high-resolution ruc cape values and their relationship to right turning supercells
DESCRIPTION
High-Resolution RUC CAPE Values and Their Relationship to Right Turning Supercells. By: Andy Mair Mentor: Dr. William A. Gallus Jr . Department of Geological and Atmospheric Sciences Iowa State University, Ames, IA. Introduction. Supercell movement important to severe weather prediction - PowerPoint PPT PresentationTRANSCRIPT
High-Resolution RUC CAPE Values and Their Relationship to Right Turning Supercells
By: Andy MairMentor: Dr. William A. Gallus Jr.
Department of Geological and Atmospheric SciencesIowa State University, Ames, IA
Introduction
• Supercell movement important to severe weather prediction
• Storm Chasing• Goal: Find a link between CAPE and right
turning supercells
Terminology• CAPE = Convective Available Potential Energy
-Energy for convection• RUC = Rapid Update Cycle
- Computer model that runs hourly• GMT Time (z)= Standard time across the world
(-6 hrs in Central time zone)• Right Turning Supercells
Right Turning Supercells
248
270
270-248 = 22
AA
A
B
B
C
O hr 30 min
1 hr
Previous Research
• Very little research• Bunkers Theory (1999)• Few older methods
Hypothesis
• A supercell will become a right turning supercell due to mesocyclone strengthening. Therefore, CAPE should increase when a supercell right turns because CAPE has been shown to strengthen the mesocyclone.
Methodology
• Data collected from June 2008• Anywhere in US, mainly in southern midwest• Prevent Changes in RUC• 13 km High Resolution RUC• 82 Cases, 54 straight path supercells, 28 right
turning cases
Methodology- Initiation/ Dissipation
• Initiation when storm shows 40 dBZ reflectivity
• Dissipation-- Storm falls below 40 dBZ- Storm merges with another storm
Methodology – Tracking/ Turning
• Turning if 20 degree change in storm motion vector observed
• Determined using GR2 Analyst storm motion• Left turners were not used• Collected right turning and straight path
storms• Collected data every half hour
Methodology- Collecting CAPE
• Used Surface Based CAPE• RUC downloaded from NCDC NOMADS site• Converted and used in Grads• Used CAPE value on the hour• When in between hours averaged hour before
and hour after
Observations- Non turners
18:00z18:30z
19:00z19:30z
20:00z20:30z
21:00z21:30z
22:00z22:30z
23:00z23:30z
00:00z00:30z
0500
100015002000250030003500400045005000
June 7th Non-Turning Supercells
1 2 3 4 5 6 7 8 9 10
Time
CAPE
(J/k
g)
Supercells
Observations- Non turners
• Very diverse data• Average initiation CAPE: 1351 J/kg• Average Dissipation CAPE: 1215 J/kg
Observations- Right Turners
3hr 30min 3hr
2hr 30min 2hr
1hr 30min 1hr
30 min
Superce
ll turn
s30min 1hr
1hr 30min 2hr
2hr 30min 3hr
3hr 30min 4hr
4hr 30min 5hr
5hr 30min
0
500
1000
1500
2000
2500
3000
CAPE of Turning SupercellsCAPE of Turning Supercells
Time during supercell life before and after turning
CAPE
(J/k
g)
Observations- Right Turners
3hr before
2hr 30min before
2hr before
1hr 30min before
1hour before
30 minutes b
efore
Superce
ll turns
30min after
1hr after
1hr 30min after
2hr after
0
1000
2000
3000
4000
5000
6000
Right Turning Supercells June 7th1 2 3 4 5
Time
Cape
(J/k
g)
Supercells
Observations- Right Turners
• CAPE values fall approximately 2 hours before turning
• Initiation CAPE : 1953 J/kg• Dissipation CAPE : 1220 J/kg• Average CAPE drop of 733 J/kg
CAPE Diurnal Cycle
3z 4z 5z 6z 7z 8z 9z 10z 11z 12z 13z 14z 15z 16z 17z 18z 19z 20z 21z 22z 23z 0z 1z 2z
-600
-400
-200
0
200
400
600
Diurnal Cycle of CAPEHour Differences in CAPE Polynomial (Hour Differences in CAPE)
Time
Chan
ge in
CAP
E (J/
kg)
by h
our
Results
Initiation
1/2 hour a
fter initiati
on
hour after
initiation
hour until d
issipati
on
1/2 hour u
ntil diss
ipation
dissipati
on0
500
1000
1500
2000
2500
Turning Supercells Compared to Non Turning Supercellsturners Linear (turners) non turners Linear (non turners)
Time
CAPE
(J/k
g)
Results
17:00z 17:30z 18:00z 18:30z 19:00z 19:30z 20:00z 20:30z 21:00z 21:30z 22:00z 22:30z 23:00z 23:30z 00:00z 00:30z0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
June 7th Average CAPE Observed in Supercellspre turning non turners post turning
Time
CAPE
(J/k
g)
Conclusions
• Right turners initialize in higher CAPE values• Right turners CAPE values fall 1-2 hours prior
to turning• Original hypothesis was incorrect
Further Research
• Low level wind shear• 0-1 or 0-3 km helicity• EHI (Energy Helicity Index)• Expanded to more years and months
Acknowledgements
• Dr. Gallus for his assistance on the project• Jeff Duda for help on running and using Grads• Dave Flory for help with my procedure• Justin Schultz for his guidance• Ryan Alliss for statistical analysis help
Resources• Brandes, 1977: Mesocyclone Evolution and Tornadogenesis: Some Observations. Monthly
Weather Review 106, 995–1011.• Bunkers, Klimowski, Zeitler, Thompson, and Weisman: Predicting Supercell Motion Using
a New Hodograph Technique. Weather and forecasting 15, 61–79. • Colquhoun, J. R., 1980: A method of estimating the velocity of a severe thunderstorm
using the vertical wind profile in the storm’s environment. Eighth Conf. on Weather Forecasting and Analysis, Denver, CO, Amer. Meteor. Soc., 316–323.
• Donaldson , and Desrochers 1989: Improvement of Tornado Warnings by Doppler Radar Measurement of Mesocyclone Rotational Kinetic Energy. Weather and forecasting 5, 247–258.
• Kerr, and Darkow, 1996: Storm-Relative Winds and Helicity in the Tornadic Thunderstorm Environment. Weather and forecasting 11, 489–505.
• Maddox, 1976: An Evaluation of Tornado Proximity Wind and Stability Data. Monthly Weather Review 104, 133-142.
• Richard, and Edwards, 2000: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak. Weather and forecasting 15, 682–699.
