Precipitation Efficiency 20032004 of Columbia_ MO

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					         Factors Influencing
     Precipitation Efficiency (PE)
in a Continental Mid-Latitude Location

     Mohd Hisham Mohd Anip

        Dr Patrick Market

 Introduction

 Literaturereview
 Methodology

 Results & Discussions

 Conclusions

 Questions/comments?
   What is PE?
     The efficiency of a system in eliminating the
     moisture it ingests from the atmosphere
     (Doswell et al. 1996)

                     total precipitat ion
             PE 
                  total available moisture
   total available moisture

    Braham (1952) – total inflow water vapor into the
    cloud base
    Ferrier et al. (1996) – total condensation over
    column of air
 Why   study the PE?

 Give an indication of how efficient a system is
 eliminating the moisture it ingests from the

 Heavy rainfall systems are associated with higher
 PE value (Fankhauser 1988, Doswell et al. 1996,
 Scofield 2000)

 Use as a forecasting tool to forecast heavy rainfall
 & flash flood events
Literature Review
 First study has been conducted in the early

    - after the Thunderstorm Project
      Braham (1952)

         - determined thunderstorm water
Braham (1952)                 Mid-latitude thunderstorm      Observed   10%
Sellers (1965)                Climatological                 Observed   5-19%
Newton (1966)                 Mid-latitude squall line       Observed   50%
Fankhauser (1966)             Mid-latitude thunderstorm      Observed   60%
Auer and Marwitz (1968)       Mid-latitude hailstorms        Observed   21-120%
Chisholm (1968)               Mid-latitude thunderstorm      Observed   21%
Hartzell (1969)               Mid-latitude hailstorm         Observed   45%
Chisholm (1970)               Mid-latitude squall line       Observed   ~100%
Marwitz (1972)                Mid-latitude hailstorm         Observed   ~4%
Foote and Fankhauser (1973)   Mid-latitude hailstorm         Observed   15%
Chalon et al. (1976)          Mid-latitude hailstorm         Observed   40%
Houze et al. (1976)           Mid-latitude frontal system    Observed   60-90%
Caracena et al. (1979)        Mid-latitude thunderstorm      Observed   85%
Gamache and Houze (1983)      Tropical MCS                   Observed   ~59%
Heymsfeld and Schotz (1985)   Mid-latitude squall line       Observed   25-40%
Lipps and Hemler (1986)       Tropical convection            Modeled    ~40%
Fankhauser (1988)             Mid-latitude thunderstorms     Observed   19-47%
Ryan et al. (1989)            Mid-latitude cold front        Observed   0%
Chong and Hauser (1989)       Tropical squall line           Observed   45-57%
McBean and Stewart (1991)     Mid-latitude frontal system    Observed   70%
Ferrier et al. (1996)         Tropical and mid-latitude      Modeled    24-45%
                                   squall lines
Rauber et al. (1996)          Tropical convection            Observed   20-30%
Szeto et al. (1997)           High-latitude frontal system   Modeled    0-80%
Li et al. (2002)              Tropical convection            Modeled    20-130%
Market et al. (2003)          Mid-Latitude MCS               Observed   4-48%
  Literature Review
Findings from later
  observational studies

i. negative correlation
   between wind shear
   and PE value
   (Marwitz 1972)
Literature Review
ii. Larger cloud base area and cloud base
   mixing ratio,  PE, higher cloud base
   height,  PE

  (Fankhauser 1988)
Literature Review
iii. PE instantaneous values vary with the
   lifetime of a system (Doswell et al. 1996)
(Market et al. 2003)
Literature Review
iv. Relatively strong negative correlation
  between Convective Inhibition (CIN) and PE
 (Market et al. 2003)
Literature Review
 Significant findings from modeling study

 i. PE in convective system is control by
 vertical orientation of the updrafts (Ferrier
 et al. 1996)

 ii. PE is higher in a heavy rain regime under
 warm environmental condition and strong
 convection (Li et al. 2002)
 Objective   of this study

 i. Examine PE variation with seasons

 ii. Examine PE variation with cloud
 types (stratiform vs. convective)

 iii. To find the relations of environmental
 factors to PE value, if any, and used them
 to support the earlier findings
Area of Study       -    Columbia, MO

Why choose Columbia?

    i. Good annual amount of rainfall ~1000mm
  ii. Sanborn & KCOU Weather Station
 iii. SuomiNet system

Criteria to select the event from Oct 1st, 2003 to
  Sept 30th, 2004

   i. Total rainfall > 0.25 in (6.4mm)
  ii. Rainfall was continuously for at least 4hrs.
Few methods to calculate PE, e.g.,

  Sellers Method (1965), P/PW
     - a climatological approach

  Scofield Method (1987), PW X RH
     - RH is a mean value taken between 1000
     and 700mb pressure level

  Water Budget Method (Braham 1952, Palmén &
     Newton 1969)
    - known as true PE because it takes into
    account all the moisture in and out of a
    rainfall system
Using water budget method by Palmén & Newton
(1969) to calculate PE assumed to be in steady
state system at a fixed point

        1 po q     1 po
    PE       dp   .qVdp
        g p t      g p
              (A)               (B)

 P = total precipitation
 E = evaporation
(A) = local change in specific humidity tendency
(B) = moisture flux divergence
 PE   Calculation
 Used analysis data from RUC20 model to
 generate water budget terms

 RUC20- latest meteorological numerical models,
 and features 50 layers and 20 km horizontal
 resolution that improves the accuracy and
 timeliness of current weather analyses and short-
 range weather forecasts

 RUC20 output acquired from the Atmospheric
 Radiation Measurement (ARM) of the Department
 of Energy (DOE)
Results and Discussions
   31 events have been identified

   PE values range from -78% to 236% were

   According to Marwitz (1972), PE value over
    the lifetime of rainfall system should be
    between 0% and 100%, but instantaneous
    value can vary from 0% to  (Doswell et
    al. 1996)
Results and Discussions
   PE value > 100% (4 cases)
    - because the values were estimated
    toward the end of the system lifetime
    (Doswell et al. 1996)

   PE value < 0% (1 case)
    - because the system was precipitating out
    as well as advecting moisture out of the
    system, experiencing a net loss in moisture
 Seasonal         variation
      Month          No. of Events   Season   Average PE (%)
   Dec, Jan, Feb          6          Winter        12
   Mar, Apr, May          9          Spring        51
   Jun, Jul, Aug          8          Summer        69
   Sept Oct, Nov          7           Fall         43

 - land heating and cooling has played a
 major factor for these variations

 - higher temperature will result in more
 evaporation which produces more moisture
 and rainfall during warmer season
 Seasonal         variation
      Month          No. of Events   Season   Average PE (%)
   Dec, Jan, Feb          6          Winter        12
   Mar, Apr, May          9          Spring        51
   Jun, Jul, Aug          8          Summer        69
   Sept Oct, Nov          7           Fall         43

 - precipitable water values are typically
 greater through the warm season and lower
 in the cold season (Ross and Elliott 1996)

 - PE value is affected by relative humidity
 and precipitable water (Doswell et al. 1996)
   Cloud/system type
     Rainfall    No of Events   Summer   Fall   Winter   Spring   PE average (%)

    Convective       19           6       7       1        5           56

    Stratiform       11           2       0       5        4           29

- PE value for convective system is higher
  because of the ability of updrafts and
  downdrafts to collect droplets that would
  become precipitation (Ferrier et al. 1996 )

- Under warm environmental condition and
  strong convective system the precipitation
  would be more efficient, which produced
  higher PE value (Li et al. 2002)
   Cloud/system type

     Rainfall    No of Events   Summer   Fall   Winter   Spring   PE average (%)

    Convective       19           6       7       1        5           56

    Stratiform       11           2       0       5        4           29

- Stratiform system generally produce little or
  no precipitation and what little might fall
  consist of minute particles such as drizzle

- Convective rainfall accounts for ~70% of the
  total rainfall, because its intensity is so much
  higher (Houze 1997)
   Environmental factors
    - only involve the convective system (19 events)
    - unfortunately no correlations have been found
    - proceed with advance analysis by selecting the
    event that extremely fulfill study assumption &
    have moderate unstable condition

    - 6 events were short listed which shows;
        i. strong inverse correlation (-0.764)
               between PE value and environmental
               wind shear (Marwitz 1972)
        ii. high probability (86%) where PE value is a
               function of precipitable water (Doswell
               et al. 1996)
   Case study ( August 24th, 2004)
    - example of perfect steady-state system passing
    through the study area
        1500 UTC : Approaching the study area
Surface Analysis chart (1500 UTC)
500 mb Height & Vorticity chart (1500 UTC)
Skew-T chart from 1500 UTC RUC20 sounding
1800 UTC: Over the study area
2000 UTC: Leaving the study area
Facts of the Event:
i. 16.76 mm rainfall amount was recorded over study
   area from 16 to 19 UTC observation
ii. Amount of precipitable water measure from UMC
    SuomiNet system drop tremendously as the
    system passing trough the study area
iii. 45% of PE value was calculated with estimation of
    37.61 mm available water between 1000 and 300
    mb pressure level

iv. Report from National Climatic Data Center reveals
   that 13 locations in Missouri were experienced
   significant weather associated with this weather
   PE value is highest during summer, followed by
    spring, fall & winter

   PE value is higher for convective type system
    than the stratiform

   After advance analyses
    - There is strong inverse correlation between
    environmental wind shear and PE value
    - There is high probability that precipitable water
    is a function of PE value

   Case study shows that 45% PE was estimated
    for the perfect steady-state convective
    weather system

   Special Thanks: Dr Market

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