scholarly journals Some dynamical aspects of meso-scale rainfall events as revealed by physical initialization

MAUSAM ◽  
2021 ◽  
Vol 49 (1) ◽  
pp. 11-20
Author(s):  
S.K. ROY BHOWMIK
Keyword(s):  
Vertical Motion ◽  
Dynamic Structure ◽  
Motion Field ◽  
Vertical Profiles ◽  
Upward Motion ◽  
Initial State ◽  
Global Spectral Model ◽  
Rainfall Events ◽  
Physical Initialization ◽  
Meso Scale

In recent years, physical initialization has emerged as a powerful tool to improve initial state of dynamical model during assimilation phase. This improved initial state at high resolution global spectral model is able to provide a tropical meso-scale coverage. In this paper, model out-put is used to study some dynamical aspects of meso-scale rainfall events. Major findings of this study are : (i) Meso-scale rainfall event carries a distinct dynamic structure in vertical profiles of divergence and vertical upward motion, (ii) Meso-scale event exhibits a large diurnal variation in these vertical profiles and (iii) Vertical motion field of meso-scale organisation appears to play a significant role in tropical storm formation.

The vertical structure and variability of the meso-scale motion field in the trades

2021 ◽  
Author(s):  
Geet George ◽  
Bjorn Stevens ◽  
Sandrine Bony ◽  
Raphaela Vogel
Keyword(s):  
Time Scales ◽  
Vertical Structure ◽  
Inversion Layer ◽  
Vertical Motion ◽  
Local Maximum ◽  
Climate Science ◽  
Cloud Layer ◽  
Trade Wind ◽  
Motion Field ◽  
Meso Scale

<p>We use measurements from the <em>Elucidating the role of clouds-circulation coupling in climate</em> (EUREC<sup>4</sup>A) campaign to characterise the variability in the meso-scale divergence and vertical motion (pressure velocity, 𝜔) ranging across time-scales from a few hours to a month (the entire campaign period from 19<sup>th</sup> January - 15<sup>th</sup> February, 2020). The area-averaged divergence is estimated using measurements of horizontal winds from dropsondes launched in a circular flight path (~200 km diameter), something that was carried out extensively during EUREC<sup>4</sup>A – 85 circles over 19 flight-days in the North Atlantic trade-wind region.</p><p>From these estimates, we characterise the vertical structure and variability of divergence and 𝜔 in the trades. We find that 𝜔 above the sub-cloud layer is quite consistent vertically when averaged over long periods. The value stays around 1-1.5 hPa/h, which agrees well with the roughly 1.5 K/day cooling rate of the trades. However, significant intra- and inter-day variability can be found between 𝜔 profiles, in terms of the magnitudes, ranging from -7 hPa/h to 6 hPa/h as well as in terms of the vertical structure of these profiles. Daily mean sub-cloud layer divergence varies significantly from that of the cloud-layer in magnitude, and for most flight days, we also observe a sign change between the two. Changes in the vertical structure over different days suggest that a local maximum of either divergence or convergence is usually seen near the inversion layer. Our findings can provide insight into how the atmospheric state varies over short time-scales, as well as their impact on cloudiness, thus providing clues about a predominantly important question in climate science — the clouds-circulation coupling.</p>

The Role of Shearwise and Transverse Quasigeostrophic Vertical Motions in the Midlatitude Cyclone Life Cycle

2006 ◽  
Vol 134 (4) ◽  
pp. 1174-1193 ◽  
Author(s):  
Jonathan E. Martin
Keyword(s):  
Life Cycle ◽  
Vertical Motion ◽  
Development Stage ◽  
Life Cycles ◽  
Vertical Shear ◽  
Mature Stage ◽  
Motion Field ◽  
Initial Development ◽  
Frontal Zones ◽  
Oriented Parallel

Abstract The total quasigeostrophic (QG) vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to, and along, the geostrophic vertical shear, respectively. The physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones. The analysis suggests that the origin and subsequent intensification of the lower-tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise QG vertical motion, which displays a single, dominant, middle-tropospheric couplet at all stages of the cyclone life cycle. The transverse QG omega, associated with the cyclones’ frontal zones, appears only after those frontal zones have been established. The absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse ω plays little role in the initial development stage of the storms examined here. Near the end of the mature stage of the life cycle, however, in what appears to be a characteristic distribution, a transverse ascent maximum along the western edge of the warm frontal zone becomes superimposed with the shearwise ascent maximum that fuels continued cyclogenesis. It is suggested that use of the shearwise/transverse diagnostic approach may provide new and/or supporting insight regarding a number of synoptic processes including the development of upper-level jet/front systems and the nature of the physical distinction between type A and type B cyclogenesis events.

Vertical Motion Inputs for Seismic Analysis of Large Span Bridge

2013 ◽  
Vol 275-277 ◽  
pp. 1403-1406
Author(s):  
Zheng Ru Tao ◽  
Xia Xin Tao
Keyword(s):  
Seismic Analysis ◽  
Three Dimensional ◽  
Low Frequency ◽  
Vertical Motion ◽  
Vertical Acceleration ◽  
Motion Field ◽  
Large Span ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Main Girder

In seismic analysis of large span bridge, inconsistent ground motions in three directions, lengthwise, lateral and vertical are required to input at the base of each of the two main girder piers. In order to adopt synthesized motion field for the inputs, a simple way to prepare the vertical motion is introduced for improvisation at this moment in this paper, since the synthesis in general consists of two parts, the low frequency ground motion calculated by a numerical method, like FEM, and the high frequency motion synthesized by random approach, and the result of the former is in three dimensional, while that of the latter has just horizontal component. The vertical acceleration time histories proposed in the paper show the way is available.

scholarly journals High-Resolution Simulation of Hurricane Bonnie (1998). Part I: The Organization of Eyewall Vertical Motion

2006 ◽  
Vol 63 (1) ◽  
pp. 19-42 ◽  
Author(s):  
Scott A. Braun ◽  
Michael T. Montgomery ◽  
Zhaoxia Pu
Keyword(s):  
High Resolution ◽  
Mesoscale Model ◽  
Dynamic Balance ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
State University ◽  
Upward Motion ◽  
Pennsylvania State University ◽  
Fifth Generation ◽  
Hurricane Bonnie

Abstract The fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is used to simulate Hurricane Bonnie at high resolution (2-km spacing) in order to examine how vertical wind shear impacts the distribution of vertical motion in the eyewall on both the storm and cloud scale. As in many previous studies, it is found here that the shear produces a wavenumber-1 asymmetry in the time-averaged vertical motion and rainfall. Several mechanisms for this asymmetry are evaluated. The vertical motion asymmetry is qualitatively consistent with an assumed balance between horizontal vorticity advection by the relative flow and stretching of vorticity, with relative asymmetric inflow (convergence) at low levels and outflow (divergence) at upper levels on the downshear side of the eyewall. The simulation results also show that the upward motion portion of the eyewall asymmetry is located in the direction of vortex tilt, consistent with the vertical motion that required to maintain dynamic balance. Variations in the direction and magnitude of the tilt are consistent with the presence of a vortex Rossby wave quasi mode, which is characterized by a damped precession of the upper vortex relative to the lower vortex. While the time-averaged vertical motion is characterized by ascent in a shear-induced wavenumber-1 asymmetry, the instantaneous vertical motion is typically associated with deep updraft towers that generally form on the downtilt-right side of the eyewall and dissipate on the downtilt-left side. The updrafts towers are typically associated with eyewall mesovortices rotating cyclonically around the eyewall and result from an interaction between the shear-induced relative asymmetric flow and the cyclonic circulations of the mesovortices. The eyewall mesovortices may persist for more than one orbit around the eyewall and, in these cases, can initiate multiple episodes of upward motion.

Influence of the vertical motion field on ozone concentration in the stratosphere

1973 ◽  
Vol 106-108 (1) ◽  
pp. 1531-1543 ◽  
Author(s):  
Reginald E. Newell ◽  
George J. Boer ◽  
Thomas G. Dopplick
Keyword(s):  
Ozone Concentration ◽  
Vertical Motion ◽  
Motion Field

scholarly journals Mesoscale Ascent in Nocturnal Low-Level Jets

2018 ◽  
Vol 75 (5) ◽  
pp. 1403-1427 ◽  
Author(s):  
Alan Shapiro ◽  
Evgeni Fedorovich ◽  
Joshua G. Gebauer
Keyword(s):  
Vertical Velocity ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Local Maximum ◽  
Buoyancy Frequency ◽  
Inertial Oscillation ◽  
Initial State ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Low Level

A theory for gentle but persistent mesoscale ascent in the lower troposphere is developed in which the vertical motion arises as an inertia–gravity wave response to the sudden decrease of turbulent mixing in a horizontally heterogeneous convective boundary layer (CBL). The zone of ascent is centered on the local maximum of a laterally varying buoyancy field (warm tongue in the CBL). The shutdown also triggers a Blackadar-type inertial oscillation and associated low-level jet (LLJ). These nocturnal motions are studied analytically using the linearized two-dimensional Boussinesq equations of motion, thermal energy, and mass conservation for an inviscid stably stratified fluid, with the initial state described by a zero-order jump model of a CBL. The vertical velocity revealed by the analytical solution increases with the amplitude of the buoyancy variation, CBL depth, and wavenumber of the buoyancy variation (larger vertical velocity for smaller-scale variations). Stable stratification in the free atmosphere has a lid effect, with a larger buoyancy frequency associated with a smaller vertical velocity. For the parameter values typical of the southern Great Plains warm season, the peak vertical velocity is ~3–10 cm s−1, with parcels rising ~0.3–1 km over the ~6–8-h duration of the ascent phase. Data from the 2015 Plains Elevated Convection at Night (PECAN) field project were used as a qualitative check on the hypothesis that the same mechanism that triggers nocturnal LLJs from CBLs can induce gentle but persistent ascent in the presence of a warm tongue.

scholarly journals Advances in Predicting Continental Low Stratus with a Regional NWP Model

2010 ◽  
Vol 25 (1) ◽  
pp. 290-302 ◽  
Author(s):  
Alexander Kann ◽  
Harald Seidl ◽  
Christoph Wittmann ◽  
Thomas Haiden
Keyword(s):  
Reference Model ◽  
Weather Prediction ◽  
Limited Area ◽  
Vertical Profiles ◽  
Initial State ◽  
Radiative Reaction ◽  
Temperature And Humidity ◽  
Nwp Model ◽  
Temperature Inversions ◽  
Autumn And Winter

Abstract In the eastern Alpine region, subinversion cloudiness associated with elevated temperature inversions is a frequent phenomenon in autumn and winter, which often persists for several days. Although the prediction of fog and low stratus by numerical weather prediction (NWP) models has improved in recent years, these models still show deficiencies in the spatial and temporal evolution of such wintertime weather phenomena. In spite of sophisticated current assimilation schemes or simply due to unknown conditions, even the analysis shows large discrepancies compared to the true atmospheric state. Inversions are often “smeared out” and the moist layer below the inversion is too far from saturation. Model integration from such an initial state leads to strong biases in the total cloudiness and, due to erroneous radiative response, in 2-m temperature forecasts. In the present paper, an empirical enhancement scheme for subinversion cloudiness is introduced within the framework of Aire Limitée Adaptation Dynamique Développement International (ALADIN), the operational limited area model (LAM) at the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). The scheme attempts to compensate for model deficiencies in the vertical temperature and humidity profiles in order to enhance or keep preexisting signals of inversions and associated low cloudiness. Thus, a positive feedback due to radiative reaction is activated, which finally leads to more realistic vertical profiles, low (and total) cloudiness, and improved 2-m temperature predictions. Case studies demonstrate the impacts of the scheme on predictions of the spatial distribution of low cloudiness and on the vertical profiles of temperature and humidity. Verification over stratus episodes within a 2-month period comparing a reference model run without the scheme with a modified model version with the subinversion cloudiness scheme confirms the ability of the scheme to improve stratus-related wintertime weather prediction.

A Numerical Study of Hurricane Erin (2001). Part II: Shear and the Organization of Eyewall Vertical Motion

2007 ◽  
Vol 135 (4) ◽  
pp. 1179-1194 ◽  
Author(s):  
Scott A. Braun ◽  
Liguang Wu
Keyword(s):  
Wind Shear ◽  
Numerical Study ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Vertical Wind ◽  
Small Scale ◽  
Strong Mixing ◽  
Upward Motion ◽  
Asymmetric Flow ◽  
Subsequent Decrease

Abstract A high-resolution numerical simulation of Hurricane Erin (2001) is used to examine the organization of vertical motion in the eyewall and how that organization responds to a large and rapid increase in the environmental vertical wind shear and subsequent decrease in shear. During the early intensification period, prior to the onset of significant shear, the upward motion in the eyewall was concentrated in small-scale convective updrafts that formed in association with regions of concentrated vorticity (herein termed mesovortices) with no preferred formation region around the eyewall. Asymmetric flow within the eye was weak. As the shear increased, an azimuthal wavenumber-1 asymmetry in storm structure developed with updrafts tending to occur on the downshear to downshear-left side of the eyewall. Continued intensification of the shear led to increasing wavenumber-1 asymmetry, large vortex tilt, and a change in eyewall structure and vertical motion organization. During this time, the eyewall structure was dominated by a vortex couplet with a cyclonic (anticyclonic) vortex on the downtilt-left (downtilt-right) side of the eyewall and strong asymmetric flow across the eye that led to strong mixing of eyewall vorticity into the eye. Upward motion was concentrated over an azimuthally broader region on the downtilt side of the eyewall, upstream of the cyclonic vortex, where low-level environmental inflow converged with the asymmetric outflow from the eye. As the shear diminished, the vortex tilt and wavenumber-1 asymmetry decreased, while the organization of updrafts trended back toward that seen during the weak shear period. Based upon the results for the Erin case, as well as that for a similar simulation of Hurricane Bonnie (1998), a conceptual model is developed for the organization of vertical motion in the eyewall as a function of the strength of the vertical wind shear. In weak to moderate shear, higher wavenumber asymmetries associated with eyewall mesovortices dominate the wavenumber-1 asymmetry associated with the shear so that convective-scale updrafts form when the mesovortices move into the downtilt side of the eyewall and dissipate on the uptilt side. Under strong shear conditions, the wavenumber-1 asymmetry, characterized by a prominent vortex couplet in the eyewall, dominates the vertical motion organization so that mesoscale ascent (with embedded convection) occurs over an azimuthally broader region on the downtilt side of the eyewall. Further research is needed to determine if these results apply more generally.

scholarly journals Prediction and Diagnosis of Tropical Cyclone Formation in an NWP System. Part II: A Diagnosis of Tropical Cyclone Chris Formation

2006 ◽  
Vol 63 (12) ◽  
pp. 3091-3113 ◽  
Author(s):  
K. J. Tory ◽  
M. T. Montgomery ◽  
N. E. Davidson ◽  
J. D. Kepert
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Vertical Motion ◽  
Limited Area ◽  
Initial State ◽  
Absolute Vorticity ◽  
Vertical Advection ◽  
The North ◽  
Convective Bursts ◽  
Vortex Cascade

This is the second of a three-part investigation into tropical cyclone (TC) genesis in the Australian Bureau of Meteorology’s Tropical Cyclone Limited Area Prediction System (TC-LAPS). The primary TC-LAPS vortex enhancement mechanism (convergence/stretching and vertical advection of absolute vorticity in convective updraft regions) was presented in Part I. In this paper (Part II) results from a numerical simulation of TC Chris (western Australia, February 2002) are used to illustrate the primary and two secondary vortex enhancement mechanisms that led to TC genesis. In Part III a number of simulations are presented exploring the sensitivity and variability of genesis forecasts in TC-LAPS. During the first 18 h of the simulation, a mature vortex of TC intensity developed in a monsoon low from a relatively benign initial state. Deep upright vortex cores developed from convergence/stretching and vertical advection of absolute vorticity within the updrafts of intense bursts of cumulus convection. Individual convective bursts lasted for 6–12 h, with a new burst developing as the previous one weakened. The modeled bursts appear as single updrafts, and represent the mean vertical motion in convective regions because the 0.15° grid spacing imposes a minimum updraft scale of about 60 km. This relatively large scale may be unrealistic in the earlier genesis period when multiple smaller-scale, shorter-lived convective regions are often observed, but observational evidence suggests that such scales can be expected later in the process. The large scale may limit the convection to only one or two active bursts at a time, and may have contributed to a more rapid model intensification than that observed. The monsoon low was tilted to the northwest, with convection initiating about 100–200 km west of the low-level center. The convective bursts and associated upright potential vorticity (PV) anomalies were advected cyclonically around the low, weakening as they passed to the north of the circulation center, leaving remnant cyclonic PV anomalies. Strong convergence into the updrafts led to rapid ingestion of nearby cyclonic PV anomalies, including remnant PV cores from decaying convective bursts. Thus convective intensity, rather than the initial vortex size and intensity, determined dominance in vortex interactions. This scavenging of PV by the active convective region, termed diabatic upscale vortex cascade, ensured that PV cores grew successively and contributed to the construction of an upright central monolithic PV core. The system-scale intensification (SSI) process active on the broader scale (300–500-km radius) also contributed. Latent heating slightly dominated adiabatic cooling within the bursts, which enhanced the system-scale secondary circulation. Convergence of low- to midlevel tropospheric absolute vorticity by this enhanced circulation intensified the system-scale vortex. The diabatic upscale vortex cascade and SSI are secondary processes dependent on the locally enhanced vorticity and heat respectively, generated by the primary mechanism.

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