Climatological aspects of convective parameters from the NCARNCEP reanalysis

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Climatological aspects of convective parameters
from the NCAR/NCEP reanalysis

• Harold E. Brooks
• NOAA/National Severe Storms Laboratory
• Norman, Oklahoma
• Harold.Brooks_at_noaa.gov

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Overall goals

• Understand what, when, and where severe
  thunderstorms occur and the environments in which
  they form
• Focus on strongest thunderstorms (2 inch hail, 65
  kt winds, F2 tornado)
• Observations of events not good enough
• Look at environments

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NCAR/NCEP reanalysis

• Distribution of data
• 27 levels above ground
• Horizontal spacing 1.92 lat., 1.88 long.
• Every 6 hours since 1 June 1957 (109 soundings)
• Many convective parameters correlate with
  collocated observed soundings (r0.6-0.8)
• Beware of strong vertical gradients!
• Review/revised estimates of distribution of events

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Significant severe
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Reanalysis discrimination compared to
observations

• Severe-no severe works about as well in
  reanalysis as in observed with similar
  relationship
• Tornado-no tornado not as good as in observed,
  somewhat different relationship
• Consider frequency of good severe environments

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Annual cycles of convective parameters

• Based on 7 years of data (73,87, 95-99)
• Take mean value for day
• 31-day running mean
• First-lowest 100 hPa mixing ratio, 700-500 hPa
  lapse rate
• Components of CAPE

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CAPE
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X Darwin
X Yulara
X Brisbane
x Perth
X Adelaide
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Summary of US results

• East-West cross-section
• West-cycle dominated by changes in lapse rate
• East-cycle dominated by changes in moisture
• Moving north
• Moisture decreases
• Spring-fall lapse rate difference decreases

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Comparing US, Europe and Australia

• Lapse rate changes in Europe and most of
  Australia are small
• Yulara looks like western US
• Spatial gradients in conditions smaller in Europe

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CAPE/Deep Shear

• Mean layer (100 hPa) CAPE
• 0-6 km wind difference
• Both computed only when CAPE is positive

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Colors-0-6 km shear, Numbers-1st of month
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Climatology and weather

• Southern Plains of US is almost ideal environment
  for significant severe weather
• Synoptic/mesoscale processes may be more
  important in Europe, Australia

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Animations of annual cycles

• Web site
• http//www.nssl.noaa.gov/brooks/climloop.html
• Single frames

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Mixing Ratio (fill)/Lapse Rate (contour)
0-6 km Shear (fill)/CAPE (contour)
May
Sept
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Seasonality in US

• Seasonality of severe weather related to size
  of thermodynamic cycle
• Lower lapse rates in fall
• Lower shear in fall
• Rocky Mountains are special

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Variability

• Averages over different periods of time
• Interannual variability

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Future Work

• Review relationships
• Complete world analysis
• Application of climate models
• Can climate models see the current world?

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It is better, and more prudent, not to ask
questions (León, Spain 2004)