Fine-Scale Observations of a Pre-Convective Convergence Line in the
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Fine-Scale Observations of a Pre-Convective Convergence Line in the Fine-Scale Observations of a Pre-Convective Convergence Line in the Central Great Plains on 19 June 2002 Central Great Plains on 19 June 2002 The Problem The Problem Questions: 1. How do mesoscale atmospheric processes and surface fluxes alter the convective boundary layer (CBL) to generate a dryline boundary? 2. How is dryline convergence maintained, at very small scales (Ziegler and Rasmussen 1998)? 3. How does deep convection initiate along a dryline at those scales? Vertical Structure and Evolution Vertical Structure and Evolution Density Current Dynamics Density Current Dynamics Sustained Convergence Sustained Convergence Early soundings through the CBL demonstrate the presence of a strong capping inversion at 850 mb and increasing values of CAPE. First series of stepped traverses shows θ e and ‘r’ differences 3 K and 1.5 g kg -1 , resp. across the dryline, later to increase to 10 K and 6 g kg -1 indicating dryline strengthening. By 21 UTC cross dryline confluence increases with values of 10 ms -1 over distances of hundreds of meters. Murphey et al. (2005) find that horizontal shearing along the dryline due to confluence yields high vertical vorticity along a contorted dryline on this day. A first stepped traverse shows that the dry air is cooler (θ v lower), consistent with the westward tilt of the dryline & the negative solenoidal circulation. Dual-Doppler analysis confirms the dryline tilt to the W and the negative solenoidal circulation. The first stepped traverse observes θ v 0.5K cooler on the dry side than moist side, anda peak of 0.5K at the dryline. A remarkable transformation occurs between the 2 nd and 3 rd dryline stepped traverses: the dryline shifts from a westward to an eastward tilt with a consistent θ v gradient reversal. Denser air flips from the W side to the E side of the dryline, possibly because of larger surface sensible heat flux to the W. The vertical velocity dipole consistently shifts, the solenoidal circulation becomes positive, and the eastward propagating fine-line becomes stationary. All this is consistent with DOW3 along with mobile mesonet data clearly show strong confluen near the dryline and along the UW flight track. During the 3 rd stepped traverse the dryline becomes quasi-stationary and better-defined, according to DOW3 data. LearJet dropsondes and UWKA stepped traverses observe a deep core of positive buoyancy near the dryline. By the last series of transects the CBL depth above the dryline exceeds 3200 m AGL. Advection of high θ e air into the CBL ‘dome’ results in the erosion of CIN. Discussion Discussion There is a weak θ v (virtual pot. temp.) gradient across the dryline. This gradient is consistent with the vertical tilt of the echo plume, and the vertical velocity couplet, indicating a thermally direct solenoidal circulation. The circulation and tilt reverse when the θ v (virtual pot. temp.) gradient reverses. At the fine-line convergence zone (the dryline), anomalously high θ v occurred, deepening in time till CI. Conclusions Conclusions • Updrafts greater than 5 m/s are observed, collocated with anomalously high values of θ v • This leads to local deepening of the CBL along the fine-line, leading to CI. • Dual-Doppler wind field demonstrates the existence of solenoidal circulations consistent with horizontal density differences, and changes Benjamin Daniel Sipprell, [email protected], and Bart Geerts , University of Wyoming, Laramie, USA Benjamin Daniel Sipprell, [email protected], and Bart Geerts , University of Wyoming, Laramie, USA JP3J.1 JP3J.1 DOW3 data, local mesonets and mobile mesonets show an increasin intense southerly jet and thus increasing confluent flow into a evolving stationary dryline. REFERENCES: Murphey, Hanne V. and Wakimoto, Roger M., 2005: Dryline on 19 June 2002 during IHOP. Part I: Airborne Doppler and LEANDRE II Analysis of the Thin Line Structure and Convection Initiation. Mon. Wea. Rev.: in press. Ziegler, Conrad L. and Rasmussen, Erik N., 1998: The Initiation of Moist Convection at the Dryline: Forecasting Issues from a Case Study Perspective. Wea. and Forecasting: Vol. 13, No. 4, pp. 1106–1131. ves: describe the kinematic and thermodynamic properties of a pre- ctive dryline at very high resolutions and in vertical cross sections. demonstrate via a case study that fine-scale convergence is n by the buoyancy gradient, sustained by density current dynamics. Early (unusual eastward tilt) Late (classic westward tilt)
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Fine-Scale Observations of a Pre-Convective Convergence Line in the Central Great Plains on 19 June 2002. JP3J.1. JP3J.1. Benjamin Daniel Sipprell, [email protected], and Bart Geerts , University of Wyoming, Laramie, USA. The Problem Questions: - PowerPoint PPT Presentation
Transcript of Fine-Scale Observations of a Pre-Convective Convergence Line in the
Fine-Scale Observations of a Pre-Convective Convergence Line in the Fine-Scale Observations of a Pre-Convective Convergence Line in the Central Great Plains on 19 June 2002Central Great Plains on 19 June 2002
The ProblemThe Problem
Questions:1. How do mesoscale atmospheric processes and surface fluxes alter the convective boundary layer (CBL) to generate a dryline boundary?
2. How is dryline convergence maintained, at very small scales (Ziegler and Rasmussen 1998)?
3. How does deep convection initiate along a dryline at those scales?
Vertical Structure and EvolutionVertical Structure and Evolution Density Current DynamicsDensity Current Dynamics Sustained ConvergenceSustained Convergence
Early soundings through the CBLdemonstrate the presence of a strong capping inversion at 850 mb and increasing values of CAPE.
First series of stepped traverses shows θe and ‘r’ differences 3 K and 1.5 g kg-1, resp. across the dryline, later to increase to 10 K and 6 g kg-1
indicating dryline strengthening.
By 21 UTC cross dryline confluenceincreases with values of 10 ms-1
overdistances of hundreds of meters. Murphey et al. (2005) find that horizontal shearing along the drylinedue to confluence yields high verticalvorticity along a contorted dryline on this day.
A first stepped traverse shows that the dry air is cooler (θv lower), consistent with the westward tilt of the dryline & the negative solenoidal circulation.
Dual-Doppler analysis confirms the dryline tilt to the W and the negative solenoidal circulation.The first stepped traverse observes θv
0.5K cooler on the dry side than moist side, anda peak of 0.5K at thedryline.
A remarkable transformation occurs between the 2nd and 3rd dryline stepped traverses: the dryline shifts from a westward to an eastward tilt with a consistent θv gradient reversal. Denser air flips from the W side to the E side of the dryline, possibly because of larger surface sensible heat flux to the W. The vertical velocity dipole consistently shifts, the solenoidal circulation becomes positive, and the eastward propagating fine-line becomes stationary. All this is consistent with density current theory.
DOW3 along with mobile mesonetdata clearly show strong confluencenear the dryline and along the UWKAflight track.
During the 3rd stepped traversethe dryline becomes quasi-stationary and better-defined, according to DOW3 data.
LearJet dropsondes and UWKA stepped traverses observe a deep core of positive buoyancy near the dryline. By the last series of transects the CBL depth above the dryline exceeds 3200 m AGL. Advection of high θe air into the CBL ‘dome’ results in the erosion of CIN.
DiscussionDiscussionThere is a weak θv (virtual pot. temp.) gradient across the dryline. This gradient is consistent with the vertical tilt of the echo plume, and the vertical velocity couplet, indicating a thermally direct solenoidal circulation. The circulation and tilt reverse when the θv (virtual pot. temp.) gradient reverses.
At the fine-line convergence zone (the dryline), anomalously high θv occurred, deepening in time till CI.
ConclusionsConclusions• Updrafts greater than 5 m/s are observed, collocated with anomalously high values of θv
• This leads to local deepening of the CBL along the fine-line, leading to CI.• Dual-Doppler wind field demonstrates the existence of solenoidal circulations consistent with horizontal density differences, and changes in dryline propagation speed.
Benjamin Daniel Sipprell, [email protected], and Bart Geerts , University of Wyoming, Laramie, USABenjamin Daniel Sipprell, [email protected], and Bart Geerts , University of Wyoming, Laramie, USA
JP3J.1 JP3J.1
DOW3 data, local mesonets andmobile mesonets show an increasinglyintense southerly jet and thus increasing confluent flow into a evolving stationary dryline.
REFERENCES:Murphey, Hanne V. and Wakimoto, Roger M., 2005: Dryline on 19 June 2002 during IHOP. Part I: Airborne Doppler and LEANDRE II Analysis of the Thin Line Structure and Convection Initiation. Mon. Wea. Rev.: in press.Ziegler, Conrad L. and Rasmussen, Erik N., 1998: The Initiation of Moist Convection at the Dryline: Forecasting Issues from a Case Study Perspective. Wea. and Forecasting: Vol. 13, No. 4, pp. 1106–1131.
Objectives:1. To describe the kinematic and thermodynamic properties of a pre-convective dryline at very high resolutions and in vertical cross sections.
2. To demonstrate via a case study that fine-scale convergence is driven by the buoyancy gradient, sustained by density current dynamics.
Early (unusual eastward tilt)
Late (classic westward tilt)
