Vertical-velocity skewness in the marine stratus-topped boundary layer

Vertical-velocity skewness, S(sub w), in a turbulent flow is important in several regards. S(sub w) is indicative of the structure of the motion when it is positive, updrafts are narrower and stronger than surrounding downdrafts, and vice versa. Aircraft measurements often suggest cool, narrow downdrafts at some distance below the stratus cloud top, indicating a negative S(sub w) (Nicholls and Leighton, 1986). This seems natural as the turbulence within the stratus-topped boundary layer (CTBL) is driven mainly by the radiative cooling at the cloud top (although sometimes surface heating can also play a major role). One expects intuitively (e.g., Nicolls, 1984) that, in the situations where cloud-top cooling and surface heating coexist, the turbulence statistics in the upper part of the CTBL are influenced more by the cloud-top cooling, while those in the lower part, more by the surface heating. Thus one expects negative S(sub w) in the upper part, and positive in the lower part, in this case. In contradistinction, large-eddy simulations (LES) of the CTBL show just the opposite: the S(sub w) is positive in the upper part and negative in the lower part of the layer. To understand the nature of vertical-velocity skewness, the simplest type of buoyancy-driven turbulence (turbulent Rayleigh-Benard convection) is studied through direct numerical simulation

Why do the maximum intensities in modeled tropical cyclones vary under the same environmental conditions?

In this study w e explored why the different initial tropical cyclone structures can result in different steady‐state maximum intensities in model simulations with the same environmental conditions. We discovered a linear relationsh ip between the radius of maximum wind (rm) and the absolute angular momentum that passes through rm (Mm) in the model simulated steady‐state tropical cyclones that rm = aMm+b. This nonnegligible intercept b is found to be the key to making a steady‐state storm with a larger Mm more intense. The sensitivity experiments show that this nonzero b results mainly from horizontal turbulent mixing and decreases with decreased horizontal mixing. Using this linear relationship from the simulations, it is also found that the degree of supergradient wind is a function of Mm as well as the turbulent mixing length such that both a larger Mm and/or a reduced turbulent mixing length result in larger supergradient winds

CORRIGENDUM

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An EF3 Multivortex Tornado over the Ionian Region: Is It Time for a Dedicated Warning System over Italy?

Abstract The possibility offered by the Internet to share pictures of tornadoes, and the storm-report archiving in the European Storm Weather Database, have made it apparent that the occurrence of tornadoes over Europe has been underestimated. Together with weak waterspouts and tornadoes, large and intense vortices are occasionally observed. Among these, an EF3 multivortex tornado with a path width of some hundreds of meters affected southeastern Italy on 28 November 2012, causing one casualty and estimated damage of €60M to the largest steel plant in Europe. A tide gauge positioned near the location of tornado landfall and a vertical atmospheric profile available a few hours later near the affected region represent unique sources of information for these events in the Mediterranean. During its transit across the port of Taranto, a waterspout, which was to become the tornado, was observed to have induced a sea level rise of about 30 cm. The supercell responsible for the tornado developed from convective cells triggered by orographic uplift over the Apennines. The 0–1-km wind shear was exceptional in comparison with other Italian tornadoes, and was remarkable in comparison with U.S. events as well. Other indices for severe convection diagnosis also showed extremely high values. The occasional occurrence of events with similar or stronger intensities over Italy emphasizes the need for the Distributed National Weather Service—which will integrate Italian meteorological institutions under one agency and is currently under development—to devise a warning system dedicated to the monitoring and prediction of severe convective events

LESSONS ON OROGRAPHIC PRECIPITATION FROM MAP

Although moisture-laden airflow towards a mountain is a necessary ingredient, the results from MAP taught us that detailed knowledge of the orographically modified flow is crucial for predicting the intensity, location and duration of orographic precipitation. Understanding the orographically modified flow as it occurs in the Alps was difficult since it depends on the static stability of the flow, which is heavily influenced by the complex effects of latent heating, and the mountain shape, which has important and complicated variations on scales ranging from a few to 100\u27s of kilometers. Central themes in all the wet-MAP studies are the ways the complex Alpine orography influenced the moist, stratified airflow to produce the observed precipitation patterns, by determining the location and rate of upward air motion and triggering fine-scale motions and microphysical processes that locally enhance the growth and fallout of precipitation. In this presentation will review the major findings from the MAP observations, along with related theoretical developments

Supercell thunderstorms in complex topography - how lakes in mountain valleys can increase occurrence frequency

While supercell thunderstorms are one of the most severe convective phenomena, their behavior in complex terrain is still poorly understood. Observational studies in the Southern Alps have revealed local supercell "hotspots" associated with valleys with large lakes. With a newly developed radar-based, mesocyclone-detection algorithm, the occurrence and evolution of supercell thunderstorms in the Alpine region were characterized. That study highlights the influence of orography on both storm intensity and occurrence frequency. To disentangle the different influential factors, an idealized modeling framework is established using the mesoscale model CM1. In different modeling experiments the key characteristics of this region have been generalized. The modeling scenarios are based on a high-CAPE environment with unidirectional shear, where a warm bubble serves to initiate the convection. Mimicking the environment of the southern Prealps in central Europe, scenarios with a high mountain ridge, valleys and lakes are explored. Varying both the topographic features and the initial conditions permits the investigation of the individual impact of slopes, valleys and moisture sources. The dynamic and thermodynamic impact of mountain valleys with lakes increases the range of atmospheric conditions that supports supercellular development through horizontal vorticity production and maintenance of high equivalent potential temperature. This influence results in a systematic location dependence of the frequency, intensity and lifetime of supercells, as also found in observations

FURTHER RESULTS ON MOIST NEARLY NEUTRAL FLOW PAST A RIDGE

A systematic numerical study has been performed in the case of moist neutral flows past a twodimensional ridge. The experiments considered here describe the effect of the Coriolis force and of wider mountains on the flow features

Acetabular fracture after cycling related falls: High index of suspicion is required to avoid missing the injury on plain radiographs

Cycling participation as a medium of transport and as a competitive sport has steadily increased in recent decades. Traumatic injuries secondary to falls and collisions occur relatively frequently. Fractures of the hip and pelvis are uncommon with no studies to date reporting their exact incidence in this sport. Injuries specific to the acetabulum are reported even less frequently. We present four cases that highlight the insidious nature of acetabular fractures in cyclists and document their management and recovery. The number of acetabular fractures following falls from bicycles directly onto the lateral hip result in a relatively high number of fractures. Many of these may be missed due to the absence of findings on plain x-ray imaging. It is therefore important to have a high index of suspicion for hip and pelvis fractures when treating cycling related traumatic injuries

Bayesian Exploration of Multivariate Orographic Precipitation Sensitivity for Moist Stable and Neutral Flows

Abstract Recent idealized studies examined the sensitivity of topographically forced rain and snowfall to changes in mountain geometry and upwind sounding in moist stable and neutral environments. These studies were restricted by necessity to small ensembles of carefully chosen simulations. Research presented here extends earlier studies by utilizing a Bayesian Markov chain Monte Carlo (MCMC) algorithm to create a large ensemble of simulations, all of which produce precipitation concentrated on the upwind slope of an idealized Gaussian bell-shaped mountain. MCMC-based probabilistic analysis yields information about the combinations of sounding and mountain geometry favorable for upslope rain, as well as the sensitivity of orographic precipitation to changes in mountain geometry and upwind sounding. Exploration of the multivariate sensitivity of rainfall to changes in parameters also reveals a nonunique solution: multiple combinations of flow, topography, and environment produce similar surface rainfall amount and distribution. Finally, the results also divulge that the nonunique solutions have different sensitivity profiles, and that changes in observation uncertainty also alter model sensitivity to input parameters