scholarly journals A Phase-Plot Method for Diagnosing Vorticity Concentration Mechanisms in Mesoscale Convective Vortices

2007 ◽  
Vol 135 (3) ◽  
pp. 801-820 ◽  
Author(s):  
James R. Kirk
Keyword(s):  
Lower Troposphere ◽  
Vertical Motion ◽  
Alternative Form ◽  
Middle Region ◽  
Phase Plot ◽  
Mesoscale Convective ◽  
Evolutionary Growth ◽  
Evolutionary Paths ◽  
Mesoscale Convective Vortex ◽  
Convective Vortices

Abstract Mesoscale convective vortex (MCV) analysis results show that these vortices form by way of different evolutionary paths. Rewriting the traditional form of the relative vertical vorticity equation in terms of momentum advection curl produces an alternative form of the equation containing two terms. When the terms are normalized and plotted on orthogonal axes, a phase-plot path depicting MCV evolutionary growth is created. Thermodynamics is included in the phase plot by correlating the path to the heating characteristics of the troposphere. The application of the phase-plot scheme to several cases shows that for MCV formation events, there are two interconnected regions that combine to produce the vortex. The upper-middle- and upper-troposphere vorticity growth is governed primarily by vertical motion, with heating driving the vorticity growth in the upper-middle region. The lower-middle and lower-troposphere vorticity growth is governed primarily by horizontal motion, with the vertical heating gradient driving the vorticity growth in the lower-middle region. Which regime leads the vorticity growth is found to be case dependent. In the middle troposphere, evolutionary paths are governed by the relative strengths of heating and heating gradient. Additional phase-plot and mesoscale analyses clarify the characteristics of two MCV formation modes. In some cases, heating drives the complete formation of the MCV, whereas in cases with lesser heating, tipping is vital to the MCV formation process. In total, these results help synthesize many of the various discoveries regarding the origin and formation of the MCV.

scholarly journals The Vertical Structure of Mesoscale Convective Vortices

2009 ◽  
Vol 66 (3) ◽  
pp. 686-704 ◽  
Author(s):  
Christopher A. Davis ◽  
Thomas J. Galarneau
Keyword(s):  
Vertical Structure ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Mesoscale Convective System ◽  
Secondary Phase ◽  
Radical Change ◽  
Convective System ◽  
Mesoscale Convective ◽  
Outflow Boundary ◽  
Convective Vortices

Abstract Simulations of two cases of developing mesoscale convective vortices (MCVs) are examined to determine the dynamics governing the origin and vertical structure of these features. Although one case evolves in strong vertical wind shear and the other evolves in modest shear, the evolutions are remarkably similar. In addition to the well-known mesoscale convergence that spins up vorticity in the midtroposphere, the generation of vorticity in the lower troposphere occurs along the convergent outflow boundary of the parent mesoscale convective system (MCS). Lateral transport of this vorticity from the convective region back beneath the midtropospheric vorticity center is important for obtaining a deep column of cyclonic vorticity. However, this behavior would be only transient without a secondary phase of vorticity growth in the lower troposphere that results from a radical change in the divergence profile favoring lower-tropospheric convergence. Following the decay of the nocturnal MCS, subsequent convection occurs in a condition of greater relative humidity through the lower troposphere and small conditional instability. Vorticity and potential vorticity are efficiently produced near the top of the boundary layer and a cyclonic circulation appears at the surface.

scholarly journals Mesoscale Convective Vortex Formation in a Weakly Sheared Moist Neutral Environment

2007 ◽  
Vol 64 (5) ◽  
pp. 1443-1466 ◽  
Author(s):  
Robert J. Conzemius ◽  
Richard W. Moore ◽  
Michael T. Montgomery ◽  
Christopher A. Davis
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Tangential Velocity ◽  
Lower Troposphere ◽  
Primary Objective ◽  
Vertical Shear ◽  
Convective System ◽  
Field Campaign ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex

Abstract Idealized simulations of a diabatic Rossby vortex (DRV) in an initially moist neutral baroclinic environment are performed using the fifth-generation National Center for Atmospheric Research–Pennsylvania State University (NCAR–PSU) Mesoscale Model (MM5). The primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm-season mesoscale convective vortices (MCVs) are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear. As a part of this objective, the simulated DRV is placed within the context of the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) field campaign by comparing its tangential velocity, radius of maximum winds, CAPE, and shear with the MCVs observed in BAMEX. The simulations reveal two distinct scales of development. At the larger scale, the most rapidly growing moist baroclinic mode is excited, and exponential growth of this mode occurs during the simulation. Embedded within the large-scale baroclinic wave is a convective system exhibiting the characteristic DRV development, with a positive potential vorticity (PV) anomaly in the lower troposphere and a negative PV anomaly in the upper troposphere, and the positive/negative PV doublet tilted downshear with height. The DRV warm-air advection mechanism is active, and the resulting deep convection helps to reinforce the DRV against the deleterious effects of environmental shear, causing an eastward motion of the convective system as a whole. The initial comparisons between the simulated DRVs and the BAMEX MCVs show that the simulated DRVs grew within background conditions of CAPE and shear similar to those observed for BAMEX MCVs and suggest that the same dynamical mechanisms are active. Because the BAMEX field campaign sampled MCVs in different backgrounds of CAPE and shear, the comparison also demonstrates the need to perform additional simulations to explore these different CAPE and shear regimes and to understand their impacts on the intensity and longevity of MCVs. Such a study has the additional benefit of placing MCV dynamics in an appropriate context for exploring their relevance to tropical cyclone formation.

scholarly journals Local and Regional Discriminators of Mesoscale Convective Vortex Development in Arizona

2003 ◽  
Vol 131 (8) ◽  
pp. 1939-1943
Author(s):  
David M. Brommer ◽  
Robert C. Balling ◽  
Randall S. Cerveny
Keyword(s):  
United States ◽  
Wind Shear ◽  
Summer Season ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Central United States ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex ◽  
Convective Vortices ◽  
Rawinsonde Data

Abstract In approximately half of Arizona's summer season (June–September) mesoscale convective systems evolve into mesoscale convective vortices (MCVs). Analysis of satellite imagery identified MCVs in Arizona over the period 1991–2000, and local and regional rawinsonde data discriminated conditions conducive for MCV development. These results indicate that MCVs are more likely to form from convective systems when the local and regional environments are characterized by relative stability in the 850–700-hPa layer and moderate wind shear in the 500–200-hPa layer. These characteristics are similar to results reported for MCV development in the central United States.

A Climatology of Midlatitude Mesoscale Convective Vortices in the Rapid Update Cycle

2010 ◽  
Vol 138 (5) ◽  
pp. 1940-1956 ◽  
Author(s):  
Eric P. James ◽  
Richard H. Johnson
Keyword(s):  
Life Cycle ◽  
Lower Troposphere ◽  
Individual Case ◽  
Relative Vorticity ◽  
Significant Feature ◽  
Composite Analysis ◽  
Mesoscale Convective ◽  
Vortex Detection ◽  
Upper Level ◽  
Convective Vortices

Abstract Climatological characteristics of mesoscale convective vortices (MCVs) occurring in the state of Oklahoma during the late spring and summer of four years are investigated. The MCV cases are selected based on vortex detection by an objective algorithm operating on analyses from the Rapid Update Cycle (RUC) model. Consistent with a previous study, true MCVs represent only about 20% of the mesoscale relative vorticity maxima detected by the algorithm. The MCVs have a broad range of radii and intensities, and their longevities range between 1 and 54 h. Their median radius is about 200 km, and their median midlevel relative vorticity is 1.2 × 10−4 s−1. There appears to be no significant relationship between MCV longevity and intensity. Similar to past estimates, approximately 40% of the MCVs generate secondary convection within their circulations. The mean synoptic-scale MCV environment is determined by the use of a RUC-based composite analysis at four different stages in the MCV life cycle, defined based on vortex detection by the objective algorithm. MCV initiation is closely tied to the diurnal cycle of convection over the Great Plains, with MCVs typically forming in the early morning, near the time of maximum extent of nocturnal mesoscale convective systems (MCSs). Features related to the parent MCSs, including upper-level divergent outflow, midlevel convergence, and a low-level jet, are prominent in the initiating MCV composite. The most significant feature later in the MCV life cycle is a persistent mesoscale trough in the midlevel height field. The potential vorticity (PV) structure of the composite MCV consists of a midlevel maximum and an upper-level minimum, with some extension of elevated PV into the lower troposphere as the vortex matures. The environment immediately downshear of the MCV is more conducive to secondary convection than the environment upshear of the MCV. This midlatitude MCV climatology represents an extension of past individual case studies by providing mean characteristics of a large MCV population; these statistics are suitable for the verification of MCV simulations. Also presented is the first high-resolution composite analysis of the MCV environment at different stages of the MCV life cycle, which will aid in identifying and forecasting these systems.

Mesoscale Convective Vortices Observed during BAMEX. Part II: Influences on Secondary Deep Convection

2007 ◽  
Vol 135 (6) ◽  
pp. 2051-2075 ◽  
Author(s):  
Stanley B. Trier ◽  
Christopher A. Davis
Keyword(s):  
Deep Convection ◽  
Potential Temperature ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Large Temperature ◽  
Equivalent Potential Temperature ◽  
Equivalent Potential ◽  
Mesoscale Convective ◽  
Conditional Instability ◽  
Convective Vortices

Abstract Observations from the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment are used to examine the role of the five mesoscale convective vortices described in Part I on heavy precipitation during the daytime heating cycle. Persistent widespread stratiform rain without deep convection occurs for two strong MCVs in conditionally stable environments with strong vertical shear. Two other MCVs in moderate-to-strong vertical shear have localized redevelopment of deep convection (termed secondary convection) on their downshear side, where conditional instability exists. The strongest of the five MCVs occurs in weak vertical shear and has widespread secondary convection, which is most intense on its conditionally unstable southeast periphery. The two MCVs with only localized secondary convection have well-defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer (PBL). Although the amplitude is significantly greater, the kinematically derived vertical motion dipole resembles that implied by steady, vortex-relative isentropic flow, consistent with previous idealized (dry) simulations and diagnoses based on operational model analyses. In the other three cases with either widespread precipitation or weak environmental vertical shear, the kinematic and isentropic vertical motion patterns are poorly correlated. Vertical motions above the PBL provide a focus for secondary convection through adiabatic cooling downshear and adiabatic warming upshear of the MCV center. The MCVs occur within surface frontal zones with large temperature and moisture gradients across the environmental vertical shear vector (Part I). Thus, the effect of vertical motions on conditional instability is reinforced by horizontal advections of high equivalent potential temperature air downshear, and low equivalent potential temperature air upshear within the PBL. On average, the quadrant immediately right of downshear (typically southeast of the MCV center) best supports deep convection because of the juxtaposition of greatest mesoscale ascent, high equivalent potential temperature PBL air, and MCV-induced enhancement of the vertical shear.

scholarly journals Application of Adjoint-Derived Forecast Sensitivities to the 24–25 January 2000 U.S. East Coast Snowstorm

2005 ◽  
Vol 133 (11) ◽  
pp. 3148-3175 ◽  
Author(s):  
Daryl T. Kleist ◽  
Michael C. Morgan
Keyword(s):  
Response Function ◽  
Initial Conditions ◽  
Forecast Error ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Initial Condition ◽  
Response Functions ◽  
Eastern United States ◽  
Surface Cyclone

Abstract The 24–25 January 2000 eastern United States snowstorm was noteworthy as operational numerical weather prediction (NWP) guidance was poor for lead times as short as 36 h. Despite improvements in the forecast of the surface cyclone position and intensity at 1200 UTC 25 January 2000 with decreasing lead time, NWP guidance placed the westward extent of the midtropospheric, frontogenetically forced precipitation shield too far to the east. To assess the influence of initial condition uncertainties on the forecast of this event, an adjoint model is used to evaluate forecast sensitivities for 36- and 48-h forecasts valid at 1200 UTC 25 January 2000 using as response functions the energy-weighted forecast error, lower-tropospheric circulation about a box surrounding the surface cyclone, 750-hPa frontogenesis, and vertical motion. The sensitivities with respect to the initial conditions for these response functions are in general very similar: geographically isolated, maximized in the middle and lower troposphere, and possessing an upshear vertical tilt. The sensitivities are maximized in a region of enhanced low-level baroclinicity in the vicinity of the surface cyclone’s precursor upper trough. However, differences in the phase and structure of the gradients for the four response functions are evident, which suggests that perturbations could be constructed to alter one response function but not necessarily the others. Gradients of the forecast error response function with respect to the initial conditions are used in an iterative procedure to construct initial condition perturbations that reduce the forecast error. These initial condition perturbations were small in terms of both spatial scale and magnitude. Those initial condition perturbations that were confined primarily to the midtroposphere grew rapidly into much larger amplitude upper-and-lower tropospheric perturbations. The perturbed forecasts were not only characterized by reduced final time forecast error, but also had a synoptic evolution that more closely followed analyses and observations.

scholarly journals Systematic Variation in Wintertime Precipitation in East Asia by MJO-Induced Extratropical Vertical Motion

2008 ◽  
Vol 21 (4) ◽  
pp. 788-801 ◽  
Author(s):  
Jee-Hoon Jeong ◽  
Baek-Min Kim ◽  
Chang-Hoi Ho ◽  
Yeon-Hee Noh
Keyword(s):  
East Asia ◽  
Large Scale ◽  
Diabatic Heating ◽  
Daily Precipitation ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Mean Value ◽  
Asian Countries ◽  
The Indian Ocean ◽  
Omega Equation

Abstract The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden–Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974–2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3–4 mm day−1, which corresponds to the climatological winter-mean value. Composite analysis with respect to the MJO suggests that the MJO–precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia upper-tropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.

scholarly journals Investigating the Local Atmospheric Response to a Realistic Shift in the Oyashio Sea Surface Temperature Front

2015 ◽  
Vol 28 (3) ◽  
pp. 1126-1147 ◽  
Author(s):  
Dimitry Smirnov ◽  
Matthew Newman ◽  
Michael A. Alexander ◽  
Young-Oh Kwon ◽  
Claude Frankignoul
Keyword(s):  
High Resolution ◽  
Surface Wind ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Atmospheric Response ◽  
Transient Eddy ◽  
Sst Front ◽  
Moisture Fluxes ◽  
Upper Level ◽  
Heat And Moisture

Abstract The local atmospheric response to a realistic shift of the Oyashio Extension SST front in the western North Pacific is analyzed using a high-resolution (HR; 0.25°) version of the global Community Atmosphere Model, version 5 (CAM5). A northward shift in the SST front causes an atmospheric response consisting of a weak surface wind anomaly but a strong vertical circulation extending throughout the troposphere. In the lower troposphere, most of the SST anomaly–induced diabatic heating is balanced by poleward transient eddy heat and moisture fluxes. Collectively, this response differs from the circulation suggested by linear dynamics, where extratropical SST forcing produces shallow anomalous heating balanced by strong equatorward cold air advection driven by an anomalous, stationary surface low to the east. This latter response, however, is obtained by repeating the same experiment except using a relatively low-resolution (LR; 1°) version of CAM5. Comparison to observations suggests that the HR response is closer to nature than the LR response. Strikingly, HR and LR experiments have almost identical vertical profiles of . However, diagnosis of the diabatic quasigeostrophic vertical pressure velocity (ω) budget reveals that HR has a substantially stronger response, which together with upper-level mean differential thermal advection balances stronger vertical motion. The results herein suggest that changes in transient eddy heat and moisture fluxes are critical to the overall local atmospheric response to Oyashio Front anomalies, which may consequently yield a stronger downstream response. These changes may require the high resolution to be fully reproduced, warranting further experiments of this type with other high-resolution atmosphere-only and fully coupled GCMs.

scholarly journals Nocturnal Relative Humidity Maxima above the Boundary Layer in the U.S. Midwest: A Diagnostic for the Mountain–Plains Solenoidal Circulation

2018 ◽  
Vol 146 (2) ◽  
pp. 641-658
Author(s):  
Amanda Mercer ◽  
Rachel Chang ◽  
Ian Folkins
Keyword(s):  
Relative Humidity ◽  
Cross Sections ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Specific Humidity ◽  
Reanalysis Dataset ◽  
Low Level Jet ◽  
Vertical Winds ◽  
Modern Era ◽  
The U.S

Measurements from the Aircraft Communications, Addressing, and Reporting System (ACARS) dataset between 2005 and 2014 are used to construct diurnal vertical cross sections of relative humidity in the lower troposphere at six airports in the U.S. Midwest. In summer, relative humidity maxima occur between 2 and 3 km during the overnight hours of 0300–0900 local solar time (LST). These maxima coincide with negative anomalies in temperature and positive anomalies in specific humidity. Vertical winds from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), reanalysis dataset show that the height and diurnal timing of these positive relative humidity anomalies are consistent with the regional diurnal pattern of vertical motion. During the day, there is rising motion over the Rocky Mountains and subsidence over the Midwest, while conversely at night, there is sinking motion over the mountains and rising motion over the Midwest. The nocturnal relative humidity maxima over the Midwest are the strongest direct observational evidence to date of this mountain–plains solenoidal circulation, and provide a useful diagnostic for testing the strength of this circulation in climate and reanalysis models. There is significant interannual variability in the strength of the nocturnal relative humidity maxima. In 2011, the relative humidity maxima are very pronounced. In 2014, however, they are almost nonexistent. Finally, the relative humidity maxima are discussed in relation to the low-level jet (LLJ). The LLJ appears to be too low to directly contribute to the nocturnal relative humidity maxima.

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