scholarly journals Numerical study of tracers transport by a mesoscale convective system over West Africa

2011 ◽  
Vol 29 (5) ◽  
pp. 731-747 ◽  
Author(s):  
C. Barthe ◽  
C. Mari ◽  
J.-P. Chaboureau ◽  
P. Tulet ◽  
F. Roux ◽  
...  
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Mesoscale Convective System ◽  
Dimensional Structure ◽  
Convective System ◽  
Upper Troposphere ◽  
Mesoscale Convective ◽  
Cloud Resolving Model ◽  
Passive Tracers ◽  
Two Peaks

Abstract. A three-dimensional cloud-resolving model is used to investigate the vertical transport from the lower to the upper troposphere in a mesoscale convective system (MCS) that occurred over Niger on 15 August 2004. The redistribution of five passive tracers initially confined in horizontally homogeneous layers is analyzed. The monsoon layer tracer (0–1.5 km) is the most efficiently transported in the upper troposphere with concentrations 3 to 4 times higher than the other tracers in the anvil. On the contrary the African Easterly Jet tracer (~3 km) has the lowest contribution above 5 km. The vertical profiles of the mid-troposphere tracers (4.5–10 km) in the MCS exhibit two peaks: one in their initial layers, and the second one at 13–14 km altitude, underlying the importance of mid-tropospheric air in feeding the upper troposphere. Mid-tropospheric tracers also experience efficient transport by convective downdrafts with a consequent increase of their concentrations at the surface. The concentration of the upper troposphere–lower stratosphere tracer exhibits strong gradients at the edge of the cloud, meaning almost no entrainment of this tracer into the cloud. No downward transport from the upper troposphere is simulated below 5 km. A proxy for lightning produced NOx is transported preferentially in the forward anvil in the upper troposphere. Additionally, lateral inflows significantly contribute to the updraft and downdraft airflows emphasizing the three-dimensional structure of the West African MCSs.

A Numerical Study of a Mesoscale Convective System over the Taiwan Strait

2003 ◽  
Vol 131 (6) ◽  
pp. 1150-1170 ◽  
Author(s):  
Qing-Hong Zhang ◽  
Kai-Hon Lau ◽  
Ying-Hwa Kuo ◽  
Shou-Jun Chen
Keyword(s):  
Numerical Study ◽  
Mesoscale Convective System ◽  
Taiwan Strait ◽  
Convective System ◽  
Mesoscale Convective ◽  
The Taiwan Strait

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.

Tornadogenesis in a Simulated Mesovortex within a Mesoscale Convective System

2012 ◽  
Vol 69 (11) ◽  
pp. 3372-3390 ◽  
Author(s):  
Alexander D. Schenkman ◽  
Ming Xue ◽  
Alan Shapiro
Keyword(s):  
Three Dimensional ◽  
Mesoscale Convective System ◽  
Surface Friction ◽  
Convective System ◽  
Grid Spacing ◽  
Near Surface ◽  
Advanced Regional Prediction System ◽  
Low Level ◽  
Regional Prediction ◽  
Mesoscale Convective

Abstract The Advanced Regional Prediction System (ARPS) is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes. The mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system (MCS) that traversed southwestern and central Oklahoma on 8–9 May 2007. The simulation used 100-m horizontal grid spacing, and is nested within two outer grids with 400-m and 2-km grid spacing, respectively. Both outer grids assimilate radar, upper-air, and surface observations via 5-min three-dimensional variational data assimilation (3DVAR) cycles. The 100-m grid is initialized from a 40-min forecast on the 400-m grid. Results from the 100-m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex-scale tornado-like vortex (TLV). Closer examination of the genesis of the TLV suggests that a strong low-level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex. Vertical cross sections and backward trajectory analyses from this low-level updraft reveal that the updraft is the upward branch of a strong rotor that forms just northwest of the simulated TLV. The horizontal vorticity in this rotor originates in the near-surface inflow and is caused by surface friction. An additional simulation with surface friction turned off does not produce a rotor, strong low-level updraft, or TLV. Comparison with previous two-dimensional numerical studies of rotors in the lee of mountains shows striking similarities to the rotor formation presented herein. The findings of this study are summarized in a four-stage conceptual model for tornadogenesis in this case that describes the evolution of the event from mesovortexgenesis through rotor development and finally TLV genesis and intensification.

scholarly journals The Sensitivity of Momentum Transport and Severe Surface Winds to Environmental Moisture in Idealized Simulations of a Mesoscale Convective System

2011 ◽  
Vol 139 (5) ◽  
pp. 1352-1369 ◽  
Author(s):  
Kelly M. Mahoney ◽  
Gary M. Lackmann
Keyword(s):  
Three Dimensional ◽  
Grid Cell ◽  
Mesoscale Convective System ◽  
Momentum Transport ◽  
Convective System ◽  
Surface Winds ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Convective Momentum Transport

Analysis of a pair of three-dimensional simulations of mesoscale convective systems (MCSs) reveals a significant sensitivity of convective momentum transport (CMT), MCS motion, and the generation of severe surface winds to ambient moisture. The Weather Research and Forecasting model is used to simulate an idealized MCS, which is compared with an MCS in a drier midlevel environment. The MCS in the drier environment is smaller, moves slightly faster, and exhibits increased descent and more strongly focused areas of enhanced CMT near the surface in the trailing stratiform region relative to that in the control simulation. A marked increase in the occurrence of severe surface winds is observed between the dry midlevel simulation and the control. It is shown that the enhanced downward motion associated with decreased midlevel relative humidity affects CMT fields and contributes to an increase in the number of grid-cell occurrences of severe surface winds. The role of a descending rear-inflow jet in producing strong surface winds at locations trailing the gust front is also analyzed, and is found to be associated with low-level CMT maxima, particularly in the drier midlevel simulation.

scholarly journals Genesis of Hurricane Julia (2010) within an African Easterly Wave: Developing and Nondeveloping Members from WRF–LETKF Ensemble Forecasts

2014 ◽  
Vol 71 (7) ◽  
pp. 2763-2781 ◽  
Author(s):  
Stefan F. Cecelski ◽  
Da-Lin Zhang ◽  
Takemasa Miyoshi
Keyword(s):  
Surface Pressure ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Upper Troposphere ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Mesoscale Convective ◽  
Rossby Radius Of Deformation ◽  
Faster Development

Abstract In this study, the predictability of and parametric differences in the genesis of Hurricane Julia (2010) are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km. Results show that the genesis of Julia is highly predictable, with all but two members undergoing genesis. Despite the high predictability, substantial parametric differences exist between the stronger and weaker members. Notably, the strongest-developing member exhibits large upper-tropospheric warming within a storm-scale outflow during genesis. In contrast, the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm-scale outflow. A reduction in the Rossby radius of deformation in the strongest member aids in the accumulation of the warmth, while little contraction takes place in the nondeveloping member. The warming in the upper troposphere is responsible for the development of meso-α-scale surface pressure falls and a meso-β surface low in the strongest-developing member. Such features fail to form in the nondeveloping member as weak upper-tropospheric warming is unable to induce meaningful surface pressure falls. Cloud ice content is nearly doubled in the strongest member as compared to its nondeveloping counterparts, suggesting the importance of depositional heating of the upper troposphere. It is found that the stronger member undergoes genesis faster due to the lack of convective inhibition near the African easterly wave (AEW) pouch center prior to genesis. This allows for the faster development of a mesoscale convective system and storm-scale outflow, given the already favorable larger-scale conditions.

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