Vertical Advection Of Vorticity Research Articles

On the dynamics of the eradication of a warm core mesoscale eddy after the passage of Hurricane Irma (2017)

Mesoscale oceanic eddies are known to influence air-sea interactions during tropical cyclone (TC) passage by either hindering or sustaining air-sea fluxes into the TC core. However, little is known as to how TCs alter the dynamical structure of such eddies during and after TC passage. Through simulations of Hurricane Irma (2017) using the Navy’s Coupled Ocean Atmospheric Mesoscale Prediction Scheme for Tropical Cyclones, it is found that a simulated mesoscale warm core eddy (WCE) located to the right of the model track disappeared shortly after the TC had passed over it. To further explore this phenomena, time series of ocean kinetic energy, available potential energy (APE), a vorticity budget, and a potential vorticity (PV) budget are examined to understand how TC-induced upper ocean currents influenced the eddy disappearance. Time series of APE within the model-simulated eddy show APE reaching a minimum as the circulation of the eddy disappeared in the model field and positive vorticity, dominated by vertical vorticity advection, became a maximum approximately 6 h after TC passage. These results were confirmed by the PV budget. The succession of subsurface vorticity changes suggest that the WCE was eradicated by a near-inertial wave wake that occurred earlier than expected. As found in a prior study, the early-onset of a near-inertial wake occurs when the model simulated TC with a small radius of maximum winds interacts with the subsurface ocean current field. The findings are important with regards to TC forecasting because the accurate representation and placement of eddies in the model field is necessary to correctly predict the coupled air-sea response during TC passage and for subsequent TCs with similar tracks. Such feedbacks from TCs can also have near-term and long-term influence on the prediction of air-sea interaction in the local and regional marine environment.

Effects of Topography and Latent Heat on the Evolution of a Mesoscale Dual-Core Southwest Vortex Over Sichuan Basin, China

The southwest vortex (SWV), a low-pressure system bringing severe rainfall in southwest China, is one of the most important synoptic systems in China. Using both the National Centers for Environmental Prediction Final (NCEP-FNL) operational global analysis dataset and the Weather Research and Forecasting (WRF) model simulation, a sophisticated SWV with dual-core structure (DCSWV) over the Sichuan Basin in 2010 was studied. The DCSWV system consisted of two cores, one near Leshan City (named “C1”) and another near Langzhong City (named “C2”). The high-resolution WRF model reproduced the life cycle of the DCSWV well. The diagnostic analysis of the vorticity budget indicated that the stretching and tilting terms played important roles in the development stage of “C1”, while the stretching and vertical advection of vorticity were the major contributors to the formation and development stage of “C2”, which implied the importance of moisture convergence and ascending motion. Sensitivity experiments showed that the DCSWV was closely associated with the release in latent heat as well as the effect of topography. The great release in latent heat provided significantly positive feedback to the DCSWV system, which was decisive to the formation and development stages of “C2”. The topography of the Tibetan Plateau and the Yun-Gui Plateau affected the location and duration of the DCSWV.

Quadrant-Averaged Structure and Evolution Mechanisms of a Northeast Cold Vortex during Its Mature Stage

AbstractA Northeast China cold vortex (NCCV) that maintained from 0200 UTC 3 July to 0500 UTC 3 July 2013 and caused several heavy rainfall events was analyzed in detail to reveal its quadrant-averaged structure and main maintaining mechanisms during its mature stage. Results indicated the vortex's intensity, divergence, ascending motions, precipitable water (PW), and thermal structures were all characterized by significant unevenness, and their main pattern changed gradually during the mature stage. Mechanisms accounting for the maintenance of the NCCV were also characterized by remarkable unevenness. Within different quadrants, dominant factors for the vortex's evolution may have differed from each other significantly. The NCCV-averaged vorticity budget revealed that the vertical advection of vorticity, which is closely related to convective activities, was the most favorable factor for maintaining the NCCV, whereas the tilting effect, which is closely related to the vertical shear of the horizontal win...

Radar analysis of a tornado over hilly terrain on 23 July 1996

A Doppler radar case study of an F1–2 tornado in the Upper Rhine valley in Germany is presented. The Ziegelhausen tornado touched down on the hilly terrain near Heidelberg in the evening of 23 July 1996. A mini-supercell was the parent storm of the short-lived funnel. During its intensification the Cb-cell behaved like an ordinary right-moving supercell, but along with transition to its tornadic phase a hook echo developed at the storm's right rear flank, indicative of anticyclonic rotation. In addition a mesocyclonic in-cloud vortex signature was found higher up and and proved to be more persistent than the small anticyclonic circulation at the hook echo tip. So both, parent storm and tornado vortex were most likely cyclonic, with the damage swath to the left of the mesocyclone's ground track. The false anticyclonic hook echo appeared to be caused by small-scale orographic forcing. Terrain structure near the tornado site may have induced a low-level anticyclonic lee-vortex in the wake of an isolated mountain. Vertical vorticity advection and orogenic horizontal deformation of the airflow could then serve to consistently explain both the false hook and its sense of rotation. Climatologically, the Ziegelhausen tornado was representative for most German tornado outbreaks. Neither was the parent thunderstorm nowcast as potentially tornadic nor was any warning issued to the public.

The Interactions between a Midlatitude Blocking Anticyclone and Synoptic-Scale Cyclones That Occurred during the Summer Season

Abstract Using the Goddard Laboratory for Atmospheres Goddard Earth Observing System 5-yr analyses and the Zwack–Okossi equation as the diagnostic tool, the horizontal distribution of the dynamic and thermodynamic forcing processes contributing to the maintenance of a Northern Hemisphere midlatitude blocking anticyclone that occurred during the summer season were examined. During the development of this blocking anticyclone, vorticity advection, supported by temperature advection, forced 500-hPa height rises at the block center. Vorticity advection and vorticity tilting were also consistent contributors to height rises during the entire life cycle. Boundary layer friction, vertical advection of vorticity, and ageostrophic vorticity tendencies (during decay) consistently opposed block development. Additionally, an analysis of this blocking event also showed that upstream precursor surface cyclones were not only important in block development but in block maintenance as well. In partitioning the basic data ...

A Diagnostic Analysis of the Presidents' Day Storm Of February 1979

Abstract A diagnostic analysis of the Presidents' Day storm of February 1979 is used to extend and quantify earlier findings of Bosart. The initial growth of cyclonic vorticity in the lower troposphere is driven primarily by convergence along the Carolina coastal front. Rapid cyclone spinup accompanies the approach of a potent midtropospheric short wave trough from the Ohio Valley. An analysis of the vorticity structure discloses that cyclone spinup is enhanced by the~vertical advection of vorticity in the strongly cyclonic in situ vorticity environment along the coast as the upper level trough overspreads the region. Similarly, a downward extension of high semige-strophic potential vorticity air accompanies a tropopause fold to the west of thecyclone and prior to the rapid cyclogenesis stage, confirming a result of Uccellini and others. Semigeostrophic potential vorticity is poorly conserved, however, and there is evidence for a separate region of semigeostrophic potential vorticity growth below 800 mb n...

An Estimate of the Summertime Tropospheric Vorticity Budget over South America

Abstract Objectively analyzed wind fields from summertime (January and February) cloud wind data are used to estimate the average values of the large-scale upper tropospheric vorticity budget components over tropical and subtropical South America. Limited vertical resolution of cloud wind data limit their use in evaluating the components involving vertical motion and vertical derivatives. The predominant component in the vorticity budget, the horizontal divergence of vorticity, is not balanced by the other large-scale components in the budget. Thus, large imbalances in the budget, interpreted as representing the effects of subgrid-scale processes, are found over the Amazon River basin. The results indicate good spatial correlation between patterns of the imbalances and intense cumulus convective activity. Based upon these results and similar studies of convectively active tropical oceanic regions elsewhere, it is suggested that the vertical advection of vorticity by subgrid-scale intense cumulus convectio...

Vortex Generation in a Numerical Thunderstorm Model

Abstract Detailed analysis of mesocyclone formation was performed using a three-dimensional numerical thunderstorm model. The vorticity equation was used to determine rates of generation and advection of vorticity in the modeled mesocyclones. Experiments were run with varied base state wind profiles to examine the role of vertical wind shear in the formation of vortices within thunderstorms. Analysis of mechanisms involved in vortex growth showed that during early and mature storm regimes important contributions were made by three processes: tilting of horizontal vorticity into the vertical stretching of these vortices by wind convergence, and vertical advection of vorticity. The combination of these processes served to create strong vortex couplets through extensive vertical columns in the modeled storms. Numerical experiments also showed that mature storm mesovortex strength was a nonlinear function of ambient vertical wind shear magnitude. Maximum vortex strength reached or exceeded 10−2 s−1 vorticity....

EVALUATION OF POTENTIAL-VORTICITY CHANGES NEAR THE TROPOPAUSE AND THE RELATED VERTITCAL MOTIONS, VERTICAL ADVECTION OF VORTPCITY, AND TRANSFER OF RADIOACTIVE DEBRIS FROM STRATOSPHERE TO TROPOSPHERE

Individual potential-vorticity change, vertical motion, vertical advection of vorticity and flow from stratosphere to troposphere are evaluated at different levels and for different times in an extratropical disturbance. Vertical motions are obtained from trajectories on three isentropic surfaces for two different times. The isentropes pass through or near a front in the upper troposphere, the lower stratosphere, and the high troposphere on the cold side of the front. Vertical motion is also evaluated at 500 mb from an adiabatic method designed to give instantaneous values to the extent that the system moves without change of shape. Negative extremes of 8 to 10 cm sec−1 occur in the upper-air front, with positive extremes of the same magnitude a short distance to the northeast, coinciding with the eastern exit of the frontal zone. From theory, it is shown that potential vorticity is not conserved if there is either a gradient of diabatic heating or a component of curl, normal to the isentropic surface, of frictional force. The sum of these two effects is evaluated over the United States for two 12-hr periods on two isentropic surfaces which were common to parts of the lower stratosphere, upper troposphere and a front in middle and upper troposphere. Generally large, positive potential-vorticity changes occur in the lower stratosphere and in the upper troposphere on the cold side of the front. Large negative values occur in the frontal zone and around the entire periphery of the positive area, or around the periphery of the trough in the upper air. The potential-vorticity changes are related to simultaneous stability and vorticity changes of like sign. The potential-vorticity changes are positive in the region of the so-called ‘tropopause funnel’ ; changes everywhere appear attributable to vertical gradient of diabatic heating rather than curl of frictional force. The terms in the vorticity equation which contain vertical velocity (vertical advection of vorticity and tilting terms) are shown by means of the thermal-wind equation to depend only on the vertical motion and temperature fields in an isobaric surface. For the frequent case where negative motion is centered in the baroclinic or frontal zone and rising motion is centered at the exit of the zone, each of the vertical-motion terms has the same characteristic distribution. Positive values of these vertical-motion terms occur on the cold side of the zone and to the right of the downwind exit of the zone, and negative values occur on the warm side of the zone and to the left of the downwind exit of the zone. The vertical advedtion and the sum of vertical advection and tilting terms are evaluated at 500 mb Magnitudes obtained compare with those of the divergence term, although magnitude depends considerably on the distances over which finite differences are evaluated. Isentropic trajectories trace air initially in the lower stratosphere downward to within 5000 ft of the surface within 24 hr. Diabatic incorporation into the troposphere is also noted. The total adiabatic mass flow into the troposphere associated with the number of typical upper-air disturbances in existence at any time is estimated and found to be sufficient to give the observed short residence times of a few months for radioactive debris injected into the stratosphere by nuclear detonations.

SOME EFFECTS OF THE WESTERN CORDILLERA OF NORTH AMERICA OF CYCLONIC ACTIVITY

Abstract Some effects of the western mountain complex of North America on cyclones are investigated from the standpoint of how the vorticity tendency field might be influenced by orographically-induced vertical motion and divergence. A detailed case study is presented which includes computations of terms in the vorticity tendency equation during a lee cyclogenesis. The local increases in low-level vorticity which occurred during formation of the lee trough and cyclone were primarily due to horizontal convergence, while the horizontal and vertical advection of vorticity opposed the increases; the contribution of the tipping term was generally negligible. The study also provides evidence that orographic effects are insufficient to explain the genesis of major cyclonic storms.

THE EFFECTS OF VERTICAL VORTICITY ADVECTION AND TURNING OF THE VORTEX TUBES IN HEMISPHERIC FORECASTS WITH A TWO-LEVEL MODEL

Abstract A 2-parameter forecasting model which includes the effects of vertical vorticity advection and turning of the vortex tubes is briefly described. Contributions of the above-mentioned terms are discussed and an example is presented. The importance of consistent truncation over a large grid is pointed out.

COMPARISON OF BAROTROPIC AND BAROCLINIC NUMERICAL FORECASTS AND CONTRIBUTIONS OF VARIOUS EFFECTS

mb. barotropic and 500-mb. baroclinic numerical forecasts for two cases, a developing baroclinic cyclone and a quasi-barotropic cyclone, are presented and compared. The barotropic forecasts did not indicate accurately the changes in circulation or the magnitude of the height falls ahead of the circulation qaxima. 700-mb. fore casts from the same initial times as the SOO-mb. barotropic and baroclinic forecasts, for each of the four terms of the frictionless vorticity equation, are presented. These 700-mb. forecasts are compared with each other and in added combinations with the 7oCb. verifications and with 700-mb. barotropic forecasts. These comparisons are then used diagnostically in an analysis of the errors in the 500-mb. barotropic forecasts. Each of the four terms of the vorticity equation is discussed. An explanation for the success of the barotropic forecasting model is suggested. Contributions of the horizontal velocity divergence, vertical advection of vorticity, and twisting terms to errors in the barotropic forecasting model are discussed in some detail. It is concluded that the major problem in developing a successful baroclinic forecasting.mode1 to substitute for the existing barotropic forecasting model is that of determining in space and time an accurate approximation of the vertical profile of vertical motion.

On Certain Integral Constraints for the Time-Integration of Baroclinic Models

On the basis of the general property of the vorticity equation that the net-production of vorticity vanishes in the average over a closed region it is in section 3 shown that provided this property should be fulfilled one should at the same time include or exclude the vertical advection of vorticity and the twisting effect in two-parameter models used for numerical weather prediction. The advection with the divergent part of the horizontal wind and the part of the divergence term which depends upon the relative vorticity has a similar opposing effect in the mean production of vorticity for the non-divergent level, but a vanishing production of thermal vorticity can only be obtained if one either include the advection with the divergent wind and the complete divergence term or exclude the advection with divergent wind, the part of the divergence term depending upon the relative vorticity and consider the Coriolis parameter in the remaining part of the divergence term as a constant. In section 4 it is shovn that the mean value over a closed region of the relative topography remains constant in a two-parameter model provided the vertical stability parameter is constant. It is further shown that the thermodynamic equation in the adiabatic case is far less sensitive to inconsistencies than the vorticity equation. Section 5 contains a comparison between the growth of “rotational energy” in general and simplified two-parameter models. It is shown that already the most simple model contains approximately the correct growth rate. A similar comparison with respect to the rate of “occlusion” is made in section 6 with a similar result. Section 7 contains a comparison between the theoretical results and the experience from practical computations. The mechanism for production of kinetic energy of the nondivergent part of the wind is discussed in section 8. DOI: 10.1111/j.2153-3490.1959.tb00004.x