Synoptic Environments Associated with the Training of Convective Cells Aylward and Dyer 2010
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Transcript of Synoptic Environments Associated with the Training of Convective Cells Aylward and Dyer 2010
Synoptic Environments Associated with the Training of Convective Cells
Aylward and Dyer 2010
The main focus is investigating the dynamics resulting in synoptically forced training convective rainfall
Synoptic conditions necessary for the generation of an SCEPT event
Define a SCEPT event to which precipitation rate and duration period satisfy a given criteria
Gather selected atmospheric variables which have a statistically significant correlation to SCEPT events
Allow forecasters to better locate regions of training convection based on findings
Introduction
Synoptically forced Convective Extreme Precipitation Training
Events linked with frontal boundaries (typically warm fronts)◦ Isentropic lift
Deep convection develops in a baroclinic environment where differential cyclonic vorticity advection is present◦ Typically ahead of a short-wave trough or jet streak
500 hPa trough nearly stationary during training events LLJ helps initiate convection and heavy rainfall
SCEPT
Near-neutral to weakly positive differential vorticity advection
Location of 850 hPa maximum moisture convergence Precipitable water maximum (moisture tongue) good
indicator of heavy rainfall High precipitable water content (>1.42 in) required Midlatitude and upper-level lows positioned to the W
or NW Strong surface moisture convergence and UVV at
700 hPa
SCEPT
Multisensor Precipitation Estimates (MPE) using a Z-R relationship to diagnose precipitation rate for each event
SCEPT event location points were gathered from the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP – NCAR) while atmospheric variables examined for each event were gathered from the North American Regional Reanalysis (NARR)
Data Acquisition
Methodology
Rainfall rates must be exceeding 17 mm/h for at least 3 consecutive hours to account as an event
Event location determined by where event occurred ◦ If multiple events occurred, location determined by data
cluster NARR data used to analyze synoptic conditions of
each event◦ diagnostic fields included geopotential heights (300, 500, and
850 hPa), 500 hPa differential vorticity, 300 hPa jet streaks, UVV at 700 hPa, 850 hPa temperature fields, and precipitable water
Methodology
For each height field, the trough axis either deepening, weakening or neutral and tilted positively, negatively, or neutral
A shortwave (long-wave) trough <8000km (>8000km) in amplitude and wavelength
Closed lows were recorded at the pressure level(s)
Axis of greatest precipitable water was noted as well
36 SCEPT events during from 2004 - 2006
Methodology
1) Closed Upper Level Low (CULL)2) Upper Level Trough (ULT)3) 850 hPa Trough-Low (850TL)
3 Cases
Contained a 500 hPa closed low Positively tilted & strengthening trough at
850 and 500 hPa Lows at 300 and 500 hPa nearly stacked 850 hPa jet generally over SCEPT event,
moving toward the NW Precipitable water averaged 36.2mm
CULL
Moisture convergence occurred along the flow of the 850 hPa jet from SW-NE
The SCEPT event was located along the warm front of the associated MLC
Accompanied by WAA Generally occurred from 7Z -16Z during
the cool season months
CULL
CULL
A) 300 hPa, B) 500 hPa, C) 850 hPa, D) Surface observations
500 hPa trough without a closed low Maximum UVV at 700hPa occurred along
the flow 850 hPa jet advecting moisture from the
SSW Precipitable water average 37.1mm
ULT
Accompanied by WAA 300 hPa trough located 915 km west of
event Generally occurred in the warm sector of
an MLC Strong, positively tilted troughs existed at
300 and 500 hPa
ULT
ULT
A) 300 hPa, B) 500 hPa, C) 850 hPa, D) Surface observations
Weak UL flow with an 850 hPa shortwave trough or low present
Trough/low averaged 565km to west of SCEPT event
Moisture convergence was greatest along flow of 850 hPa jet
Advection occurred from the SSW
850TL
Little to no UL forcing existed and no relationship could be found with the 500 hPa and 300 hPa flows
Precipitable water averaged 42.2mm Primarily a warm season phenomena
850TL
850TL
A) 300 hPa, B) 500 hPa, C) 850 hPa, D) Surface observations
Results
Each case has its own characteristics◦ However, Strong UVV at 700 hPa, WAA and High Moisture
content common to all Of the 36 events, 47% had a closed 500 hPa low
and 25% had a longwave 500 hPa trough ◦ Overall, 72% of the SCEPT events were synoptically forced with
a long-wave trough
SCEPT event locations were concentrated across the western region of study◦ Gulf moisture and Atlantic moisture transport influenced
events
Results
500 hPa trough was slightly positive or neutrally tilted for CULL and ULT events
SCEPT events developed right of the 300 hPa jet streak
Surface moisture convergence maximum within 230 km of event location, training parallel to 850 hPa flow
700 hPa UVV maximums within 270 km of SCEPT event with training at the 700 hPa on a WSW to ENE orientation
Conclusion
Why SCEPT events occurred during the early morning hours associated with the least thermal instability
Possibility of a weakening LLJ during morning leading to system speed reduction
Longer research period needed examining more variables
Finer look surface moisture convergence and UVV to reduce error
Discussion
Questions