scholarly journals Synoptic and dynamic characteristics of selected deep depressions over Cyprus

2006 ◽  
Vol 7 ◽  
pp. 175-180 ◽  
Author(s):  
K. A. Nicolaides ◽  
S. C. Michalelides ◽  
T. Karacostas
Keyword(s):  
Dynamic Characteristics ◽  
Vertical Motion ◽  
Static Stability ◽  
Relative Vorticity ◽  
Stability Parameter ◽  
Cold Period ◽  
Spatial And Temporal Distributions ◽  
Selection Of

Abstract. In this study, the spatial and temporal distributions of dynamic and synoptic characteristics of a selection of 32 deep baroclinic depressions have been investigated. The study covers the cold period months of November till March, in the period from 1 November 1986 to 31 March 2003. For the needs of the study, several synoptic characteristics of these depressions have been extracted. Also, several dynamic characteristics during the evolution of the depressions were studied: relative vorticity, divergence, vertical motion and a static stability parameter. The results are presented in the form of isobaric distributions over, three tropospheric isobaric levels, namely the lower 850 hPa, the middle 500 hPa and the upper 300 hPa.

scholarly journals The Effect of Moist Convection on the Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques

2013 ◽  
Vol 70 (12) ◽  
pp. 4089-4111 ◽  
Author(s):  
William R. Boos ◽  
Tiffany A. Shaw
Keyword(s):  
Vertical Motion ◽  
Static Stability ◽  
Moist Convection ◽  
Motion Response ◽  
Clear Sky ◽  
Double Itcz ◽  
Highly Sensitive ◽  
Equatorial Wave ◽  
Meridional Overturning ◽  
Basic States

Abstract Tropospheric winds can be altered by vertical transfers of momentum due to orographic gravity waves and convection. Previous work showed that, in dry models, such zonally asymmetric torques produce a pattern of tropical ascent that is well described by linear dynamics, together with meridional shifts of the midlatitude jet. Here a series of idealized models is used to understand the effects of moisture on the tropospheric response to tropical and subtropical zonally asymmetric, upper-tropospheric torques. The vertical motion response to a torque is shown to be amplified by the reduction in effective static stability that occurs in moist convecting atmospheres. This amplification occurs only in precipitating regions, and the magnitude of subsidence in nonprecipitating regions saturates when clear-sky radiative cooling balances induced adiabatic warming. For basic states in which precipitation is concentrated in an intertropical convergence zone (ITCZ), most of the vertical motion response is thus confined within the basic-state ITCZ, even when the torque is remote from the ITCZ. Tropical and subtropical torques perturb the extratropical baroclinic eddy field and the convectively coupled equatorial wave field. Resulting changes in momentum flux convergence by transient eddies induce secondary meridional overturning circulations that modify the zonal-mean response to a torque. The net effect allows tropical torques to merge a double ITCZ into a single equatorial ITCZ. The response of tropical transient eddies is highly sensitive to the representation of convection, so the zonal-mean response to a torque is similarly sensitive, even when the torque is located in the subtropics.

Comparing Polar Lows in Atmospheric Reanalyses: Arctic System Reanalysis versus ERA-Interim

2017 ◽  
Vol 145 (6) ◽  
pp. 2375-2383 ◽  
Author(s):  
Julia Smirnova ◽  
Pavel Golubkin
Keyword(s):  
Strong Dependence ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Static Stability ◽  
Relative Vorticity ◽  
Reference List ◽  
Near Surface ◽  
Polar Lows ◽  
Polar Low ◽  
Definition Of

Abstract Representation of polar lows in the new high-resolution Arctic System Reanalysis (ASR) was for the first time assessed and compared to that in the ERA-Interim. Substantial improvements were found in the 850-hPa relative vorticity and near-surface wind speed information. The latter was found to be in close agreement with satellite-derived estimates. Representation of polar lows from a widely used selective list in ERA-Interim and ASR was estimated as 48% and 89%, respectively. The proportion of polar lows represented in ASR is substantially higher than reported for other reanalyses in previous studies. Verifications were found to be sensitive to the polar low reference list used, and to the definition of a polar low. As found, when a more complete polar low list from a recent satellite-derived climatology was used, the proportion of represented events decreased to 26% and 66% for ERA-Interim and ASR, respectively. Variations in polar low representation in reanalyses were also observed in different regions, with the highest proportion resolved in the Norwegian Sea. Strong dependence between polar low sizes and their representation in ERA-Interim was found. In the case of ASR, polar low representation remains constant in the size range of 200–500 km and slightly decreases only for the smallest systems with diameters less than 200 km. Usage of the strict threshold of 43 K for the atmospheric static stability criterion was found to exclude a considerable number of otherwise well-represented polar lows.

scholarly journals Case Study of Potential Vorticity Tower in Three Explosive Cyclones over Eastern Asia

2017 ◽  
Vol 74 (5) ◽  
pp. 1445-1454 ◽  
Author(s):  
Huaji Pang ◽  
Gang Fu
Keyword(s):  
Potential Vorticity ◽  
Morphological Characteristics ◽  
Lower Troposphere ◽  
Static Stability ◽  
Relative Vorticity ◽  
Eastern Asia ◽  
The North ◽  
Surface Cyclone ◽  
Explosive Cyclones

AbstractThree cases of explosively developing extratropical cyclones over eastern Asia are analyzed using ERA-Interim data. The morphological characteristics of the upper-tropospheric potential vorticity (PV) were examined. The common feature of all of these three cases is a hook-shaped high-PV streamer wrapping counterclockwise around the center of surface cyclones on the southern and eastern sides and an arch-shaped low-PV tongue that wrapped the high-PV hook head from the north. The hook-shaped high-PV tongue overlaps with the maximum centers of both the relative vorticity and static stability parameter, indicating the stratospheric nature of the PV source inside the hook-shaped high-PV tongue.The analysis indicates that there existed a deep tower of high PV above the surface cyclone at the time when these cyclones underwent explosive cyclogenesis. The high PV in the upper troposphere originates from the polar stratospheric PV reservoir associated with the tropopause-folding process. The high PV in the lower troposphere, however, is associated with the latent heat release, as nearly 70%–90% of the high-PV values in the lower troposphere reside in the region where the rainfall is the heaviest.

An evaluation of East Asian Extratropical cyclones in CMIP5 models and their response to greenhouse warming

2020 ◽  
Author(s):  
Jaeyeon Lee ◽  
Jaeyoung Hwang ◽  
Seok-Woo Son ◽  
John Gyakum
Keyword(s):  
East Asia ◽  
East Asian ◽  
Vertical Wind Shear ◽  
Coupled Model ◽  
Static Stability ◽  
Relative Vorticity ◽  
Cmip5 Models ◽  
Leeward Side ◽  
Extratropical Cyclones ◽  
The Tibetan Plateau

<p>The extratropical cyclones (ETCs) over East Asia and their possible future changes are evaluated using the Coupled Model Intercomparison Project phase 5 (CMIP5) models. The East Asian ETCs are identified using an automated tracking algorithm applied to the 850-hPa relative vorticity field for both reference data (ERA-Interim reanalysis data) and model data. The CMIP5 models well capture the spatial distribution of East Asian ETC properties, although significant biases are present around the high-topography regions. Based on the individual model biases, Best 5 models are selected and used for examining the future changes of East Asian ETCs. In future climate, Best 5 shows declined cyclogenesis in the leeward side of the Tibetan Plateau, which is partly responsible for the decreased ETC frequency over the western North Pacific. The intensity of individual ETCs is also projected to decrease in a warm climate. These changes could be attributed to the combined effect of increased static stability and decreased vertical wind shear in East Asia, which means reduced local baroclinicity. It is also found that CMIP6 models have smaller bias than Best 5 CMIP5 models, indicating that the result documented in this study may change in quantity when newly-available CMIP6 models are utilized.</p>

Controlling the Dynamic Characteristics of a Hydrostatic Bearing by Using a Pocket-Connected Accumulator

1983 ◽  
Vol 197 (4) ◽  
pp. 255-258 ◽  
Author(s):  
M J Goodwin ◽  
C J Hooke ◽  
J E T Penny
Keyword(s):  
Experimental Investigation ◽  
Dynamic Characteristics ◽  
System Performance ◽  
Journal Bearings ◽  
Careful Selection ◽  
Hydrostatic Bearing ◽  
Optimum System ◽  
Flexible Rotors ◽  
Rotor Support ◽  
Selection Of

This paper describes a theoretical and experimental investigation of the dynamic characteristics of a capillary-compensated oil-lubricated hydrostatic bearing which has an accumulator connected to the bearing pocket via a second capillary restrictor. Results show that by careful selection of accumulator and restrictor the bearing can be tuned to give an optimum system performance. Such a facility can be of considerable use if the hydrostatic bearing is being used to support other machinery, for example in the support of journal bearings used with flexible rotors. By tuning the hydrostatic bearing dynamic characteristics, optimum rotor support impedance might be achieved thereby giving the engineer some control over system resonances and stability.

A new database for Intense Mediterranean Cyclones 

2021 ◽  
Author(s):  
M. Carmen Alvarez-Castro ◽  
David Gallego ◽  
Pedro Ribera ◽  
Cristina Peña-Ortiz ◽  
Davide Faranda
Keyword(s):  
Relative Vorticity ◽  
Sea Level Pressure ◽  
Robust Detection ◽  
Detection Algorithms ◽  
Mediterranean Cyclones ◽  
Detection And Tracking ◽  
Detection Approach ◽  
Local Extrema ◽  
Atmospheric Mass ◽  
Selection Of

<p>To better assess the future risks associated with Intense Mediterranean Cyclones (IMC) a better understanding of their features, variability, frequency and intensity is required, including a robust detection method. The application of different detection algorithms provides results that are remarkably similar in some aspects but may be very different in others even using the same data. Thus, the selection of a particular method can significantly affect the results. For these reasons it is necessary to use different approaches and datasets to study the sensitivity and robustness of the detection approach. Those approaches often use minima in sea-level pressure (SLP) or extrema in relative vorticity or both to first identify the eye of the cyclone. SLP reflects the atmospheric mass distribution, and is representative of synoptic-scale atmospheric processes. On the other hand, the relative vorticity displays higher variability and is representative of the atmospheric circulation, being able to detect several local extrema (more than one centre), it can reduce uncertainties in the cyclone detection and tracking.</p><p>Therefore, within the framework of the EFIMERA project and to detect and track IMC we use a combination of different methods based on previous studies found in the literature. This new list of detected IMC events, together with the observed and well documented ones, are used here to create a new IMC database to be used for the study of their impacts and risk associated.</p>

Diagnosing the Influence of a Receding Snow Boundary on Simulated Midlatitude Cyclones Using Piecewise Potential Vorticity Inversion

2020 ◽  
Vol 148 (11) ◽  
pp. 4479-4495
Author(s):  
Melissa L. Breeden ◽  
Ryan Clare ◽  
Jonathan E. Martin ◽  
Ankur R. Desai
Keyword(s):  
Life Cycle ◽  
Snow Cover ◽  
Potential Vorticity ◽  
Detailed Examination ◽  
Static Stability ◽  
Relative Vorticity ◽  
Surface Boundary ◽  
Snow Removal ◽  
The Impact ◽  
Midlatitude Cyclones

AbstractPrevious research has found a relationship between the equatorward extent of snow cover and low-level baroclinicity, suggesting a link between the development and trajectory of midlatitude cyclones and the extent of preexisting snow cover. Midlatitude cyclones are more frequent 50–350 km south of the snow boundary, coincident with weak maxima in the environmental Eady growth rate. The snow line is projected to recede poleward with increasing greenhouse gas emissions, possibly affecting the development and track of midlatitude cyclones during Northern Hemisphere winter. Detailed examination of the physical implications of a modified snow boundary on the life cycle of individual storms has, to date, not been undertaken. This study investigates the impact of a receding snow boundary on two cyclogenesis events using Weather Research and Forecasting Model simulations initialized with observed and projected future changes to snow extent as a surface boundary condition. Potential vorticity diagnosis of the modified cyclone simulations isolates how changes in surface temperature, static stability, and relative vorticity arising from the altered boundary affect the developing cyclone. We find that the surface warm anomaly associated with snow removal lowered heights near the center of the two cyclones investigated, strengthening their cyclonic circulation. However, the direct effect of snow removal is mitigated by the stability response and an indirect relative vorticity response to snow removal. Because of these opposing effects, it is suggested that the immediate effect of receding snow cover on midlatitude cyclones is likely minimal and depends on the stage of the cyclone life cycle.

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