a climatology of the convective system morphology over northeast united states kelly lombardo &...
Post on 21-Dec-2015
214 views
TRANSCRIPT
A Climatology of the Convective System Morphology over Northeast United States
Kelly Lombardo & Brian Colle
School of Marine and Atmospheric SciencesStony Brook University
(m)
(Gallus et al. 2008)
Convective Structures
IC: Isolated CellsCC: Cluster of CellsBL: Broken Line
NS: No StratiformTS: Trailing StratiformPS: Parallel StratiformLS: Leading StatiformBE: Bow Echo
NL: Nonlinear
>60
50-60
40-50
30-40
<30
dBZ
Motivational Questions
What are the convective structures across the NE and how do they compare to the Central US?
What is the evolution of the convective types across the domain?
Are there specific ambient conditions that favor each type?
Is there a preferred type of severe weather associated with these structures ?
070803 1530 UTC – 070804 0800 UTC
Data & Methods
• Examined 2 km NOWrad (available from NCAR) every 15 minutes from May-August 2007.
• Identified the structure of convection across the Northeast U.S., matching the structures defined by Gallus et al. 2008.
• Noted the time and location of initiation and decay for each structure.
• Multiple structures can exist across the entire domain. All were cataloged.
Structural Distribution
Central Plains(Gallus et al. 2008)
925 events+24 LS & PS (Parker and Johnson 2000)
Northeast454 events
Upslope18%
HighTerrain
34%
East Slope&
Coastal Plain24%
Coastal Ocean
24%
Where do the convective types initiate?Methodology:*Noted domain & time of initiation.*Binned the times into 6 hr increments: 00-06 UTC, 06-12 UTC, 12-18 UTC, 18-00 UTC.*Normalized to account for variations in domain size.
Types of Evolutions
• Upscale growth from cellular to linear and/or nonlinear systems.
• Cellular with no upscale growth.• MCS propagating into the region from upstream.• Embedded convection within widespread
precipitation and banding features associated with baroclinic systems.
• Example of upscale growth…
070627 1700 UTC 070627 2000 UTC 070627 2115 UTC
070627 2245 UTC 070628 0100 UTC 070628 0300 UTC
Cluster of Cells No Stratiform Bow Echo
Trailing Stratiform Trailing Stratiform Nonlinear
KALB070627 1200 UTCCAPE 1154 Jkg-1
June 27 2007 Transition Event
Surface AnalysisSounding
070627 1800 UTC
900 hPa
700 hPa
500 hPa
600 hPa
400 hPa
mean sea level pressure (blue solid), surface thte (K, green dashed), surface wind (ms-1), CAPE (Jkg-1, shaded)
Composite of Transition Events:
Included 17 events
Selected at random from May-August, 2005-2007
20 km RUC analyses
Closest time within 3 hrs prior to the first sign of cellular convection
070627 event was excluded from the composite
850 hPa hght (blue contours), 850 hPa wind (ms-1), 850 hPa thte (K, shaded), 850 hPa tmpc (light blue dashed)
700 hPa hght (blue contours), 700 hPa relative vorticity (*10-5 s-1, black dashed contours), 300 hPa mag wind (ms-1, shaded)
Composite of Transition Events
What convective type is associated with themost severe wind reports?
(Gallus et al. 2008)
Methodology:*SPC svr storm report archive.*Noted the time and lat/lon point of each individual storm report.*Examined NOWrad data for that time.*Noted the structure of precip at lat/lon point of svr wx report.*That convective structure was responsible for that svr wx report.*Normalized by the total number of events.
IC: Isolated Cells CC: Cluster of CellsBL: Broken Line NS: No StratiformTS: Trailing Stratiform PS: Parallel StratiformLS: Leading Statiform
BE: Bow Echo NL: Nonlinear
Trailing Stratiform070609:0000
IC CC BL NL NS TS LS PS BE
IC CC BL NL NS TS LS PS BE
Number of svr wind reports per event
What convective type is associated with themost hail reports?
(Gallus et al. 2008)
Clusters of Cells070713:2045
Broken Line070510:1800
IC CC BL NL NS TS LS PS BE
What convective type is associated with themost tornado reports?
(Gallus et al. 2008)
Bow Echo070809:1530
Nonlinear070808:1015
IC CC BL NL NS TS LS PS BE
Summary• Northeast U.S. has a similar distribution of different convective
structures as the Central Plains, perhaps more clusters of convection over the NE.
• Convective initiation (IC, CC, NL) begins in the UP & HT regions early in the day, peaking 18–00 UTC. This initiation shifts eastward to the coast & becomes more linear/NL later in the day.
• Transition events (isolated cell to linear) have moderate instability, westerly flow, weak shear & weak synoptic forcing.
• TS systems are associated with the largest number of severe wind reports per event in the NE, but the largest number of tornados per event are produced by BE.
Future Work• Include more warm season events in climatology.• Obtain a better understanding of the reasons for the convective
evolution and structures over the NE.