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 ID: 772951
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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 eventDefine 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 eventsAllow forecasters to better locate regions of training convection based on findings Introduction
Synoptically f orced Convective Extreme Precipitation TrainingEvents linked with frontal boundaries (typically warm fronts)Isentropic liftDeep convection develops in a baroclinic environment where differential cyclonic vorticity advection is presentTypically ahead of a short-wave trough or jet streak500 hPa trough nearly stationary during training eventsLLJ helps initiate convection and heavy rainfall SCEPT
Near-neutral to weakly positive differential vorticity advection Location of 850 hPa maximum moisture convergencePrecipitable water maximum (moisture tongue) good indicator of heavy rainfallHigh precipitable water content (>1.42 in) requiredMidlatitude 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
M ethodology
Rainfall rates must be exceeding 17 mm/h for at least 3 consecutive hours to account as an eventEvent location determined by where event occurred If multiple events occurred, location determined by data clusterNARR data used to analyze synoptic conditions of each eventdiagnostic 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 neutralA shortwave (long-wave) trough <8000km (>8000km) in amplitude and wavelengthClosed lows were recorded at the pressure level(s) Axis of greatest precipitable water was noted as well36 SCEPT events during from 2004 - 2006 M ethodology
1) Closed Upper Level Low (CULL) 2) Upper Level Trough (ULT)3) 850 hPa Trough-Low (850TL)3 Cases
Contained a 500 hPa closed lowPositively tilted & strengthening trough at 850 and 500 hPaLows at 300 and 500 hPa nearly stacked850 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-NEThe SCEPT event was located along the warm front of the associated MLCAccompanied by WAAGenerally occurred from 7Z -16Z during the cool season monthsCULL
CULL A) 300 hPa, B) 500 hPa , C) 850 hPa, D) Surface observations
500 hPa trough without a closed lowMaximum UVV at 700hPa occurred along the flow850 hPa jet advecting moisture from the SSWPrecipitable water average 37.1mm ULT
Accompanied by WAA 300 hPa trough located 915 km west of eventGenerally occurred in the warm sector of an MLCStrong, positively tilted troughs existed at 300 and 500 hPaULT
ULT A) 300 hPa, B) 500 hPa , C) 850 hPa, D) Surface observations
Weak UL flow with an 850 hPa shortwave trough or low presentTrough/low averaged 565km to west of SCEPT eventMoisture convergence was greatest along flow of 850 hPa jetAdvection occurred from the SSW850TL
Little to no UL forcing existed and no relationship could be found with the 500 hPa and 300 hPa flowsPrecipitable water averaged 42.2mmPrimarily a warm season phenomena850TL
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 allOf 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 eventsResults
500 hPa trough was slightly positive or neutrally tilted for CULL and ULT eventsSCEPT events developed right of the 300 hPa jet streakSurface 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 C onclusion
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 reductionLonger research period needed examining more variablesFiner look surface moisture convergence and UVV to reduce errorDiscussion
Questions