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Journal articles on the topic 'Cumulonimbus Towers'
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1
Bhat, G. S., and Shailendra Kumar. "Vertical structure of cumulonimbus towers and intense convective clouds over the South Asian region during the summer monsoon season." Journal of Geophysical Research: Atmospheres 120, no. 5 (March 6, 2015): 1710–22. http://dx.doi.org/10.1002/2014jd022552.
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Montgomery, M. T., M. E. Nicholls, T. A. Cram, and A. B. Saunders. "A Vortical Hot Tower Route to Tropical Cyclogenesis." Journal of the Atmospheric Sciences 63, no. 1 (January 1, 2006): 355–86. http://dx.doi.org/10.1175/jas3604.1.
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Abstract A nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions. Observations motivate the focus on the problem of how a midtropospheric cyclonic vortex, a frequent by-product of mesoscale convective systems during summertime conditions over tropical oceans, may be transformed into a surface-concentrated (warm core) tropical depression. As a first step, the vortex transformation is studied in the absence of vertical wind shear or zonal flow. Within the cyclonic vorticity-rich environment of the mesoscale convective vortex (MCV) embryo, the simulations demonstrate that small-scale cumulonimbus towers possessing intense cyclonic vorticity in their cores [vortical hot towers (VHTs)] emerge as the preferred coherent structures. The VHTs acquire their vertical vorticity through a combination of tilting of MCV horizontal vorticity and stretching of MCV and VHT-generated vertical vorticity. Horizontally localized and exhibiting convective lifetimes on the order of 1 h, VHTs overcome the generally adverse effects of downdrafts by consuming convective available potential energy in their local environment, humidifying the middle and upper troposphere, and undergoing diabatic vortex merger with neighboring towers. During metamorphosis, the VHTs vortically prime the mesoscale environment and collectively mimic a quasi-steady diabatic heating rate within the MCV embryo. A quasi-balanced toroidal (transverse) circulation develops on the system scale that converges cyclonic vorticity of the initial MCV and small-scale vorticity anomalies generated by subsequent tower activity. The VHTs are found to accelerate the spinup of near-surface mean tangential winds relative to an approximate axisymmetric model that excises the VHTs. This upscale growth mechanism appears capable of generating a tropical depression vortex on time scales on the order of 1–2 days, for reasonable parameter choices. Further tests of the VHT paradigm are advocated through diagnoses of operational weather prediction models, higher resolution simulations of the current configuration, examination of disruption scenarios for incipient vortices, and a meteorological field experiment.
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Li, Yan, Wei Lian Qu, Bin Wang, Yi Fei Wang, and Bai Feng Ji. "Three-Dimensional Numerical Simulation of Downburst Wind Occurrded in Wuhan." Advanced Materials Research 243-249 (May 2011): 5037–40. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.5037.
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Downburst is a strong downdraft generated below a cumulonimbus cloud, which hits the ground rapidly and causes significant low-level wind shear. It is a strong destructive regional weather phenomenon, which is the main reason for the transmission towers. In recent years, some scholars have researched the finer wind field characteristics and wind load of downburst by using the method of CFD. But the initial conditions are all assumed due to the small synoptic scale, the short lifecycle and the big measurement difficulty of downburst. So downburst wind load can not be taken into account in structural design. Based on the 3-D convective storm numerical model, by inputting temperature, humidity and wind fields detected in Wuhan radiosonde station at 8pm on July,27th,2007, simulation has been accomplished to understand the characteristics of the wind field in the place where the downburst incurred actually. The result provides model data and parameters for CFD simulation, which has directive significance to concern the high intensity downburst wind load in structure design.
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Demko, J. Cory, Bart Geerts, Qun Miao, and Joseph A. Zehnder. "Boundary Layer Energy Transport and Cumulus Development over a Heated Mountain: An Observational Study." Monthly Weather Review 137, no. 1 (January 1, 2009): 447–68. http://dx.doi.org/10.1175/2008mwr2467.1.
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Abstract Aircraft and surface measurements of the boundary layer transport of mass and moisture toward an isolated, heated mountain are presented. The data were collected around the Santa Catalina Mountains in Arizona, 20–30 km in diameter, during the North American monsoon, on days with weak winds and cumulus congestus to cumulonimbus development over the mountain. Flights in the boundary layer around the mountain and surface station data indicate that mountain-scale anabatic surface wind generally develops shortly after sunrise, peaking at ∼1 m s−1 in strength close to solar noon. There is some evidence for a toroidal heat island circulation, with divergence in the upper boundary layer. The aircraft data and mainly the diurnal surface temperature and pressure patterns confirm that this circulation is driven by surface heating over the mountain. Three case studies suggest that growth spurts of orographic cumulus and cumulonimbus are not preceded by enhanced mountain-scale mass convergence near the surface, and that the decay of orographic deep convection is associated with divergence around the mountain.
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Fischer, H., M. de Reus, M. Traub, J. Williams, J. Lelieveld, J. de Gouw, C. Warneke, et al. "Deep convective injection of boundary layer air into the lowermost stratosphere at midlatitudes." Atmospheric Chemistry and Physics Discussions 2, no. 6 (November 11, 2002): 2003–19. http://dx.doi.org/10.5194/acpd-2-2003-2002.
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Abstract. On 22 August 2001 a measurement flight was performed with the German research aircraft FALCON from Sardinia to Crete as part of the Mediterranean Oxidant Study (MINOS). Cruising at 8.2 km, the aircraft was forced to climb to 11.2 km over the southern tip of Italy to stay clear of the anvil of a large cumulonimbus tower. During ascent into the lowermost stratosphere in-situ measurements onboard the FALCON indicated several sharp increases in the concentrations of tropospheric trace gases, e.g. CO, acetone, methanol, benzene and acetonitrile, above the anvil. During one particular event deep in the stratosphere, at O3 concentrations exceeding 200 ppv, CO increased from about 60 to 90 ppv, while the concentration of acetone and methanol increased by more than a factor of 2 (0.7 to 1.8 ppv for acetone; 0.4 to 1.4 ppv for methanol). Enhancements for the short lived species benzene are even higher, increasing from 20 pptv in the stratosphere to approx. 130 pptv. The concentrations during the event were higher than background concentrations in the upper troposphere, indicating that polluted boundary layer air was directly mixed deep into the lowermost stratosphere.
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Fischer, H., M. de Reus, M. Traub, J. Williams, J. Lelieveld, J. de Gouw, C. Warneke, et al. "Deep convective injection of boundary layer air into the lowermost stratosphere at midlatitudes." Atmospheric Chemistry and Physics 3, no. 3 (June 17, 2003): 739–45. http://dx.doi.org/10.5194/acp-3-739-2003.
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Abstract. On 22 August 2001 a measurement flight was performed with the German research aircraft FALCON from Sardinia to Crete as part of the Mediterranean Oxidant Study (MINOS). Cruising at 8.2 km, the aircraft was forced to climb to 11.2 km over the southern tip of Italy to stay clear of the anvil of a large cumulonimbus tower. During ascent into the lowermost stratosphere in-situ measurements onboard the FALCON indicated several sharp increases in the concentrations of tropospheric trace gases, e.g. CO, acetone, methanol, benzene and acetonitrile, above the anvil. During one particular event deep in the stratosphere, at O3 concentrations exceeding 200 ppv, CO increased from about 60 to 90 ppv, while the concentration of acetone and methanol increased by more than a factor of 2 (0.7 to 1.8 ppv for acetone; 0.4 to 1.4 ppv for methanol). Enhancements for the short lived species benzene are even higher, increasing from 20 pptv in the stratosphere to approx. 130 pptv. The concentrations during the event were higher than background concentrations in the upper troposphere, indicating that polluted boundary layer air was directly mixed into the lowermost stratosphere.
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Hyvärinen, Otto, Elena Saltikoff, and Harri Hohti. "Validation of Automatic Cb Observations for METAR Messages without Ground Truth." Journal of Applied Meteorology and Climatology 54, no. 10 (October 2015): 2063–75. http://dx.doi.org/10.1175/jamc-d-14-0222.1.
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AbstractIn aviation meteorology, METAR messages are used to disseminate the existence of cumulonimbus (Cb) clouds. METAR messages are traditionally constructed manually from human observations, but there is a growing trend toward automation of this process. At the Finnish Meteorological Institute (FMI), METAR messages incorporate an operational automatic detection of Cb based solely on weather radar data, when manual observations are not available. However, the verification of this automatic Cb detection is challenging, as good ground truth data are not often available; even human observations are not perfect as Cb clouds can be obscured by other clouds, for example. Therefore, statistical estimation of the relevant verification measures from imperfect observations using latent class analysis (LCA) was explored. In addition to radar-based products and human observations, the convective rainfall rate from EUMETSAT’s Nowcasting Satellite Application Facility and lightning products from the Finnish lightning network were used for determining the existence of Cb clouds. Results suggest that LCA gives reasonable estimates of verification measures and, based on these estimates, the Cb detection system at FMI gives results comparable to human observations.
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KORNEEV, V. P., B. P. KOLOSKOV, A. A. BYCHKOV, A. M. PETRUNIN, and A. V. CHASTUKHIN. "CLOUD SEEDING FOR IMPROVING WEATHER IN MEGALOPOLISES." Meteorologiya i Gidrologiya, no. 7 (July 2022): 61–70. http://dx.doi.org/10.52002/0130-2906-2022-7-61-70.
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Some results of activities on improving weather conditions (weather protection) in megacities by cloud seeding are presented. The main tasks of the activities were to dissipate clouds and reduce or stop precipitation in the protected area during political, cultural, and sport events. In accordance to the methodological guidelines, four seeding methods are recommended depending on synoptic conditions: the dissipation of stratiform cloudiness; the initiation of premature precipitation on the windward side of the protected area by cloud seeding to form the precipitation “shadow”; the intense seeding (“overseeding”) of precipitation-forming clouds moving toward the protected area to reduce the efficiency of precipitation formation in them; the dissipation of deep cumulonimbus clouds by the dynamic method. To perform weather protection operations, up to 12 aircraft equipped with measuring equipment necessary for seeding, the “ground-air-ground” data communication system, and cloud seeding means were used. Liquid nitrogen, solid carbon dioxide, silver iodide, and coarse powder were used as reagents for cloud seeding. Ground-based automated weather radar systems were used to control aviation operations and to monitor the results of the seeding. The results of more than 100 large-scale operations on the creation of favorable weather conditions performed in various regions of Russia and neighboring countries indicate the efficiency of the methods and technical means of cloud seeding developed in the USSR and Russia for the artificial precipitation control.
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Črnivec, Nina, and Bernhard Mayer. "Towards an improved treatment of cloud–radiation interaction in weather and climate models: exploring the potential of the Tripleclouds method for various cloud types using libRadtran 2.0.4." Geoscientific Model Development 14, no. 6 (June 22, 2021): 3663–82. http://dx.doi.org/10.5194/gmd-14-3663-2021.
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Abstract. The representation of unresolved clouds in radiation schemes of coarse-resolution weather and climate models has progressed noticeably over the past years. Nevertheless, a lot of room remains for improvement, as the current picture is by no means complete. The main objective of the present study is to advance the cloud–radiation interaction parameterization, focusing on the issues related to model misrepresentation of cloud horizontal inhomogeneity. This subject is addressed with the Tripleclouds radiative solver, the fundamental feature of which is the inclusion of the optically thicker and thinner cloud fraction. The research challenge is to optimally set the pair of cloud condensates characterizing the two cloudy regions and the corresponding geometrical split of layer cloudiness. A diverse cloud field data set was collected for the analysis, comprising case studies of stratocumulus, cirrus and cumulonimbus. The primary goal is to assess the validity of the global cloud variability estimate along with various condensate distribution assumptions. More sophisticated parameterizations are subsequently explored, optimizing the treatment of overcast as well as extremely heterogeneous cloudiness. The radiative diagnostics including atmospheric heating rate and net surface flux are consistently studied using the Tripleclouds method, evaluated against a three-dimensional radiation computation. The performance of Tripleclouds mostly significantly surpasses the calculation on horizontally homogeneous cloudiness. The effect of horizontal photon transport is further quantified. The overall conclusions are intrinsically different for each particular cloud type, encouraging endeavors to enhance the use of cloud-regime-dependent methodologies in next-generation atmospheric models. This study, highlighting the Tripleclouds potential for three essential cloud types, signifies the need for more research examining a broader spectrum of cloud morphologies.
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Kumar, Shailendra, and G. S. Bhat. "Vertical Profiles of Radar Reflectivity Factor in Intense Convective Clouds in the Tropics." Journal of Applied Meteorology and Climatology 55, no. 5 (May 2016): 1277–86. http://dx.doi.org/10.1175/jamc-d-15-0110.1.
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AbstractThis study is based on the analysis of 10 years of data for radar reflectivity factor Ze as derived from the TRMM Precipitation Radar (PR) measurements. The vertical structure of active convective clouds at the PR pixel scale has been extracted by defining two types of convective cells. The first one is cumulonimbus tower (CbT), which contains Ze ≥ 20 dBZ at 12-km altitude and is at least 9 km deep. The other is intense convective cloud (ICC), which belongs to the top 5% of the population of the Ze distribution at a prescribed reference height. Here two reference heights (3 and 8 km) have been chosen. Regional differences in the vertical structure of convective cells have been explored by considering 16 locations distributed across the tropics and two locations in the subtropics. The choice of oceanic locations is based on the sea surface temperature; that of the land locations is based on propensity for intense convection. One of the main findings of the study is the close similarity in the average vertical profiles of CbTs and ICCs in the mid- and lower troposphere across the ocean basins whereas differences over land areas are larger and depend on the selected reference height. The foothills of the western Himalaya, southeastern South America, and the Indo-Gangetic Plain contain the most intense CbTs; equatorial Africa, the foothills of the western Himalaya, and equatorial South America contain the most intense ICCs. Close similarity among the oceanic profiles suggests that the development of vigorous convective cells over warm oceans is similar and that understanding gained in one region is extendable to other areas.
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Dolling, Klaus P., and Gary M. Barnes. "The Creation of a High Equivalent Potential Temperature Reservoir in Tropical Storm Humberto (2001) and Its Possible Role in Storm Deepening." Monthly Weather Review 140, no. 2 (February 2012): 492–505. http://dx.doi.org/10.1175/mwr-d-11-00068.1.
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Thirty global positioning system dropwindsondes (GPS sondes) were used to identify and examine the creation of a reservoir of high equivalent potential temperature (θe) in the nascent eye of Tropical Storm Humberto (2001). The θe did not increase in the high surface wind portion of the storm as it does in mature hurricanes; instead air spiraled into the light-wind center of the developing storm where it was trapped by subsidence under a mesoscale convectively generated vortex (MCV). An energy budget revealed that the inflow column took 7 h to reach the storm center during which a combined average surface enthalpy flux of ~230 W m−2 was diagnosed via the bulk aerodynamic equations. This estimate is close to the 250 W m−2 required for balance based on the energy acquired by the column. The high θe in the lowest kilometer, overlain by a near dry-adiabatic layer under the anvil base, resulted in convective available potential energy (CAPE) exceeding 2500 m2 s−2. This conditionally unstable air later served as fuel for the convection within the nascent eyewall. The authors speculate that CAPE of such a large magnitude could accelerate the updraft and stretch the vorticity field, essentially turning garden-variety cumulonimbi into the vortical hot towers argued by several researchers to play a role in tropical cyclone formation and intensification.
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Houze, Robert A. "Clouds in Tropical Cyclones." Monthly Weather Review 138, no. 2 (February 1, 2010): 293–344. http://dx.doi.org/10.1175/2009mwr2989.1.
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Abstract Clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere. Convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts. Within the eyes of mature tropical cyclones, stratus clouds top a boundary layer capped by subsidence. An outward-sloping eyewall cloud is controlled by adjustment of the vortex toward gradient-wind balance, which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state. This balance is intermittently upset by buoyancy arising from high-moist-static-energy air entering the base of the eyewall because of the radial influx of low-level air from the far environment, supergradient wind in the eyewall zone, and/or small-scale intense subvortices. The latter contain strong, erect updrafts. Graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left aloft surround the eyewall, and aggregates are advected radially outward and azimuthally up to 1.5 times around the cyclone before melting and falling as stratiform precipitation. Electrification of the eyewall cloud is controlled by its outward-sloping circulation. Outside the eyewall, a quasi-stationary principal rainband contains convective cells with overturning updrafts and two types of downdrafts, including a deep downdraft on the band’s inner edge. Transient secondary rainbands exhibit propagation characteristics of vortex Rossby waves. Rainbands can coalesce into a secondary eyewall separated from the primary eyewall by a moat that takes on the structure of an eye. Distant rainbands, outside the region dominated by vortex dynamics, consist of cumulonimbus clouds similar to non–tropical storm convection.
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Hisada, Yukiko, Yuji Sugihara, and Nobuhiro Matsunaga. "Meteorological Characteristics of Local Heavy Rainfall in the Fukuoka Plain." Journal of Disaster Research 10, no. 3 (June 1, 2015): 429–35. http://dx.doi.org/10.20965/jdr.2015.p0429.
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Heavy local rainfall has been increasingly observed in urban Fukuoka on fine summer afternoons in recent years. Such rainfall tends to occur suddenly on calm afternoons and is considered to be caused by local wind conditions influenced by local topography rather than by weather fronts or typhoons. This local rainfall is considered to be caused by a mechanism different from similar rainfalls occurring on fine Kanto plain afternoons. We set up 14 rain gauges in urban Fukuoka in this study to clarify and confirm actual local rainfall conditions there. Maximum local rain is about 64 km2lasting 10 to 30 minutes. The maximum 10-minute rainfall was 13.8 mm. The average surface air temperature on days with local rainfall differs 2°–3°C from that on fine days. Upper atmosphere humidity distribution differs greatly between fine days and those with heavy local rain. Accordingly, heavy local rain is more likely to occur if surface air temperature and humidity in upper atmosphere rise above a certain level. Some difference is seen between days of heavy local rainfall and fine day in terms of the K index (KI), a measure of atmospheric stability. We confirmed that the atmospheric state becomes more unstable on days with heavy local rainfall than on fine days. Heavy local rainfall often begins in either the eastern or western inland Fukuoka plain and moves toward the coast. That is, based on numerical simulation using the meteorological mesoscale weather research and forecasting (WRF) model, wind blowing opposite to the sea wind blows in the upper atmosphere, moving cumulonimbus clouds causing heavy local rainfall toward the coast. We also confirmed that heavy local rainfall tends to occur in eastern inland areas with wind from the west, but tends to occur in western areas with wind from the east. We therefore assumed that heavy local rainfall in urban Fukuoka was triggered by updrafts generated when wind struck the inland Fukuoka plain mountain system.
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Lajoie, France, and Kevin Walsh. "A Diagnostic Study of the Intensity of Three Tropical Cyclones in the Australian Region. Part I: A Synopsis of Observed Features of Tropical Cyclone Kathy (1984)." Monthly Weather Review 138, no. 1 (January 1, 2010): 3–21. http://dx.doi.org/10.1175/2009mwr2875.1.
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Abstract Objective streamline analyses and digitized high-resolution IR satellite cloud data have been used to examine in detail the changes in the environmental circulation and in the cloud structure that took place in and around Tropical Cyclone Kathy (1984) when it started to intensify, and during its intensification and dissipation stages. The change of low-level circulation around Tropical Cyclone Kathy was measured by the change in the angle of inflow (α4) at a radius of 4° latitude from the cyclone center. When Kathy started to intensify, α4 increased suddenly from 20° to 42.5° in the northerly airstream to the north and northeast of the depression, and decreased to 0° to the south of the depression. At that stage the low-level circulation around the depression appeared as a giant swirl that started some 600 km to the north and northeast of the depression and spiraled inward toward its center, while trade air, which is usually cool, dry, and stable, did not enter the cyclonic circulation. The angle α4 remained the same during intensification. During the dissipation stage, α4 returned to 20° and trade air started to participate in the cyclonic circulation. Satellite cloud data were used to determine the origin, evolution, and importance of the feeder bands in the intensification of the cyclone, to follow the moist near-equatorial air that flowed through them and to estimate the maximum height of cumulonimbi that developed in them, to observe the changes in the convective activity in the central dense overcast (CDO) area, as well as in the area around the CDO. Most of the observed changes in Kathy have also been observed in other tropical cyclones during intensification and dissipation. Using the sequence of observed changes of the circulation and of convective activity in and around the CDO of Kathy, a mathematical model has been developed to forecast the intensity of a tropical cyclone. The model and its application to three tropical cyclones in the Australian region are described in Part II of this paper.
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"A cumulonimbus calvus towers above the hills of Tuscany in the Province of Siena." Weather 75, no. 7 (July 2020). http://dx.doi.org/10.1002/wea.3804.
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