal quality

6
Good data from soundings

• Profiler data missing )

7
Good wind profiler case

• ?

8
what to learn

• usability of wind profiler data in LLJ detection
• to get very preliminary overview the frequency of
  occurrence of LLJs