Showing papers on "Air-mass thunderstorm published in 2010"

Thunderstorms over a tropical Indian station, Minicoy: Role of vertical wind shear

Abstract: In this study, an attempt has been made to bring out the observational aspects of vertical wind shear in thunderstorms over Minicoy Case studies of thunderstorm events have been examined to find out the effect of vertical wind shear and instability on strength and longevity of thunderstorms Role of vertical wind shear in thunderstorms and its mechanism has been explored in this study Results reveal that for prolonged thunderstorms high and low instability along with moderate to high vertical wind shear (moderate: 0003 S−1 ≤ vertical wind shear ≤ 0005 S−1 and high: > 0005 S−1) play a significant role in longevity and strength of thunderstorms The mechanism of vertical wind shear in thunderstorms was investigated in a few cases of thunderstorm events where the duration of thunderstorm was covered by the radiosonde/rawin ascent observation taken at Minicoy Empirical model has been developed to classify thunderstorm type and to determine the strength and longevity of thunderstorms Model validation has been carried out for selected cases Model could classify thunderstorm type for most of the cases of thunderstorm events over island and coastal stations

Improved thunderstorm weather information for pilots through ground and satellite based observing systems

Abstract: Today’s weather information for pilots on thunderstorm conditions on their flight path is insufficient. Weather charts provided by the World Area Forecasting Centres and taken onboard by pilots before take-off are based on forecasts of large scale weather models which are initialized only twice a day. The information of the charts is therefore outdated, at least with respect to thunderstorm occurrence, at the time of use. They can only provide a rough estimation of thunderstorm hazards for relatively large areas. In contrast, thunderstorms develop quickly within tenths of minutes up to an hour and their exact time of occurrence and location is more or less impossible to predict deterministically hours in advance. In this paper, the value of the satellite information on thunderstorm detection over the oceans is demonstrated by applying the DLR Cb-TRAM cloud tracker (Zinner et al., 2009) to last years occurrences of aircraft accident and incident over the Atlantic. In addition, two incidents over the European area with severe turbulence and hail encounter are investigated by satellite, radar and lighting data. The aim of the study is to demonstrate the improved information pilots would gain once the thunderstorm analyses and forecasts of the satellite and ground based systems would be brought, i.e. up-linked, to the cockpit during flight. Today, pilots have information on thunderstorm activity through onboard radar equipment which provides quite good indication on thunderstorm activity within the close range part in flight direction, about 50 miles or so, provided there is precipitation within the convective up-droughts, strong enough to give radar returns. However, the radar returns are strongly attenuated when precipitation cells are large and intense, or several cells behind one another, due to the short wave length of the radars which operate at 3 cm. In that case the pilot’s information of the situation is quite incomplete which makes it difficult for them to choose a proper path around thunderstorm cells or through a thunderstorm line. In addition there are cases where thunderstorm cells are just about to develop with weak or no returns on the radar, yet they can produce convective turbulence which can propagate to levels above the developing cells. In that case the aircraft might experience sudden turbulence without any pre-warning. Also, at high flight levels through tropical storms over the oceans, radar returns might be weak due to small droplet sizes, thereby giving a wrong indication of the severity of the storm. In contrast to this onboard radar information, remote sensing by satellite, ground based radar and lightning can provide a more complete picture of the thunderstorm situation. Ground based systems have been developed which use this data to inspect cells from above, below and multiple viewing angles thereby providing a more complete picture of the thunderstorm situation (e.g.; Tafferner et al., 2009; Senesi et al., 2009). Thunderstorms can well be detected from satellite due to their cold cloud tops and characteristic cloud shape at already early development stage, the precipitation they produce can well be detected by radar and lightning discharges by lightning detectors. References Senesi, S., Y. Guillou, A. Tafferner, and C. Forster, 2009: Cb nowcasting in FLYSAFE: Improving flight safety regarding thunderstorm hazards. WMO Symposium on Nowcasting , 30 August - 4 September 2009 , Whistler, B.C., Canada Tafferner, A. , C. Forster, S. Senesi, Y. Guillou, P. Tabary, P. Laroche, A. Delannoy, B. Lunnon, D. Turp, T. Hauf, and D. Markovic, 2009: Nowcasting thunderstorm hazards for flight operations: the CB WIMS approach in FLYSAFE. European Air and Space Conference (CEAS) , 26 - 29 Oct. 2009, Manchester, UK Zinner, T., Mannstein, H., Tafferner, A. , 2008: Cb-TRAM: Tracking and monitoring severe convection from onset over rapid development to mature phase using multi-channel Meteosat-8 SEVIRI data. Meteorol. Atmos. Phys. 101, 191–210

Detection of Possible Thunderstorm Formation Inferred from Weather Element Changes at Ground Level on a Mountain Slope

Abstract: In India, Kerala state is known to have relatively high lightning incidence. The nature of spatial and temporal distribution of past incidents, type of thunderclouds which cause lightning, the topography, proximity to a mountain range and sea point to the possibility of the mountain weather aiding in Cb formation. For investigating the role of mountain weather in convective Cb formation a field station consisting of an automatic weather station and a lightning detector was established on the slope of the nearby Western Ghats mountain range. On thunderstorm days the mountain weather data show specific reduction in air temperature with synchronized increase in relative humidity along with a reduction in pressure of the order of 0.5 hPa between 10:00 h and 18:00 h. The variations in data are indicative of a strong updraft. The lightning detector showed thunderstorm activity, aligned with the direction of the mountain range, about an hour after detecting the changes in weather elements. Water vapour for thunderstorm formation seems to come from the nearby sea as indicated by the wind data. Data collected for three years show that existence of strong updrafts seem to be a characteristic of the mountain weather during thunderstorm months. Data from a coastal station located 40 km south west of the mountain station do not indicate updrafts either on the thunderstorm days or otherwise. As updrafts can lead to Cb formation monitoring weather elements as discussed here is useful for detecting thunderstorms at the developing stage itself.

Thunderstorm warning and forecast with atmosphere electric field data

Abstract: Based on the description of changing reg ulation about atmosphere electric field and the function of ground atmospheric electric field instrument,the corresponding relation and their characters between changing of atmosphere electric field and thunderstorm weather were analyzed,and threshold method was put out to forewarn and forecast the occurrence and development of thunderstorm according to changing regulation about atmosphere electric fieldThe result shows that the atmosphere electric field intensity fluctuations occurs irregularly when thunderstorm happensthe method of setting abnormal value for great change of atmosphere electric field intensity,threshold,can carry on thunderstorm warning and forecast in advanced

Numerical study on formation and diffusion wind fields for thunderstorm microburst

Abstract: As a type of high intensity winds, thunderstorm microbursts have caused numerous structural failures around the world The numerical method was employed to investigate the formation and diffusion unsteady wind fields for thunderstorm microburst related high intensity winds Unsteady simulations of formation and diffusion wind fields were conducted using time-filtered Reynolds Averaged Navier-Stokes (RANS) numerical simulation method The numerical results indicate that the wind fields present quite different characteristics at different time during the whole formation and diffusion process The magnitude of wind velocity changes greatly during the whole formation and diffusion process The maximum wind velocity occurs at the moment when the downdraft impacts on the ground and the main vortex is acting separation-reattachment, the secondary vortex is arising Unsteady simulations supply a promising solution to study the thunderstorm microburst wind characteristics under the current conditions with lack detailed full scale data

Comments on “A Comparison of Tropical and Midlatitude Thunderstorm Evolution in Response to Wind Shear”

Abstract: In a recent paper, Wissmeier and Goler (2009, hereafter WG09) presented the results of a numerical experiment meant to examine the different potential for convective storm splitting in the tropics versus the midlatitudes. WG09 found that simulated storms in tropical environments were less likely to undergo classical supercellular splitting because the storms’ outflow quickly spread out and cut the storms off from their source of inflow before the splitting process could occur. The main conclusion reached by WG09 is that higher vertical wind shear values are necessary for storm splitting to occur in the tropics than in the midlatitudes because the comparatively large vertical wind shear weakens and delays the convective outflow produced by storms. These are thought-provoking results and conclusions, but they hinge on some questionable assumptions and choices in the experimental design. The purpose of the present comment is to document and discuss several aspects of the study that bias WG09’s results and diminish the generality of their conclusions.

Notice of Retraction Computational simulation study on thunderstorm downburst-induced high intensity winds

Abstract: Thunderstorm downbursts are major cause of concern for engineering structures both on ground as well as those in air, namely aircrafts. The wind velocity profile of a thunderstorm downburst-induced wind is significantly different compared to natural atmospheric boundary layer winds. As a type of high intensity winds, thunderstorm microbursts have caused numerous structural failures around the world and have become the present research focus in structural wind engineering. The current study proposes a computational simulation method on thunderstorm downburst-induced winds. The computational fluid dynamics numerical method was employed to investigate the wind fields of thunderstorm downburst-induced wind. Unsteady simulations of wind fields were conducted using time-filtered Reynolds Averaged Navier-Stokes (RANS) numerical simulation method. The case study numerical results indicate that the wind fields present quite different characteristics at different time during the whole formation and diffusion process. The computational simulation method supplies a promising solution to study the thunderstorm downburst-induced wind characteristics for structural wind engineering.

Cloud-to-ground Lightning Characteristics and Environmental Conditions of Two Kinds of Convective Storm in Hubei Province

Abstract: The Cloud-to-ground Lightning Characteristics and Environmental Conditions are studied on 30 heavy rain cases and 10 hail or thunderstorm cases, the results show: (1)The convective weather dominating by precipitation whose negative CG lightning flashes account for the majority of the total flashes; quantity and frequency of CG lightning flashes are relatively high and the maximum number of CG lightning flashes within 10 minutes in every case is more than 50; the position of CG lightning flashes are relatively dense and consistent with strong radar echo. However, the convective weather dominating by hail or thunderstorm whose positive CG lightning flashes amount to or even more than negative CG lightning flashes, quantity and frequency of CG lightning flashes are relatively less and the CG lightning flashes distribute sporadically under the hail cloud anvil at the direction of the wind in convective weather. (2) The convective weather dominating by hail or thunderstorm has lower specific humidity in all layers, deeper layer under 0 ℃ and higher wind shear in vertical than the convection weather dominating by precipitation.