Tilted updraft

Abstract: A mesoscale convective system (MCS) embedded in the circulation of Typhoon (TY) Robyn was investigated by two aircraft missions during the tropical cyclone motion (TCM-93) mini field experiment. The MCS initially formed north of the typhoon center, but was rapidly advected to the west by the strong midlevel easterlies located between Robyn and the subtropical ridge to the north. Coincident with the occurrence of the MCS, the motion of the typhoon changed from west-northwestward to a slow drift to the north. The structure of the MCS is investigated to examine whether the changes in motion of TY Robyn could be related to a midtropospheric vortex circulation in the MCS. During the mature stage, the MCS has a convective region and an extensive stratiform region. A vigorous updraft in the convective region is tilted southward by the primary circulation around TY Robyn. Below the tilted updraft, descent in a mesoscale downdraft contributes to drying in the low levels, with a shallow surface layer of di...

Abstract: The paper deals with a diagnostic study of the three-dimensional kinematic and dynamic structure of the Harrah tornadic storm. Wind fields were computed from data collected over a 28 min interval in four dual-Doppler radar volume scans during a tornado occurrence. Associated with this storm, there was a strong low-level inflow jet supplying warm, moist air to a tilted updraft, a mid-level vortex doublet, and downdrafts on both storm flanks. The left flank downdraft intensified, undercut the tilted updraft, and formed a gust front along the right rear flank. The gust front propagated cyclonically around the mesocyclone. Calculations of divergence and vorticity showed that in the middle troposphere, the updraft nearly coincided with cyclonic vorticity approximately 10−2 s−1. The low-level tornado cyclone was between the horizontally sheared inflow-outflow region. A mechanism for producing and intensifying this vorticity and downdraft structure is presented on the basis of calculations of the tiltin...

Abstract: Three-dimensional simulation of cold-front rain-band (NCFR) associated with a straight cold front has been studied by use of a non-hydrostatic, full compressible storm-scale model (ARPS) including multi-phase microphysical parameterization. The dynamical and physical features of the frontal cloud de-velopment have been well simulated and analyzed. It is in evidence that the frontal cloud is triggered by the updraft of the secondary frontal circulation. However, the long persistence of diabatic frontogenesis only can be attributed to positive feedback between the frontal baroclinicity and the prefrontal latent heat release. The simulations indeed demonstrate that the potential temperature gradient enhancement in front zone is strongly related with the re-distribution of cloud moisture, by the action of tilted updraft. In conse-quence, the splice of cooling and heating pool that is respectively created from the evaporation of cloud wat-er and condensing J freezing of water vapor J rain droplet, wich is in favor of the strong contrast of cool and warm air mass across the frontal zone to diabatic frontogenesis.

Abstract: This paper presents a case study of mesoscale convective band (MCB) development along a quasi-stationary front over the Seoul metropolitan area. The MCB, which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010, produced a total precipitation amount of 259.5 mm. The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet. The analyses show that the evolution of the MCB can be classified into five periods: (1) the cell-forming period, when convection initiated; (2) the frontogenetic period, when the stationary front formed over the Korean peninsula; (3) the quasi-stationary period, when the convective band remained over Seoul for 3 h; (4) the mature period, when the cloud cover was largest and the precipitation rate was greater than 90 mm h−1; and (5) the dissipating period, when the MCB diminished and disappeared. The synoptic, thermodynamic, and dynamic analyses show that the MCB maintained its longevity by a tilted updraft, which headed towards a positive PV anomaly. Precipitation was concentrated under this area, where a tilted ascending southwesterly converged with a tilted ascending northeasterly, at the axis of cyclonic rotation. The formation of the convective cell was attributed in part by tropopause folding, which enhanced the cyclonic vorticity at the surface, and by the low-level convergence of warm moist air and upperlevel divergence. The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front.