The role of horizontal rolls in rapid intensification of cyclonic vortex

<p>The present laboratory study is focused on the role of convective rolls in enhancement of the heat flux from the sea and triggering of the process of rapid intensification of tropical cyclones. The appearance of coherent convective structures such as thermals and rolls are registered by different optical techniques and temperature measurements. Two-dimensional velocity fields are used for the study of the structure and characteristics of the flow. The heat flux from the heating plate to the fluid is measured directly. Obtained results clearly show that rapid intensification of a laboratory analog of a tropical cyclone is tightly linked with the heat transfer process in the boundary layer. Formation of secondary convective structures strongly increases the heat transfer and intensity of convective circulation. Intensity of radial inflow is a crucial aspect for the intensification of cyclonic vortex, hence rapid variation of the heat transfer is a factor that has a substantial influence on the dynamics of a laboratory vortex. </p>

MECHANISMS OF FORMING OF DYNAMIC STRUCTURES IN DEEP WATERS OF MARMARA SEA

Based on the numerical calculation using the eddy-resolving thermohydrodynamic model of the MHI, the fields of hydrodynamic and energy characteristics of the deep waters of the Marmara Sea averaged for the hydrological seasons of 2008 were obtained and analyzed. It is established that in winter period, at horizons from 20 to 75 m, the system consisting of mesoscale anticyclones and cyclone, as well as eddies near the northwestern and northeastern coastal regions and in the Dardanelles region, are determined by the work of the buoyancy force. In the winter-autumn period, the main contribution to the dynamic processes at the indicated depths is made by the work of the wind force. Thus, in spring and summer, the waters of the basin are involved in a mesoscale central anticyclonic vortex. In autumn, the central anticyclone, decreasing in radius, shifts to the west, and in the eastern part there is a mesoscale cyclonic vortex. In the indicated range of depths, the radii of the eddies vary from 5 to 35 km. Below 75 m the generation of dynamic structures is mainly determined by the work of the buoyancy force. In this case, the radii of the eddies vary from 7 to 16 km

Contrasting Pre-Mei-Yu and Mei-Yu Extreme Precipitation in the Yangtze River Valley: Influencing Systems and Precipitation Mechanisms

The mei-yu season over the Yangtze–Huai Rivers basin, typically occurring from mid-June to mid-July, is one of three heavy-rainfall periods over China and can contribute 50% of the annual precipitation. In this study, the first and second heaviest daily precipitation events at the Wuhan station have been selected to represent typical mei-yu and pre-mei-yu precipitation events where the differences in the atmospheric thermodynamic characteristics, precipitation nature, influencing systems, and mechanisms are investigated. During the mei-yu case, moist air mainly came from the South China Sea. Precipitation occurred south of the mei-yu front where abundant moisture and favorable thermodynamic conditions were present. The main influencing systems include a stable blocking pattern and strong and stable western Pacific subtropical high in the midtroposphere, and a small yet intense mesoscale cyclonic vortex in the low troposphere. Rainfall in Wuhan was continuous, caused by a well-organized convective line. A heavy rainband was located along the narrow band between the elongated upper-level jet (ULJ) and the low-level jet (LLJ) where the symmetric instability was found in the midtroposphere near Wuhan. Quite differently, for the pre-mei-yu precipitation case, moist air primarily came from the Beibu Gulf and the Bay of Bengal. Precipitation happened in the low-level convective instability region, where a short-wave trough in the midtroposphere and a mesoscale cyclonic vortex in the low-troposphere were found. Precipitation in Wuhan showed multiple peaks associated with independent meso-β-scale convective systems. A rainstorm occurred at the exit of the LLJ and the right entrance of the ULJ, where convective instability exited in the mid- to low troposphere.

Observations of Misovortices within a Long-Lake-Axis-Parallel Lake-Effect Snowband during the OWLeS Project

Recent lake-effect snow field projects in the eastern Great Lakes region have revealed the presence of misovortices with diameters between 40 and 4000 m along cyclonic horizontal shear zones within long-lake-axis-parallel bands. One particular band in which an abundance of misovortices developed occurred on 7 January 2014. The leading hypothesis for lake-effect misovortexgenesis is the release of horizontal shearing instability (HSI). An analysis of three-dimensional dual-Doppler wind syntheses reveals that two criteria for HSI are satisfied along the horizontal shear zone, strongly suggesting that HSI was the likely cause of the misovortices in this case. Furthermore, the general lack of anticyclonic–cyclonic vortex couplets throughout the event reveal that tilting of horizontal vorticity into the vertical is of less importance compared to the release of HSI and subsequent strengthening via vortex stretching. A WRF simulation depicts misovortices along the horizontal shear zone within the simulated band. The simulated vortices display remarkable similarities to the observed vortices in terms of intensity, depth, spacing, and size. The simulated vortices persist over the eastern end of the lake; however, once the vortices move inland, they quickly dissipate. HSI criteria are also calculated from the WRF simulation and are satisfied along the shear zone. Competing hypotheses of misovortexgenesis are presented, with results indicating that the release of HSI is the likely mechanism of vortex formation.