Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “mesoscale convection”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Deep convection in mesoscale convective systems

A study was undertaken to examine the evolution of radar echoes and lightning attending the convective storms in mesoscale convective systems (MCS) and the relationships between the spatial and temporal evolution of deep convection and the storm environment, precipitation, severe weather, and lightning. The total number of ground discharges ranges from 10,000 to 30,000 over the life cycle of the MCS with peak sustained rates (for up to 10 consecutive hours) in excess of 2000 per hour. The peak lightning activity occurs from 5 to 20 hours after the first storms and anywhere from 7 hours prior to 7 hours after the time of the maximum areal extent of the MCS for very similar synoptic environments. Thus, it appears that mesoscale and sub-synoptic scale mechanisms are responsible for these large temporal variation in lightning activity. In addition, we have found that the lightning rates in MCS's are not related to either the size or the duration of the MCS. Preliminary results suggest that the MCA's with embedded squall lines produce the greatest flash rates.

Goodman, S. J.↗
NASA NTRS1989

Observed structural variability of deep moist convection within a mesoscale convective system

Some radar observations of the convective cloud structure within and around a developing mesoscale convective system (MCS), which attained an eventual horizontal dimension of approximately 100 by 200 km, are reported. Similarities in cloud structure within and outside the MCS include a downshear tilt of the cloud precipitation core and generation of new cells toward the direction of cloud motion and parallel to the major axis of the cloud line. The systematic difference in the longevity and intensity of the clouds is examined.

Knupp, Kevin R.↗
NASA NTRS2010

Global Variability of Mesoscale Convective System

Mesoscale convective systems (MCSs) in the tropics produce extensive anvil clouds, which significantly affect the transfer of radiation. This study develops an objective method to identify MCSs and their anvils by combining data from three A-train satellite instruments: Moderate Resolution Imaging Spectroradiometer (MODIS) for cloud-top size and coldness, Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) for rain area size and intensity, and CloudSat for horizontal and vertical dimensions of anvils. The authors distinguish three types of MCSs: small and large separated MCSs and connected MCSs. The latter are MCSs sharing a contiguous rain area. Mapping of the objectively identified MCSs shows patterns of MCSs that are consistent with previous studies of tropical convection, with separated MCSs dominant over Africa and the Amazon regions and connected MCSs favored over the warm pool of the Indian and west Pacific Oceans. By separating the anvil from the raining regions of MCSs, this study leads to quantitative global maps of anvil coverage. These maps are consistent with the MCS analysis, and they lay the foundation for estimating the global radiative effects of anvil clouds. CloudSat radar data show that the modal thickness of MCS anvils is about 4--5 km. Anvils are mostly confined to within 1.5--2 times the equivalent radii of the primary rain areas of the MCSs. Over the warm pool, they may extend out to about 5 times the rain area radii. The warm ocean MCSs tend to have thicker non-raining and lightly raining anvils near the edges of their actively raining regions, indicating that anvils are generated in and spread out from the primary raining regions of the MCSs. Thicker anvils are nearly absent over continental regions.

Yuan, J.↗
NASA NTRS2020

High Ice Water Content Associated with a Darwin, Austrailia, Mesoscale Convective System

A mesoscale convective complex that occurred during the 2014 Darwin, Australia, flight campaign is examined via a three-dimensional, numerical simulation. The focus of the study is to better understand the presence and development of High Ice Water Content (HIWC) that was observed in the actual storm. Although peak values of ice water content may occur early in the storm lifetime, large areas of high concentrations expand with time and persist even when the storm tops begin to warm. The storm canopy which contains HIWC, has low radar reflectivity factor and is fed by an ensemble of regenerating thermal plumes. Detection via weather radar of the aviation hazard associated HIWC is challenging due the low values of radar reflectivity factor.

Aviation hazards↗
NASA NTRS1986

Cloud-to-ground lightning activity in mesoscale convective complexes

An analysis of the evolution of cloud-to-ground lightning discharges attending convective storms in mesoscale convective systems was conducted in the framework of the mesoscale convective complexes (MCCs) life cycle. The lightning discharge data were acquired by a commercially available lightning detection and location system. Peak rates averaged 42/min for the MCCs analyzed; these rates are comparable to the highest observed rates within other mesoscale storm systems and are greater than 20 times the rates previously observed in isolated thunderstorms. Lightning damage occurs with half of the MCCs and is most frequent between the development and the mature phases of the MCC life cycle. The most active period is also characterized by the greatest average number of discrete strokes and largest fraction of multiple-stroke discharges. The total cloud-to-ground lightning activity and maximum flashing rate do not appear to be directly related to either the size of the cloud shield or total duration of the MCC.

Goodman, S. J.↗
NASA NTRS1987

Convective cell development and propagation in a mesoscale convective complex

A case study was made of the mesoscale convective complex (MCC) which occurred over southern Oklahoma and northern Texas on 27 May 1981. This storm moved in an eastsoutheasterly direction and during much of its lifetime was observable by radars at Oklahoma City, Ok. and Stephenville, Tx. It was found that the direction of cell (VIP level 3 or more reflectivity) propagation was somewhat erratic but approximately the same as the system (VIP level 1 reflectivity) movement and the ambient wind. New cells developed along and behind the gust front make it appear that once the MCC is initiated, a synergistic relationship exists between the gust front and the MCC. The relationship between rainfall patterns and amounts and the infrared (IR) temperature field in the satellite imagery were examined. The 210 K isotherm of GOES IR imagery was found to encompass the rain area of the storm. The heaviest rainfall was in the vicinity of the VIP level 3 cells and mostly contained within the 205 K isotherm of GOES IR imagery.

Ahn, Yoo-Shin↗
NASA NTRS1985

Ability of a regional-scale model to predict the genesis of intense mesoscale convective systems

The mesoscale part of a two-part evaluation of 30 forecasts by a mesoscale numerical weather prediction model (MASS 2.0) is presented. Unfiltered fields are combined into convective predictor fields, the loci of which are then related at two-hour intervals to the loci of strong mesoscale convective systems identifiable in national radar summary plots and GOES satellite imagery. Examples of model 'forecasts' of intense convective storm clusters, a severe squall line triggered along a dryline, orographically induced hailstorms, and sea breeze thunderstorms are provided.

Koch, S. E.↗
NASA NTRS1989

Observed structure of mesoscale convective systems and implications for large-scale heating

The model for the idealized tropical mesoscale convective system proposed by Houze (1982) is examined. Observations of the structure of mesoscale convective systems are used to determine the applicability of the conceptual model. Data on the vertical distribution of vertical air motion in the convective and stratiform regions of mesoscale convective systems are discussed and the treatment of this distribution in Houze's model is considered.

Houze, Robert A., Jr.↗
NASA NTRS1993

Nonhydrostatic effects in numerical modeling of mesoscale convective systems and baroclinic waves

The present investigation is concerned with the role of convection upon mesoscale modeling results, particularly when the grid resolution becomes small enough that there is not a clear scale separation between the explicitly resolved circulations and the parameterized clouds. In those situations, the vertical accelerations in explicitly resolved circulations become strong enough that the hydrostatic assumption may no longer be valid. These concerns arise from interests in improving mesoscale modeling per se and in improving the subgrid-scale parameterizations in global models. The hydrostatic and the nonhydrostatic options of the Colorado State University Regional Atmospheric Modeling System were used to simulate dry gravity currents in two dimensions, using several different horizontal grid sizes. With horizontal grid intervals of 10 km or less, nonhydrostatic simulations produce wider and colder heads and weaker but wider forced updrafts than do the hydrostatic simulations. Comparing the hydrostatic and nonhydrostatic models show that the difference between the vertical mass fluxes is much less than the difference between the vertical velocities. When the grid is fine enough to resolve the head of the gravity current, horizontal convergence at the gust front extends upwards almost to the head of the cold air. Vertical mass flux in the forced updraft at the front varies with horizontal grid size mainly as a function of the height of the simulated head. For coarser grids, which do not resolve the head, vertical mass flux at all heights decreases with increasing horizontal grid size. A comparison on nonhydrostatic simulations with horizontal grid intervals of 1 km and 2 km illustrates how decreasing the grid size does not necessarily increase the intensity of the resolved circulation. The smaller grid enables the simulated gravity current to entrain a bubble of warm air behind the head, which results in a weaker circulation with a shorter head and weaker updraft.

Cohen, Charles↗
NASA NTRS1988

Budget study of a mesoscale convective system - Model simulation

A tropical squall-type cloud cluster is examined as an example of a mesoscale convective complex. The precipitation growth processes and air circulations that develop in the convective and stratiform regions are studied using a data set generated from a time-dependent numerical cloud model. The relationship of the stratiform region of the mesoscale convective complex is discussed. The vertical profiles of heating and drying are calculated. Comparisons are made between simulations with and without ice-phase microphysical processes and a simulation with forcing by weaker lifting at middle and upper levels.

Tao, Wei-Kuo↗
NASA NTRS1998

Characterization of Mesoscale Convective Systems by Means of Composite Radar Reflectivity Data

A mesoscale convective system (MCS) is broadly defined as a cloud and precipitation system of mesoscale dimensions (often too large for most aircraft to circumnavigate) with deep-convective activity concentrated in at least part of the MCS, or present during part of its evolution. A large areal fraction of MCSs is stratiform in nature, yet estimates from MCSs over the Great Plains, the Southeast, and tropical waters indicate that at least half of the precipitation is of convective origin. The presence of localized convection is important, because within convective towers cloud particles and hydrometeors are carried upward towards the cloud top. Ice crystals then move over more stratiform regions, either laterally, or through in situ settling over decaying and spreading convection. These ice crystals then grow to precipitation-size particles in mid- to upper tropospheric mesoscale updrafts. The convective portion of a MCS is often a more or less continuous line of thunderstorms, and may be either short-lived or long-lived. Geerts (1997) presents a preliminary climatology of MCSs in the southeastern USA, using just one year of composite digital radar reflectivity data. In this study MCSs are identified and characterized by means of visual inspection of animated images. A total of 398 MCSs were identified. In the warm season MCSs were found to be about twice as frequent as in the cold season. The average lifetime and maximum length of MCSs are 9 hours, and 350 km, respectively, but some MCSs are much larger and more persistent. In the summer months small and short-lived MCSs are relatively more common, whereas in winter larger and longer-lived systems occur more frequently. MCSs occur more commonly in the afternoon, in phase with thunderstorm activity, but the amplitude of the diurnal cycle is small compared to that of observed thunderstorms. It is estimated that in the Southeast more than half of all precipitation and severe weather results from MCSs.

Geerts, Bart↗
NASA NTRS1990

A comparison of cloud radiation fields obtained by in-situ aircraft measurements and a numerical simulation of a tropical mesoscale convective system

The radiation budget of a tropical mesoscale convective system (MCS) is investigated by comparing in situ aircraft measurements obtained in a tropical MCS during the Equatorial Mesoscale Experiment (EMEX), and coordinated aircraft radiation measurements, with radiation profiles calculated using cloud properties obtained from a cloud model simulation of a tropical MCS. Preliminary results indicate that the stratiform region of the tropical System B simulation represents the gross properties of the observed stratiform system between 4.5 to 15 km. The flux profiles predicted by the model are consistent with observed fluxes.

Wong, Takmeng↗
NASA NTRS1991

Kinematic and precipitation structure of a small, long-lived mesoscale convective system

A comprehensive analysis using conventional single Doppler radar analyses, analysis of multiparameter (CP-2) data, network sounding and surface data, and GOES satellite data is presented to characterize the internal kinematic and precipitation structure of a small, long-lived mesoscale convective system. The data pertain to the Cooperative Huntsville Meteorological experiment conducted over northern Alabama and central Tennessee during June and July of 1986. The mesoscale convective system pulsations visible in the IR patterns were associated with the development of closely interacting aggregates of convective elements. The aggregates were about 20 km in diameter, attained echo tops of about 13 km, and were dominated by a single relatively intense convective element. The measured difference in radial velocity across the upper portion of these elements was about 20 m/s over a distance of about 10 km.

Knupp, Kevin R.↗
NASA NTRS2024

High Ice Water Content in Tropical Mesoscale Convective Systems (A Conceptual Model)

The phenomenon of high ice water content (HIWC) occurs in mesoscale convective systems (MCSs) when a large number of small ice particles with typical sizes of a few hundred micrometers, concentrations of the order of 10 2 –10 3 L −1 , and IWC exceeding 1 g m −3 are present at high altitudes. HIWC regions in MCSs may extend vertically up to 10 km above the melting layer and horizontally up to hundreds of kilometers, filling large volumes of the convective systems. HIWC has great geophysical significance due to its effect on precipitation formation, the hydrological cycle, and the radiative properties of MCSs. It is also recognized as a hazard for commercial aviation operations since it can result in engine power loss and in the malfunctioning of aircraft data probes. This study summarizes observational and numerical simulation efforts leading to the development of a conceptual model for the production of HIWC in tropical MCSs based on the data collected during the HAIC–HIWC campaign. It is hypothesized that secondary ice production (SIP) in the vicinity of the melting layer plays a key role in the formation and sustainability of HIWC. In situ observations suggest that the major SIP mechanism in the vicinity of the melting layer is related to the fragmentation of freezing drops (FFDs). Both in situ data and numerical simulations suggest that the recirculation of drops through the melting layer led to the amplification of SIP. The proposed conceptual model and simulation results motivate further efforts to extend reproducible laboratory measurements.

high ice water content↗
NASA NTRS2007

The Impact of Microphysics on Intensity and Structure of Hurricanes and Mesoscale Convective Systems

During the past decade, both research and operational numerical weather prediction models, e.g. Weather Research and Forecast (WRF) model, have started using more complex microphysical schemes originally developed for high-resolution cloud resolving models (CRMs) with a 1-2 km or less horizontal resolutions. WRF is a next-generation mesoscale forecast model and assimilation system that has incorporated modern software framework, advanced dynamics, numeric and data assimilation techniques, a multiple moveable nesting capability, and improved physical packages. WRF model can be used for a wide range of applications, from idealized research to operational forecasting, with an emphasis on horizontal grid sizes in the range of 1-10 km. The current WRF includes several different microphysics options such as Purdue Lin et al. (1983), WSM 6-class and Thompson microphysics schemes. We have recently implemented three sophisticated cloud microphysics schemes into WRF. The cloud microphysics schemes have been extensively tested and applied for different mesoscale systems in different geographical locations. The performances of these schemes have been compared to those from other WRF microphysics options. We are performing sensitivity tests in using WRF to examine the impact of six different cloud microphysical schemes on precipitation processes associated hurricanes and mesoscale convective systems developed at different geographic locations [Oklahoma (IHOP), Louisiana (Hurricane Katrina), Canada (C3VP - snow events), Washington (fire storm), India (Monsoon), Taiwan (TiMREX - terrain)]. We will determine the microphysical schemes for good simulated convective systems in these geographic locations. We are also performing the inline tracer calculation to comprehend the physical processes (i.e., boundary layer and each quadrant in the boundary layer) related to the development and structure of hurricanes and mesoscale convective systems.

Tao, Wei-Kuo↗
NASA NTRS2009

Anvil Clouds of Tropical Mesoscale Convective Systems in Monsoon Regions

The anvil clouds of tropical mesoscale convective systems (MCSs) in West Africa, the Maritime Continent and the Bay of Bengal have been examined with TRMM and CloudSat satellite data and ARM ground-based radar observations. The anvils spreading out from the precipitating cores of MCSs are subdivided into thick, medium and thin portions. The thick portions of anvils show distinct differences from one climatological regime to another. In their upper portions, the thick anvils of West Africa MCSs have a broad, flat histogram of reflectivity, and a maximum of reflectivity in their lower portions. The reflectivity histogram of the Bay of Bengal thick anvils has a sharply peaked distribution of reflectivity at all altitudes with modal values that increase monotonically downward. The reflectivity histogram of the Maritime Continent thick anvils is intermediate between that of the West Africa and Bay of Bengal anvils, consistent with the fact this region comprises a mix of land and ocean influences. It is suggested that the difference between the statistics of the continental and oceanic anvils is related to some combination of two factors: (1) the West African anvils tend to be closely tied to the convective regions of MCSs while the oceanic anvils are more likely to be extending outward from large stratiform precipitation areas of MCSs, and (2) the West African MCSs result from greater buoyancy, so that the convective cells are more likely to produce graupel particles and detrain them into anvils

Cetrone, J.↗
NASA NTRS2010

Global Variability of Mesoscale Convective System Anvil Structure from A-Train Satellite Data

Mesoscale convective systems (MCSs) in the tropics produce extensive anvil clouds, which significantly affect the transfer of radiation. This study develops an objective method to identify MCSs and their anvils by combining data from three A-train satellite instruments: Moderate Resolution Imaging Spectroradiometer (MODIS) for cloud-top size and coldness, Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) for rain area size and intensity, and CloudSat for horizontal and vertical dimensions of anvils. The authors distinguish three types of MCSs: small and large separated MCSs and connected MCSs. The latter are MCSs sharing a contiguous rain area. Mapping of the objectively identified MCSs shows patterns of MCSs that are consistent with previous studies of tropical convection, with separated MCSs dominant over Africa and the Amazon regions and connected MCSs favored over the warm pool of the Indian and west Pacific Oceans. By separating the anvil from the raining regions of MCSs, this study leads to quantitative global maps of anvil coverage. These maps are consistent with the MCS analysis, and they lay the foundation for estimating the global radiative effects of anvil clouds. CloudSat radar data show that the modal thickness of MCS anvils is about 4-5 km. Anvils are mostly confined to within 1.5-2 times the equivalent radii of the primary rain areas of the MCSs. Over the warm pool, they may extend out to about 5 times the rain area radii. The warm ocean MCSs tend to have thicker non-raining and lightly raining anvils near the edges

Yuan, Jian↗
NASA NTRS1990

Electrical and kinematic structure of an Oklahoma mesoscale convective system

The case study examines the dynamics and kinematics of a mesoscale convective system (MCS) by comparing its meteorological parameters with in situ electrical measurements. Conventional MCS characteristics are reported including a rear inflow jet, wake low, and a bipolar cloud-to-ground pattern, but some nonclassical conditions are also reported. Horizontally long cloud-to-ground electrical strikes are noted which demonstrate that cloud-to-ground electrical data alone cannot entirely characterize stratiform electrification in MCSs.

Hunter, Steven M.↗