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  • Author or Editor: Hanne V. Murphey x
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Tammy M. Weckwerth
,
Hanne V. Murphey
,
Cyrille Flamant
,
Janine Goldstein
, and
Crystalyne R. Pettet

Abstract

The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and operational water vapor measuring systems and retrievals, via in situ and remote sensing techniques, were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. Convection initiation (CI) sampling strategies were designed to optimally employ the array of ground-based and airborne sensors to observe the processes leading to the development of deep, moist convection. This case study examines several clear-air features and their impact on CI on 12 June 2002. The supercells that developed produced damaging winds and hail. The clear-air, preconvective features included (i) a mesoscale low pressure region, (ii) a dryline, (iii) an old outflow boundary, (iv) the intersection of (ii) and (iii), (v) internal gravity waves, and (vi) horizontal convective rolls.

A unique combination of instruments was positioned to sample the preconvective environment on 12 June 2002. The Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE II) water vapor differential absorption lidar (DIAL), the airborne Electra Doppler Radar (ELDORA), and the Navy Research Laboratory (NRL) P3 aircraft in situ measurements provided information on the moisture and vertical velocity distribution within the boundary layer. Radiosondes, dropsondes, wind profilers, and an Atmospheric Emitted Radiance Interferometer (AERI) provided temperature, moisture, and wind profiling information. Although other ground-based sensors (i.e., S-band dual-polarization Doppler radar, Mobile Integrated Profiling System) were 50–150 km west of the CI area, they were useful for illustrating the boundary layer kinematics and reflectivity fields.

Results suggest that the mesolow and mesoscale boundaries, respectively, acted to enhance the low-level moisture advection and convergence in the CI region. While internal gravity waves were present and appeared to modulate water vapor along the old outflow boundary, they did not play an obvious role in CI in this case. Horizontal convective rolls were observed beneath the new storms that initiated and may have helped to focus the CI in this case.

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Roger M. Wakimoto
,
Hanne V. Murphey
,
David C. Dowell
, and
Howard B. Bluestein

Abstract

A detailed aerial and ground survey of a long-track (∼50 km) F5 tornado is presented. The survey revealed that the tornado exhibited unusual nonlinear movements at two different locations. One portion of the track was associated with a pronounced sinusoidal pattern while another location was characterized by a cusplike pattern. For the first time, high-resolution dual-Doppler wind measurements can be used to evaluate mechanisms for such deviations from a linear tornado path. The analyses of data collected with Electra Doppler Radar (ELDORA) suggest that these departures are trochoidal marks produced as the tornado was revolving within the larger-scale mesocyclone. Retrieved perturbation pressures indicate that the mesocyclone departed significantly from a cyclostrophically balanced state during these deviations. The maximum vorticity associated with the mesocyclone at low levels was shown to be an unreliable indicator of the tornado's intensity.

Vertical cross sections of wind, vertical vorticity, radar reflectivity, and perturbation pressure were photogrammetrically superimposed onto two pictures of the tornado. This merger of data provides a unique view of the structural relationship between the hook echo and the mesocyclone. One of the important conclusions was the lack of a definitive relationship between the widths and strengths of the mesocyclone and the tornado.

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Roger M. Wakimoto
,
Hanne V. Murphey
,
Robert G. Fovell
, and
Wen-Chau Lee

Abstract

Finescale radar observations of intense thermals/starting plumes, during the early stages of precipitation formation, were collected by an airborne Doppler radar on two separate days. The radar data were recorded as the aircraft flew underneath the developing echoes. Mantle echoes (echoes that often appear as an inverted U shape) were observed on both days. Striking in one of the scans was the resemblance of the echo to a mushroom cloud resulting from a nuclear explosion. Numerical simulations using a two-dimensional cloud-resolving model were run to augment the interpretation of the observations. One of the important conclusions was the proposed modification to the default bulk microphysical scheme used in the model. The default scheme yields “a rush to precipitation” leading to the early establishment of large precipitation contents, which is not supported by the observations. Suggested modifications to the scheme are presented.

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Huaqing Cai
,
Wen-Chau Lee
,
Tammy M. Weckwerth
,
Cyrille Flamant
, and
Hanne V. Murphey

Abstract

The detailed analysis of the three-dimensional structure of a dryline observed over the Oklahoma panhandle during the International H2O Project (IHOP_2002) on 11 June 2002 is presented. High-resolution observations obtained from the National Center for Atmospheric Research Electra Doppler Radar (ELDORA), S-band dual-polarization Doppler radar (S-Pol), water vapor differential absorption lidar (DIAL) Lidar pour l'Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l'Eau (LEANDRE II; translated as Lidar for the Study of Aerosol–Cloud–Dynamics–Radiation Interactions and of the Water Cycle) as well as Learjet dropsondes are used to reveal the evolution of the dryline structure during late afternoon hours when the dryline was retreating to the northwest. The dryline reflectivity shows significant variability in the along-line direction. Dry air was observed to overrun the moist air in vertical cross sections similar to a density current. The updrafts associated with the dryline were 2–3 m s−1 and were able to initiate boundary-layer-based clouds along the dryline. The formation of this dryline was caused by high equivalent potential temperature air pushing northwestward toward a stationary front in the warm sector.

Middle-level clouds with radar reflectivity greater than 18 dBZ e near the dryline were detected by ELDORA. A roll boundary, which was associated with larger convergence and moisture content, was evident in the S-Pol data. It is found that the instability parameters most favorable for convection initiation were actually associated with the roll boundary, not the dryline. A storm was initiated near the roll boundary probably as a result of the combination of the favorable instability parameters and stronger upward forcing. It is noted that both the 11 June 2002 dryline and the roll boundary presented in this paper would not be identified if the special datasets from IHOP_2002 were not available.

Although all model runs [fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), Meso Eta, and Rapid Update Cycle (RUC)] suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms. The reasons why the dryline failed to produce any storm inside the IHOP_2002 intensive observation region are discussed. Both synoptic-scale and mesoscale conditions that were detrimental to convection initiation in this case are investigated in great detail.

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Hanne V. Murphey
,
Roger M. Wakimoto
,
Cyrille Flamant
, and
David E. Kingsmill

Abstract

The evolution and finescale structure of a dryline that initiated a line of thunderstorms is presented. Both the along-line variability and mean vertical structure were examined using data collected by an airborne Doppler radar and a water vapor differential absorption lidar (DIAL). The initiation of convection appeared to result from the diurnally induced easterly flow in the maritime air east of the dryline that typically develops late in the day. This flow increased the low-level convergence and allowed rising parcels of air to reach the level of free convection. The along-line variability was largely attributed to numerous misocyclones distorting the thin line of radar reflectivity by advecting dry (moist) air across the dryline south (north) of the misocyclone. The misocyclones also influenced the location of the updrafts, with most of the peak values positioned north of the circulations. As a result, these updrafts were fortuitously positioned in regions of high mixing ratio where the first convective cells initiated.

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