MultiScale Observations and Analysis of an Extremely Active MidLatitude Weather Pattern

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Multi-Scale Observations and Analysis of an
Extremely Active Mid-Latitude Weather Pattern

• Scott Rudlosky
• Department of Meteorology
• Florida State University
• 4 December 2008

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From the Global Scale to the Mesoscale
My focus will be on May 2003

• The larger scale environment
• Cloud-to-ground lightning patterns
• Daily analyses
• Weather maps
• CG lightning and severe storms
• 15-16 May 2003
• Hourly lightning and precipitation
• RUC and WSR-88D analyses
• Vorticity Generation/Distribution

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Larger Scale Environment
May 2003

• Characterized by features of varying spatial and
  temporal scales
• Interactions result in the cascading of energy
  between scales
• Anomalies induced by individual features
  influence more than their local environment

• A couplet of warm and cold anomalies was observed
  during May 2003 (top right)
• Largely influenced by the 2002-2003 El Niño event
  

May 2003 Top
Temperature Anomalies Bottom - Global
Temperatures
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Cloud-to-Ground Lightning Activity

• Data were obtained from the National Lightning
  Detection Network
• May 2003 mean daily CG count 4 x average for
  the remaining years
• Maxima exist and typically correspond to
  individual mid-latitude systems

Cloud-to-Ground Flash Density May 2003
Above May 2001 May 2007 1) Average Daily CG
Flash Count (?) 2) Observed Daily CG
Flash Count (?)
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Daily Weather Map Analyses

• Interactions between upper and lower tropospheric
  systems control the
• Surface weather conditions
• Poleward transfer of heat and momentum
• Future system development and evolution
• The progression and intensity of systems are most
  important

Top 500 hPa Plot Left 24-hr Precipitation Right
Surface Map
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Rapid Progression of Systems

• Lightning activity and severe storm counts both
  peak during the first half of the month
• Spatial coverage of systems decreases
• Intensity of systems decreases
• Tracks shift throughout the month
• Series of feedback processes

• Suggests larger scale environment has been
  modified by systems
• Mid-latitude cyclones efficiently transfer heat
  and momentum
• Interactions at all scales are intrinsic to
  conditions at all other scales and contribute to
  the whole

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RUC 20 km Analysis
U Component of the Wind

• RUC-derived data converted to Near Storm
  Environment (NSE) information within WDSS-II
• Active subtropical jet stream
• Systems are apparent in both the temperature and
  moisture fields

16 May 0600 UTC Cross-Section Temperature Plan
view Temperature 13 km AGL Radar
16 May 0600 UTC Cross-Section Dew Point Plan
view Dew point 7 km AGL Radar
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Merging of Multiple Radars and RUC
15 May 1600 UTC - 16 May 1600 UTC Merged
composite reflectivity - CG Lightning

• Combine near-storm environment information with
  WSR-88D data

RUC (20 km)
WSR-88D
ReflectivityQC
Moisture Parameters
Stability Parameters
ReflectivityQCComposite
Wind Profile
AzShear0-3km
Isotherm Levels
Rotation Tracks
Reflectivity -10 C
Reflectivity -20 C
Reflectivity 0 C
Precip. Rate
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Convective Patterns
1600 1959 UTC
2000 2359 UTC

• Significant impacts at the surface
• Abundant CG Lightning throughout
• Heavy Rainfall ( 5 inches in 4 hours)
• Many severe storm reports
• May 15 49, 206, 79 (Torn, Wind, Hail)
• May 16 42, 120, 145 (Torn, Wind, Hail)

0000 0359 UTC
0400 0759 UTC
0800 1159 UTC
1200 1559 UTC
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Low Level Generation of Vorticity

• Helicity is a measure of streamwise vorticity
• Includes both directional and speed shear
• Baroclinic generation of vorticity
• Horizontal vorticity is tilted to the vertical
• Updrafts along leading line then stretch the
  vertical vorticity
• Feedback on the storm scale
• Vorticies can enhance the rear-inflow jet and in
  turn the updraft, increasing the vorticity

Storm Relative Helicity
RUC-Derived Helicity
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Vorticity Generation Calculations

• K-Means clusters of merged reflectivity are
  identified
• Clusters are used to modify 3-D NSE wind field
• Vorticity and Divergence are then calculated for
  the modified winds
• Significant contributors
• Along line generation (tilting)
• Stratiform region (stretching)

Composite Reflectivity
Vorticity 120 min
May 16 0522 UTC Along Line Generation
Merged Reflectivity
K-Means Clusters
May 16 0859 UTC Stratiform Generation
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Interacting Cyclones

• 3-D NSE windfield with WSR-88D
• Surface low not evident at 8 km
• Two cyclones depicted at 4 km
• Southern system shows upshear tilt

Top 0000 UTC Bottom 0900 UTC (V-Wind)

• Strong southerly flow at low levels throughout
• Couplet of winds broadens and deepens as the
  system intensifies
• Two maxima
• 10 km
• 2 km

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Conclusions

• Interactions between scales can be observed by
  examining individual features and their evolution
• The progression and intensity of mid-latitude
  systems are most important
• Mid-latitude systems modify the larger scale
  environment
• Activity trails off as the month progresses
• Anomalous temperature gradient mixes out
• Vorticity in two main regions
• Along line generation
• Stratiform generation
• Feedback processes
• Occur at all scales
• Occur between scales

June 2003