scholarly journals Properties of a Mesoscale Convective System in the Context of an Isentropic Analysis

2015 ◽  
Vol 72 (5) ◽  
pp. 1945-1962 ◽  
Author(s):  
Agnieszka A. Mrowiec ◽  
O. M. Pauluis ◽  
A. M. Fridlind ◽  
A. S. Ackerman
Keyword(s):  
Mass Transport ◽  
Mass Flux ◽  
Potential Temperature ◽  
Substantial Reduction ◽  
Flux Ratio ◽  
Mesoscale Convective System ◽  
Convective System ◽  
High Entropy ◽  
Mixing Ratios ◽  
Mesoscale Convective

Abstract Application of an isentropic analysis of convective motions to a simulated mesoscale convective system is presented. The approach discriminates the vertical mass transport in terms of equivalent potential temperature. The scheme separates rising air at high entropy from subsiding air at low entropy. This also filters out oscillatory motions associated with gravity waves and isolates the overturning motions associated with convection and mesoscale circulation. The mesoscale convective system is additionally partitioned into stratiform and convective regions based on the radar reflectivity field. For each of the subregions, the mass transport derived in terms of height and an isentropic invariant of the flow is analyzed. The difference between the Eulerian mass flux and the isentropic counterpart is a significant and symmetric contribution of the buoyant oscillations to the upward and downward mass fluxes. Filtering out these oscillations results in substantial reduction of the diagnosed downward-to-upward convective mass flux ratio. The analysis is also applied to graupel and snow mixing ratios and number concentrations, illustrating the relationship of the particle formation process to the updrafts.

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.

scholarly journals Discrimination of Mesoscale Convective System Environments Using Sounding Observations

2007 ◽  
Vol 22 (5) ◽  
pp. 1045-1062 ◽  
Author(s):  
Ariel E. Cohen ◽  
Michael C. Coniglio ◽  
Stephen F. Corfidi ◽  
Sarah J. Corfidi
Keyword(s):  
Deep Layer ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Strong Relationship ◽  
Convective System ◽  
Wind Speeds ◽  
Mesoscale Convective ◽  
The Mean ◽  
Wind Events

Abstract The prediction of the strength of mesoscale convective systems (MCSs) is a major concern to operational meteorologists and the public. To address this forecast problem, this study examines meteorological variables derived from sounding observations taken in the environment of quasi-linear MCSs. A set of 186 soundings that sampled the beginning and mature stages of the MCSs are categorized by their production of severe surface winds into weak, severe, and derecho-producing MCSs. Differences in the variables among these three MCS categories are identified and discussed. Mean low- to upper-level wind speeds and deep-layer vertical wind shear, especially the component perpendicular to the convective line, are excellent discriminators among all three categories. Low-level inflow relative to the system is found to be an excellent discriminator, largely because of the strong relationship of system severity to system speed. Examination of the mean wind and shear vectors relative to MCS motion suggests that cell propagation along the direction of cell advection is a trait that separates severe, long-lived MCSs from the slower-moving, nonsevere variety and that this is favored when both the deep-layer shear vector and the mean deep-layer wind are large and nearly parallel. Midlevel environmental lapse rates are found to be very good discriminators among all three MCS categories, while vertical differences in equivalent potential temperature and CAPE only discriminate well between weak and severe/derecho MCS environments. Knowledge of these variables and their distribution among the different categories of MCS intensity can be used to improve forecasts and convective watches for organized convective wind events.

scholarly journals NO<sub>x</sub> production by lightning in Hector: first airborne measurements during SCOUT-O3/ACTIVE

2009 ◽  
Vol 9 (4) ◽  
pp. 14361-14451 ◽  
Author(s):  
H. Huntrieser ◽  
H. Schlager ◽  
M. Lichtenstern ◽  
A. Roiger ◽  
P. Stock ◽  
...  
Keyword(s):  
Production Rate ◽  
Mass Flux ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Stroke Rate ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Different Types ◽  
Gas Measurements

Abstract. During the SCOUT-O3/ACTIVE field phase in November–December 2005 airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several research aircraft (German Falcon, Russian M55 Geophysica, and British Dornier-228). Here a case study from 19 November is presented in large detail on the basis of airborne trace gas measurements (NO, NOy, CO, O3) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: 1) a continental thunderstorm developing in a tropical airmass near Darwin, 2) a mesoscale convective system (MCS) developing within the tropical maritime continent (Tiwi Islands) known as Hector, and 3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol−1 in the main anvil outflow at ~11.5–12.5 km altitude. The mean NOx (=NO+NO2) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol−1. The NOx contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NOx was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NOx (LNOx) in the well-developed Hector system was estimated to 0.6–0.7 kg(N) s−1. The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s−1 (here only strokes with peak currents ≥10 kA contributing to LNOx were considered). The LNOx mass flux and the stroke rate were combined to estimate the LNOx production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 4.1–4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s−1), the annual global LNOx production rate based on Hector would be ~5.7–6.6 Tg(N) a−1 and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a−1, respectively. The latter thunderstorm type produced much less LNOx per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNOx production per flash.

scholarly journals Reducing the Biases in Simulated Radar Reflectivities from a Bulk Microphysics Scheme: Tropical Convective Systems

2011 ◽  
Vol 68 (10) ◽  
pp. 2306-2320 ◽  
Author(s):  
Stephen E. Lang ◽  
Wei-Kuo Tao ◽  
Xiping Zeng ◽  
Yaping Li
Keyword(s):  
Mesoscale Convective System ◽  
Convective System ◽  
Microphysics Scheme ◽  
Upper Troposphere ◽  
Convective Systems ◽  
Mixing Ratios ◽  
Ice Nuclei ◽  
Mesoscale Convective ◽  
Immersion Freezing ◽  
Cloud Ice

Abstract A well-known bias common to many bulk microphysics schemes currently being used in cloud-resolving models is the tendency to produce excessively large reflectivity values (e.g., 40 dBZ) in the middle and upper troposphere in simulated convective systems. The Rutledge and Hobbs–based bulk microphysics scheme in the Goddard Cumulus Ensemble model is modified to reduce this bias and improve realistic aspects. Modifications include lowering the efficiencies for snow/graupel riming and snow accreting cloud ice; converting less rimed snow to graupel; allowing snow/graupel sublimation; adding rime splintering, immersion freezing, and contact nucleation; replacing the Fletcher formulation for activated ice nuclei with that of Meyers et al.; allowing for ice supersaturation in the saturation adjustment; accounting for ambient RH in the growth of cloud ice to snow; and adding/accounting for cloud ice fall speeds. In addition, size-mapping schemes for snow/graupel were added as functions of temperature and mixing ratio, lowering particle sizes at colder temperatures but allowing larger particles near the melting level and at higher mixing ratios. The modifications were applied to a weakly organized continental case and an oceanic mesoscale convective system (MCS). Strong echoes in the middle and upper troposphere were reduced in both cases. Peak reflectivities agreed well with radar for the weaker land case but, despite improvement, remained too high for the MCS. Reflectivity distributions versus height were much improved versus radar for the less organized land case but not for the MCS despite fewer excessively strong echoes aloft due to a bias toward weaker echoes at storm top.

scholarly journals NO<sub>x</sub> production by lightning in Hector: first airborne measurements during SCOUT-O3/ACTIVE

2009 ◽  
Vol 9 (21) ◽  
pp. 8377-8412 ◽  
Author(s):  
H. Huntrieser ◽  
H. Schlager ◽  
M. Lichtenstern ◽  
A. Roiger ◽  
P. Stock ◽  
...  
Keyword(s):  
Production Rate ◽  
Mass Flux ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Stroke Rate ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Different Types ◽  
Gas Measurements

Abstract. During the SCOUT-O3/ACTIVE field phase in November–December 2005, airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several research aircraft (German Falcon, Russian M55 Geophysica, and British Dornier-228. Here a case study from 19 November is presented in detail on the basis of airborne trace gas measurements (NO, NOy, CO, O3) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: (1) a continental thunderstorm developing in a tropical airmass near Darwin, (2) a mesoscale convective system (MCS), known as Hector, developing within the tropical maritime continent (Tiwi Islands), and (3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol−1 in the main anvil outflow at ~11.5–12.5 km altitude. The mean NOx (=NO+NO2) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol−1. The NOx contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NOx was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NOx (LNOx) in the well-developed Hector system was estimated to 0.6–0.7 kg(N) s−1. The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s−1 (here only strokes with peak currents ≥10 kA contributing to LNOx were considered). The LNOx mass flux and the stroke rate were combined to estimate the LNOx production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 4.1–4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s−1), the annual global LNOx production rate based on Hector would be ~5.7–6.6 Tg(N) a−1 and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a−1, respectively. The latter thunderstorm type produced much less LNOx per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNOx production per flash.

scholarly journals Isentropic Analysis on the Intensification of Hurricane Edouard (2014)

2017 ◽  
Vol 74 (12) ◽  
pp. 4177-4197 ◽  
Author(s):  
Juan Fang ◽  
Olivier Pauluis ◽  
Fuqing Zhang
Keyword(s):  
Relative Humidity ◽  
Mass Transport ◽  
Mass Flux ◽  
Inner Core ◽  
Potential Temperature ◽  
Tangential Velocity ◽  
Vertical Circulation ◽  
High Entropy ◽  
Upper Level ◽  
Radial Outflow

Abstract An isentropic analysis technique is adopted in this study to investigate the intensification of Hurricane Edouard (2014) predicted by an experimental real-time convection-permitting hurricane analysis and forecast system. This technique separates the vertical mass transport in terms of equivalent potential temperature θe for the rising air parcels at high entropy from the subsiding air at low entropy. It is found that as Edouard intensifies the vertical circulation becomes wider via the expansion of upward (downward) mass flux to higher (lower) θe. In the early developing stages, the asymmetric convection dominates the vertical circulation and leads to a remarkable upward mass flux maximum center in the upper troposphere. When Edouard becomes intense, the axisymmetric convection becomes important to the upper-level vertical mass transport while the asymmetric convection still dominates the low-level vertical mass transport. Development of the warm core in the eye leads to double maxima along the θe axis for both the isentropic-mean relative humidity and tangential velocity. The isentropic-mean properties such as the mid- to upper-level relative humidity, vertical velocity, and radial outflow decrease considerably while the mid- to upper-level vorticity enhances on the high-θe side before the onset of rapid intensification. The isentropic analysis also reveals that as Edouard intensifies the eye characterized by warm and dry core first forms in the low to middle troposphere and then gradually expands upward. The abovementioned results indicate that the isentropic framework may have the advantages of binning common variables with θe that could reflect the changes of the tropical cyclone structure in the inner-core region without a prior specification of the location of the storm center.

Numerical Simulations of the Postsunrise Reorganization of a Nocturnal Mesoscale Convective System during 13 June IHOP_2002

2011 ◽  
Vol 68 (12) ◽  
pp. 2988-3011 ◽  
Author(s):  
Stanley B. Trier ◽  
John H. Marsham ◽  
Christopher A. Davis ◽  
David A. Ahijevych
Keyword(s):  
Structural Characteristics ◽  
Type System ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Mixing Ratios ◽  
Stratiform Precipitation ◽  
Mesoscale Convective ◽  
Strong Surface ◽  
Large Water

Abstract A convection-permitting numerical model is used to simulate the postsunrise reorganization of a nocturnal mesoscale convective system (MCS) observed over western and central Oklahoma on 13 June 2002 during the International H2O (IHOP_2002) Field Experiment. The MCS reorganization consists of a transition from northwest–southeast-oriented convective rainbands near sunrise to a single northeast–southwest (NE–SW)-oriented convective rainband with trailing stratiform precipitation later in the morning. Results indicate the importance of environmental preconditioning on MCS reorganization. In particular, the development of the NE–SW rainband that redefines the MCS organization is facilitated by a similarly oriented zone of antecedent mesoscale upward motion, which increases the depth of large water vapor mixing ratios. This allows convective updrafts to be fed primarily by moist and conditionally unstable air from 1 to 2.5 km AGL in the NE–SW-oriented rainband, which lacks a surface cold pool during its incipient postsunrise stage. The MCS develops a strong surface cold pool from latent cooling–induced downdrafts by midmorning and evolves into an upshear-tilted squall-type system. These downdrafts and the resulting cold pool are not necessary for the overall reorganization and maintenance of the MCS in this environment where earlier mesoscale ascent has occurred. However, the latent cooling from downdrafts does influence the MCS strength, vertical structure, and horizontal motion by early in the postsunrise stage. In contrast, surface heating of the preconvective environment has little effect on the strength and structural characteristics of the MCS until midday, by which time the convection has become primarily surface based.

Ensemble Probabilistic Prediction of a Mesoscale Convective System and Associated Polarimetric Radar Variables Using Single-Moment and Double-Moment Microphysics Schemes and EnKF Radar Data Assimilation

2017 ◽  
Vol 145 (6) ◽  
pp. 2257-2279 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan A. Snook ◽  
Guifu Zhang
Keyword(s):  
Mesoscale Convective System ◽  
Radar Data ◽  
Convective Precipitation ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Verification Methods ◽  
Probabilistic Forecasts ◽  
Mesoscale Convective ◽  
Single Moment ◽  
Double Moment

Abstract Ensemble-based probabilistic forecasts are performed for a mesoscale convective system (MCS) that occurred over Oklahoma on 8–9 May 2007, initialized from ensemble Kalman filter analyses using multinetwork radar data and different microphysics schemes. Two experiments are conducted, using either a single-moment or double-moment microphysics scheme during the 1-h-long assimilation period and in subsequent 3-h ensemble forecasts. Qualitative and quantitative verifications are performed on the ensemble forecasts, including probabilistic skill scores. The predicted dual-polarization (dual-pol) radar variables and their probabilistic forecasts are also evaluated against available dual-pol radar observations, and discussed in relation to predicted microphysical states and structures. Evaluation of predicted reflectivity (Z) fields shows that the double-moment ensemble predicts the precipitation coverage of the leading convective line and stratiform precipitation regions of the MCS with higher probabilities throughout the forecast period compared to the single-moment ensemble. In terms of the simulated differential reflectivity (ZDR) and specific differential phase (KDP) fields, the double-moment ensemble compares more realistically to the observations and better distinguishes the stratiform and convective precipitation regions. The ZDR from individual ensemble members indicates better raindrop size sorting along the leading convective line in the double-moment ensemble. Various commonly used ensemble forecast verification methods are examined for the prediction of dual-pol variables. The results demonstrate the challenges associated with verifying predicted dual-pol fields that can vary significantly in value over small distances. Several microphysics biases are noted with the help of simulated dual-pol variables, such as substantial overprediction of KDP values in the single-moment ensemble.

scholarly journals Comprehensive Analysis of a Coast Thunderstorm That Produced a Sprite over the Bohai Sea

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 718
Author(s):  
Cong Pan ◽  
Jing Yang ◽  
Kun Liu ◽  
Yu Wang
Keyword(s):  
Bohai Sea ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Return Stroke ◽  
Absolute Value ◽  
Transient Luminous Events ◽  
Stratiform Region ◽  
Before And After ◽  
Mesoscale Convective ◽  
Cloud To Ground Lightning

Sprites are transient luminous events (TLEs) that occur over thunderstorm clouds that represent the direct coupling relationship between the troposphere and the upper atmosphere. We report the evolution of a mesoscale convective system (MCS) that produced only one sprite event, and the characteristics of this thunderstorm and the related lightning activity are analyzed in detail. The results show that the parent flash of the sprite was positive cloud-to-ground lightning (+CG) with a single return stroke, which was located in the trailing stratiform region of the MCS with a radar reflectivity of 25 to 35 dBZ. The absolute value of the negative CG (−CG) peak current for half an hour before and after the occurrence of the sprite was less than 50 kA, which was not enough to produce the sprite. Sprites tend to be produced early in the maturity-to-dissipation stage of the MCS, with an increasing percentage of +CG to total CG (POP), indicating that the sprite production was the attenuation of the thunderstorm and the area of the stratiform region.

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