Mesoscale Convective Vortices Observed during BAMEX. Part I: Kinematic and Thermodynamic Structure

2007 ◽  
Vol 135 (6) ◽  
pp. 2029-2049 ◽  
Author(s):  
Christopher A. Davis ◽  
Stanley B. Trier
Keyword(s):  
Potential Temperature ◽  
Tangential Velocity ◽  
Vertical Shear ◽  
Thermodynamic Structure ◽  
Temperature Anomalies ◽  
Strong Shear ◽  
Central United States ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Convective Vortices

Abstract Five cases of mesoscale convective vortices (MCVs) are described from observations collected during the Bow Echo and MCV Experiment (BAMEX) over the central United States during the period from 20 May to 6 July 2003. In the present paper, the kinematic and thermodynamic structure of each vortex and its environment are emphasized. Data consist of BAMEX dropsondes, the National Oceanic and Atmospheric Administration profiler network, and National Weather Service soundings. In addition, Weather Surveillance Radar-1988 Doppler observations documented the signatures of nascent MCVs within nocturnal convection systems as well as the spatial pattern of convection within MCVs during the following day. The vertical structure of each vortex was highly dependent on the vertical shear and the presence of upper-tropospheric cyclonic vorticity anomalies. In strong shear, a pronounced downshear tilt of the vortex was evident, but with the presence of an upper-tropospheric trough, the tilt was upshear in the upper troposphere. In only one case did the tangential velocity of the vortex greatly exceed the vertical shear across its depth, and thus the vortex could maintain itself against the shear. The vortices were generally deep structures, extending through 5–8 km in all cases and maximizing their tangential winds between 550 and 600 hPa. In one of the five cases, vertical penetration into the boundary layer was unambiguous. Lower-tropospheric virtual potential temperature anomalies were generally 1–2 K, greatest when not directly beneath the midtropospheric MCV center but rather on its upshear and downshear flanks. Upper-tropospheric warm anomalies were found above and downshear from the midtropospheric MCV center, with a cool anomaly upshear, the latter being stronger in cases with an upshear tropopause-based trough. A diagnostic balance calculation was performed and indicated that the temperature anomalies were approximately balanced on the scale of the vortex.

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.

Convection-Permitting Simulations of the Environment Supporting Widespread Turbulence within the Upper-Level Outflow of a Mesoscale Convective System

2009 ◽  
Vol 137 (6) ◽  
pp. 1972-1990 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman
Keyword(s):  
Deep Convection ◽  
Potential Temperature ◽  
Mesoscale Convective System ◽  
Forecast Model ◽  
Static Stability ◽  
Vertical Shear ◽  
Convective System ◽  
Mesoscale Convective ◽  
Northern Edge ◽  
Upper Level

Abstract Widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern Kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system (MCS) on 17 June 2005. A noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection (i.e., large reflectivity) regions of the MCS. Herein, the MCS life cycle and the turbulence environment in its upper-level outflow are studied using Rapid Update Cycle (RUC) analyses and cloud-permitting simulations with the Weather Research and Forecast Model (WRF). It is demonstrated that strong vertical shear beneath the MCS outflow jet is critical to providing an environment that could support dynamic (e.g., shearing type) instabilities conducive to turbulence. Comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the local Richardson number (Ri) to ∼0.25 at the northern edge of the anvil were almost entirely a consequence of the MCS-induced westerly outflow jet. The large vertical shear is found to decrease Ri both directly, and by contributing to reductions in static stability near the northern anvil edge through differential advection of (equivalent) potential temperature gradients, which are in turn influenced by adiabatic cooling associated with the mesoscale updraft located upstream within the anvil. On the south side of the MCS, the vertical shear associated with easterly outflow was significantly offset by environmental westerly shear, which resulted in larger Ri and less widespread model turbulent kinetic energy (TKE) than at the northern anvil edge.

Mesoscale Convective Vortices in Multiscale, Idealized Simulations: Dependence on Background State, Interdependency with Moist Baroclinic Cyclones, and Comparison with BAMEX Observations

2010 ◽  
Vol 138 (4) ◽  
pp. 1119-1139 ◽  
Author(s):  
Robert J. Conzemius ◽  
Michael T. Montgomery
Keyword(s):  
Tangential Velocity ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Pressure Amplitude ◽  
Moist Convection ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Common Center ◽  
Deep Moist Convection ◽  
Convective Vortices

Abstract A set of multiscale, nested, idealized numerical simulations of mesoscale convective systems (MCSs) and mesoscale convective vortices (MCVs) was conducted. The purpose of these simulations was to investigate the dependence of MCV development and evolution on background conditions and to explore the relationship between MCVs and larger, moist baroclinic cyclones. In all experiments, no mesoscale convective system (MCS) developed until a larger-scale, moist baroclinic system with surface pressure amplitude of at least 2 hPa was present. The convective system then enhanced the development of the moist baroclinic system by its diabatic production of eddy available potential energy (APE), which led to the enhanced baroclinic conversion of basic-state APE to eddy APE. The most rapid potential vorticity (PV) development occurred in and just behind the leading convective line. The entire system grew upscale with time as the newly created PV rotated cyclonically around a common center as the leading convective line continued to expand outward. Ten hours after the initiation of deep moist convection, the simulated MCV radii, heights of maximum winds, tangential velocity, and shear corresponded reasonably well to their counterparts in BAMEX. The increasing strength of the simulated MCVs with respect to larger values of background CAPE and shear supports the hypothesis that as long as convection is present, CAPE and shear both add to the strength of the MCV.

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.

scholarly journals Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part II: Column Model Simulations

2009 ◽  
Vol 137 (4) ◽  
pp. 1186-1205 ◽  
Author(s):  
Joseph A. Grim ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Andrea M. Smith ◽  
Brian F. Jewett
Keyword(s):  
Mesoscale Convective Systems ◽  
Sharp Change ◽  
Melting Layer ◽  
Thermodynamic Structure ◽  
Column Model ◽  
Convective Systems ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Microphysical Processes

Abstract This study employed a nondynamic microphysical column model to evaluate the degree to which the microphysical processes of sublimation, melting, and evaporation alone can explain the evolution of the relative humidity (RH) and latent cooling profiles within the trailing stratiform region of mesoscale convective systems observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). Simulations revealed that observations of a sharp change in the profile of RH, from saturated air with respect to ice above the melting layer to subsaturated air with respect to water below, developed in response to the rapid increase in hydrometeor fall speeds from 1–2 m s−1 for ice to 2–11 m s−1 for rain. However, at certain times and locations, such as the first spiral descent on 29 June 2003 within the notch of lower reflectivity, the air may remain subsaturated for temperatures (T) < 0°C. Sufficiently strong downdrafts above the melting level, such as the 1–3 m s−1 downdrafts observed in the notch of lower reflectivity on 29 June, could enable this state of sustained subsaturation. Sensitivity tests, where the hydrometeor size distributions and upstream RH profiles were varied within the range of BAMEX observations, revealed that the sharp contrast in the RH field across the melting layer always developed. The simulations also revealed that latent cooling from sublimation and melting resulted in the strongest cooling at altitudes within and above the melting layer for locations where hydrometeors did not reach the ground, such as within the rear anvil region, and where sustained subsaturated air is present for T < 0°C, such as is observed within downdrafts. Within the enhanced stratiform rain region, the air is typically at or near saturation for T < 0°C, whereas it is typically subsaturated for T > 0°C; thus, evaporation and melting result in the primary cooling in this region. The implications of these results for the descent of the rear inflow jet across the trailing stratiform region are discussed.

scholarly journals Thermodynamic Properties of Mesoscale Convective Systems Observed during BAMEX

2008 ◽  
Vol 136 (11) ◽  
pp. 4242-4271 ◽  
Author(s):  
James Correia ◽  
Raymond W. Arritt
Keyword(s):  
Potential Temperature ◽  
Mesoscale Convective Systems ◽  
Lapse Rate ◽  
Spatiotemporal Variability ◽  
Cold Pool ◽  
Convective Systems ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Lapse Rates

Abstract Dropsonde observations from the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) are used to document the spatiotemporal variability of temperature, moisture, and wind within mesoscale convective systems (MCSs). Onion-type sounding structures are found throughout the stratiform region of MCSs, but the temperature and moisture variability is large. Composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the MCS. The calculated air vertical velocity helped identify subsaturated downdrafts. It was found that lapse rates within the cold pool varied markedly throughout the MCS. Layered wet-bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions. It was also found that lapse-rate transitions across the 0°C level were more common than isothermal, melting layers. The authors discuss the implications these findings have and how they can be used to validate future high-resolution numerical simulations of MCSs.

scholarly journals Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part I: Observations

2009 ◽  
Vol 137 (4) ◽  
pp. 1165-1185 ◽  
Author(s):  
Andrea M. Smith ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Joseph A. Grim ◽  
Michael S. Timlin ◽  
...  
Keyword(s):  
Life Cycle ◽  
Mesoscale Convective Systems ◽  
Melting Layer ◽  
Thermodynamic Structure ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Horizontal Flight ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex

Abstract This study used airborne and ground-based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the NOAA P-3 aircraft in the trailing stratiform regions (TSRs) of mesoscale convective systems (MCSs) observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) to characterize microphysical and thermodynamic variations within the TSRs in the context of the following features: the transition zone, the notch region, the enhanced stratiform rain region, the rear anvil region, the front-to-rear flow, the rear-to-front flow, and the rear inflow jet axis. One spiral from the notch region, nine from the enhanced stratiform rain region, and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones. The spiral performed in the notch region on 29 June occurred early in the MCS life cycle and exhibited subsaturated conditions throughout its depth. The nine spirals performed within the enhanced stratiform rain region exhibited saturated conditions with respect to ice above and within the melting layer and subsaturated conditions below the melting layer. Spirals performed in the rear anvil region showed saturation until the base of the anvil, near −1°C, and subsaturation below. These data, together with analyses of total number concentration and the slope to gamma fits to size distributions, revealed that sublimation above the melting layer occurs early in the MCS life cycle but then reduces in importance as the environment behind the convective line is moistened from the top down. Evaporation below the melting layer was insufficient to attain saturation below the melting layer at any time or location within the MCS TSRs. Relative humidity was found to have a strong correlation to the component of wind parallel to the storm motion, especially within air flowing from front to rear.

scholarly journals GoAmazon2014/5 campaign points to deep-inflow approach to deep convection across scales

2018 ◽  
Vol 115 (18) ◽  
pp. 4577-4582 ◽  
Author(s):  
Kathleen A. Schiro ◽  
Fiaz Ahmed ◽  
Scott E. Giangrande ◽  
J. David Neelin
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Deep Convection ◽  
Potential Temperature ◽  
Strong Relationship ◽  
Field Campaign ◽  
Convective Systems ◽  
Tropical Oceans ◽  
Mesoscale Convective ◽  
Environmental Air

A substantial fraction of precipitation is associated with mesoscale convective systems (MCSs), which are currently poorly represented in climate models. Convective parameterizations are highly sensitive to the assumptions of an entraining plume model, in which high equivalent potential temperature air from the boundary layer is modified via turbulent entrainment. Here we show, using multiinstrument evidence from the Green Ocean Amazon field campaign (2014–2015; GoAmazon2014/5), that an empirically constrained weighting for inflow of environmental air based on radar wind profiler estimates of vertical velocity and mass flux yields a strong relationship between resulting buoyancy measures and precipitation statistics. This deep-inflow weighting has no free parameter for entrainment in the conventional sense, but to a leading approximation is simply a statement of the geometry of the inflow. The structure further suggests the weighting could consistently apply even for coherent inflow structures noted in field campaign studies for MCSs over tropical oceans. For radar precipitation retrievals averaged over climate model grid scales at the GoAmazon2014/5 site, the use of deep-inflow mixing yields a sharp increase in the probability and magnitude of precipitation with increasing buoyancy. Furthermore, this applies for both mesoscale and smaller-scale convection. Results from reanalysis and satellite data show that this holds more generally: Deep-inflow mixing yields a strong precipitation–buoyancy relation across the tropics. Deep-inflow mixing may thus circumvent inadequacies of current parameterizations while helping to bridge the gap toward representing mesoscale convection in climate models.

Upscale Impact of Mesoscale Convective Systems and Its Parameterization in an Idealized GCM for an MJO Analog above the Equator

2019 ◽  
Vol 76 (3) ◽  
pp. 865-892 ◽  
Author(s):  
Qiu Yang ◽  
Andrew J. Majda ◽  
Mitchell W. Moncrieff
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Interaction Mechanism ◽  
Global Climate Models ◽  
Mesoscale Convective Systems ◽  
Vertical Shear ◽  
Collective Effects ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Westerly Wind Burst

Abstract The Madden–Julian oscillation (MJO) typically contains several superclusters and numerous embedded mesoscale convective systems (MCSs). It is hypothesized here that the poorly simulated MJOs in current coarse-resolution global climate models (GCMs) is related to the inadequate treatment of unresolved MCSs. So its parameterization should provide the missing collective effects of MCSs. However, a satisfactory understanding of the upscale impact of MCSs on the MJO is still lacking. A simple two-dimensional multicloud model is used as an idealized GCM with clear deficiencies. Eddy transfer of momentum and temperature by the MCSs, predicted by the mesoscale equatorial synoptic dynamics (MESD) model, is added to this idealized GCM. The upscale impact of westward-moving MCSs promotes eastward propagation of the MJO analog, consistent with the theoretical prediction of the MESD model. Furthermore, the upscale impact of upshear-moving MCSs significantly intensifies the westerly wind burst because of two-way feedback between easterly vertical shear and eddy momentum transfer with low-level eastward momentum forcing. Finally, a basic parameterization of the upscale impact of upshear-moving MCSs modulated by deep heating excess and vertical shear strength significantly improves key features of the MJO analog in the idealized GCM with clear deficiencies. A three-way interaction mechanism between the MJO analog, parameterized upscale impact of MCSs, and background vertical shear is identified.

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